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Energy and protein feed-to-food conversion efficiencies in the US and potential food security gains from dietary changes

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Feeding a growing population while minimizing environmental degradation is a global challenge requiring thoroughly rethinking food production and consumption. Dietary choices control food availability and natural resource demands. In particular, reducing or avoiding consumption of low production efficiency animal-based products can spare resources that can then yield more food. In quantifying the potential food gains of specific dietary shifts, most earlier research focused on calories, with less attention to other important nutrients, notably protein. Moreover, despite the well-known environmental burdens of livestock, only a handful of national level feed-to-food conversion efficiency estimates of dairy, beef, poultry, pork, and eggs exist. Yet such high level estimates are essential for reducing diet related environmental impacts and identifying optimal food gain paths. Here we quantify caloric and protein conversion efficiencies for US livestock categories. We then use these efficiencies to calculate the food availability gains expected from replacing beef in the US diet with poultry, a more efficient meat, and a plant-based alternative. Averaged over all categories, caloric and protein efficiencies are 7%–8%. At 3% in both metrics, beef is by far the least efficient. We find that reallocating the agricultural land used for beef feed to poultry feed production can meet the caloric and protein demands of ≈120 and ≈140 million additional people consuming the mean American diet, respectively, roughly 40% of current US population.
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Environ. Res. Lett. 11 (2016)105002 doi:10.1088/1748-9326/11/10/105002
LETTER
Energy and protein feed-to-food conversion efciencies in the US
and potential food security gains from dietary changes
A Shepon
1
, G Eshel
2
, E Noor
3
and R Milo
1
1
Department of Plant and Environmental Sciences, Weizmann Institute of Science, Rehovot 7610001, Israel
2
Radcliffe Institute for Advanced Study, Harvard University, 10 Garden Street, Cambridge, MA 02138, USA
3
Institute of Molecular Systems Biology, ETH Zürich, Auguste-Piccard-Hof 1, CH-8093 Zürich, Switzerland
E-mail: ron.milo@weizmann.ac.il
Keywords: livestock, food security, sustainability
Supplementary material for this article is available online
Abstract
Feeding a growing population while minimizing environmental degradation is a global challenge
requiring thoroughly rethinking food production and consumption. Dietary choices control food
availability and natural resource demands. In particular, reducing or avoiding consumption of low
production efciency animal-based products can spare resources that can then yield more food. In
quantifying the potential food gains of specic dietary shifts, most earlier research focused on calories,
with less attention to other important nutrients, notably protein. Moreover, despite the well-known
environmental burdens of livestock, only a handful of national level feed-to-food conversion
efciency estimates of dairy, beef, poultry, pork, and eggs exist. Yet such high level estimates are
essential for reducing diet related environmental impacts and identifying optimal food gain paths.
Here we quantify caloric and protein conversion efciencies for US livestock categories. We then use
these efciencies to calculate the food availability gains expected from replacing beef in the US diet
with poultry, a more efcient meat, and a plant-based alternative. Averaged over all categories, caloric
and protein efciencies are 7%8%. At 3% in both metrics, beef is by far the least efcient. We nd
that reallocating the agricultural land used for beef feed to poultry feed production can meet the
caloric and protein demands of 120 and 140 million additional people consuming the mean
American diet, respectively, roughly 40% of current US population.
1. Introduction
The combination of ongoing population rise and the
increasing demand for animal-based products places a
severe strain on world natural resources (Smil 2002,
Steinfeld et al 2006, Galloway et al 2007, Wirsenius
et al 2010, Bonhommeau et al 2013). Estimates suggest
that global meat demand would roughly double over
the period 20002050 (Pelletier and Tyedmers 2010,
Alexandratos and Bruinsma 2012, Pradhan et al 2013,
Herrero et al 2015). Earlier analyses (Steinfeld
et al 2006, Godfray et al 2010, Foley et al 2011, Herrero
et al 2015)of food supply chains identied inefciency
hotspots that lend themselves to such mitigation
measures as improving yield (through genetics and
agricultural practices), increasing energy, nutrient and
water use efciencies, or eliminating waste. Others
focused on the environmental performance of specic
products, for example animal-derived (de Vries and de
Boer 2010, Pelletier et al 2010,2011,2014, Thoma
et al 2013). A complementary body of work (Pimentel
and Pimentel 2003, Eshel and Martin 2006, Eshel
et al 2010, Hedenus et al 2014, Tilman and Clark 2014,
Springmann et al 2016)quanties the environmental
performance of food consumption and dietary pat-
terns, highlighting the large environmental impacts
dietary choices can have.
Key to estimating expected outcomes of potential
dietary shifts is quantifying the amount of extra food
that would become available by reallocating resources
currently used for feed production to producing
human food (Godfray et al 2010, Foley et al 2011,
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© 2016 IOP Publishing Ltd
Cassidy et al 2013, Pradhan et al 2013, West et al 2014,
Peters et al 2016). One notable effort (Foley et al 2011,
Cassidy et al 2013,)suggested that global reallocation
to direct human consumption of both feed and biofuel
crops can sustain four billion additional people. Yet,
most cultivated feed (corn, hay, silage)is human ined-
ible and characterized by yields well above those of
human edible crops. Moreover, most previous efforts
focused on calories (Cassidy et al 2013, Pradhan
et al 2013), while other key dimensions of human diet
such as protein adequacy are equally important.
Here we quantify efciencies of caloric and protein
uxes in US livestock production. We answer such
questions as: How much feed must enter the livestock
production stream to obtain a set amount of edible
end product calories? What is the composition of these
feed calories in the current US system? Where along
the production stream do most losses occur? We pro-
vide the analysis in terms of both protein and calories
and use them to explore the food availability impacts
of a dietary change within the animal portion (exclud-
ing sh)of the American food system using the dietary
shift potential method as described below. While diet-
ary changes entail changes in resource allocation and
emissions (Hedenus et al 2014, Tilman and Clark
2014, Eshel et al 2016, Springmann et al 2016), here we
highlight the food availability gains that can be realized
by substituting the least efcient food item, beef, with
the most efcient nutritionally similar food item,
poultry. Because beef and poultry are the least and
most efcient livestock derived meats respectively, this
substitution marks the upper bound on food gains
achievable by any dietary change within the meat por-
tion of the mean American diet (MAD). In this study
we focus on substitution of these individual items, and
plan to explore the substitution of full diets elsewhere.
As a yardstick with which to compare our results, we
also present the potential food availability gains asso-
ciated with replacing beef with a fully plant-based
alternative.
2. Methods and data
The parameters used in calculating the caloric and
protein Sankey ow diagrams (gures 1and 2)are
based on Eshel et al (2015,2014)and references and
sources therein. Feed composition used in gures 1
and 2are derived from NRC data (National Research
Council 1982,2000). For this work, the MAD is the
actual diet of the average American over 20002010
(United States Department of Agriculture ERS 2015),
with approximate daily loss-adjusted consumption of
2500 kcal and 70 g protein per capita (see SI and
supplementary data for additional details).
Figure 1. A Sankey ow diagram of the US feed-to-food caloric ux from the three feed classes (left)into edible animal products
(right). On the right, parenthetical percentages are the food-out/feed-in caloric conversion efciencies of individual livestock
categories. Caloric values are in Pcal, 10
12
kcal. Overall, 1187 Pcal of feed are converted into 83 Pcal edible animal products, reecting
a weighted mean conversion efciency of approximately 7%.
2
Environ. Res. Lett. 11 (2016)105002
2.1. Calculating the dietary shift potential
The dietary shift potential, the number of additional
people that can be sustained on a given cropland
acreage as part of a dietary shift, is
D= -
--
()
() ()PPl l
lll 1
ab US a b
per capita land gain
MAD a b
updated per capita
MAD land requirement


In equation (1), the left-hand side (ΔP
ab
)is the
number of additional people that can be fed on
land spared by the replacement of food item a
with food item b. P
US
300 million denotes the
20002010 mean US population;
l
a
and
l
bdenotes
the annual per capita land area for producing a set
number of calories of foods a and b. This denition
readily generalizes to protein based replacements,
and/or to substitution of whole diets rather than spe-
cic food items.
To derive the mean per capita land requirement of
the MAD,
l
,
MAD
we calculate the land needs of each of
the non-negligible plant and animal based items
the MAD comprises. We convert a given per capita
plant item mass to the needed land by dividing the
consumed item mass by its corresponding national
mean loss adjusted yield. The land needs of the
full MAD is simply the sum of these needs over all
items (see supplementary data). The per capita crop
land requirements of the animal based MAD cate-
gories (e.g.,
l,
poultry )
l
beef are based on Eshel et al
(2014,2015).
The modest land needs of poultry mean that repla-
cing beef with an amount of poultry that is caloric- or
protein-equivalent spares land that can sustain addi-
tional people on a MAD. We denote by
c
ite
m
the kcal
(person yr)
1
consumption of any MAD item. The set
number of calories (or protein)consumed in the
MAD is different for beef and thus for the calculation
of substituting beef with poultry, we multiply the per
capita land area of poultry by /cc
,
beef poultry the per
capita caloric (or protein)beef:poultry consumption
ratio in the MAD, which is 1.2 for calories and 0.6 for
protein.
Using equation (1), the caloric dietary shift poten-
tial of beef is
D
=
-
--
P
Pl l c
c
lll
c
c
.
beef poultry
US beef poultry beef
poultry
MAD beef poultry beef
poultry
For the beef replacement calculation, the resultant
post-replacement calories (light orange arrows in
gure 3(a)) comprise (1)the poultry calories that
replace the MAD beef calories, plus (2)calories that
Figure 2. The US feed-to-food protein ux from the three feed classes (left)into edible animal products (right). On the right,
parenthetical percentages are the food-protein-out/feed-protein-in conversion efciencies of individual livestock categories. Protein
values are in Mt (10
9
kg). Overall, 63 Mt of feed protein yield edible animal products containing 4.7 Mt protein, an 8% weighted mean
protein conversion efciency.
3
Environ. Res. Lett. 11 (2016)105002
the spared lands can yield if allocated to the production
of MAD-like diet for additional people (national feed
land supporting beef minus the land needed to
produce the replacement poultry). The MAD calories
that the spared land can sustain is calculated by
multiplying the spared land area by the mean caloric
yield of the full MAD with poultry replacing beef,
1700 Mcal (ac yr)
1
. The national annual calories
due to substituting beef for poultry is
=+
´
-
--
()
CPcc
Pl l c
c
lll
c
c
365 365
2
beef poultry
nat. US beef MAD
US beef poultry beef
poultry
MAD beef poultry beef
poultry
where
and
l
are the per capita daily caloric consump-
tion and annual land requirements of poultry, beef or
the full MAD, respectively. The rst and second terms
on the right-hand side of equation (2)are terms (1)
and (2)of the above explanation, respectively.
To derive the difference between the above repla-
cement calories and the replaced beef calories (percen-
tages in gure 3), we subtract the original national
consumed beef calories Pc
3
65 US beef from the above
equation. The difference between replacement and
replaced caloric uxes is
-
=
-
--
()
CC
c
Pl l c
c
lll
c
c
365 3
beef poultry
nat. beef
nat.
MAD
US beef poultry beef
poultry
MAD beef poultry beef
poultry
As noted above, the quotient on the right-hand side
gives the number of extra people that can be fed,
reported in gure 3. An analogous calculation repla-
cing calories with protein mass, yields the protein
dietary shift potential shown in gure 3(b). The
current calculation of the dietary shift potential also
enables calculating the food availability gains asso-
ciated with any partial replacement. Figure S2 depicts
the relation between the dietary shift potential (addi-
tional people that can be fed a full MAD diet)and the
percentage of national beef calories (from MAD)
replaced with poultry.
2.2. The choice of poultry as the considered
substitute
We use poultry as the replacement food in our food
availability calculations for several reasons. First, US
poultry consumption has been rising in recent decades
often substituting for beef (Daniel et al 2011), suggest-
ing it can serve as a plausible replacement. In addition,
poultry incur the least environmental burden among
the major meat categories and thus the calculation of
Figure 3. Dietary shift potential of substituting beef with poultry in the mean American diet (MAD). Percent change in available
calories due to substituting beef with poultry (panel (a)),+520%. The number of additional people consuming 2500 kcal d
1
that
these calories can sustain (the dietary shift potential)is 116 million (upper right parenthetical value). Caloric values are in Pcal, i.e.
10
12
kcal. The protein gain due to dietary shift from beef to poultry will increase by 380% (panel (b)), meeting the protein needs of 142
million additional people consuming 70 g protein d
1
(as in the MAD). Protein values are in Mt (10
9
kg). The caloric loss following
substitution is calculated based on the conversion efciency for poultry and the MAD. The loss of the plant-based portion of MAD is
calculated by assessing the loss of each individual plant item throughout the supply chain (see supplementary data); the loss of the
animal-based portion of MAD is based on the caloric efciency conversion estimates shown in table 1. A similar calculation is
performed for protein.
4
Environ. Res. Lett. 11 (2016)105002
the dietary shift potential presented here serves as an
upper bound on possible food gains achievable by any
substitution within the meat portion of the MAD.
Plant-based diets can also serve as a viable replace-
ment for animal products, and confer larger mean
environmental (Eshel et al 2014,2016)and food avail-
ability gains (Godfray et al 2010). Recognizing that the
majority of the population will not easily become exclu-
sive plant eaters, here we choose to present the less radi-
cal and perhaps more practical scenario of replacing the
environmentally most costly beef with the more
resource efcient poultry. We also augment this calcul-
ation witha plant-based alternative diet as asubstitute.
Finally, poultry stands out in its high kcal g
1
and g
protein g
1
values and its desirable nutritional prole.
Per calorie, it can deliver more protein than beef while
delivering as much or more of the other essential
micronutrients (gure S1). While it is tricky to compare
the protein quality of beef and poultry, we can use the
biological value (modied essential amino acid index
and chemical score index Ihekoronye 1988)and the
protein digestible corrected amino acid score, the pro-
tein indicator of choice of the FAO. Within inevitable
variability, the protein quality of poultry is similar to
that of beef using both metrics (Sarwar 1987,Ihekor-
onye 1988,Lópezet al 2006,Barrón-Hoyoset al 2013).
While the FAO has recently introduced an updated pro-
tein quality score (DIAASdigestible indispensable
amino acid score)(FAO Food and Nutrition paper No.
92 2011), to our knowledge no reliable DIAAS data
comparing beef and poultry exists.
3. Results
The efciency and performance of the animal portion
of the American food system is presented in table 1
(see detailed calculations in supplementary les),
highlighting a dichotomy between beef and the other
animal categories, consistent with earlier environmen-
tal burden estimates (Eshel et al 2014).
The calories ow within the US from feed to live-
stock to human food is presented in gure 1. From left
to right are primary inputs (concentrated feed, pro-
cessed roughage and pasture)feeding the ve second-
ary producer livestock categories, transformed into
human consumed calories. We report energy uxes in
Pcal=10
12
kcal, roughly the annual caloric needs of a
million persons. Annually, 1200 Pcals of feed from
all sources (or 800 Pcals when pasture and bypro-
ducts are excluded)become 83 Pcals of loss adjusted
animal based human food. This is about 7% overall
caloric conversion efciency. The overall efciency
value arises from weighting the widely varied category
specicefciencies, from 3% for beef to 17% for eggs
and dairy, by the average US consumption (rightmost
part of gure 1). Concentrate feed consumption, such
as maize, is distributed among pork, poultry, beef and
dairy, while processed roughage and pasture (50% of
total calories)feed almost exclusively beef. The con-
centrated feed category depicted in gure 1also
includes byproducts. We note that because detailed
information on the distribution of byproducts as feed
for the different animal categories is lacking, we can-
not remove them from the feed to food efciency calc-
ulation. Yet, our analysis shows that for the years
20002010 the contribution of byproducts to the total
feed calories (and protein)was less than 10% (see SI
spreadsheet)and so their effect on the values is quanti-
tatively small. The results reported in all gures are
corrected for import-export imbalances, such that the
presented values refer to the feed used to produce the
animal-derived food domestically consumed in the US
(i.e., excluding feed used for livestock to be exported,
and including imported feed, albeit quite minor in the
US context).
While calories are widely used to quantify food
system performance, proteinwhich is often invoked
as the key nutritional asset of meatoffers an impor-
tant complementary dimension (Tessari et al 2016).
The ow of protein in the American livestock produc-
tion system, which supplies 45 g protein person
1
Table 1. Key parameters (±std. dev.)used in evaluating US feed allocation and conversion among animal categories (Eshel
et al 2015)and energy (caloric)and protein efciency.
Parameter Units Beef Poultry Pork Dairy Eggs
Feed intake per LW kg/kg LW 14±4 1.9±0.4 3.1±1.3 N/AN/A
Feed intake per EW kg/kg EW 36±13 4.2±0.8 6±2.5 N/AN/A
Feed intake per CW kg/kg CW 49±9 5.4±1.4 9±4 2.6±0.6 2.4±1.2
Feed caloric content kcal g
1
2.3±0.6 3.4±1.4 3.6±2 2.8±0.9 3.4±2.4
Food caloric content kcal g
1
3.2±0.3 2.3±0.1 2.8±0.2 1.2±0.1 1.4±0.1
Caloric conversion efciency % 2.9±0.7 13±49±417±417±9
Feed protein content % 12±317±717±11 15±517±12
Food protein content % 15±220±214±1.4 6±0.6 13±1.3
Protein conversion efciency % 2.5±0.6 21±79±4.5 14±431±16
Note: LW=live weight (USDA reported slaughter live weight);EW=edible weight (USDA reported retail boneless edible
weight);CW=consumed weight (USDA reported loss-adjusted weight).N/A, denotes not applicableas the parameter is
relevant only for CW. Feed caloric content refers to metabolizable energy and feed protein content refers to crude protein. For
further information on all data sources and calculations see SI and supplementary data.
5
Environ. Res. Lett. 11 (2016)105002
d
1
to the MAD, is shown in gure 2. Overall, 63 Mt (1
Mt=10
9
kg)feed protein per year are converted by
US livestock into 4.7 Mt of loss-adjusted edible animal
based protein. This represents an overall weighted-
mean feed-to-food protein conversion efciency of
8% for the livestock sector. Protein conversion ef-
ciencies by individual livestock categories span an
11-fold range, more than twice the corresponding
range for calories, from 31% for eggs to 3% for beef
(see SI for more details).
By isolating visually and numerically the contribu-
tions from pasture, which are derived from land that is
unt for production of most other foods, gures 1and
2quantify expected impacts of dietary shifts. Of those,
we choose to focus on substituting beef with poultry.
Because these are the most and least resource intensive
meats, this substitution constitutes an upper bound
estimate on food gains achievable by any meat-to-
meat shift. Lending further support to the beef-to-
poultry substitution choice, poultry is relatively nutri-
tionally desirable (see the methods section and gure
S1), andjudging by its ubiquity in the MADpala-
table to many Americans.
We quantify the dietary shift potential (a term we
favor over the earlier diet gap Foley et al 2011), the
number of additional people a given cropland acreage
can sustain if differently reallocated as part of a dietary
shift. While here we estimate the dietary shift potential
of the beef-to-poultry substitution, the methodology
generalizes to any substitution (see methods section
for further information and equations). The beef-to-
poultry dietary shift potentials are premised on reallo-
cating the cropland acreage currently used for produ-
cing feed for US beef (excluding pastureland)to
producing feed for additional poultry production.
Subtracting from beefs high quality land require-
ments those of poultry gives the spared land that
becomes available for feeding additional people.
Dividing this spared acreage by the per capita land
requirements of the MAD diet (modifying the latter
for the considered substitution)yields the number
of additional people sustained by the dietary
substitution.
We calculate the dietary shift potential for beef (as
dened above and in the methods section)by quanti-
fying the land needed for producing calorie- and pro-
tein-equivalent poultry substitution, and their
differences from the land beef currently requires. We
derive the number of additional people this land can
sustain by dividing the areal difference thus found by
the per capita land demands of the whole modied
MAD, 0.5 acres (2×10
3
m
2
)per year.
Evaluating this substitution, and taking note of full
supply chain losses, we obtain the overall dietary shift
potential of beef to poultry on a caloric basis to be
120 million people (40% of current US popula-
tion; gure 3, panel (a)). That is, if the (non-pasture)
land that yields the feed US beef currently consume
was used for producing feed for poultry instead, and
the added poultry production was chosen so as to yield
exactly the number of calories the replaced beef cur-
rently delivers, a certain acreage would be spared,
because of poultrys lower land requirements. If, in
addition, that spared land was used for growing a vari-
ety of products with the same relative abundance as in
the full MAD (but with poultry replacing beef), the
resultant human edible calories would have risen to six
times the replaced beef calories (gure 3, panel (a)).
For protein-conserving dietary shift (gure 3, panel
(b)), the dietary shift potential is estimated at 140
million additional people (consuming 70 g protein
person
1
d
1
as in the full MAD). As the protein qual-
ity of poultry and beef are similar (see the methods
section and references therein), this substitution
entails no protein quality sacrices.
As a benchmark with which to compare the beef to
poultry results, we next consider the substitution of
beef with a plant based alternative based on the metho-
dology developed in Eshel et al (2016). In that study,
we derive plant based calorie- and protein-conserving
beef-replacements. We consider combinations of 65
leading plant items consumed by the average Amer-
ican that minimize land requirements with the mass of
each plant item set to 15 g d
1
to ensure dietary
diversity. We nd that these legume-dominated plant-
based diets substitute beef with a dietary shift potential
of 190 million individuals.
4. Discussion
In this study we quantify the caloric and protein
cascade through the US livestock system from feed to
consumed human food. Overall, <10% of feed
calories or protein ultimately become consumed meat,
milk or egg calories, consistent with mean or upper
bound values of conversion efciency estimates of
individual animal categories (Herrero et al 2015). Our
results combine biologically governed trophic cascade
inefciency with such human effects such as consumer
preferences (e.g., using some animal carcass portions
while discarding others)or leaky supply chains which
is shared also by plant items. As conversion efciencies
reect resource efciencies (Herrero et al 2015), these
results mirror our earlier ones quantifying the envir-
onmental performance of the US livestock system,
highlighting the disproportionate impact of beef
(Eshel et al 2014,2015). Building on and enhancing
earlier studies that considered direct human con-
sumption of feed calories (Cassidy et al 2013, West
et al 2014), our results quantify possible US calorie and
protein availability gains that can be achieved by
reallocating high quality land currently used for feed
production for beef into producing the same amount
of calories and protein from poultry and any extra land
remaining is used to produce the MAD (only with
poultry replacing beef). Using caloric and protein
needs, we estimate 120 and 140 million additional
6
Environ. Res. Lett. 11 (2016)105002
sustained individuals, respectively. This potential
production increase can serve as food collateral in face
of uncertain food supply (e.g. climate change),or
exported to where food supply is limited. In the case of
envisioning various scenarios resulting in only partial
substitution to poultry consumption, the current
calculation also enables to deduce the food gains
associated with substituting only a certain percentage
of national beef calories with poultry (see gure S2).
Our purpose here is not to endorse poultry consump-
tion, nor can our results be construed as such. Rather,
the results simply illustrate the signicant food avail-
ability gains associated with the rather modest and
tractable dietary shift of substituting beef with less
inefcient animal based alternatives. Substitution of
other food items with other nutritionally similar
animal food items is also plausible (e.g., pork for beef),
yet the food gains expected from such replacements
are considerably lower (see supplementary data).
Substitution of beef with non-meat animal based
products (dairy and eggs)is possible on a caloric or
protein basis (see supplementary data), yet given their
dissimilar nutritional prole, a more elaborate metho-
dology is required to construct and analyze such a shift
(Tessari et al 2016). The dietary shift potential of
replacing beef with a plant based alternative (domi-
nated by legumes)(Eshel et al 2016)amounts to 190
million additional people. Thus while plant based
alternatives offer the largest food availability gains,
poultry is not far behind.
We note that the substitution of beef for either
poultry or plants also entails vast reductions in
demand for pastureland. The effects of dietary shifts
on demand for agricultural inputs (such as fertilizer or
water)for the production of food on the land spared
from growing feed for beef requires further
investigation.
This paper offers a system wide view of feed to
food production in the US, and introduces the dietary
shift potential as a method for quantifying possible
food availability gains various dietary shifts confer.
Building on this work, future work can quantify the
dietary shift potential of full diets (e.g. Peters
et al 2016), enhance the realism of various considered
dietary shifts, and better integrate nutritional con-
siderations, micronutrients in particular, in the assess-
ment of expected outcomes.
Acknowledgments
We thank David Canty, David St-Jules, Avi Flamholz,
Avi Levy, Tamar Makov, and Lisa Sasson for their
important help with this manuscript. This research
was funded by the European Research Council (Pro-
ject NOVCARBFIX 646827). RM is the Charles and
Louise Gartner professional chair.
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... Taken together, it becomes increasingly clear that human diets have to change and alternative proteins sources need to be developed and exploited. There is an opportunity to improve the situation especially if the comparably low feed-to-food conversion ratio of livestock and the high amount of unused food side-streams are considered (Morone et al., 2019;Shepon et al., 2016). For example, the same amount of land used for livestock could be used to produce up to 20-times the amount of legumes and meals, yielding key nutrients such as oil, carbohydrates, and proteins (Chéreau et al., 2016;Nadathur et al., 2016;Tang, 2011). ...
Thesis
Consumer diversification and concerns about insufficient protein supply and global malnutrition demand for an exploitation of alternative protein sources such as plant proteins. While manufacturers have made substantial progress in industrially scaled extraction processes and structuring of plant proteins e.g. by extrusion, there is still a lack of information on their fundamental functional and organoleptic properties and interactions with other ingredients in traditional formulations. As a result, food product developers are facing a lot of challenges and are often forced to base their work on trial-and-error rather than mechanistically guided approaches. This is in particular the case for foods where complex raw material requirements and production processes make the manufacture of products with high acceptance and shelf stability not trivial. This includes the design of hybrid meat products that are composed of mixtures of meat and plant proteins. There, traditional meat products are often set as a benchmark, making the performance of such mixed products mostly unsatisfactory. Establishing composition material property functionality relationships may be a first step to overcome these obstacles. Therefore, a variety of plant proteins was assessed for their composition, physicochemical properties, and techno functionalities to gain an understanding of their suitability for the formulation of hybrid meat products. This included their dispersibility, the miscibility of select plant protein fractions with solubilized meat proteins at varying pH and mixing ratios, and the characterization of their odor-active compounds. The latter included powdered as well as extruded plant proteins due to their increasing relevance in the manufacture of hybrid meat and analogue products. Following this, plant proteins were screened in terms of their performance in hybrid meat formulations and during traditional manufacture with a special focus on dry cured products in order to define feasible protein sources and application thresholds. The first part of this thesis showed that aqueous solubility, native pH, and appearance of a variety of 26 plant protein powders from carbohydrate and vegetable oil production correlated with purity and the extraction process. Solubility ranged from as low as 4 % to as high as 100 % based on the protein concentration and prevalence of select protein fractions. For example, large amounts of prolamins (wheat) or glutelins (rice, pumpkin) resulted in low values, while high shares of albumins and globulins promoted moderate to high solubility in sunflower, pea, and potato proteins. A highly soluble (100 %) small molecular weight fraction (< 24 kDa) of the latter was subsequently screened for its particle size and electrostatic and hydrophobic properties as compared to solubilized water and salt soluble meat proteins and the miscibility of both proteins was assessed at pH 3.0 to 7.0 and at select mixing ratios. Phase behavior of mixtures started to change below the isoelectric point (pI) of salt soluble meat proteins (pH ~ 5.5), which was identified as a defining boundary value. Here, one-phase/co-soluble systems (pH > pI) transitioned to two-phased/aggregated ones mediated by interactions (pH ≤ pI) in between individual meat and meat and potato proteins. This resulted in dense, irregularly shaped meat-potato heteroprotein particles, that deviated from the characteristic assembly of pure meat proteins into regular, anisotropic aggregates. A perturbing effect of potato proteins on the structural, organized association of meat proteins below their pI was found. Protein-protein interactions were based on both electrostatics and hydrophobics as shown by variations in surface charge, hydrophobicity, and particle size if sole potato/meat and mixtures were compared. For example, particle size of solubilized meat proteins increased from 18.0 ± 2.9 µm (pH 3.0) to 26.8 ± 9.0 µm (pH 3.0) in 50:50 mixtures. FTIR results confirmed alterations as a function of mixing ratio and pH. Image analysis of microstructures revealed a shift from elongated regular networks towards more disorder and irregularity along with a lower degree of branching. Besides solubility, organoleptic properties influence the suitability of plant proteins as food ingredients. Therefore, odor active compounds of two pea isolates were analyzed by gas chromatography mass spectrometry-olfactometry (GC MS O) after direct immersion stir bar sorptive extraction (DI SBSE), and results were compared to those of their respective extrudates to define changes during dry and wet extrusion. Twenty-four odor-active compounds were found, whereof nine represented major (off-) flavor contributors in peas: hexanal, nonanal, 2 undecanone, (E)-2-octenal, (E, Z)-3,5-octadiene-2-one, (E, E) 2,4 decadienal, 2 pentyl furan, 2-pentyl-pyridine, and γ-nonalactone. The quantity of these nine volatiles was affected distinctively by extrusion. Hexanal was reduced from 3.29 ± 1.05 % (Isolate I) to 0.52 ±â€‰0.02 % (Wet Extrudate I) and (E,Z)-3,5-Octadiene-2-one and (E,E)-2,4-decadienal decreased by 1.5- and 1.8-fold when powdered and dry texturized pea proteins were compared. As a result of the perturbing effect of soluble potato proteins and the higher amount of off flavors in pea isolates compared to their extrudates, use of plant powders as additives was rejected in favor of extruded ones for all subsequent studies. As the focus of this work was the development of dry cured hybrid meat products, the effect of various amounts of extrudates on the traditional formulation and manufacture of this product class was assessed. This included the susceptibility of extrudates towards acid-induced pH changes as compared to pork meat, as well as their behavior in a traditional acidification and drying processes. To that purpose, pork meat and six wet extrudates from peas, pumpkin, or sunflower seeds were analyzed in their proximate composition and subjected to titration starting from the same pH value and using the same acid concentrations. It was shown that wet texturized pumpkin and sunflower proteins had the highest buffering capacity (BC), especially between pH 7.0 and pH 4.5, while pea protein extrudates and pork meat were more prone to acidification and similar in buffering capacity with an average of 881 ± 5 mmol H+/(kg*ΔpH). The obtained data was then used to relate BC with the compositional elements of extrudates such as minerals, proteins, select amino acid, and non–protein nitrogen. These findings on varying susceptibility towards acids were extended by studies on a minced meat model systems containing pork meat, curing salt, and various amounts (0 to 100 wt%) of wet extrudates and the chemical acidifier Glucono delta-lactone (GDL). It was shown, that increasing concentrations of plant extrudates resulted in a linear increase of the initial (pH0h), intermediate (pH6h), and final (pH48h) pH of minced meat model systems. A sufficient acidification to common target pH values in dry cured meat products (pH ~ 5.0) could be achieved with acidifier amounts of 1.0 wt% up at no more than 15 wt% of extrudates. A mathematical model was proposed to correlate pH, time, acidifier, extrudate concentration, and plant protein origin to aid in the adjustments of formulations at higher extrudate contents, and to describe thresholds of feasible extrudate and acidifier concentrations. The calculated concentrations were then implemented to manufacture dry cured hybrid sausages where meat was partially replaced by 12.5, 25, 37.5, and 50 % of pumpkin seed extrudates. All recipes reached the target pH value with an accuracy of pH 5.0 ± 0.06 thereby validating the proposed mathematical correlations. Hybrid recipes with up to 25 % of extrudates were comparable to the traditional all-meat formulation in both the drying behavior and the distribution of moisture and free water. However, higher meat replacement levels promoted distinct changes in drying behavior and product texture where chewiness, hardness, and cohesiveness decreased by up to 70 %. In conclusion, plant protein functionality differs profoundly from the one of meat proteins, and this functionality also depends on the respective protein source as well as the applied extraction process. Their structuring by extrusion provides beneficial organoleptic changes and eases their incorporation in hybrid formulations. The fundamental characterization of plant proteins in terms of their proximate composition and (physico)chemical properties may be used to establish mathematical correlations to estimate the effect of these novel ingredients in hybrid meat products. Thus, the obtained results offer a valuable basis that manufacturers can draw upon not only to create new foods within this product class but also to broaden and facilitate the application of plant proteins on a large scale.
... Feed-to-Food Caloric Conversion Efficiency of Different Animal Products.17,18 Calories of animal feed divided by caloric yield of product. ...
... The DM food protein content of 33% reflects an average value across different ruminant meat products including beef, ground beef and processed meat. The corresponding fresh matter food protein content of 13.5% is comparable to other estimates for the average food protein content of beef products 53,54 . We used the DM protein content for the per-capita substitution of ruminant meat with MP. ...
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