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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With the goal of developing a defined medium for the production of desiccation-tolerant blastospores of the bioinsecticidal fungus Paecilomyces fumosoroseus, we evaluated the impact of various media components such as amino acids, carbohydrates, trace metals and vitamins on hyphal growth and sporulation of P. fumosoroseus cultures and on the freeze-drying tolerance of blastospores produced under these conditions. A comparison of 13 amino acids as sole nitrogen sources showed that glutamate, aspartate, glycine and arginine supported biomass accumulations (12-16 mg ml-1) and blastospore yields (6-11 x 108 blastospores ml-1) comparable to our standard production medium which contains casamino acids as the nitrogen source. Using glutamate as the sole nitrogen source, tests with various carbohydrates showed that P. fumosoroseus grew best on glucose (18.8 mg biomass ml-1) but produced similar blastospore concentrations (7.3-11.0 x 108) when grown with glucose, glycerol, fructose or sucrose. P. fumosoroseus cultures grown in media with sodium citrate or galactose as the sole carbohydrate produced lower blastospore concentrations but more-desiccation-tolerant spores. Zinc was the only trace metal tested that was required for optimal growth and sporulation. In a defined medium with glutamate as the nitrogen source, vitamins were unnecessary for P. fumosoroseus growth or sporulation. When blastospores were freeze-dried in the absence of a suspension medium, residual glucose (>2.5% w/v) was required for enhanced spore survival. Thus, a defined medium containing basal salts, glucose, glutamate and zinc can be used to produce optimal concentrations of desiccation-tolerant blastospores of P. fumosoroseus.

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Conidia of seven Trichoderma strains were applied on cucumber or radish seeds as a simple methyl cellulose coating or through an industrial film coating process. The seeds were sown in a peat-based soil artificially infested by R. solani or P. ultimum. Four strains controlled damping-off caused by R. solani when applied as a simple coating or as an industrial film-coating. Also, four strains significantly reduced damping-off caused by P. ultimum in cucumber. A correlation was found between production of volatile antibiotics in vitro and control of P. ultimum. Survival during storage varied according to the strain. Better survival was observed for two strains, with a decrease in conidial viability of one order of magnitude after storage for three and five months at 15 o C and 4 o C, respectively. The results show the feasibility of biocontrol of seedling diseases by some antagonists applied onto seeds through an industrial film-coating process.

The impact of growing cultures of Paecilomyces fumosoroseus in liquid media containing four combinations of glucose and casamino acids (8 g l(-1) or 80 g l(-1) glucose, 1.32 g l(-1) or 13.2 g l(-1) casamino acids) was evaluated, based on blastospore production, germination rate, viability after freeze-drying and short-term storage stability. When blastospores were produced using a high casamino acid concentration, blastospore yields and germination rates were significantly higher (13.2-18.5 x 10(7) blastospores ml(-1), 50-60% germination after 4 h), compared to cultures grown in media containing lower casamino acid concentrations (0.4-2.3 x 10(7) blastospores ml(-1), 10-20% germination after 4 h). Chemical analyses of blastospore composition showed that accelerated blastospore germination may be related to increased proteinaceous reserves rather than to glycogen or lipid accumulation. Tolerance to freeze-drying by blastospores suspended in spent medium was enhanced by a high initial casamino acid concentration in the culture medium (75% survival) and by the residual glucose concentrations in the spent medium. Under the conditions of this study, the storage stability of blastospores of P. fumosoroseus was unaffected by the nutritional condition in which they were produced.

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Summary — To improve the production of Bradyrhizobium japonicum in liquid culture media, different carbon and nitrogen substrates at different concentrations were tested. In order to study simultaneously these qualitative and quantitative factors, a suitable experimental design was necessary. We develop here the principle leading to such fractional factorial designs. The specific design used allowed us to decrease the theoretical number of treatments from 1 024 to 128 and to get estimates of factorial main effects and 2-factor interactions. Five of the 7 tested factors, pH, carbon and organic nitrogen sources, yeast extract concentration and organic nitrogen concentration, were found to have a significant effect on optical density. They also were found to interact with each other. The design allowed us to select 2 media that produced more than 10 10 bacteria/ml.