Study On Raw Milk Flavor Profile And Influenced Factors

Sensory quality is one of the main drivers of consumer preference.All technical treatments applied in the dairy production process are designed to ensure that consumers have received to safe and high-quality products,and the volatility and non-volatile components in raw milk determine the aroma and taste of the final product.In order to evaluate the sensory quality of milk scientifically,it is necessary to fully understand the composition and characteristics of raw milk flavor.However,due to the differences and limitations of detection methods,it is difficult to meet the testing requirements for the diversity and complexity of volatile organic compounds in milk,which restricts the systematic study of milk flavors.The purpose of this study is to establish a high-throughput detection method,analyze the composition and characteristics of flavor substances in raw milk comprehensively and systematically,and construct a basic database and fingerprint of raw milk flavor.The effects of geographical location,sampling season,feeding system and health status on the flavor of raw milk were further explored.Differences between these data and some potential linkages have been identified to assess the quality of raw milk.Trial I: A high-throughput method for the determination of milk flavor.Headspace Solid-Phase Microextraction(HS-SPME)as a pretreatment method to enrich volatile organic compounds,combined with gas chromatography-mass spectrometer(GC-MS)for separation and identification,and then quantitative flavor substances.According to the specificity of raw milk,the pretreatment conditions and instrument parameters were optimized,and the optimal parameters were determined,which improved the enrichment effect and chromatographic resolution of volatile organic compounds in raw milk and increased the applicability and accuracy of the method.It can quantify volatile organic compounds in raw milk comprehensively,including acids,aldehydes,esters,alcohols,sulfurs,nitrogenous,heterocyclics,etc.Trial II: Effect of geographical origin on raw milk flavor.This trial explored differences in taste and aroma in raw milk from different geographical origins.Twenty-four medium-and large-scale dairy pastures were selected in 19 cities in China to collect raw milk samples from Holstein cows for two consecutive days.The fragrance composition and taste properties of raw milk were evaluated in combination with chromatography and intelligent sensory technology.The electronic nose’s W6S(sensitivity to hydrogen)and W3S(sensitivity to long-chain alkanes)sensors of the electronic nose play a major differentiating role.The taste attribute results showed that raw milk from northern regions was significantly higher in saltiness and richness than in southern(P < 0.05),while raw milk samples from southern showed prominence in bitterness(P < 0.01).Stoichiometric results show that Pyridine,Nonanal,Dodecane,Furfuraldehyde,1-Decyne,octanoic acid and 1,35.7-cyclooctane are characteristic components of the difference between the flavor of raw milk in the north and south.For the traceability of milk production sites,taste properties have more discriminating potential than aroma.Trial III.: Effect of sampling season on flavor of raw milkThis trial explored the differences in the aroma of raw milk collected from different seasons.Nine farms in nine cities were selected in China to collect raw milk samples from Holstein cattle for two consecutive days each quarter.The electronic nose was used to detect the overall aroma characteristics,and the electronic tongue was used to detect the taste attributes of raw milk.Stoichiometric results show that the application of intelligent sensory technology to distinguish raw milk in different sampling seasons is effective and feasible.Both sampling seasonality and geographical origin had significant effects on the flavor of raw milk(P <0.05),but season was a more decisive factor.Trial IV: Effect of Dairy Feeding System on Raw Milk FlavorThis trial explored the differences in the taste and aroma of raw milk in dairy cows under different feeding systems.Raw milk in the indoor feeding mode and grazing mode of pasture was collected in the same area at the same time.The overall aroma characteristics and taste properties of raw milk were evaluated by electronic nose and electronic tongue,and the detection method based on HS-SPME/GC-MS was used to characterize and quantify volatile organic compounds.Stoichiometric results showed that 13 volatiles were identified in the raw milk of cows fed intensively on pasture,and 12 volatiles were identified in the raw milk of dairy cows in grazing system,and some of the compounds were duplicated,but the content was different.W1S(sensitive to methane),W2S(sensitive to ethanol),and W5S(with a broad-spectrum response and sensitive to nitrogen oxides)Sensors made a major contribution to distinguishing the two groups of samples.The astringency,bitterness,sourness,and richness of raw milk in grazing system were significantly different from those in the indoor feeding system(P < 0.05).Oxime-,methoxy-phenyl,Octadecanoic acid,Furfural and Dodecanoic acid are characteristic components of raw milk in grazing system.The content of raw milk2-Nonone,Heptanoic acid and Decanoic acid in pasture intensive feeding mode is higher.And through Person correlation analysis,these volatile organic compounds were significantly associated with key sensors of electronic sensory technology.Electronic nose,electronic tongue and HS-SPME/GC-MS were used to distinguish raw milk from different feeding system sources,and the discrimination results were reliable,and the methods were effective and feasible.Trial V: Effect of ketosis on raw milk flavorThis experiment investigated the differences in taste and odor in raw milk of ketotic and healthy cows.The results of routine and biochemical parameters showed that ketosis cows and healthy cows had differences in neutrophil percentage(NEU),lymphocyte percentage(LYMPH),mean platelet volume(MPV),platelet somatic distribution width(PDW),medium fluorescence intensity reticulocyte ratio(MFR),total bilirubin(TBIL),direct bilirubin(DBIL),glucose(GLU),bile acids(TBA),creatine kinase(CK),β-hydroxybutyric acid(HBA),total cholesterol(CHOL)and triglycerides(TG)indices were highly significant(P <0.01).Chemometric results showed that the W1W(sensitive to sulfur-containing compounds)and W5C(sensitive to alkanes and aromatic compounds)sensors of electronic nose were the main contributing sensors.Taste attributes were analyzed based on Partial Least Squares Discriminant Analysis(PLS-DA)model and Variable Important for the Projection(VIP)analysis values for acidity,freshness richness,astringency and astringent aftertaste(VIP >1)played an important role.Non-target metabolism showed that 142 species showed significant differences(P < 0.05)in positive ion mode and 118 in negative ion mode(P < 0.05).Based on the PLS-DA model,two significant enrichment pathways(P < 0.05)were screened: glutathione metabolism,vitamin digestion and absorption.A total of 566 different metabolites were identified in positive and negative ion patterns in liposome analysis,with more than half coming from GP(Glycerophospholipid),PC(Phosphatidylcholines),PE(Phosphatidylethanolamines),PG(Phosphatidylglycerols),PA(Phosphatidic acids)and PS(glyceryl serine)subclass.No significant enrichment pathways were found.In summary,a high-throughput non-targeted detection method based on GC-MS was established for the determination of volatile organic compounds in raw milk,which provided a technical means for the systematic description of the microscopic composition of milk.A comprehensive analysis of the flavor composition and characteristics of raw milk was carried out by combining chromatographic techniques and intelligent sensory techniques,and a basic database and fingerprint of raw milk flavor was constructed.The flavor study of raw milk is applied to geographical traceability,characteristic product identification,authenticity identification and cow health monitoring,and the method is effective and feasible.This study aims to provide data support for the regulation of animal feed and the improvement of milk product quality in a more scientific and systematic manner,so as to provide a basis for protecting the inherent flavor of raw milk and controlling bad flavor.