Accumulation Technology Ofγ-aminobutyric Acid In Maize Seed And Development Of Maize Beverage

Maize (maize Zea mays L.) is not only one important economic crop, but also absolutely a necessary food in daily life. Maize contains comprehensive health-promoting compounds such as starch, vitamins, minerals and other functional components. However, the utilization of maize has been largely limited as a result of the low absorption and digestion abilities of most nutrients in human body. In addition, the protein composition of maize is not reasonable. Hence, the utilization of maize in food industry accounts for only6%of all the maize production. Germination of maize grain under the artificial control can enhance its nutritional quality, reduce the level of anti-nutritional factors, and improve the taste as well as benefit the food processing. Moreover, the accumulation of y-aminobutyric acid (GABA) during maize germination draws the most attention.In the present study, five maize varieties including normal maize (SY-1、 SY-24) and waxy maize (ZY、ZHN、SYN-11) were germinated under hypoxia. The metabolism of physiological and biochemical compounds including GABA of the above maize varieties during germination were investigated. Then the most promising variety for accumulating GABA with a high germination rate was selected for further experiment. Subsequently, a treatment of firstly germinating under hypoxia stress, followed by cold stress with thaw, and refined with warmly incubation was conducted in order to accumulate GABA. Besides, the treating parameters of hypoxia and cold stress with thaw were optimized. In the end, a GABA-enriched maize beverage was developed using the maize obtained from the optimized condition. The main results were summarized as follows:1. The physiological and biochemical components of five maize varieties significantly changed during72h germination under hypoxia. At the end of germination period, the sprout length increased by15.5～26.3mm, the respiratory rate was improved by1.7～3.2folds, the dry matter lost by35.6～40.6%, the starch content was consumed by15.5～28.9%, the content of reducing sugar and free amino acid increased by1.67～4.69and6.43～12.23 folds, respectively. GABA content in germinated maize increased by9.31～12.15folds compared to that of the ingerminated one, reaching a content of0.46～0.65mg/g DW. There were significant differences in GABA content and germination rate among different maize varieties during germination. Germination rate of ZHN was the highest (85%) with a maximum GABA content of0.65mg/g DW, making it the most promising maize variety for accumulating GABA. In addition, the fact that the water and oil absorption capacity as well as emulsion capacity of starch of maize ZHN increased with germination could further promote its edible quality.2. During germinating for72h under hypoxia, the GAD activity of maize increased significantly and maintained at a high level, while no obvious changes were detected in DAO and AMADN activity. This indicated that GABA synthesis in germinating maize was mainly produced by the GABA shunt. Result showed that the optimal conditions for GABA accumulation in72h-germinated maize during cold stress with thaw were firstly freezed at18℃for6h and then thawed for4h at25℃. Under these conditions, the maximum GABA formation (1.53mg/gDW) was obtained, which was1.44folds of the corresponded control. Besides, the effects of incubation conditions (liquid to solid ratios of3-11, pH values of incubation solution of3-7, incubation time of0～120min, incubation temperature of30～50℃) on GABA accumulation were not significant (p<0.05).3. The maize germinated under hypoxia and cold stress with thaw process was made into a kind of GABA-enriched beverage. Results showed that the basic ingredients of GABA-enriched maize beverage were as follows:the optimal ratio of sample to solution was1:8, the addition quantity of white granulated sugar was4.8%, pH4.6. The stabilizer prescription of GABA-enriched maize beverage was:0.03%of CMC,0.09%of PGA0.04%of sodium alginate and0.06%of xanthan. Sensory qualities of the maize beverage were carried out using a hedonic scale sensory questionnaire. Results revealed that the GABA-enriched maize beverage was easily acceptable and met the drinking requirements of consumers.