Optimized heat-moisture treatment decreases the starch digestibility of polished maize flour from predominant varieties consumed in Uganda

• Consumption of polished/refined maize flour is a risk factors for non-communicable diseases in Uganda • Heat-moisture treatment (HMT) is an eco-friendly physical method used to decrease starch digestibility • Optimal conditions for HMT to decrease the starch digestibility were established using response surface methodology • HMT decreases starch digestibility through improving of slowly digestible and resistant starch content of polished maize flour for four maize varieties • Development of slowly digestible and resistant starch varied according to the maize varieties. In Uganda, maize flour is the major carbohydrate food source for over 90% of households. It is largely consumed in polished form characterized by high digestibility, rapidly releasing glucose into the bloodstream, making it unsuitable for metabolic health. This calls for the reduction of maize flour digestibility through increasing its slowly-digestible (SDS) and resistant-starch (RS) contents, typical function of Heat-moisture Treatment (HMT). However, HMT efficacy depends on the botanical starch source and HMT conditions necessitating its optimization. This study investigated optimal HMT conditions to produce polished maize flour with lower starch digestibility by increasing SDS and RS contents for four maize varieties (UH5354, DK777, Longe 10H, and DT Max). Response surface methodology (Box-Bakhen design) was used to set the experimental design with moisture (20-30%), temperature (80-100°C), and heating-time (4-8 hours) conditions, and corresponding SDS and RS contents, analysed using mega-enzyme procedure. Composite SDS and RS (SDS+RS) were used in the optimisation. Quadratic function was the most appropriate model that fitted the data as exhibited by non significant lack of fit (p>0.05) and explained at least 80% of the variance for each variety considered. Optimum moisture (%), temperature (°C) and heating-time (hours) were 23.17, 80.00, and 4.12 for UH5354, 20.83, 95.43, and 5.42 for DK777, 34.51, 90.46, and 3.01 for Longe 10H and 19.24, 97.02, and 5.88 for DT Max varieties. Relative to the control, these optimal HMT conditions improved the contents of SDS+RS by 8-14% suggesting their promotion to reduce the high digestibility of polished maize flour among households.