Study On Recognition Of Reconstituted Milk And Photo-oxidation Of Milk Based On Omics Technology

Milk has been become one of the fastest growing per capita consumption food products.In recent years,the dairy industry has shown rapid development and broad market prospects,but a series of dairy quality and safety incidents have seriously threatened the consumers'health and dairy market.Although milk production has been increasing,the supply of raw milk is still in short supply.Some illegal vendors use reconstituted milk to blend into liquid milk for sale without labeling,which continuously impact the raw milk market in China.However,the existing detection methods are relatively single,complex,low identification capacity,and unable to high throughput detection.Therefore,it is vital important to establish a comprehensive and efficient method to identify reconstituted milk.On the other hand,as consumers'demand for the quality and aesthetic of dairy product,more and more transparent packagings causing milk photo-oxidation problem,which lead to off-flavors and deteriorating milk nutrition.However,the mechanism of milk photo oxidation is not clear,and the method to evaluate photo-oxidation level has not been widely reported,so it is very necessary to establish a comprehensive and efficient method for evaluating the photo-oxidation level.Therefore,the establishment of the identification method of reconstituted milk and ultra-high temperature sterilized milk(UHT)and the construction of milk photooxidation evaluation index system based on omics technology are valuable for controlling the quality of raw milk,optimizing product design,and ensuring the safety of milk quality.The main contents and results as follows:Firstly,an untargeted metabolomics approach that used ultra-performance liquid chromatography quadrupole time-of light mass spectrometry(UPLC–Q-TOF-MS)was established to discover 60biomarkers that could be used to classify UHT milk and reconstituted milk.Based on the screened differential metabolites,a targeted metabolomics method was established to achieve high-throughput analysis of liquid milk,and to detect the actual blended reconstituted milk samples.The results showed that the method and model could identify the lowest blend of reconstituted milk with the mixing ratio reaching 10%.Secondly,through hierarchical cluster analysis,it was found that the reconstituted milk had a greater loss of peptides,lipids and nucleotides than UHT milk.This result provideed a new technology and data support for realizing the identification of reconstituted milk blending and ensuring the quality of raw milk.Secondly,an untargeted peptides omics technology was established using UPLC–Q-TOF-MS,33significantly different peptides were finally discovered and identified,of which 11 peptides were derived from?s1-casein and 22 peptides were derived from?-casein.It is found that these peptides were all related to the heating temperature though thermal processing experiments and storage period experiments.Peptides derived from?-casein were mainly associated with cathepsin hydrolysis,and showed a significant increase during the storage period.The peptides derived from?_s1-casein were mostly caused by thermal processing,and there was no obvious difference in the milk storage process for ten weeks.These peptides could be used to evaluate the storage period of the milk and the level of thermal processing technology.Metabolomics and peptide omics played important roles in the identification of reconstituted milk adulteration.Finally,an untargeted metabolomics method based on UPLC-QTOF mass and multivariate data analysis was used to figure out the characteristic metabolites and how they were affected by oxygen exposure and light intensity.Four products,i.e.,indole-3-carboxaldehyde,uric acid,lumichrome,and riboflavin,identified as biomarkers.Afterwards,the effects of oxygen content and light intensity on the biomarkers and the sensory evaluation were investigated.Studies have found that light and oxygen were the necessary factors leading to the occurrence of milk photo-oxidation,the content of oxygen determines the degree of milk photo-oxidation,while light intensity determines the rate of milk photo-oxidation occurrence.Both oxygen exposure and light intensity influenced the content of photo oxidation biomarkers in milk samples.The degradation of uric acid was related to the oxidation of singlet oxygen,which was a good antioxidant in milk.The indole-3-formaldehyde was related to the photooxidation of tryptophan and the correlation of sensory evaluation(r>0.87),and was one of the important indicators for evaluating milk photooxidation.As an important photosensitizer in milk,riboflavin induces milk photooxidation.Therefore,this result provided a new reference and theoretical support for evaluating the level of milk photooxidation and understanding the mechanism of photooxidation.