Study On Differences Of Fatty Acids And Tryptophan Metabolites In Milk Products With Different Processing Technology

In recent years,people pay more attention on food quality and nutrition.Milk was regarded as a necessity of the daily life,it's quality evaluation plays an important role in insuring human health.Milk contains six major nutrients,but also contains biologically active substances such as bioactive peptides and tryptophan.Fatty acids,a kind of heat-sensitive substance,the content and type are susceptible to temperature.Tryptophan and its metabolites have received much attention because of the biological functions,but their distribution,content,detection methods in different milk have not been fully reported.Thus,the study of fatty acids and tryptophan metabolites in different milk products has great significance in the nutritional evaluation.In this study,the ~1H NMR was used for detecting the contents of fatty acids;and high-performance liquid chromatography-tandem mass spectrometry was used for detecting the levels of tryptophan and twelve metabolites in four types milk produced by different processes.With a view to providing data and a new method for the nutritional evaluation of milk.The research contents are as follows.The difference of fatty acids'contents in UHT and reconstituted milk were studied by using ~1H NMR.In the UHT and reconstituted milk,the contents of linolenic acid were(0.98±0.11)%,(0.90±0.04)%;the linoleic acid contents were(1.15±0.36)%and(1.11±0.36)%;the oleic acid contents were(27.30±0.56)%and(26.78±0.78)%,respectively.The contents of saturated fatty acids were(43.26±1.56)%and(43.81±2.34)%.In addition,The OPLS-DA and Student's t-test were used to further analyze the difference of fatty acids in the two kinds of milk,and the nutritional levels were evaluated.A method was developed for detecting the levels of tryptophan and twelve metabolites in milk.The analytes were extracted by using the QuEChERS procedure and were analyzed by liquid chromatography-tandem mass spectrometry(LC-MS/MS).The final detection method was determined by optimizing sample preparation and LC-MS/MS conditions.The proposed method resulted in suitable accuracy(RSD?10.31%)and high sensitivity(the LOQs were between 0.05-5 ng/mL).The recoveries were in the range of44.67%-126.78%.The developed method was successfully applied to compare the content of tryptophan and metabolites in four milk products produced by different processes,i.e.,pasteurized milk,UHT milk,milk powder and yogurt.The tryptophan contents in 4 types of milk were between 8896.70-11771.40 ng/100mL;the kynurenine(KYN)content in UHT milk was the lowest(56.25±13.69 ng/100 mL);the kynurenine acid(KA)content was the lowest in pasteurized milk(103.95±5.36 ng/100 mL);the content of metabolites in the indole pathway was higher in yogurt than in the others.In addition,the PLS-DA was carried out on the four types of milk by using nine compounds with significant differences in content,and then the nutritions were evaluated.