Phenolics and related in vitro functional activities of different varieties of fresh waxy corn: a whole grain

Abstract

The polyphenol distribution in fresh waxy corns of different color varieties and their functional activities, which may be useful for treating various chronic diseases, were investigated. The in vitro antioxidant activity, and hypoglycemic and hypocholesterolemic effects of the free and bound corn phenolics were determined to evaluate the edible value of fresh waxy corn. The colored varieties contained more phenols than the common varieties (white and/or yellow). The total free phenolic acid content of the six varieties was 6637.73 µg/g DW (dry weight), which was slightly higher (P > 0.05) than that of the total bound form (6276.65 µg/g DW). The total free flavonoid content was 5850.09 µg/g DW, which was higher (P < 0.05) than that of the total bound form (4874.51µg/g DW). No bound anthocyanin was detected in the methanol extracts of the tested varieties. For all the varieties, free polyphenols contributed 86-100 % and 70-78 % of the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radical scavenging abilities, respectively, and 100 % of the ferric reducing capacity. The free phenolics in fresh waxy corn showed better (P < 0.05) hypoglycemic effect than the bound form in terms of inhibition of α-amylase activity, whereas the bound phenolics of most varieties showed higher α-glucosidase inhibitory activity than the free forms. The free phenolics showed better (P < 0.05) glycocholesterol binding than the bound form for all varieties. The bound polyphenols showed better sodium cholate and taurocholate binding than the free form for most varieties. In conclusion, the difference between free and bound polyphenol content and functional activities indicates that fresh waxy corn can be potentially used for the development of functional food.

Keywords: Antioxidant activity; Fresh waxy corn; Hypocholesterol; Hypoglycemic; Polyphenol.

Fig. 1

Tested varieties of fresh waxy corn

Fig. 2

DPPH scavenge rate (a), hydroxyl radical scavenge rate (b), and FRAP (c) of the free ( ) and bound ( ) form polyphenols of different varieties of fresh waxy corn. All values are means of replicate determinations ± standard deviation (n = 3). Different uppercase letters in the same variety indicate statistical differences (P < 0.05) in the LSD test. Different lowercase letters in the different varieties of free or bound polyphenols indicate statistical differences (P < 0.05) in the LSD test

Fig. 3

α-Amylase (a) and α-glucosidase (b) inhibitory activity of the free ( ) and bound ( ) forms of polyphenols of different varieties of fresh waxy corn. All values are means of replicate determinations ± standard deviation (n = 3). Different uppercase letters in the same variety indicate statistical differences (P < 0.05) in the LSD test. Different lowercase letters in the different varieties for free or bound polyphenols indicate statistical differences (P < 0.05) in the LSD test

Fig. 4

Bile acid binding capacity of the free ( ) and bound ( ) forms of polyphenols of different varieties of fresh waxy corn. All values are means of replicate determinations ± standard deviation (n = 3). Different uppercase letters in the same variety indicate statistical differences (P < 0.05) in the LSD test. Different lowercase letters in the different varieties indicate statistical differences (P < 0.05) in the LSD test. a sodium glycocholate binding capacity; b sodium cholate binding capacity; c sodium taurocholate binding capacity