Preparation And Stability Of Probiotic Goat Milk Powder Containing Antioxidant Peptides

Dairy goat population,production of goat milk and dairy products in Shaanxi province are ranked first in China.Infant formula milk powder and industrial milk are the main products in processing of goat milk.Less variety,lack of function and low added value are the main problem in goat milk industry.Four strains probiotic Lactobacillus producing antioxidant peptides had been screened in our previous work.In this study,probiotic goat milk powder containing antioxidant peptides was developed on this basis.Lactobacillus casei L61 was used as a test strain by the ability of producing peptide and heat resistance.Optimal conditions of preparing antioxidant peptides from goat milk fermented by L.casei L61 were obtained via single factorial experiments and orthogonal design.Formula of nutritive substance which can promote the production of antioxidant peptides were obtained by response surface methodology.The optimal condition of spray drying was obtained by exploring composite heat protective agents of preparing antioxidant peptides from goat milk.Storage stability of milk was explored by accelerated test.The conclusions were shown as follows:1.The results of heat resistance test performed by Lactobacillus casei L49,L61,Lactobacillus plantarum L60 and Lactobacillus acidophilus LA5 showed that Lactobacillus casei L61 had the strongest heat resistance and viable number was significantly higher than the other three strain Lactobacillus after heated at 60?,65?,70? and 75? for 5 minutes,respectively.2.The optimum fermentation goat milk conditions of Lactobacillus casei L61 were as follows: the recovery milk concentration,inoculation amount,fermentation temperature and time were 11%,5%,41? and 16 h,respectively.The scavenging rate of DPPH free radicals in fermented milk was(59.97±0.87)%,which improved by 18% compare with control group(41.97±1.37)%.The optimal formula of preparing antioxidant peptides via Lactobacillus casei L61 from goat milk were 0.13% of glucose,1.10% of calcium lactate and 0.25% of casein peptone.And the DPPH radical scavenging rate of fermented milk was(62.48±1.22)% under the optimal condition,and the scavenging rate of hydroxyl radical was(88.01±0.69)%,which increased by 31.51% than before optimization(56.50±0.92)%.3.The optimal composite heat protective agent formula of Lactobacillus casei L61 was 6.03% of glucose,18.98g/L of skim milk and 12.50mL/L of glycerol.There was no significant difference between experimental value and the predicted one.The survival rate of the cells was(14.58±0.72)%,which increased by 13.14% compared to the control group(1.44±0.36)%.4.The optimum spray drying conditions were as follows: the inlet temperature was 130? and the feed flow rate was 4.5mL/min.The viable number and viability in milk powder were 7.46×108 cfu/g and(23.41±1.28)% under this condition.The results of accelerated test to predict the stability of antioxidant probiotic goat milk powder showed that the equation between the inactivation rate constant and the temperature was Lgk=-1867.5/T+4.2765(R2=0.9489).The inactivation rate constants were k4=3.4×10-4 and k25=1.02×10-3 at 4? and 25?,the shelf life of probiotic goat milk powder containing antioxidant peptides was predicted to be 352 days at 4? and 117 days at 25?.The results showed that it was feasible to adopt the process condition established in this work for preparing antioxidant probiotic goat milk by spray drying.Besides,the milk prepared by this method has high antioxidant activity and viable number.Thus,the study could provide technical support for the development of the subsequent antioxidant probiotics goat milk powder product.