Department of Food Science

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Browsing Department of Food Science by Author "Bala, Shuaibu Mallam"

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    Effect of forced convection roasting on physicochemical and antioxidant properties of whole grain maize (Zea mays L.) and optimisation of roasting conditions
    (Stellenbosch : Stellenbosch University, 2016-03) Bala, Shuaibu Mallam; Manley, Marena; Opara, Umezuruike Linus; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Maize (Zea mays L.) is the most cultivated cereal and grain crop in the world and it is used as a staple food in developing countries such as Nigeria, South Africa, Mexico and economically less privileged countries. The grains of maize are processed into intermediate products (flour and meal) which are utilised for the production of different types of ready to eat foods. In most cases, the flour or meal used is refined (bran and germ removed) and not pregelatinised. Heat-processing methods of maize that uses dry heat reduced the nutritional quality of intermediate and end products. Forced convection roasting (FCR), a novel heat-processing technique, that has an additional advantage of using superheated steam was used to study the changes in physicochemical, proximate composition and antioxidant properties of Nigerian (S28, S33) and South African (H2G1, H7D1) maize varieties. Roasting temperature and rotating speed (determining roasting time) limits (150 to 220 °C) and (30 to 90 Hz), respectively were used for the roasting in a forced convection continuous tumble roaster (FCCTR). Roasting conditions (temperature/rotating speed) of the maize varieties were optimised for the production of whole grain flour or meal. Comparison of the proximate composition, antioxidant and pasting properties of the optimally processed whole grain flour or meal with raw whole grain flour or meal and an unroasted refined commercial maize meal (CMM) was made. The nutritional quality and antioxidant properties (content and activity) of the Nigerian maize S28 (yellow kernel) and S33 (white kernel) were not negatively affected by FCR. For the South African maize varieties, FCR did not show a negative effect on the proximate composition and antioxidant properties except the increase in total phenolics content of H2G1. Variations in the physicochemical properties such as bulk density, kernel hardness, colour and pH of the roasted maize varieties did not compromise the quality of the optimally processed whole grain flours. The prediction models of moisture content, whiteness index (WI), yellowness index (YI), total essential amino acids (TEAA) and total amino acids (TAA) had good fit (R2 >0.8) with the experimental data and non-significant (p ≤0.05) lack-of-fits. The desirability profiling of moisture content, WI and YI indicated 189.9 °C/90 Hz and 140.9 °C/49.8 Hz as the mean optimum roasting conditions of S28 and S33 maize varieties, respectively for the production of high quality whole grain flour or meal. Similarly, the desirability profiling of moisture content, WI, YI, TEAA and TAA showed the mean optimum roasting conditions of H2G1 and H7D1 white maize varieties to be 185.0 °C/65.5 Hz and 182.6 °C/55.0 Hz, respectively. The carbohydrate, crude protein, fat and fiber, ash, total phenolics and flavonoids as well as free radical scavenging capacity of the optimally processed whole grain flours did not significantly differ from those of the raw whole grain flours of each of the maize varieties. Both whole grain flours of the raw and roasted maize grains had higher proximate composition, total phenolics, total flavonoids and antioxidant activity than CMM, except the carbohydrate content which was found to significantly higher in the later. The optimally processed whole grain flour of each maize variety had a non-significantly lower pasting temperatures and significantly higher pasting viscosities compared to the raw whole grain flour. This indicated better pasting characteristics of the optimally processed whole grain flours with reference to the raw whole grain flours of the maize varieties. However, CMM had significantly lower pasting temperatures and higher pasting viscosities than the whole grain flours which indicated better pasting properties of the former. Considering the non-negative effect on proximate composition and antioxidant properties, and better pasting characteristics of whole grain flours of the roasted maize varieties, it could be concluded that FCR is a good alternative for roasting maize grains in the process of producing whole grain flours with the best quality for human consumption. It was also observed that the whole grain flours had better nutritional and antioxidant properties, but poorer pasting properties compared to CMM.