Kinetic Studies on Cocoa Roasting Including Volatile Characterization

Despite roasting being the most crucial step in cocoa manufacture, its thermochemical effects on cocoa are not entirely understood. This work aims to understand the kinetics and chemical composition of the volatile compounds formed during roasting. The weight loss of two sizes of cacao powder was evaluated in thermogravimetric analysis (TGA) with five heating rates (10 to 180 °C min-1), using air and nitrogen as the carrier gas. A global Friedman isokinetic model was used to obtain kinetic data from the TGA measurements. For this, seven different stages were discriminated, and the kinetics were determined for each stage separately. PTV-GC-MS identified the gas phase, and SPME-GC-MS quantified the volatile compounds trapped in the solid phase. At intermediate temperatures (150 to 250 °C), aromatics (e.g., pyrazines, aldehydes, ketones, phenols, and pyrroles) are formed and transferred to the gas at higher temperatures for a prolonged time. Typical Maillard and Strecker degradation reaction products in both gas and solid phases were identified and used to set up a reaction network for cocoa roasting.