Improving dietary citric acid production by the wild-type Aspergillus niger ASP26 strain isolated from date by-product.

This research investigates citric acid (CA) synthesis using the indigenous strain Aspergillus niger ASP26, which was isolated from date by-products. The study initially involved isolating fungi capable of CA production and identifying the most potent strain based on its characteristic enzymatic activity. A. niger ASP26 was acknowledged in a previous study for its remarkable ability to produce extracellular enzymes, such as cellulase and amylase, which enable it to degrade organic materials effectively. After the identification phase, these isolates were screened for CA production using a modified Czapek-Dox medium. The research identified significant factors affecting CA production in submerged fermentation, including pH, carbon source, inoculum size, and fermentation time. Optimal conditions were determined for A. niger ASP26, resulting in a maximum CA yield of 16.89 g/L. These conditions included a 2.5% spore suspension at 2 × 107 spores/mL, an initial glucose concentration of 125 g/L, and incubation at 30°C for 144 h. Notably, A. niger ASP26 demonstrated the ability to produce CA under stress conditions as well. Citric acid is essential for various biological processes, such as cellular respiration, and is naturally present in citrus fruits. It also serves as a preservative and flavor enhancer in processed foods and beverages. The ability of A. niger ASP26 to produce CA from agricultural residues positions it as a viable candidate for sustainable CA production, harnessing the value from organic waste materials.

The efficiency of Lactiplantibacillus plantarum S61 strain as protective cultures in ground beef against foodborne pathogen Escherichia coli.

The aim of the study was the bio-control effectiveness of the Lactiplantibacillus plantarum S61 strain, isolated from traditional fermenting green olives, against Escherichia coli B805 in ground beef. The bio-control effect of L. plantarum S61 against E. coli B805 was evaluated in ground meat during storage under refrigeration at 4 °C. The results showed that L. plantarum S61 reduced the biomass of pathogenic bacteria (E. coli) in ground meat during 10 days of storage at 4 °C. Moreover, the treatment with L. plantarum S61 has no adverse effect on the sensory properties of ground meat after 10 days of storage at 4 °C. The treatment with L. plantarum S61 and storage at 4 °C effectively decreases the growth and risk of pathogenic bacteria in ground meat and, consequently, increases the product's shelf life. Therefore, the application of L. plantarum S61 during the storage of ground meat beef may help reduce the use of chemical preservatives in meat products. Consequently, L. plantarum S61 can be applied as a bio-control agent against spoilage and pathogenic bacteria in meat and meat products.

Antifungal activity of lactic acid bacteria and their application in food biopreservation.

Lactic acid bacteria (LAB) are ubiquitous bacteria associated with spontaneous lactic fermentation of vegetables, dairy and meat products. They are generally recognized as safe (GRAS), and they are involved in transformation of probiotic lacto-fermented foods, highly desired for their nutraceutical properties. The antifungal activity is one of the exciting properties of LAB, because of its possible application in food bio-preservation, as alternative to chemical preservatives. Many recent research works have been developed on antifungal activity of LAB, and they demonstrate their capacity to produce various antifungal compounds, (i.e. organic acids, PLA, proteinaceous compounds, peptides, cyclic dipeptides, fatty acids, and other compounds), of different properties (hydrophilic, hydrophobic and amphiphilic). The effectiveness of LAB in controlling spoilage and pathogenic fungi, demonstrated in different agricultural and food products, can be due to the synergistic effect between their antifungal compounds of different properties; where the amphiphilic-compounds allow the contact between the target microbial cell (hydrophilic compartment) and antifungal hydrophobic-compounds. Further studies on the interaction between compounds of these three properties are to de be developed, in order to highlight more their mechanism of action, and make LAB more profitable in improving shelf life and nutraceutical properties of foods.

Characterization of antimicrobial compounds obtained from the potential probiotic Lactiplantibacillus plantarum S61 and their application as a biopreservative agent.

This work aimed to characterize the antimicrobial compounds obtained from the potential probiotic Lactiplantibacillus plantarum S61, isolated from traditional fermented green olive, involved in their activity against fungi and bacteria responsible for food spoilage and poisonings. Their application as a biopreservative agent was also investigated. The culture of L. plantarum S61 showed substantial antifungal and antibacterial activity against yeasts (Rhodotorula glutinis and Candida pelliculosa), molds (Penicillium digitatum, Aspergillus niger, Fusarium oxysporum, and Rhizopus oryzae), and pathogenic bacteria (Listeria monocytogenes ATCC 19,117, Salmonella enterica subsp. enterica ATCC 14,028, Staphylococcus aureus subsp. aureus ATCC 6538, Pseudomonas aeruginosa ATCC 49,189), with inhibition zones > 10 mm. Likewise, the cell-free supernatant (CFS) of L. plantarum S61 showed an essential inhibitory effect against fungi and bacteria, with inhibition diameters of 12.25-22.05 mm and 16.95-17.25 mm, respectively. The CFS inhibited molds' biomass and mycelium growth, with inhibition ranges of 63.18-83.64% and 22.57-38.93%, respectively. The antifungal activity of the CFS was stable during 4 weeks of storage at 25 °C, while it gradually decreased during storage at 4 °C. Several antimicrobial compounds were evidenced in the CFS of L. plantarum S61, including organic acids, ethanol, hydrogen peroxide, diacetyl, proteins, and fatty acids. The protein fraction, purified by reversed-phase high-performance liquid chromatography (RP-HPLC), demonstrated important antifungal activity, in relation to the fraction with molecular weight between 2 and 6 kDa. L. plantarum S61 and its CFS, tested in apple and orange fruit biopreservation, demonstrated their protective effect against P. digitatum spoilage. The CFS exhibited effectiveness in reducing Salmonella enterica subsp. enterica ATCC 14,028 in apple juice. L. plantarum S61 and/or its bioactive compounds CFS represent a promising strategy for biocontrol against pathogens and spoilage microorganisms in the agro-industry.

Bio-preservation Effect of Probiotic Lactiplantibacillus plantarum S61 Against Rhodotorula glutinis and Listeria monocytogenes in Poultry Meat.

The objective of this work is the study of the antifungal and antibacterial activity of Lactiplantibacillus plantarum S61 strains, isolated from traditional fermenting green olives against Rhodotorula glutinis UMP 22 and Listeria monocytogenes ATCC 19117, and its application in meat as bio-preservative agent. The cell-free supernatant (CFS) of Lpb. plantarum S61 shows high inhibition zones, which are 22.45 ± 0.49 and 17.75 ± 0.35 mm, against Rhodotorula glutinis and Listeria monocytogenes. The minimum fungicidal and bactericidal concentrations of the CFS obtained are 8% (v/v) and 10% (v/v), respectively. The competition assay, realized in liquid medium by co-culture of Lpb. plantarum S61 with Rho Rhodotorula glutinis and L. monocytogenes, led to inhibition percentages of 77.72% and 89.52%, respectively. However, the antimicrobial activity of Lpb. plantarum S61 was revealed a proteinaceous nature. Lpb. plantarum S61 strain allowed the reduction of L. monocytogenes in minced poultry meat during 7 days of storage at 4 °C. In addition, Lpb. plantarum S61 improved the physicochemical and color parameters of poultry minced meat. Lpb. plantarum S61 and/or its antimicrobial compounds can be applied as bio-preservative agent in meat product and food industry.

Characterization of ß-glucosidase of Lactobacillus plantarum FSO1 and Candida pelliculosa L18 isolated from traditional fermented green olive.

BACKGROUND: Oleuropein, the main bitter phenolic glucoside responsible for green olive bitterness, may be degraded by the ß-glucosidase enzyme to release glucose and phenolic compounds. RESULTS: Lactobacillus plantarum FSO1 and Candida pelliculosa L18 strains, isolated from natural fermented green olives, were tested for their ß-glucosidase production and activity at different initial pH, NaCl concentrations, and temperature. The results showed that strains produced extracellular and induced ß-glucosidase, with a molecular weight of 60 kD. The strains demonstrated their biodegradation capacity of oleuropein, associated with the accumulation of hydroxytyrosol and other phenolic compounds, resulting in antioxidant activity values significantly higher than that of ascorbic acid. The highest production value of ß-glucosidase was 0.91 U/ml obtained at pH 5 and pH 6, respectively for L. plantarum FSO1 and C. pelliculosa L18. The increase of NaCl concentration, from 0 to 10% (w/v), inhibited the production of ß-glucosidase for both strains. However, the ß-glucosidase was activated with an increase of NaCl concentration, with a maximum activity obtained at 8% NaCl (w/v). The enzyme activity was optimal at pH 5 for both strains, while the optimum temperature was 45 °C for L. plantarum FSO1 and 35 °C for C. pelliculosa L18. CONCLUSIONS: L. plantarum FSO1 and C. pelliculosa L18 strains showed their ability to produce an extracellular and induced ß-glucosidase enzyme with promising traits for application in the biological processing of table olives.

Characterization and optimization of extracellular enzymes production by Aspergillus niger strains isolated from date by-products.

BACKGROUND: This work aims to study the optimal conditions of the fermentation culture medium used for the production of extracellular enzymes (amylase, cellulase, lipase, and protease) from previously isolated Aspergillus niger strains in date by-products. RESULTS: The five most powerful isolates selected based on the zone of degradation formed on Petri plates by the substrate were subjected to the quantitative evaluation of their enzymatic production. All five strains showed almost similar API-ZYM profiles, with minor variations observed at the level of some specific enzyme expression. The production of cellulase and amylase was depending on pH and incubation temperatures. ASP2 strain demonstrated the high production rate of amylase (at pH 5 and 30 °C) and cellulase (at pH 6 and 30 °C) for 96 h of incubation. CONCLUSION: The A. niger showed the ability to produce several extracellular enzymes and can be used in the valorization of different agroindustrial residues.

Characterization of Probiotic Properties of Antifungal Lactobacillus Strains Isolated from Traditional Fermenting Green Olives.

The aim of this work is to characterize the potential probiotic properties of 14 antifungal Lactobacillus strains isolated from traditional fermenting Moroccan green olives. The molecular identification of strains indicated that they are composed of five Lactobacillus brevis, two Lactobacillus pentosus, and seven Lactobacillus plantarum. In combination with bile (0.3%), all the strains showed survival rates (SRs) of 83.19-56.51% at pH 3, while 10 strains showed SRs of 31.67-64.44% at pH 2.5. All the strains demonstrated high tolerance to phenol (0.6%) and produced exopolysaccharides. The autoaggregation, hydrophobicity, antioxidant activities, and surface tension value ranges of the strains were 10.29-41.34%, 15.07-34.67%, 43.11-52.99%, and 36.23-40.27 mN/m, respectively. Bacterial cultures exhibited high antifungal activity against Penicillium sp. The cell-free supernatant (CFS) of the cultures showed important inhibition zones against Candida pelliculosa (18.2-24.85 mm), as well as an antibacterial effect against some gram-positive and gram-negative bacteria (10.1-14.1 mm). The neutralized cell-free supernatant of the cultures displayed considerable inhibitory activity against C. pelliculosa (11.2-16.4 mm). None of the strains showed acquired or horizontally transferable antibiotic resistance or mucin degradation or DNase, hemolytic, or gelatinase activities. Lactobacillus brevis S82, Lactobacillus pentosus S75, and Lactobacillus plantarum S62 showed aminopeptidase, ß-galactosidase, and ß-glucosidase activities, while the other enzymes of API-ZYM were not detected. The results obtained revealed that the selected antifungal Lactobacillus strains are considered suitable candidates for use both as probiotic cultures for human consumption and for starters and as biopreservative cultures in agriculture, food, and pharmaceutical industries.

Physicochemical and microbiological characterization of olive mill wastewater (OMW) from different regions of northern Morocco.

This work examined the influence of crop season, extraction system and production site on the composition of fresh olive mill wastewater collected from northern Morocco. ANOVA analysis showed that most of the traits were largely affected by the extraction system (≥60% of total variance). Comparison among extraction systems showed significant differences for all traits, except for chlorides. Three phase centrifugation system (C3) displayed the highest value of total phenols, while all the remaining traits were higher in two phase centrifugation system (C2). Concerning crop seasons, we noticed a general decrease in values of total solids, chemical oxygen demand, chlorides, C/N ratio and total aerobic mesophilic flora, from 2014 to 2016 season; in contrast, an increase in suspended solids, total kjeldahl nitrogen and proteins was detected. OMW with highest total phenols content and then more acidic were collected during 2015 season. Between production sites, Bni Frassen produced OMW with the highest values for salt and total phenols, but the lowest ones were obtained for microbiological traits. OMW from Taza were rich in total kjeldahl nitrogen and proteins. An increase in organic load indicators was observed in Bouchfaa. Principal component analysis (PCA) explained about 82% of total variability: 58%, 16% and 8% for principal component 1 (PC1), PC2 and PC3, respectively. Extraction system fitted the variability of PC1. PC2 was mainly explained by production sites, while PC3 separated crop seasons. Correlation studies showed significant relationships especially among the traits expressing organic load, while microbiological counts were largely associated to total phenols and pH.