PROCESSING EFFECT ON SOYBEAN NUTRIENTS AND POTENTIAL IMPACT ON CONSUMER HEALTH: REVIEW

Abstract

Global soybean production and soy product consumption are rising due to their perceived health benefits. However, processing methods can impact soy’s sensory qualities, nutritional value, and consumer health. Processing soy below 100 °C for short durations generally preserves its nutritive value. Beneficial changes include heat-induced inactivation of trypsin inhibitors and denaturation of globulins and haemagglutinins, which enhance protein bioavailability. Excessive heating, however, can degrade essential amino acids like lysine, tryptophan, and methionine. Alkali-catalyzed reactions produce lysinoalanine, a compound linked to toxicity in rats but not shown to harm humans at dietary levels. Alkaline heat treatments also degrade arginine and cysteine, and reduce serine, threonine, and lysine—conditions common in alkali-refined soy oil. The Maillard reaction, involving carbohydrates and proteins, and heat above 200 °C at alkaline pH, causes amino acid isomerization into L and D forms. D-isomers, such as D-proline, have lower bioavailability and potential toxicity. Lipid changes include oxidation, loss of lipid-soluble vitamins, and conversion of cis to trans fatty acids. Autoxidation of unsaturated fats generates free radicals, reducing essential fatty acids and contributing to atherosclerotic plaque formation. Processing also affects vitamins: carotenoids are lost during bleaching, reducing vitamin A potential, and vitamin E diminishes during oil refining. Soy isoflavones remain stable during roasting and toasting but are removed by organic solvents; fermentation boosts their bioavailability. Dehulling lowers mineral content, with sodium and potassium lost in wash water. To preserve soy’s nutritional integrity, recommended practices include minimal washing, fermentation, reduced hydrogenation temperatures, and brief thermal processing below 100 °C.