Structural modification of waxy,regular, and high‐amylose maize and hulless barley starches on partial acid hydrolysis and their impact on physicochemical properties and chemical modification

Waxy (WX), regular (RA), and high‐amylose (HA) maize and hulless barley (HB) starches were subjected to partial acid hydrolysis with 1.0 and 2.2 N HCl for 30–240 min. In both starches, the extent of hydrolysis with 1.0 N HCl followed the order: HA>WX>RA, whereas with 2.2 N HCl, the order was: HA>WX>RA (maize) and WX>HA>RA (HB), respectively. The relative crystallinity increased (HA>WX>RA) and the X‐ray pattern remained unchanged, whereas the swelling factor decreased (WX>RA>HA in maize and WX>HA>RA in HB) at both acid concentrations. Starches hydrolyzed with 1.0 N HCl exhibited increased gelatinization temperatures (WX>RA>HA in maize, WX>HA ∼ RA in HB), a narrower gelatinization temperature range (WX>RA>HA in maize, WX>RA ∼ HA in HB) and a decreased gelatinization enthalpy (WX>HA>RA in maize and HB). Acid hydrolysis increased the accessibility of the phosphorylating reagent into the amorphous regions. The extent of phosphorylation was more pronounced (maize>HB) in starches hydrolyzed with 1.0 N HCl for 60–90 min. The bound phosphorus content (BPC) followed the order: HA>WX>RA in maize and HB starches hydrolyzed with 1.0 N HCl for 240 min. In both starches, the extent of cationization was not influenced either by acid concentration or hydrolysis time. In general, acid hydrolysis significantly affected the reactivity of starch towards phosphorylation, where the optimum hydrolysis condition differed with starch source. The results would benefit the starch industry, since the amount of the phosphorylating reagent required for increasing thermal stability and/or freeze‐thaw stability could be decreased substantially, if starches are subjected to partial acid hydrolysis prior to derivatization.