.Spontaneous and inoculated fermentations of cocoa in a farm scale were performed in this study. For inoculations, the starter culture containing S. cerevisiae, P. kluyveri and H. uvarum yeast species was used. The dynamic behavior of the population of the starter culture species during cocoa fermentations in the two assays (control and inoculated) was monitored by qPCR. The sequences and product sizes of the primers are summarized in Table 1, as well as the qPCR parameters obtained for standard curves. Standard curves were established for each primers set. The reaction efficiencies ranged between 88% (P. kluyveri) and 96% (S. cerevisiae) with high reproducibility. The lowest detection limit was 102 cells mL−1. The melt curve analysis for each PCR showed a single peak (data not shown).
The yeasts S. cerevisiae, P. kluyveri and H. uvarum were detected and quantified during control and inoculated fermentations by qPCR ( Fig. 1). S. cerevisiae was predominant in both fermentations; however, in the control the population was lower (ranging from 4.4 to 5.9 log cell/g) than in the inoculated fermentation (ranging from 6.7 to 7.9 log cell/g). In the control, the population of H. uvarum and P. kluyveri ranged from 3.4 to 4.5 log cell/g and 2.8 to 3.7 log cell/g, respectively. Whereas in the inoculated assay, P. kluyveri showed higher population than in the control (3.6–5.0 log cell/g) and H. uvarum showed similar population (3.6–4.5 log cell/g). It was expected that higher populations of these species would be found in the inoculated fermentation than in the control; however this was not the case for H. uvarum. It seems that the other yeasts, mainly S. cerevisiae, detected in highest numbers may inhibit the H. uvarum growth.