Survival of Escherichia coli O157:H7 during manufacture and storage of traditional and low lactose yogurt

Yogurt has been considered safe due to its low pH, although recent researchers have demonstrated the survival of Escherichia coli O157:H7 in dairy products. In this context, the aim of the study was to verify survival of E. coli O157:H7 in yogurts with different lactose content. Six different yogurts were prepared: Traditional yogurt (TY); Pre hydrolyzed yogurt (PHY); Lactose free yogurt (LFY); Traditional inoculated yogurt (TIY); Pre hydrolyzed inoculated yogurt (PHIY); and Lactose free inoculated yogurt (LFIY). Three of them were inoculated with E. coli O157:H7 (TIY, PHIY and LFIY). The survival of E. coli, carbohydrates, lactic acid and pH of yogurts were determined during fermentation and storage. HPLC showed lactose content of 3.13, 0.47, 0.27, 3.02, 0.22 and 0.44 g.100 L-1 after 24 h of storage for TY, PHY, LFY, TIY, PHIY and LFIY respectively. It was also observed that E. coli counts decreased during fermentation and that E. coli was able to survive for 10 days in TIY and PHIY, and for 22 days in LFIY. LAB counts were with minimum of 7 log cfu g(-1) in all groups. These results suggest that contamination by E. coli O157:H7 before fermentation increases its survival, especially in lactose free milk. (C) 2016 Elsevier Ltd. All rights reserved.