Survival of Escherichia coli O157:H7 during manufacture and storage of traditional and low lactose yogurt Camila Sampaio Cutrim a, * , Raphael Ferreira de Barros a , Marion Pereira da Costa b , Robson Maia Franco c , Carlos Adam Conte-Junior b , Marco Antonio Sloboda Cortez a a Laboratory of Technology of Milk and Milk Products, Food Technology Department, Facultyof Veterinary Medicine, Fluminense Federal University, 24230- 340, Niter oi, Rio de Janeiro, Brazil b Laboratory of Physicochemical Control of Animal Products, Food Technology Department, Faculty of Veterinary Medicine, Fluminense Federal University, 24230-340, Niter oi, Rio de Janeiro, Brazil c Laboratory of Microbiological Control of Animal Products, Food Technology Department, Faculty of Veterinary Medicine, Fluminense Federal University, 24230-340, Niter oi, Rio de Janeiro, Brazil article info Article history: Received 29 November 2015 Received in revised form 12 February 2016 Accepted 19 February 2016 Available online 26 February 2016 Keywords: Fermented milk Lactic acid bacteria b-Galactosidase Lactose hydrolysis HPLC-RID-DAD Chemical compounds studied in this article: Lactose (PubChem CID:440995) Glucose (PubChem CID:5793) Galactose (PubChem CID:6036) Lactic acid (PubChem CID:612) abstract 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 mL  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. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction The most popular fermented dairy product is yogurt and its consumption is increasing worldwide (Shiby & Mishra, 2013). Ac- cording to the Codex (2011) standard for fermented milks, yogurt is a fermented milk characterized by fermentation using specific acid lactic cultures Streptococcus thermophilus and Lactobacillus del- brueckii subsp. bulgaricus, that perform three major biochemical conversions of milk components: conversion of lactose into lactic acid, proteolysis of caseins into peptides and free amino acids and lipolysis of milk fat into free fatty acids (Smit, Smit, & Engels, 2005). Yogurts are one of dairy products that are perceive as healthy by consumers and had the largest relative importance as carrier of functional ingredients in comparison with non dairy sources (Vecchio & Annuziata, 2013). The utilization of probiotic bacteria and prebiotics are two of the most import technologies in func- tional food processing and its use results in benefit to consumers health, but it is still a challenge for the food industry, requiring the understanding of factors intrinsic and extrinsic to processing (Granato, Branco, Cruz, Faria, & Shah, 2010). Some new technologies have been researched to enhance the dairy products quality like the utilization of chemometric tech- niques to discriminate yogurts (Batista et al., 2015) and the addition of glucose oxidase, which main function is to minimize oxidative stress and increase viability of probiotic cultures (Cruz et al., 2013). Despite of these new technologies, a well known technology has been improved because of the large number of consumers with lactose intolerance worldwide and it became a huge niche market to dairy industry. The development of dairy products with reduced lactose content is increasing, especially in Brazil and there are many * Corresponding author. E-mail address: camila.cutrim@yahoo.com.br (C.S. Cutrim). Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt http://dx.doi.org/10.1016/j.lwt.2016.02.047 0023-6438/© 2016 Elsevier Ltd. All rights reserved. LWT- Food Science and Technology 70 (2016) 178e184