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Abstract:Hazelnut kernels became rancid on storage under ambient conditions in the presence of air. The kernels have a high oil content. The oil contains approximately 75 g per 100 g oleic acid (18: 1) and 9 g per 100 g linoleic acid (1 8 : 2). Rancidity was detected organoleptically, by gas chromatography/mass spectrometry of the volatile off-flavour compounds and by reduction in both the total fatty acid content (g per 100 g oil) and the iodine value (g per 100 g oil).There was an accumulation of volatile alkanals, 2-alkenals and alkanoic acids on storage of the kernels at ambient temperature in the presence of oxygen. Hexanal (derived from oxidation of linoleic acid) and octanal (derived from oxidation of oleic acid) increased over tenfold on storage, whilst there was concomitant decrease in fatty acid content (83 g per 100 g oil) and iodine value (79) during the same period. It is suggested that analysis of volatile aldehydes such as hexanal and octanal could be used to assess rancidity in foods or oils rather than relatively nonspecific tests such as iodine or peroxide value. There was no evidence in this work that the rancidity was due to microbial spoilage.

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A number of fungal detoxification reactions of sorbic acid have been reviewed. These include decarboxylation to give trans-1,3-pentadiene, esterification to give ethyl sorbate, reduction to give 4-hexenol and 4-hexenoic acid. It was shown that seven Penicillium species could convert sorbic acid into 1,3-pentadiene whilst P. bilaii, P. fellutanum and P. glabrum did not. However, most Eurotium species were unable to bring about this conversion. Considerable differences in the resistance of two isolates of P. crustosum to sorbic acid were found. An isolate from coconut was more resistant than one isolated from hazelnuts. Both sorbic acid and caproic acid (hexanoic) brought about disorganization of the mitochondrial membranes in P. crustosum. It is suggested that these lipophilic acids inhibit growth by interfering with the electrochemical membrane potential across the mitochondrial membranes.

. 1997. 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 (a w ) 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 (a w 0·89) with chocolate (a w 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°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.