Surface structure and composition of fresh and bloomed chocolate analysed using X-ray photoelectron spectroscopy, cryo-scanning electron microscopy and environmental scanning electron microscopy.

摘要

Bloom on chocolate is an unsightly surface condition resulting in a white, powdery appearance that consumers interpret as a sign of poor quality. Bloom results from incorrect processing or storage. Two innovative methods have been developed, and used in conjunction, to investigate the morphology and composition of bloomed chocolate. Environmental scanning electron microscopy (ESEM) was used to image the morphology of the surface of fresh and bloomed chocolate and to observe the changes in morphology, in real time, during heating and cooling. The nodular morphology of sugar bloom was easily distinguished from the blade like crystals of fat bloom. Surface details for the fat blades indicated an extrusion mechanism during their formation on the chocolate surface. 'Cold stage' X-Ray Photoelectron Spectroscopy (XPS) was used to analyse the surface composition of fresh and bloomed samples. The carbon species present in the bloom on poorly tempered chocolate were a combination of CH2, C-OH, O=C-OH and O-C-O groups indicating a mixture of sugar and fat bloom. Conversely the species present on bloomed, well tempered chocolate comprised only CH2, C-OH, O=C-OH indicating the bloom was comprised of fat (from cocoa butter) and no sugar. All rights reserved, Elsevier.