Comparative Studies on Some Physico-chemical, Thermal, Morphological, and Pasting Properties of Acid-thinned Jicama and Maize Starches

Comparative studies on acid hydrolysis of jicama and maize starch were carried out using concentrations of hydrochloric acid of 1.5%, 3.0%, and 4.5% (w/v), for 3 and 6 h, at 40°C. Native maize and jicama starches showed important morphological, thermal, and structural differences from those of tubers and cereals which potentially offer diverse industrial applications. Jicama starch showed low amylose content (12%) and small size of starch granules. Due to these characteristics, jicama starch was more susceptible to degradation during hydrolysis process than maize starch. Under the experimental conditions employed, the acid degradation was not particularly severe, as shown by scanning electronic microscopy analysis which showed small degraded zones and similar X-ray patterns in both starches. However, jicama starch was more susceptible to acid hydrolysis than maize starch, as revealed by the considerable increase in water solubility index, damaged starch, and crystallinity values. Also, the higher susceptibility of jicama starch than maize starch to the hydrolysis conditions was reflected in the sugar content release during hydrolysis. The relative crystallinity of hydrolyzed maize starches decreased during hydrolysis, while those of hydrolyzed jicama starches increased attributable to the lower amylose content of jicama starch in relation to maize starch. Maize and jicama hydrolyzed starches showed low viscosity values with relation to their native starch counterparts. However, native jicama starch showed lower viscosity values than maize starch, suggesting a lower internal stability of the starch granules during hydrolysis. Both native and hydrolyzed maize starches showed higher enthalpy, T _o, T _p, and T _c values than jicama starch and the broadening of the endotherms decreased during the hydrolysis of both starches.