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The aim of the present study was to evaluate the nutritional quality of traditional sun-dried maize grain, subjected to further heat treatment. The maize grains were obtained from three different locations, namely Moree in NSW, Emerald in QLD and Darling-Downs on the NSW-QLD border, Australia. Once received, one batch (sun-dried) was assessed without further drying. The other two batches from each source were dried artificially using a forced draught-oven at 105°C for 30 min or 24 h. The morphological structures (starch granules) of grains were changed due to heat-treatment for 30 min at 105°C and far-reaching structural changes occurred when samples were heated for 24 h. Proximate analysis of maize revealed that the DM (897.3-967.4 g kg-¹), CP (92.1-108.7 g kg-¹), EE (49.0-57.5 g kg-¹), phytate-P (1.2-2.4 g kg-¹) and ash (14.1-19.7 g kg-¹) contents of samples varied due to source and heating period. The starch, amylose, available amino acid and mineral contents increased with increasing heating duration. Variable anomeric proton peaks (H-NMR) were found with an increase in the oven drying period in all maize samples. 'In vitro' digestibility of DM, starch and CP was improved due to heat-treatment at 105°C for 30 min 24 h. It may be concluded that the chemical composition, ultra-structural characteristics and energy values of maize samples varied by source and were changed through heating of low-moisture maize over varying time periods. These changes could impact on the nutritive value of the grains and animal performance. |
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