Abstract
This study evaluated the preservative ability of protein-like cell free supernatants produced by lactic acid bacteria (LAB) isolates from samples of Ictalurus punctatus (Cat fish) and slurry of fermented Zea mays (Ogi). The LAB strains were separately isolated from understudied samples using De Man, Rogosa and Sharpe (MRS) media at 37°C for 48 h. The isolated strains were characterized with Gram staining, oxidase and catalase tests, microscopy study, carbohydrate fermentation, acid production and NaCl tolerance. Thereafter, the protein concentrations of crude bacteriocin supernatants from the Gram positive, rod shaped, oxidase and catalase negative strains were studied. Also, the growth inhibition of Bacillus subtilis, Staphyloccocus aureus and Escherichia coli, heat stability, pH tolerance, effect of proteolytic enzyme and biopreservation efficiency of protein-like cell free supernatants (crude bacteriocins) were determined. Biopreservative efficiency of the crude bacteriocin samples was also determined in orange (Citrus sinenses) and Titus fish (Scomber scombrus). The isolates from intestine of I. punctatus and fermented Z. mays fermented carbohydrate, and grew optimally at 3% NaCl, and 10 and 37°C, respectively. They inhibited the multiplication of E. coli at various extents, but more effective on different strains. The bacteriocins from slurry of fermented Z. mays on the other hand, were more potent in E. coli (22.7 ± 0.8 mm) than S. aureus (7.9 ± 0.1 mm). The biopreservative efficiency of crude bacteriocin from I. punctatus was greater than that of Z. mays. The LAB obtained from the selected samples produced protein-like substances in form of bacteriocins with potent antibacterial and biopreservative proficiencies through the growth inhibition of tested pathogens and low colony counts on tested food samples, respectively. Bacterial isolates obtained from samples of I. punctatus and Z. mays can be successfully used in the preservation of food and vegetables. Key words: Ictalurus punctatus, Zea mays, bacteriocin, protein-like substances, biopreservative ability.
Highlights
Ictalurus punctatus and fermented Zea mays are parts of the many functional foods that are consumed in West African countries, and are produced through the use of lactic acid bacteria (LAB) during metabolism or production processes
Like any other aquatic animals, the GIT or gut of I. punctatus contains series of bacteria which include LAB or compounds obtained from LAB, and these candidates are known for probiotic activity against both Gram-positive or negative pathogens (Ringø and Gatesoupe, 1998)
Morphological and biochemical properties of LAB isolates from intestine of I. punctatus and slurry of fermented Z. mays (Table 1) revealed the presence of eight (8) white colour rod shaped micro-organisms in intestine of I. punctatus compared to the seventeen (17) that were found in slurry of fermented Z. mays
Summary
Ictalurus punctatus and fermented Zea mays are parts of the many functional foods that are consumed in West African countries, and are produced through the use of lactic acid bacteria (LAB) during metabolism or production processes. I. punctatus (Channel Catfish) is a fresh water fish and commonly used as one of the protein sources in African diets. It is widely known as ‘Eja aro’ in western part of Nigeria. Like any other aquatic animals, the GIT or gut of I. punctatus contains series of bacteria which include LAB or compounds obtained from LAB (bacteriocins, organic acid and many more), and these candidates are known for probiotic activity against both Gram-positive or negative pathogens (Ringø and Gatesoupe, 1998). The presence of probiotic LAB or their products in aquatic animals converses immunity to the animals (Behnsenet al., 2013; Shahid et al, 2017)
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