Limiting Amino Acids

The most limiting amino acid in cereals is lysine, followed by threonine, methionine, and valine.

From: Barley (Second Edition) , 2014

Volume 1

C.G. Schwab , N.L. Whitehouse , in Encyclopedia of Dairy Sciences (Third Edition), 2022

Limiting Amino Acids

Limiting AA have traditionally been thought of as those in shortest supply relative to need for protein synthesis. The first limiting AA is the one in shortest supply relative to need. The second limiting AA is the one in second shortest supply relative to need, etc. Methionine, lysine, and histidine have been identified most often as the most limiting AA for lactating dairy cows. The extent and sequence of their limitation is affected primarily by the amount of RUP in the diet and its AA composition.

Methionine can be first limiting for growth and milk protein production when cattle are fed high forage or high fiber diets and intake of RUP is low. In this case, microbial protein provides most of the absorbed AA. Methionine has also been identified as first limiting for cattle fed a variety of diets in which most of the supplemental RUP was provided by soybean protein, animal-derived proteins (e.g., blood, feather and meat meals), or a combination of the two. Note the low content of methionine in most forages, soybean meal, and most of the animal proteins as compared to rumen microbes and milk and lean tissue (Table 1).

Lysine has been identified as first limiting for growth and milk protein synthesis when corn or feeds corn origin provided most or all of the RUP in the diet. Relative to concentrations in microbial protein, feeds of corn origin are exceptionally low in lysine content and similar in methionine content, whereas soybean products and most animal-derived proteins are similar in lysine content and low in methionine content (Table 1).

Methionine and lysine have been identified as co-limiting AA for milk protein synthesis when cows are fed diets based on corn silage with little-or-no protein supplementation. Histidine has been identified as first limiting for milk protein production when dairy cows are fed diets of grass silage and barley or oats, with or without feather meal as the sole source of RUP supplementation.

It should not be too surprising that these AA have all been shown to be limiting. First, all have been identified as being among the most limiting AA in microbial protein. Methionine has been identified as first limiting and lysine as second limiting in microbial protein for nitrogen retention of both growing cattle and growing lambs. Histidine has been identified as a possibly third limiting amino acid for ruminants, but this would likely occur only in a few instances.

Second, concentrations of methionine and lysine in most feed proteins are lower than those in microbial protein (Table 1). Thus, most feed proteins are not complementary to microbial protein and instead, when they are fed, will exacerbate rather than eliminate deficiencies of methionine and lysine in metabolizable protein. This is also why methionine and lysine become more limiting (relative to the other essential AA) with increasing intakes of complementary sources of RUP.

Third, lysine is more vulnerable to heat processing than other AA. Overheating feed proteins can decrease lysine concentrations as well as decrease the digestibility of the remaining lysine more than that of total protein.

And finally, concentrations of histidine are lower in grasses and legumes, oats, barley, and particularly feather meal, as compared to most other feeds (Table 1). This is probably why diets consisting solely of these feeds have been shown to be more limiting in histidine than in methionine or lysine.

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Protein and Amino Acids in Human Nutrition

L. Hambræus , in Reference Module in Biomedical Sciences, 2014

Amino Acid Analysis

Limiting amino acids. Mitchell and Block (1946) introduced the chemical score concept as an indicator of the nutritive value of protein referring to the fact that all amino acids must be provided simultaneously for protein synthesis. The scoring is based on amino acid analysis of food proteins followed by calculations of which essential (indispensable) amino acid that occurs in the least relative percentage when compared with a reference pattern. This amino acid is identified as the limiting amino acid as this would limit protein synthesis. The absolute percent value is referred to as chemical score or amino acid score. The relevance of this estimation depends on the selection of optimal amino acid pattern. It is thus essential to know which reference pattern has been used when comparing data on amino acid scores from various publications throughout the years. The concept of limiting amino acid is also used when the indicator amino acid oxidation (IAAO) method is used during stable isotope studies on protein requirement (see below).

The amino acid scores can be corrected for digestibility (PDCAAS = protein digestibility corrected amino acid score) if the amino acid score value is multiplied with the digestibility divided by 100. In the case of animal proteins (except gelatin) no amino acids have a PDCAAS value lower than the reference pattern (PDCAAS being >100) while wheat has a PDCAAS value less than 50%. Interestingly potato has the highest PDCAAS value among the vegetable proteins listed (Table 6).

Table 6. Essential amino acids (mg g− 1 nitrogen) and PDCAAS in some selected animal and vegetable food items

Component Milk (cow) Egg Beef Gelatin Beans and peas Soy Wheat Potato
Histidine 185 160 220 41 155 170 145 105
Isoleucine 390 360 300 98 280 270 230 230
Leucine 630 570 480 180 480 450 410 340
Lysine 570 490 520 280 410 370 200 360
Methionine + cysteine 218 350 204 48 140 133 189 135
Phenylalanine + tyrosine 560 630 450 138 450 500 440 370
Threonine 260 300 270 120 260 250 190 210
Tryptophan 82 89 69 0 80 76 80 95
Valine 450 470 330 10 630 280 310 370
PDCAAS 100 100 100 0 79 82 48 93

PDCAAS, protein digestibility corrected amino acid score.

Four essential amino acids dominate as limiting amino acids: lysine and threonine in cereals, sulfur amino acids in legumes, and tryptophan in maize. As the protein intake is based on a mixture of protein sources from vegetable and animal food products, the total content of amino acids in the food is of greater interest than that from single protein sources. This is especially essential in vegetarian diets. Thus, combination of cereals where the limiting amino acid is lysine with legumes, for example, peas and beans, which have a higher lysine but lower content of sulfur amino acids, results in an increase in PDCAAS value from that in wheat, 48, and beans, 79, respectively, to 89 in the mixture for adults. This is called the supplementary effect of various protein sources. As animal proteins usually have a surplus of essential amino acids in relation to the reference, they have a supplementary effect in a mixed diet based on vegetable and animal food items. There are, however, also animal protein sources with low PDCAAS values as a result of unbalanced amino acid content. Blood protein has a low content of isoleucine. Collagen, which occurs in varying amounts in many cured meat and provisions, is extremely low in tryptophan and cysteine. Thus declaration of the content of animal protein in a product does not necessarily guarantee a high protein quality.

Reference amino acid patterns. From the beginning casein was used as reference protein, especially in biological evaluations using animals, probably as this was the first purified animal protein available. However its amino acid composition is rather extreme characterized of extremely low cysteine and high phenylalanine contents. Egg protein was also used but lead to an exaggeration of some essential amino acids. The selection of a reference pattern is also complicated as the need of essential amino acids does not seem to be the same for growth as for maintenance. Today it is suggested that the amino acid pattern in breast milk should be used as reference for infants 0–6 months of age and other theoretical patterns for other age groups. This is illustrated in Table 7.

Table 7. Protein need (g kg− 1 bodyweight and day) for growth and maintenance as well as reference amino acid pattern (mg amino acid per g protein) for calculation of protein score at different ages. The values for amino acid pattern are calculated as follows: amino acid requirement per kg body weight and day divided with total protein requirement

Age group (years) Protein need for growth Protein need for maintenance His Ile Leu Lys Thr Trp Val SAA AAA
0.5 0.46 0.66 20 32 66 57 27 8.5 43 28 52
1–2 0.2 0.66 18 31 63 52 27 27 42 26 46
3–10 0.07 0.66 16 31 61 48 25 25 40 24 41
11–14 0.07 0.66 16 30 60 48 25 25 40 23 41
15–18 0.04 0.66 16 30 60 47 24 24 40 23 40
>18 0 0.66 15 30 59 45 23 23 39 22 38

SAA = Sulfur amino acids. AAA = Aromatic amino acids. Source: WHO, 2007. Protein and Amino Acid Requirement in Human Nutrition, Report of a Joint WHO/FAO/UNU Expert Consultation. Technical Report Series, vol. 935. WHO, Geneve.

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PROTEIN

TOM BRODY , in Nutritional Biochemistry (Second Edition), 1999

Complementary Proteins

The most limiting amino acid of wheat protein is lysine. The study described earlier revealed the growth-promoting effects of supplementing wheat protein with lysine. The most limiting amino acid of soybeans is methionine. Soybean-based infant formulas are supplemented with methionine. Generally, people do not supplement their diets with amino acids. The dinner table does not bear shakers containing methionine or lysine, along with the salt and pepper shakers. On the other hand, people do supplement their moderate-quality proteins with the limiting amino acids. People also supplement their moderate-quality proteins with other moderate-quality proteins. What does this mean? The major staples of the world include sweet potatoes, cassava, beans, rice, corn, and wheat. The first two foods in this list contain relatively little protein; however, the legumes and grains are moderately good sources of protein. Legumes contain ample amounts of lysine, threonine, and tryptophan, but are limiting in methionine. Grains contain methionine, but are limiting in lysine and sometimes threonine or tryptophan. A diet containing both legumes and grains supplies a mixture of amino acids that is of higher quality than a diet containing legumes alone or grains alone. These mixtures are not as high in quality as the protein of meat, milk, or fish, but they are better than that in legumes or grain alone. The use of both legume and grain proteins in a diet supplies complementary proteins. Complementary proteins are supplied by such time-tested food combinations as the beans and rice consumed in Central and South America, the tofu and rice consumed in Asia, and the peanut butter sandwiches consumed by American children.

The following study illustrates the effect of using complementary proteins. Growing rats were fed diets containing various combinations of rice and bean protein (Figure 8.30). For example, one test diet consisted of 100% rice protein and no bean protein, whereas another diet contained 40% rice protein and 60% bean protein. The PER was determined for each combination. The results demonstrate that the most valuable sources of protein were those containing 50 to 80% rice protein, with the remainder consisting of bean protein.

FIGURE 8.30. Protein efficiency ratio versus type of diet.

 (Redrawn with permission from Hulse et al., 1977.) Copyright © 1977

An interesting sidelight concerning the use of complementary proteins is that they must be consumed together, or at about the same time, to be of maximal benefit as a protein source. For example, eating beans at breakfast and corn at dinner would fail to supply complementary proteins. The following description is paraphrased from a brief report concerning complementary mixtures of amino acids (Cannon et al., 1947): Protein-deficient rats recovered weight steadily when fed a diet containing 10 indispensable amino acids. If, however, the diet is divided into two portions — one containing arginine, histidine, leucine, lysine, and threonine and the other containing isoleucine, methionine, phenylalanine, tryptophan, and valine — and these two incomplete rations are fed alternately, the recovery of weight is poor. Poor weight recovery occurs when the rations are offered to rats at alternate hours over a 14-hour period. The rats lose weight. On the other hand, the animals eat well and recover weight rapidly when the two incomplete rations are mixed together.

A fine point might be added concerning differences in human and animal nutrition. Some populations seem to thrive and grow on diets containing only one source of a moderate-quality protein. Persians, in particular, may consume diets where grain may be the sole source of protein (Vaghefi et al., 1974). Although the growth of rats consuming diets containing only bread protein may be impaired, such effects are not readily detected in humans. Human children require a lower density of protein in the diet than do rats for supporting a maximal rate of growth. Rats require diets containing close to three times higher amounts of protein per total energy content than do children. A human infant is expected to grow at a near-maximal rate when its only source of protein is bread or beans. This situation is clearly not the case with rats. Rat growth is strikingly impaired when grain protein-based or bean protein-based diets are used.

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Mathematical Modeling in Experimental Nutrition

M.J. Gahl , ... M.D. Finke , in Advances in Food and Nutrition Research, 1996

B Protein Quality Improvement by Addition of the Limiting Amino Acid

Addition of the limiting amino acid is one method of improving the quality of a protein. Methionine (0.4%) was added to the MCM to determine the effect of adding a limiting amino acid to a protein source. The methionine supplementation improved growth and nitrogen gain which is illustrated by the changes in both response curve scale and response curve shape; the c and k parameters were significantly different (Finke et al., 1987b). Using MCM + Met as the reference, MCM alone was always a lower quality protein and the relative value decreased as higher levels of nitrogen were fed (from 90 to 62%). The different response curve shape and scale suggest that MCM + Met when fed to rats results in a different diminishing returns response. The diminishing returns responses can be compared by examining the first derivative of the response curves (Fig. 3). The slope (dr/dI) of the response curve is termed marginal efficiency and reflects the efficiency of use of a "small" increment of nitrogen added to a diet. When MCM is fed to rats, diminishing returns are observed at intakes near zero (maximum efficiency of nitrogen gain was 47%) and the efficiency of nitrogen use rapidly declines and approaches zero as maximum gain is approached. However, when MCM is supplemented with methionine, the efficiency of nitrogen gain increases to a maximum of 60% at 25% of R max and then declines as R max is approached. The curvilinear response and decreasing efficiency could be due to a change in the limiting amino acid as intake is increased since the pattern of amino acid requirements for maintenance is clearly different than the requirement for maintenance + growth (Benevenga et al., 1994). The change in limiting amino acid could also explain the change in relative values of proteins from maintenance to maximum gain. Amino acids could be used with different efficiencies and could evoke a different diminishing returns response when fed to rats.

Fig. 3. (A) Body nitrogen gain (g) vs nitrogen intake (g) over 21 days for groups of four rats fed graded levels of Mormon cricket meal or Mormon cricket meal with supplemental methionine. Lines are the best fits using the logistic equation (Finke et al., 1987b). Each data point represents the mean ± SEM of four rats. (B) Marginal efficiency (dr/dI) of nitrogen intake used for nitrogen gain. The marginal efficiency reflects the efficiency of utilization of an increment of nitrogen added to the diet.

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Nutrition

In Clinical Veterinary Advisor: The Horse, 2012

Threonine

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The second limiting amino acid for horses based on improved average daily gain observed in yearling horses

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Improvement in muscle mass for exercising horses was also observed for horses receiving both supplemental lysine and threonine.

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Management guidelines:

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Be sure to provide a good quality source of protein to ensure a good amino acid profile to the protein source (milk-based protein for young; soybean meal for all functions).

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Synthetic forms of threonine are available to improve the quality of the protein in the diet should the source of protein be poor quality.

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Whey Protein-Based Nutrition Bars

Naiyan Lu , Peng Zhou , in Whey Proteins, 2019

13.2.1.5.2 Nutrition Loss

Lysine is the first limiting amino acid in many high-protein foods. In high-protein nutrition bars made with both dairy and soy proteins, the reduction in active lysine induced by the Maillard reaction leads to a significant quality loss during storage (Ha & Zemel, 2003). As mentioned earlier, glycation is dependent on the reducing sugar involved, depending on the reactivity of the α-hydroxy carbonyl of the sugar molecule. Substitution of fructose with sorbitol can significantly slow down active lysine reduction during storage (Fig. 13.3).

Figure 13.3. Active lysine of high-protein nutrition bar model systems made of whey proteins with sorbitol (WS) or fructose (WF).

Overall, the Maillard reaction is responsible for the quality losses of many protein bars during long-term storage, and exclusion of reducing sugar seems to be the most efficient solution to inhibit these undesired changes.

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Meal Nutrition and Utilization

Susan Arntfield , Dave Hickling , in Canola, 2011

Research and Improvements for Dairy Feed

The empirical information on the value of canola meal in dairy cow diets is compelling, and it seems likely that the benefits are due to protein degradability in the rumen and amino acid balance. Knowing that feeding canola meal will increase milk production does not help dairy nutritionists formulate diets. To be practical, additional mechanistic information on amino acid utilization is required as outlined below.

1.

What are the first limiting amino acids for dairy cows when fed canola meal under different dietary and production scenarios?

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Is the milk production response to canola meal primarily due to higher histidine levels?

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Could canola meal increase milk production through supply of other limiting amino acids? For example, there could be situations in which canola meal could replace corn Dried Distillers Grains with Solubles (DDGS) in the diet and provide higher lysine intake.

2.

What are the utilization efficiencies of essential amino acids in canola meal and other ingredients under different dietary and production scenarios (e.g., RUP levels, duodenal digestion, splanchnic tissue flow, milk gland uptake)? There is some research that indicates that certain essential amino acids have a lower rumen degradability than nonessential amino acids (Kendall et al., 1991; Boila & Ingalls, 1992).

3.

What factors affect response to histidine (e.g., glucose availability [Huhtanen et al., 2002], metabolism with carnosine [Lapierre et al., 2007])? What is the true nature of group 2 amino acid requirements (e.g., lysine required at the milk gland for nonessential amino acid synthesis [Lapierre et al., 2007])?

The next stage of canola meal research for dairy cows should attempt to answer the above questions.

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Application of Plant Breeding and Genomics for Improved Sorghum and Pearl Millet Grain Nutritional Quality

Ashok Kumar Are , ... Jayakumar Jaganathan , in Sorghum and Millets (Second Edition), 2019

2.2 Pearl Millet

As with most cereals, the first limiting amino acid of pearl millet protein is lysine. A significant relation of lysine content of a protein is its inverse correlation with level of protein in the grain (Deosthale et al., 1971). However, the essential amino acid profile of pearl millet protein shows more lysine, threonine, methionine, and cysteine than in the proteins of sorghum and other millets. Its tryptophan content is also higher. In fact, it has been reported that pearl millet grain contains a 27%–32% higher concentration of indispensible (essential) amino acids than maize, sorghum, and wheat (Ejeta et al., 1987; Davis et al., 2003). Furthermore, it has a less disparate leucine/isoleucine ratio (Hoseney et al., 1987; Rooney and McDonough, 1987) than cereals such as wheat, barley, and rice (Ejeta et al., 1987). The majority of pearl millet lipids are triglycerides (Gupta, 1980). Although the fat content of pearl millet has been reported as factor in flour rancidity, it has been found that the fat content of different genotypes showed variable expression against rancidity, indicating that fat content alone is not responsible for rancidity (Arya et al., 2013). Kim et al. (2003) reported that resistant starch significantly lowers plasma total lipid and cholesterol concentrations in diabetic rats. Hence, the pearl millet's resistant starch may contribute to cholesterol metabolism and optimizing the levels of cholesterol in the human body.

Pearl millet is a good source of niacin, pyridoxine, and B-group of vitamins. The yellowish seed coat pigments generally contribute to the β-carotene content of pearl millet (Jiji et al., 2017). The high polyphenol content of millets has already been mentioned. The other prominent phytochemical in pearl millet is phytate (myoinositol hexaphosphate), which in addition to its effect as an inhibitor of mineral absorption, also can exert some health benefits due to its metal chelating properties, especially "Fe" chelation and thereby hindering free radical formation (Jain et al., 2016). Minnis-Ndimba et al. (2015) studied the spatial distribution of micronutrients in pearl millet grains and showed that both iron and zinc are predominantly concentrated in the germ, which consists of the scutellum and embryo and in the seed coat, plus the pericarp and aleurone. Since pearl millet can be consumed in the whole grain form, this distribution of these minerals would have no adverse implications on processing.

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CULTURAL DIFFERENCES IN PROCESSING AND CONSUMPTION

J.M. Jones , C.I.M. Jones , in Encyclopedia of Grain Science, 2004

Cultural Differences in Processing and Consumption – Protein

In terms of protein, each cereal offers distinct nutritional characteristics. These become important only if the staple is relied on as a major protein source. For example, oats offer a higher protein content than other grains and an amino acid pattern closer to the FAO standard than other grains. Historically, the high quality of protein from oats was once important in the UK and in parts of northern Europe. Similarly the high protein content of pseudocereal buckwheat provided important protein nutriture in parts of the former Soviet Union.

In most Western countries, protein quality and quantity is not an issue so cultural practices have little impact. However, for parts of the Indian subcontinent, Asia, and Africa, processing of cereals such as milling, fermentation, and cooking have important nutritional impacts. Milling may make protein more available and fermentation may improve biological availability of essential amino acids.

Fermentation and germination are important for improving the nutritional quality of grains. Fermentation, together with cooking and de-hulling, reduces the tannin of sorghum and millet. Since tannins complex with protein, they inactivate digestive enzymes and reduce protein digestibility. The presence of tannins in food can therefore depress growth and increase protein loss. Germination not only increases the synthesis of lysine and tryptophan, it also improves digestibility.

Cereals are incomplete proteins and have lysine as their most limiting amino acid. Corn protein is also limiting in the essential amino acid tryptophan, while other cereals are often limiting in threonine. Throughout the world, the practice of combining cereals with pulses makes a complete protein, so-called protein complementarity. In reciprocal fashion cereal grains contribute methionine, which is deficient in legumes. A survey of national dishes from around the world shows the many interesting and unique ways that different cultures have chosen to complement the protein. These time-honored national dishes are popular for vegetarians around the world. Some of them are listed below:

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India/Sri Lanka – "rice pilaf," "dhal" (legume);

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India/Sri Lanka – "chapati," "dhal";

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Middle East – "pita" bread, "Hummus" ("garbonzo" bean/"tahini spread"); and

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China – "congee" (rice gruel), small amounts of meat, tofu, or fish.

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MUSHROOMS AND TRUFFLES | Use of Wild Mushrooms

S. Rajarathnam , M.N. Shashirekha , in Encyclopedia of Food Sciences and Nutrition (Second Edition), 2003

Food Value

Determination or prediction of the nutritional value of mushrooms (Table 5) has been made possible based on their content of essential amino acids.

Table 5. Estimated nutritive values of mushrooms

Mushroom species Essential amino acid index Biological value Nutritional index Amino acid score a
Agaricus bisporus 55.8 49.1 17.0 36
Boletus edulis 76.6 71.8 9.3 37
Cantharellus cibarius 86.2 82.3 3.0 68
Lentinus edodes 55.8 49.1 9.8 40
Pleurotus florida 84.5 80.4 15.9 67
Russula vesca 88.9 85.2 6.0 70
Termitomyces microcarpus 74.7 69.7 20.5 45
Volvariella displasia 87.6 84.1 25.1 71
a
Using egg as reference protein.

The amino acid score is the amount of the most limiting amino acid in the food protein expressed as a percentage of that amino acid present in a reference protein. Amino acid score = mg of amino acid in 1 g test protein mg of amino acid in 1 g reference protein × 100

The essential amino acid (EAA) index evaluates the quality of dietary protein in terms of the ratio of the EAA contained in a food, relative to the EAA content of the reference protein, mostly egg. EAA = Lysine p − tryptophan p − histidine p Lysine s − tryptophan s − histidine s n

where p  =   food protein, s  =   standard (egg), and n = the number of amino acids.

The biological value is a measure of the nitrogen retained by the body after consuming the test protein. Biological value = 10.9 ( EAA index ) − 11.7

In an attempt to resolve the difficulties inherent in comparisons between those mushrooms containing small amounts of high-quality protein with those containing larger amounts of a protein of lesser nutritional quality, the use of a nutritional index has been proposed: Nutritional index = EAA index × percentage protein 100

Amino acid scores and EAA indices of the most nutritive mushrooms (highest values) rank in potential nutritive value with those of meat and milk, and are significantly higher than those for most legumes and vegetables. The least nutritive mushrooms rank appreciably lower but are still comparable to some common/nutritious vegetables.

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