Method for efficiently producing lactic acid by fermenting brewers' spent grains
The present disclosure relates to a method for efficiently producing lactic acid by fermenting brewers' spent grains. The method specifically includes the following steps: (1) adding water to brewers' spent grains after alkali pretreatment so as to adjust a solid content of a fermentation production system to 10%-15%, adding cellulase to the brewers' spent grains according to an addition amount of 5 FPU/g-10 FPU/g, carrying out hydrolysis at 50° C.-60° C. and pH of 4.5-5.2 for 20 hours-48 hours, and obtaining a prehydrolyzed substrate; and (2) inoculating hydrolysate prepared in step (1) with a lactic acid bacteria seed solution with a viable count of 1×10 8 CFU/mL-1×10 10 CFU/mL according to an inoculation amount of 10%-15% (v/v), conducting fermentation at 40° C.-55° C. and pH of 6.0-7.2 for 72 hours-96 hours, and obtaining a fermentation broth.
1 . A method for efficiently producing lactic acid by fermenting brewers' spent grains, specifically comprising the following steps:
adding an alkali solution with a concentration of 0.5-3.0 wt % into brewers' spent grains according to a solid-liquid weight ratio of 1:5-1:10, cooking at 100-120° C. for 10-20 min, carrying out a solid-liquid separation, obtaining and washing solid residues to a neutral state, and obtaining alkali-pretreated brewers' spent grains;
adding water to the alkali-pretreated brewers' spent grains so as to adjust a solid content of a fermentation production system to 10%-15%, adding cellulase into the alkali-pretreated brewers' spent grains according to an addition amount of 5 FPU/g-10 FPU/g, carrying out hydrolysis at 50° C.-60° C. and pH of 4.5-5.2 for 20 hours-48 hours, and obtaining a prehydrolyzed substrate; and
inoculating the prehydrolyzed substrate with a lactic acid bacteria seed solution with a viable count of 1×10 8 CFU/mL-1×10 11 CFU/mL according to an inoculation amount of 10%-15% (v/v), fermenting at 40° C.-55° C. and pH of 6.0-7.2 for 72 hours-96 hours, and obtaining a fermentation broth containing the lactic acid; and
wherein a lactic acid concentration of the fermentation broth is not smaller than 45 grams per milliliter (g/L).
2 . The method according to claim 1 , wherein the brewers' spent grains are waste biomass materials produced when industrial production is carried out with barley, and comprise residues from industrial brewing, beverage processing and food production processes and processing residues.
3 . The method according to claim 1 , wherein a cellulose content of the alkali-pretreated brewers' spent grains is 15%-30% of a brewers' spent grain dry basis and a hemicellulose content of the alkali-pretreated brewers' spent grains is 20%-40% of the brewers' spent grain dry basis.
4 . The method according to claim 1 , wherein the lactic acid bacteria seed solution is prepared by the following steps: transferring Enterococcus mundtii China General Microbiological Culture Collection Center (CGMCC) 22227 glycerol-frozen bacteria into a deMan-Rogosa-Sharpe (MRS) culture medium, incubating for 24 hours-48 hours to obtain an activated seed solution, then transferring the activated seed solution into a modified MRS (mMRS) culture medium according to an inoculation amount of 10%-15%, carrying out an anaerobic culture at 40° C.-45° C. for 8 hours-12 hours, and obtaining the lactic acid bacteria seed solution with a viable count of 1×10 8 CFU/mL-1×10 10 CFU/mL.
5 . The method according to claim 1 , wherein a lactic acid concentration of the fermentation broth is not smaller than 50 g/L.
6 . The method according to claim 1 , wherein a lactic acid conversion rate of substrate fermentable sugar is not smaller than 0.60 g/g.
7 . The method according to claim 1 , wherein a lactic acid production rate is not smaller than 3.0 g/h/L.
8 . The method according to claim 1 , wherein an acetic acid concentration of the fermentation broth is smaller than 2.0 g/L.
9 . The method according to claim 1 , wherein a lactic acid yield obtained through unit enzyme preparation addition is greater than 9 grams of lactic acid per filter paper unit (g-Lac/FPU).
10 . The method according to claim 4 , wherein the modified mMRS culture medium comprises components as follows: each liter of deionized water contains 10 g of peptone, 8 g of beer extract, 5 g of sodium acetate trihydrate (CH 3 COONa·3H 2 O), 4 g of yeast extract, 2 g of potassium hydrogen phosphate (K 2 HPO 4 ), 2 g of ammonium citrate, 0.2 g of magnesium sulfate heptahydrate (MgSO 4 ·H 2 O), 0.05 g of manganese(II) sulfate tetrahydrate (MnSO 4 ·4H 2 O), 1 mL Tween 80, 10 g of cellobiose and 10 g of xylose; where an initial pH value is adjusted to 7.0, and sterilization is carried out at 115° C. for 15 min.
11 . A method for efficiently producing lactic acid by fermenting brewers' spent grains, comprising the following steps:
adding a NaOH alkali solution with a concentration of 1.0 wt % into brewers' spent grains according to a solid-liquid weight ratio of 1:10, cooking at 120° C. for 15 min, carrying out a solid-liquid separation, obtaining and washing solid residues to a neutral state, and obtaining alkali-pretreated brewers' spent grains;
adding water to 20 g of the alkali-pretreated brewers' spent grains so as to adjust a solid content of a fermentation production system to 10%, adding cellulase into the alkali-pretreated brewers' spent grains according to an addition amount of 5 FPU/g, carrying out hydrolysis at 50° C. and pH of 5.0 for 20 hours, and obtaining a prehydrolyzed substrate;
inoculating the prehydrolyzed substrate with a lactic acid bacteria seed solution with a viable count of 3.7×10 8 CFU/mL according to an inoculation amount at a volume ratio of 10%, fermenting at 43° C. and pH of 6.0 for 96 hours, and obtaining a fermentation broth containing the lactic acid; and
wherein a dry basis of the alkali-pretreated brewers' spent grains contains 18.2% of cellulose and 20.4% of hemicellulose; and
wherein a lactic acid concentration of the fermentation broth is not smaller than 50 g/L.
12 . A method for efficiently producing lactic acid by fermenting brewers' spent grains, comprising the following steps:
adding a NaOH alkali solution with a concentration of 1.0 wt % into brewers' spent grains according to a solid-liquid weight ratio of 1:10, cooking at 120° C. for 15 min, carrying out a solid-liquid separation, obtaining and washing solid residues to a neutral state, and obtaining alkali-pretreated brewers' spent grains;
adding water to 20 g of the alkali-pretreated brewers' spent grains so as to adjust a solid content of a fermentation production system to 10%, adding cellulase into the alkali-pretreated brewers' spent grains according to an addition amount of 7.5 FPU/g, carrying out hydrolysis at 50° C. and pH of 5.0 for 30 hours, and obtaining a prehydrolyzed substrate;
inoculating the prehydrolyzed substrate with a lactic acid bacteria seed solution with a viable count of 3.7×10 8 CFU/mL according to an inoculation amount at a volume ratio of 10%, fermenting at 43° C. and pH of 6.0 for 84 hours, and obtaining a fermentation broth containing the lactic acid; and
wherein a dry basis of the alkali-pretreated brewers' spent grains contains 18.2% of cellulose and 20.4% of hemicellulose; and
wherein a lactic acid concentration of the fermentation broth is not smaller than 45 g/L.