Effect of TBC of raw milk and thermal treatment intensity on endotoxin contents of milk products

Abstract Endotoxin in dairy products may pose risks to consumers’ health, but the effects of raw-milk total bacterial count (TBC) and thermal treatment temperature on endotoxin content of dairy products are not clear. In this study, TBC of raw milk and processed milk with different thermal treatment temperatures were detected by pilot processing experiment. We then verified it by detecting the endotoxin content of commercial dairy products. TBC was determined by conventional culture method, and the changes in alkaline phosphatase (ALP) and lactoperoxidase (LPO) activities in bovine milk before and after heat treatment were determined. The levels of fatty acids in bovine milk were detected by gas chromatography using a flame ionization detector (GC-FID). In the pilot experiment, raw milk was treated at 72, 75, 80, 85, 90, 95, 100, 105, 110, 115, and 120 ℃ for 15 s. After that, the raw milk was stored at 20 ℃ for 24 hours and 48 hours to greatly increase the TBC, and treated at 75 ℃ for 15 s and 90 ℃ for 15 s. The results show that the endotoxin content of sterilized milk increased with the increase in TBC and thermal treatment temperature. With the increase in thermal treatment temperature, the activities of ALP and LPO with endotoxin inhibition decreased. In addition, a total of 226 dairy samples were tested. The endotoxin content of 37 commercial PM milk samples were 6 EU/ml to 231 EU/ml, with 31 EU/ml to 1437 EU/ml for 40 commercial UHT milk samples, and 6 EU/ml to 9080 EU/ml for 149 reconstituted IFM samples. There was a significant difference in the endotoxin content of different dairy products (P 0.05). This study found that TBC and thermal treatment temperature of raw milk could affect the endotoxin content of dairy products.