Research On The Quality And Photooxidation Of Different Kinds Of Milk By Peptidomics

Milk is one of the most important kinds of food,which is closely related to people’s life.The quality and safety of milk is also a common concern of consumers.At this stage,the main problems faced by China’s dairy industry include shoddy milk,such as using other varieties of milk to pass off the high price of Jersey milk.In addition,the photooxidation of milk in processing and marketing stage also seriously reduces the quality of milk and brings food safety risks.In this study,we established a method to identify the adulteration of Jersey milk by using polypeptidomics technology,as well,to find the characteristic markers of photooxidized milk,in order to accurately evaluate the degree of milk photooxidation.The main research contents are as follows:Firstly,based on high performance liquid chromatography-time of flight tandem mass spectrometry,a method for the analysis of polypeptidomics was established.Eighteen brands of milk samples were treated with light.A total of 10 kinds of different peptides were identified.Among them,m/z 529.2783,the most significantly different peptide,could be used as a potential marker of photooxidation of milk.Secondly,based on the peptidomics,the milk differential peptides in Chinese Holstein,Jersey and Uruguay Holstein cows were characterized,and the milk components of different kinds of milk were analyzed.The results showed that the milk protein,milk fat and non fat milk solids in Jersey milk were significantly higher than those in Chinese Holstein milk and Uruguayan Holstein milk（P<0.05）,and the milk protein and non fat milk solids in Chinese Holstein milk were significantly higher than those in Uruguayan Holstein milk（P<0.05）.There were 21 peptides which had common differences among the three dairy cows.Among them,α_S1-casein172-198,α_S1-casein 181-198,α_S1-casein 183-199 andα_S1-casein 180-198 with high content in Jersey milk can be used as potential marker peptides to distinguish Jersey milk from other kinds of milk.Finally,sensory evaluation of different kinds of milk after photooxidation was carried out,and the differential peptides exhibiting photooxidation in different kinds of milk were compared based on peptidomics.The results showed that the oxidation flavor and sunshine flavor of Chinese Holstein milk were significantly higher than those of Jersey milk and Uruguayan Holstein milk after one day of light exposure（P<0.05）,and reached the plateau on the third day.The differential peptides in Chinese Holstein milk,Jersey milk and Uruguayan Holstein milk were two,eight,and three respectively.The peptide m/z 529.2783 in three kinds of milk increased with the increase of light exposure time.Under the condition of the same oxygen content and light intensity,the slowest increment of m/z 529.2783 was in Jersey milk.