Resource Utilization Of Brewers’ Spent Grain Based On DES Pretreatment

Brewers’ spent grain(BSG)is the main by-product of beer brewing industry,accounting for about 85% of the total by-product.BSG is not only contain rich cellulose,hemicellulose and lignin,but also contain a large amount of protein(23.75%).Based on this,firstly,this paper developed a pretreatment method of BSG with "Fermentable deep eutectic solvent(DES).The effective separation of BSG components was studied.Secondly,the tolerance of Rhodotorula glutinis to the inhibitors from lignocellulose during pretreatment was analyzed.Finally,the method of microbial fermentation using hemicellulose and proteinto to ferment lipid was explored.The solid residue dominated by cellulose was enzymatically hydrolyzed to ferment ethanol.(1)Firstly,a "Fermentable DES" system consisting of glycerol,choline chloride and phosphoric acid was developed to treat BSG in this paper.The pretreatment conditions(molar ratio,solid-liquid ratio,acid addition,reaction temperature and time)were optimized.When the molar ratio of choline chloride to glycerol was 1:10,the solid-liquid ratio of DES to BSG was 1:15,the amount of phosphoric acid was 6%,and the temperature was 140 ℃ for 4 h,protein(92.23%),hemicellulosic(97.63%)and lignin(73.21%)were extracted into the pretreatment solution by DES.Lignin that cannot be fermented by microorganisms is washed out with water.Cellulose was present in the solid residue.The effective separation of each component provides a basis for the resource utilization of BSG.(2)In this paper,the tolerance of R.glutinis to furan compounds(furfural,furfuryl alcohol,5-hydroxymethylfurfural)and phenolic compounds(vanillal,ferulic acid)produced under the above pretreatment conditions was analyzed with "Fermentable DES" as the sole carbon source.Low concentration(0.5 g/L)of furans inhibited cell growth and lipid accumulation.Among the three furan compounds,the strain had the highest tolerance to 5-hydroxymethylfurfural,with biomass and lipid of11.04 g/L and 1.96 g/L,which were 90.90% and 81.33% of the blank control group(12.10 g/L and 2.41 g/L).Furfuryl alcohol followed.Tolerance to furfural was lowest.The low concentration(0.5 g/L)of the two phenolic compounds inhibited the growth of bacteria(11.21 g/L,10.94 g/L)but promoted the synthesis of lipid(2.67 g/L,2.55 g/L).It is proved that the system can be used in lipid fermentation with low concentration inhibitor.(3)Finally,the microbial fermentation of DES pretreatment solution(including fermentable sugars and nitrogen sources from hemicellulose and protein)and enzymatic hydrolysate from solid residue dominated by cellulose were carried out.When R.glutinis was cultured with DES pretreatment solution for lipid fermentation,the effects of DES pretreatment cycle times and dilution times of pretreatment solution were explored.The results showed that the biomass and lipid of R.glutinis were 9.21 g/L and 2.34 g/L respectively.The utilization rates of hemicellulose and protein were 92.46% and 81.58%.When Saccharomyces cerevisiae was cultured with cellulase hydrolysate to ferment ethanol,the effects of enzymatic hydrolysis efficiency and fermentation were studied.The maximum enzymatic hydrolysis efficiency was 84.27%.The maximum yield of ethanol was 10.12 g/L and the utilization rate of cellulose was 78.26%.The resource utilization of BSG is basically realized.