Model Fermentation of Cocoa (Theobroma cacao) can Produce Similar Microbial and Chemical Quality of Cocoa Compared to Conventional On‐Farm Cocoa Fermentation

Abstract

Polyphenols in cocoa beans contribute from 12 to 18% dry weight of the whole bean. The major constituent polyphenols in cocoa are catechins (37%), procyanidins (58%) and anthocyanins (4%). Despite the high content of polyphenols in cocoa, cocoa processing including fermentation significantly affects the composition and concentration of polyphenols. Study of cocoa fermentation at the laboratory scale is challenging since industrial cocoa fermentation requires at least 25 kg of fresh wet beans to achieve the proper conditions for fermentation. In this study, dried unfermented cocoa bean and a simulated pulp were used as substrate for laboratory scale fermentation. Microbial and chemical characteristics were monitored over the course of fermentation. Commercially available dried unfermented cocoa bean was first rehydrated with water and then mixed with simulated pulp media developed to ensure the growth of yeast, lactic acid bacteria and acetic acid bacteria, the essential microorganisms for cocoa fermentation. A temperature profile similar to on‐farm cocoa fermentation was acheived using a laboratory incubator. Aeration by shaking the fermentation box at 150 rpm promoted growth of acetic acid bacteria. As a result, internal pH of the cocoa bean decreased from pH 5.73 to pH 4.8 over 7 days of fermentation. By using selective and differential media, yeast growth reached 5.28 × 108 CFU/ml at day 4 and anaerobic bacteria was detected from day 1 and reached the highest concentration of 3.16 × 109 CFU/ml at day 4. Aerobic bacteria was also detected from day 1 and increased gradually to reach a maximum of 2.29 × 109 CFU/ml at day 4. Total concentration of procyanidin (mean ± STDEV) in fermented cocoa bean was analyzed using 4‐Dimethylaminocinnemaldehyde (DMAC) method. Total procyanidin decreased by 64% from day 0 to day 7 (day 0: 0.19 ± 0.01 g procyanidin B2 equivalents/g cocoa extract, day 7: 0.07 ± 0.01 g procyanidin B2 equivalents/g cocoa extract). Folin‐Ciocalteu colorimetric method was performed to determine the total polyphenol content (mean ± STDEV) during fermentation and a 33% decrease was observed from day 0 to day 7 (day 0: 3.63 ± 0.2 g gallic acid equivalents/g cocoa extract, day 7: 2.45 ± 0.2 g gallic acid equivalents/g cocoa extract). The cocoa fermentation model developed in this study will be further employed to evaluate the effect of fermentation conditions on concentration and composition of bioactive compounds and bioactivity thereof in cocoa.Support or Funding InformationVirginia Agricultural Experiment Station salary and startup support for A. Stewart