Effect of Processing Methods on Antinutritional Factors in Horse Gram

Abstract

Horse gram (Macrotyloma uniflorum) is a drought-hardy pulse that is eaten in many dry regions of South Asia and is valued for its protein and its traditional use as a cheap food, yet it is also known for being hard to cook and for carrying a heavy load of antinutritional factors. This narrative review asks what the published literature says about how soaking, dehulling, germination, cooking, roasting, fermentation and combinations of these affect the main antinutrients, namely protease inhibitors, phytic acid, polyphenols and tannins, lectins, flatulence-causing oligosaccharides and oxalate. It draws on work on horse gram where that exists and on better-studied pulses where it does not, and it reports no new data. Heat and germination act on different factors, dehulling removes mostly the compounds held in the seed coat, and leaching depends as much on water volume and temperature as on time. A reduction in one factor frequently comes with a loss of something worth keeping, and the polyphenols that lower mineral absorption are the same ones credited with antioxidant activity. Studies of horse gram vary in cultivar, method and units, and few measure absorption in people, so a lower laboratory value is not the same as a better-nourished eater. The review concludes that sequences of simple household steps are the most defensible approach and sets out what a comparable study of processing should report.