Study On The Formation Rule And Control Technology Of Oxidized Flavor Compounds During The Processing And Storage Of Goat Milk Powder

Flavor is a crucial parameter in determining the quality of goat milk products and a decisive factor affecting the consumer acceptance of dairy products.The constant occurrence of oxidative flavor changes in goat milk powder during processing and long-term storage poses a significant practical challenge,limiting its usage.This study aims to investigate the formation patterns and influencing factors of flavor substances during the production and subsequent storage of dairy powder,using whole goat milk as the research object.Based on these findings,natural antioxidant components were added to goat milk to enhance the flavor stability of goat milk powder during storage.These results provide a theoretical basis for addressing the bottleneck issues in the application of dairy powder.The main research contents and findings are outlined below:(1)The abundance and high concentration of volatile compounds associated with fat oxidation in whole goat milk powder,compared to skimmed goat milk powder,indicate that milk fat serves as a significant precursor for oxidized flavor substances during the production of goat milk powder.The differences in oxidized flavor substances and their relationships with the degree of fat oxidation and milk fat particle morphology were analyzed in goat milk powder at various processing stages,using flavor substance composition,fat oxidation degree,and milk fat globule morphology as indicators.The analysis revealed the presence of 31 volatile flavor compounds in goat milk,including 7 ketones,7 aldehydes,7 acids,4 alcohols,4 esters,and 2 lactones.Among them,9 compounds,namely 2-pentanone,2-heptanone,2-nonanone,2,3-butanedione,hexanal,nonanal,heptanal,octanal,and decanal,were identified as characteristic oxidized flavor compounds in dairy powder processing.Comparisons with raw milk showed that the content of 2-butanone decreased after homogenization,and the overall total amount of flavor substances decreased.However,the content of compounds with oxidative characteristics increased after heating,concentration,and drying.Additionally,the enzymatic activity of enzymes related to fat oxidation significantly decreased after homogenization,sterilization,concentration,and drying of raw milk,while the peroxide value and acid value significantly increased.Furthermore,the particle size of milk fat globules in raw milk was 2.34 μm,which reduced to 2.04 μm after concentration and further to 1.36 μm after drying.The decrease in globule diameter resulted in an increase in specific surface area,making the milk fat more susceptible to oxidation.These findings suggest that changes in milk fat globule morphology contribute to the formation of oxidized flavor substances during the processing of milk powder.(2)By adding natural antioxidants to inhibit the flavor deterioration of goat milk powder,the difference of oxidative flavor between the milk powder with antioxidants and that without antioxidants was compared.The compounds with oxidative flavor characteristics verified in the first two chapters included 2-pentanone,2-heptanone,nonanal and heptanal.The results showed that the overall flavor of milk powder with antioxidants was weaker than that without antioxidants.The relative contents of 2-heptanone and heptanal in milk powder added with VC decreased significantly;The relative contents of 2-heptanone,heptanal and nonanal in milk powder added with VE decreased significantly;In the milk powder added with VC and VE,the relative content of 2-pentanone increased,while the relative content of 2-heptanone,heptanal and nonanal decreased significantly.At the same time,after adding antioxidants,the acid value decreased significantly,the diameter of fat globules became larger,the specific surface area decreased,and the oxidation of milk fat was inhibited.There was no difference in sensory evaluation between the two groups.(3)Using headspace solid-phase microextraction combined with gas chromatographymass spectrometry,the volatile components of goat milk powder stored at 37 ℃ for 12 weeks were analyzed.A total of 26 volatile flavor compounds were detected,including 4 ketones,5aldehydes,6 acids,5 alcohols,4 esters and 2 lactones.Among them,the content of 2-heptanone,2-nonone,2,3-butanedione,hexanal,heptanal and decanal,which have oxidative flavor characteristics,increased significantly after 12 weeks of storage.At the same time,taking the degree of fat oxidation and the particle morphology of milk powder as indicators,the changes of sheep milk powder after 12 weeks of storage were analyzed,including the decrease of enzyme activity related to fat oxidation,the increase of peroxide value and acid value.After 12 weeks storage,the diameter of milk fat globules became smaller,the specific surface area increased,and the milk fat was easier to oxidize,resulting in a higher concentration of oxidized flavor substances.From the sixth week,the relative contents of oxidized flavor compounds such as 2-pentanone,2-heptanone,hexanal,and heptanaldehyde were significantly reduced after the addition of antioxidants compared with the control group.With the extension of storage time,the degree of fat oxidation also changed,and the peroxide value,acid value,lipohydrolase enzyme activity,TBARS value gradually changed significantly compared with the control group,and the result of the control group was higher than that of other groups.At the 12 th week,all indicators changed significantly,and the control group was significantly higher than the experimental group.Notably,the peroxide value and TBARS were significantly lower in the VC+VE group compared to the other groups,indicating that the antioxidant effect of VC+VE was better.