title: Influence of pH, type of acid and recovery media on the thermal inactivation of Listeria innocua.
abstract: Acidification of foods with organic acids, either by fermentation or by intentional addition, is an important and common mechanism for controlling foodborne pathogens in a diversity of food products. The objective of this work was to study thermal inactivation of Listeria innocua, an acid tolerant microorganism, at 52.5, 60.0 and 65.0 degrees C, at different pH values (4.5, 6.0 and 7.5), using three types of acid (lactic, acetic and hydrochloric) and three different plating media (Tryptic Soy Agar with 0.6% yeast extract-TSAYE; TSAYE plus 5% NaCl-TSAYE+5%NaCl; and Palcam Agar with selective supplement-Palcam Agar), according to a 3(4) factorial experimental design. Survival data experimentally obtained were fitted with a Gompertz-inspired model and kinetic parameters (shoulder, maximum inactivation rate-k(max), and tail) were estimated for all conditions considered. The influence of temperature, pH, type of acid and enumeration media on kinetic parameters was assessed. Results showed that, with the exception of the type of acid, all the remaining factors and their combinations significantly affected the shoulder period and k(max). In relation to tail, temperature and recovery media were the affectable factors. It was concluded that the survival of this bacteria is higher when combining low temperature with neutral pH, and when TSAYE is the enumeration medium. Bigelow-inspired models were successfully developed and describe accurately the temperature and pH effects on the kinetic parameters.
authors.affiliation: CBQF, Universidade Católica Portuguesa, Rua Dr. António Bernardino de Almeida, Porto, Portugal.
authors.forename: Fátima A
authors.initials: FA
authors.lastname: Miller
authors.forename: Bárbara
authors.initials: B
authors.lastname: Ramos
authors.forename: Maria M
authors.initials: MM
authors.lastname: Gil
authors.forename: Teresa R S
authors.initials: TR
authors.lastname: Brandão
authors.forename: Paula
authors.initials: P
authors.lastname: Teixeira
authors.forename: Cristina L M
authors.initials: CL
authors.lastname: Silva
mesh_terms: D000143:Acids / Q000494:pharmacology*; D000362:Agar; D003470:Culture Media; D005506:Food Contamination / Q000517:prevention & control; D005516:Food Microbiology; D006358:Hot Temperature; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008087:Listeria / Q000254:growth & development*; D050296:Microbial Viability / Q000187:drug effects; D008954:Models, Biological; D012965:Sodium Chloride / Q000494:pharmacology; D013025:Glycine max; D015003:Yeasts
chemical_list: D000143:Acids; D003470:Culture Media; D012965:Sodium Chloride; D000362:Agar