Total Polyphenols and Bioactivity of Seeds and Sprouts in Several Legumes

Sang-Uk      Chon

Abstract

Seeds and sprouts from legume crop plants have received attention as functional foods, because of their nutritive values including amino acid, fiber, trace elements, vitamins, flavonoids, and phenolic acids. Consumption of seeds and sprouts has become increasingly popular among people interested in improving and maintaining their health status by changing dietary habits. The seeds and sprouts are excellent examples of functional food defined as lowering the risk of various diseases and/or exerting health promoting effects in addition to its nutritive value. Phenolic compounds are considered as secondary metabolites that are synthesized by plants during normal development and in response to stress conditions, and the compounds occur ubiquitously in plants as the diversified group of phytochemicals derived from phenylalanine and tyrosine. Plant phenolics include simple phenols, phenolic acids, coumarins, flavonoids, stilbenes, hydrolyzable and condensed tannins, lignans, and lignins. In plant, phenolics may act as phytoalexins, antifeedants, attractants for pollinators, contributors to the plant pigmentation, antioxidants, and protective agents against UV light, among others. In food, phenolics may contribute to the bitterness, astringency, color, flavor, odor, and oxidative stability of products. In addition, health-protecting capacity of some and antinutritional properties of other plant phenolics are of great importance to producers, processors and consumers. Several researches were conducted to compare the content of phenolics and flavonoids, antioxidant activity and antioxidant enzyme activity from seeds and sprouts of legume plants. Total phenolics (TP) content and total flavonoids (TF) level were highest in soybean sprout extracts, followed by cowpea and mungbean sprout extracts (p < 0.05). DPPH (1, 1-diphenyl-2-picryl hydrazyl radical) free radical scavenging activity was higher in cowpea or mungbean sprouts than in soybean sprouts. Among antioxidant enzymes, ascorbate peroxidase (APX) and peroxidase (POX) activities were highest in cowpea sprouts and catalase (CAT) and superoxide dismutase (SOD) activities in soybean sprouts. During sprouting in mungbean, TP and TF levels significantly increased and improved free radical scavenging, tyrosinase inhibition, anticancer, and ADH (alcohol dehydrogenase) activities, showing higher contents and activities in sprouts than in seeds. Sprouting of seeds is known to increase the nutritive value such as phenolics and flavonoids and the health qualities of foods in a natural way. Phasic bioactive responses from dry seeds to 7-day-old seedlings of cowpea showed differential growth, contents of TP and TF, antioxidant activity and antioxidant enzyme activity. Plant length and weight of cowpea sprouts were significantly increased until 7 days after seeding. TP content, however, was highest in dry seed (DS) extracts of cowpea (63.9 mg kg^-1), followed by imbibed seed (IS) (56.8 mg kg^-1) and 1-day-old sprout (1DOS) (46.4 mg kg^-1) extracts, and significantly reduced with increase of sprout age (p < 0.05). DPPH free radical scavenging activity was higher in DS or IS than in cowpea sprouts. APX, POX, and POX activities were highest in 7DOS and lowest in DS. SOD activity was lowest in DS and much higher in additional sprouting days.

Keywords: Seeds, sprouts, legumes, total phenolics, total flavonoids, DPPH free radical scavenging activity, antioxidant enzyme activity.

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