Mycotoxin mixtures in the rice food chain: current situation, and pre- and postharvest strategies to minimize contamination

Abstract

Rice (Oryza sativa L.) is one of the most important cultivated grain crops, and is the main energy source and the staple food of nearly half of the worlds population. Almost 500 million metric tons of rice are produced worldwide, and about half of them are from China and India. Rice grains can be affected by different diseases, some of them due to fungi, and these diseases may affect rice in the field and post-harvest. The worldwide yield loss due to different types of pest, at pre-harvest stages, is estimated as 37 %, while the post-harvest losses are estimated as 15 % to 50 % depending on the region, on the challenging climatic conditions, and on agricultural and handling practices. Most of latter losses result from inadequate drying and unsuitable storage facilities. Cereal crops are very prone to fungal infection and to mycotoxins occurrence. Fungi can infect crops in the field and maintain their activity during storage, under conducive ecological conditions. Although not as well studied as in other cereal crops, fungal contamination and the associated production of toxic metabolites in rice, even at lower occurrence levels compared to other crops, is of concern because of the high consumption of rice in many countries. Well-known mycotoxin-producing fungi are able to contaminate rice. Mycotoxin accumulation will result from the combination of different factors such as the mould species, their interactions with other microorganisms, the production area, and the agricultural and post-harvest practices. Due to the diversity of fungi that may contaminate the rice food chain, the co-occurrence of mycotoxins is possible. Co-occurrence of mycotoxins has not been clearly reported; however, based on the occurrence of each single mycotoxins, it is clear that some co-occurrence of mycotoxin mixtures exists. The most evident ones refer to the production of different mycotoxins by the same fungus (as Fusarium toxins and aflatoxins mixtures), but co-occurrence of toxins produced by different fungus were also reported in rice aflatoxins and ochratoxin A, and fumonisin B1, toxin T-2 and HT-2. In Red Yeast Rice, the co-occurrence of citrinin with the previously mentioned mycotoxins was reported. The different ecological needs of the different fungal genera make them a continuous hazard. To prevent and to mitigate the occurrence of mycotoxins, specific strategies may be applied at the pre-harvest part, at harvest, and at post-harvest stages of the crop chain. Appropriate management to mitigate this problem, includes the control of the agronomic and post-harvest practices, taking into account that processing can reduce mycotoxins content, but not overcame their occurrence in the final product.