Protein in Feed

The importance of protein in feed recipes is given by the functions that its composing amino acids play when absorbed by animals in the intestine, following digestion (Table 2).

From: Encyclopedia of Mycology , 2021

The Application of Fungal Biomass as Feed

Sajjad Karimi , ... Mohammad J. Taherzadeh , in Encyclopedia of Mycology, 2021

Protein and Amino Acid Profile

The importance of protein in feed recipes is given by the functions that its composing amino acids play when absorbed by animals in the intestine, following digestion ( Table 2). The major roles of amino acids include participation in protein synthesis, use as a substrate for necessary metabolite synthesis, e.g., peptides (glutathione, carnosine, etc.) and neurotransmitters, and use as energy source through amino acid oxidation (Deutz et al., 2014). Supplementing feed with the appropriate amount of amino acids can reduce the risk of cardiovascular disease, prevent cholestasis, liver problems, and have neuro-modulation effects, antioxidant activity, and intestinal health and immunity (Dwyer, 2003; Holeček, 2018; Wu, 2016).

Table 2. Functions of amino acids in organisms

Amino acid Functions
Essential amino acids
Arginine (Arg) Protein synthesis and anabolic processes, urea production, metabolism of several amino acids such as proline and glutamic acid, precursor for creatine and nitric oxide synthesis, stimulant of insulin and growth hormone, effect on immunological functions in mammals, modulate innate immune mechanisms, regulating endocrine and reproductive functions, extra-endocrine signaling, waste detoxification, wound healing, bone repair.
Histidine (His) Involved in the one-carbon metabolism and DNA and protein synthesis, energy fuel during starvation, induces desirable taste (e.g., sweetness), improves sensory attributes (e.g., flavor).
Isoleucine (Ile) Anabolic activity, amino acid synthesis, energy source.
Leucine (Leu) Critical roles in protein structure and composes relatively high proportion of most proteins, stimulates muscle protein synthesis, inhibits proteolysis, stimulates muscle protein synthesis.
Lysine (Lys) Regulation of carnitine synthesis, fatty acid metabolism, osmoregulation in aquatic animals, maintaining the acid-base balance, nitrogen retention in the tissue, increasing the muscle growth, increasing weight gain.
Methionine (Met) Precursor for other amino acids, innate immunity modulator, lipid metabolism, antioxidant activity.
Phenylalanine (Phe) Precursor for neurotransmitter production such as cholecystokinin (CCK) and norepinephrine (NE), induces saturation feeling after eating, needed for thyroid gland, amino acid synthesis, melanin synthesis.
Threonine (Thr) Affect immunity responses, component of mucin in the small intestine, maintaining the intestinal barrier integrity and function, immunological responses.
Valine (Val) Deposited in skeletal muscles, key roles in determination of 3D shapes of structural proteins, synthesis of myelin, anabolic activity.
Tryptophan (Trp) Serotonin (5-HT) synthesis, pain sensitivity reduction, reduces anxiety and tension, sleep induction.
Non-essential amino acids
Alanine (Ala) Gluconeogenesis precursor, energy supplier, nitrogen carrier for amino acid metabolism, stimulatory effects on feeding rate.
Asparagine (Asp) Roles in stress tolerance, weight gain, increase feed intake.
Cysteine (Cys) Antioxidant and detoxifying activity in particular in case of heavy metal removal from the body, DNA repair.
Glutamine (Glu) Purine and pyrimidine nucleotide synthesis, acid-base balance regulation, protein synthesis stimulation, energy substrate for enterocytes, enhances weight gain, feed intake, intestinal development and digestive enzymes activity, essential for fish immunity response. Regulatory effects on hormones secretion such as norepinephrine and glucan-like peptide 1, glutathione production, cell regeneration, brain nutrient.
Glycine (Gly) Hepatic thyroxine monodeiodinase activity increase, enhances the efficiency of nutrient absorption and anabolic events, protein synthesis.
Ornithine (Orn) Synthesis of proline and polyamines, role in the synthesis of arginine in the urea cycle, growth promotor, immune enhancer, detoxifier.
Proline (Pro) Metabolic precursor for glutamine, osmoregulation, roles in protein structure formation, collagen synthesis.
Serine (Ser) Participates in gluconeogenesis, sulfur amino acid metabolism, fat digestion, stimulates feed intake.
Tyrosine (Tyr) Precursor for CCK and NE, regeneration of red and white blood cells, improve memory, mental alertness.

Note: NRC, 2011. Nutrient Requirements of Fish and Shrimp. Washington DC: The National Academies Press. Wu, G., 2010. Functional amino acids in growth, reproduction, and health. Advances in Nutrition 1, 31–37. Holeček, M., 2018. Branched-chain amino acids in health and disease: Metabolism, alterations in blood plasma, and as supplements. Nutrition & Metabolism 15, 33.

The 22 amino acids identified among living organisms have been grouped into essential amino acids (EAAs), conditionally essential amino acids (CEAAs), and non-essential amino acids (NEAAs). EAAs represent those that animals are unable to synthesize in contrast to NEAAs, while CEAAs represent those amino acids which carbon skeleton is not synthesized de novo in animals (Wu, 2013). The synthesis of CEAAs may be influenced by the life stage and physiological conditions of the body when its consumption rate surpasses synthesis (Reeds, 2000). Several factors can affect amino acid synthesis in the animal body including availability of substrate, animal species, animal life stage, physiological circumstances, composition of intestinal microbiota, environmental condition, and animal health status (NRC, 2011). Although the essentiality of each single amino acid is dependent on animal species, most of EAAs are common among animals (Table 3).

Table 3. Profile of different groups of amino acids in different animals, namely in mammals, poultry, and fish

Mammals Poultry Fish
EAA NEAA CEAA EAA NEAA CEAA EAA NEAA CEAA
Arg Ala Gln Arg Ala Gln Arg Ala Gln
Cys Asn Glu Cys Asn Glu Cys Asn Glu
His Asp Gly Gly Asp Tau His Asp Gly
Ile Ser Pro His Ser Ile Ser Tau
Leu Tau Ile Leu
Lys Leu Lys
Met Lys Met
Phe Met Phe
Thr Phe Pro
Trp Pro Thr
Tyr Thr Trp
Val Trp Tyr
Tyr Val
Val

Note: Wu, G., 2010. Functional amino acids in growth, reproduction, and health. Advances in Nutrition 1, 31–37. Halver, J., Hardy, R., 2002. Fish Nutrition, third ed. New York: Academic Press.

With a few exceptions, the protein content (%w/w dry weight) of the filamentous fungal biomass obtained following growth in various substrates had been within 40%–60% (Table 4), which points out the potential of fungal biomass for feed applications, when compared with feed recipes and main sources of protein for animal feed (Table 1). Furthermore, the profile of EAAs of filamentous fungal biomass show a high level of compatibility with that from fishmeal (Fig. 2). Although lower levels of lysine and methionine are available in fungal biomass in comparison to those in fishmeal, their concentrations are still higher than in soybean meal that currently is the preferred alternative protein source of fishmeal (Fig. 3). Filamentous fungal biomass contains high concentrations of valine, threonine, and phenylalanine in comparison to those in fishmeal that can stimulate growth, elevate immune responses, and lead to efficient physiological and hormonal responses, respectively (NRC, 2011). With the exception of glycine, present at higher concentrations in fishmeal, the remaining NEAAs are present at higher levels in fungal biomass than in fishmeal. Although NEAAs can be synthesized in the body, their supplementation in the diet may have an energy sparing effect for the organism. Furthermore, in some life stages such as the reproduction period or a disease outbreak, the body may not provide sufficient levels of required NEAAs (Wu, 2013).

Table 4. Protein content present in the biomass originated from cultivation of filamentous fungi in various substrates

Fungi Substrate Protein content (%w/w dry weight) References
Aspergillus oryzae Palm oil waste 39 Barker et al. (1981)
Rhizopus oligosporus Starch processing wastewater 46 Jin et al. (1999)
Rhizopus sp. Spent sulfite liquor 50–60 Ferreira et al. (2012)
Mucor circinelloides Corn ethanol stillage 30.4 Mitra et al. (2012)
Pythium irregulare Corn ethanol stillage 28 Liang et al. (2012)
Rhizopus, Mucor, Rhizomucor Tempeh 47–63 Wikandari et al. (2012)
Mucor indicus Rhizopus sp. Spent sulfite liquor 30–50 Lennartsson (2012)
Rhizopus oryzae Vinasse 49.7 Nitayavardhana et al. (2013)
Neurospora intermedia Wheat ethanol stillage 56 Ferreira et al. (2014)
Aspergillus oryzae 48
Rhizopus sp. 55
Rhizopus oligosporus Corn ethanol stillage 43 Rasmussen et al. (2014)
Aspergillus oryzae Wheat ethanol stillage 43 Bátori et al. (2015)
Neurospora intermedia
Rhizopus oligosporus Wheat bran 40 Yunus et al. (2015)
Neurospora intermedia Dairy waste 40 Mahboubi et al. (2017)
Aspergillus oryzae
Neurospora intermedia Wheat lignocellulosic residues 50 Nair (2017)

Fig. 3

Fig. 3. Comparison of profiles of EAAs and NEAAs found in filamentous fungi (Aspergillus oryzae (AO), Neurospora intermedia (NI), Rhizopus oryzae (RO)), fishmeal (FM), and soybean meal (SBM).

 Reproduced from Karimi, S., Mahboobi Soofiani, N., Lundh, T., et al., 2019. Evaluation of filamentous fungal biomass cultivated on vinasse as an alternative nutrient source of fish feed: Protein, lipid, and mineral composition. Fermentation 5, 99.

In addition to the amino acid composition, amino acid balance is another important aspect while considering potential protein sources for feed applications. An imbalanced amino acid profile may induce amino acid antagonism and toxicity, which in the long run, can decrease feed intake, induce aggression and abnormal activity, and a suboptimal growth rate (Dwyer, 2003).

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Insect Protein as a Partial Replacement for Fishmeal in the Diets of Juvenile Fish and Crustaceans

Eric W. Riddick , in Mass Production of Beneficial Organisms, 2014

16.1.2 Aims of this Chapter

Although there is some published information on the usefulness of insects as sources of protein in feed for terrestrial livestock (poultry and swine), the purpose of this chapter is to highlight research on insects as sources of protein for juvenile fish and crustaceans (prawn). This chapter attempts to review and synthesize the evidence that protein from insects can partially replace animal protein in fishmeal in feed for juvenile stages of cultured fish. This research is in support of the aquaculture industry and its efforts to provide plentiful fish and prawns for human consumption and remain competitive in a global economy.

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Assessment of the microbiological risks in feedingstuffs for food-producing animals

E. Liebana , M. Hugas , in Animal Feed Contamination, 2012

Animal-derived protein

To prevent the spread of BSE, a total ban on feeding processed animal protein in feeds for any animal farmed for the production of food was introduced on 1 January 2001. Since then, some exceptions have been introduced, such as the use of fish meal and certain blood products and dicalcium phosphate as feed for non-ruminants, as described in the current legislation (EC No. 1292/2005, http://europa.eu.int/eur-lex/lex/LexUriServ/site/en/oj/2005/l_205/l_20520050806en00030011.pdf).

When allowed as ingredients of animal feed, mammalian meat and bone meal (MBM) and poultry offal meal were found to be frequently contaminated by Salmonella, a logical consequence of the risk from the rendering of animals infected with Salmonella (Thal et al., 1957; Hirsch and Sapiro-Hirsch, 1958; Knox et al., 1963). Fish meal also has been historically found to be contaminated by Salmonella, according to the EFSA's zoonoses reports (EFSA, 2006a, 2007a). In 2009, a marked decrease in contamination was observed (0.7% in 2009 compared to 2.1% in 2008) (EFSA, 2011). Contaminated fish meal was the source of the most well-known example of feed-borne transmission of Salmonella, when S. Agona emerged as a public health problem in several countries (Clark et al., 1973; Crump et al., 2002).

There is also a potential risk for the spread of Salmonella by feeding some dairy by-products to animals (EFSA, 2006b). In summary, animal-derived protein is considered as a high-risk product for Salmonella. However, that risk is currently limited in the EU, though it may exist in third world countries and recur in the EU if in the future such products are again allowed as animal feed.

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Gossypol

A. de Peyster , in Encyclopedia of Toxicology (Third Edition), 2014

Chronic Toxicity

Relatively high doses employed in early chronic animal studies produce symptoms of wasting and malnutrition. Livestock consuming cottonseed protein in feed have developed liver toxicity. Aquacultured fish fed unpurified cottonseed protein meal have manifested growth suppression. Normal processing to purify cottonseed oil fit for human consumption removes naturally occurring gossypol to very low or nondetectable levels. Therefore, humans consuming food cooked in or containing cottonseed oil even on a regular basis are unlikely to experience any of these effects unless crude cottonseed oils are used extensively.

Low potassium level (hypokalemia) is a concern for some users of gossypol as a male contraceptive, and also irreversibility, with an estimated 10% chance of non-recovery of fertility with prolonged use. In female patients being treated for endometriosis or uterine myoma, undesirable side effects observed initially were weakness, anemia, and hypokalemia, as well as a slight elevation of cholesterol and altered liver function. Chronic effects of gossypol when consumed intentionally in these larger doses to produce the desired pharmacologic effect (e.g., reduced fertility in men) are discussed in more detail in clinical reports summarized in one of the reviews shown in Further Reading.

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Feeds, Prediction of Energy and Proteins | Feed Proteins

J.E.P. Santos , J.T. Huber , in Encyclopedia of Dairy Sciences (Second Edition), 2002

Fractionation of Dietary Protein from Feedstuffs

Crude protein is determined by quantifying the total N content and multiplying that value by a specific factor. Because it is generally assumed that N represents 16% of the total weight of an amino acid, determination of CP in feeds have been based on their total N content multiplied by 6.25 (6.25   =   100/16). However, proteins vary in N content, and not all N is of true protein origin.

Until recently, protein nutrition of ruminants was based upon their requirements for CP. However, because of the increased level of productivity of these animals and increased knowledge of feed analysis and nutrient requirements, proteins have been fractionated into different categories such as CP, soluble protein, ruminally degraded protein (RDP), RUP and unavailable protein. In addition to those protein measurements, the amino acid profile of protein supplements can also be determined.

The Cornell Net Carbohydrate and Protein System (CNCPS) fractionates dietary protein into three major fractions: nonprotein N (fraction A), true protein (fraction B) and bound true protein (fraction C). True protein is further divided into three subfractions, B1, B2 and B3, based on their rates of ruminal degradation. Determination of protein fractions is based upon protein solubility in borate phosphate buffer, neutral detergent and acid detergent solutions ( Table 1 ). Fraction A is constituted by ammonia N, nitrate, soluble amino acids and proteins, and it represents the soluble protein fraction. Fraction B1 is the rapid degrading protein composed by globulins. Fraction B2 is the medium degrading protein, and it is composed by albumins and glutelins. Fraction B3 is the slowly degrading protein, and it is composed by prolamins. Fraction C is the protein fraction associated with fiber, which is mostly unavailable and composed by bound protein and Maillard products. Fractions A, B1, and most of B2 represent the RDP. Part of B2 and fractions B3 and C represent the RUP.

Table 1. Determination of protein fractions according to the Cornell Net Carbohydrate and Protein System

Solution Solubility
Soluble Insoluble
Borate–phosphate buffer A, B1 B2, B3, C
Neutral detergent solution A, B1, B2 B3, C
Acid detergent solution A, B1, B2, B3 C

Because ration formulation systems require partition of dietary CP into fractions degraded in the rumen (RDP) and resistant to ruminal degradation (RUP), fractionation of proteins in feedstuffs becomes an important aspect of feed analyses. Protein sources highly degradable in the rumen, such as soybean meal and canola meal, are rich in fractions A and B1, but those that are resistant to rumen degradation, such as fish meal and blood meal, have fractions B2, B3 and C as their major components.

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Bovine Spongiform Encephalopathy (BSE)☆

N. Fernández-Borges , ... J.M. Torres , in Reference Module in Neuroscience and Biobehavioral Psychology, 2017

Diagnosis and Control of BSE

Bovine brain affected by BSE is characterized by PrPSc accumulation and spongiform changes (Novakofski et al., 2005). By microscopic examination of fixed brain spongiform change in the gray matter neuropil, neuronal vacuolation, neuronal loss, and astrocytosis can be found in brain of affected cattle. Other affected tissues in naturally or orally infected cattle revealed by immunohistochemistry, Western blot analysis, protein misfolding cyclic amplification or bioassay were spinal cord, retina, optic nerve, nasal mucosa, digestive tract tissues like tongue, esophagus, rumen, abomasum, jejunum and ileum, adrenal gland, muscle spindles, tonsil, nictitating membrane, mesenteric lymph node, spleen, bone marrow, peripheral nerves and ganglia like dorsal root, trigeminal, nodose, stellate, cranial cervical and mesenteric ganglia (Iwata et al., 2006; Buschmann and Groschup, 2005; Konold et al., 2010; Sohn et al., 2009; Balkema-Buschmann et al., 2011a,b; Franz et al., 2012; Wells et al., 2005; Kaatz et al., 2012; Murayama et al., 2010). Detection of the prion in non-neural peripheral tissues is usually inconsistent, only achieved by the most sensitive diagnostic methods, such as protein misfolding cyclic amplification or bioassay, and often in animals experimentally infected and at terminal stage of disease.

Clinical diagnosis is not fully reliable and BSE can only be confirmed post-mortem by microscopic examination of the brain for vacuolation or PrPSc detection by immunoblot and/or immunohistochemistry (Londhe et al., 2012).

In Europe, the national reference laboratories (NRLs) and the EU reference laboratory for TSEs are responsible for the sampling and diagnosis of TSE cases. For BSE diagnosis following the slaughter or death of an animal a sample of the brain or medulla oblongata is taken from the animal and tested in a laboratory with the approved rapid tests able to detect the BSE agent (Prionics-Check Western test; Enfer test amp; Enfer TSE Kit version 2.0, automated sample preparation; Enfer TSE Version 3; Bio-Rad TeSeE rapid test; Prionics-Check LIA test; IDEXX HerdChek BSE Antigen Test Kit, EIA; Prionics Check PrioSTRIP; Roboscreen Beta Prion BSE EIA Test Kit and Roche Applied Science PrionScreen). As per EU legislation, samples from inconclusive or positive cases must be confirmed by an alternative method, such as histopathology, immunohistochemistry, immunoblotting, demonstration of characteristic fibrils by electron microscopy or a different rapid test (see Relevant Websites).

Since BSE was declared an epidemic disease of cattle in Europe the EU has implemented several control strategies with particular focus on the prevention of BSE. These strategies include:

•

Monitoring: each Member State has to carry out an annual monitoring programme for BSE based on active surveillance (testing without previous suspicion) in addition to passive surveillance (testing of clinical suspects).

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Feed ban: preventive measure against BSE that consists of a ban on the use of PAP in feed for farmed animals.

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Specified risk material (SRM): preventive measure based on the removal of SRM from slaughtered cattle to prevent these tissues from entering the food chain.

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Products of animal origin derived from or containing ruminant material: some prohibitions on the use of ruminant material for products of animal origin like mechanically recovered meat.

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Control and eradication of BSE: whenever BSE is suspected the competent authority must be notified and if it is confirmed the entire body of the animal must be disposed of by incineration and an inquiry to identify all animals at risk of having BSE must be carried out.

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Placing on the market, export and import: rules on trade are laid down for live animals, their semen, embryos and ova as well as products of animal origin.

•

Reference laboratories, sampling and testing: The NRLs and the EU reference laboratory for TSE are responsible for BSE confirmation based on the current regulations.

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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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Prophylactic and Prevention Methods Against Diseases in Aquaculture

Parasuraman A. Subramani , R. Dinakaran Michael , in Fish Diseases, 2017

4.2.4.3 Proteins

Proteins are very important for proper functioning of immune system since most of the immune molecules such as antibodies, cytokines, serum enzymes, complements, and so on are proteins. However, very high protein diet also retards the immune system (Kiron et al., 1995b). Hence, a balance must be struck. Finfishes, like other vertebrates, need 10 dietary amino acids (FAO: Nutritional requirements, 2016). Farmers must optimize protein concentration in fish feed in order to get better results (Collins et al., 2012). According to the methods given by Kiron et al. (1995b) , 20–35% protein in feed is considered to be optimal for protecting rainbow trout from viral infection.

Source of protein play an important role in protecting fishes from diseases. Currently plant-based protein sources are used widely in aquaculture, which include soy bean and cottonseed (Yue and Zhou, 2008). However, uses of conventional sources of proteins, e.g., fish meal, are becoming limited in aquaculture. On the other hand, effect of different sources of proteins on health status of fish is now being explored. For instance, fishes fed with protein hydrolyzates of animal origin (tilapia, krill, or shrimp) showed better resistance to E. tarda infection compared to that of fishes fed with protein hydrolyzates of plant (soybean) origin (Khosravi et al., 2015a, 2015b; Krogdahl et al., 2000). An interesting reason behind this fact is the difference in the composition of amino acids between plant and animal source. Arginine is one of the major components that differ in its concentration between the two sources. To add to the story, supplementation of arginine alone to fish diets augmented important immune parameters (Zhou et al., 2015). However, at very high concentration (3.3% w/w) arginine inhibited some of the immune functions. An optimum level of 2.7% arginine was recommended for catfish from this study. Another inexpensive alternative to fish hydrolyzate is poultry feather lysate which had better performances than that of soybean hydrolyzate (Zhang et al., 2014a). Methionine, another amino acid found in low levels in plant can impair growth and immune responses of fishes (Belghit et al., 2014).

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Amino Acids

L.B. Willis , ... A.J. Sinskey , in Encyclopedia of Genetics, 2001

Sources and Uses of Amino Acids

Plants and many bacteria synthesize all 20 of the amino acids listed in Figure 2. Amino acids are synthesized from a variety of primary metabolites in living cells. However, vertebrates, including humans, are only able to manufacture a subset of these amino acids. Hence they must obtain the remainder of their amino acids from their diet. Amino acids that must be obtained in this manner are known as essential amino acids (Figure 2). Since proteins are composed of amino acids, diets that are rich in protein are more likely to contain sufficient amounts of each of the essential amino acids to preclude any deficiencies.

In animal feeds, however, where the bulk of the protein present may come from a single source such as grain, imbalances in the individual essential amino acids can occur. For example, corn (maize) provides the bulk of protein in feed for livestock. Yet the protein found in normal field corn is disproportionately low in lysine. To compensate, farmers routinely add lysine to animal feed to improve its nutritional value.

Amino acids are produced commercially from a variety of sources and for a variety of uses. For example, lysine, tryptophan, and threonine to be used as feed supplements are produced by fermentation. In these processes, genetically altered bacteria that produce more of an amino acid than they need for their own growth excrete the excess amino acid into their growth medium. Once the desired amino acid accumulates to a sufficient level, the bacteria can be removed and the amino acid purified for use directly or as an ingredient in feed formulations. Glutamic acid, which is often used as the flavor-enhancer monosodium glutamate (MSG), is similarly produced by microbial fermentation. Other amino acids are produced commercially by chemically hydrolyzing proteins. Thus cysteine, which is particularly abundant in the protein keratin, is produced from hair.

In addition to industrial applications in animal feed, human nutrition, and flavor enhancers, amino acids are also important components of cosmetics and medications. Amino acids or their chemical analogs can be used as precursors for synthesis of pharmaceutical agents. Synthetic polymers of amino acids are used to encapsulate drugs so as to aid in their absorption or to control their release into the bloodstream. Current research into amino acids promises to yield new polymers that can be used as textile fibers, novel antibiotics to combat infectious diseases, and nutritionally enhanced plants to feed a hungry world.

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