Screening And Application Of Germinated Brown Rice Varieties With High γ-aminobutyric Acid Content

When brown rice(BR) was slightly germinated under certain circumstance,γ-aminobutyric acid(GABA) content in germinated brown rice(GBR) would greatly increase due to the catalytic transformation of glutamic acid by vivo activated glutamate decarboxylase(GAD),both nutritive absorption and flavor of brown rice were also improved.However,GABA content in GBR was greatly influenced by rice varieties,and it is necessary for research on variation of GABA content among different varieties. Difference of GABA content in GBR among 181 rice varieties(lines) and heritability of high GABA production were studied.Dynamic changes of GABA content in different rice ecotypes during germination and its relationship with GAD activity,free amino acid were analyzed.The mechanisms of the reason why GABA content in GBR was different among rice cultivars were also studied.The rice cultivars with high GAD activity and high GABA production were selected for germination and the GBR slurry were used for transformation of glutamic acid to GABA.The transformation conditions for GABA production were optimized,and this laid foundation for development of functional GBR foods with high GABA content.Main research results were as follows:(1) GABA contents in 181 varieties(lines) GBR were determined,and the differences among varieties and heritability of GABA production were studied.After brown rice was soaked at 30℃for 6 h and then germinated for 24 h,among all the tested materials,the highest,lowest and average GABA content were 87.88 mg·(100g)^-1, 34.62 mg·(100g)^-1 and 56.84 mg·(100g)^-1,respectively.GABA content in GBR was different among photothermic ecotypes.GABA content in early season rice was higher than that in semi-late rice and late rice,and that in indica rice was slightly higher than that in japonica rice.The trait of high GABA production in rice could be inherited.(2) Dynamic changes of GABA content,GAD activity,various free amino acid concentration,root and shoot length in three typical varieties and their differences were analyzed.Both GABA content and GAD activity were up to the maximum after germination of 72 h,and they were significantly different among varieties,those in early indica rice were higher than those in early japonica rice and semi-late indica rice.During the germination,almost all free amino acid concentration increase first and then decrease. Various free amino acid in GBR hardly showed difference among varieties at the beginning of germination,but that was significantly different after germination of 48～72 h. (3) The mechanism that GABA content in GBR was different among varieties was analyzed.GABA content increase was positively related to shoot length and GAD activity in GBR during germination.Difference of GABA production in GBR among varieties was probably due to the differences of GAD activity in shoot or in root.Synthesis of GABA was also regulated by synthesis of Ala,Glu,Val,Lys,Arg,Met,Ser and His.(4) The GBR slurry with high GAD activity was used for GABA production by adding glutamic acid,and effects of transformation condition on GABA production were studied.Results showed that adding of monosodium glutamine(MSG) was better than adding of glutamic acid.Moderate concentration of CaCl₂ and MSG were more propitious to GABA production.Four critical factors were selected for influencing transformation ratio and GABA production:MSG concentration,ratio of liquid to GBR,transformation temperature,and transformation pH.The transformation condition was optimized through response surface methodology(RSM).The optimum ranges for critical factors were 3.15～4.72 of liquid to GBR,7.67～10.35 mmol·L^-1 MSG,transforming at 37.4～41.3℃and pH of 6.1～6.5.Under the optimized condition:3.67:1 of liquid to GBR, 9.13 mmol·L^-1 MSG,transformation temperature 39.0℃and pH of 6.4,the GABA concentration increase,transformation ratio and GABA content in GBR slurry were 973.47 mg·L^-1,0.8971,1403.21 mg·(100gDW)^-1,respectively.GABA content in treated rice slurry was 3.2 folds than that in control,and was about 10～20 folds higher that that in common GBR.