Phenotypic grouping, genotypic characterization of lactic acid bacteria and Ochratoxin A (OTA) production by moulds isolated from cocoa beans

Abstract

A total number of 196 strains of lactic acid bacteria isolated from Nigerian fermented cocoa beans were grouped phenotypically (by means of their reactions to gram stain, gas production, catalase, diaminopimelic acid content, sugar fermentation and growth at different temperatures). The lactic acid bacteria strains consisted of 40 obligately heterofennentative lactobacilli that produced gas from glucose and were DL-Iactate; 110 facultatively hetero/obligately homofennentative lactobacilli that did not produce gas from glucose and were DL-Iactate; one facultatively hetero/obligately homofermentative lactobacillus that did not produce gas from glucose but was Dlactate; one facultatively hetero/obligately homofermentative lactobacillus that produced gas from glucose and was D-Iactate; 36 presumptive pediococci, cocci in tetrads that did not produce gas from glucose and was DL-Iactate and also 8 presumptive enterococci that was L-Iactate with one presumptive pediococcus which was L-Iactate. The cluster of 110 obligately homo/facultatively heterofennentative rods were observed to comprise of 107 facultative heterofermentative strains belonging to the L. plantarum group that fermented arabinose, ribose or xylose, produced DL-Iactate and possessed diaminopimelic acid (mDAP) in the cell wall and 3 obligately homofermentative rods which did not ferment the sugars, produced DL-lactate and also possessed mDAP. All pediococci isolates (100%) fermented arabinose, galactose, ribose and xylose; 0 % fermented lactose and maltose while 2.7% fermented melezitose. Genotypic characterization was by Rep-Polymerase Chain Reaction (Rep-PCR) and sequencing. Mould isolates, namely Aspergillus ochraceus, A. niger and Penicillium nordicum grown on YES, Coffee and Cocoa media and analysed for ochratoxin A (OTA) production by HPTLC method showed YES and Coffee media supported higher OTA production than Cocoa media for all the mould isolates; with the highest OTA production by Aspergillus ochraceus. A. niger produced the least amounts in all the three media