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Postharvest Handling

Roots and Tubers

Marita Cantwell

Dept. Plant Sciences

University of California, Davis

Root, Tubers & Bulbs

CBA

PotatoTurnipGarlic

JicamaParsnipOnion

TaroSalsifyBeet

YamCeleriacRadish

SweetpotatoHorseradishCarrots

CassavaSunchokeRutabaga

Root, Tubers & Bulbs

General Characteristics

Storage organs (carbohydrates)

Relatively low respiration rates

Low surface to volume ratios

Bulky and weighty

Relatively long shelf-life (months)

Postharvest sprouting, rooting

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Root, Tubers & Bulbs

CBA

PotatoTurnipGarlic

JicamaParsnipOnion

TaroSalsifyBeet

YamCeleriacRadish

SweetpotatoHorseradishCarrots

CassavaSunchokeRutabaga

Storage Temperatures

Roots and Tubers

Chilling insensitive roots: 0-5C (32-41F)

Most chilling sensitive roots: 10-15C (50-59F)

Potatoes, Mature: 7.5C (45F)

Potatoes, Immature: 4-7C (40-45F)

Many root crops are chilling sensitive: Jicama as example

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cv Yellow Finn stored 5 mo. at 2C

Potatoes can show similar internal breakdown

Curing or wound healing

is essential for many root

and tubers

High humidity is essential

to maintain live cells that

are capable of healing

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Roots cured in the labor in commercial storage

Curing Conditions

1-75-10Time, days

95 or higher95 or higher% RH

25-35C

(77-85F)

15-20C

(59-68F)

Temperature

TropicalsPotato

Torque (lb-inch)

0 2 4 6 8 10

%w

eightloss

0

1

2

3

4 y= 0.0059 + (4.32/x)

R2= 0.66

Weight loss during 5d at 7.5 C and skin integrity of potatoes

Torquemeter

Potato skin development

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Harvest and storage of jicama in Mexico

Sweetpotato storages Evaporative cooling

Mechanical refrigeration

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Composition of Potato Tubers

0.7722051100% leaves

dead

0.873213380% leaves

dead

2.9721928Leaves decline

5.2661711Flowering ends

4.864169Flowering

Sugar, %Starch,

%

dry wt,

%

Weight,

g

cv. Irish Cobbler; data from Burton, 1966

1.210.50.30.86.02.29.3LSD.05

5.30--5.00.543.515.739.011 Aug22 Jul

4.704.33.90.629.917.738.86 Aug22 Jul

5.603.03.22.160.215.243.51 Aug22 Jul

6.352.72.12.566.115.534.627 Jul22 Jul

6.001.52.04.1102.615.230.022 Jul22 Jul

4.906.24.70.546.214.321.46 Aug17 Jul

6.304.43.91.859.114.123.41 Aug17 Jul

7.252.82.21.265.914.621.527 Jul17 Jul

6.751.12.03.387.513.222.522 Jul17 Jul

6.751.22.14.1132.613.821.717 Jul17 Jul

Respiration

L CO2/g-h

Torque

lb-inch

Skin

Score

% wt loss

(5d 7.5C)

Sugar,

mg/g DW

% dry

wt.

Ave. wt.

g/potato

Harvest

Date

Kill

Date

Quality characteristics of Morning Gold potatoes

harvested at different times and at different plant kill dates.

Cantwell and Carlson, Tule Lake, CA, 2002

Salad Potatoes

http://www.kimberly.uidaho.edu/potatoes/sp-grvty.htm

Specific Gravity

1.05 1.06 1.07 1.08 1.09 1.10 1.11

Dryweight,%

14

16

18

20

22

24

26% DW = 219.488 sp. grav - 216.325

R2=0.9998

Specific gravity = Weight in air/(Weight in air - Weight in water)

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Starch-Sugar Conversions

Higher storage temperature favors starch

accumulation

Lower temperatures favor sugar increase Maturity at harvest

Cultivar

Length of storage

senescent sweetening

sugar increase with sprouting

Days stored

0 7 14 21 28

Sugar(mg/gdrywt.)

100

200

300

400

500

600

700A. cv. Penta

(data averaged over 5 atmospheres)

5C 41F

10C 50F

Days stored

0 7 14 21 28

5C 41F

10C 50F

B. cv. Cherry Red

Storage of new potatoes at 5C (41F) in air results in

significant increases in sugar concentrations, while sugar

levels do not increase much at 10C (50F).

Tule Lake potatoes, 2001

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Potato Storage

Early crop or Short-term storage Usually not store; ship immediately

Cure, store 4-7C (40-45F) 2-4 months

Late crop or Long-term storage Sprout inhibitor

5-8C (41-47F) >90% RH

Store 7 to 12 months

Seed potato storage Low temperature (2-5C) in the dark

Diffuse light storage at 10-20C

Preharvest Control

Maleic hydrazide 2-3 wks before harvest, 2500ppm foliar spray

Postharvest Control

CIPC as dust or aersol, 10-20 pp, after curing Irradiation, .03-.15 kGy

Temperature: no sprouting if store below 4C

Natural sprout inhibitors, carvone

Sprouting is undesirable:Higher weight loss

Texture changes

Compositional changes

Undesirable greening and increases in glycoalkaloids

may occur readily during marketing of specialty potatoes

Glycoalkaloids affect the nervous system by interfering with the bodys

ability to regulate acetylcholine, a chemical responsible for conductingnerve impulses

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CH2OH

O

N

CH3

CH3

CH3

CH3

O

H

H

O

H

O

CH2OH

H

OH

HHH

OCH

3

OH OH

HH

OH

H

O

OH H

H OH

OH

H-Solanine

-D-glucose

-L-rhamnose

CH3

O

N

CH3

CH3

CH3

CH3

O

H

H

O

H

O

CH2OH

H

OH

H

HH

O

CH3

OH OH

HH

OH

H

O

OH

H

H

OH

OH

H

-Chaconine

-L-rhamnose

-L-rhamnose

-D-glucose

H

-D-galactose

Major glycoalkaloids in Potatoes

-Solanine-Chaconine

Critical TGA

Concentration:

20 mg/g FW

Cultivars vary in TGA; lack of info for CA-grownProduction conditions/location affect

Postharvest conditions, especially light affects

Potato variety

1 2 3 4 5 6 7 8 9 10 11 12

mg

per100g

freshweight

0

1

2

3

4

5

6

7

8

9

10

111 Satina2 Crispin3 Moly4 Yukon Gold5 Red LaSoda6 Cal Red7 Ruby Red8 Adora9 White Rose10 Cal White11 Morning Gold12 Durango

Potato varieties differ considerably

in glycoalkaloid content

Toxic glycoalkaloid formation isclosely associated with greening

Control greening & glycoalkaloids:

No Light- opaque packaging Low Temperature

Short Duration

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Reflectance Colorimeter0 3 6days

Exposed to cool-fluorescent light 20C

CalRed

Durango VC1015

A94381

5.44.53.5Yukon Gold (w/w)

10.04.42.4Satina (w/y)

12.15.93.8Latona (w/y)

26.79.94.7CalWhite (w/w)

7.05.64.3VC1015 (r/y)

9.96.64.8Durango (r/w)

29.421.68.0CalRed (r/w)

6.63.02.1A94381 (r/y)

9d light9d dark0 timeCultivar (color)

Average TGA Concentrations (mg/100g FW)

Satina Yukon Gold

LatonaCalWhite6 days

20C

Dark L

Light R

Glycoalkaloids in Potatoes-Solanine, -Chaconine

Highest content in peel and sprouts

Cultivars vary considerably

5 mg/100 g fresh wt. is typical

>20 mg/100 g is a health hazard

>30 mg/100g causes bitterness

Increase with bruising, wounding

Increase greatly with light and warmer

storage temperatures

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Harvest of early mature

potatoes in California

Flume handling

Chlorination

Water sanitation and decay due to Erwinia

Sorting and sizing

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Bulk andConsumer Packaging

Drops and other mechanical

damage cause internal bruising

and discoloration

Growth cracks

Poor shape, irrigation irregularGreening, not covered with soilWeed roots penetrate tubers

Physical damage at harvestDecay