Study On Sodium Gluconate Fermentation Using The Hydrolysate Of Dioscorea Zingiberensis C. H. Wright And Control Of Inhibitors

Sodium gluconate is a multi-hydroxy organic acid salt. Bio- fermentation has become the main method of producing sodium gluconate in industry by virtue of mild reaction conditions, low equipment requirements, no waste water and gas produced, etc. However, mature fermentation uses glucose as carbon source, resulting in the high price of acid glucose and its derivatives. In this paper, we took the cheap non-grain hydrolysate of Dioscorea zingiberensis C. H. Wright(DZW) as carbon source and chose Aspergillus niger 1 for sodium gluconate fermentation. From the point of fermentation yield, analyzed the factors to inhibit fermentation and adopted the method of pretreatment and enzymatic degradation to remove inhibitors and achieve the purpose of reducing costs and improving the fermentation yield. The results obtained were as follows.(1) For the first time,the hydrolysate of DZW was used for fermentation of sodium gluconate and the initial convert ratio was 26.0%. The result showed that the hydrolysate of DZW directly for fermentation had certain inhibitory effect. By quantitative detection, we detected that abundant amino acids and vitamins existed in the hydrolysate of DZW. After further analyzing the composition and removing inhibitors, the hydrolysate of DZW can be as quality carbon sources for sodium gluconate fermentation.(2) By single factor experiments we confirmed that when the concentration of these substances higher than 0.1 g/L, the inhibition on the microbial cell growth and product synthesis was significant. By comparing the sodium gluconate conversion rate and biomass, it was concluded that phenolics in the hydrolysate had a stronger inhibitory effect than furfural and 5-HMF, especially for product synthesis. The concentration of furfural, 5-HMF, vanillin, syringaldehyde and 4-hydroxybenzaldehyde in the hydrolysate were respectively 0.11 g/L, 0.09 g/L, 0.54 g/L, 0.63 g/L and 0.47 g/L by HPLC quantitative analysis, beyond the safety concentration(0.1 g/L), and would inhibit sodium gluconate fermentation.(3) After the hydrolysate of DZW was treated by activated carbon, the alkali, sulfite and ion exchange resins, sodium gluconate conversion rate was respectively increased by 26%, 7%, 9% and 15%. Fermentation conversion rate was increased nearly 1 times by activated carbon pretreatment, indicating that the activated carbon pretreatment effect is best. After the pretreatment of activated carbon, the concentration of furfural, 5-HMF, vanillin, syringaldehyde and 4-hydroxybenzaldehyde were reduced to 0.02 g/L, 0.02 g/L, 0.23 g/L, 0.32 g/L and 0.21 g/L, revealing that removing or reducing inhibitors in the hydrolysate can relieve the inhibition on sodium gluconate fermentation to some extent.(4) Through studying the laccase degradation on the inhibitors, it was concluded that laccase can degrade 80% of phenolics, which the concentration of vanillin, syringaldehyde and 4-hydroxybenzaldehyde were reduced to 0.14 g/L, 0.19 g/L and 0.1 g/L, close to the safe concentration(0.1 g/L). Using the hydrolysate for sodium gluconate fermentation, the convert ratio was increased by 50.5%. After pretreatment of activated carbon the hydrolysate was again treated by laccase. The results show that more than 80% of furan derivatives and phenolics were removed, sodium gluconate convert ratio reached 76.5%, and compared with the hydrolysate for fermentation directly without any pretreatments, the sodium gluconate convert ratio was increased 2 ~ 3 times.