Abstract
The succession of the dominant microbial population during cacao fermentation with or without adjunct inoculation of yeast and lactic acid bacteria (LAB) were monitored on a laboratory scale using culture-dependent and culture-independent methods. Yeasts and acetic acid bacteria (AAB) population throughout a five-day fermentation process showed no significant differences but the LAB population increased through adjunct inoculation. Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) identification method showed the dominance of only Lactobacillus plantarum, one of the species used as the adjunct inoculum, which resulted in higher lactic acid production. On the other hand, Acetobacter spp. and Gluconobacter spp. were markedly observed in the spontaneously fermented set-up resulting in increased acetic acid production, significantly different (p>0.05) at three to five days of fermentation. LAB and yeast inoculation resulted in a more desirable temperature and pH of the fermenting mash which may result in better product quality.
Highlights
The plate count method showed no recognizable differences in the growth of yeasts and acetic acid bacteria (AAB) observed during the course of laboratory -simulated cacao fermentation for both the uninoculated and inoculated setups
It was observed that yeasts and lactic acid bacteria (LAB) dominated in the fermentation while AAB declined in counts after 48 hrs of fermentation
PCR-Denaturing Gradient Gel Electrophoresis (DGGE) showed that Acetobacter and Gluconobacter were the dominant acid-forming bacteria for the naturally-fermented setup, but which seemed to have been already killed by plate count observation
Summary
The increase in local and international demand for cacao led to surging world prices, reviving interests in cacao growing and processing. Local annual production of only approximately 10,00012,000 metric tons is far less than the estimated local consumption of more than 50,000 metric tons, more efforts are needed to increase production and processing into good quality cacao products (Department of Agriculture, Phillipines, 2017). Lactic acid bacteria (LAB) and acetic acid bacteria (AAB) are the important microorganisms in cacao fermentation (Ho et al, 2018). Yeasts and heterofermentative LAB convert pulp sugars to ethanol which is converted into acetic acid by AAB. Some yeasts and LAB convert pulp sugars and citric acid into lactic acid which, together with the acetic acid, inhibit growth and activity of putrefactive microorganisms. The acetic acid and lactic acid can penetrate cacao seed which leads to the formation of precursors for the defined chocolate flavor (Schwan and Wheals, 2004; Castro-Alayo et al, 2019), providing safer and good quality end products
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