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.
In continuation of our studies on the bioaccessibility of phenolic compounds from food grains as influenced by domestic processing, we examined the uptake of phenolics from native/sprouted finger millet and green gram and native/heat-processed onion in human Caco-2 cells. Absorption of pure phenolic compounds, as well as the uptake of phenolic compounds from finger millet, green gram, and onion, was investigated in Caco-2 monolayer model. Transport of individual phenolic compounds from apical compartment to the basolateral compartment across Caco-2 monolayer was also investigated. Sprouting enhanced the uptake of syringic acid from both these grains. Open-pan boiling reduced the uptake of quercetin from the onion. Among pure phenolic compounds, syringic acid was maximally absorbed, while the flavonoid isovitexin was least absorbed. Apparent permeability coefficient P of phenolic compounds from their standard solutions was 2.02 x 10cm/s to 8.94 x 10cm/s. Sprouting of grains enhanced the uptake of syringic acid by the Caco-2 cells. Open-pan boiling drastically reduced the uptake of quercetin from the onion. The permeability of phenolic acids across Caco-2 monolayer was higher than those of flavonoids.
Enzymatic browning is a major factor affecting the quality of sugarcane juice, mainly due to the activities of polyphenol oxidase (PPO) and peroxidase (POD). Effect of bentonite (0-1%, w/v) on the activities of these enzymes, when employed alone and also in combination with acidulants, was determined. Bentonite alone could reduce the activities of PPO and POD enzymes to 160 and 24.2 u/mL, respectively. The PPO and POD activity was completely inhibited below pH 4.1 when ascorbic acid was used alone or in combination with bentonite. However, PPO and POD activity was inhibited to 60 and 51 u/mL, respectively, at pH 3.7 when citric acid was used individually and to 112 and 15.36 u/mL, respectively, when employed along with bentonite. In addition, color changes at 4 and 10 °C were measured during the storage of sugarcane juice.
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