Identification Of Three Lactic Acid Bacteria And The Basic Medium Optimization Of The Sweet Sorghum Stalks Juice Used For Lactic Acid Fermentation

Lactic acid is recognized as one of three major organic acid in the world,which was extensively used in theses areas of food,pharmaceutical and light industry.Recently,especially in chemical industry,lactic acid is generally used as raw material of poly lactic acid.The production of lactic acid was by the method of microbial fermentation in this paper.Three kinds of Lactic acid bacteria were inoculated into sweet sorghum juice medium to ferment lactic acid..The study contained four main blocks.Firstly,three bacterial strains,usingsweet sorghum juice to ferment lactic acid,were identified.Secondly,the ultrasonic-assisted enzymatic hydrolysis experiment was optimized by BBD of RSM in Design-Expert V8.0,which made the glucose/sucrose conversion rate improved.Third,the innovation fermentation medium was optimized.Finally,the proportion of L-lactic acid in total lactic acid was measured by HPLC.The optimization of enzymatic hydrolysis in the sweet sorghum juice:the sweet sorghum juice was pretreated by three methods ranging from enzymatic hydrolysis,ultrasonic enzymolysis to ultrasonic-assisted enzymolysis.Through above treatments,the Glucose/Sucrose conversion rate in the sweet sorghum juice that had pretreated by the way of ultrasonic-assisted enzymolysis was higher than the other two treatments.The experimental conditions:the ultrasonic power was 42.5W;the extraction time was 40min;the amount of enzyme was 30mg/L;the extraction temperature was 43?;the conversion rate of Glucose/Sucrose was up to?64.78±1.20?%.Identification of bacterial strains:the 16SrDNA sequence of bacterium were analysed to identify the species.By the analysis of 16SrDNA in bacterium,the conclusions were showed:the strain A2 is highly similar to L.plantarum strain S4;the strain C2 is highly similar to L.fermentum strain KF3;the strain C3 is highly similar to L.sp.KLDS 1.0707.The bacterium was dyeing by the Gram's staining method,the result showed that three bacteria strains?A2,C2.C3?were G^?.And then the nearby zone surrounding them occurred the CaCO3-solved circles.Finally,the biochemistry tubes used for lactobacillus identification showed that three bacteria strains can efficiently utilize maltose,sucrose,lactose,raffinose,salicin solution.The scanning electron microscope was used for the strain morphology observation.According to analysis,stain A2 was L.plantarum stain C2 was L.fermentum strain C3 was L.casel subsp.pseudoplantarum.The innovative fermentation medium was optimum by analysis the component of the sweet sorghum.Through AAS?Atomic absorption spectrophotometer?and EA?Elemental analyzer?,we eventually come to conclusions:peptone,K₂HPO₄ and MnSO₄·4H₂O were deficit.Additionally,the fermentation medium was optimum by BBD of RSM.Thirdly,three bacteria?No.A2?C2?C3?were utilized in the optimum medium with the sweet sorghum juice.Finally,we came to conclusions:1.A2?L.plantarum strain?:the L-lactic acid yield was 61.20±1.36 g/L,L-lactic acid/sucrose conversion rate was 47.20±1.81%,L-lactic acid/glucose conversion rate was71.80±1.71%;The optimum medium of A2:sorghum juice 327.83 g/L,peptone 1.67g/L,K₂HPO₄ 4.7 g/L,MnSO₄·4H₂O 0.17 g/L.2.C2?L.fermentum strain?:the L-lactic acid yield was?66.89±2.69?g/L,L-lactic acid/sucrose conversion rate was?52.45±2.05?%,L-lactic acid/glucose conversion rate was?95.74±1.45?%;The optimum medium of C2:sorghum juice 338.67g/L,peptone 3.33 g/L,K₂HPO₄ 5 g/L,MnSO₄·4H₂O 0.033 g/L.3.C3?L.casel subsp.pseudoplantarum?:the L-lactic acid yield was?64.89±3.32?g/L,L-lactic acid/sucrose conversion rate was?49.90±2.25?%,L-lactic acid/glucose conversion rate was?91.46±2.18?%;The optimum medium of C3:sorghum juice 396.8 g/L,peptone 3.33 g/L,K₂HPO₄ 3.33 g/L,MnSO₄·4H₂O 0.17g/L.HPLC measured the content of L-lactic acid in total lactic acid,which demonstrated that the proportion of L-lactic acid/total lactic acid was 55.74%towards the fermentation situation of L.plantarum,the proportion of others?C2,C3?were separately 71.35%and 68.95%.In conclusion,the three bacteria can good utilize sweet sorghum juice to ferment lactic acid.And L.fermentum can utilize sweet sorghum juice to ferment more L-lactic acid than L.plantarum and L.casel subsp.Pseudoplantarum,Which demonstrated that L.fermentum would have a great development prospect.