Abstract
Citric acid esterification of two accessions of white yam (Dioscorea rotundata), ‘Aro’ and ‘Efuru’, Yellow yam (D. cayanensis) flours were carried out with four different concentrations of citric acid (10%, 20%, 30%, 40%w/v /100g sample) under varying reaction temperature and time
(110oC for 2 hours, 110oC for 3 hours, 120oC for 2hours and120oC for 3hours). The Degree of substitution (DS), Reaction Efficiency, and alpha – amylase digestibility of the products were determined. The DS obtained was 0.011 – 0.178. The reaction efficiency at 110oC for 2 hours, 110oC for 3 hours, 120oC for 2 hours and 120oC for 3hours across all samples were (11.33% - 34.05%), (12.96% - 52.14%), (26.67% - 39.94%) and (32.01% - 65.11%) respectively. For esterification at 120oC for 3hours, the reaction efficiency were higher than 50% for almost all samples at citric acid concentration of 10% - 30%w/v. However, at 40%w/v, the reaction efficiency decreased to less than 50%. Alpha amylase digestibility reduced as the concentration of citric acid, temperature and reaction time of the esterification process increased. The least reduction in digestibility (1.15%) was obtained at 110oC for 2hours at 10% citric acid concentration, while the highest reduction in digestibility (93.42%) was obtained at 120oC for 3hours at 30% citric acid concentration. From the results obtained, it can be concluded that concentration of citric acid, reaction temperature and time correlate positively with the degree of substitution and alpha amylase resistivity, however steric effect reduced the reaction efficiency as the concentration of citric acid dosages increased.