Few antifungal protective cultures adapted to fermented dairy products are commercially available because of the numerous constraints linked to their market implementation. Consumer's demand for naturally preserved food products is growing and the utilization of lactic acid bacteria is a promising way to achieve this goal. In this study, using a 2(5-1) factorial fractional design, we first evaluated the effects of fermentation time, of initial sucrose concentration and of the initial contamination amount of a spoilage yeast, on antifungal activities of single and mixed cultures of Lactobacillus rhamnosus K.C8.3.1I and Lactobacillus harbinensis K.V9.3.1Np in yogurt. L. harbinensis K.V9.3.1Np, the most relevant strain with regard to antifungal activity was then studied to determine its minimal inhibitory inoculation rate, its antifungal stability during storage and its impact on yogurt organoleptic properties. We showed that L. harbinensis K.V9.3.1Np maintained a stable antifungal activity over time, which was not affected by initial sucrose, nor by a reduction of the fermentation time. This inhibitory activity was an all-or-nothing phenomenon. Once L. harbinensis K.V9.3.1Np reached a population of ∼ 2.5 × 10(6) cfu/g of yogurt at the time of contamination, total inhibition of the yeast was achieved. We also showed that an inoculation rate of 5 × 10(6) cfu/ml in milk had no detrimental effect on yogurt organoleptic properties. In conclusion, L. harbinensis K.V9.3.1Np is a promising antifungal bioprotective strain for yogurt preservation.

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eThe apparent heat resistance of spores of Bacillus weihenstephanensis and Bacillus licheniformis was measured and expressed as the time to first decimal reduction (␦ value) at a given recovery temperature and pH. Spores of B. weihenstephanensis were produced at 30°C and 12°C, and spores of B. licheniformis were produced at 45°C and 20°C. B. weihenstephanensis spores were then heat treated at 85°C, 90°C, and 95°C, and B. licheniformis spores were heat treated at 95°C, 100°C, and 105°C. Heat-treated spores were grown on nutrient agar at a range of temperatures (4°C to 40°C for B. weihenstephanensis and 15°C to 60°C for B. licheniformis) or a range of pHs (between pH 4.5 and pH 9.5 for both strains). The recovery temperature had a slight effect on the apparent heat resistance, except very near recovery boundaries. In contrast, a decrease in the recovery pH had a progressive impact on apparent heat resistance. A model describing the heat resistance and the ability to recover according to the sporulation temperature, temperature of treatment, and recovery temperature and pH was proposed. This model derived from secondary mathematical models for growth prediction. Previously published cardinal temperature and pH values were used as input parameters. The fitting of the model with apparent heat resistance data obtained for a wide range of spore treatment and recovery conditions was highly satisfactory.T he multiplication of spore-forming bacteria in foods can cause poisoning and/or spoilage. The heat process applied to foods (from mild in cooked and refrigerated foods to very intense in canned or ultrahigh-temperature foods) creates a positive selection of spore-forming species of bacteria because of the high resistance of their spores (1). Therefore, control of spore-forming bacteria in foods first of all requires inactivation of dormant spores by heat (or by any other appropriate inactivation treatment). The extent of inactivation depends on a number of factors, naturally including the inactivation process intensity and more importantly the spore resistance properties at the time of treatment, which may vary with the conditions and environment of sporulation (2). Respect for the organoleptic quality of food may limit the intensity of the process and therefore the extent of spore inactivation. Controlling the recovery of surviving spores in processed food strengthens the safety and stability level achieved after the inactivation process. Recovery is a complex phenomenon, comprising germination of spores, restoration of metabolic activity in suboptimal or favorable conditions and emergence of the first vegetative cell able to multiply. The incubation temperature during storage and food pH are among factors that will deeply influence the recovery of surviving spores (3).Spore recovery is influenced by multiple physical and (bio) chemical factors, such as temperature, pH, and water activity (a w ) and by the presence of germinants (such as amino acids, ribosides, and minerals) or enzymes, such as lysozyme (4,7,8,37). The...