Effects Of Different Heating Conditions And Addition Of Reconstituted Milk On The Heat Indices In The Milk

The purpose of the present study was to evaluate the effect of heat treatment and reconstituted milk on the heat induced indices (lactulose, furosine, beta-lactoglobulin and lactoperoxidase) in milk. The raw milk and composite milk (raw milk plus 75% reconstituted milk) were heated after 65℃/15s,75℃/15s,85℃/15s,95℃/15s, 105℃/15s and 115℃/15s using laboratory-scale tubular heat-exchanger system respectively, then the concentrations of lactulose, furosine and beta-lactoglobulin and the lactoperoxidase activity were determinated and the relations beteewn these heat induced indicators have been discussed.It is shown that the lactulose and furosine contents increased with higher temperature, especially above 95℃in the raw milk; while the beta-lactoglobulin content and the lactoperoxidase activity decreased with higher temperature, the beta-lactoglobulin content decreased steeply at 85℃and inactiviation of lactoperoxidase occurred when milk was heated above 85℃. Additionally, addition of reconstituted milk increased the contents of lactulose and furosine in the milk, the contents of lactulose and furosine in the composite milk were higher than of that in the raw milk from 65 to 95℃. The reduction of the beta-lactoglobulin concentration became noticeable after adding reconstituted milk and only 0.07 mg/mL beta-lactoglobulin could be detected in composite milk when it was heated at 105℃for 15 s, the content of beta-lactoglobulin was not detected in the reconstituted milk used in this study.The lactoperoxidase activity decreased (P<0.05) in the presence of the reconstituted milk, and it inactivitied at 85℃of heating temperature. The correlation between the contents of lactulose and furosine of the milk samples was appeared to be a straight line (R2=0.98), whereas no straight linear correlation was observed between the contents of lactulose and furosine in the pasteurized composite milk samples. The ratios of lactulose to furosine in composite pasteurized milk were higher than that in pasteurized milk, the ratio between the levels of lactulose and furosine will be allowed the presence of reconstituted milk to be detected in pasteurized milk.It is concluded that lactulose, furosine and beta-lactoglobulin are suit for evaluating the heat treatments in high pasteurized milk as well as lactoperoxidase can monitor the mild heat treatments. Moreover, the useful information for authenticating the presence of reconstituted milk in raw milk or pasteurized milk was provided.