Nutritional and health benefits of heat - moisture treated maize starch and maize meal with stearic acid

Abstract

ABSTRACT Nutritional and health benefits of hydrothermally treated maize starch and maize meal with stearic acid By Isaac Kwabena Asare Supervisor: Prof M.N Emmambux Co-Supervisor Prof Bruce R. Hamaker Diet-related non-communicable disease such as obesity and type – 2 diabetes is increasing especially in the Sub-Sahara African region, and this is related to the increased consumption of processed foods and the decline of high fibre foods. In Sub-Saharan Africa, maize meal stiff pap or soft porridge is a staple food, and it is presumed to be rapidly digestible and estimated as high glycaemic index food. Resistant starch is considered as dietary fibre and can also lower the glycaemic index of starchy foods. This study investigates the formation of resistant starch from maize through the use of heat moisture treatment alone, stearic acid addition alone and their combination on both maize starch and maize meal on upper gastro-intestinal tract (GIT) in vitro digestibility as well as the in vitro faecal fermentation to simulate the lower GIT. Stearic acid was added to both maize starch and maize meal at 1.5 % (w/w) alone, maize starch and maize meal were also treated with heat-moisture treatment at the moisture of 20 % at 110 ℃ for 16 h, and the combination of both stearic acid and heat – moisture treatment was done, as well as their control. Addition of stearic acid moderately changed the peak, breakdown and final viscosities of the paste compared to untreated maize starch and maize meal. The lower peak viscosity was attributed to the coating of the granule surface by the stearic acid to reduce the intake of water that prevents swelling. Stearic acid treatment pastes were non-gelling resulting from complex formation which prevents the development of junction zones among starch molecules which is an integral part of gel formation. Heat moisture treatment without stearic acid more significantly reduced peak, breakdown and final viscosities and produced a stronger gel than the untreated maize starch and maize meal. The strong gel can be attributed to increased cross-linking between the starch polymer v chains to form more junction zones. Also, addition of stearic acid followed by heat moisture treatment similarly reduced the peak, breakdown and final viscosities compared to untreated maize starch and maize meal. XRD and DSC of unpasted maize starch and maize meal with added stearic acid alone, heat moisture treatment alone and their combination increased gelatinization temperatures and crystallinity compared to the control. Following of pasting of maize starch and maize meal, there was the formation of amylose – lipid complex of type I and IIa and IIb with a corresponding increase in the degree of crystallinity. There was a decrease in the in vitro starch digestibility and lower estimated glycaemic index with addition of stearic acid alone, heat moisture treatment alone and in combination treatments for both maize starch and maize meal. This reduced digestibility is attributed to an increase in crystallinity due to formation of resistant starch as amylose-lipid complexes. In vitro faecal fermentation of both maize starch and maize meal with added stearic acid, heat moisture treatment alone, and the combination saw increased production of short-chain fatty acids with the corresponding rise in gases and a decrease in the pH. Although fructooligosaccharides produced higher concentrations of the short-chain fatty acid, the combination treatment was seen having significantly higher concentrations in terms of the indigestible residue compared to its control. With regards to individual short-chain fatty acids produced, acetate and butyrate were in higher concentrations compared to propionate. DNA sequencing showed that the production of short-chain fatty acids was of these modified and unmodified starches was associated with certain of the microbes in the colon. Firmicutes was the dominate phylum followed by Bacteroidetes and then Actinobacteria. Comparably high butyrate levels were associated with Firmicutes, as it contains the major butyrogenic bacteria. In conclusion, the results from this study demonstrated that modification of both maize starch and maize meal by HMT with added stearic acid produced resistant starch containing amylose-lipid complexes that has the potential to reduce estimated glycaemic index and to act as a potential prebiotic. The combination treatment produced a high amount of short-chain fatty acids, which has beneficial effects associated with diet-related non-communicable diseases like obesity and type-2 diabetes.