Changes Of Heat Indicators And Functional Proteins In Milk Under Various Heat Treatments

Bovine milk contains many ingredients which are important for human health.But milk is doomed to be subject to heat treatments before it goes into the market.Under heat treatments,many useful ingredients degrade.Therefore,many researchers found out various indicators to indicate various heat treatments,among these indicators,furosine,lactulose,α-lactoalbumin andβ-lactoglobulin are wildly used indicators.Besides,α-lactoalbumin,β-lactoglobulin and lactoferrin are also important functional whey proteins in milk.The aim of this study is to investigate the changes and relationship of heat indicators and functional proteins in milk under various heat treatments,and to evaluated commercial various types of milk purchased from China supermarket.Experiment 1:A method for determining native lactoferrin in milk using HiTrap Heparin HP column coupled with HPLC was developed and validated in this part.The conditions for enrichment of lactoferrin in milk using HiTrap Heparin HP were optimized.A linear range from 2 to 100 mg/L of lactoferrin standards was obtained,with a value of R~2 equal to 0.9989.The limit of detection(LOD)and quantification(LOQ)for detection of lactoferrin standard were 2.00 and 6.67 mg/L,respectively;and considering the enrichment factor involved in the pre-treatment procedures,LOD and LOQ for detection of milk sample were 0.57 and 1.90 mg/L,respectively.In addition,results of determination of milk samples spiked with lactoferrin at three concentration levels(2,5 and 10 mg/L)showed that overall mean recovery were 88.3%,90.2%and 95.1%,respectively.Relative standard deviation of intra-day and inter-day precision was 1.3%~4.8%,and 2.1%~5.7%,respectively,demonstrating good performances of the proposed method was obtained.In addition,quantification of lactoferrin in raw milk and processed milk using this method displayed the usefulness and effectiveness of the proposed method.Experiment 2:Raw milk samples were heated under 60℃/15 s,65℃/15 s,70℃/15 s,75℃/15 s,80℃/15 s,85℃/15 s,90℃/15 s,95℃/15 s,100℃/15 s,105℃/15 s,110℃/15 s,115℃/15 s,120℃/15 s,and135℃,137℃,139℃,141℃,143℃,145℃for 4 or 5 s.Then,furosine,lactulose,lactoferrin,α-lactoalbumin andβ-lactoglobulin in raw and processed milk samples were determined.Results showed that the severer heat treatment employed to raw milk,the more furosine and lactulose will be contained in processed milk samples and the more degradation of lactoferrin,α-lactoalbumin andβ-lactoglobulin took place in processed milk samples.In addition,the concentration ofα-lactoalbumin strongly correlated to that of furosine and lactulose in milk samples processed under 60℃~120℃.However,the concentration ofβ-lactoglobulin strongly correlated to that of furosine and lactulose in milk samples processed under 135℃~145℃.This experiment provide much information which could be helpful to direct the production of milk and dairy products.Experiment 3:94 domestic brand UHT milk,55 abroad brand UHT milk and 8 abroad brand pasteurized milk were collected from both northern and southern part of China.Furosine,lactulose,lactoferrin,α-lactoalbumin andβ-lactoglobulin in these commercial milk samples were determined.Results showed that there was no significant difference between at home and abroad brand UHT milk from the perspective ofα-lactoalbumin,lactulose and furosine.However,abroad brand UHT milk has significantly higher concentration ofβ-lactoglobulin,and exhibited great discrepancy between theses analysed milk samples from the comprehensive perspective.In addition,there was no significant difference between at home and abroad brand UHT milk from the perspective of lactulose and lactoferrin.However,abroad brand UHT milk has significantly higher concentration of furosine,and much lessα-lactoalbumin andβ-lactoglobulin.Therefore,abroad brand UHT milk may underwent severer heat treatments than that of domestic brand milk.This may also be indicated by longer shelflife of abroad brand milk.Thus,we conclude that the quality of domestic brand UHT milk is better than abroad brand milk because they have more functional ingredient alive and less heat by-products.Although pasteurized milk has much more functional ingredients and is regarded as high quality milk.But there is small market share of pasteurized milk.Therefore,we should improve the market share of pasteurized milk and guide consumers to consume pasteurized milk if conditions permit.