Evaluation of dry nuts for aflatoxins and their reduction by chemical and γ ray treatments

Abstract

Aflatoxins are secondary metabolites of mould Aspergillus section Flavi species. These toxins are very carcinogenic, mutagenic and teratogenic in nature. They are opportunist toxins and can exist in any food or feed commodity. Nuts are inspired worldwide for their nutritional, sensory and health promoting attributes. Aflatoxin contamination of tree nuts (almonds, pistachios and walnuts) and ground nut is a significant food safety related problem worldwide. Infect, aflatoxins were first reported in 1960’s in peanut feed. As nuts are mostly consumed mostly directly, so the chances of aflatoxin decontamination during food processing procedures are also minimized. Aflatoxin contamination can occur pre-harvest, in field, postharvest like transport, handling and storage. The lack of preharvest control of mycotoxins has made them a postharvest threat. The contamination of a single nut in a lot can lead to the deterioration of the entire lot due to proliferating mycoflora. There are a number of outbreaks reported in literature in different countries throughout the world due to the consumption of aflatoxin contaminated food and feed stuffs. No single method is currently available which can detoxify aflatoxins and eliminate fungal load responsible for aflatoxin contamination along with the guarantee of wholesomeness of all types of food commodities. The present study emphasizes on multiplication of fungal species and the formation of aflatoxins in selected nuts during storage at two different moisture levels. The second major focal point of the study was decontamination of aflatoxins, along with elimination of contaminating fungal species using physical method, gamma and ultra violet irradiation, and chemical method like citric, lactic and propionic acid in ground and tree nuts. The results of the study showed that physical methods like γ and UV radiations can effectively reduce total aflatoxin content as well as aflatoxin B1 (AFB1), the most toxic aflatoxin. The irradiation (γ and UV) also significantly reduced the contaminating mycoflora. The degradation of aflatoxins by irradiation was also kinetically evaluated and found to follow first order rate kinetics. The degradation rate constants are also reported. The advantage of using irradiation is that it does not result in the formation toxic chemical residues. Organic acids also reduced the total as well as AFB1 to permissible limits. The degradation of aflatoxins by organic acids was found to follow exponential decay function. Citric acid was more effective than lactic and propionic acids in detoxifying aflatoxins. The results revealed that lactic and propionic acids can more efficiently reduce the fungal count than citric acid. The lipid fraction, tocopherol content and free fatty acid profile of the ground and tree nuts were also estimated at different time intervals during storage. The fungal growth significantly affected the oil quality of nuts, in view of the fact that being consumed as substrate by the infecting mycoflora. The tocopherol content was not significantly affected by gamma irradiation, where as UV irradiation significantly degraded the tocopherol content following first order rate kinetics. In case of fatty acids, γ-irradiation selectively affected saturated, monounsaturated and polyunsaturated fatty acids, resulting in a decrease in oxidation index, ensuring an extension of shelf life. Over all irradiation particularly gamma ray treatment proved to be effective in reducing fungal count and aflatoxin content without significantly affecting the quality of the selected food.