ASSESSMENT OF PRESERVATIVE EFFICACY OF BACTERIOCIN PRODUCED BY LACTIC ACID BACTERIA ISOLATED FROM SELECTED TRADITIONALLY FERMENTED PRODUCTS

Abstract

The potential use of bacteriocin-producing lactic acid bacteria (LAB) isolated from traditionally fermented food products as biopreservatives was assessed using conventional methods. A total of sixty-three (63) lactic acid bacteria (LAB) isolates obtained from different samples of traditionally fermented products (“burukutu”, “pito”, yoghurt, “wara”, and “iru”) were screened for bacteriocin production. Thirty-seven (59%) of these LAB isolates showed antimicrobial activity against two or more of the reference organisms used as indicator strains (Staphylococcus aureus ATCC 25923, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853). After excluding inhibition due to organic acids and hydrogen peroxide from the cell-free culture supernatants of these 37 LAB isolates, only 6 (16%) of the 37 selected LAB isolates (10% of the 63 initial LAB isolates) continued to show antimicrobial activity against three of the reference strains. The inhibitory effects of these six (6) LAB strains (BE1, BO2, IO1, PO4, PO9 and YO7) showed the presence of bacteriocins. Four (4) strains (BE1, IO1, PO4 and PO9) of the bacteriocin producers also exhibited antifungal properties when tested against some moulds (Aspergillus flavus, A. fumigatus, A. repens and Penicillium species) associated with spoilage of bakery products. The selected bacteriocin-producing LAB strains (BE1, BO2, IO1, PO4, PO9 and YO7) were identified as Lactobacillus cellobiosus, L. brevis, Pediococcus pentosaceus, L. rhamnosus, Tetragenococcus halophilus, and L. fermentum respectively. These bacteriocin producers were found to be non-haemolytic and sensitive to erythromycin and zinacef. Bacteriocin-producing LAB strains (L. cellobiosus BE1, P. pentosaceus IO1, and T. halophilus PO9) were selected for further study. Protein concentrations of crude bacteriocins produced by these LAB isolates ranged from 4.55 to 7.08 mg/ml. The molecular weights of the partially purified bacteriocins ranged from 20.5 kDa to 92.0 kDa. The crude bacteriocins of LAB strains BE1, IO1, and PO9, were highly thermostable, retaining their activity even after heat treatment at 115oC for 15 min, and stable at pH range of 2 – 9 with higher activity at acidic pH (pH 2 and 5). The use of bacteriocin supernatant of P. pentosaceus IO1 as biopreservative in baked cakes and fruit juices (watermelon and orange) had no adverse effect on their organoleptic properties and reduced the microbial counts in the products. The addition of bacteriocinogenic LAB strains (PO9 and IO1) as adjunct culture in bread production improved the quality and extended the shelf life of the bread by 4 days compared to control (bread leavened by yeast, without calcium propionate). Oral administration of bacteriocinogenic P. pentosaceus IO1 strain and its bacteriocin improve growth performance and modulate intestinal microbiota of albino rats without detrimentally affecting the basic haematological and histological parameters assessed. Hence, these LAB isolates from the traditionally fermented products were capable of producing bacteriocin that could be used in the preservation of bakery products and fruit juices.