Studies on the morphological and rheological properties of granular cold water soluble corn and potato starches

Granulated cold water soluble (GCWS) starches were prepared from corn starch and starches separated from four potato cultivars using alcoholic-alkaline method. The morphological, thermal and rheological properties of GCWS corn and potato starches were studied. The amylose content of the GCWS starches from corn and potato starches were significantly lower as compared to their counterparts native starches. GCWS potato starches showed higher cold water solubility than GCWS corn starch. Cold water solubility of GCWS starches prepared from different potato cultivars also differed significantly. Native potato starch granules were larger in size (15–45 μm), smooth, oval and irregular or cuboidal shaped while native corn starch granules were smaller in size (5–18 μm), less smooth, rounded and angular shaped. Both corn and potato starches were distorted and indented during conversion to GCWS starches, however, this effect was more pronounced in potato starches than corn starch. The extent of distortion in GCWS starches differed significantly in starches prepared from different potato cultivars. The potato cultivars having starch with large sized granules showed more granular distortion as compared in those having small sized granules during GCWS starch production. Native corn starch showed higher transition temperatures and lower enthalpy of gelatinization (ΔHgel) than native potato starches. GCWS corn and potato starches did not show any gelatinization endotherm during heating between 20 and 100 °C. The rheological properties such as G′, G″, η′ and of GCWS corn and potato starches also showed significant variation, when subjected to frequency sweep testing. GCWS potato starches showed higher G′, G″, η′ and lower than GCWS corn starch. The G′, G″, η′ of the GCWS starches from both corn and potato increased and decreased with the increase in temperature. The turbidity of GCWS and native corn and potato starches increased during storage at 4 °C, however, the increase was less pronounced in GCWS starches.