Malnutrition influences more than half of the world’s population, especially in developing countries where plants are a major source of food. Deficiencies of micronutrients such as minerals and vitamins cause serious health problems. The total micronutrient content is not important in food because their bioavailability is more an effective factor than their level. In unrefined foods, the low bioavailability of minerals causes metabolic disorders related to these nutritional factors. Therefore, improving the nutritional value of such types of foods will improve the nutritional status of the population.
Compounds such as phytic acid, tannin and polyphenols found in legumes, vegetables, nuts, seeds and cereal grains are known as anti-nutritional factors affecting the bioavailability of proteins. Antinutrients reduce the maximum utilisation of nutrients (especially proteins, vitamins or minerals), and as a consequence, they obstruct an optimal bioavailability of the nutrients present in a food and decrease its nutritive value.
Phytate has long been recognised as an anti-nutritional factor affecting the bioavailability of major minerals such as calcium, iron, copper, zinc and manganese.
Other antinutrients of importance in foods are tannins, polyphenols, oxalates and trypsins. They limit the bioavailability of food materials. Decreasing of anti-nutritional factors is very advantageous due to their influences on nutrition. However, many anti-nutrients, besides their primary effects on the bioavailability of nutrients may also be toxic beyond a certain dose, for example, oxalate or cyanogenic acid. Therefore interest has grown to reduce their antinutritional effects nowadays.
Legumes and cereals contain high amounts of macronutrients and micronutrients but also antinutritional factors which combine with nutrients and act as the major concern because of reduced nutrient bioavailability. Various other factors like trypsin inhibitors and phytates, which are present mainly in legumes and cereals, reduce the digestibility of proteins and mineral absorption. Antinutrients are one of the key factors which reduce the bioavailability of various components of the cereals and legumes. These factors can cause micronutrient malnutrition and mineral deficiencies. There are various traditional methods and technologies, which can be used to reduce the levels of these antinutrient factors. Several processing techniques and methods such as fermentation, germination, soaking etc., are used to reduce the antinutrient contents in foods. By using various methods alone or in combinations, it is possible to reduce the level of antinutrients in foods.
Soaking: This is an easy method which is used generally in daily life as it helps in germination and fermentation of cereals. During soaking, phytase enzyme activates and affects the antinutrient compounds. Soaking process has both physical and chemical positive effects in the structure of foods. The soaking duration along with cooking the cereals makes it more effective. On the other hand, the disadvantages can be the loss of water-soluble protein and minerals.
Fermentation & germination: Fermentation is one of the important processes that decrease the levels of antinutrients in food grains and increase minerals extractability, in-vitro protein digestibility and nutritive value of grains. Germination and fermentation enhance the nutritional value of pearl millet by causing significant changes in chemical composition and elimination of antinutritional factors. Germination is a highly effective method to reduce phytic acid content by up to 40%.
Autoclaving & cooking: Most foods become useful and healthy when they are cooked. All legumes and some cereals are usually cooked either by simple boiling or in a pressure cooker for their consumption. Boiling improves the nutritional quality of food grains due to reduction in antinutrients.
These traditional and technological methods reduce antinutrient compounds. The pre-treatment and processing techniques such as soaking, fermentation,
germination and autoclaving help improve the nutritional quality of foods.
(The author is a consultant dietician.)