Toxicants And Anti-nut Factors

TOXICANTS AND ANTI-NUTRITIONAL FACTORS IN FOODS. Many plants and food stuff naturally contain substances that inhibit nutrient uptake in various ways or are toxic to human. They may interfere with intestinal cell function, reduce the ability to break down complex molecules such as protein and starch, or may be toxic if consumed in sufficient quantity. Some of these substances are rendered harmless with cooking or processing, but others are resistant to digestion, heat treatment or other forms of processing. Biotechnological approach is taken as essencial tools to enhance nutrition either by means of biofortification and supplementation as well as by reducing the anti-nutritional factor present in foods. The process and use of biotechnology for the production and improvement of functional food is today’s one of essential tools. Cereals are a staple food in many developing country and improvements in micronutrient level or removal of anti-nutritional substances would greatly benefit consumers where micronutrient deficiency and malnutrition is very prevalent. Some anti-nutritional substances present in foods are shown in table 1. Table 1. Anti-nutrients in plant foods that reduce nutrient bioavailability, or impair health. Anti-Nutrient Effect Dietary source Phytic acid (phytate) Binds minerals, K,Mg, Ca, Whole legume seeds,cereal Fe, Zn grains Fiber, e.g. cellulose, Decreases fat and protein Whole cereal grains, e.g., hemicellulose, lignin digestibility; may decrease wheat, corn, rice vitamin and mineral absorption Trypsin inhibitor Reduces the activity of the Legumes, e.g., soy; cereals, enzyme trypsin and other potatoes closely related enzymes that help digest protein Polyphenolics, tannins Forms complexes with iron, Tea, coffee, beans, sorghum zinc, copper that reduces mineral absorption Hemaglutinins, e.g., lectins Interfere with cells lining legumes the gastrointestinal tract causing acute symptoms; can bind metals and some vitamins; can be toxic Cyanogens or Inhibit acetyl cholinesterase Cassava, linseed, pea, beans glycoalkaloids activity which impairs nerve transmission; can damage cell membranes Glucosinolates May adversely affect Cabbage, broccoli thyroid activity Saponins May irritate the Soybeans, peanuts, sugar gastrointestinal tract and beets interfere with nutrient

absorption Suppresses thyroid function

Goitrogens Oxalic acid Phytotoxins, e.g., solanine Mycotoxins, e.g., aflatoxin, fumonisin Gossypol Heavy metals e.g., cadmium, mercury, lead

Binds calcium to prevent its absorption Can be toxic; affects gastrointestinal and nervous systems Toxins produced by certain molds; toxic to humans and animals; can be carcinogenic May harm kidney function and reduce sperm counts; can be toxic May have toxic effect, e.g., high levels of Hg impair fetal brain development

Brassica and allium foods, e.g., broccoli, garlic Spinach leaves, ruhbarb Green part of potato Grain ,peanuts, other crops

Cottonseed Contaminated leafy vegetables

NUTRITIONAL IMPORTANCE Though toxicants and anti-nutritional substances are generally known for their negative contribution, they also have beneficial effects in human nutrition. These effects include the following. • Legume seed protease inhibitors have shown to poses anti-carcinogenic proteins. • The potential of legume lectins have been discovered to act as a mucosal adjuvant. • Gossypol found in cotton seeds have anti-cancer properties towards several human prostate and breast cancer cell line • Tubers such as potatoes contain protinase inhibitors which acts as an effective deffence against micro-organisms and insects •

Plant foods such as potato, contains proteinase inhibitors which act as an effective defense against insects and micro-organisms but pose no problem to humans because they are destroyed by heat. Lectins or haemogglutenins are also present in potato. These toxins are capable of agglutinating the erythocytes of several mammalian species including humans (Goldstein and Hayes, 1978), but this is of minimal nutritional significance as haemogglutenins are also destroyed by heat, and potatoes are normally cooked before they are eaten. Vitamin B12 in the form of hydroxycobalamin probably influences the conversion of cyanide to thiocyanate. Hydroxycobalamin has been reported to increase the urinary excretion of thiocyanate in experimental animals given small doses of cyanide

The regulatory techniques for efficient processing of foods to achieve reduction or eradication of toxicants and anti-nutritional substances include. 1. Drying 2. Freezing 3. Flash drying 4. Air drying 5. Heated air drying 6. Drum drying 7. Soaking 8. Plant breeding 9. Fermentation 10. Genetic engineering Chemical Composition of some Anti-nutritional substances found in some plant food •

Cassava= the main toxic principle that occurs in cassava plant is a chemical compound called linamarin. Linamarin is a cyanogenic glycoside that is converted to toxic hydrocyanic acid or prussic acid when in contact with the enzyme linamarase. Ingested linamarin librates cyanide in the gut during digestion.

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Sweet potato= it contains raffinose, a sugar responsible for flatulence. On exposure of wounded tissues to fungal contamination, sweet potato produces certain metabolites such as furano-terpenoids which are known to be toxic.