Study On The Quality Characteristic And Functionality Of Goat Milk Products With The Additive Of Oligopeptides Assisted By Ultrasound

Pasteurisation is the traditional method of sterilisation in the dairy industry,but its products lack shelf life.Ultrasound is an emerging non-thermal technology in the food industry for destroying microorganisms and enzymes and extending the shelf life of food products.Therefore,in this study,the effect of ultrasound-assisted pasteurisation on the quality of goat milk was investigated,including its physicochemical properties,microstructure(fat globule size,particlesize,scanning electron microscopy and Zeta-potential),functional properties(foaming and its stability,emulsion viability and its stability),protein secondary structure,and digestive properties,and furthermore,its quality during storage was assessed.To date,functional dairy products are one of the hotspots of research on functional foods,but oligopeptide functional dairy products are still vacant in the market,moreover,the addition of oligopeptides can easily lead to precipitation in dairy products,causing some damage to stability.Therefore,in this project,high Fisher Ratio Oligopeptide from whey protein(W-HFO)was added to goat milk as an active ingredient to made oligopeptides dairy products assisted by the process of ultrasound and pasteurisation.The effect of the addition of oligopeptides on the physicochemical properties stability and functional properties ofliquid goat milk was investigated,and its protein composition,antioxidantactivity and functional properties were further evaluated.Meanwhile the effect of HFO on the curdability,water holding capacity,textural properties,antioxidant activity and probiotic effect of fermented goat milk was alsofurtherdiscussed.The optimal conditions for ultrasonic treatment were determined to be 600 W,20 min,1:1,by orthogonal experiments,using p H,acidity,turbidity and fat flotation rate as reference indicators.Under this condition,fat separation in goat milk was effectively prevented.The size of fat globules and protein particle size in goat milk were significantly reduced by ultrasound treatment,as was viscosity(P<0.05).It was inferred from the results of simulated in vitro digestion that ultrasound treatment benefited to improve the rate of fat digestion during gastric digestion and increased protein bioavailability.Meanwhile,the ultrasonic treatment had an effect on the network structure on the surface of the milk protein particles,causing different degrees of fragmentation of the milk proteinparticles,which wasconsistent withthe results oftheparticlesizedetermination.Inaddition,the absolute value of the Zeta potential of goat milk also showed a significant increase(P<0.05),and the stability of the protein solution during storage was made an improvement,and the shelf life of the pasteurised goat milk was further extended by the ultrasound treatment.Furthermore,the results of the protein secondary structure experiments indicated a decrease in the β-folded structure and an increase in the α-helical structure in the goat milk after the ultrasound treatment.The results of the functional property experiments also showed that the ultrasound treatment significantly improved the emulsification and emulsion stability of goat milk(P<0.05)and increased the foamingcapacity(P<0.05),butat thesametimeshoweda slightlypoorerfoam stability.High F-value oligopeptides of whey protein(W-HFO)were added to goat milk as active ingredients after the ultrasound-assisted pasteurisation process was established.A comparative study of the characteristics of goat milk at different content levels of W-HFO has shown that the addition of W-HFO has been demonstrated an increase in the total protein and whey protein content(P<0.05).The antioxidant properties of the goat milk with W-HFO were significantly improved(P<0.05),as were the functional properties of foaming and emulsification.Compared to the control samples,the addition of W-HFO made an increase in the viscosity and particle size of thegoat milk andreduction in the Zeta-potentialofthe system,but had noa significant effecton the distribution of fat globules in goat milk.Further results from the storage period experiments confirmedthat W-HFOwasbeneficialin extendingtheshelflifeofpasteurised milk.Furthermore,pasteurised goat milk with W-HFO was fermented.It was found that W-HFO could accelerated the curdling rate of fermented goat milk,reducing the time required for fermentation in a positive correlation with the proportion of W-HFO added.The better water-holding capacity were observed in the samples with the addition of W-HFO(P<0.05),and as was the scavenging rate of DPPH,ABTS and hydroxyl radicals,improving the overall antioxidant properties of fermented goat milk.Moreover,W-HFO was found to contribute to the growth and reproduction of lactic acid bacteria,and the number of viable bacteria in the fermented goat milk with W-HFO also showed significantly increase.The results of the storage experiments indicated that the water-holding capacity of all groups of fermented goat milk with W-HFO remained above75% throughout the storage period,and the post-acidification situation was significantly improved.Therefore,the application of W-HFO as a functional ingredient was benefit to the nutritional value and functional activity of pasteurized goat milk products.This work is of practical importance for improving the process in production and processing of goat milk products,to further provide guidance for the practical production of a series of functional goat milk products or special medical purposeformulaewitholigopeptides asthecorefunctionalingredients.