Changes Of Functional Substances Of Four Chinese Soybean Cultivars And Accumulation Mechanism Of ?-Aminobutyric Acid During Germination

Soybean is one of the most important oil-bearing crops in China and occupies an important position in the dietary structure of Chinese.Significant changes in the biochemical and nutritional of soybean seeds occur due to degradation of reserve materials which are used for respiration during germination.Especially GABA content can rapidly increase after germination,which suggested that germination is an effective way to elevate the content of GABA.The changes of content of total phenolic contents(TPC),total flavonoid contents(TFC),isoflavone and ?-aminobutyric acid(GABA)and antioxidant activities of germinated soybeans were investigated in this paper.Four Chinese soybean cultivars QD 7,ZH 13,HH 43 and XD 14 were evaluated.At the same time,in order to clarify the physiological mechanism of GABA accumulation in soybean during germination,the changes in concentration of metabolites and enzymatic activities associated with the GABA shunt,as well as the mRNA for glutamate decarboxylase(GAD),GABA transaminase(GABA-T)and succinic semialdehyde dehydrogenase(SSADH)were investigated.The results have important implications for adding value to one of the world's most widely cultivated crops and sprouted vegetables and establishing scientific base for the future research of soybean.The result showed that:1.Significant changes of functional ingredients and antioxidant activities occur after germination,and there has a significant correlation between functional ingredients content and germination time(P < 0.01).2.GABA content of HH 43,QD 7,XD 14 and ZH 13 were significantly increased,with a 30-,37-,6.8-,and 6.5-fold increase at peak level compared to ungerminated seeds,and QD 7 had the highest content of GABA.3.Correlation analysis showed that there was a positive correlation between antioxidant activity and content of TFC,TPC and isofalvone.QD 7 had the highest contents of TFC and isoflavone,and therefore exerted the strongest antioxidant activity.4.Germination can improve the nutritional value of soybean and that the QD 7 soybean is a cultivar which can be used to produce functional food.5.GAD(glutamate decarboxylase)activity has a positive effect on the accumulation of GABA,as well as the GABA-T activities was found to play a significant role in the degradation of GABA.6.The expression levels of GmGAD and GmGABA-T(GABA transaminase)may affect the GABA content by regulate the respective enzyme activity.7.A positive relationship was identified among glutamate content and GABA content.8.The up-regulation of GAD and down-regulation of GABA-T may cause GABA accumulation.