Comparative Evaluation of the Capacity of Commercial and Autochthonous Saccharomyces cerevisiae Strains to Remove Ochratoxin A from Natural and Synthetic Grape Juices.

In this paper, we assessed the ability of two strains of Saccharomyces cerevisiae, in viable and dead forms, to remove ochratoxin A (OTA) from an artificially contaminated synthetic grape juice medium (SGM) (10 µg OTA/L) and a naturally contaminated grape juice (6.64 µg OTA/L). The first strain, named Levulin FB, is a commercial yeast used in making wine. The second, named SC5, is an autochthonous strain isolated from table grapes. OTA concentrations in juices before and after their contact with yeast cells were assessed. A significant decrease in OTA level (p < 0.05) in the SGM medium and in the natural grape juice was observed after 1 h of adding yeast cells (20 g/L) in viable and heat-treated forms. It was inferred that the dead forms of the two strains were more able to eliminate OTA than their viable forms in both media. This study demonstrates the potential application of an autochthonous yeast for the natural decontamination of grape juice from fungal toxins.

Exploring potential new galactomannan source of Retama reatam seeds for food, cosmetic and pharmaceuticals: Characterization and physical, emulsifying and antidiabetic properties.

In this study, physicochemical, interfacial and emulsifying properties of Retama reatam and guar galactomannans were comparatively investigated. The results showed that Retama reatam galactomannan is mainly composed of total carbohydrates (95.52%) and lower protein contents (0.87%). The sugars identified were mannose (Man) and galactose (Gal), with a Man:Gal ratio of 1.85 compared to guar gum (1.83). The results of thermal properties indicated were transition temperature (Tg) and melting temperature (Tm) very similar to those of the guar gum. Moreover, results also revealed that there is no significant difference in terms of equilibrium interfacial tension of Retama reatam gum at 10 and 20°C. Moreover, preliminary tests show that stable oil-in-water nanoemulsions may be formulated using Retama reatam gum. Therefore, measurement of mean oil droplet diameter d after heating at 80°C, shows that stable nanoemulsions may be formulated using Retama reatam galactomannan. Further in vivo experiments confirmed that Retama reatam gum can reduce the glycemic index of starchy foods and inhibit the surge of postprandial blood glucose level.

Identification of peptides with antioxidant and antihypertensive capacities by RP-HPLC-Q-TOF-MS in dry fermented camel sausages inoculated with different starter cultures and ripening times.

Low molecular weight peptides are produced during meat fermentation. They contribute to generate flavor compounds but they can also exert certain bioactivities. The aim of this work was to evaluate, for the first time, the generation of bioactive peptides during the preparation of dry fermented camel sausages and to study the influence of the ripening time and the starter culture on bacteria growing, peptide concentration and size, and antioxidant and antihypertensive capacities of peptides. Camel meat sausages inoculated with different starter bacteria and non-inoculated were ripened up to 28days. Results demonstrated that bacteria population, peptide concentration, and peptide size were affected by the ripening time and the inoculated bacteria. Moreover, the ripening process resulted in an increasing antioxidant and antihypertensive capacity showing the highest bioactivities in fractions with peptides below 3kDa. Peptides in these fractions were identified by RP-HPLC-Q-TOF-MS analysis. Identified peptides showed common features with peptides with antioxidant or antihypertensive activity.

Optimization of enzymatic hydrolysis and fermentation conditions for improved bioethanol production from potato peel residues.

The aim of this work was the optimization of the enzyme hydrolysis of potato peel residues (PPR) for bioethanol production. The process included a pretreatment step followed by an enzyme hydrolysis using crude enzyme system composed of cellulase, amylase and hemicellulase, produced by a mixed culture of Aspergillus niger and Trichoderma reesei. Hydrothermal, alkali and acid pretreatments were considered with regards to the enhancement of enzyme hydrolysis of potato peel residues. The obtained results showed that hydrothermal pretreatment lead to a higher enzyme hydrolysis yield compared to both acid and alkali pretreatments. Enzyme hydrolysis was also optimized for parameters such as temperature, pH, substrate loading and surfactant loading using a response surface methodology. Under optimized conditions, 77 g L-1 of reducing sugars were obtained. Yeast fermentation of the released reducing sugars led to an ethanol titer of 30 g L-1 after supplementation of the culture medium with ammonium sulfate. Moreover, a comparative study between acid and enzyme hydrolysis of potato peel residues was investigated. Results showed that enzyme hydrolysis offers higher yield of bioethanol production than acid hydrolysis. These results highlight the potential of second generation bioethanol production from potato peel residues treated with onsite produced hydrolytic enzymes. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:397-406, 2017.

Study of the microbial ecology of wild and aquacultured Tunisian fresh fish.

Eighty samples of fresh fish were collected in Tunisia and analyzed for microbial load. Quality and hygienic safety of the meat and intestines of wild and aquacultured fresh fish were determined. The mesophilic aerobic plate count and populations of psychrotrophic lactic acid bacteria (LAB) and other psychrotrophic bacteria ranged from 5.67 to 7.29, 4.51 to 6, and 5.07 to 6.21 log CFU/g, respectively. For all microbiological determinations, bacterial counts were lower in meat than in the intestines of fresh fish. For all samples lower microbial populations were found in most of the wild fish than in the aquacultured fish. No isolates of the pathogenic genera Salmonella and Listeria were detected in any sample. Among the 160 strains of biopreservative psychrotrophic LAB and the 150 strains of spoilage psychrotrophic gram-negative bacteria identified by biochemical and molecular methods, Lactobacillus (six species) and Pseudomonas (six species) predominated. Lactococcus, Leuconostoc, Carnobacterium (C. piscicola and C. divergens), Aeromonas, and Photobacterium were the most common genera, and Lactococcus lactis, Lactobacillus plantarum, Pseudomonas fluorescens, and Aeromonas hydrophila were the most common species. These findings indicate that the microbiological quality of fresh fish in Tunisia can be preserved by controlling pathogenic and psychrotrophic bacteria.

Biopreservation of refrigerated and vacuum-packed Dicentrarchus labrax by lactic acid bacteria.

Two lactic acid bacteria (LAB) were selected from 100 LAB isolated from various sea products to examine their use in Dicentrarchus labrax preservation. The isolates, tentatively named strain nr 3 and 7, were identified as Lactobacillus plantarum and L. pentosus, respectively. They showed antagonistic activity against psychrotroph, pathogenic, and coliform bacteria. The antagonistic activity of strain 3 was suggested to be by bacteriocins since activity was abolished by protease treatment, while that of strain 7 was due to the effect of pH decrease caused by the produced organic acids. Their use prevented total volatile basic nitrogen contents (TVB-N) and trimethylamine (TMA) to some extent, suggesting that inoculation could extend the period of storage.

Technological and safety properties of Lactobacillus plantarum strains isolated from a Tunisian traditional salted meat.

A total of 17 strains of Lactobacillus plantarum, isolated from a Tunisian traditional salted meat and identified by biochemical and molecular methods, were characterized according to their technological properties including acidifying, antimicrobial and enzymatic activities as well as antibiotic resistance in order to select the most suitable for use as starter cultures for the production of fermented sausages. All the strains studied showed good acidifying activity and were able to reduce the pH to less than 4.3 in 72, 48 and 24h at 15, 25 and 37°C respectively. The majority of strains displayed antimicrobial activities against Salmonella arizonae, Staphylococcus aureus, Pseudomonas aeuroginosa and Escherichia coli, however characterization of the antimicrobial substances showed that none of the strains could produce bacteriocins. All the L. plantarum strains were able to hydrolyze casein, whereas none of them was found to possess lipolytic activity. The majority of strains of L. plantarum were resistant to tetracycline, erythromycin, rifampicin, ampicillin and penicillin G.

Characterization and technological properties of Staphylococcus xylosus strains isolated from a Tunisian traditional salted meat.

The technological properties of strains of Staphylococcus xylosus were studied to select the most suitable for use as starter cultures for the production of dried fermented meat products. Strains of S. xylosus were isolated from traditional salted Tunisian meat and were identified by biochemical and molecular methods. Thirty strains of S. xylosus were studied to evaluate their catalase, nitrate reductase, lipolytic, proteolytic and antibacterial activities as well as growth ability at different temperatures, pH's and NaCl concentrations. All strains of S. xylosus had catalase activity and were able to reduce nitrates to nitrites. The nitrate reductase activity increased when the strains were kept under anaerobic conditions. Proteolytic activity on milk and on gelatin agar was demonstrated for 100% and 83.3% of the S. xylosus isolates, respectively. However extracellular proteolytic activity as assessed by the azocasein method was poor in all the strains. Lipolytic activity as assessed by the agar method showed that 76.6% of strains of S. xylosus could hydrolyze Tween 20 against 33.3% that could hydrolyze tributyrin. Tween 80 was hydrolyzed by only 10% of strains. Strains of S. xylosus hydrolyzed pork fat better than beef and lamb fat. The majority of strains had antibacterial activity against Salmonella arizonae, Staphylococcus aureus, Pseudomonas aeuroginosa, Escherichia coli and Enterococcus faecalis.