| Soybean sprouts rich in lots of free amino acids, unsaturated fatty acids, vitamin C, phenolics, flavonoids and other phytochemicals. In addition, soybean sprouts are good sources of dietary fiber and protein in our daily life. Many studies have shown that germination of soybeans can increase the content of vitamin C, vitamin E, phenolics, flavonoids. However, the expression levels of key genes in these nutrients synthesis pathway have not yet been reported. One of the objectives of this study was to determine the transcription levels of key-encoding genes in ascorbic acid and tocopherols biosynthesis pathways, the accumulations of ascorbic acid and tocopherols and total antioxidant activity of soybean sprouts.In the first section of our study, the objective was to study the dynamic changes of ascorbic acid, tocopherols, phenolics and their antioxidant activity of soybean sprouts during germination. The changes of vitamin C, tocopherols, phenolic acids, the key encoding genes relative expression levels and total antioxidant activity were determined by using 2, 6-dichloroindophenol titration, HPLC, Folin-Ciocalteu, real-time PCR and PSC methods, respectively. Results showed that the expression levels of genes related to biosynthesis of ascorbic acid and tocopherols dramatically increased during germination. The expression levels of most genes were up to the peak at day 3 and kept constantly until the end of germination. The contents of ascorbic acid, α-tocopherol, γ-tocopherol, δ-tocopherol and phenolic acids increased during soybean sprouts germination and reached peak levels on day 5, of 74.42 ± 1.64 mg/100 g DW, 7.64 ± 0.13 mg/100 g DW, 15.84 ± 1.85 mg/100 g DW, 12.37 ± 1.06 mg/100 g DW, 569.70 ± 66.55 mg/100 g DW, respectively. The antioxidant activity of soya bean sprouts increased during germination and reached peak level on day 5 to 311.01 ± 49.01 μmol ASA equiv./100 g DW. Therefore, germination significantly increased the biosynthesis of ascorbic acid, tocopherols, the phenolic acids content and antioxidant activity of soybean sprouts.In the second section of our study, the objective was to study the effects of three plant growth regulators(6-BA, gibberllin, NAA) on phytochemical profiles and antioxidant activity of soybean sprouts. The period of study was day 1, day 3 and day 5. Moreover, the soybean sprouts without plant growth regulators was as control. The changes of vitamin C, phenolic acids, flanovoids, the key encoding genes relative expression levels and total antioxidant activity were determined by using 2, 6-dichloroindophenol titration, Folin-Ciocalteu, SBC, real-time PCR and ORAC methods, respectively. Results showed that 6-BA, followed by gibberellins and then NAA, had the most improving effect on the contents of vitamin C, phenolic acids, which was mainly correlative with the key encoding genes expression levels. Gibberellins, followed by 6-BA and then NAA, showed the most improving effect on the content of flanoviods among three plant growth regulators. In addition, the 6-BA group and the gibberellins group showed the strongest antioxidant activity. While, it’s not obvious to regulate the phytochemical profiles of soybean sprouts. On the whole, the contents of vitamin C, phenolic acids, flanoviods, and antioxidant activity were improved by adding 6-BA or gibberellins.In the last section of our study, the objective was to study the effects of different concentrations of chitosan oligosaccharide on phytochemical profiles and antioxidant activity of soybean sprouts. The period of study was day 5. Moreover, the soybean sprouts without chitosan oligosaccharide was as control. The changes of vitamin C, phenolic acids, flanovoids, isoflavones and the key encoding genes relative expression levels in these nutrients biosynthesis pathway and total antioxidant activity were determined. In addition, the activities of ascorbate oxidase(AO), polyphenol oxidase(PPO), Peroxidase(POD) were measured. Results showed that the optimal concentration for soybean germination was 10 mg/L. In addition, the high concentration of chitosan oligosaccharide will cause the root browning phenomenon during the germination process, however, too low concentration of chitosan oligosaccharide would have little promotional effect on the nutrients of soybean sprouts. Chitosan oligosaccharide had a slightly decreasing effect on the vitamin C content. When the concentration of chitosan oligosaccharide was 10 mg/L, the phenolics and flavonoids contents of soybean sprouts were higher than soybean sprouts of the control group. At the same time, the total antioxidant activity was higher than that of the control group. Therefore, the appropriate concentration of chitosan oligosaccharide can increase the content of some nutrients and antioxidant activity of soybean sprouts. |
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