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Title: Potential uses of lactic acid bacteria as biopreservatives in the preservation of Tsire, a Nigerian stick meat
Author: Olaoye, Olusegun Ayodele
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2011
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Research efforts on the control of spoilage and pathogenic organisms in meat products have attracted intensive attention worldwide in the past decades. Tsire is a spiced Nigerian meat product tradionally produced by grilling over an open charcoal fire. The spices added to the meat are principal sources of contamination, coupled with the unhygienic method of preparation by the handlers. At the end of the day of production, producers don't usually exhaust their sales leading to leftovers of the tsire product. Due to poor storage facilities, these leftovers are not properly kept thereby increasing further risk of contamination. Therefore, in the present study, the potential of selected strains of lactic acid bacteria (LAB) were evaluated as protective cultures to control spoilage / pathogenic organisms in the meat product. One hundred and thirty eight strains of LAB were isolated from Nigerian beef, phenotypically characterised and identified. Ten strains, presumptively identified as Pediococcus pentosaceus (six isolates), Pediococcus acidilactici (two isolates), and Lactococcus lactis (two isolates), were selected based on their higher production of lactic acid during preliminary tests, and subjected to further characterisation using pulsed field gel electrophoresis (PFGE). From among the ten LAB isolates, five strains" which showed differences in their PFGE fingerprints, were identified by 16S rDNA-V3 sequencing as Pediococcus pentosaceus (3 isolates) and Ped. acidilactici (two isolates). Identification of the LAB strains by 16S rDNA sequencing demonstrated confirmation of their presumptive identities obtained by phenotypic methods, with the exception of one strain of Ped. acidilactici that was phenotypically identified as Lactococcus lactis. Assessment of the isolates' abilities to produce a number of antimicrobial agents was measured and these were evaluated against a range of spoilage and pathogenic bacteria typical of meat. Strains of Ped. pentosaceus showed higher production of lactic, acetic, diacetyl and hydrogen peroxide, compared to those of Ped. acidilactici. While there was no evidence of bacteriocin production among the five Pediococcus strains identified from Nigerian beef, two type culture strains Lc. lactis NCIMB 8586 and Ped. acidilactici NCIMB 700993, were shown to produce nisin and pediocin respectively in vitro; the genes encoding their production were also confirmed by polymerase chain reaction (PCR). This was the first report of pediocin production by the NCIMB strain as a result of this study (Olaoye and Dodd, 2010). Among the LAB strains, only the bacteriocin producing Le. lactis and Ped. acidilactici strains demonstrated antimicrobial activity against Bro. thermosphacta and Lis. monocytogenes respectively, after neutralisation of organic acids and hydrogen peroxide from the growth media. Tsire samples which were inoculated with selected LAB cultures and stored at 30°C, to mImIC ambient storage in Nigeria, demonstrated reduction in the levels of enterobacteriaceae, yeast & moulds, Staphylococcus spp., and total bacteria counts. In challenge experiments, Bro. thermosphacta and Lis. monocytogenes were also observed to be controlled in situ in the meat samples by the respective bacteriocin producing Le. lactis and Ped. acidilactici strains. Using Gas Chromatography-Mass Spectrometry, many volatile compounds were identified in the tsire during storage. The overall results indicated that significant effects were exerted by the selected Pediococcus cultures; there was reduction in the production of undesirable volatile compounds in the inoculated samples, compared to the control, during storage of the meat product at ambient temperature. Anti-oxidative activities by the LAB cultures were also noticeable, following reduction in compounds whose production has been linked with the process of oxidation which could lead to flavour deterioration. Such compounds include ethylbenzene, hexanal, heptanal and nonanal, 2-hexanone, 2-heptanone and 2-butanone, and have been reported as associated with spoilage of meat. This becomes very significant in this study as the anti-oxidation properties of the Pediococcus strains could reduce rancidity in the meat product. In conclusion, the strains Ped. acidilactici NCIMB 700993 and Le. lactis NCIMB 8586 were shown to have good potential as protective cultures in the biopreservation of tsire. These cultures could also be used in combination with Ped. pentosaceus strain HI0l due to its ability to produce a comparatively higher concentration of diacetyl than other LAB strains isolated in this study. However, further studies are required in the evaluation of nutritional and biochemical qualities of the product during storage which may be influenced by the cultures. Even though LAB are generally regarded as safe, it would also be important to ascertain the safety of the culture processed meat products.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available