Utilization of hydroxypropylated waxy rice and corn starches in Korean waxy rice cake to retard retrogradation

A traditional waxy rice gel cake in Korea, Injulmi, was prepared with hydroxypropylated waxy rice and corn starches (molar substitutions 0.13 and 0.11, respectively), and the textural and retrogradation characteristics of the cake were compared with a conventional cake made of waxy rice flour. In the pasting viscogram, hydroxypropylated starches exhibited reduced pasting temperatures, but increased peak viscosities compared with the unmodified starches. Under differential scanning calorimetry, the T_g¹ and ice melting enthalpy of the starch gel cakes were reduced by hydroxypropylation, which indicated that the modified starches had higher water-holding capacity than the unmodified starches. The degree of retrogradation, as measured by the hardness of the gel cake and the melting enthalpy, was significantly reduced by hydroxypropylation and hydroxypropylated waxy rice starch was more effective in retarding the retrogradation than hydroxypropylated waxy corn starch.