Improving carbohydrate quality of polished maize flour using heat-moisture treatment
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Date
2026-08
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Gulu University
Abstract
Polished maize flour, consumed by more than 90% of Ugandan households, has fast starch digestibility and low resistant starch (low carbohydrate quality), which may make its high consumption a risk factor for non-communicable diseases. Among many methods used to modify starch and reduce its digestibility, heat moisture treatment (HMT) is a preferable and extremely attractive method due to its effectiveness for promoting high resistant starch development, flexibility in relation to heat sources, low cost and the non-generation of chemical residues. However, limited studies exist on application conditions of HMT to decrease starch digestibility of polished maize typically consumed in Uganda and other African countries. The overall objective of this study, therefore, was to improve the carbohydrate quality of polished maize flour using HMT. Out of 86 maize varieties promoted in Uganda, thirteen widely cultivated and consumed were selected for evaluation of their carbohydrate quality in terms of the carbohydrate-to-fiber ratio and glycemic index, and internal factors affecting their starch digestibility. Four varieties among the thirteen varieties, UH5354, DK777, Longe 10H, and DT Max, were further assessed for optimal HMT conditions using Box–Behnken design. The effect of optimal HMT conditions on the physicochemical and techno-functional properties of maize was assessed. Finally, the effect of polishing grade on the physicochemical, techno-functional properties, starch digestibility, and sensorial properties of HMT-treated maize grains was determined. The results revealed that the CHO-to-fiber ratios of the thirteen maize varieties ranged between 5.28 and 10.15, whereas their glycemic indices ranged from 79.38 to 87.43, indicating low carbohydrate quality. The internal parameters affecting starch digestibility varied significantly across the maize varieties (p < 0.05), and these subjected the varieties to be grouped into four distinct clusters (p < 0.05) based on hierarchical cluster analysis. The optimal HMT conditions to minimize starch digestibility for the four varieties selected from the identified clusters were as follows: UH5354 (23.17%, 80°C, 4.12 h), DK777 (20.83%, 95.43°C, 5.42 h), Longe 10H (34.51%, 90.46°C, 3.01 h), and DT Max (19.24%, 97.02°C, 5.88 h). These optimal conditions had no significant effect on the physicochemical composition of the maize varieties. However, HMT affected some techno-functional properties. Particularly, the swelling volume of DT Max (7.13 ml/g) and Longe 10H (8.23 ml/g) reduced by 0.45 and 0.60ml/g, respectively while water absorption xv capacity of Longe 10H (1.20 ml/g) and UH5354 (1.27 ml/g) increased by 0.08 and 0.10 ml/g, respectively. The pasting temperature increased from 82.4°C to 90.8°C for DK777, 86.0°C to 87.3°C for UH5354, 79.9°C to 82.3°C for Longe 10H and 89.2°C to 94.4°C for DT Max. These changes potentially may affect the maize dough and posho quality and thus may decrease flour acceptability. In contrast, polishing significantly improved the amylose content and color (p < 0.05) and the swelling volume of UH5354 and Longe 10H (p < 0.05). The solubility, water absorption capacity, and pasting temperature consistently decreased
after polishing (p < 0.05), whereas the peak and holding viscosities increased (p < 0.05). Sensory quality improved substantially from unpolished to semi-polished forms, particularly for DK777, UH5354, and Longe 10H. Although HMT effectively reduces starch digestibility, it also negatively impacts the techno-functional properties of flour, which may affect flour acceptability. Conversely, polishing tends to improve these technofunctional properties of HMT-treated flour and thus enhances the sensory attributes of posho. It is therefore recommended that maize milling industries and processors in Uganda and other East African countries adopt the optimized heat-moisture treatment conditions
together with an appropriate polishing grade to produce polished maize flour of improved carbohydrate quality and acceptable sensory quality. Policymakers should also integrate this technology into national food and nutrition strategies to help mitigate diet-related noncommunicable diseases. Finally, further research should investigate the optimal conditions for both HMT and polishing to achieve lower starch digestibility as well as improved
sensory qualities while minimizing nutrient losses.
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Keywords
Carbohydrate quality, heat‒moisture treatment, starch digestibility, techno functional properties, polishing, sensory acceptability.