evaluation of the effect of aspergillus flavus inoculation on fatty acids, proxide value and aflatoxin production in four common varieties of peanut cultivated in golestan province

introduction:toxigenic fungi such as a. flavus grow widely in peanut and produce aflatoxins, a group of carcinogenic metabolites. aflatoxin produced in peanut differed from the genetic variety of plant. the high humidity and moderate temperatures in the subtropical caspian littoral of northern iran could increase the growth of a. flavus and the production of aflatoxin. the objectives of this study were 1) to determine the chemical composition of peanut cultivars grown in golestan province, iran, 2)to select resistant variety of peanut to aflaoxigenic a. flavus growth and 3) to evaluate relationship between a. flavus growth and changes in oleic and linoleic acid content and peroxide value. materials and method: peanut samples were used from four important varieties of peanut, goli, mahalli, china and india. those have been harvested from farms in golestan province, iran. fat, protein, ash, moisture, reducing sugar, afb1 content and peroxide value in each sample were measured by the standard method of aoac. fatty acids of the peanut seed oil were analyzed using gas chromatography (gc, varian cp-3800 model) with a flame ionization detector (fid) and a db-wax column (50 m × 0.32 mm ×0.2 µm). to study the effects of a. flavus on peanut varieties, they were sterilized with 0.5% naclo solution and then one ml of a. flavus spore suspension was added to every 20gr disinfected peanut and was placed in the incubator for eight days at 26°c. after incubation, the number of seeds colonized by fungi, spore production, afb1 production, the association between colonization rate of hydrolysis of fatty acids and peroxide value were determined. results and discussion: the results showed that there were significant differences (p<0.05) in the oil, moisture, protein, ash, reducing sugar, oleic acid and linoleic acid content between peanut varieties. average values for the main constituents of peanuts are the following: (oil: 44.77-51.26% , moisture: 3.33-3.56%, protein: 20.02-24.28%, ash: 1.98-2.43%, reducing sugar: 3.56-4.53%, oleic acid: 43.16-59.33% and linoleic acid: 25.19-36.84%). in order to study the susceptibility of peanut varieties to aflatoxigenic, a.flavus growth, colonization rate, aflatoxin b1 and spore production on peanut kernels were evaluated at the end of 8 days of incubation. the results showed that there were also significant differences (p<0.05) between the colonization rates for different peanut varieties at the eighth day of inoculation. the india and china varieties had the highest colonization rates, at 100 and 95.21%, respectively. the goli and mahali varieties had the lowest colonization rates, at 81.61 and 89.6%, respectively. furthermore, at the end of the eighth day of inoculation, a. flavus had covered the india and china varieties completely, but had covered the goli and mahali varieties only slightly. for this reason, additional experiments evaluated the content of spore production with a haemocytometer. it was observed that the goli variety had the minimum spore production, and the india variety had the maximum spore production. therefore, it can be said that the india variety was most susceptible to the a. flavus, followed by (in descending order) the china, goli and mahali varieties. dissimilarity in host resistance to aflatoxigenic a. flavus is due to difference in host genotype. one of the strategies to decrease the risk of aflatoxin contamination is the cultivation of genotypes with resistance to aspergillus infection. some factors found to be associated with resistance to seed colonization by aflatoxigenic a. flavus are cell structure, cell arrangement, permeability, wax layer and tannin content, fatty acid and amino-acid peanut components. in another part of the study, the production of aflatoxin was assessed. results indicated that the india (highest sensitivity to mold) and goli (least sensitivity to mold) varieties were contained the maximum and minimum aflatoxin content, respectively. results also showed that growth of a. flavus on peanut increased the proxide value whereas decreased oleic and linoleic acid content. a. flavus hydrolyzes oil when grown on the oil medium and produces free fatty acid. aspergillus uses of free fatty acid (oleic and linoleic acid) in form of hydroperoxy for production of sexual and asexual bodies. therefore with production of hydroperoxy molecules increase proxide value and decreased oleic and linoleic acid content in the oil peanut that extracted of peanut with mycelium. conclusion: linoleic acid and fat content had significant relationship with a. flavus growth and afb1 production. it seems, it is possible to control the a. flavus growth and afb1 production by choosing varieties that have less acid linoleic and fat content.