Detection of insect necrotic internal damage and aflatoxin reductionin stored pistachio nuts


Abstract: In recent years, a commercial issue exists due to the occurrence of pistachio nuts withkernel necrosis symptoms, which are considered of reduced quality and cannot be marketed.Furthermore, results from our previous study concerning aflatoxin contamination of Greekpistachios suggested higher probability of aflatoxin contamination in those nuts. Pistachios withkernel necrosis symptoms are considered to be infected by the stigmatomycosis disease thatresult from insect (hemipteran) feeding punctures before harvest that remain untill storage. Theobjectives of this work were to investigate a) the cause pathogen of the kernel necrotic spot inGreek pistachios. b) the correlation among pistachios with kernel necrotic symptoms, Aspergillussc flavi presence and aflatoxin contamination and c) the potential of X-ray imaging for detectingnuts with necrotic spots in the kernel; there is not currently available a non-destructive method ofinspection and removal of such nuts.To achieve these goals, three samples of stored dried pistachios with a high percentage ofkernels with necrotic spots were obtained. First sample (A) was assessed for the naturaloccurrence of Aspergillus fungi as well as for the isolation and identification of the causalpathogen of the kernel necrotic spot. X-ray images were acquired in 100 randomly selectedwhole shelled pistachios from the second and third sample (B and C). Afterwards, colour picturesof the kernels of each nut examined were taken. Kernels with and without necrotic symptomswere analyzed for aflatoxin contamination separately in both samples (B and C.The results for aflatoxin contamination showed that the pistachios with kernel necrotic spotscontained about 60 times more aflatoxin than the pistachios without spots in contaminatedsamples. Also, necrotic spots could be identified in X-ray images as a darker gray area of adistinctive shape. The development of an automatic separation method based on this techniquewill eliminate these nuts and thus will reduce total aflatoxin amount up to 98% in aflatoxincontaminated batches and will improve the quality in batches free of aflatoxin removingpistachios with unacceptable defects.

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