Gama-aminobutyric acid(GABA),non-protein amino acid,is ubiguitous.Many studies have reported that GABA is important in some physiological functions.Accumulation of GABA in plant and plant tissues could be induced via environmental stresses.Therefore,the effect of processes(immersing and cold shock)conditions of millet brown rice on GABA accumulation were investigated in this study and the specific content as follows:GABA in millet brown rice were extracted by deionized water.The extraction conditions were speed 150 r/min,temperature 35℃and time 1 h.GABA content in millet,brown rice and polished rice were:7.21~17.02 mg/100 g,8.16~19.92 mg/100 g and4.25~10.68 mg/100 g,respectively.The varieties,planting year,storage time and temperature could effect on the content of GABA in millet brown rice.The effects of the soaking treatment on the accumulation of GABA in millet brown rice were evaluated.Influence of soaking time,soaking temperature,p H,concentration of Ca Cl2 and MSG on optimal conditions for GABA accumulation in brown rice were investigated by Single-factor experiment.The optimum conditions were time 12 h,temperature 35℃,p H 4.0,PLP 60μg/m L,Ca Cl2 100μg/m L and MSG 20 mg/m L.Then,Plackett-Burman design was used to screen the significant factors on the accumulation of GABA in millet brown rice,and the results showed the significant factors were p H,concentration of Ca Cl2 and MSG.Then,the optimal conditions of p H,Ca Cl2 and MSG were optimized by Box-Behnken design.The results showed that the optimal soaking conditions were MSG 18 mg/m L,Ca Cl2 90μg/m L,p H 4.3,PLP 60μg/m L,soaking temperature 35℃and soaking time 12 h.GABA yield reached 96.18±0.44 mg/100 g(dry substrate)under the optimal soaking conditions,which was 13.25-fold compared to that of the non-soaked samples.This investigation suggested that the soak stress was an efficient method for the preparation of millet brown rice for GABA accumulation.The effects of the cold shock treatment on the content of GABA and glutamic acid decarboxylase activity in millet brown rice were evaluated.Freezing could accumulation of GABA in brown rice.The conditions of cold shock treat to accumulation of GABA in millet brown rice were evaluated by Single-factor experiment.The optimal conditions of cold shock were temperature-18℃and time 8 h.and thawing were temperature 35℃and time 4 h.Based on the single factor experiment,the GABA yield reached 24.16±0.34mg/100 g(dry substrate),which was 3.03 times compared to that of the not frozen yield.Under the optimal soaking conditions,the combination of soaked pretreatment and cold shock could accumulate the content of GABA in millet brown rice.The results showed that freezing could accumulate the content of GABA in millet brown rice,moreover,eighteen degrees below zero is the best,which was increased 22.50%compared to that of the only soaked brown rice.Thus,the results suggest that the combination of soaked pretreatment and cold shock treatment could applied to the preparation of brown rice with high GABA. |