Immature corn grains are becoming increasingly popular as a snack/vegetable, facilitating human consumption in some countries. Of particular interest were their nutritional and functional properties. Therefore, plants at stages M1 (74 DAS), M2 (86 DAS), M3 (98 DAS), and maturity stage (116 DAS), where DAS refers to days after seeding, were investigated for changes of the nutrients, phytochemicals, and antioxidant activity in corn grains during maturation. Results revealed that during maturation of corn grains, the content of reducing sugar and crude protein decreased while starch and total lipids increased (p < 0.05). Total carotenoids first decreased, then increased, and then decreased to minimum at maturity stage. Analysis of the main carotenoid compounds determined by HPLC showed that lutein first increased and then decreased (p < 0.05), whereas the reverse was found for beta-cryptoxanthin. The change in zeaxanthin was consistent with total carotenoids. Total phenolic content decreased; nevertheless, different phenolic fractions varied with various maturation stages. The antioxidant activity determined by DPPH and FRAP assay in total phenolic extracts decreased during maturation, which may explain that antioxidant activity can be attributed to soluble phenolic and total phenolic content.

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The presence of phenolic compounds and organic acids in vinegars can make great contribution to sensory quality and functional activity. Results indicated that cereal vinegars exhibited higher total phenolic content, flavanols and DPPH radical-scavenging activity index than fruit vinegars. Gallic acid, catechinhydrate and vanillic acid were detected to be the major phenolic compounds in cereal vinegars. In apple vinegar chlorogenic acid was the characteristics while the most abundant mono-phenol in persimmon and kiwifruit was gallic acid. The most plentiful organic acids were acetic acid and lactic acid, which aggregately accounted for more than 70% of the total acids among all simples. Furthermore, it was observed that fruit vinegars and cereal vinegars could be clearly discriminated by principle component analysis and cluster analysis. PRACTICAL APPLICATIONSOrganic acids and polyphenols are vital compounds of vinegars because they greatly contribute to sensory quality and functional activity. In vinegars, the content of organic acids and polyphenols is variable and depends on several factors, mainly raw materials, techniques of processing and microbiological growth. Previous researchers have extensively investigated traditional cereal vinegars and emerging fruit vinegars, respectively. We performed a comparative analysis of cereal vinegars and fruit vinegars and found the characteristic compounds of these two kinds of vinegars. Consequently, this research could give some help to vinegar making and the distinction between the cereal and fruit vinegar.

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