Study On Bacteria And Enzyme In Improving The Quality Of Peanut Meal

Peanut meal,a by-product of peanut oil extraction,is an important raw material of protein feed.However,the imbalance of amino acids,especially the serious unbalanced ratio between arginine and lysine,as well as the inclination to be oxidized and the difficulty to store,impeded its application in animal breeding.Therefore,it is of great practical value to screen lactic acid bacteria that can efficiently absorb arginine without harmful products like amines,for applying in peanut meal fermentation,which will help solve the imbalance ofamino acids and improve the nutrition and function of peanut meal.Lactic acid bacteria were preliminarily isolated from peanut meal,rice soaking water,rice wine fermentation broth,kimchi fermentation broth,and Northeast sauerkraut,and screened using the improved MRS-Arg liquid medium and improved bioamine medium with bromocresol purple indicator,13 strains with the capability to absorb arginine but produce little bioamines were subsequently selected.By high performance liquid chromatography,their absorption rate of arginine and yield of bioamines were quantified,showing that the strain Z-73 could completely absorb the arginine in the medium but yield no bioamines.Z-73 was then identified to be Lactobacillus brevis through 16S r DNA sequencing analysis.The strain was named L.brevis Z-73.Through single-factor enzymatic hydrolysis process optimization and response surface experimental design,the arginine releasing directed enzymatic hydrolysis process of peanut meal was optimized:the material to water ratio is 1:10(w·v^-1),pretreatment at 97°C for 10 min,acid protease addition amount is 1500 U·g^-1,the addition amount of flavor protease is 5000U·g^-1,the addition amount of trypsin is 250 U·g^-1,and the temperature of trypsin digestion is40℃.Under these conditions,the hydrolysis degree of peanut meal reached 27.9%,and the release rate of arginine got to 35.3%.Thereafter,the hydrolysate was fermented with L.brevis Z-73.The optimal fermentation conditions were determined through single factor experiments:the inoculation amount of Z-73 is 5%(v·v^-1),the fermentation temperature is 37℃,and the fermentation period is 48 h.Under these conditions,the free arginine in the fermented peanut meal was completely utilized;the highest contents of total acid and peptide were 4.7%and37.2%,respectively;and the IC₅₀（the amount required for scavenging 50%of the hydroxyl radical）was the lowest 3.5×10^-3 mg.The quality trace of fermented peanut meal was systematically evaluated.It was proved that synergistical treatment with lactic acid bacteria and enzymes could greatly improve the feeding quality of peanut meal.The acid-soluble protein accounted for the crude protein content increased from 5.9%to 87.0%,the content of total arginine decreased from 5.3%to 3.2%,while the content of total methionine and lysine increased by 77.1%and 41.9%,respectively.Most importantly,the ratio of arginine to lysine reduced from 3.7 to 1.6,leading to the significant improvement of amino acid imbalance in peanut meal.The content of total acid increased from0.6%to 4.7%,of which lactic acid,acetic acid and citric acid increased the most.Furthermore,the treated peanut meal possesses a high antioxidant activity,the DPPH·scavenging rate,iron reducing power,hydroxyl radical and superoxide anion scavenging power per dry gram of which are equivalent to 8.2,22.4,315.6 and 4.2 mg of Vc,respectively.It was found that the antioxidant peptides were generated during enzymatic hydrolysis and fermentation of peanut meal.In specific,peptides with a molecular weight less than 3 k Da have the strongest scavenging activity towards hydroxyl free radicals,which is prospected to be the vital contributor of the high oxidation resistance of the treated peanut meal.