PROCEEDINGS OF ECOS 2016 - THE 29TH INTERNATIONAL CONFERENCEON

EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS

JUNE19-23, 2016, PORTOROŽ, SLOVENIA

Energy use and CO2 emissions of the Mexican white maize agroindustry

Sergio Juárez-Hernándeza, Claudia Sheinbaum Pardo

b

a Instituto de Ingeniería, Universidad Nacional Autónoma de México, Ciudad de México, México,

sergiojh.mx@gmail.com (CA) b Instituto de Ingeniería, Universidad Nacional Autónoma de México, Ciudad de México, México,

CSheinbaumP@iingen.unam.mx

Abstract:

Social and economic changes in modern societies have favored an integration of primary product sector and industrial processing sector leading to the formation of complex agroindustry systems. In Mexico, maize is the most important cereal for domestic consumption so that maize agroindustry plays a relevant role in social and economic terms. White maize is the dominant maize variety planted in Mexico mainly for direct human consumption. White maize agroindustry demands different types and amounts of energy sources to produce, transport, store, preserve and process the grain into a variety of derived products. The purpose of this paper is to estimate energy use and related greenhouse gas (GHG) emissions of the key sectors of the Mexican white maize agroindustry based on information from the literature. Sectors examined include domestic white maize production, maize transportation, maize storage and preservation, maize processing and tortilla manufacturing. Estimated total energy use of the white maize agroindustry is in region of 123.3-217.3 PJ. Domestic white maize production (58.5-62.8 PJ) and mechanized tortilla manufacturing (31.4-92.9 PJ) are the major energy consumers. Commercial fossil-derived energy inputs such as diesel, synthetic fertilizers, LP gas and electricity are the main energy sources. However, non commercial energy forms (e.g. human and animal work) make a substantial contribution to total energy requirements especially in domestic maize production. Total GHG emissions range from 9.0 to 16.5 million tons CO2eq with mechanized tortilla production (2.3-6-9 million tons CO2eq) and domestic white maize production (3.7-4.5 million tons CO2eq) as the main GHG sources. In general, published information on energy use in the key sectors of the Mexican white maize agroindustry is scarce, out of date, and reports widely dispersed values. Further research is needed to perform more accurate calculations. In particular, domestic maize production, maize transportation and industrial processing should be investigated more in detail.

Keywords:

Maize human consumption, Maize processing, Maize production, Maize tortilla, Mexico.

1. Introduction Social and economic changes in modern societies have favored an integration of primary product

sector and industrial processing sector leading to the formation of complex agroindustry systems. In

general, an agroindustry system articulates industrial inputs production, agricultural production,

primary products conditioning, preservation and industrial processing, transport distribution, and final consumption of processed products [1, 2].

Agroindustry systems are usually tied to strategic primary products. In case of Mexico, maize is the

most important cereal for domestic consumption so that maize agroindustry system plays a relevant

role from social and economic perspectives. In the period 2010-2014, annual average maize grain

planted area was 7.6 million hectares, i.e. around one third of total country’s cropland, and

production amounted to 21.8 million tons (average yield of 3.2 t/ha) representing nearly 20% of the

economic value of total domestic crop production [3]. According to the 2007 National Agriculture

Census [4], there are nearly 2.8 million maize production units spread all along the country

resulting in an average size of 3.0 ha per production unit.

Maize is cultivated in diverse agro-climatic conditions and production scales combining a variety of

farming practices. However, two basic maize production systems can be distinguished: Traditional

production and commercial production [5–7]. Traditional maize production is typically practiced in

small rainfed lands using traditional labor-intensive techniques and low modern agricultural inputs

producing mainly for sefl-consumption (for human and animal use). On the other hand, large

commercial producers use extensive areas in good rainfed and irrigated lands and make intensive

use of mechanization, mineral fertilizers, agrochemicals and improved seeds. In between there is a

numerous group of transition producers that combine practices from both traditional and commercial maize production systems [8].

Despite many maize varieties are cultivated in Mexico, white maize is the most important one.

White maize represents around 94% (7.1 million hectares) and 90% (19.6 million tons) of 2010-

2014 total annual average maize grain planted area and production, respectively [3]. All white

maize production is for domestic consumption with foreign trade representing a marginal share

(around 3%) of total white maize supply. Dominant role of white maize derives from its use to

prepare various food products extensively consumed by Mexican population. According to [9] more than half of total white maize domestic production is for commercial direct human consumption.

White maize for direct human consumption is generally treated by nixtamalization. Nixtamalization

process consists on cooking and steeping maize grains in a lime solution and next cooked maize

grains (called nixtamal) are washed with clean water and grinded to produce a wet paste known as

nixtamal masa (dough) from which several traditional foods and beverages are made [10, 11].

Nixtamalization causes a series of chemical and structural changes on maize grain that improve

maize nutritional features [10].

Most of the white maize for human consumption is processed into maize tortilla, i.e. a flat, circular-

shaped and baked nixtamalized maize-derived food product commonly consumed to accompany

daily meals. For the period 2004-2006, [12] reports that around 10.1 million tons of white maize

was annually processed into maize tortillas. Further, it has been estimated [12] that the maize

tortilla value chain generates around 1% of gross domestic product.

White maize processing for commercial tortilla production is carried out by two industries: The

traditional nixtamalized maize masa industry and the maize masa flour industry. Traditional

nixtamalized masa industry is predominantly composed of small, family-owned millings called

nixtamal millings that process maize following the traditional nixtamalization process [13]. Nearly

92,000 establishments related to nixtamalized maize milling and tortilla production operate across

the country [14]. On the other hand, maize masa flour industry is a relatively modern industry

concentrated in two major private companies that operate 25 plants with a combined annual

processing capacity of 3.6 million tons of maize masa flour [15, 16]. Currently about 56-66% of

total tortilla production relies on traditional nixtamalized maize masa [15, 16].

Maize tortilla is manufactured in different ways. In rural communities tortilla is regularly

homemade by hand for self-consumption of peasant families whereas in urban locations

mechanized tortilla is the main form of production. Reference [17] reports that between 63,000 and

84,000 tortilla machines might operate in the country, most of which use traditional nixtamalized

masa as raw material.

One distinctive characteristic of the Mexican white maize agroindustry is the combination of

traditional and modern practices in all key sectors from maize production to maize processing. This

particularity affects agroindustry’s energy requirements and associated environmental impacts such

as greenhouse gas (GHG) emissions. Therefore, examining the sources and demand of energy along

the white maize agroindustry value chain might provide useful information to promote efficient

energy use as a critical aspect to assure long-term sustainability of this strategic agroindustry

system. The purpose of this paper is to estimate energy use and related GHG emissions of key

sectors of the Mexican white maize agroindustry based on information reported in the literature in

order to figure out a preliminary energy profile of this important agroindustry system. Manuscript is

organized as follows: Section 2 details white maize agroindustry system examined as well as

methodology and sources of information used. Section 3 presents and discusses the results on

energy use and GHG emissions for each of the sectors examined and the agroindustry system as a whole. Finally, Section 4 is devoted to the conclusions.

2. Methodology and data sources White maize agroindustry sectors examined were: domestic maize grain production, maize grain

transportation, maize grain storage and preservation, and maize grain processing (Fig. 1). Energy

use and GHG emissions (in terms of CO2eq) accounted for upstream energy and GHG emissions of the main energy and material inputs associated to each of the sectors analyzed.

In case of white maize domestic production, basic data on planted area, grain production and

consumption were obtained from [3, 9]. Energy use in domestic white maize production was

estimated from data reported for some maize production systems typically practiced in Mexico [18–

21] (Table 1). Note that these works examine maize production in a few locations so that they might

not be fully representative of all the variety of maize production systems within the country.

However, to date available information on energy use in maize production in Mexico is scarce to

enable a more accurate calculation. Energy related to transportation of harvested maize was

excluded from total energy requirements for maize production because maize grain transportation

energy was calculated separately. If not reported, upstream energy and GHG emissions of main

agronomic inputs were calculated based on data from [20–23].

Fig. 1. Boundaries of the Mexican white maize agroindustry system examined.

Consulted authors classified maize production systems according to the main source of traction

used in agricultural field operations (i.e. human labor, draft animals, machinery, and mixed

traction). Consequently, white maize surface shares corresponding to each source of traction was

derived from [24, 25]. Greenhouse gas emissions from white maize production included direct N2O

emissions related to nitrogen fertilizer application. Default emission factor of 0.01 kg N2O-N/kg N

applied was used [26]. Nitrogen content of manure used as organic fertilizer was obtained from [27] and conversion to CO2eq was done using 100-year global warming potentials [28].

Maize transportation comprised grain shipments from fields to commercial storage facilities (WMf-

s) and from the later to large maize grain buyers (WMs-b). Calculations were based on the modal

transportation structure and weighted average traveled distances estimated by [29] for domestic

maize shipments (Table 2). Average energy intensities (MJ/ton-km) of freight transportation modes

were taken from [30]. The amount of WMf-s was calculated as total domestic production less maize

used for self-consumption and for seed whereas the amount of WMs-b was calculated as WMf-s plus initial stock and imports less shrinkage and final stock.

Table 1

. Estim

ated

energ

y inputs p

er hecta

re for so

me m

aize p

roductio

n system

s pra

cticed in

Mexico

acco

rdin

g to

vario

us a

uth

ors

S

mall- an

d m

ediu

m-scale m

aize pro

du

ction

L

arge co

mm

ercial pro

ductio

n

Sou

rce of traction

O

nly h

um

an lab

or

Draft an

imals

Mech

anical tractio

n

Mix

ed traction

M

echan

ical traction

Referen

ce [2

1]

[18

, 19

] [2

1]

[18

, 19

] [1

8, 1

9]

[20

] [2

0]

/h

Inpu

t, MJ/h

a

Hu

man

labor

2,4

65.1

2

30

.5

82

5.3

1

78

.9

241.1

259.0

96.1

An

imal lab

or

1

,08

7.4

2

,07

1.1

442.7

718.0

71.4

Seed

s 153.2

2

20

.9/b

15

3.2

2

94

.6/b

294.6

/b 300.0

3,1

77.9

Mach

inery

69.3

/a

17

3.2

/d

1,8

15.0

3,4

07.4

/k

Diesel

1

,10

9.6

/e 577.0

638.0

2,2

16.8

/k

N fertilizer

4

,97

7.1

/c

1,6

40.3

/f 2,1

61.5

/h 1,0

37.8

/i 12,8

04.8

/l

P fertilizer

2

66

.3/c

2

21

.9/f

44.4

/h 256.2

/i 1,3

44.5

/l

K fertilizer

336.1

/l

Man

ure

245.0

Herb

icides

12.0

221.7

Insecticid

es

714.4

Electricity

221.7

Tran

sport (h

arvested

maize)

1

69

.9/g

169.9

/g 41.0

/j

Tran

sport (in

pu

ts, farm w

ork

ers, etc.)

57

7.0

88.8

22.2

Total

2,6

87.5

6

,78

2.3

3

,22

2.8

4

,19

2.2

4,0

20.0

5,3

22.0

24,6

35.0

Maize yield

, kg

-maize/h

a 1,9

44.0

1

,14

5.0

9

41

.0

1,0

60.0

1,2

60.0

882.0

7,5

09.0

En

ergy in

tensity

, MJ/k

g-m

aize 1.3

8

5.9

2

3.4

2

3.9

5

3.1

9

6.0

3

3.2

8

/a Man

ufactu

re of ax

and h

oe.

/b Estim

ated v

alue co

nsid

ering

14

.73

MJ/k

g seed

[21

]. /c A

uth

ors rep

ort that 3

0 k

g o

f min

eral fertilizers is applied

durin

g seed

ing, an

d 2

00 k

g d

urin

g

weed

ing

. Fertilizer ap

plied

durin

g seed

ing, h

ow

ever, typ

e of fertilizer u

sed is n

ot sp

ecified. V

alues w

ere estimated

assum

ing th

at diam

mon

ium

ph

osp

hate is u

sed in

seedin

g an

d th

at

urea is u

sed in

weed

ing in

accord

ance w

ith [2

0]. E

nerg

y con

tent fro

m [2

0]. /d M

anu

facture o

f draft an

imal im

plem

ents. /e In

cludes u

pstream

energ

y calculated

as suggested

in [2

2]. /f

Au

thors rep

ort 2

5 k

g o

f min

eral fertilizer applied

durin

g seed

ing

and

60

kg

durin

g w

eedin

g. S

ee note

/c. /g G

asolin

e fueled

ligh

t truck

. /h A

uth

ors rep

ort 5

kg o

f min

eral fertilizer

app

lied d

urin

g seed

ing an

d 9

0 k

g d

urin

g w

eedin

g. S

ee note /c. /i A

uth

or rep

orts 6

74

MJ/h

a of m

ineral fertilizers u

sed in

seedin

g an

d 6

20 M

J/ha in

secon

d fertilization

. For th

e form

er

diam

mon

ium

ph

osp

hate w

as con

sidered

and fo

r the later u

rea. En

ergy co

nten

t from

[20

]. /j D

iesel for h

arvested

maize an

d ag

ricultu

ral inputs tran

sportatio

n.

/k Estim

ated v

alues.

/l

Estim

ated v

alues b

ased o

n reco

mm

ended

fertilization

dose fo

r maize p

rod

uction

[37

] and en

ergy co

nten

t from

[20

].

Table 2. Estimated modal shares and weighted average travelled distances in Mexican domestic

maize grain transportation

% of total

maize

shipped

Modal shares,

% of maize shipped

Weighted

average

travelled distance, km

Light

truck

Medium

truck

Heavy

truck Rail Maritime

Maize supplier From maize fields to grain storage facilities

Individual farmers 71.3 49.4 43.7 6.9 19.2

Groups of farmers 8.4 22.4 50.0 26.3 1.3 69.2

Domestic companies 12.6 7.1 42.9 46.9 3.1 448.2

International companies 1.5 16.7 33.3 33.3 16.7 131.6

Associates of warehouse 6.2 56.5 41.3 2.2 24.7

Total 100.0

Maize buyer From storage facilities to maize buyers

Individual farmers 33.7 31.3 42.5 23.5 2.6 95.5

Groups of farmers 7.4 12.5 45.8 39.6 2.1 82.2

Domestic companies 49.1 3.4 29.8 59.2 7.6 190.7

International companies 3.2 5.0 25.0 45.0 25.0 332.3

Exports 3.2 14.3 9.5 76.2 251.0

Associates of warehouse 3.5 92.3 7.7 12.1

Total 100.0

Source: Own calculations based on data from [29]

Operations examined in white maize storage and preservation were grain artificial drying,

mechanical handling, aeration and pesticide production for stored maize. Average energy

requirements for conventional high temperature grain artificial drying were obtained from [31].

Upstream energy and GHG emission for domestic electricity production were approximated based on data reported in [22, 23, 32–35].

Grain artificially dried was assumed to be only white maize produced by large commercial farmers.

Maize grain from peasant producers was excluded because it is normally dried by direct solar

radiation and natural air circulation in the field or in traditional small barns [8, 36]. White maize

production from large commercial farmers was estimated based on the Mexican maize producers

typology suggested by [25] considering that this group of farmers achieves yields greater than 5.0

t/ha. Energy use associated to mechanical transportation, aeration, and pesticide manufacture for

stored maize grain was estimated from specific energy consumption calculated by [22]. The amount

of white maize associated to these operations was assumed to be the volume of grain transported

from fields to storage facilities (WMf-s). The rationale behind this assumption is that according to

[29] most (87.8%) of the total grain storage capacity in Mexico corresponds to large size

warehouses (>5,000 tons of capacity) with basic equipment for mechanical transportation,

conditioning and preservation of grains.

In the white maize processing sector the following activities were considered: traditional

nixtamalized maize masa production, maize masa flour production, and mechanized maize tortilla

manufacturing. Energy and GHG emissions associated to lime production for maize nixtamalization

were also included. The amount of white maize processed by each of these industries was calculated

based on rural and urban daily per capita consumption of maize-derived food products as reported

in [38] with basic data about Mexican population taken from [39]. The volume of white maize

processed by traditional nixtamalized masa and masa flour industries accounted for average grain

processing losses as reported in [40]. Energy use in traditional nixtamalized maize masa production

in typical nixtamalized maize millings was obtained from [41-43], whereas that for maize masa flour production was consulted in [44-46].

Regarding maize tortilla production, it was assumed that total domestic tortilla consumption

estimated as previously corresponded to mechanized tortilla manufacturing. Additionally, all tortilla

consumed by rural population was assumed to be made from traditional nixtamalized maize masa.

Based on [15, 16], it was considered that 60% of commercial tortilla consumed by urban population

was produced from traditional nixtamalized masa and the remaining from maize masa flour. Energy

consumption estimated for most widely used maize tortilla machines models was obtained from [17,

41]. For conversion purposes, the following average transformation coefficients were used: 0.94 kg

maize masa flour/kg maize; 1.75 kg tortilla/kg maize masa flour; 1.70 kg nixtamal maize masa/kg maize; 0.81 kg tortilla/kg nixtamal maize masa [47].

3. Results and discussion

3.1. White maize supply and demand flows

Based on 2012 figures, total white maize supply flow amounted to around 22.2 million tons of

which 20.0 million tons corresponded to domestic production whereas imports represented less than 3% of total supply so the country is virtually self-sufficient in white maize (Table 3).

Table 3. Estimated supply and demand flows of white maize in Mexico

103×tons %

Total supply 22,207.00 100.0

of which:

Domestic production 20,006.00 90.1

Imports 589.00 2.7

Initial stock 1,612.00 7.3

Total demand 20,345.76 100.0

of which:

Exports 493.00 2.4

Commercial human consumption 11,838.46 58.2

of which:

Traditional nixtamalized maize masa production

For consumption as nixtamalized masa 972.60 8.2

For tortilla manufacturing 5,925.56 50.1

Maize masa flour production

For consumption as maize masa flour 975.50 8.2

For tortilla manufacturing 2,449.54 20.7

Consumption as grain 1,515.26 12.8

Self-consumption 4,348.30 21.4

Animal Consumption 2,671.00 13.1

Seed 161.00 0.8

Shrinkage 834.00 4.1

Final stock 1,861.24

Regarding consumption, commercial direct human consumption amounted to nearly 12.0 million

tons of grain. About 60% of total white maize for direct human consumption was processed into

traditional nixtamalized maize masa and 29% into maize masa flour. Approximately 8.4 million

tons of processed white maize was used for tortilla production. White maize consumption as grain

was close to 13% of total volume of grain for human use. Note that this last figure refers only to

urban consumption as grain because rural use as grain was allotted to self-consumption (around 4.3

million tons of grain). However, per capita maize consumption as grain as reported in [38] includes

white maize as well as other varieties of maize so that calculated use as grain might be

overestimated. Animal feed use amounted to about 13% of total white maize domestic consumption

and shrinkage to 4%. Shrinkage percentage seems to be low given that some authors [48] report

shares of up to 25% of total maize grain production probably due to different assumption in the accounting methodology.

3.2 Energy use in domestic white maize production

In 2012, around 7.0 million hectares of white maize were planted nationwide for a total production

of about 20.0 million tons of grain. Based on previous planted area, energy use for domestic white

maize production might range from 58.5 to 62.8 PJ (Table 4). In terms of kilogram of maize

produced, energy use is about 2.9-3.1 MJ/kg maize. Most of energy use is associated to large scale

commercial white maize production due to intensive use of machinery, agrochemicals and synthetic

fertilizers in particular nitrogen fertilizers. Further, it was estimated that synthetic fertilizer and

agrochemical use accounted for around 50% of total energy use in white maize production whereas diesel for farm machinery represented about 12%.

Table 4. Estimated energy inputs in domestic white maize production

Small- and medium-scale producers

Large

commercial

producers Total

Source of traction

Only

human labor

Only draft

animal

Mixed

traction

Mechanical

traction

Mechanical

traction

Planted area, 103×ha 1,343.28 528.96 1,705.19 1,781.75 1,600.79 6,959.98

Total energy use, PJ 3.61 1.70-3.59 6.57-9.01 7.17 39.44 58.48-62.81

Human and animal

energy, PJ 3.31 0.70-1.53 1.17-1.67 0.32 0.27 6.26-6.60

Fertilizers and

agrochemicals, PJ/a

0.00 0.00-2.77 2.28-3.76 3.32 24.69 31.77-33.01

Diesel, PJ 0.00 0.00 1.09-1.14 3.01 3.58 7.68-7.72

Other inputs, PJ/b 0.30 0.12-0.17 0.50-4.02 0.52 10.90 12.40-15.86

/a Includes N, P and K synthetic fertilizers, herbicides and insecticides. /b Depending on the source, it might include

seeds, machinery, manure, electricity, and agricultural inputs transportation

Nevertheless, both human and animal work related mainly to peasant white maize production

contributed with 6.3-6.6 PJ of total energy, i.e. a similar range to that estimated for diesel fuel use.

This result suggests that mechanization level of white maize production in Mexico is still somewhat

low. Note that un-mechanized, low-input peasant maize production concentrated almost 27% of

total planted area. However, estimated energy use per kilogram of maize is within the range of

cradle-to-farm gate nonrenewable energy use in high-input, intensive maize production in the USA

(1.44-3.50 MJ/kg maize) [23]. Despite maize production in the USA makes intensive use of

commercial fossil derived agronomic inputs, more favorable agroclimatic conditions for maize

growth contribute to increase yields and thus reduce average energy use per unit mass of maize

produced.

Energy use associated to other inputs such as seeds and farm machinery production amounted to

12.4-15.9 PJ. Only Pimentel and Pimentel [21] and Orozco [20] evaluate indirect energy use in farm

machinery production. Approximately 14% of total energy use in large commercial maize

production reported in [20] might relate to machinery production. For maize production in the USA,

[49] calculates a similar percentage (ca. 17%) for embodied energy in farm machinery. However,

Kim et al. [23] suggest that energy use in capital goods manufacture is uncertain as reliable

information to estimate it is still unavailable.

3.3. Energy use in white maize transportation

Domestic maize grain transportation relies heavily on road transportation. Most of maize is

transported from fields to storage facilities by light and medium trucks with weighted average

travelled distances ranging from around 19 to 450 km. Note that more than 70% of maize grain

shipped proceeds from dispersed individual maize farmers possibly explaining the modal structure

observed. Maize transportation from storage facilities to large grain buyers depends primarily on

medium and heavy trucks, although an important fraction is transported by rail. Major maize grain

buyers seem to be domestic processing companies maize that demand large volumes of grain.

Almost one-third of maize is shipped to individual farmers probably for retail commercialization in

rural locations.

Energy for white maize transportation from fields to storage facilities was estimated at 440.9

MJ/ton-maize whereas that for transport distribution from storage facilities to large maize grain

buyers was 676.3 MJ/ton-maize. Difference on energy use might be explained mainly because

transportation from storage facilities to large maize buyers involves longer distances. Given the

amount of grain shipped in each case (WMf-s=15,497 million tons and WMs-b=15,002 million tons),

total maize grain transportation energy was estimated at 17.0 PJ. Approximately 3.7 PJ related to

transportation by gasoline-fueled light trucks, and 13.3 PJ to diesel-fueled transport modes especially medium trucks (ca. 9.6 PJ) and heavy trucks (ca. 3.7 PJ).

Other authors report different energy use in maize grain transportation. For instance, from data

reported by Masera [19], it can be estimated around 150 MJ/ton-maize for maize transportation

from fields to local barns. Camarena and Salgado [50] calculate about 590 MJ/ton-maize for

shipments of Mexican maize grain imports, and Orozco [20] reports a range from 190 to 1,220

MJ/ton-maize. Similarly, works on the energy balance of maize ethanol production [22, 48, 50–52]

calculate values in the region of 164-575 MJ/ton-maize. These discrepancies arise mainly due to different assumptions on modal structure, travelled distances and energy intensities.

3.4. Energy use in white maize storage and preservation

White maize storage and preservation is calculated to require 2.2-6.8 PJ of energy. Most energy

(2.1-6.7 PJ) corresponded to LP gas and electricity consumption for grain artificial drying

considering that grain moisture content is reduced from 20-30% to 14-15%. As pointed out by Kim

et al. [23], energy use for grain drying is commonly aggregated in total fuel consumption figures

reported for maize production, and hence it is difficult to determine the share of energy that exclusively relates to artificial drying.

Energy for mechanical transportation, aeration and chemical pesticide production associated to

stored maize accounted for less than 0.1 PJ. Marginal energy use in these operations probably explains why most of the authors consulted omit energy needs for maize storage and preservation.

3.5. Energy use in white maize processing

3.5.1. Traditional nixtamalized maize masa production

Around 6.9 million tons of white maize was processed into traditional nixtamalized maize masa

with grain processing losses accounting for about 0.9 million tons. Total nixtamalized masa

production was calculated at nearly 10.1 million tons of which about 8.7 million tons was devoted

to commercial tortilla production.

Energy inputs reported for traditional nixtamalized maize millings vary in the range of 8.6-18.75 L

of LP gas (mean 14.5 L) and 15-106 kWh of electricity (mean 42.1 kWh) per ton of nixtamalized

masa produced [41-43]. Wide range of variation results in part from the diversity of nixtamalization

processes practiced all around the country [43]. Some of the millings examined by Ambriz and

Paredes [42] report higher LP gas use (up to 126 L per ton of nixtamalized masa produced) because

it includes for LP gas use by tortilla machines installed at the millings. In overall terms, thermal

energy represents 52-96% and electricity 4-48% of total energy inputs of typicla nixtamalized

maize masa millings. Consequently, total energy use associated to traditional nixtamalized maize

masa production was calculated at 3.8-15.3 PJ with LP gas derived energy amounting to 2.3-5.0 PJ

and electricity to 1.4-10.2 PJ. Note that large energy contribution associated to electricity is due to

primary energy efficiency calculated for domestic electricity generation (ca. 38.1%).

In traditional nixtamalization process about 8 to 12 kg of lime is added per ton of grain [41, 53–

55]. Therefore, total lime use for nixtamalization of white maize processed into traditional

nixtamalized masa was estimated at 55.2-83.8 thousand tons with an embodied energy ranging from 0.1 to 0.2 PJ, a small share compared to the amount associated to energy carriers used in processing.

3.5.2 Maize masa flour production

It was calculated that around 3.4 million tons of white maize was processed into maize masa flour

reporting grain processing losses of about 0.5 million tons. Total domestic maize masa flour

production reached 2.8 million tons of which approximately 2.0 million tons would have been

processed into tortilla.

Public available information on energy use in maize masa flour industrial production is scarce and

out of date. Per ton of maize masa flour produced, energy inputs reported in [44] consists of 140 L

of diesel and 110 kWh of electricity. Reference [45] estimates 2,446 MJ of thermal energy

(probably from heavy fuel oil) and 107 kWh of electricity, and [46] calculates 2,954 MJ and 190

kWh, respectively. Therefore, energy requirements for producing one ton of maize masa flour range

from 2,446 to 5,101 MJ of thermal energy and from 110 to 190 kWh of electricity. Additionally,

cited authors report that lime requirements for maize nixtamalization vary between 8 and 16 kg per ton of maize masa flour produced.

Total energy use in domestic maize masa flour production was calculated in the region of 10.5-22.5

PJ. Thermal energy from fossil fuels accounted for 7.6-17.4 PJ and electricity use for 2.8-5.0 PJ.

Total lime consumption ranged from 22.4 to 44.8 thousand tons with and estimated embodied

energy of 0.04 to 0.08 PJ. Probably because maize masa flour production process is more

standardized, estimated consumption figures show less variation in comparison with those obtained

for nixtamalized masa production. However, data available in the literature might not fully reflect

the current energy performance of maize masa flour industry, for example, in terms of energy

carries used and specific energy consumption.

3.4.3 Commercial maize tortilla production

It was calculated that about 8.4 million tons of white maize was processed into 10.6 million tons of

commercial maize tortilla. Despite tortilla is the main maize-derived food product consumed in

Mexico, updated and reliable statistics on total domestic tortilla production are lacking. The more

reliable source that could be found [57] estimates that in 2013 about 5.0 million tons of maize grain

was used to produce around 7.4 million tons of tortilla, of which 6.0 million tons corresponded to

mechanized tortilla production. However, these calculations are based on minimum consumption

levels of maize-derived food products for Mexican rural and urban population sectors established in

[58] and hence actual consumption of tortilla might be higher.

Electricity and LP gas are the main energy inputs for commercial mechanized tortilla production.

Energy use for most popular tortilla machine models processing traditional nixtamalized masa range

from 93 to 380 L of LP gas (mean 238 L) and 4 to 36 kWh (mean 20 kWh) of electricity per ton of

tortilla produced [17, 41]. Those reported for masa flour-based tortilla machines are in the region of

142-210 L of LP gas (mean 176 L) and 28-35 kWh of electricity (mean 31 kWh). Differences on

energy consumption of tortilla machines are related to various factors such as working principle,

production capacity, and type of raw material used [17] as well as methodology applied to estimate

energy inputs. Reported values suggest that tortilla machines using traditional nixtamalized masa

are more energy intensive than masa flour-based tortilla machines. One possible reason for this is

the substantial proportion of old and improvised nixtamalized masa tortilla machines that operate in

the country [17].

Based on the estimated domestic tortilla production, total energy use in commercial mechanized

tortilla production was calculated at 31.4-92.9 PJ. Nixtamalized masa tortilla machines would

consume 17.4-72.5 PJ and masa flour tortilla machines, 13.9-20.4 PJ. In both cases thermal energy

from LP gas made the largest contribution to total energy use (17.2-70.1 PJ and 13.0-19.2,

respectively). Hernández [17] calculates 42.7-64.7 PJ with about 98% corresponding to thermal

energy from LP gas. However, this estimation does not take into account upstream energy of LP gas and electricity production and considers a domestic tortilla production of around 7.1 million tons.

3.5 Total energy use in the Mexican white maize agroindustry

From previous calculations, energy use of the Mexican white maize agroindustry might range from

123.3 to 217.3 PJ (Fig. 2). Most of energy use corresponded to domestic white maize production

and mechanized maize tortilla production. If only energy associated to diesel, synthetic fertilizers

and agrochemicals is considered, energy use in white maize production would represent 31-32% of

total commercial energy use in crop production sector in Mexico in 2010 (125.6 PJ) [59]. This

percentage seems reasonable given that maize surface covers about one-third of total domestic crop

planted area.

Fig. 2. Estimated minimum and maximum energy use of Mexican white maize agroindustry

Between 8 and 14% of total energy related to domestic white maize grain transportation. Authors

examining maize ethanol production [22, 48, 50–52] estimate that 2-5% of total energy use in the

production system correspond to maize shipping. Further, calculated maize transportation energy

would represent 2.5% of total energy use reported by [60] for the Mexican freight transportation

sector in 2010 (671.6 PJ). Higher transportation energy estimated for white maize transportation results from the large use of light and medium trucks with high energy intensities.

Energy use in traditional nixtamalized masa production and mechanized tortilla production showed

a large range of variation. Difference between maximum and minimum energy consumption is

around three-fold due to wide dispersion of data reported in the literature. Large variations in

reported data might be attributed to the heterogeneity of equipment, operational conditions, and

particularities of production processes of these two key sectors of the Mexican white maize

agroindustry. However, differences in time, location, and estimation methodologies might also affect reported values.

3.6 Greenhouse gas emissions of the Mexican white maize agroindustry

Total GHG emissions of the Mexican white maize agroindustry ranged from 9.0 to 16.5 million

tons of CO2eq (Fig.3). Domestic white maize production and mechanized tortilla production appear

to be the major sources of GHG emissions. Domestic white maize production would generate about

3.7-4.5 million ton CO2eq that represent less than 10% of total GHG emissions associated to crop

production in Mexico (ca. 46.7 million tons CO2eq) reported by [61]. Direct N2O emission related

to N fertilizer use (1.6-2.0 million tons CO2eq) comprised about 44% of total GHG emissions from

white maize production. Kim et al. [23] report a similar percentage (48-64%) related to GHG

emissions of maize production in the USA. Most synthetic N fertilizer is used in intensive

commercial white maize production system which is similar to that typically practice in industrialized countries.

Fig. 3. Estimated minimum and maximum GHG emissions of Mexican white maize agroindustry

On a per kilogram basis, GHG emissions from white maize production resulted in 0.19-0.23 kg

CO2eq/kg maize. Orozco [20] reports 0.11 kg CO2eq/kg maize and 0.13 kg CO2/kg maize for

traditional and intensive maize production. Note that estimations of Orozco [20] refer only to maize production related to a rural community in the state of Michoacán, Mexico.

Regarding white maize storage and preservation, grain artificial drying was by far the main source

of GHG emissions (0.17-0.51 million tons CO2eq) due to large use of LP gas for thermal energy

production. About 1.6 million tons CO2eq related to white maize domestic transportation that

represents 9-17% of total GHG emissions of the agroindustry system. Considering the amount of

white maize shipped, it results around 0.05 kg CO2eq/kg maize transported. Orozco [20] estimates

0.08 kg CO2eq/kg maize due to different assumptions on modal structure and transportation energy intensities.

White maize processing would emit between 3.5 and 9.9 million tons CO2eq primarily due to

mechanized tortilla production (2.3-6.9 million tons CO2eq). Combustion of LP gas for thermal

energy used in tortilla baking appeared to be the main source of GHG emissions concentrating

around 97% of total GHG emissions of mechanized tortilla production. Considering estimated total

mechanized tortilla production, average GHG emissions resulted in 0.22-0.66 kg CO2eq/kg tortilla

produced. Mechanized tortilla production using maize masa flour would generate lower GHG

emissions (0.30-0.43 kg CO2eq/kg tortilla) than production using traditional nixtamalized masa

(0.18-0.77 kg CO2eq/kg tortilla) due to low energy intensities reported for masa flour-based tortilla

machines. For mechanized tortilla production using traditional nixtamalized masa, [20] calculates 0.9 kgCO2eq/kg tortilla that is close to upper limit estimated.

Approximately 0.9-1.9 million tons CO2eq were calculated to industrial production of maize masa

flour due to the use of fossil fuels with high carbon content, e.g. heavy fuel oil. However, as data

used for calculations date from between 1950’s and 1990’s, currently the maize masa flour industry

might use low-carbon energy sources, for instance natural gas. Further, according to [61] the food

processing, beverage, and tobacco industries in Mexico all emit about 2.4 million tons of CO2eq.

Therefore, actual GHG emissions of maize masa flour production are likely to be lower than

estimated.

4. Conclusions Energy use and CO2 emissions of the Mexican white maize agroindustry were estimated based on

data reported in the literature. Agroindustry’s sectors examined comprise domestic white maize

production, white maize domestic transportation, white maize storage and preservation, and white

maize processing, including mechanized maize tortilla production.

The Mexican white maize agroindustry is a complex system that demands different types and

amounts of energy to produce, transport, store, preserve and process the grain into a variety of

products primarily for human consumption. Commercial fossil-derived energy inputs such as diesel,

synthetic fertilizers, LP gas and electricity are the main energy sources along the entire value chain

of white maize. However, non commercial energy forms like human and animal work make an

important contribution to meet energy requirements in particular in domestic maize production.

Dependence on fossil energy affects the environmental performance of the Mexican white maize

agroindustry. Substantial amounts of GHG emissions are produced due to the use of fossil energy-

derived inputs primarily involved in white maize production and commercial processing.

Nevertheless, information available in the literature is in general scarce, out of date, and reports

widely dispersed values so that there is nearly a 2-fold difference between total minimum and

maximum energy use and GHG emissions estimated figures. These results highlight the need for

further research to enable more accurate and complete calculations on energy use and GHG

emissions. In particular, domestic maize production, transportation and industrial processing should be investigated more in detail to uncover current trends in energy use and GHG emissions.

White maize agroindustry plays a critical role in food production and supply for a large group of the

Mexican population. Energy consumption and GHG emissions are decisive aspects for long-term

sustainability of this agroindustry. A reliable evaluation of these two indicators calls for additional

research to obtain more complete, precise, and updated data specific for the Mexican context.

Acknowledgements First author acknowledges the support given by the Consejo Nacional de Ciencia y Tecnología

(CONACyT) through the National Scholarship Program for Postgraduate Studies.

References [1] Villarespe V., Aspectos económicos y tecnológicos en la agroindustria alimentaria mexicana: el

caso de los cereales. México D.F., México: Instituto de Investigaciones Económicas-UNAM;

1985.

[2] Torres F., Dinámica económica de la industria alimentaria y patrón de consumo en México. México D.F., México: Instituto de Investigaciones Económicas-UNAM; 1997.

[3] SIAP, Producción agrícola anual por cultivo. México D.F., México: Servicio de Infromación

Agroalimentaria y Pesquera, Secretaría de Agricultura, Ganadería, Desarrollo Rural, Pesca y

Alimentación; 2015 - Available at: <http://www.siap.gob.mx/cierre-de-la-produccion-agricola-

por-cultivo/> [accessed: 6.3.2015].

[4] INEGI, Tabulados Básicos. Censo agrícola, ganadero y forestal 2007. Aguascalientes, México:

Instituto Nacional de Estadística y Geografía, 2009 - Available at:

<http://www3.inegi.org.mx/sistemas/tabuladosbasicos/default.aspx?c=17177&s=est> [accessed: 4.5.2015].

[5] Montañez R., Warman A., El cultivo del maíz en México. Diversidad, limitaciones y

alternativas. Seis estudios de caso. México, D.F., México: Centro de Ecodesarrollo; 1982.

[6] Toledo V.M., Carabias J., Toledo C., González C., La producción rural de México: Alternativas

ecológicas. México, D.F., México: Fundación Universo XXI; 1989.

[7] Mejia M., Peel D., White corn and yellow corn production in Mexico: Food versus feed? Analysis & Comments 2009;25:1–10.

[8] CIA, El cultivo del maíz en México. México D.F., México: Centro de Investigaciones Agrarias;

1980.

[9] SIAP, Balanza disponibilidad consumo de maíz blanco. México D.F., México: Servicio de

Infromación Agroalimentaria y Pesquera, Secretaría de Agricultura, Ganadería, Desarrollo

Rural, Pesca y Alimentación; 2015 - Available at:

<http://www.numerosdelcampo.sagarpa.gob.mx/publicnew/productosAgricolas/cargarPagina/4

> [accessed: 2.3.2015].

[10] Bressani R., Cambios nutrimentales en el maíz inducidos por el proceso de nixtamalización. In:

Rodríguez M., Serna-Saldivar S., Sánchez-Sinencio F., editors. Nixtamalización del maíz a la

tortilla. Aspectos nutrimentales y toxicológicos. Querétaro, México: Universidad Autónoma de Querétaro, 2008. p. 19–80.

[11] Ranum P., Peña-Rosas J., García-Casal M., Global maize production, utilization and

consumption. Ann. N.Y. Acad. Sci. 2014;1312:105–12.

[12] Polanco A., Flores T., Bases para una política de I&D e innovación de la cadena de valor del maíz. México D.F., México: Foro Consultivo Científico y Tecnoloógico; 2008.

[13] Torres F., La agroindustria del maíz en México. El espacio y el dilema entre tradición y

modernismo: El caso de la Zona Metropolitana de la Ciudad de México. Probl. Desarrollo 1994; 25(98):203–33.

[14] INEGI, Directorio Estadístico Nacional de Unidades Económicas (DENUE). Aguascalientes,

México: Instituto Nacional de Estadística y Geografía; 2015 - Available at: <http://www3.inegi.org.mx/sistemas/mapa/denue/> [accessed: 3.11.2015].

[15] GRUMA, Reporte Anual. Nuevo León, México: GRUMA S.A.B. de C.V.; 2015 - Available at:

<https://www.gruma.com/media/611051/reporte_anual_gruma_2014_versi_n_final_con_anexos.pdf> [accessed: 12.4.2015].

[16] MINSA, Reporte Anual. Edo. Mex., México: Grupo MINSA, S.A.B. de C.V., 2015 - Available

at: <http://www.bmv.com.mx/docs-pub/infoanua/infoanua_604917_2014_1.pdf> [accessed: 12.4.2015].

[17] Hernández L., Evaluación del potencial de ahorro de energía en México por la substitución de

máquinas tortilladoras [dissertation]. México D.F., México: Universidad Autónoma Metropolitana - Iztapalapa; 2011.

[18] Masera O., Almeida R., Cervantes J., Dutt G., García L., Garza J., Joaquín R., Juárez C.,

Marquéz C., Martínez M., Navia J., Ortiz A., Pérez M., Sheinbaum C., El patrón de consumo

energético y su diferenciación social. Estudio de caso en una comunidad rural de México

(Cuadernos sobre prospectiva energética no. 108). México D.F., México: El Colegio de México; 1987.

[19] Masera O., Crisis y mecanización de la agricultura campesina. México D.F., México: El

Colegio de México; 1990.

[20] Orozco Q., El sistema alimentario del maíz en Pátzcuaro, Michoacán [dissertation]. Michoacán, México: Centro de Investigaciones en Ecosistemas-UNAM; 2007.

[21] Pimentel D., Pimentel M., Food, energy and society. Boca Raton, USA: CRC Press; 2008.

[22] Graboski M., Fossil energy use in the manufacture of corn ethanol. Washington DC, USA:

National Corn Growers Association; 2002.

[23] Kim S., Dale B., Keck P., Energy Requirements and Greenhouse Gas Emissions of Maize Production in the USA. BioEnergy Res. 2014; 7(2):753–64.

[24] Cruz A., Martínez T., Omaña J., Fuentes de fuerza , diversidad tecnológica y rentabilidad de la

producción de maíz en México. Cienc. Ergo Sum 2004; 11(3):275–83.

[25] Vega V., Ramírez M., Situación y perspectivas del maíz en México. Cited in: Polanco A. and

Flores T., Bases para una política de I&D e innovación de la cadena de valor del maíz. México

D.F., México: Foro Consultivo Científico y Tecnoloógico; 2008.

[26] IPCC, 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergovernmental

Panel on Climate Change, 2006 - Available at: <http://www.ipcc-nggip.iges.or.jp/public/

2006gl/index.html> [accessed: 19.7.2015].

[27] Trinidad A., Utilización de Estiércoles (Fichas técnicas sobre actividades agrícolas, pecuarias y

de traspatio No.7). México D.F., México: Secretaria de Agricultura, Ganadería, Desarrollo

Rural, Pesca y Alimentación; 2014 - Available at:

<http://www.sagarpa.gob.mx/desarrolloRural/Documents/fichasaapt/Utilizaci%C3%B3n de

esti%C3%A9rcoles.pdf> [accessed: 26.9.2015].

[28] IPCC, IPCC Fourth Assessment Report: Climate Change 2007. Working Group I: The physical

science basis. Intergovernmental Panel on Climate Change, 2007 - Available at:

<https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-10-2.html> [accessed: 12.9.2015].

[29] SAGARPA, Estudio de gran visión y factibilidad económica y financiera para el desarrollo de

infraestructura de almacenamiento y distribución de granos y oleaginosas para el mediano y

largo plazo a nivel nacional. México D.F., México: Secretaría de Agricultura, Ganadería,

Desarrollo Rural, Pesca y Alimentación; 2011 - Available at:

<http://www.sagarpa.gob.mx/agronegocios/Documents/Estudios_promercado/GRANOS.pdf>

[accessed: 05:06:2015].

[30] NRC, Freight transportation secondary energy use by energy source an transportation mode.

Ottawa, Canada: Natural Resources Canada; 2014 - Available at:

<http://oee.nrcan.gc.ca/corporate/statistics/neud/dpa/showTable.cfm?type=HB&sector=tran&juris=00&rn=8&page=0> [accessed: 18.10.2015].

[31] Shouse S., Hanna M., Petersen D., Energy considerations for low temperature grain drying.

Agriculture and Environment Extension Publications. Book 200, 2012 - Available at:

<http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1197&context=extension_ag_pubs>

[accessed: 13.03.2015].

[32] Delucchi M., Emissions of criteria pollutants, toxic air pollutants, and greenhouse gases from

the use of alternative transportation modes and fuels. California, USA: University of California,

Davis, Institute of Transportation Studies; 1996 Jan. Technical Report No.: UCD-ITS-RR-96-12.

[33] SENER, Balance Nacional de Energía 2013. México D.F., México: Secretaria de Energía; 2014

- Available at: <http://www.gob.mx/cms/uploads/attachment/file/41975/Balance_2013.pdf> [accessed: 20.7.2015].

[34] Ghanta M., Fahey D., Subramaniam B., Environmental impacts of ethylene production from

diverse feedstocks and energy sources. Appl. Petrochem. Res. 2014; 4(2):167–79.

[35] Stanek W., Bialecki R., Can natural gas warm the climate more than coal? Fuel 2014;136:341–48.

[36] Moreno M., Almacenamiento y conservación de granos en el medio rural. In: Moreno E.,

Torres F., Chong I., editors. El sistema poscosecha de granos en el nivel rural: problemática y

propuestas. México D.F., México: Programa Universitario de Alimentos-UNAM, 1995. p. 247–

68.

[37] Gavi F., Uso de fertilizantes (Fichas técnicas sobre actividades agrícolas, pecuarias y de

traspatio No. 12). México D.F., México: Secretaria de Agricultura, Ganadería, Desarrollo

Rural, Pesca y Alimentación, 2014 - Available at:

<http://www.sagarpa.gob.mx/desarrolloRural/Documents/fichasaapt/Uso%20de%20Fertilizant

es.pdf.> [accessed: 15.06.2015].

[38] López D., El consumo de productos y subproductos de maíz en México. Enlace 2014; 5(17):21–3.

[39] WBG, Population Data, Mexico. The World Bank Group, 2015 - Available at:

<http://data.worldbank.org/country/mexico> [accessed: 10.6.2015].

[40] Serna-Saldivar S., Amaya C., El papel de la tortilla nixtamalizada en la nutrición y

alimentación. In: Rodríguez M., Serna-Saldivar S., Sánchez-Sinencio F., editors.

Nixtamalización del maíz a la tortilla. Aspectos nutrimentales y toxicológicos. Querétaro, México: Universidad Autónoma de Querétaro, 2008. p. 105–51.

[41] Santin H., Consumo y conservación de energía en la industria de la masa y la tortilla. México

D.F., México: Universidad Nacional Autónoma de México; 1985.

[42] Ambriz J., Paredes H., Uso de la energía en molinos de nixtamal y tortillerías. In : de Teresa

A., Viniegra G., editors. Temas selectos de la cadena maíz-tortilla. Un enfoque

multidisciplinario. México D.F., México: Universidad Autónoma Metropolitana - Iztapalapa, 2009, p. 203–31.

[43] Garzón A., Consumo de energía térmica y eléctrica en molinos de nixtamal en México

[dissertation]. México D.F., México: Universidad Autónoma Metropolitana - Iztapalapa; 2012.

[44] Estrada J., Obtención industrial de harina de maíz y proyecto de una fábrica de 50 toneladas

diarias de capacidad [dissertation]. México D.F., México: Univerisidad Nacional Autónoma de

México; 1956.

[45] Hernández A., Márquez F., Miranda F., Aguilar G., Jiménez J., Estudio de factibilidad de una

planta de harina de maíz [dissertation]. México D.F., México: Universidad Nacional Autónoma

de México; 1984.

[46] Facio M., Proyecto de Factibilidad de una planta procesadora de harina de maíz nixtamalizado

en el municipio de Celaya Guanajuato [dissertation]. México D.F., México: Univerisidad

Nacional Autónoma de México; 1991.

[47] Cebreros M., Innovación y desarollo industrial. El caso de la harina de maíz. In: Torres-Salcido

G., Morales M., editors. Maíz-Tortilla. Política y alternativas. México D.F., México: Centro de

Investigaciones Interdisciplinarias en Ciencias y Humanidades-UNAM, 1997, p. 141–55.

[48] Ortiz M., Ramírez O., González J., Velázquez A., Almacenes de maíz en México: tipología y caracterización. Estudios Sociales 2015; 23(45):163–84.

[49] Pimentel D., Ethanol fuels: Energy balance, economics, and environmental impacts are

negative. Nat. Resour. Res. 2003; 12(2):127–34.

[50] Camarena M., Salgado M., Transporte de las importaciones de gráneles agrícolas. Elementos

para su estudio energético. In: Bauer M., Chong I., Moreno E., Quintanilla J., Torres F., editors.

El agua y la energía en la cadena alimentaria. Granos básicos, México D.F., México: Programa Universitario de Alimentos-UNAM, 1994, p. 323–41.

[51] Shapouri H., Duffield J., Wang M., The energy balance of corn ethanol: An update.

Agricultural Economic Report No.813. U.S. Dept. of Agriculture, 2002.

[52] Shapouri H., Gallagher P., Nefstead W., Schwartz R., Noe S., Conway R., 2008 Energy balance

for the corn-ethanol industry. Agricultural Economic Report No.846. U.S. Dept. of Agriculture,

2010.

[53] Yang Q., Chen G., Nonrenewable energy cost of corn-ethanol in China. Energy Policy 2012;41:340–47.

[54] Durán-Domínguez M., La contaminación en la industria de la masa y la tortilla. In: Torres F.,

editor. La industria de la masa y la tortilla. Desarrollo y tecnología, México D.F., México: Programa Universitario de Alimentos-UNAM, 1996, p. 173–93.

[55] Ferrer J., Manix: Solución ecológica y económica para los molinos. In: Torres F., editor. La

industria de la masa y la tortilla. Desarrollo y tecnología, México D.F., México: Programa Universitario de Alimentos-UNAM, 1996, p. 167–72.

[56] Ramírez G., Viniegra G., Orozco C., El nejayote, su tratamiento y uso. In : de Teresa A.,

Viniegra G., editors. Temas selectos de la cadena maíz-tortilla. Un enfoque multidisciplinario. México D.F., México: Universidad Autónoma Metropolitana - Iztapalapa, 2009, p. 233–56.

[57] CEDRSSA, Consumo, distribución y producción de alimentos: el caso del complejo maíz-

tortilla. México D.F., México: Centro de Estudios para el Desarrollo Rural Sustentable y la

Soberanía Alimentaria; 2014 - Available at: <http://www.cedrssa.gob.mx/?idnot=186>

[accessed: 10:6:2015]

[58] CONEVAL, Construcción de las líneas de bienestar. Documento metodológico. Metodología

para la medición multidimensional de la pobreza. México D.F., México: Consejo Nacional de

Evaluación de la Política de Desarrollo Social; 2012 - Available at:

<http://www.coneval.gob.mx/Informes/Coordinacion/INFORMES_Y_PUBLICACIONES_PD

F/Construccion_lineas_bienestar.pdf> [accessed: 10.5.2015].

[59] Cruz-Delgado J, Energía y agricultura en México [dissertation]. México, D.F., México; Universidad Nacional Autónoma de México; 2013.

[60] SENER-AIE, Indicadores de Eficiencia Energética en México: 5 sectores, 5 retos. México D.F.,

México: Secretaría de Energía - Agencia Internacional de Energía; 2011 - Available at: <http://www.energia.gob.mx/taller/res/1858/iee_mexico.pdf> [accessed: 9.4.2015].

[61] INECC, México. Quinta comunicación nacional ante la Convención Marco de las Naciones

Unidas sobre Cambio Climático. México D.F., México: Secretaria de Medio Ambiente y Recursos Naturales - Instituto Nacional de Ecología y Cambio Climático; 2012.