Changes in swelling and rheological properties of corn starches after acid-methanol degradation

Corn starches were acid treated in methanol containing 0.36% HCl for different durations to investigate the swelling, molecular and rheological characteristics of acid-methanol-treated (AMT) starches during gelatinization. The molecular size of starches were ranged from 736 × 103 to 6.9 × 103, 675 × 103 to 4.2 × 103 and 410 × 103 to 2.8 × 103 anhydrous glucose unit (AGU) for waxy corn, normal corn and Hylon V starch, respectively. AMT caused increasing in close packing concentration (C*) and granular collapse, as well as decreasing in the maximum value of storage modulus (G′max) of starch. Effect of AMT on waxy corn starch was more profound than on normal corn and Hylon V starches. AMT waxy corn starch showed undetectable G′max when molecular size was lower than 678 × 103. AMT Hylon V starches with molecular size lower than 62.3 × 103 AGU showed dramatically increasing in G′max-decrement value. Results reveal that AMT enhances the discrepancy in molecular swelling and pasting characteristics of starch granules.