Industrially, the sensitivity of acetic acid bacteria (AAB) to the high temperatures and the high ethanol concentrations is the major concerns for manufacturers. This study was conceived and designed to isolate and identify new thermo-and ethanol-tolerant AAB from Opuntia ficus-indica L. fruits. As a result, among 140 isolated bacterial strains, five selected strains (CR1, CR5, CR23, CZ2, and CZ15) exhibited important acetic acid production until 40°C. The use of 16S rDNA gene analysis was insufficient to identify selected bacteria. Indeed, except CR5 that presented 100% similarity to A. cerevisiae, the other strains presented similar homology rates simultaneously to the 16S rDNA sequences of A. cerevisiae and A. malorum. The reidentification by 16S-23S rDNA gene sequencing showed that CR1, CR23, and CZ15 were A. malorum, which were shown tolerance to the highest concentration of ethanol (12%) and produced elevated amount (40 g/L) of acetic acid at 37°C. In summary, we showed the thermotolerance and ethanol tolerant character of new A. malorum strains, which can be used as a starter for vinegar production. Furthermore, during the molecular characterization of the isolated strains, we concluded that 16S-23S rDNA internal transcribed spacer sequence is of great importance for discriminating between AAB species as a complement to the identification by 16S rDNA sequencing.

A total of 270 lactic acid bacteria (LAB) was isolated and screened for their antifungal activity against Penicillium expansumMUCL2919240. Fourteen isolates showed wide antifungal spectrum against seven molds involved in food spoilage. Among these, three LAB strains named 4F, 4JC, and 3MI3 were selected for their high activity and broad antifungal spectrum. To identify these isolates, API CH50 and 16S rRNA gene sequencing were performed. Results showed that 4F and 4 JC were identified as lactobacillus plantarum and 3MI3 as lactobacillus paracasei. Various treatments of Cell‐free supernatant (CFS) from LAB showed that the inhibitory effect was due to proteinaceous substances, organic acids, and hydrogen peroxide. Scanning electron microscope (SEM) was carried out to assess the effects of CFS on the morphology of fungi. Efficacy of the CFS as biopresevative in tomato paste, bread, black olives, and grapes was tested and showed fungal inhibition suggesting its use in different food technologies. Practical applications Food spoilage caused by molds and yeasts represents an important issue in industries. The preservation of these products is done through the use of chemicals that are harmful. And with the trend toward the consumption of natural products and the demand for clean labels it becomes essential to research natural preservative. In our study we report the improvement of quality and shelf life of tomato paste, bread, black olives, and grapes using antifungal lactobacillus plantarum 4F against Penicillium expansum and Aspergillus fumigatus, by producing antifungal substances that cause mycelial breakage of target mold.

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In order to improve the germination rate of carob seeds (Ceratonia siliqua L.), we studied the morphological characteristics of the fruits (pod and seeds, integumentary hardness and tolerance to abiotic stress of the seeds) of seven ecotypes of carob trees from four regions of Morocco. The fruits of its seven populations were studied according to seven discriminative characteristics relating to the pods (length, width, thickness, total number of seeds, total weight of the pulp, seeds  per pod and yield of pods per tree) and four discriminative characteristics relating to the seeds namely length, width, thickness and total fresh weight of seeds. Integumentary hardness was evaluated by pretreating the seeds with boiling water and 95% sulfuric acid. Similarly, we also followed the evolution of water absorption by the seeds during 4 days and we evaluated on these seeds pre-treated, effects of different incubation temperatures (10°C, 25°C and 40°C), their tolerance to different concentrations of NaCl, PEG6000 (0MPa, -0.5MPa, -1MPa and -1.5MPa ) and their reversibility. The morphological characterization of the fruits allowed us to group the populations studied into three groups. Soaking the carob seeds in sulfuric acid for 20 minutes improved the germination rate and time. The evolution of water absorption makes it possible to distinguish two phases. The first phase is obtained during the first 24 hours and characterized by a rapid penetration of water, and second phase which lasts over the last 72 hours and which is characterized by a slow entry of water. The optimum temperature for germination of seeds from all provenances is 25°C. The germination behavior of carob under conditions of osmotic stress demonstrated a highly significant treatment effect (concentration of PEG6000) on the rate and mean time of germination and revealed that this species is very resistant to drought. This study also showed that, salt has a depressive effect on the average germination rate, time and length of radicles. The results of the reversibility test showed that the germination of seeds transferred from osmotic stress and salt stress (-0.5, -1 and -1.5MPa) and from the temperature of 40°C. is totally inhibited. On the other hand, seeds transferred from a temperature of 15°C resume germination under optimal conditions. This study allowed us to select a variety with high yield and tolerant to various biotic constraints.

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