Correlation between metabolites of lactic acid bacteria isolated from dairy traditional fermented Tunisian products and antifungal and antioxidant activities.

AIMS: The objective of this study is to identify and investigate the antifungal and antioxidant potential of lactic acid bacteria (LAB) isolated from traditional fermented products. METHODS AND RESULTS: In this work, a collection of LAB was isolated from traditional fermented products collected in four Tunisian regions. After first screening using the overlay method, seven bacterial strains were retained due to their high antifungal effect. Four strains of Limosilactobacillus fermentum were identified, one strain of Lacticaseibacillus paracasei, one strain of Lacticaseibacillus rhamnosus and one strain of Enterococcus faecium. The antifungal and the antioxidant potential of these bacteria were then evaluated. Bacterial strains were effective against six fungal strains with minimum inhibitory concentrations ranging from 25 to 100 mg/ml and minimum fungicidal concentrations ranging from 50 to 200 mg/ml. Cell-free supernatants of LAB were analysed by HPLC-DAD and LC-MS-qTOF-MS analysis. Results showed significant production of organic acids as well as several phenolic compounds. Correlation analysis confirmed that PLA and 1,2-dihydroxybenzene were positively correlated with antifungal potential. The results of the antioxidant activity highlighted an ABTS radical cation scavenging activity ranging from 49% to 57% and a DPPH trapping percentage ranging from 80% to 97%. CONCLUSIONS: Therefore, due to these characteristics, identified lactic acid bacteria strains have shown their effectiveness to perform as antifungal and antioxidant agents. SIGNIFICANCE AND IMPACT OF THE STUDY: Since microbial contamination is at the root of extensive losses in the food sector, the identified strains or their metabolites can potentially be used as additives to limit micro-organism spoilage in food products and increase their shelf life.

Two novel peptides with angiotensin I converting enzyme inhibitory and antioxidative activities from Scorpaena notata muscle protein hydrolysate.

Fish protein hydrolysate was prepared from muscle of small red scorpionfish (Scorpaena notata) by treatment with a protease from the fungus Penicillium digitatum. Protein hydrolysate was found to strongly inhibit the angiotensin I converting enzyme and exhibited high antioxidative activity through 1,1-diphenyl-2-picrylhydrazyl free radical scavenging assay. After ultrafiltration, peptides were isolated by a two-step procedure: size exclusion chromatography on a Toyopearl HW-40 followed by reversed-phase high-performance liquid chromatography with a high purification yield of 2.5 mg of peptide per gram of initial protein. Two major peptides were then identified by nanoscale liquid chromatography coupled to tandem mass spectrometry (nano-LC-MS/MS), corresponding to the following sequences: Leu-Val-Thr-Gly-Asp-Asp-Lys-Thr-Asn-Leu-Lys (1,204.665 Da) and Asp-Thr-Gly-Ser-Asp-Lys-Lys-Gln-Leu (992.511 Da). These peptides, mainly composed of hydrophilic amino acids, showed high antioxidative and angiotensin I converting enzyme inhibitory activities. These data suggest that the two novel peptides isolated from the muscle hydrolysate of small red scorpionfish can be a beneficial ingredient for functional foods or pharmaceuticals against hypertension and oxidative stress.

Purification and Biochemical Characterization of a Neutral Serine Protease from Trichoderma harzianum. Use in Antibacterial Peptide Production from a Fish By-Product Hydrolysate.

This study reports the purification and biochemical characterization of an extracellular neutral protease from the fungus Trichoderma harzianum. The protease (Th-Protease) was purified from the culture supernatant to homogeneity by a three-step procedure with 14.2% recovery and 9.06-fold increase in specific activity. The purified enzyme appeared as a single protein band after sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with a molecular mass of about 20 kDa. The optimum pH and temperature for the proteolytic activity were pH 7.0 and 40 °C, respectively. The enzyme was then investigated for its potential application in the production of antibacterial peptides. Interestingly, Scorpaena notata viscera protein hydrolysate prepared using the purified serine protease (Th-Protease) showed remarkable in vitro antibacterial activities. A peptide with a high antibacterial activity was further purified by a three-step procedure, and its sequence was identified as FPIGMGHGSRPA. The result of this study offers a promising alternative to produce natural antibacterial peptides from fish protein hydrolysate.

Bioactive compounds contents, antioxidant and antimicrobial activities during ripening of Prunus persica L. varieties from the North West of Tunisia.

Bioactive molecules from fruits of four varieties of Prunus persica at different stages of ripening (green, small orange, red) were studied. For example, contents on polyphenols (20.36mg GAE/g FW) and flavonoids (0.764mg RE/g FW) were high and varied according variety. The antioxidant activity, using four different tests (DPPH radical scavenging activity, reducing power, ß carotene bleaching system and TBARS assay) showed that the variety Chatos exhibited the highest antioxidant activity comparing with others varieties. The antibacterial activity of Prunus persica varieties studied seems to be more sensitive against Staphylococcus aureus and Listeria monocytogenes. The capacity of peach DMSO extracts to inhibit Candida albicans growth was more pronounced, especially, in the presence of Chatos DMSO extract. Enzymes inhibition gives results which correlate with polyphenols, flavonoids and condensed tannins contents, and so, confirm the fascinating bioactivity of this fruit.

Neutral serine protease from Penicillium italicum. Purification, biochemical characterization, and use for antioxidative peptide preparation from Scorpaena notata muscle.

In the present study, purification and properties of an extracellular neutral serine protease from the fungus Penicillium italicum and its potential application as an antioxidant peptides producer are reported. The protease was purified to homogeneity using ammonium sulfate precipitation, Sephacryl S-200 gel filtration, diethylaminoethanol (DEAE)-Sepharose ion exchange chromatography, and TSK-HPLC gel filtration with a 10.2-fold increase in specific activity and 25.8 % recovery. The purified enzyme appeared as single protein band with a molecular mass of 24 kDa in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The optimum pH and temperature for the proteolytic activity were pH 7.0 and 50 °C, respectively. The enzyme was stable in the pH range of 6.0-9.0. The protease was activated by divalent cations such as Ca(2+) and Mg(2+). Complete inhibition of the purified enzyme by phenylmethylsulfonyl fluoride confirmed that the protease was of serine-type. The purified enzyme revealed high stability and relatively broad specificity. Scorpaena notata muscle protein hydrolysates prepared using purified serine protease (protease from P. italicum (Prot-Pen)) showed good in vitro antioxidative activities. The antioxidant activities of Scorpaena muscle protein hydrolyzed by Prot-Pen (SMPH-PP) were evaluated using various antioxidant assays: 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, reducing power, ferrous chelating activity, and DNA nicking assay. SMPH-PP showed varying degrees of antioxidant activity and almost the same strongest protection against hydroxyl radical induced DNA breakage.

Purification and biochemical characterization of a novel protease from Penicillium digitatum - Use in bioactive peptides production.

This work reports the production of a novel serine protease enzyme (P. dig-protease) from the fungus Penicillium digitatum. The protease was purified from the culture supernatant to homogeneity using ammonium sulfate precipitation, Sephadex G-150 gel filtration and carboxymethyl-sepharose ion exchange chromatography with a 13-fold increase in specific activity. The apparent molecular weight of P.dig-protease was estimated to be 120 kDa by native high performance liquid chromatography (HPLC), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed a single polypeptide at about 30 kDa that indicates a tetrameric protein. The proteolytic activity was inhibited by phenylmethylsulfonyl fluoride suggesting a serine-protease enzyme. P.dig-protease stability was investigated over broad range of pH, temperature, salt concentrations, surfactants and metal ions. The purified P.dig-protease was used for the production of bioactive peptides. Red scorpionfish (Scorpaena notata) muscle was hydrolyzed with P.dig-protease in order to obtain peptides with biological activities. Interestingly, the hydrolysate revealed the presence of antioxidant and angiotensin-I converting enzyme inhibitor peptides.