Kinetics of hot air roasting of cocoa nibs and product quality

Abstract

AbstractCocoa beans are widely used in the manufacturing of various food and beverage products such as chocolates, powdered drink, cookies, confectioneries, and others. Processing plays a vital role in governing the final flavor profile of cocoa beans especially during roasting. The current studies aimed to determine the transport properties of cocoa nibs during roasting and also to investigate the quality of roasted cocoa nibs. Cocoa nibs were roasted at temperatures of 120, 130, and 140 °C inside a hot air convective oven. Kinetics analyses showed that overall rates of sensible heating (from T = 27 to 100 °C) were in the range of 5.1–9.5 °C/min as compared to overall rates of effective roasting (from T = 100 °C onwards) in the range of 0.9–1.4 °C/min. The observed moisture content profiles followed the typical exponential decay as commonly explained by the Fick's second law of diffusion. The dependency of thermal and moisture diffusivities with temperatures could be described using quadratic and Arrhenius models, respectively. It was determined that the average order of magnitude for moisture diffusivity was 10−10 m2/s as compared to 10−9 m2/s for thermal diffusivity. High roasting temperature had a negative impact on cocoa polyphenols where greater degradation was observed. Sensory evaluation showed that cocoa liquor produced from the higher temperature treatment (T = 140 °C) had the highest cocoa flavor.Practical applicationsInformation on the roasting kinetics and moisture/thermal diffusivities are important design parameters for cocoa roaster. Changes in flavor quality during roasting are important in governing the development of flavor in the finished chocolate products. Therefore, the current studies contribute knowledge to the cocoa industry for both equipment and chocolate manufacturers.