Acoustic and mechanical testing of commercial cocoa powders

Abstract

In the present study, commercial cocoa powders with different cocoa fat contents were studied. It was found that the cocoa powders' flow patterns were of a cohesive to highly cohesive characters. It was demonstrated, that the powders of higher crystalline structure were less flowable compared to the ones with the more amorphous ones. It was observed by SEM that the studied cocoa powders of higher cocoa fat content and the ones with the dietary fibers content (sample 2) exhibited more amorphous structure. The predominantly smooth surface structure of the higher fat content cocoa powder allowed its higher dense packing, triggering the decreased sound absorption typical for non-porous materials as quantified by NRC of 0.289 (sample 1, 100 mm material height) and 0.227 (sample 3) to 0.182 (sample 2). The latter conclusions were also supported by the observed increase of the structural mechanical stiffness of the freely poured powder bed of high cocoa fat amorphous powders, as resulting in the increasing magnitude of the K-l of 12.83 MPa (sample 1, 100 mm material height) and 19.29 MPa (sample 3) to 37.82 MPa (sample 2). Melting temperatures of the samples were determined by DSC. Results were directly corresponded to the cocoa butter content. The highest enthalpy of fusion (Delta H (m)) of (23.32 +/- 0.21) J/g was obtained for the highest cocoa butter containing sample 2 (of 20-22 wt. %). Obtained values of Delta H (m) for samples 1 and 2 were of (12.38 +/- 0.20) J/g and (10.27 +/- 0.17) J/g. T-p (melt) for reversing heat flow was ranging from (30.16 +/- 0.10) degrees C to (32.28 +/- 0.10) degrees C indicating the melting of stable beta polymorph. The melting peaks observed at distinct temperatures in the non-reversing heat flow patterns were indicating melting of the unstable alpha and metastable beta' and stable beta cocoa butter polymorphic forms.