Bioaccessibility of polyphenols from wheat (Triticum aestivum), sorghum (Sorghum bicolor), green gram (Vigna radiata), and chickpea (Cicer arietinum) as influenced by domestic food processing.

Cereals (wheat and sorghum) and legumes (green gram and chickpea) commonly consumed in Asia and Africa were evaluated for polyphenolic content. Bioaccessibility of polyphenols from these grains as influenced by domestic processing was also estimated. Total polyphenol content of wheat and sorghum was 1.20 and 1.12 mg/g respectively, which was increased by 49% and 20% respectively, on roasting. In contrast, a significant reduction of the same was observed in both the cereals after pressure-cooking, open-pan boiling, and microwave heating. Total flavonoids, which was 0.89 mg/g in native sorghum, reduced drastically after processing. Tannin content of both the cereals significantly increased on sprouting as well as roasting. Total polyphenol content reduced by 31% on sprouting but increased to 24% on roasting in green gram. Pressure-cooking (53%), open-pan boiling (64%), and microwave heating (>2-fold increase) significantly increased total polyphenol content in chickpea, while drastic reduction was observed in the total flavonoid content. Bioaccessible total polyphenols from these grains were in the following order: green gram > chickpea > wheat > sorghum. Domestic processing of these grains had minimal/no effect on the bioaccessible total flavonoid content. Not all the phenolic compounds present in them were bioaccessible. Concentration of bioaccessible phenolic compounds increased especially on sprouting and roasting of these grains, except chickpea, where sprouting significantly reduced the same (476 to 264 μg/g). Microwave heating significantly enhanced the concentration of bioaccessible polyphenols especially from chickpea. Thus, sprouting and roasting provided more bioaccessible polyphenols from the cereals and legumes studied.