An untargeted metabolomic assessment of cocoa beans during fermentation

Abstract

Fermentation is a critical step in the processing of high quality cocoa; however, the biochemistry behind is still not well understood at a molecular level. In this research, using a non-targeted approach, the main metabolomic changes that occur throughout the fermentation process were explored. Genetically undefined cocoa varieties from Trinidad and Tobago (n = 3), Costa Rica (n = 1) and one clone IMC-67 (n = 3) were subjected to spontaneous fermentation using farm-based and pilot plant controlled conditions. Samples were collected daily, and acetone/water/acetic acid (70/29.5/0.5%) extracts were obtained and measured using a UPLC-ESI+-Q-Tof-MS system. Analysis of pre-processed data, applying a PLS-DA model, highlighted significant differences between the three fermentation periods, observed at 0–2, 3–4 and 5–6 days, respectively. Among the most discriminating metabolites, sucrose, flavanols such as (epi) catechin, procyanidin dimers and trimers, anthocyanins and oligopeptides ranging in size from 3 to 12 amino acids were tentatively identified. In general, flavanols and sugars tended to decrease throughout fermentation, whereas most oligopeptides increased to maximal levels after 3 to 4 days of fermentation and decreased thereafter. These results shed new insight into cocoa fermentation optimization strategies and may also contribute to the development of novel alternatives for cocoa processing based on biochemical and functional values.