Study On The Preparation And Stability Of Probiotic Goat Milk Powder Containing Bioactive Peptides

Bioactive peptides have become the focus of current research due to their functions such as anti-oxidation,blood pressure lowering,immunity enhancement and so on.They are mainly produced by microbial fermentation or enzyme hydrolysis proteins.Shaanxi Province is a large province which is rich in goat milk resources.But its types of goat milk products are single,lowgrade repetition,homogenization seriously and competive fiercely.This project used probiotics to interact with enzymes to develop a probiotic goat milk powder containing bioactive peptide by using goat milk as a raw material.First,the effects of different proteases on two strains probiotics Lactobacillus plantarum L60 and Lactobacillus rhamnosus LR22 fermented goat milk production active peptides were studied.Screening out proteases to assist in the production of active peptides with high antioxidant and ACE inhibitory properties,optimized the process of protease-assisted probiotic fermentation of goat milk.Then peptides below 3K Da were obtained by ultrafiltration and identified by mass spectrometric.Experiment study on the anti-heat effects of different thermoprotectants on probiotics,optimized to obtain the composite thermoprotectants.Based on this,a probiotic goat milk powder containing bioactive peptides was developed,investigate its stability,electron microscope and chroma analysis.The main research conclusions are as follows:1.The screened protease can significantly improve DPPH free radical scavenging rate,ACE inhibition rate and active peptide content of Lactobacillus plantarum L60 and Lactobacillus rhamnosus LR22 fermented goat milk.The addition of Alcalase enzyme assisted Lactobacillus plantarum L60 to ferment goat milk,the DPPH free radical scavenging rate reached 74.65%,the peptide content increased by 2.32 times compared with the control and reached 1.89 mg/mL,added composite enzymes(Alcalase and papain)increased the ACE inhibition rate by 75.73%compared with the control and reached 43.23%.The addition of composite enzymes assisted Lactobacillus rhamnosus LR22 to ferment goat milk,the DPPH free radical scavenging rate increased by 54.22%compared with the control and reached 72.33%,added Alcalase enzyme made the ACE inhibition rate reach 74.98%,added papain increased the peptide content by 1.34 times compared with the control and reached 1.45 mg/mL.2.The single-factor test and response surface method optimization determined the best process parameters for Alcalase enzyme assisted Lactobacillus plantarum L60 and Lactobacillus rhamnosus LR22 to ferment goat milk,enzyme addition amount 0.15%,fermented 12h at 37?.Under these conditions,the DPPH free radical scavenging rate was 75.17%,the ACE inhibition rate was 84.15%,which increased by 16.87%and 22.74%compared with the control without protease respectively.There was no significant difference between the verified value and the predicted value.The results indicated that it is feasible to optimize the fermentation process of Lactobacillus plantarum L60 and Lactobacillus rhamnosus LR22 ferment goat milk by response surface methodology.3.Five kinds of goat milk containing bioactive peptides GM-L60,GM-LR22,GM-L60+LR22,GM-L60+LR22+Alc and GM-Alc were isolated and identified 24,30,14,22 and 9 peptides by LC-MS/MS,both exist three identical peptides:FFDDK,NMAHIPR,SCQDQPTTLAR.There are eight identical peptides in goat milk fermented by two probiotics,indicating that the enzymes produced by different probiotics have the same restriction sites,and the peptides produced by these two probiotics fermented are mainly derived from whey protein and casein.However,the peptide obtained by the hydrolysis of Alcalase enzyme mainly came from casein.The effect of protease assisted probiotics to ferment goat milk to produce bioactive peptides better than a single enzymatic hydrolysis.4.The single factor test and response surface method determined the best ratio of the composite thermoprotectants which improve the probiotic survival rate in the probiotic goat milk powder containing bioactive peptides:full milk powder 54.69g/L,trehalose 4.5%,Inulin 5.57%.Under this condition,the probiotic survival rate was 9.98%,which increase by 6.28 times compared with that of the control.There is no significant difference between the verified value and the predicted value,which indicates that it is feasible to optimize the ratio of the composite thermoprotectants by response surface method.5.The effects of single and composite thermoprotectants on the spray-dried preparation of bioactive peptide goat milk powder were compared.The results showed that the number of viable count in goat milk powder with added thermoprotectants was significantly higher than the control.The probiotic goat milk powder containing bioactive peptides added with composite thermoprotectants has the highest number of viable count,which is 4.72×108cfu/g,the survival rate of the bacteria was increased by 12.78 times compared with the control and reached 18.88%,the peptide content was 15.2mg/g,the DPPH free radical scavenging rate was 73.87%,the ACE inhibition rate was 84.94%.The results of accelerated experiments predicted the stability of the activity indicated that the storage activity is stable at normal temperature and the storage effect is better at low temperature.6.Electron microscopy scans of five probiotic goat milk powders containing bioactive peptides GM,GM-G,GM-T,GM-I,GM-GTI prepared by spray drying showed that the surface of GM-G and GM-GTI formed so many irregular concave surfaces.Some cracks are formed on the surface of the GM,GM-T and GM-I microcapsules,the cracks will have a greater impact on the survival of the bacteria.The chromaticity analysis of five types of goat milk powder GM,GM-G,GM-T,GM-I and GM-GTI showed that the addition of thermoprotectants would not affect the color and lustre of milk powder.In this study,protease assisted Lactobacillus plantarum and Lactobacillus rhamnosus fermented goat milk were used to prepare goat milk powder containing bioactive peptide.Using mass spectrometry identified the active peptide.The prepared bioactive peptide probiotic goat milk powder contains Lactobacillus plantarum,Lactobacillus rhamnosus,antioxidant peptides,ACE inhibitory peptides and inulin.It have multiple functions of probiotics,bioactive peptides and prebiotics,which can provide a technical reference for the development of new functional goat milk products in the future.