| γ-aminobutyric acid (GABA), a kind of non-protein amino acid in nature, is an important inhibitory neurotransmitter in mammalian nervous system. GABA has bioactivities like hypotensive activity, treatment of epilepsy, promoting procreation, brain function-enhancing effects, enhancing memory, controlling asthma function and so on. GABA as a functional factor can be widely used in the field of food and pharmaceutical industries.Lactic acid bacteria as a presence of probiotics in human is often regarded as a healthy food, which can use carbohydrate to produce lactic acid for helping digestion and intestinal health function. Research results show that the probiotic is essential for the body and has important physiological functions e.g. not only directly affect human health but also affect the people longevity. Using of Lactic acid bacteria to product GABA can reach the level of food safety and health efficacy. Therefore, it has a broad ranges of application and market prospects.In this study, Lactobacillus brevis L2was used to product GABA, and building a model which can reflect the nonlinear between factors and yield to ensure the optimum combination for improving the yield of GABA; Effectively using these two of inexpensive by-product (wheat bran and millet bran) can provide a novel method of reducing GABA production costs.Finally, it was studied the purification process of GABA from broth fermented.First, the critical medium components and fermentative conditions for this strain were identified by Plackett-Burman (PB) design e.g. carbon source, nitrogen source, initial pH, temperature, time and so on. Subsequently, based on central composite design (CCD), an error back propagation neural network model linking to genetic algorithm (BPN-GA) was constructed and used to compute the optimal conditions for enhancing GABA production. The content of GABA in optimum fermentation medium reached27.765g/L, which was106.4%higher than that of original fermentation medium (13.452g/L).Second, fermentative production of GABA by Lactobacillus brevis using millet bran or wheat bran as the sole raw material, supplemented with L-MSG as the synthetic substrate was researched. Through analyzing the influence of pH, culture temperature, fermentation time, the results showed that the optimal fermentation conditions were as follows:pH4.0, culture temperature30℃, fermentation time72h. Subsequently, the D-optimal mixture design was applied to optimize the ratio of the three kinds of components above-mentioned for GABA production.The results showed that when the mixing ratio of wheat and millet bran and L-MSG reached22.454:20.000:57.546(g/L), the maximum GABA yield of Lactobacillus brevis L2reached27.2069g/L.Third, in order to obtain high-purify GABA, this paper also studied the decolorization process of GABA from broth fermented. After screening from six types of macroreticular resins and activated carbon, we found ADS-7exhibit high decoloring ratio and high GABA yield. On this basis, the series of experiments were carried out to optimize the parameters such as pH, decolorization time and temperature, and the optimum decolorization condition were:pH5.0, decolorization time1h, temperature25℃. Under the optimum decolorization condition, the decolorization ratio was above95%, and the loss rate of GABA was7%. Finally, the GABA was extracted by D001iron-exchange resins. The optimum parameters were as follows:initial pH5.0, sample flow-rate of1BV/h, elution method of two steps by using water and1mol/L aqueous ammonia.Finally, nuclear magnetic resonance (NMR) was used to estimate the extract. The extract was compared with the sample bought from Sigma. Almost no impurity peaks in the hydrogen NMR spectrum and the peak position consistent with GABA standard. The results prove that the purity of the extract was close to100%. |
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