Process Optimization And Quality Evaluation Of Okara And Cassava Residue Fermented By Compound Strain

In recent years,the rapid development of fermented feeds has made full use of various industrial by-products or agricultural by-products,providing strong technical support for developing unconventional feed materials in China.It has been found that unconventional feeds such as okara and cassava residue can effectively reduce fiber level,increase digestible carbohydrate and protein contents,and improve their biological values via microbial fermentation.Due to the large demand gap for feed raw materials in animal husbandry in China,the use of microbial fermentation of unconventional feed raw materials is a current research hotspot.This project focuses on the characteristics of raw materials such as okara and cassava residue,and utilizes multiple microbial compound fermentation to produce high-quality biological feed through solid-state fermentation technology.This research has important practical significance for utilizing unconventional raw materials such as okara and cassava residue to improve their utilization value and achieve long-term preservation.Experiment 1: Isolation and screening of microorganisms in okara.The strains R1,R2,R3,R4,R5,J and Z were obtained by using MRS agar(containing 1.5% calcium carbonate),YPD agar and PDA agar media to isolate,screen and purify the strains from the fermented okara samples using natural fermented okara as the isolation source.Through morphological observation,it was found that strains R1,R2,R3,R4,R5 all produced calcium soluble circles,colony color was beige,white and milky white and opaque,the state was slightly transparent,transparent,and opaque,and the surface was smooth and protruding.The colony diameter was about 1.0～1.7 mm,with an acid aroma.Microscopically,it was found to be rod-shaped or chain spherical,and Gram staining was blue,indicating that they were all Gram positive bacteria.It was preliminarily speculated that strain R1～R5 were lactic acid bacteria;the colony of strain J was milky white and opaque,with a diameter of about 2.5 mm.The surface was smooth and had a sauce aroma.It was ellipsoidal on microscopic examination and blue on Meilan staining.It was preliminarily speculated that it was a yeast;strain Z had mycelium,the colony was felted,the late growth becomed deep red,and make the medium color,the mycelium had cross partition,the melan stain was blue,through the morphology of the preliminary identification of its fungus.Physiological and biochemical test results showed that strain R1,R2,R3,R4,R5 could use hesperidin,lactose,sorbitol,cottonseed sugar,salicin,sucrose,maltose,cellobiose,gelatin liquefaction,peroxidase test results were negative,further identified strain R1～R5 as lactic acid bacteria;strain J could use glucose,galactose,fructose and sucrose,cannot use lactose,sorbitol,arabinose,xylose,Strain J could use glucose,galactose,fructose and sucrose,but not lactose,sorbitol,arabinose,xylose and ribose,nitrogen source assimilation,no vitamin culture test results were negative,further identified strain J as yeast.Molecular biology was used to analyze the 16 Sr DNA,26 Sr DNA D1/D2 region,ITS gene sequence comparison and homology analysis of the isolated lactic acid bacteria,yeast and fungi,respectively,and the results showed that seven typical strains were obtained from the strain isolation test,and five strains of lactic acid bacteria were identified as R1: Levilactobacillus brevis,R2: Weissella confusa,R3:Lactobacillus paracasei,R4: Enterococcus faecalis,R5: Lacticaseibacillus paracasei;One strain of yeast and one strain of fungus each,J: Candida tropicalis,Z: Monascus ruber.Experiment 2: Optimization of non-conventional feed fermentation process for okara and cassava residue.With three kinds of lactic acid bacteria,including Enterococcus faecalis,Lactobacillus paracasei and Lactobacillus casei,Bacillus subtilis and Saccharomyces boulardii as the fermentation bacteria,and the mixed raw materials such as okara,cassava residue and soybean meal as the fermentation substrate,a single factor experiment was conducted according to the fermentation time,water content,strain ratio and strain addition amount to study the influence of different factors on the quality of fermented feed.The response surface method test was carried out based on the results of the single factor test.The fermentation process parameters were as follows: water content 35%,40%,45%,strain addition 6%,8%,10%,strain ratio of yeast∶Bacillus subtilis∶compound lactic acid bacteria was 1∶1∶1、1∶1∶3 、2∶1∶3(wherein the compound ratio of lactic acid bacteria was Enterococcus faecalis∶ Lactobacillus paracasei∶ Lactobacillus casei =1∶1∶1),anaerobic fermentation for 5 d,10 d,15 d,27 d.Acid soluble protein and p H were selected as the response values,and the best optimized fermentation conditions were obtained with moisture content of 45%,strain addition of 10%,and strain ratio of yeast∶Bacillus subtilis∶lactobacillus=1∶1∶3.Under this condition,the acid soluble protein content of fermented feed was 34.24%,p H was 3.62,and it had a strong sour wine aroma,bright color,good color,loose texture with good quality.The optimized process parameters of fermented feed calculated by the response surface model were real and reliable,and have been applied to production with good results.It solved the problem of utilizing and developing unconventional raw materials such as okara and cassava residue to a certain extent and provided a certain theoretical basis for improving its utilization value.