Chrysosporium species, potential spoilage organisms of chocolate.

Abstract

Standard methods of analysing foods for the presence of moulds are inadequate for the detection of genera such as Chrysosporium which do not grow at the high water activities of most mycological media. The use of malt, yeast, 50% glucose agar (MY50G) in sealed containers as an enrichment medium allowed time for germination and growth of heat-stressed spores. Three Chrysosporium spp., C. xerophilum Pitt, C. inops (Carmichael) and C. farinicola (Burnside) Skou, were isolated from commercial chocolate bars with a water activity (aw) of approximately 0.28. Chrysosporium inops was isolated from commercial milk crumb and a new Chrysosporium sp. was isolated from Ghanaian cocoa beans. In chocolates made by coating MY50G agar (aw = 0.89) with chocolate (aw = 0.27) containing C. inops arthroconidia, two types of deterioration were seen after storage. The first was fat bloom due to recrystallization of the cocoa butter on the outer and inner chocolate surface. The second was growth of C. inops which occurred on the inside chocolate surface adjacent to the MY50G agar filling and on the outside surface after holding at 92% equilibrium relative humidity (erh) for 12 d. There was some evidence that C. inops could grow on the outside of chocolates held at 5.7% erh after 4 months' storage at 25 degrees C. The appearance of the white fungal growth was not unlike fat bloom to the naked eye but was clearly different with the electron microscope.