Influence of soaking and cooking on the thiamin, riboflavin and niacin contents of legumes

The effects on thiamin, riboflavin and niacin contents of faba beans (Vicia faba, L.), chickpeas (Cicer arietinum, L.) and lentils (Lens culinaris, L.), of soaking in different solutions (citric acid solution pH 4.96±0.02, distilled water pH 7.00±0.02 and sodium bicarbonate solution pH 7.85±0.02) and cooking of the presoaked legumes in distilled water have been studied. The main factor determining the vitamin retention after each treatment was the legume genus. Soaking faba beans for 9 h produced losses of 0 and 15% thiamin, 0 and 11% riboflavin and no changes in niacin content (P⩽0.05). In the case of chickpeas the effect of the treatment was more acute. Losses of 0–18% thiamin, 0–4% riboflavin and 0–46% available niacin was observed while in lentils, the thiamin and available niacin contents decreased by 5–10% and 26–42%, respectively and the riboflavin increased by up to 98%. In general, vitamin losses were greater when soaking was carried out in alkaline solution. In most of the studied legumes, cooking produced further decreases in vitamins. Faba beans lost up to 35 and 32%, respectively, of their thiamin and available niacin contents, while riboflavin was not affected. Chickpeas and lentils were more liable to lose their vitamins: up to 51% thiamin, 66% riboflavin and 78% available niacin in chickpeas and up to 61% thiamin and 61% available niacin in lentils. Cooking did not cause any additional loss of the riboflavin content of lentils. With few exceptions, cooking caused greater vitamin losses when a prior soaking was carried out in alkaline solution.