Effect of freezing-thawing pre-treatment on enzymatic modification of corn and potato starch treated with activated a-amylase: Investigation of functional properties

Owing to the semi-crystalline structure of native starch granules, enzymatic modification is low efficient. In order to achieve highly effective amylolysis by alpha-amylase, freezing/thawing pre-treatment (FTF) of starch was per -formed to produce damaged starch with raised surface area. Afterwards, the effect of non-activated and activated alpha-amylase by the concomitant performance of ultrasonication (64.5 W, 25 + 40 kHz, 5 min) and Ca2+ ions (12.5 and 25 mM) on starch digestibility were investigated. Corn (NCS) and potato (NPS) starches were suspended in water by being exposed to activated and non-activated alpha-amylase (0.15% w/v) for a period of 10 h at a tem-perature of 25 ?. The physicochemical, morphological, and structural properties of native, FTF starches and hydrolyzed starches were studied. An increasingly damaged starch was the result of FTF according to the porous and cracking surface observed on starch granules. FTF of potato (PFTF) and corn (CFTF) starches exposed to non-activated and activated alpha-amylase showed a significantly greater percentage of hydrolysis, consequently destroyed the integrity of starch granules. The ratio of 1047/1022 cm(-1) reduced from 1.112 to 0.947 (NPS), 0.987 to 0.670 (PFTF), 1.293 to 1.154 (NCS) and 1.211 to 1.038 (CFTF) after being treated with activated alpha-amylase by 25 mM Ca2+ + 64.5 W sonication; additionally, relative crystallinity decreased respectively from 34.1% to 13.8% (PFTF) and 39.3%-17.7% (CFTF). Significantly low pasting viscosities (determined by RVA) along with the gelatinization temperature and enthalpy (determined by DSC) of FTF treated with alpha-amylases could be the reason behind the degradation of granular and molecular structures and low swelling power as well.