title: Microbiological shelf life at different temperatures and fate of Listeria monocytogenes and Escherichia coli inoculated in unflavored and strawberry yogurts.
abstract: Three different trials were performed on unflavored and strawberry yogurts produced in a small-scale dairy plant. In the first trial, the microbiological shelf life of the products was evaluated at 4, 8, and 20°C. At 4°C the product showed low total viable counts until the end of the trial (d 35=3.0±0.7 and 1.5±0.0 log cfu/g in unflavored and strawberry yogurt, respectively). The loads were lower in strawberry yogurt at 4°C compared with unflavored yogurt because of the antimicrobial activity exerted by potassium sorbate present in the fruit puree added. Yeasts were confirmed to be the specific spoilage agents of this product, reaching rapidly high loads with thermal abuse (5.9-7.4 log cfu/g at d 18). In the second trial, Escherichia coli and especially Listeria monocytogenes added at 2 concentrations (2 and 5 log cfu/g) showed a rapid decrease in both types thanks to the acidic conditions provided by the products, but L. monocytogenes was very resistant; its presence was always detected until the end of the period considered (d 68). In the third trial, no statistically significant differences were detected between wild and acid-adapted strains of L. monocytogenes added to the products, due to the quick adaptation that probably occurred after inoculation.
authors.affiliation: Department of Health, Animal Science and Food Safety, Università degli Studi di Milano, Via G. Celoria, 10-20133 Milano, Italy. Electronic address: erica.tirloni@unimi.it.
authors.forename: E
authors.initials: E
authors.lastname: Tirloni
authors.affiliation: Department of Health, Animal Science and Food Safety, Università degli Studi di Milano, Via G. Celoria, 10-20133 Milano, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Bernardi
authors.affiliation: Department of Health, Animal Science and Food Safety, Università degli Studi di Milano, Via G. Celoria, 10-20133 Milano, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Colombo
authors.affiliation: Department of Health, Animal Science and Food Safety, Università degli Studi di Milano, Via G. Celoria, 10-20133 Milano, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Stella
mesh_terms: D000222:Adaptation, Physiological; D004926:Escherichia coli / Q000502:physiology*; D005421:Flavoring Agents / Q000032:analysis; D005519:Food Preservation; D031985:Fragaria / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008089:Listeria monocytogenes / Q000502:physiology*; D013696:Temperature; D015014:Yogurt / Q000382:microbiology*
chemical_list: D005421:Flavoring Agents
keywords: Escherichia coli; Listeria monocytogenes; acid adaptation; survival; yogurt