It is surprising to note that few studies have been conducted if poor postharvest practices can result in the nutritional quality loss of grain due to the activity of spoilage fungi (Sinha 1982). Different grains have different levels of intrinsic calorific values and, thus deterioration by different spoilage fungi will affect these values to different extents. Elegant studies by Demenyk and Sinha (1988), Sinha (1995), and Sinha et al. (1986) demonstrated that the bioenergetics of insects feeding on different grain types enables energy budgets to be established and provided useful information on the impact that pests have on actual calorific value of stored cereals. However, in stored grain ecosystems factors such as aw, temperature, gas composition, and level of fungal contamination will all have a significant impact on calorific losses and provide a useful link with quantifiable levels of dry matter losses for different cereals.
Studies by Prasada and Prasad (1982) reported changes in the calorific value of linseed (Linum usitatissimum; L = 1.896 kJ/g) due to seed-borne infection by spoilage fungi. They found that A. niger infection resulted in maximal calorific losses of 25.2% within 15 days, and almost 50% in 30 days at 28°C on surface sterilized seeds. Losses from autoclaved and inoculated seeds were higher. However, water availability was not monitored or controlled. More recent studies where both aw and temperature were carefully controlled have examined the effects caused by the mycotoxin producing species of F. verticillioides and F. proliferatum and A. ochraceus (Marin et al. 1999c; Ramos et al. 1999a,b). The Fusarium spp. were found to maximally cause calorific losses of maize based substrates (= 19.69 kJ/g) at 0.98 aw (17-64%) after 4 weeks depending on temperature of incubation, but negligible at 0.92 aw (0-9%). An inverse correlation was found between calorific losses and fungal biomass and fumonisin production. For A. ochraceus calorific losses were maximal at 0.95 aw and 20-30°C on similar maize-based substrates. Losses were in the region of 10-17% over 4 weeks with much lower losses at 0.85 aw (0-7%). There was a direct relationship between increase in fungal biomass and calorific losses. As each grain type has a different intrinsic calorific value it is critical that these studies are expanded to include rice and other staple cereals to enable the relationship between the activity of spoilage fungi in stored cereals to be quantified both on the basis of the significance of nutritional losses and in terms of dry matter losses.
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