| Lactic acid is a naturally organic acid At present,domestic and foreign commonly used method of microbial fermentation to produce lactic acid.Soybean molasses are byproduct of alcohol soybean protein concentrate.Because soybean molasses are rich in oligosaccharides,but most of microorganism are difficult to use it,however,lactic acid bacteria in the metabolic process can produce ?-galactosidase to hydrolysis stachyose and raffinose.During this study,six lactic acid bacteria strains were used as starter cultures to produce lactic acid by using soybean molasses,which were Lactobacillus plantarum subsp.plantarum CICC 23168,Lactobacillus delbrueckii ssp.bulgaricus KLDS 1.8501,Lactobacillus acidophilus ATCC 11975,Lactobacillus acidophilus KLDS 1.0327,Lactobacillus casei ATCC 393 and Lactobacillus plantarum NAU 322,respectively.Via growth characteristics of lactic acid bacteria,lactate production and sugar metabolism to analyze the ability of lactic acid bacteria use soybean molasses and lactic production.The main findings are as follows:(1)Determination of the components of the fermentation broth of soybean molasses by HPLC,The chromatographic conditions of the carbohydrate were as follow: Waters XBridge Amide column and the eluate phase was acetonitrile aqueous solution(75:25),column temperature was 55? and injection volume was 20?L.The chromatographic conditions of fermentation products were as follows: chromatographic column was Bio-Rad Aminex HPX-87 H,the mobile phase was 5mmol/L H2SO4,column temperature was 40? and injection volume was 20?L.(2)Comparative the abilities of six lactic acid bacteria strains fermentation 15 °Brix soybean molasses to produce lactic acid.The results indicated that the six lactic acid bacteria strains all have the abilities of using 15°Brix soybean molasses to produce lactic acid.Lactobacillus plantarum subsp.plantarum CICC 23168 has the highest number of viable cells,the yield of lactic acid was 12.18 g/L,the total sugar consumption was 22.48 g/L within 24 h,Lactobacillus plantarum subsp.plantarum CICC 23168 compared to the other five lactic acid bacteria strains has a significant advantage.Lactobacillus plantarum subsp.plantarum CICC23168 has the characteristics of short fermentation time,high viable cells,high total sugar consumption and high lactic acid yield.All above indicated that the Lactobacillus plantarum subsp.plantarum CICC 23168 were the dominant strains of lactic acid production from fermented soybean molasses.(3)Comparative analysis the effects of concentration of soybean molasses on cell growth of Lactobacillus plantarum subsp.plantarum CICC 23168,carbon source metabolism and lactic acid production.The results indicated that the Lactobacillus plantarum subsp.plantarum CICC 23168 was inoculated in different concentrations of soybean molasses,and adjusted to p H 6.0,temperature stay at 37? for 48 h,The growth curves of Lactobacillus plantarum subsp.plantarum CICC 23168 at 5 °Brix,10 °Brix,15 °Brix and 20 °Brix soybean molasses were very similar,and the number of viable cells reached 1010 CFU/m L.The lactic acid bacteria grew slowly at 30 °Brix and 40 °Brix soybean molasses,the number of viable cells was low.The strain was cultured in high concentration soybean molasses for 0 to 16 h,The number of viable cells showed a downward trend.The lactic acid bacteria was fermented at 10 °Brix soybean molasses for 48 h,sugar consumption rate was 19.84% and lactic acid yield from sugar was 90.04%,which was much higher than that other low concentration soybean molasses.These indicated that 10 °Brix soybean molasses medium has sufficient carbohydrates for the fermentation,and the strain has high utilization of the 10 °Brix soybean molasses medium,lactic acid yield is high.(4)The nitrogen source and inorganic saltion of soybean molasses medium were optimized.The effects of six kinds of nitrogen nutrient sources and four kinds of inorganic salts were studied in the fermentation of soybean molasses by Lactobacillus plantarum subsp.plantarum CICC23168.The optimum 10 °Brix soybean molasses medium needs to added nitrogen nutrient sources and inorganic salts,the nitrogen nutrient sources was peptone and diammonium citrate,its yield was 20 g/L,the ratio of peptone and diammonium citrate was 2: 1,inorganic salts was sodium acetate and dihydrogen phosphate,its yield was 6 g/L,the ratio of sodium acetate and dihydrogen phosphate was 1:2.The optimal yield of lactic acid was 19.49 g/L for 48 h.In summary,carbohydrate consumption,fermentation product yield,lactic acid conversion and carbohydrate utilization are tested by HPLC.Lactobacillus plantarum subsp.plantarum CICC23168,which was screened from six lactic acid bacteria strains,was used as a new type lactic acid starter by using soybean molasses as fermentation substrate.The optimum 10 °Brix soybean molasses medium was used peptone and diammonium citrate as nitrogen,CH3 COONa and K2HPO4 as inorganic salt.The ratio of peptone and diammonium citrate was 2:1,the yield of nitrogen was20 g/L,the ratio of CH3 COONa and K2HPO4 was 1:2,the yield of inorganic salt was 4 g/L.The lactic acid yield reached the highest value of 19.49 g/L under the optimum conditions. |
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