Gelatinization, pasting and retrogradation properties of hydroxypropylated normal wheat, waxy wheat, and waxy maize starches

Normal wheat starch (NWS), waxy wheat starch (WWS), and waxy maize starch (WMS) were hydroxypropylated with 3-9% propylene oxide (PO). The objectives of this study were to correlate morphology changes to pasting properties of hydroxypropylated starches and establish the relationship between molar substitution (MS) and degree of retrogradation of the hydroxypropylated starches. Gelatinization temperatures and enthalpy of the starches decreased after hydroxypropylation, and the extent of decrease was positively correlated to MS. Hydroxypropylation reduced retrogradation of the gelatinized starches during cold storage as determined by differential scanning calorimetry, but the effects varied among the starches. For the same level of PO (3 and 5%) reaction, hydroxypropylated WWS retrograded less than WMS. WWS and WMS had no retrogradation after reacted with 6% PO. However, a higher level of PO (9%) was needed to react with NWS, an amylose containing starch, to achieve no retrogradation. Hydroxypropylation promoted the swelling of the starch granules as observed by light microscopy, and Micro Visco-Amylograph results showed that hydroxypropylated starches had lower pasting temperatures and improved hot and cold viscosities.