Studies On Lactic Acid Production With Wheat Bran By Yeast

Wheat bran is the by-product of wheat,which contains many nutrients such as cellulose,protein,minerals and so on.Wheat bran was chosen as raw materials in this experiment,the content of reducing sugar was improved by extrusion process.Extruded wheat bran was treated with Saccharomyces cerevisiae to produce lactic acid by two-stage fermentation,the optimum fermentation parameters were determined.The flavor compounds of fermentation products were studied by chromatography technology.The temperature of extrusion,the moisture content and the die hole diameter were selected as experimental conditions.The single factor experiment was conducted with the content of reducing sugar of wheat bran.Based on the single factor experiments,the orthogonal experiment was used to confirm the optimization conditions.The optimum conditions were as follows:temperature 130 ?,moisture content 43%,and die hole diameter 4 mm.Under this condition,the content of reducing sugar can be raised from 0.96±0.03 mg/g to 17.94±0.04 mg/g.Through compare the ingredient of wheat bran before and after extrusion,the fat content decreased,the other ingredients were not obvious.The structure of wheat bran starch vanished after extrusion by scanning electron microscope.Both qualitative and quantitative experiments had demonstrated the content of free amino acids and monosaccharides increased.This amino acids and monosaccharides can provide adequate nutrients for yeast.Lactic acid has a great influence on the flavor of fermented products.To improve lactic acid production through fermentation with wheat bran as raw materials,the two-stage fermentation on wheat bran was developed,based on the growth properties of Saccharomyces cerevisiae,that is,wheat bran was fermented at 17? for 36 h(first-stage)followed by 24 h subsequent fermentation at 27?(second-stage).The optimal technological conditions of two-stage fermentation were gained through the single-factor and orthogonal experiment as follows,solid-liquid ratio of 1:15(w/w),yeast inoculation dose of 30%(w/w),and shaking speed of 100 r/min.In this condition,the content of lactic acid in fermented products were 185.10±2.55 mg/L.The wheat bran before and after extrusion was fermented respectively,the flavor compounds in the fermentation products were detected and analyzed.In addition to lactic acid,the results showed that the content of other organic acids in fermented products was also increased,in which the content of malic acid and citric acid were increased 49.40 mg/L and 67.01 mg/L respectively.It made fermentation products more refresh sour.The content of umami nucleotides(5'-GMP and 5'-IMP)in the fermented products were also increased 0.021 mg/L after extrusion treatment,which indicated that the extrusion pretreatment could make the fermented products of wheat bran more delicious.The ratio of sweet and delicious amino acids in fermentation products increased from 30.63%to 32.84%and the proportion of essential amino acids accounted for also increased from 25.28%to 29.22%by extrusion treatment.This shows that extrusion can improve the sensory quality and nutritional value of fermented products.The analysis of volatile substances in fermented products showed that the types of volatile compounds in fermented wheat bran were more abundant after extrusion pretreatment.Among them,the esters in fermentation products increased from 8 to 18,which made fermented products have sweet flavor.