ارزیابی وضعیت آلودگی خشکبار استان خراسان شمالی به Aspergillus section Flavi و ارزیابی توان توکسین‌زایی تعدادی از جدایه‌ها

Alfatoxins are a large group of mycotoxins that have been extensively studied and are among the most toxic and carcinogenic substances. Since the discovery of aflatoxin in the 1960s, Aspergillus flavus has always been mentioned as the most common fungus contaminating food, especially dried fruit, in scientific references, which indicates the economic importance of this fungus. The present study was conducted in order to investigate the contamination status of dried-fruits (pistachios, almonds and walnuts) to Aspergillus section Flavi in North Khorasan province and to evaluate the toxin-producing ability of the isolates. In order to compare the level of contamination of dried-fruit kernels to the aforementioned fungus, 20 samples of pistachios, 20 samples of almonds, and 10 samples of walnuts were taken from different cities of this province. The samples were ground and then cultured on AFPA, as a selection medium, using dilution culture method. Three to five days after cultivation, Aspergillus section Flavi colonies were isolated, identified and counted; and their relative abundance in different samples was compared. Characteristics such as shape, color and size of conidium, conidiophore, vesicle and basal foot cell, as well as characteristics of strigmata, growth in different culture media and temperatures were used for morphological identification of Aspergillus section Flavi isolates (Klich, 2002). The obtained results indicated that the rate of contamination to Aspergillus section Flavi in different samples of pistachio and almond is varied from each other, so that out of 20 pistachio samples tested, 12 cases (60%), and out of 20 almond samples, 6 cases (30%) were infected with Aspergillus section Flavi. Also, in order to evaluate and determine the potential of aflatoxin production in different isolates, one milliliter of the suspension of spore from each isolate (at a concentration of 103 spores per milliliter) was cultured on 22 grams of sterile chopped rice and was kept for one week at 28°C. After this period, aflatoxin produced on rice was extracted by chloroform. The type and amount of aflatoxin produced was measured by thin layer chromatography (TLC). The results of the experiments showed that out of 50 isolates of Aspergillus section Flavi that were evaluated in this research, 42 isolates (84%) were able to produce one or more types of aflatoxin (B1, B2, G1 and G2), and 8 isolates (16%) were unable to produce any type of aflatoxin. Among the toxin-producing isolates, the range of aflatoxin B1 production ranged from 50 to 10358 ppb, aflatoxin B2 from 21 to 3017 ppb, aflatoxin G1 from 112 to 2362 ppb, and aflatoxin G2 from 64 to 249 ppb.