Antinutritional factors

Not all constituents of cereals are advantageous for health. Although many nutritionally beneficial components are concentrated in the outer layers of the grain, it may also happen that residues from crop sprays such as pesticides or fumigants from stored grain may remain. This may pose a problem for processors, who must also ensure that these residues do not become concentrated in the products. Other hazards include mycotoxins, which can be dangerous at low levels. 

Skills in separation of grain components and their analysis are needed to address these problems. Some examples of naturally occurring antinutritional compounds are phytates (already mentioned), phenols, tannins, and trypsin- and a-amylase inhibitors. Phenols and tannins bind with and precipitate proteins in food systems, thus decreasing digestibility. Minimizahon of these compounds in cereals is an objective. 

The chemical reactions that participate in metabolism are numerous and coordinated. Cereal chemists have a role in identifying the constituents provided by cereals in the diet and how they may interact. Basically, there are two main types of metabolic processes  

After these substances are transported to the cells, anabolic reactions, the second main type of reaction, occur. In this phase of metabolism. 

Unraveling of the reaction pathways that influence healthy and nonhealthy effects of diefary compounds promises to be an exciting and challenging area of research for fhe future. 

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Since feeds contain other substances than those required by the animals of interest, studies have also been conducted on antinutritional factors in feedstuffs and on the use of additives. Certain feed ingredients contain chemicals that retard growth or may actually be toxic. Examples are gossypol in cottonseed meal and trypsin inhibitor in soybean meal. Restriction on the amount of the feedstuffs used is one way to avoid problems. In some cases, as is tme of trypsin inhibitor, proper processing can destroy the antinutritional factor. In this case, heating of soybean meal is effective. 

Sundower Seed. Compared to the FAO/WHO/UNU recommendations for essential amino acids, sunflower proteins are low in lysine, leucine, and threonine for 2 to 5-year-olds but meet all the requirements for adults (see Table 3). There are no principal antinutritional factors known to exist in raw sunflower seed (35). However, moist heat treatment increases the growth rate of rats, thereby suggesting the presence of heat-sensitive material responsible for growth inhibitions in raw meal (72). Oxidation of chlorogenic acid may involve reaction with the S-amino group of lysine, thus further reducing the amount of available lysine. 

Formulas tend to contain isolates as the protein source to eliminate or reduce the presence of carbohydrates that ate the cause of flatulence and abnormal stools. Care is taken to provide adequate nutrition and to use proteins processed in such a way as to minimize or eliminate any antinutritional factors. The formulation of a typical soy-based infant formula is also given in Table 17. 

Some legumes, including raw soy or peanut flour are known to contain certain antinutritional factors such as proteinase inhibitors and hemagglutinins or lectins (21,22). These factors can be inactivated, for the most part, by moist heat, during processing. Interestingly, peanut flour contained more trypsin inhibitor and lectin than did soy flour (22). 

Tannins are one of several antinutritional factors present in dry beans. Any polyphenolic compound that precipitates proteins from an aqueous solution can be regarded as a tannin (11). Tannins precipitate proteins due to functional groups that complex strongly with two or more protein molecules, building up a large cross-linked protein-tannin complex (12). 

Cheek, P. R. and Kelly, J. D. 1989. Metabolism, Toxicity and Nutritional Implications of Quinolizidine (Lupin) Alkaloids. In Recent Advances of Research in Antinutritional Factors in Legume Seeds Animal Nutrition, Feed Technology, Analytical Methods. Proceedings of the First International Work shop on Antinutritional Factors ANF) in legume seeds. November 23-25, 1988 (Huisman, J., Poel, T. F. van der and Liener, I. E. eds.), pp. 189-201. Agricultural University, Wageningen. 

Various excellent reviews are available on phenolic compounds, their chemistry and analysis, content in foods and nutritional significance (Bravo, 1998 Dykes and Rooney, 2006 Manach et al., 2004 Naczk and Shahidi, 2006 Robbins, 2003). From a nutritional perspective, phenolic compoimds (especially tannins) are regarded as antinutritional factors due to their ability to form complexes with dietary proteins and minerals and digestive enzymes (Bravo, 1998). However, lately there has been increasing focus on the positive aspects of phenolics due to their ability to act as antioxidants which may offer potential health benefits such as prevention of diseases such as cancer and cardiovascular disease. 

The influence of processing on amino acid availability may be profound, especially under extreme conditions. Processing can increase amino acid availability, often by increasing digestibility or inactivating antinutritional factors. Processing may also serve to decrease amino acid availability. 

The advantages of an animal bioassay are that protein digestibility, amino acid bioavailability, and the presence of antinutritional factors can be ascertained. However, animal-based feeding studies can be difficult. First, these assays are expensive to conduct and time-consuming. Secondly, these assays require animals... 

Such chemical changes may lead to compounds that are not hydrolyzable by intestinal enzymes or to modifications of the peptide side chains that render certain amino acids unavailable. Mild heat treatments in the presence of water can significantly improve the protein s nutritional value in some cases. Sulfur-containing amino acids may become more available and certain antinutritional factors such as the trypsin inhibitors of soybeans may be deactivated. Excessive heat in the absence of water can be detrimental to protein quality for example, in fish proteins, tryptophan, arginine, methionine, and lysine may be damaged. A number of chemical reactions may take place during heat treatment including decomposition, dehydration of serine and threonine, loss of sulfur from cysteine, oxidation of cysteine and methio-... 

Moisture is present in all materials rendered or cooked and plays an important role in the cooking reactions. Without sufficient moisture, the desired cook would not be achieved. Water or steam or both are often added to elevate moisture and to ensure proper denaturing and hardening of protein, rupturing of oil cells, and inactivation of undesirable enzymes, micro-organisms, and antinutritional factors. Water also assists in the displacement of fat from the surfaces of solid materials. Solids have a greater physicochemical affinity for water than for fat. 

To deactivate the antinutritional factors in oilseeds for use in animal feed and human food... 

Soybeans also contain lectins, urease, saponins, goitrogenic factors, rachitogenic factors, allergic factors, and metal chelating factors, all of which can have a negative impact on performance (15). Fortunately, many of these antinutritive factors are heat labile, and adequate heat treatment renders full-fat soybean meal safe for use in nonruminant diets. Hence, given a cost effective means of heat processing, the nutritional potential of this valuable raw material can be unlocked. 

The term dry extrusion, as opposed to wet extmsion, refers to the fact that this type of extruder does not require an external source of heat or steam (29). Dry extruders generate heat and pressure mechanically as a result of the frictional and shear forces produced within the extruder barrel. Provided that adequate operating temperatures are achieved (138°-150°C), this combination of heat and pressure is sufficient to substantially denature the important antinutritive factors in soybeans and render... 

The nutritional value of a food is determined by its protein quality, which depends mainly on its amino acid content, digestibility, influence of antinutritional factors, and the tryptophan to a large neutral amino acids ratio (Comai et al., 2007). 

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