Green modification of corn starch through repeated freeze-thaw cycles (RFTC), microwave assisted solid state acetic acid esterification (MSAE), and by dual RFTC/MSAE treatment

Freeze-thaw treatment as a green technology has been extensively applied to improve the functional properties in types of starches. The present work aimed to compare the effects of repeated freeze-thaw cycles (RFTC), microwave assisted solid state acetic acid esterification (MSAE), and their combination (RFTC/MSAE) on structural and functional properties of corn starch (NS). RFTC/MSAE treatment provided higher esterification efficiency (68.7%) for the esterified starches compared to MSAE alone (32.6%) due to raised surface area of starch granules after applying RFTC. Esterification of starch chains by using acetic acid was confirmed through FTIR (1700 cm−1) and 1H NMR (2 ppm). SEM images showed that the pores and channels were formed on granules after applying RFTC treatment, while no change in their size was observed. Also, XRD and DSC were employed to scrutinize the changes in crystalline structure of granules after applying each modification. The dual treatment decreased crystallinity, viscosity, swelling power, digestibility rate, and gelatinization temperatures, while increased amylose extent, whiteness, solubility, and paste clarity compared to those of NS. The conformity of the dual treatment with principles of green chemistry was investigated by Eco-scale methodology. Starch acetate synthesized through the dual modification can be utilized in formulation of low-calorie foods due to its highlighted features such as low digestibility rate (RS: 54.7%) and viscosity (455 cp).