Screening, isolation and characterization of lactic acid bacteria strains in fermenting cocoa heaps from the Eastern Region of Ghana

Abstract

Cocoa fermentation is the primary process of producing quality chocolate taste and flavour. Lactic acid bacteria (LAB) are one of the key microorganisms in this heterogeneous fermentation process. They break down the sugars and citric acid in the cocoa pulp to produce lactic acid, acetic acid, and mannitol that influence the quality of the fermented bean. LAB strains as monoculture or co-culture could be an essential component of starter culture aimed at the control of cocoa bean fermentation process. This study screened, isolated and characterized LAB strains in cocoa heap fermentation to compare the amount of lactic acid produced by the various strains. Cocoa beans were fermented and enumeration of microorganisms was carried out. Microbial colonies were randomly selected and subcultured on MRS medium. Pure isolates were screened for LAB by carrying out catalase test and gram reaction. The isolated pure LAB strains were subjected to morphological, physiological and biochemical characterization. The amounts of lactic acid produced by the various strains were determined. There were two presumptive Lactococcus species as well as two presumptive Lactobacillus species. Different NaCl concentrations as well as citrate hydrolysis test were used to subdivide both species. C16 was identified to be presumptive Lactobacillus fermentum, C17 was identified to be Lactococcus lactis subsp. cremoris, C20 was identified to be presumptive Lactobacillus brevis and C23 was identified to be Lactococcus lactis subsp. lactis biovar diacetylactis. Lactococcus lactis subsp. cremoris produced the highest amount of lactic acid (185g lactic acid / L of culture medium) with Lactococcus lactis subsp. lactis biovar diacetylactis producing the least amount of lactic acid (95g lactic acid / L of culture medium). The above presumptive LAB species especially one with the highest amount of lactic acid produced could be a potential strain in producing a starter culture for a controlled cocoa fermentation.