Processing of almonds and apricot kernels: new insights on evolution of aflatoxins

Objectives Almonds and apricot kernels have several health benefits. They are a good source of proteins, fiber, unsaturated fats, vitamins and minerals. They are consumed as raw nuts or as ingredients of derived products. However they can be contaminated by aflatoxins (AFs), well known carcinogenic mycotoxins. We evaluated the evolution of AFs during transformation processes of almonds into traditional Italian products, such as pastries, nougat and syrup which involves blanching, peeling, cooking, roasting and water infusion. The efficacy of sorting to segregate AFs contaminated apricot kernels was also assessed. Materials and Methods Experiments were conducted on naturally contaminated apricot kernels and almonds inoculated with a toxigenic strain of Aspergillus flavus. A robust and horizontal HPLC-FLD method was optimized and used for AFs determination in all the matrices considered in this study1. Results Blanching processes (by steaming or boiling in water) did not reduce AFs levels in peeled almonds and apricot kernels. Standard roasting conditions produced up to 50% reduction of AFs. During nougat preparation it was observed a 54-70% AFs reduction due to the caramelisation of sugar on almond surface. AFs were instead stable during cooking of pastries. During almond syrup preparation 18-25% of AFs passed in the final syrup and the whole process produced a marked increase of total AFs. This increase was probably due to the water infusion of ground peeled almonds that activates endogenous almond enzymes that release free AFs from masked AFs1. To reduce AFs contamination in apricot kernels we applied the manual colour sorting to peeled kernels and obtained excellent results: 97-99% AFs reduction by removing only discoloured kernels. Conclusions Roasting, caramelisation and manual sorting of peeled nuts were identified as effective processes to reduce AFs in nuts. We observed, for the first time, a marked increase of AFs during almond syrup preparation which suggests the existence of masked AFs never reported before. The separation of discolored apricot kernels is a feasible strategy to remove almost all AFs in contaminated peeled kernels. These information are extremely useful and can be exploited by food producers to improve the safety of nuts and derived products. 1 Zivoli et al. 2014. Effect of Almond Processing on Levels and Distribution of Aflatoxins in Finished Products and By-products. J. Agric. Food Chem. 62: 5707-5715.