title: The combined effect of pasteurization intensity, water activity, pH and incubation temperature on the survival and outgrowth of spores of Bacillus cereus and Bacillus pumilus in artificial media and food products.
abstract: The objective of the study was to evaluate the combined effects of pasteurization intensity (no heat treatment and 10 min at 70, 80 and 90 °C), water activity (aw) (0.960-0.990), pH (5.5-7.0) and storage temperature (7 and 10 °C) on the survival and outgrowth of psychrotolerant spores of Bacillus cereus FF119b and Bacillus pumilus FF128a. The experiments were performed in both artificial media and a validation was performed on real food products (cream, béchamel sauce and mixed vegetable soup). It was determined that in general, heat treatments of 10 min at 70 °C or 80 °C activated the spores of both B. cereus FF119b and B. pumilus FF128a, resulting in faster outgrowth compared to native (non-heat treated) spores. A pasteurization treatment of 10 min at 90 °C generally resulted in the longest lag periods before outgrowth of both isolates. Some of the spores were inactivated by this heat treatment, with more inactivation being observed the lower the pH value of the heating medium. Despite this, it was also observed that under some conditions the remaining (surviving) spores were actually activated as their outgrowth took place after a shorter period of time compared to native non-heated spores. While the response of B. cereus FF119b to the pasteurization intensity in cream and béchamel sauce was similar to the trends observed in the artificial media at 10 °C, in difference, outgrowth was only observed at 7 °C in both products when the spores had been heated for 10 min at 80 °C. Moreover, no inactivation was observed in cream or béchamel sauce when the spores were heated for 10 min at 90 °C in these two products. This was attributed to the protective effect of fat in the cream and the ingredients in the béchamel sauce. The study provides some insight into the potential microbial (stability and safety) consequences of the current trend towards milder heat treatments which is being pursued in the food industry.
authors.affiliation: Laboratory of Food Microbiology and Food Preservation, Department of Food Safety and Food Quality, Faculty of Bioscience Engineering, Ghent University, Member of Food2Know, Coupure Links 653, 9000 Gent, Belgium. Electronic address: Simbarashe.Samapundo@UGent.be.
authors.forename: S
authors.initials: S
authors.lastname: Samapundo
authors.affiliation: Institute of Agricultural and Fisheries Research, Technology and Food Sciences Unit, Member of Food2Know, Brusselsesteenweg 370, 9090 Melle, Belgium.
authors.forename: M
authors.initials: M
authors.lastname: Heyndrickx
authors.affiliation: Laboratory of Food Microbiology and Food Preservation, Department of Food Safety and Food Quality, Faculty of Bioscience Engineering, Ghent University, Member of Food2Know, Coupure Links 653, 9000 Gent, Belgium.
authors.forename: R
authors.initials: R
authors.lastname: Xhaferi
authors.affiliation: Laboratory of Food Microbiology and Food Preservation, Department of Food Safety and Food Quality, Faculty of Bioscience Engineering, Ghent University, Member of Food2Know, Coupure Links 653, 9000 Gent, Belgium.
authors.forename: I
authors.initials: I
authors.lastname: de Baenst
authors.affiliation: Laboratory of Food Microbiology and Food Preservation, Department of Food Safety and Food Quality, Faculty of Bioscience Engineering, Ghent University, Member of Food2Know, Coupure Links 653, 9000 Gent, Belgium.
authors.forename: F
authors.initials: F
authors.lastname: Devlieghere
mesh_terms: D001407:Bacillus / Q000502:physiology*; D001409:Bacillus cereus / Q000502:physiology*; D005511:Food Handling / Q000592:standards*; D005516:Food Microbiology; D006863:Hydrogen-Ion Concentration; D050296:Microbial Viability; D061352:Pasteurization; D013171:Spores, Bacterial / Q000502:physiology*; D013696:Temperature; D013995:Time; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water
keywords: Activation; Béchamel sauce; Cream; Heat treatment; Spore-formers; Vegetable soup