Study On Fermentation Technology And Nutritional Components Of Goat Milk Yoghurt

Goat milk is rich in protein,fat,lactose,minerals,vitamins and a variety of biologically active ingredients.Its nutritional components are close to human milk,and it is regarded as a boutique in milk.Yogurt produced with goat milk is rich in nutrition,unique flavor,smooth and delicate tissue state,and has a good development prospect.Due to the goaty flavor of goat milk,less casein particles than cow milk,and smaller fat globules,goat milk yogurt is prone to curd fragility and whey precipitation,which seriously affects the sensory quality of goat milk yogurt.Therefore,in this paper,the effects of fermentation conditions on the quality of goat milk yogurt and the flavor and nutritional characteristics of goat milk yogurt were systematically studied with whole goat milk powder as raw material,in order to provide a basis for the industrial production of goat milk yogurt.Firstly,the process conditions for the preparation of goat milk yogurt by YO-MIX 611and YO-MIX 187 were studied.The effects of sterilization conditions,milk solids content,fermentation temperature,fermentation time,inoculation amount and sugar content on the quality of yogurt were studied.The Box-Behnken model was used to optimize the process parameters of goat milk yogurt fermented by two starters,and the best process parameters were selected.The overall sensory score of goat milk yogurt prepared by YO-MIX 611 was better than that prepared by YO-MIX 187,which was more suitable for the development of goat milk yogurt products.The optimized process parameters of YO-MIX 611 were as follows:14.32%reconstituted milk was prepared,7%white granulated sugar was added,mixed evenly,preheated at 60°C for 30 min,homogenized,sterilized at 95°C for 10 min,inoculated with 2%yeast starter after cooling,fermented at 42.27°C for 5.04 h,stirred for demulsification,and refrigerated at 4°C for ripening.Secondly,the pilot production of full-fat goat milk powder as raw material and YO-MIX611 as starter under optimized conditions was studied.The changes of physical and chemical indexes and rheological properties during the pilot production process,the safety of the pilot products and the quality changes of the products during the shelf life were studied.The results showed that the p H of goat milk yogurt decreased during the fermentation process,the acidity,gel strength and apparent viscosity increased,and the water holding capacity decreased first and then increased.During the shelf life,the overall acceptability score was≥7.0 in the first 16 days,the number of viable bacteria could reach 1×10~9 CFU/g,coliform,mold and yeast were less than 1 CFU/g,staphylococcus aureus and salmonella were not detected.According to the third-party test report,all the items tested met the requirements,indicating that the product safety and quality stability of goat milk yogurt were high.Finally,the physicochemical indexes,rheological properties,flavor components and nutritional components of goat milk yogurt and cow milk yogurt prepared under the same fermentation conditions were analyzed and compared.The results showed that goat milk yogurt had higher acidity,lower p H,water holding capacity,elasticity and viscosity,and its gel structure was weaker than that of cow milk yogurt,and the ability to restore the structure was stronger than that of cow milk yogurt.The fermentation process had a significant effect on the formation of volatile compounds.There were 12 kinds of volatile compounds in goat milk yoghurt before fermentation and 33 kinds after fermentation.The volatile compounds mainly included ketones,acids,esters,hydrocarbons,aldehydes,alcohols,aromatics,furans and sulfur compounds.Ketones were important contributors to the flavor of goat milk yogurt,and the relative content increased from 7.10%before fermentation to 47.37%after fermentation.The capric acid in the acid substances is the main reason for the unique flavor of goat milk.The capric acid content of goat milk yogurt prepared by YO-MIX 611 decreased from 3.60%to 1.88%,which effectively reduced the goaty flavor.The fermentation process had no significant effect on fatty acids.The fatty acid types of goat milk yogurt and cow milk yogurt were consistent before and after fermentation,and the content was close.The fatty acid composition of goat milk yoghurt is more balanced than that of cow milk yoghurt,which is easier to be digested and absorbed.The total amount of hydrolyzed amino acids and free amino acids in goat milk yogurt was higher than that in cow milk yogurt.The amino acid SRC of goat milk yogurt was 87.15,while that of cow milk yogurt was 82.69,indicating that the content of essential amino acids in goat milk yogurt was more balanced and the nutritional value was higher.The calcium content of goat milk yogurt is significantly higher than that of cow milk yogurt,which is more suitable for the nutritional needs of modern people.In summary,this paper screened a set of starter cultures and fermentation conditions for the preparation of goat milk yoghurt.This method can be used to prepare goat milk yoghurt products with significantly reduced goaty flavor,good flavor and high nutritional value.The third-party detection meets national standards and lays a foundation for the development of high-quality products.