Study On The Retrogradation Of Various Glutinous Rice Cakes

Retrogradation properties of various traditional glutinous rice cakes and the key factor onhardening of glutinous rice cake were studied in this paper. Delaying the hardeningphenomenon and retrogradation of starch in glutinous rice cake was the purpose.First, the chemical composition of japonica glutinous rice, blood glutinous rice andindica glutinous rice and their relationship to retrogradation properties of rice cake starch wasstudied. Results showed that texture parameters including hardness, gumminess and chewing,and XRD parameters crystallinity of Indica glutinous rice cake, are higher than japonicaglutinous rice cake and blood glutinous rice cake. The amylopectin structure of japonicaglutinous rice shows lower peakⅠ, higher peak II and no peakⅢ, the amylopectin structureof blood glutinous rice shows higher peakⅠ, lower peak II and no peakⅢ, the amylopectinstructure of indica glutinous rice shows higher peakⅠ, lower peak II and higher peakⅢ.Ⅱpeak area and hardness, the degree of crystallinity was significantly negatively correlated(p<0.05, r=0.998,0.999). The Indica waxy rice cake was easier retrogradation. During storage,the water holding capacity of glutinous rice cakes all decreased. The enthalpy, the textureparameters including hardness, gumminess and chewiness of three glutinous rice cakes weresignificantly increased. The ultrastructure of starch changed to rough and porous after storage.The typical A-type crystals of starch granules were change to the B-type crystals and thedegree of crystallinity were increased. Hardness and degree of crystallinity, enthalpy ofglutinous rice cake were significantly correlated (p<0.01, r=0.951,0.979). It was speculatedthat the hardness of glutinous rice cake was affected by the retrogradation of starch.Secondly, the relationship between hardness and water activity, moisture content ofglutinous rice cake during aging was studied. When15%-60%trehalose or sorbitol wereadded, significant negative correlation (p<0.05, r=0.313) was found between the hardness andthe water activity of japonica rice cake. But no significant correlation was found betweenhardness and moisture content. No significant correlation ship was found between hardnessand water activity, moisture content either in blood or indica glutinous rice cake. It can beinferred that though the hardness was influenced by the water change, greater influence wascontributed by the retrogradation of starch. The key factor on glutinous rice cake hardeningwas the retrogradation of starch.Thirdly, quality of three glutinous rice cakes was analyzed by both sensory evaluationand physical properties tester, inorder to establish an evaluation system of glutinous rice cake.Results showed that: the composite score of sensory evaluation and hardness of japonica,blood and indica glutinous rice cake were significant correlated (p<0.01, r=-0.979,-0.976,-0.983); significant correlation (p<0.01, r=-0.969,-0.978,0.908) was found between thecomposite score of sensory evaluation and gumminessness; the composite score of sensoryevaluation and chewiness were significant correlated (p<0.01, r=-0.954,-0.963,-0.973). Itmeans that hardness, gumminess and chewiness can be used as the main index of the qualityevaluation of glutinous rice cakes. Hardness less than600g, gumminess less than400g,chewiness less than400g can be used for the visual standard of taste acceptable glutinous rice cakes.Finally, the effects of different types of sugar, sugar alcohols, modified starch andamylase on retrogradation properties of glutinous rice cake were studied on the basis of theevaluation system of glutinous rice cake. Results showed that: trehalose, sorbitol,β-cyclodextrin, and amylase could reduce the hardness of japonica glutinous rice cakerespectively at the percentage of93.16%,93.02%,90.49%and90.78%; reduce the hardnessof blood glutinous rice cake at the percentage of56.70%,94.66%,96.12%and90.67%; and itreduce the hardness of indica glutinous rice cake at the percentage of27.27%,79.42%,80.63%and86.40%.