Identification of microbial diversity associated with post-harvest storage of rice in India

Abstract

The microbial communities associated with eleven samples of milled and un-milled rice from various storage facilities and local trade markets of Haryana, India were analyzed using high-throughput pyrosequencing. Comparison of the microbial community compositions of freshly harvested paddy and stored rice led to identification of the dominant fungi and bacteria specifically present or enriched during storage. Greater microbial diversity of fresh paddy as compared to milled rice suggests that milling may be responsible for the removal of many microbes from paddy. Lactococcus, Lactobacillus, and Leuconostoc were the major bacterial genera specific to stored rice. Clostridium, although low in abundance, was significantly enriched during storage. The dominant fungus specific to stored rice was the well-known ‘storage fungus’ Aspergillus. It was present along with ‘field fungi’ Fusarium, Alternaria and Cladosporium. The wide range of temperature tolerance of lactic acid bacteria and Aspergillus may be leading to their high abundance at storage sites. The presence of lactic acid bacteria together with ‘field fungi’ is indicative of high moisture contents (>20%) and anaerobic conditions at storage sites. The lactic acid bacteria as well as Clostridium produce volatile organic compounds and biogenic amines which enhance spoilage of food grains. Aspergillus and Fusarium, on the other hand, are mycotoxigenic fungi known to produce toxins that are carcinogenic to humans. In conclusion, the microbes identified are suggestive of inappropriate post-harvest storage conditions leading to negative implications on grain quality and human health.