Impact of cocoa variety on physical and chemical properties, reconstitutability, and flowability of cocoa powders

Abstract

Cocoa of the Criollo, Forastero, and Trinitario varieties grown in the same production area of the Republic of the Congo were simultaneously harvested and similar post-harvesting operations (fermentation in crates followed by sun-drying) were performed. Cocoa powders were then produced according the same process consisting in successive roasting, grinding, fat extraction by pressing, and ultrafine grinding of the defatted mass. In order to investigate the influence of cocoa variety, the main physical and chemical properties (proximate composition, pH, particle size and shape distributions) of powders were characterized and related to cocoa powders abilities to reconstitute and flow. The three varieties showed very close proximal compositions, with lipid contents varying between 21 and 23 % (w/w), which classifies them as defatted cocoa powders. Cocoa powders of all varieties were non-wettable, and not soluble (solubility index around 0.15 g/g), consistently with their high lipid content. The fatty, fibrous, and proteic nature of the product has an impact on the grinding process, resulting in non-wettable powders and particles of varying sizes and shapes. All powders had bimodal particle size distributions, with large particles around 500 μm and small ones around 25 μm. However, slight differences between varieties were observed for some shape and functional properties. Trinitario and Forastero cocoa particles were slightly less spherical. The Criollo cocoa powder was relatively more compressible than the Trinitario variety. No significant difference of flow properties was attributable to cocoa variety. Basic flowability energy of all cocoa powders were relatively high, ranging from 908 to 973 mJ, which could denote a low aptitude to flow that may be related to the probable softness and stickiness of particle surface due to the high lipid content of cocoa powders. Specific energy values required to make studied cocoa powders flow were in the range between 6.61 and 6.99 mJ/g, which corresponds to intermediate values indicating a moderate level of cohesion and thus a fair flowability. The flow parameters obtained from the shear cell test showed no significant difference of cohesion (comprised between 1.54 and 1.70 kPa), flow factor (ranging from 2.53 to 2.76), and internal angle of friction (between 33.4 and 33.9°) linked to cocoa variety. This may be explained by the impact of particle size, as higher particles are generally less cohesive due to their lower surface specific area implying less interparticular contact points. Apart from these slight differences, all varieties showed similar properties and thus could be blended instead of being sorted in the cocoa manufacturing process. This study permitted to highlight that the terroir, the method of harvesting and preparing the beans, and then producing the powder have probably more impact on the physical and chemical and functional properties of cocoa powders than their variety.