Influence of Turning Intervals on Microbial Succession and Volatile Aroma Development During On-Farm Cocoa Bean Fermentation

The present study examined the effects of microbial communities and their associated physicochemical characteristics during on-farm cocoa fermentation in Chiang Mai, Northern Thailand, evaluated at a 60-kg wooden box scale. Two fermentation processes, 24- and 48-h interval turning processes, were comparatively evaluated. Microbial populations were monitored using both culture-based enumeration and culture-independent molecular techniques. The results showed that lactic acid bacteria and acetic acid bacteria were the predominant microbial populations throughout fermentation. Multivariate analysis found that fermentation time significantly shifted the community from yeast-based communities (Saccharomyces and Hanseniaspora) and bacterial (Limosilactobacillus fermentum) towards a late-stage community dominated by acid-tolerant Acetobacter pasteurianus. Moreover, the turning interval strongly influenced the microbial community, with a 24-h interval favoring Saccharomyces and Komagataeibacter, whereas a longer 48-h interval selectively promoted Candida, Meyerozyma, and Acinetobacter. Physicochemical properties also showed that total acidity increased and pH decreased in both processes, while reducing sugars declined over time. In the 24-h turning process (T24), reducing sugars decreased from 64.80 mg/g at 0 h to 3.73 mg/g at 144 h. Similarly, in the 48-h turning process (T48), reducing sugars decreased from 64.29 mg/g at 0 h to 3.21 mg/g at 144 h. Pectinase activity was detected as the main enzyme activity in both processes. In addition, the T24 process showed that Saccharomyces, Limosilactobacillus, and Lentilactobacillus were positively correlated with key fruity/sweet esters, whereas Lentilactobacillus and Acinetobacter were correlated with volatile markers linked to off-flavor notes (butanoic acid and dimethyl disulfide) in the T48 process. Overall, more frequent turning clearly promotes more volatile compounds associated with desirable aroma profiles, and standardizing turning schedules could help improve batch-to-batch consistency for aroma development and reduce the risk of undesirable flavor formation during scale-up.