Research On Discrimination Methods Of Different Heat Treatment Milk And Reconstituted Milk

In this study, the contents of lactulose and furosine in milk samples after heat treating in different conditions and adding of reconstituted milk were detected to evaluate the effects of heat process and addition of reconstituted on the heat-sensitive components in milk. The purpose is to discrimine reconstituted milk and over-processed milk in pasteurized milk and ultra high temperature (UHT) sterilization milk. The UHT sterilization milk in different packaging were used to study the effects of storage consitions on the heat-sensitive components in milk, and provide research foundation of the discrimination of reconstituted milk and over-processed milk in pasteurized milk and UHT milk. The results are showed as follows:Trial1Discrimination of reconstituted milk and over-processed milk in pasteurized milkIn this experiment, the contents of lactulose and furosine in milk samples after pasteurizing in different conditions and adding of reconstituted milk were detected to evaluate the effects of heat process and addition of reconstituted on the heat-sensitive components in milk. The purpose is to reveal the relationship between heat process and the heat-sensitive components in milk and to discrimine reconstituted milk and over-processed milk in pasteurized milk. Raw milk was collected and pasteurized (75℃/15s and85℃/15s), over-temperature heat treated (95℃/15s,105℃/15s and115℃/15s), over-time heat treated (85℃/30s and85℃/45s) and added different proportion of reconstituted milk (5%,10%,20%and100%). The contents of lactulose and furosine were detected by enzymic method and high performance liquid chromatography (HPLC) method, respectively. The results showed that lactulose and furosine barely existed in raw milk. The furosine was lower than12mg/100g protein the ratio of lactulose to furosine (L/F) was about1after normal pasteurization. Higher the heating temperature and longer the heating time, the more lactulose and furosine were formed, and the furosine concentration was more than12mg/100g protein. Especially, the content of lactulose significantly increased above90℃. Furthermore, the impact of heat treatment on the content of lactulose was more obvious compared with furosine. Both furosine and lactulose increased linearly with increasing the proportion of reconstituted milk, and the impact of adding reconstituted on the content of furosine was more obvious compared with lactulose. Therefore, we can discrimine reconstituted milk and over-processed milk in pasteurized milk by the furosine concentration and L/F:the content of furosine was less than12mg/100g protein, when the milk was pasteurized from pure raw milk; if the content of furosine was more than12mg/100g protein, it can be considered as over-processed milk when L/F was higher than1, otherwise it could be regarded as reconstituted milk when L/F was less than1.Trial2Discrimination of reconstituted milk and over-processed milk in UHT milkIn this part of study, the contents of lactulose and furosine in milk samples after UHT sterilizating in different conditions and adding of reconstituted milk were detected to evaluate the effects of heat process and addition of reconstituted on the heat-sensitive components in milk. The purpose is to reveal the relationship between heat process and the heat-sensitive components in milk and to discrimine reconstituted milk and over-processed milk in UHT sterilization milk. Raw milk was collected and UHT sterilizated (138℃/4s and140℃/4s), over-temperature heat treated (142℃/4s and144℉/4s), over-time heat treated (140℃/6s and140℃/8s) and added different proportion of reconstituted milk (5%,10%,20%and100%). The contents of lactulose and furosine were detected by enzyme method and HPLC method, respectively. The results showed that the furosine was less than140mg/100g protein the ratio of lactulose to furosine (L/F) was about2after normal UHT sterilization milk. Higher the heating temperature and longer the heating time, the more lactulose and furosine were formed, and the furosine concentration was more than140mg/100g protein. Furthermore, the impact of heat treatment on the content of lactulose was more obvious compared with furosine. Furosine increased with increasing the proportion of reconstituted milk, but the lactulose reduced. Therefore, we can discrimine reconstituted milk and over-processed milk in UHT sterilization milk by the furosine concentration and L/F:the content of furosine was less than140mg/100g protein, when the milk was UHT sterilizated from pure raw milk; if the content of furosine was more than140mg/100g protein, it can be considered as over-processed milk when L/F was higher than2, otherwise it could be regarded as reconstituted milk when L/F was less than2.Trial3Effects of storage conditions on the heat-sensitive components in UHT milk This work aimed to analysis the effect of storage time and storage temperature on the lactulose and furosine in different packing and protein concentration UHT milk. Accurately calculate the increasing amount of them, and applied to identify the presence of reconstituted milk. Tetra Fino, Tetra Brik, Combibloc and Jindian UHT milk samples were collected and stored at4℃, room temperature and37℃for3months. The content of lactulose and furosine were detected every3days in first one month, and about15days in next two months. The results showed that the daily increasement of lactulose and furosine in UHT milk increased with extending the storage time and improving the storage temperature. Different packing and protein concentration influence the daily increasement of lactulose and furosine.