| Stover sugar technology is one of the effective ways to solve the low added value of stover resource utilization and alleviate the food crisis.However,the inhibition of cells by toxic substances produced during stover sugar production and the high production cost are bottlenecks limiting the industrial production of stover biorefinery chemicals.In this study,four different Lactobacillus bulgaricus T15 gel beads,such as calcium alginate,low acylated gellan gum,poloxamer F127-BUM and F127-IEA,were prepared and their properties were characterized,and an immobilized cells-recycle fermentation process for D-LA production based on the four materials was established by optimizing the fermentation conditions of the strains.The immobilized cells-recycle fermentation technology was combined with the biorefinery of non-detoxified corn stover to produce D-LA using mechanical strength,encapsulation rate,water retention,acid production,number of cycles,and cell growth inhibitor tolerance as indicators,and the recirculation fermentation process of D-LA production from cells of non-detoxified corn stover was established.The main research results are as follows.1.calcium alginate empty carrier gel beads Hencky stress was 40.725 KPa,embedding rate was 80.221%,water retention rate was 32.4%;low acylated cold gel empty carrier gel beads Hencky stress was 102.095 KPa,embedding rate was 94.145%,water retention rate was 72%;F127-BUM empty carrier gel beads Hencky stress was 159.112 KPa,95.418% encapsulation rate and 85.6% water retention rate,respectively;F127-IEA empty carrier gel beads Hencky stress was 160.402 KPa,94.997% embedding rate and 84.7% water retention rate,respectively.The results showed that F127-BUM and F127-IEA showed superior results in the above properties,which proved to be more suitable as immobilization materials for Lactobacillus T15.2.The gel beads immobilized with T15 were subjected to fermentation experiments,and the optimum fermentation conditions obtained by single-factor and orthogonal experiments were41°C,initial glucose concentration of 90 g/L,and inoculum of 6%.The total D-LA yieldof F127-BUM immobilized T15 cells was 1982.97±1.81 g,and the average D-lactate yield was2.76±0.25 g/L-h,which could be fermented for 100 d.The total D-lactate yield of F127-IEA immobilized T15 cells was The total D-LA yield was 3467.48±1.22 g,with an average D-lactate yield of 2.71±0.85 g/L-h and 150 d.F127-IEA has a longer service life than the conventional calcium alginate material,resulting in higher acid production and economic benefits.This proved that it is the most suitable vehicle for the immobilized T15 cells of Lactobacillus immobilized for recycling fermentation.3.Tolerance analysis of immobilized T15 to different concentrations of 5-hydroxyme thylfurfural(5-HMF),ferulic acid(FA)and vanillin in the substrate showed that F127-IEA increased D-lactate acid production by 25% compared with F127-BUM at high concentr ation of 5-HMF,increased D-lactate acid production by 57.1% at high concentration of FA,and improved fermentation start time by 12 h at high concentration of vanillin.The fermentation start time was improved by 12 h.By comparing the above parameters,F127-IEA was the most suitable material for immobilization of Lactobacillus T15,while co rn stover was pretreated with enzymatic digestion to obtain 8.932 g/L concentration of glucose,which could be prepared as 40 g/L glucose solution after concentration.The total yield of D-LA production from F127-IEA immobilized Lactobacillus T15 cells-recycle fermentation using corn stover enzymatic digest as the sole carbon source for fermentation was 929.69 ± 1.59 g with a yield of 1.29 ± 0.39 g/L-h,and the F127-IEA wear rate did not exceed 5%.Finally,this study finally succeeded in establishing a corn stover b iorefinery process for D-LA production based on F127-IEA as immobilized material. |
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