The Effects of Storage on Nutrient Composition and Mycoflora of Stored Guinea Corn (Sorghum bicolor) Grains

Abstract

Aims: This research work aims to determine the changes in nutritional (proximate, mineral) composition and mycoflora of Sorghum bicolor grains stored for 5 months in order to determine its fitness in meeting nutritional demand.                         Study Design: Experimental study design was carried out Place and Duration of Study: Department of Microbiology, Ekiti State University, Ado-Ekiti, from February 2017 to August 2018. Methodology: The grain was procured from Usi market in Usi-Ekiti. It was further sundried for seven days and stored in an airtight container in the laboratory at room temperature. They were visually examined for external changes on the caryopsis and cultured to determine the spoilage fungi. Mineral and proximate analyses were routinely carried out to determine the changes in nutrient composition. These analyses were carried out monthly for five months to determine the changes in physicochemical properties and mycoflora associated with Sorghum bicolor on storage. Results: During storage, spoilage such as external mouldiness, discoloration, musty odour and progressive depletion of external caryopsis were observed on the grain. Seven species of fungi namely Penicillium glabrum, Aspergillus flavus, Penicillium spp., Fusarium spp., Alternaria spp., Aspergillus niger and Saccharomyces cerevisiae were isolated using a combination of direct plating, dilution and washing method. The colony count of the mycoflora population increased from 6 to 16 spore-forming units per gram. The proximate component comprising ash, moisture, crude protein, fat and fiber content decreased but an increase in carbohydrate content was recorded. A negative Pearson correlation (r = - .990) between crude protein and carbohydrate content was recorded. This was attributed to the presence of resistant starch in Sorghum bicolor and the use of alternative source(s) of carbon for energy by the fungi. The entire mineral component decreased during storage. Copper was the barest mineral while magnesium was the most stable mineral in the stored grain. Conclusion: Sorghum bicolor grains contain vital minerals and nutrients. Prolonged storage of Sorghum bicolor increased the mycoflora population and consequently decreased the nutrient composition excluding the carbohydrate component. Some minerals and proximate components of the grain were relatively stable while others experienced pronounced depletion. Nutritionally deficient grains may lead to malnutrition especially in growing animals and human populations were adequate minerals and nutrients are required for rapid growth.