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UTILIZATION OF UNMARKETABLE POTATOES FOR
PREPARATION OF INSTANT POTATO SOUP POWDER
by
Sajan Palanchoke
Food Technology Instruction Committee
Institute of Science and Technology
Tribhuvan University, Nepal
2008
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ii
Utilization of Unmarketable Potatoes for Preparation of Instant
Potato Soup Powder
A dissertation submitted to theFood Technology Instruction Committee
in Tribhuvan University in partial fulfillment of the requirements
for the degree of B. Tech. in Food Technology
by
Sajan Palanchoke
Food Technology Instruction Committee
Institute of Science and Technology
Tribhuvan University
Dharan, Hattisar, Nepal
December 2008
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iii
Tribhuvan University
Institute of Science and Technology
Food Technology Instruction Committee
Central Campus of Technology, Dharan
Approval Letter
This dissertation entitled Utilization of Unmarketable Potatoes for Preparation of
Instant Potato Soup Powderpresented by Sajan Palanchoke has been accepted as the
partial fulfillment of the requirements for the B. Tech. in Food Technology.
Dissertation Committee
1. Chairperson
(Mrs. Geeta Bhattarai, Lecturer)
2. External examiner
(Mr. Bhisma Nanda Baidhya, Prof.)
3. Supervisor
(Mr. Shyam Kumar Mishra, Lecturer)
Date: December, 2008
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iv
Acknowledgements
It is my great privilege to work for the present investigation under the expert guidance and
kind supervision of lecturer Shyam Kumar Mishra, Central Campus of Technology,
Dharan. I express my deep sense of gratitude to him for his soulful advice, painstaking
efforts, fruitful discussion and constant encouragement during the course of work and also
highly indebted and grateful for his personal efforts and sacrifice of his most precious and
valuable time to have made it possible to bring the experiment to completion.
To me it is a matter of great satisfaction and pleasure to express my humble gratitude to
Associate ProfessorDr. Ganga Kharel, Asst. Dean, Central Campus of Technology. I also
gratefully express my sincere gratitude to Mrs. Geeta Bhattarai, Chairperson, FoodTechnology Instruction Committee, Mr. Pushpa Prasad Acharya, Chairman, Department of
Quality Control Surendra Bahadur Katawal Associate Professor, Lecturer Pashupati
Mishra, Assistant Campus Chief and Lecturer, Basanta Kumar Rai (Central Campus of
Technology, Dharan) for their support to work.
I am very much conscious to express my department and thanks to all the teachers and staff
members Hari Khanal, Sujan Dhakal and all my friends especially Rajkumari Shah, Bimala
Pokhrel, Roshna Ojha, Sussanna K.C., Amit Bhusan Suman, Santosh Dahal and kindly
juniors Rewati Raman Bhattarai, Sudip Thaguna, Nawaraj Gautam, Roshan Shrestha and
Mahalaxmi Pradhananga for their helping hands.
Finally, I am highly indebted to my parents and all family members for their constant
support, encouragement and frequent inspirations in this endeavor, by which I am able to
stand at this point of life.
Sajan Palanchoke
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v
Abstract
Potato flour is a highly versatile raw material that can be used in several processed foodproducts. Unmarketable potatoes were turned into flour and used to prepare instant potato
soup powder. The samples of potatoes were studied for peeling losses from different
peeling methods viz; hand peeling, abrasive peeling and mashing peeling, chemical
characteristics between potatoes and its flour and functional properties of the flour.
The abrasive peeling method was more economical for producing potato flour due to its
higher yield compared to other two peeling methods.
The chemical composition of the potato (dry basis) and the flour varied significantly.
Slight variations in functional properties between the different sizes of flour particle were
observed.
The recipies for the standardization of instant potato soup powder (IPSP) were worked out
by mixing potato flour made from unmarketable potatoes with ingredients like salt, citric
acid and msg in different proportions. The best IPSP recipe was selected on the basis of
higher sensory score for prepared soups on 9-point Hedonic scale. The results indicated the
recipie containing 3.33 parts of flour (m/v), 1.33 parts of salt (m/v), 0.04 parts of citric
acid (m/v), 0.13 parts of msg (m/v) and 100 parts of water (v/v) was rated superior from
different optimizing steps. The potato flour particle size of 150m was found to be
superior among the other two particle sizes. The cost of production per 100g of IPSP was
Rs 30.3. It is estimated to serve 3 liters of soup from 100g of instant potato soup powder.
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Contents
Approval letter ....iii
Acknowledgements ... iv
Abstract ... v
List of Tables and Figures ix
1 Introduction ...........................................................................................................................1
1.1 General Introduction ......................................................................................................... 1
1.2 Statement of the Problem ................................................................................................. 2
1.3 Objective of the study ....................................................................................................... 3
1.3.1 General objective ..................................................................................................... 3
1.3.2 Specific objectives .................................................................................................. 3
1.4 Significance of the study .................................................................................................. 4
1.5 Limitations of the study .................................................................................................... 4
2 Literature review ................................................................................................................... 5
2.1 Historical background....................................................................................................... 5
2.2 Structure of Potato Tuber ................................................................................................. 6
2.3 Chemical Composition of Potato ...................................................................................... 82.4 Nutritive Value of Potatoes and Potato Flour ................................................................... 9
2.5 Potatoes in Nepal ............................................................................................................ 11
2.5.1 Geography and Production zones .......................................................................... 12
2.5.1.1 Physical Geography ................................................................................................. 12
2.5.1.2 Climate ........................................................................................................................ 13
2.5.1.3 Regional Distribution of Potato Production ..................................................... 13
2.5.2 Production Systems and Constriants .................................................................... 14
2.5.2.1 Land Use and Land Tenure ................................................................................... 14
2.5.2.2 Cropping Calendar ................................................................................................... 15
2.5.2.3 Cropping Patterns and Fertility ............................................................................ 152.5.2.4 Occurrence and Control of Potato Diseases and Pests .................................. 17
2.5.3 Varieties and Seed Systems .................................................................................. 18
2.5.3.1 Varieties ...................................................................................................................... 18
2.5.3.2 The "Informal" Seed System................................................................................. 19
2.5.3.3 The "Formal" Seed System.................................................................................... 20
2.5.4 Consumption, Storage and Marketing .................................................................. 21
2.5.4.1 Consumption.............................................................................................................. 21
2.5.4.2 Storage ......................................................................................................................... 21
2.6 Grading and Marketing of Potatoes ................................................................................ 22
2.6.1 Size Grading of Potatoes ....................................................................................... 22
2.6.2 Economics of Grading ........................................................................................... 23
2.6.3 Potatoes preferences of Consumers ....................................................................... 23
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2.7 Utilization of Potatoes .................................................................................................... 24
2.7.1 Food uses: fresh, "frozen", dehydrated .................................................................. 24
2.7.2 Non-food uses: Glue, animal feed and fuel-grade ethanol .................................... 26
2.7.3 Seed potatoes: renewing the cycle ......................................................................... 26
2.7.4 Potato flour ............................................................................................................ 262.7.4.1 Methods of Manufacture ......................................................................................... 27
2.7.4.2 Uses of Potato flour .................................................................................................. 29
3 Materials and methods ........................................................................................................ 30
3.1 Raw materials ................................................................................................................. 30
3.1.1 Collection of raw materials.................................................................................... 30
3.2 Preparation of Potato Powder ......................................................................................... 30
3.2.1 Cleaning ................................................................................................................. 32
3.2.3 Peeling and slicing ................................................................................................. 32
3.2.4 Blanching and pretreatment of the potato slices .................................................... 323.2.5 Dehydration ........................................................................................................... 32
3.2.6 Size Reduction and Sieving ................................................................................... 32
3.2.7 Preparation of Instant Potato Soup Powder (IPSP) ............................................... 32
3.3 Analytical method .......................................................................................................... 33
3.3.1 Physical Parameter ................................................................................................ 33
3.3.1.1 Dimensions, sp. gr., shape of the tubers, peeling loss and flour yield ....... 33
3.3.1.2 Determination TSS (Total Soluble Solid) .......................................................... 33
3.3.1.3 Determination of Gelatinization temperature of potato flour ....................... 34
3.3.1.4 Determination of water absorption capacity of flours of different size ..... 34
3.3.1.5 Determination of Bulk density of flours of different size..............................
34
3.3.2 Chemical parameters ........................................................................................... 34
3.3.2.1 Determination of moisture content, protein content, crude fiber Reducing
sugar, sugar,sugar,Total sugar, Starch, vitamin C and Ash content ................................... 34
3.4 Optimization of ingredients in Instant Potato Soup Preparations ................................... 35
3.4.1Optimization of water ............................................................................................ 35
3.4.2 Optimization of salt ............................................................................................... 36
3.4.3 Optimization of citric acid ..................................................................................... 36
3.4.4 Optimization of monosodium glutamate (msg) ..................................................... 36
3.4.5 Optimization of potato flour particle size... 36
3.5 Sensory evaluations ........................................................................................................ 363.5.1 Sensory evaluation of Peeled Potatoes by different methods ................................ 36
3.5.2 Sensory evaluation of the instant potato soup preparations .................................. 36
3.6 Statistical Analysis ......................................................................................................... 37
3.7 Cost Calculation ............................................................................................................. 37
4 Results and Discussion ........................................................................................................ 38
4.1 Physical Characteristics of Unmarketable potato (Solanum tuberosum) ........................ 38
4.2 Chemical composition of Potato and Potato flour ........................................................... 40
4.3 Effect of Flour Particle size on Bulk Density and Water Absorption ............................. 41
4.4 Sensory Evaluation ......................................................................................................... 43
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4.4.1 Sensory Evaluation of Peeled Potatoes, peeled by different methods ................... 43
4.4.2 Optimization of Water Amount in Potato Soup .................................................... 43
4.4.3 Optimization of Salt Amount in Potato Soup ........................................................ 45
4.4.4 Optmization of Citric Acid Amount in Potato Soup ............................................. 46
4.4.5 Optimization of MSG Amount in Potato Soup ...................................................... 47
4.4.6 Optimization of Potato Flour Particle Size in Potato Soup .................................... 48
5 Conclusions and Recommendations .................................................................................. 51
5.1 Conclusions ..................................................................................................................... 51
5.2 Recommendations ........................................................................................................... 51
6 Summary .............................................................................................................................. 53
References ............................................................................................................................ 56
APPENDICES ...................................................................................................................... 61
Appendix A ........................................................................................................................... 61
Appendix B ............................................................................................................................ 62
Appendix C ............................................................................................................................ 63
Appendix D ........................................................................................................................... 65
Appendix E ............................................................................................................................ 67
Appendix F ............................................................................................................................ 69
Appendix G ........................................................................................................................... 71
Appendix H ........................................................................................................................... 73
Appendix I ............................................................................................................................. 75
Appendix J ............................................................................................................................. 81
Appendix K ........................................................................................................................... 82
Appendix L ............................................................................................................................ 86
Appendix M ........................................................................................................................... 87
Appendix N ........................................................................................................................... 89
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List of Tables and Figures
Tables
Table 2.1 Proximate analysis of white potatoes .................................................................... 8
Table 2.2 Inorganic Constituents of Potatoes ..................................................................... 10
Table 2.3 Cropping Calender in Nepal ................................................................................ 15
Table 2.4 Utilization of U.S. Potato Crops ......................................................................... 25
Table 4.1 Physical Characteristics of Unmarketable potato ............................................... 38
Table 4.2 Physical Characteristics of Unmarketable potato. ............................................... 39
Table 4.3 Chemical composition* of Potato and Potato flour ............................................ 41
Table 4.4 Summary of LSD (5%) test for difference between formulation (panelist =5)* . 43
Table 4.5 Summary of LSD (5%) test for difference between formulation (panelist =5)* . 44
Table 4.6 Summary of LSD (5%) test for difference between formulation (panelist =5)* . 45
Table 4.7 Summary of LSD (5%) test for difference between formulation (panelist =5)* . 46
Table 4.8 Summary of LSD (5%) test for difference between formulation (panelist =5)* . 47
Table 4.9 Summary of LSD (5%) test for difference between formulation (panelist =5)* . 49
Table B.1: The Average Chemical Composition of Flours Produced From Potatoes Grown
In Various Areas of USA ..................................................................................................... 62
Table D.1 Two way ANOVA (no blocking) for color in the optimization of water amount
in potato soup ....................................................................................................................... 65
Table D.2 Two way ANOVA (no blocking) for consistency in the optimization of water
amount in potato soup .......................................................................................................... 65
Table D.3 Two way ANOVA (no blocking) for flavor in the optimization of water amount
in potato soup. ....................................................................................................................... 65
Table D.4 Two way ANOVA (no blocking) for overall acceptance in the optimization of
water amount in potato soup ................................................................................................. 66
Table D.5 Two way ANOVA (no blocking) for taste in the optimization of water amount in
potato soup ............................................................................................................................ 66
Table E.1 Two way ANOVA (no blocking) for color in the optimization of salt amount inpotato soup ............................................................................................................................ 67
Table E.2 Two way ANOVA (no blocking) for consistency in the optimization of salt
amount in potato soup ........................................................................................................ 67
Table E.3 Two way ANOVA (no blocking) for flavor in the optimization of salt amount in
potato soup ............................................................................................................................ 67
Table E.4 Two way ANOVA (no blocking) for overall acceptance in the optimization of
salt amount in potato soup ..................................................................................................... 68
Table E.5 Two way ANOVA (no blocking) for taste in the optimization of salt amount in
potato soup ............................................................................................................................ 68
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Table F.1 Two way ANOVA (no blocking) for color in the optimization of citric acid
amount in potato soup ........................................................................................................ 69
Table F.2 Two way ANOVA (no blocking) for consistency in the optimization of citric
acid amount in potato soup ................................................................................................... 69
Table F.3 Two way ANOVA (no blocking) for flavor in the optimization of citric acid
amount in potato soup ......................................................................................................... 70
Table F.4 Two way ANOVA (no blocking) for overall accepatance in the optimization of
citric acid amount in potato soup .......................................................................................... 70
Table F.5 Two way ANOVA (no blocking) for taste in the optimization of citric acid
amount in potato soup ........................................................................................................... 70
Table G.1 Two way ANOVA (no blocking) for color in the optimization of msg amount in
potato soup ............................................................................................................................ 71
Table G.2 Two way ANOVA (no blocking) for consistency in the optimization of msgamount in potato soup .......................................................................................................... 71
Table G.3 Two way ANOVA (no blocking) for flavor in the optimization of msg amount in
potato soup ............................................................................................................................ 71
Table G.4 Two way ANOVA (no blocking) for overall acceptance in the optimization of
msg amount in potato soup .................................................................................................... 72
Table G.5 Two way ANOVA (no blocking) for taste in the optimization of msg amount in
potato soup ............................................................................................................................ 72
Table H.1 Two way ANOVA (no blocking) for color in the optimization of potato flour
particle size in potato soup .................................................................................................... 73Table H.2 Two way ANOVA (no blocking) for consistency in the optimization of potato
flour particle size in potato soup ........................................................................................... 73
Table H.3 Two way ANOVA (no blocking) for flavor in the optimization of potato flour
particle size in potato soup .................................................................................................... 73
Table H.4 Two way ANOVA (no blocking) for overall acceptance in the optimization of
potato flour particle size in potato soup ................................................................................ 74
Table H.5 Two way ANOVA (no blocking) for taste in the optimization of potato flour
particle size in potato soup .................................................................................................... 74
Table I.1 Scores of sensory attributes in the optimization of water amount in potato soup 75
Table I.2 Scores of sensory attributes in the optimization of salt amount in potato soup ... 76
Table I.3 Scores of sensory attributes in the optimization of citric acid amount in potato
soup ....................................................................................................................................... 77
Table I.4 Scores of sensory attributes in the optimization of msg amount in potato soup .. 78
Table I.5 Scores of sensory attributes in the optimization of potato flour particle size in
potato soup ............................................................................................................................ 79
Table I.6 Scores of sensory attributes in the sensory evaluation of the peeled potatoes. ..... 80
Table J.1 Two way ANOVA (no blocking) for of the grade points for the peeled potatoesappearance ............................................................................................................................ 81
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Table K.1 t-test (Two-Sample Assuming Equal Variances) for the ash content of potato
and potato flour. ..................................................................................................................... 82
Table K.2 t-test (Two-Sample Assuming Equal Variances) for the crude fibre of potato and
potato flour ........................................................................................................................... 82
Table K.3 t-test (Two-Sample Assuming Equal Variances)for the starch content of potato
and potato flour ...................................................................................................................... 83
Table K.4 t-test (Two-Sample Assuming Equal Variances) for the reducing sugar content
of potato and potato flour ..................................................................................................... 83
Table K.5 t-test (Two-Sample Assuming Equal Variances)for total sugar of potato and
potato flour ........................................................................................................................... 84
Table K.6 t-test (Two-Sample Assuming Equal Variances) for vitamin C of potato and
potato flour ........................................................................................................................... 84
Table K.7 t-test (Two-Sample Assuming Equal Variances) for protein content of potato andpotato flour ........................................................................................................................... 85
Table K.8 One way Anova (no blocking) for peeling losses between hand peeling, the
abrasive peeling and mashing peeling .................................................................................. 85
Table L.1 Cost calculation of potato flour ............................................................................ 86
Table L.2 Cost calculation of instant potato soup powder (IPSP) ....................................... 86
Table M.1 Recipe for the formulations for optimization of water ..................................... 87
Table M.3 Recipe for the formulations for optimization of citric acid .............................. 87
Table M.4 Recipe for the formulations for optimization of msg ........................................ 88Table M.5 Recipe for the formulations for optimization of flour particle size. ................ 88
Table N.1: Functional properties of Potato flour .................................................................. 89
Figures
Fig 2.1 Structure of Potato Tuber ........................................................................................... 7
Fig 3.1 Methodology for the preparation of instant potato soup powder ............................ 31
Fig 3.2 Preparation of Soup from instant potato soup powder ............................................. 33
Fig 4.1 Effect of potato flour particle size on bulk density ................................................. 42
Fig 4.2 Effect of potato flour particle size on water absorption ........................................... 42
Fig C.1 A grading scale for peeled potatoes description of the quality grades for peeled
Potatoes potatoes ................................................................................................................... 64
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Part I
Introduction
1.1 General introductionPotato is the term which applies either to the starchy tuberous crop from the perennial plant
Solanum tuberosum of the Solanaceae, or nightshade, family, or to the plant itself. Potato is
the world's most widely grown tuber crop, and the fourth largest food crop in terms of
fresh produce after rice, wheat, and maize ('corn') (Anon. 1, 2008).
Potato is a versatile, carbohydrate-rich food highly popular worldwide and prepared and
served in a variety of ways. Freshly harvested, it contains about 80 percent water and 20
percent dry matter. About 60 to 80 percent of the dry matter is starch. On a dry weight
basis, the protein content of potato is similar to that of cereals and is very high in
comparison with other roots and tubers. In addition, the potato is low in fat. Potatoes are
rich in several micronutrients, especially vitamin C - eaten with its skin; a single medium
sized potato of 150 g provides nearly half the daily adult requirement (100 mg). The potato
is a moderate source of iron, and its high vitamin C content promotes iron absorption. It is
a good source of vitamins B1, B3 and B6 and minerals such as potassium, phosphorus andmagnesium, and contains folate, pantothenic acid and riboflavin. Potatoes also contain
dietary antioxidants, which may play a part in preventing diseases related to ageing, and
dietary fiber, which benefits health. (Prokop, 2008).
Potatoes produce more nutrition, energy and edible biomass per unit area and time than
any other major crop (Anderson, 2008).Potatoes contain lower levels of phytic acid than
other plant foods and reasonable amounts of all the essential amino acids except
methionine and cystine. (Kulkarni et al., 2008).The nutritional value per 100g potato is 80
Kcal (320 kJ).(Anon. 1, 2008).
World potato production reached a record 320 million tonnes in 2007.Consumption has
increased: from an average of 9 kg/person in 1961-63 to over 14 kg/person nowadays.
Long taken for granted in developed countries, the potato has the potential to relieve the
pressure of increasing cereal prices on the poorest people and contribute significantly to
food security. World potato production and consumption are currently expanding more
slowly than global population. (Prakash, 2008).
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The United Nations is appealing for continued global attention on the role the potato can
play in providing food security and eradicating poverty in helping to achieve the
Millennium Development Goals. It said the potato is a staple, nutritious food that can
provide poor people with an inexpensive food that can stop hunger and keep people
healthy (Schlein, 2008).
Hundreds of millions of people in the developing countries are facing crisis as the cost of
their staple foods continues to rise. Rice prices have almost doubled during 2008 and wheat
prices are climbing rapidly. But the price of the potato, the worlds third most important
food crop, has remained stable ( Prokop, 2008).
In Nepal potato is grown over an area of1,53,534 ha with an annual average production
of1,943,246 t with an average yield of 12.6 t/ha (FAOSTAT, 2008). By estimated 2003
data, Nepal's population of slightly more than 25 million people consumed 1,650,000
metric tons of potatoes, or about 65 kilograms (kg) annual per capita consumption (Brown
and Scheidegger, 1995).
Different sized potatoes are produced at farm level. Consumer preferences of the
potatoes are high for large and medium sized potatoes. At farm level it is not preventable to
produce grade A and B potatoes without the production of grade D potatoes
(unmarketable) (Devraj et al., 2007). In potato production small tubers are considered as
losses because of low marketability characteristics (Haravani and Ahmadabad, 2008).
Unmarketable potatoes (
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Furthermore small tubers show a greater weight loss during storage relative to that of the
larger tubers in same storage environment (Wiersema et al., 1987).This prompts for the
immediate processing of such potatoes after harvesting.
Slow increase in world food production and declining rates of yield growth in main food
crops threaten world food security. Land and water constraints, underinvestment in rural
infrastructure and agricultural innovation lack of access to agricultural inputs, and weather
disruptions are impairing productivity growth and the needed production responses. These
factors, combined with sharp increases in food prices in recent years, have added to
concerns about the food and nutrition situation of people around the world, especially the
poor in developing countries. (Braun et al., 2008).As cereal prices rise, potatoes have the
potential to be the affordable food for the developing countries. So optimum utilization of
the produced potatoes is necessary.
International trade in potatoes and potato products still remains thin relative to
production, as only around 6 percent of output is traded. (Prakash, 2008). Processing of
potato can increase the trade of potato products.
In many developing countries, and especially in urban areas, rising levels of income are
driving a "nutrition transition" toward more energy-dense foods and prepared food
products. As part of that transition, demand for potato is increasing. (Dr Anderson, 2008).
In Nepal, by most accounts, potato seed generally consists of either smaller tubers culled
from a previous harvest (especially at higher altitudes), or smaller potatoes purchased from
ware markets (more common at lower altitudes) (Anon. 4, 2000).No attention has been
paid to prepare the value added products and emphasize the food use of the unmarketable
potatoes.
1.3 Objective of the study
1.3.1 General objective
The main objective of this research work is to prepare a value added product from
unmarketable potatoes.
1.3.2 Specific objectives1. To study peeling loss of the unmarketable potatoes from different peeling methods.
2. To study the total cost for formulation of new product and determine how economic
is it.
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3. To prepare potato powder and formulate a product; Instant Potato Soup Powder.
1.4Significance of the studyThe processing of unmarketable potatoes prevents colossal loses, adds value to the produce
and gives better returns to the growers.
In the present context of food insecurity and malnutrition, the utilization of the waste
going and sound unmarketable potatoes by some value addition can contribute to meet the
complex challenge of reducing poverty and ending hunger and malnutrition in a
sustainable manner.
This technological approach can be easily and economically applied in small scale,
creating additional employment opportunities.
Also this work introduces a new value added commodity prepared from potatoes.
1.5Limitations of the studyDespite the importance of the study, several inevitable circumstances limit the scope of the
work. The limitations are:
a. The study is limited to only a single potato variety, due to time constrains.
b. The sampling was done at the local region of Dharan, so it may not represent
the whole population in general.
c. The study is only to prepare a product; the potatoes can also be processed into
other varieties of products which couldnt be done due to lack of time and
adequate knowledge.
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Part II
Literature review
2.1 Historical background
The origin of the potato was the South American continent. Various species of wild tuber-
bearing Solanums are found in Central America, Mexico, and as far north as Colorado. But
before the coming of Columbus the potato was not cultivated outside of South America.
Possibly 2000 years before the Spanish conquest the native South Americans brought
potatoes under cultivation. In 1537, the Spaniards first came in contact with the potato in
one of the valleys of the Andes. (Smith, 1976).
The diffusion of the potato from the Andes to the rest of the globe reads like an
adventure story, but it began with a tragedy. The Spanish conquest of Peru between 1532
and 1572 destroyed the Inca civilization and caused the deaths - from war, disease and
despair - of at least half the population. The conquistadores came in search of gold, but the
real treasure they took back to Europe was Solanum tuberosum. The first evidence of
potato growing in Europe dates from 1565, on Spain's Canary Islands. By 1573, potato was
cultivated on the Spanish mainland. Soon, tubers were being sent around Europe as exotic
gifts - from the Spanish court to the Pope in Rome, from Rome to the papal ambassador in
Mons, and from there to a botanist in Vienna. Potatoes were grown in London in 1597 and
reached France and the Netherlands soon after. But once the plant had been added to
botanical gardens and herbalists' encyclopedias, interest waned. European aristocracy
admired its flowers, but the tubers were considered fit only for pigs and the destitute.
Superstitious peasants believed the potato was poisonous. At the same time, however,Europe's "Age of Discovery" had begun, and among the first to appreciate potatoes as food
were sailors who took tubers to consume on ocean voyages. That is how the potato reached
India, China and Japan early in the 17th century. The potato also received an unusually
warm welcome in Ireland, where it proved suited to the cool air and moist soils. Irish
immigrants took the tuber - and the name, "Irish potato" - to North America in the early
1700s. (FAO, 2008).
The potato (Solanum tuberosum L.) was introduced to coastal southern Asia in the late
sixteenth or early seventeenth century by European (initially Portuguese) mariners, but the
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6
historical record for roughly the following two centuries is complicated by the word itself
(Purseglove, 1968).
The first unambiguous evidence of potato cultivation in Nepal dates to 1793, in records
by a British Colonel Kirkpatrick (Akius et. al. 1990, cited in Khatri and Rai 2000, p. 61).
The potato remained a relatively minor and unrecognized crop in Nepal for over 150 years,
until the first official attempt to improve potato production in Nepal occurred in 1962
under a program sponsored jointly by Nepal and India. In 1972 the National Potato
Development Programme was founded by the Government of Nepal, focusing on the
production of higher quality potato seed tubers. Over the past few decades, potato has
become the fastest growing staple crop in Nepal. (Chapagain, 2001).
2.2 Structure of potato tuber
As the potato plant grows, its compound leaves manufacture starch that is transferred to the
ends of its underground stems (or stolons). The stems thicken to form a few or as many as
20 tubers close to the soil surface. The number of tubers that actually reach maturity
depends on available moisture and soil nutrients. Tubers may vary in shape and size, and
normally weigh up to 300 g (10.5 oz) each. At the end of the growing season, the plant's
leaves and stems die down to the soil level and its new tubers detach from their stolons.The tubers then serve as a nutrient store that allows the plant to survive the cold and later
regrow and reproduce. Each tuber has from two to as many as 10 buds (or "eyes"),
arranged in a spiral pattern around its surface. The buds generate shoots that grow into new
plants when conditions are again favorable. (FAO, 2008)
Morphologically the tuber is a fleshy stem bearing buds or eyes in the axils of scale-like
leaves which soon shed, leaving a ridge or leaf scar subtending the bud. (Clark, 1921).
The anatomy of the potato plant, including the tuber, has been described in detail by
Artschwager (1918 and 1924) and others. The tuber itself is essentially an abruptly
thickened underground stem closely resembling the aerial stem of the plant (Talburt et al,
1975).
Externally the tuber clearly shows its relation to the aerial stem. Each eye is a
rudimentary scale leaf or leaf scar with its auxiliary buds. As on the stem, these are
arranged in a right-handed or left-handed spiral around the tuber, 13 eyes to 5 turns of the
helix (5/13 phyllotaxy). Each eye contains at least three buds together with protecting
scales. (Schwimmer et al, 1957).
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The principal areas in the mature tuber from the exterior inward are the periderm, cortex,
vascular cylinder, perimedullary zone and central pith. The periderm is 6 to 10 cell layers
thick acting as a protective area over the surface of the tuber. Small lenticel-like structures
occur over the surface of the tuber. Small lenticel-like structures occur over the surface of
the tuber. These develop in the tissue under the stomates and are initiated in the young
tuber when it still has an epidermis. Periderm thickness varies considerably between
different varieties. Cultural conditions also, however, influence thickness of periderm
rendering this characteristic too variable to use for variety identification (Fig 2.2).The
cortex is a narrow band of storage tissue next to the periderm. The outer layers of cells
contain protein crystals, tannins, pigments in colored varieties, and some starch. The
vascular cylinder and the perimedullary zones are narrow. These zones contain secondary
xylem and phloem. The principal region of storage parenchyma is immediately inside the
vascular ring (Talburt et al, 1975). Tuber growth is largely due to enlargement of the
perimedullary zone and is of procambial origin (Reeve et al, 1973).
The pith consists of a small central core with arms of medullary parenchyma radiating
from it. The cells are low in starch, high in water, and are more translucent than other
tissues (Talburt et al, 1975).
Fig. 2.1 Structure of potato tuber
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2.3 Chemical composition of potato
Starch, comprising some 65 to 80 percent of the dry weight of the potato tuber, is
calorically the most important nutritional component. The two main or perhaps sole
components of the starch, amylose and amylopectin, are present in a ratio of 1:3
(McCready and Hassid, 1947). Of the minor constituents of the starch granule only
phospho9rus has been shown to be chemically combined with the starch (Posternak,
1951).The sugar content of potatoes may vary from only trace amounts to as much as ten
percent of the dry weight of the tuber and thus 1/3 to of the non-starch solids (Barker,
1938).Sucrose, glucose, and fructose comprise the major sugar of the potato (Schwimmer
et al., 1954).Nonstarch polysaccharides largely comprise the cell wall and cementing
substances between the cells of the tuber. These largely are (1).Celluloseis present in the
cell wall and comprises 10-20% of the nonstarch polysaccharide of the potato (2) Crude
fiber consists largely of cell wall components including suberin and lignin. Approximately
one per cent of the dry weight of tubers is crude fiber although extremes of 0.2-3.5% have
been found. (3) Pectic substances are polymers of galac-turonic acid with the carboxyl
groups largely methylated. It ranges from 0.7 to 1.5% of the dry weight of the potato, the
skin being especially high in this substance (Potter and McComb, 1957). (4)Hemicelluloses
are mixed glycosidic chains containing combinations of glucuronic acid with xylose and of
galacturonic acid with arabinose. Approximately 1% of the total crude polysaccharide of
the potato is hemicellulose and occurs largely in the cell walls (Schwimmer and Burr,
1975). (5)Potatoes also contains ethanol-soluble oligosaccharides which consists of
glucose and fructose residues (Schwimmer and Weston, 1956).
Table 2.1 Proximate composition of white potatoes.
Average percent Range percent
Water 77.5 63.2-86.9
Total solids 22.5 13.1-36.8
Protein 2.0 0.7-4.6
Fat 0.1 0.02-0.96
Carbohydrate
Total 19.4 13.3-30.53
Crude fiber 0.6 0.17-3.48
Ash 1.0 0.44-1.9(Source: Kroner and Volksen, 1950)
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The total nitrogen content of potatoes ranges from one to two percent of the dry weight.
About 1/3 to of the total nitrogen is present as protein. The proteins of potato tubers are
comprised of about 60-70% globulins and 20-40% glutelins with no albumins or
prolamines present. Amino acid composition of these two fractions differs: glutelins
contain more cystine, aspartic acid, proline, and tryptophan than do the globulins. Free
ammo acids amounted to 4050% of nonprotein N (Tavrovyskaya, 1964).The bulk of non
protein fraction, comprising up to two-thirds of the total nitrogen, is present as free amino
acids as shown by work of Ashford and Levitt (1965).21 amino acids have been identified
as normal constituents of the alcohol soluble nitrogen of potato tuber tissue (Dent et al.,
1947).
The average fat content (ether-extractible matter of the potato is in the neighborhood of
0.01 percent on a fresh weight basis, with a range of about 0.02 to 0.2 percent (Schwimmer
and Burr, 1967) of which 40% linoleic, 30%linolenic, 5% oleic, and 25% saturated acids
are present (Highlands et al., 1954).
In addition to the amino and fatty acid the following organic acids have been found in
potaotes: citric, isocitric, ascorbic, lactic, malic, tartaric, succinic, oxalic, hydroxymalonic,
aconitic, phytic, alpha ketoglutaric, quinic, caffeic, and chlorogenic (Kroner and Volksen,
1950). The total acid content in the juice of potatoes is several times greater than the
content of acids capable of being initially titrated and is 0.84-1.15% calculated as citric
acid. One medium sized potato contains 20 mg. of vitamin C (Mc cay, 1956).The phenolic
compounds of poatatoes are associsated with the color of the raw poataotes. Tyrosine, the
major monohydric phenol of potatoes, is present in the inner portion of the tuber and
constitutes 0.1 to 0.3 % of the dry weight of the potato. The inorganic constituents or
mineral content of potatoes are tabulated in table 2.2.
2.4 Nutritive value of potatoes and potato flour
Nature has designed only a few foods that are capable of nourishing the great population of
the world. Of these, the white potato is one. Beneath its skin are liberal stores, not only of
energy, but of nitrogen and a high quality protein that will support growth and health.
Valuable minerals are there such as iron and magnesium and essential vitamins such as
vitamin C and several of the B vitamins. These are ample reasons why nutritional
deficiencies are little known in the countries whose populations depend on potatoes as their
basic food. The composition of potatoes varies as to varieties, storage, season, soils, and
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fertilization. However, average values to remember for the chief components of potatoes
are: protein and protein-like substances, two percent; carbohydrates about 18 percent; fat,
one-tenth of one percent; and water almost 80 percent. In addition of course are the
vitamins and minerals in potatoes, expressed in milligrams.The high water content of
potatoes should be noted, because when potatoes are compared in values to a food such as
rice which is nearly dry, the impression given is unfair. For instance, potatoes with two
percent protein would appear inferior to rice with sevent percent protein. For a truer
comparison, one should multiply the values of potatoes by five. This gives a value of ten
percent for the protein. If the quality of the protein is equally good, this explains why
millions of men can live on a diet comprised mostly of rice and others can thrive equally
well or even better upon a diet rich in potatoes. This matter of expressing chemical values
on a moist or dry basis is well known to food chemists, but it is poorly understood by
those who are not accustomed to thinking in these terms.(McCay, 1956).
Table 2.2 Inorganic constituents of potatoes.
Dry Basis (mg per 100 gm.)
Dry Basis (ppm.)
P 43.0-605 Br 4.8-8.5
Ca 10-120 B 4.5 -8.6Mg 46-216 I 0.5 -3.87
Na 0-332 Li TraceK 1394-2825 As 0.35
Fe 3-18.5 Co 0.065
S 43-423 Ni 0.26Cl 45-805 Mo 0.26
Zn 1.7-2.2
Cu 0.6-2.8
Si 5.1 -17.3
Mn 0.18-8.5
Al 0.2-35.4
(Source: Lampitt and Goldenberg, 1940)
Although potato flour is used in the baking industry, it has not been used much in home
cookery and is not widely available in retail stores. Hence, it is a product somewhat
foreign to the housewife, but one that could be used. Potato flour has found some use in
preparing special foods in mental hospitals for groups such as the spastic feeble-minded.It
is very useful in making mixtures of high nutritive value. In these cases it is easily prepared
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as a gruel with hot water on milk. Such gruels have special merit because they are slightly
sticky and hence not easily rejected by those who must be fed regularly. (McCay, 1956).
2.5 Potatoes in Nepal
Agriculture remains the mainstay of the national economy of Nepal, accounting for
approximately 40 percent of the Gross Domestic Product (GDP) and 81 percent of
employment (Chapagain, 2001). Most agricultural production is still characterized by
relatively low mechanical and chemical inputs. Since the 1960s, productivity of major
crops such as wheat, paddy rice, and sugarcane has grown in absolute terms, but relatively
less than Nepal's neighboring South Asian countries which raised productivity at a faster
rate with more rapid and intensive adoption of green revolution technologies (Chapagain,
2001). Agricultural production in Nepal has been enhanced by an expansion of land
accessible to irrigation, from approximately 6,200 hectares in 1956 to nearly 583,000
hectares by 1990 (Anon. 2, 2008).
In the 1970s, a national potato development programme, focused on improving the
quality of seed potato, stimulated a rapid expansion of both cultivated area and production,
which increased from 300 000 tonnes in 1975 to a record 1.97 million tonnes in 2006. The
potato is now Nepal's second staple food crop, after rice, and per capita consumption hasalmost doubled since 1990 to 51 kg a year. Potatoes are widely grown in Nepal, at below
100 m altitude in the south to as high as 4 000 m in the northern mountains. The tuber is
particularly favored by farmers in high hills areas (roughly 1 800 to 3 000 m): it is more
productive than rice and maize and the cool climate is well suited to production of seed
tubers for sale at lower altitudes. (FAO, 2008).
Current and potential gains in agricultural productivity should, however, be considered in
light of population growth, increasing at an annual rate of 2.3 percent as of 2003, and the
diminishing quality of agricultural land. Population density is particularly high in the
valleys and lowlands where the vast majority of the population of Nepal is concentrated.
Potato, as a crop capable of high productivity relative to land and time, is likely to remain
important to Nepal's food security and agricultural economy (Chapagain, 2001).
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2.5.1 Geography and production zones
2.5.1.1 Physical geography
Nepal is a landlocked country of approximately 147,000 square kilometers located between
China and India, "a yam caught between two rocks" (Anon. 2, 2008). However, for a small
country, Nepal is a land of great physical diversity, from tropical plains in the south of less
than 100 meters above sea level (masl) to hills and mountain ranges, reaching the world's
highest peak, Sagarmatha (Mount Everest) at over 8,800 masl. The increasing elevation isnot always uniform, but rather is characterized by a maze of mountains, hills, and lower
altitude valleys, resulting in a wide diversity of ecotypes and strong variations over short
horizontal distances. Differences in altitude, slope and aspect (the direction in which the
slope of the land faces) can result in a tremendous diversity of soils, drainage, solar
exposure, diurnal temperature regimes, and evapotranspiration conditions.
Nepal can be classified very generally into altitudinal zones which form roughly parallel
belts from east to west, occasionally bisected by the country's river systems. These zones
can be described as (Dhital 2000, pp. 7-10):
Terai (below 350 masl), the southern belt, forming the northern rim of the greater
alluvial Indo-Gangetic Plain stretching from the Punjab of Pakistan and India to the
delta of the Ganga (or Ganges) in Bangladesh, accounting for 17 percent of total
land area, but 42 percent of cultivated land, much of it devoted to rice and wheat;
Low Hills (350 - 1,000 masl), characterized by river valleys which support rice,
maize, and wheat, and in some areas double cropping of rice where irrigation isavailable;
Mid Hills (1,000 - 1,800 masl), with a warm climate that supports citrus, as well as
maize, rice, wheat, finger millet, soybean, and some potato;
High Hills (1,800 - 3,000 masl), where potato becomes the most important crop,
both for subsistence and commercial production, other crops including temperate
fruits, barley, and buckwheat;
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Mountains (above 3,000 masl), where permanent settlement is not common and
agriculture is possible only in valleys along southeastern slopes, and people are
otherwise dependent on livestock production and tourism.
2.5.1.2 Climate
Although Nepal's latitudinal range is narrowly restricted from approximately 27 to 30 N,
climatic variations, determined primarily by altitude, range from tropical and subtropical to
cool temperate to permanent arctic cold. The complexity of factors which determine
Nepal's climate can make it highly variable not only over space, but also over time. Local
climatic variation is one of the most serious risk factors facing farmers in Nepal; hazards
can include drought, extreme rain, and even hail (Dhital 2000, pp 8-10).
Precipitation is determined by several factors, especially altitude, longitude, and local
aspect. Up to approximately 3,000 masl, annual precipitation generally increases with
greater altitude, but thereafter decreases. Longitude is a factor since the summer monsoon,
generated by moist tropical air over the Bay of Bengal, decreases from east to west. At
lower altitudes, eastern Nepal receives approximately 2,500 millimeters (mm) of rain
annually, the Kathmandu area about 1,420 mm, and western Nepal about 1,000 mm. The
monsoon, generally from June through September, is the most important source ofprecipitation to farmers, providing more than 70 percent of the annual precipitation
received by the plains and lower altitude Himalayas. However, within this general pattern,
local conditions can vary over short distances. Aspect is locally significant since slopes
facing predominately east or south receive more precipitation, while slopes facing north
toward Tibet are especially arid. Winter snowfalls in the Himalayas are also an important
source of water for spring and summer crops, especially as more land has been made
accessible to irrigation (Anon. 2, 2008).
2.5.1.3 Regional distribution of potato production
Potatoes are widely grown throughout Nepal, from the southern terai at altitudes below
100 masl, to the northern mountains as high as 4,000 masl. The potato crop becomes
relatively more important in the high hills areas (from roughly 1,800 to 3,000 masl), as it
becomes more productive relative to staples such as rice, maize and finger millet. This
altitude range is also well suited to the production of potatoes to be used as seed tubers in
lower altitude areas, since viral degeneration generally occurs more slowly at higher
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altitudes and storage is much less of a challenge. The harvest in the high hills area, from
July to September, also complements the cropping calendar of the terai and low hills,
where planting takes place from September through December (Dhital 2000, p. 12).
2.5.2 Production systems and constriants
2.5.2.1 Land use and land tenure
As of 1998-99, land use distribution in Nepal was estimated by percentage as: Agriculture
27; Forest 38; Pasture 12; Other 23 (e.g. scrubland, permanent snow, and rock) (Khatri and
Rai 2000, p. 5). Forests in Nepal are being lost very rapidly, by roughly half from 1950 to
1980 (Anon. 2, 2008). Maintaining a forest cover of approximately 38 percent has become
a policy goal, but a difficult challenge as much of the remaining forest cover is in the terai,
the destination over the past several decades of settlers from higher latitudes (Chapagain,
2001). Nepal's future agricultural sustainability will have to rely on the productivity of
existing agricultural land, not new land developments.Nepal is still contending with a long
history of feudalism, whereby landlords held most of the kingdom's agricultural land.
Beginning in the 1950s, several legal remedies have been initiated by the state to limit land
ownership and regulate rent paid by tenants, but with limited results. In some cases, legal
reforms were expected well in advance of their passage, allowing landlords to redistribute
surplus land (on paper) among relatives or to otherwise conceal ownership. The amount of
land clearly redistributed under legal remedies has been estimated at less than two percent
of all agricultural holdings (Chapagain, 2001).
Due partly to the continued concentration of landholding, as well as the effects of a
rapidly growing population on land division via inheritance, most agricultural land
holdings are very small-scale and fragmented. A farm usually consists of several small
nonadjacent parcels. According to the 1991 National Sample Census of Agriculture (cited
by Chapagain, 2001), the average number of parcels per farm was nearly four, while the
number of parcels per hectare was just above four. These figures are regionally variable,
but that average is characteristic of the hills region where the potato crop is most
important. Land fragmentation partly reflects a strategy to minimize risk by exploiting a
wider range of ecologies, but can also be considered a structural challenge to agricultural
modernization, as small and fragmented holdings can inhibit the adoption of new
technologies, such as irrigation structures, to enhance production (Chapagain, 2001).
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2.5.2.2 Cropping calendar
The great agro-ecological diversity of Nepal allows for potato cultivation to occur
somewhere at any time of year. Potato is a winter crop in the terai and low hills, a spring
and autumn crop in the mid hills, and a summer crop in the high hills and mountains. The
duration of a crop is variable by variety, but is longer at higher altitudes. The generalized
cropping calendar is summarized in Table 2.3 (Dhital 2000, p. 13).
2.5.2.3 Cropping patterns and fertility management
Agriculture in Nepal remains predominately subsistence-based with minimal use of
external inputs, depending on a close interrelationship among crops, forestry and
livestock. Crops supply feed to livestock, while crop production depends on animal draft
power and manure as fertilizer (Dhital 2000, p. 10). Forest management has long been an
essential component of land management, given the extremely high potential for erosion
facing most land in Nepal.
Table 2.3 Cropping calender in Nepal
Zone Altitude (masl) Planting Months Harvesting Months
Terai Up to 350 October - November January - February
Low Hills 350 - 1,000 September - December December - March
Mid Hills 1,000 - 1,800 January - February April - June
August - September November - December
High Hills 1,800 - 2,200 February - March July - August
2,200 - 3,000 March - April July - September
Mountains 3,000 - 4,000 Late April - Early May September - October
(Source: Dhital, 2000)
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Given the extreme features of the physical geography above the terai and low hills,
effectively isolating small communities, many farmers have had minimal access to either
markets or wider social networks. That isolation, combined with the capricious climate
across much of Nepal, has favored agricultural strategies driven more by risk aversion than
profit seeking, although this situation is changing in some places with greater road access.
Intercropping, as opposed to crop specialization, remains a common practice, especially at
higher altitudes.The Nepal Agricultural Research Council (NARC) has reported that
studies conducted to assess the effects of intercropping various legume crops on the
production of rice and potato did not provide evidence of enhanced yields of potatoes,
though the grain and straw production of rice were both positively influenced by previous
legume crops, and potatoes contributed a high share of food energy relative to time and
land area. Two cropping patterns which provided high grain and straw yields of rice were:
faba bean-potato-rice, and sweet lupine-potato-rice (Anon. 3, 2008).
The Potato Development Section (PDS) of the Department of Agriculture has
recommended soil amendments of either farmyard manure at the rate of 20 tons per hectare
(T/HA) or commercial fertilizer at the approximate rate (by T/HA) of: Nitrogen 100;
Phosphorous 100; and Potassium 60 (PDS, 2002, pp. 11-37). In practice, application
depends on the availability of commercial fertilizer and/or animal resources and labor to
apply manure. Since seed tubers are a major factor of production costs, farmers have to
weigh the relative benefits of larger tubers, which produce faster initial growth and higher
potential yields, but at higher cost. By most accounts, potato seed generally consists of
either smaller tubers culled from a previous harvest (especially at higher altitudes), or
smaller potatoes purchased from ware markets (more common at lower altitudes). General
recommendations of potato crop spacing by the Department of Agriculture are to plant 25-
50 gram tubers 60-75 centimeters (cm) row to row and 20-30 cm plant to plant, for anoverall seed rate of one to two tons per hectare. A crop stand of 30 main stems per square
meter is considered optimal (ibid.).The recommended practice for harvesting is to cut
haulms approximately ten days prior to harvest in order to promote maturation of the
potato skin and therefore minimize bruising and damage during harvest. It is not reported
to what extent this practice is followed. Potato harvesting in Nepal is predominately
manual, as mechanization is rarely feasible in the steep and isolated areas where much of
the crop is grown. (Anon. 4, 2008)
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2.5.2.4 Occurrence and control of potato diseases and pests
This list is not complete, but includes several diseases and pests known to be serious
constraints to potato cultivation in Nepal.
Late Blight (LB), possibly the greatest biological constraint to potato cultivation
worldwide, is caused by a fungus-like oomycete, Phytophthora infestans, which is a
specialized pathogen of potato and, to a lesser extent, tomato (another member of the plant
family Solanaceae).
Late blight was first reported in Nepal between 1883 and 1897 and has been appearing as
an epidemic since the mid 1990s (Ghimire et. al. 2003, p. 236). According to Dhital and
Ghimire (1996, cited in Ghimire et. al. 2003), a nation-wide crop failure due to LB
occurred in 1996, although production data reported by FAO for that year do not reflect a
drop in either yields or production. Regional outbreaks are common, and cultivars once
considered LB resistant are apparently becoming less so.
Isolates of P. infestans collected during the 1999 and 2000 cropping seasons and
characterized for nuclear and mitochondrial DNA polymorphisms provided evidence of the
introductions of relatively new populations including both A1 and A2 mating types,
possibly with implications regarding resistance to metalaxyl, a systemic fungicide widely
used in LB control, though probably not widely used in the lower input cultivation of
Nepal (Ghimire et. al. 2003).
Several varieties selected by CIP for resistance to LB have been evaluated in Nepal,
including CIP clones 387146.48, 387199.33, 388764.6, 387224.11 and 388764.26 (Khatri
and Rai 2000, p. 63).
Black Scurfis a fungus,Rhizoctonia solani, that attacks tubers, underground stems, and
stolons of potato plants, especially in cool, damp soils. Although generally described as
more of a cosmetic problem due to black irregular encrustations of fungal sclerotia, it has
been described as a major concern, spreading from the plains into the hills of Nepal. Seed
treatment of two percent acetic acid and 0.2 percent zinc sulfate or three percent boric acid
alone has been reported as an effective control (Khatri and Rai 2000, p. 63), although these
materials are probably not readily available to most farmers.
Bacterial Wilt ( Ralstonia solanacearum) is the most destructive bacterial disease of
potato and several other plants of economic importance. The bacterium identified in Nepal
has been identified as Race 3, biovar 2. Yield losses have been reported as annually andspatially variable, but potentially capable of nearly complete crop loss.
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Due to its wide host range and a lack of resistant varieties, the disease is difficult to
control, except via long-term rotation with non-host crops, use of disease-free planting
material, and hygienic practices in general (Khatri and Rai 2000, p. 63). There is some
evidence that non-solanaceous summer weeds might play a greater role as disease vectors
than was previously assumed (Pradhanang et. al. 2000). Control efforts are challenging,
but feasible with widespread community involvement.
Vulnerability appears to correlate with soil amendments. Various treatments of urea,
lime and stable bleaching powder (or SBP,) have been shown to correlate with varying
degrees of infection of the highly susceptible variety "Kufri Jyoti" in a field naturally
infested with R. solanacearum for over 15 years. A treatment of urea (428 kg/ha) and
lime (5 t/ha) followed by SBP (25 kg/ha) seemed to provide a suppressant effect, though
the use of SBP alone at the rate of 25 - 37 kg/ha might be more economically efficient
(Anon.5, 1998).
Viral Diseases. The common practice of keeping smaller potatoes (or larger potatoes cut
into smaller pieces) from a general harvest for seed, with little regard for disease, favors
the transmission of viral infection. Potato Virus X (PVX) has been reported as more
serious in the hills, while PVY is prevalent in the lower altitude plains. PVM and PVS are
found in both areas. Degeneration studies have indicated that yield can be decreased by
3.6 percent for each 10 percent increase in viral infection (Khatri and Rai 2000, p. 63).
2.5.3 Varieties and seed systems
2.5.3.1 Varieties
Since the potato is of relatively recent origin to Asia, far fewer varieties are cultivated than
in the potato's Andean homeland range. Brown and Scheidegger, writing in 1995, reported
that only eight varieties were in local cultivation in Nepal, of which four were included in
seed multiplication programs (Brown and Scheidegger 1995, p. 19). Nepal has very likely
received, formally or through less formal diffusion, several varieties developed by the
Central Potato Research Institute (CPRI) of India, including Kufri Jyoti, introduced to
Nepal in the mid 1960s and currently considered the oldest and most widely grown of
"improved varieties" (Dhital 2000, p. 47). Varieties that have been present for several
generations are likely to bear several local names. Sikha Local and Gumda Local are
popular varieties in the mid to high hills, both grown under various local names. Severalother varieties persist from their introduction via the British colonial presence in India
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several generations ago, e.g. Darjeeling Red Round and Magnum Bonum. Cultivar CIP-
379693.110 has more recently been introduced under the name P-110, recommended for
cool tropical to warm tropical regions. NPI/T-0012 was introduced via Mexico as a testing
material in the late 1960s and has since been maintained by farmers in the high hills of the
western region. All of these cultivars belong to Solanum tuberosum spp. tuberosum,
except NPI/T-0012, which may belong to the subspecies andigena (Dhital 2000, p. 47).
This brief listing is by no means complete. A section of the 1996-97 annual report
posted by the Nepal Agricultural Research Council (NARC) pertaining to varietal
improvement efforts noted that sixteen local cultivars collected from different areas of
Nepal were being used in trials, in addition to recently introduced varieties. Nonetheless,
the introduction of new varieties is a recent effort in Nepal (Anon. 3, 2008).
2.5.3.2 The "Informal" seed system
A "seed system" is broadly defined as "an interrelated set of components including
breeding, management, replacement and distribution of seed." (Thiele, 1998, p. 84). Most
tuber seed used in Nepal has been produced and distributed by farmers themselves (the
informal system). The replacement interval can depend on several factors, such as a
gradual decline in yields due to viral degeneration or a natural calamity such as hail,drought, or severe late blight (Rhoades 1985, cited in Dhital 2000, p.14).
In the terai zones, farmers often depend for seed on the ware potato market in India, much
of it based on potatoes kept in cold storage. In the mid-hills, farmers sometimes acquire
new seed from the mountains, taking advantage of slower viral degeneration at higher
altitudes. But even in the mid-hills, seed from the lower altitude terai probably accounts
for a greater volume than seed from higher altitude sites (Brown and Scheidegger 1995, p.
9).
Potato farmers at higher altitudes have traditionally been almost entirely self-sufficient in
seed, depending either on a portion of their own harvests retained for seed, or very local
exchanges. Varietal population structures at remote higher altitude locations have
generally reflected minimal input from the formal system. Tubers retained for seed are
usually small, typically ten to fifty grams (Dhital 2000, p. 14).
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2.5.3.3 The "Formal" seed system
The formal system refers to seed tubers produced and distributed by state-sponsored
institutions (possibly with some involvement of the private sector and/or non-government
organizations). Seed from the formal sector has generally been subject to inspections and
controls intended to assure that the seed is of the variety claimed, with low incidence of
disease or pest infestation, of appropriate physiological age and otherwise viable. "Pre-
basic" and "basic" seed are multiplied into "certified seed," generally in the form of smaller
seed tubers (tuberlets) available for distribution to farmers, although the precise definitions
of these terms are locally variable.
The higher altitude regions of Nepal, among the most isolated places in the world where
access by road is extremely limited, pose an especially difficult challenge to any attempt by
a formal system to make improved potato seed tubers more accessible to farmers. This
limitation, combined with the advantages offered by higher altitudes being less subject to
viral diseases, favors the placement of the last stages of seed multiplication by the formal
system as close as possible to the ultimate users. Such locations, however, pose a
challenge to regular supervision by a technical staff, leaving farmers with more
responsibility for the management of any certified seed made available to them by the
formal system.
This effort, under the direction of NARC with assistance from the Swiss Development
Corporation (SDC) and the International Potato Center (CIP), has depended on groups of
farmers who receive training, but little subsequent supervision or direct incentives. Since
many of these groups are located in mountainous regions, the "head points" in the
traditional seed system, the goal is to inject the entire system with higher quality seed,
including some of promising new varieties, and thereby to enhance yields widely
throughout Nepal. Potato production by farmers involved in this effort seems to have
improved significantly (Brown and Scheidegger, 1995 p. 17).
A program is operated by NARC to provide certified seed.
A history of recent efforts to distribute improved quality seed, with the current
focus on Seed Producer Groups (SPGs), is well described in the CIP Program.
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2.5.4 Consumption, storage and marketing
2.5.4.1 Consumption
By estimated 2003 data, Nepal's population of slightly more than 25 million people
consumed 1,650,000 metric tons of potatoes, or about 65 kilograms (kg) annual per capita
consumption. This is very high by world standards, about the same as Peru, within the
potato's center of origin, and over twice the average consumption rate of India. Higher
production in the high hills zone is reflected in higher consumption. Brown and
Scheidegger (1995, p. 39) estimated that in 1991-92, per capita consumption was
approximately 24 kg in the terai, and over twice that, 51 kg, in the hills and mountains.
Production and consumption have considerably increased in both areas since then.
The potato has been creatively adapted to Nepali cuisine, as for example potato curry
(Brown and Scheidegger, 1995).
2.5.4.2 Storage
In keeping with the great diversity of agro-ecologies and agricultural practices in Nepal,
there are several methods used to store potatoes. Generally, however, there is not much
initial distinction between seed and ware potatoes; all are stored the same way.
In the terai, at altitudes up to 350 masl where high temperatures do not allow for longer-
term storage (more than perhaps two months), potatoes are usually sold soon after harvest.
The cold storage industry, which has become very important to potato marketing in India,
has yet to develop in Nepal. More recently introduced "improved varieties" are generally
more susceptible to high storage temperatures (Dhital 2000, p. 16).
In the low and mid hills (approximately 350 - 1,800 masl), farmers do not generally try tostore potatoes for seed, but rather rely on seed obtained from other areas. At higher
altitudes within this range, seed potato storage in partial diffused light is an old established
practice, as potatoes are often kept in different layers in bamboo baskets. Diffused light
promotes the growth of sprouts which are short and stout, ideal for viable seed tubers
(ibid.). Longer-term storage becomes much more feasible in the high hills, above 1,800
masl. Several methods are used, including storage in darkness in any available space in a
farmhouse, in clamps dug into the ground, or in some cases leaving potatoes unharvested
in the field for an extended period, although this last option is uncommon due to a high
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instance of rotting (ibid.).Although the viability of traditional methods generally increases
with altitude, storage losses in general appear to be increasing due to growing infestations
of several diseases and pests, e.g. late blight, bacterial wilt, soft rot (Erwinia spp.), dry rot
(Fusarium spp.), and potato tuber moth (Phthorimaea operculella) (ibid.). (Dhital, 2000).
2.6 Grading and marketing of potatoes
The purpose of grading is to aid in standardization of a product and to facilitate marketing
it. Sorting and packing potatoes to a set of recognized official standards enables producer
and buyer to communicate more intelligently concerning the value of the product. An
important aspect of grading is the use of a set of uniformly accepted standards. Grading is
of direct benefit to all parties concerned in the buying and selling transaction (Smith,
1976).
Profitable marketing of an agricultural commodity is an essential part of the total
production program for the producer. Marketing provides the necessary step from the farm
to the consumer. Without an efficient marketing procedure, even the finest quality crop can
be an unprofitable one (Smith, 1976).
Marketing in potato production begin with some vital decisions as choice of variety and
planting practices which will affect tuber size, shape and consumer acceptance.Market demand for potatoes is made up of such factors as variety, color, size and shape of
tuber, grade, uniformity, cooking quality, package size and type, cleanliness, and other
quality factors. It also involves the form in which the commodity is marketed, i.e., fresh vs.
one of the many processed forms of potato products (Schoenemann, 1976).
In Nepal Although many farmers who grow potatoes do so for cash income (especially at
lower altitudes in relatively accessible areas), there are not yet any organized marketing
services or cooperative organizations to facilitate regular marketing. Such organizations
could develop from the seed producer groups, farmers organized to multiply and distribute
high quality seed tubers, but so far this subject has not yet been reported (Dhital, 2000).
2.6.1 Size grading of potatoes
In addition to various physical grading of the product, modern grade standards for potatoes
also provide for marketing in various tuber size classes. Sizing of potatoes has become a
more widespread practice in recent years. The development of individual tuber sizing
machines has led to marketing of potatoes in special count packs. It is now possible for a
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buyer to purchase containers of potatoes with all tubers practically identical in weight and
to a large degree identical in shape. This is of special value to the hotel and restaurant
trade, where uniformity is required in preparing and serving baked potatoes. Housewives,
too, often prefer buying packages of potatoes in which tubers are sized to definite limits
(Eberhard and Eke, 1951).
In potato production small tubers (smaller than 35 mm) are considered as losses because
of low marketability characteristics (Haravani and Ahmadabad, 2008). At farm level it is
not preventable to produce grade A and B potatoes without the production of grade D
potatoes (unmarketable) (Devraj et al., 2007).
In USA, it has been found that, whole potatoes, usually smaller than 1.5 inches in diameter,
make up the greatest part of the potatoes that are canned. The potatoes used are not
specifically grown for canning but are primarily the small sizes of potatoes not suitable for
fresh market (Talburt, 1975).
Since seed tubers are a major factor of production costs, In Nepal, farmers have to weigh
the relative benefits of larger tubers, which produce faster initial growth and higher
potential yields, but at higher cost. By most accounts, potato seed generally consists of
either smaller tubers culled from a previous harvest (especially at higher altitudes), or
smaller potatoes purchased from ware markets (more common at lower altitudes) (Anon. 4,
2008).
2.6.2 Economics of grading
The economics of grading potatoes often poses certain problems for the producer. Sorting
out the top premium quality tubers leaves a residue of potatoes of rather low general grade
quality which often commands a relatively low price (Kross, 1952). The residue is usually
of adequate quality to allow for their use in various processed products (Smith,
1976).Unmarketable potatoes due to their small size (
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sized potato tubers indicate the desire for a medium-sized potato. The reasons most often
given are: (1) right size for judging portions; (2) easy to peel and handle; (3) easily adapted
to several cooking methods, and (4) less waste in peeling (Anon.6, 1948). For baking
purposes at home a 7-10 oz. p