Study On The Fermentation Process And Antioxidant Function Of Rice Vinegar With High Content Of γ-Amino Butyric Acid

In this study, the high contentγ-aminobutyric acid （GABA） sprouted rice was prepared firstly. Then during liquid-solid state fermentation brewing process rice vinegar with high content of GABA was prepared using sprouted rice as raw material, supplemented with red yeast rice, and raw starter complex during saccharification and alcohol fermentation, and the brewing conditions of the rice vinegar with high GABA content were studied. Through Plackett-Burman design the significant factors were identified, which were subsequently optimized using Box-Benhnken center-united experiment design. After that, the optimum conditions in liquid-solid state were carried on. On this basis, the main antioxidant functions of rice vinegar with high content of GABA were analyzed. The research contents were as follow:1. Optimization of rice germination with high content of GABA conditionsAccording to the research reported, sprouted rice was used as raw material and the single factors （the amount of calcium chloride, sodium glutamate, germination time and temperature） were analyzed to determine the appropriate range. The results showed that the impact of GABA content in primary-secondary were confirmed by orthogonal design: amount of calcium chloride > amount of sodium glutamate > germination time > temperature. The best germinated conditions were optimized: 0.2% calcium chloride （w/w）, 3% sodium glutamate （w/w） and germinated at 31℃for 3d. The content of GABA was 28.49mg in 100g dry sprouted rice on optimum condition.2. Optimization of fermentation process for rice vinegar with high content ofγ-amino butyric acidThrough Plackett-Burman design, the liquid-solid state fermentation brewing process was studied and three factors （adding amounts of raw starter complex, red yeast rice and glucoamylase preparation） were identified as significant factors from eight factors （adding amount of adding amounts of red yeast rice, raw starter complex, water, glucoamylase preparation and sodium glutamate, and fermentation time, temperature and pH）, which were subsequently optimized using Box-Benhnken center-united experiment design. The production of GABA could be predicted by the model through various analysis of regression: Y=147.1-7.4A+2.2B-1.8C-14.1A²-3.7B²-2.6C²-0.2AB-2.1AC +0.4BC [Y, the content of GABA in fermented mash, mg/100mL; A, the amount of red yeast rice, % （w/w）; B. the amount of water, % （v/w）; C, the amount of glucoamylase preparation, % （v/w）]. According to the regression equation the maximum estimated value of Y was calculated and the content of GABA was 147.09mg in 100mL fermentation mash. The variables corresponding to equation were: the amount of red yeast rice, 0.8% （w/v）; the amount of water, 67% （v/w）; the amount of glucoamylase preparation, 0.32% （v/w）.On the basis of the above-mentioned study, in order to verify equation model, at the optimal conditions, which were 500g smashed sprouted rice, 4g red yeast rice, 1.5g raw starter complex, 1.6mL glucoamylase preparation, 5g sodium glutamate, 335mL water, fermented at pH 6, 28℃for 5 days, the estimated value of GABA was reached at 147.09 mg per 100mL fermenting mash, and the average experimental GABA value was 145.18/100mL. This value and the estimated value of 147.09mg have not statistically significant differences, indicating that the equation was fited well.According to the liquid fermentation conditions of saccharification process, the acetic acid fermentation carried on in conventional acetic acid fermentation process through adding 750g wheat bran and 500g rice chaff, inoculated with 17mL culture media （OD600nm =0.8） of Acetobacter pasteurianus CICC 7009, and fermented at 28℃for 7d by turning over in every 5-7 h, then matured for 8d in the sealed container. The content of GABA in finished rice vinegar was 100mg/L.At the same time of preparation of rice vinegar with high content of GABA, red rice vinegar, common rice vinegar and germinated rice vinegar were prepared with relevant process parameters.3. Antioxidant function of rice vinegar with high content ofγ-amino butyric acidWith rice vinegar prepared above （rice vinegar with high content of GABA, red rice vinegar, common rice vinegar, germinated rice vinegar） and Zhenjiang vinegar, the main antioxidant functions were measured. The results showed that the clear action on DPPH radical of five rice vinegars in sequence were: 96.13%, 92.59%, 83.13%, 80.34%, 90.99%.; the clear action on O₂^-· radical of five rice vinegars in sequence were: 72.95%, 67.15%, 63.45%, 62.26%, 63.26%; the clear action on·OH radical of five rice vinegars in sequence were: 86.98%, 76.32%, 67.77%, 61.13%, 63.0%. The main antioxidant function of rice vinegar with high content of GABA was distinctly higher than the others’.4. Changes of content of GABA during the aging processThe effect on condition of light, temperature and sealing on GABA content in rice vinegar with high GABA content during aging was analyzed. The results showed that after aging 28d, in the conditions of fluorescent lamps, UV lamps and avoiding light, the content of GABA respectively fell down from 100.0 mg/L to 97.5 mg/L, 94.7 mg/L, 98.0mg/L; in the conditions of 0℃, 30℃, 60℃and 90℃, the content of GABA respectively fell down from 100.0 mg/L to 98.5 mg/L, 98.0 mg/L, 80.2 mg/L, 65.3 mg/L; in the conditions of open and sealing, the content of GABA respectively fell down from 100.0 mg/L to 98.0 mg/L, 83.2 mg/L. So the optimum conditions of aging at 30℃with avoiding light and sealing were determined. After aging 28d at the optimal conditions, the content of GABA fell down from 100.0 mg/L to 97.9 mg/L, the decrease was 2.1%; the content of amino nitrogen fell down from 0.335 mg/100g to 0.320 mg/100g; the content of reducing sugar fell down from 0.442 mg/100g to 0.429 mg/100g; the content of acidity fell down from 3.85 mg/100g to 3.76mg/100g,, the decrease were separately 2.3%, 4.5%, 2.9%.