Effect Of Xanthan On The Retrogradation Of Rice Starch And Preliminary Study On Its Mechanism

Rice products are easily available staple sources as a long history of traditional food, thusthey have profound commercial potential, and the market for rice products is growingprosperously nowadays. Rice products mainly comprise rice starch, which is one of the mostintriguing starches. However, rice starch suffers from some disadvantages, especially thesevere retrogradation during storage that undermines rice products quality and shortens shelflives. Xan is usually applied in food industry to offer good texture, control water mobility,improve overall food quality and stability. Therefore, this study aims to clarify the effects ofXan on the short-term retrogradation and long-term retrogradation of rice starch, based onwhich the retrogradation mechanism of RS/Xan mixtures was also elucidated. On the basis aguiding significance for the actual production can be found.First, the weight ratios in RS/Xan mixtures of100:0,40:1,20:1and10:1(w/w) werechosen in this study. The short-term retrogradation of the rice starch (RS)/xanthan (Xan)mixtures was investigated by Brabender-E viscograph and dynamic rheometer while thelong-term retrogradation was investigated by texture analyzer and differential scanningcalorimetry (DSC) respectively. With the ratio of10:1, the setback value reduced from239(BU) to98(BU) compared to the native rice starch. The G′values of the RS/Xan mixturesinitially increased steadily and then remained constant, suggesting that Xan inhibited thestarch gelation. The mixtures could form softer gel with higher adhesiveness and lowercohesiveness and the retrogradation enthalpy of the mixing ratios of40:1,20:1and10:1alldecreased after stored for14days. Also, recrystallization of the mixtures decreased,comparing with the native RS. The growth of amylopectin recrystallization in RS/Xanmixtures was primary nucleation (n<1). However, the rate of recrystallization and nucleationreduced which indicated that the long-term retrogradation was evidently inhibited.Secondly, the retrogradation mechanism was also discussed. With the increase ratio ofXan, the leached amylose in the mixtures decreased, suggesting that the some interactionsbetween Xan and amylose existed. Combining the measurement of interaction forceexperiment and FTIR analysis of the mixtures, there was no new functional group. Theamylose and exterior chains in amylopectin juxtaposed each other by bydrogen bond, whichexisted inner and exterior chains. The molecular weight distribution of amylose andamylopectin were determined by HPSEC. When adding Xan, the amylose weight-averagemolecular weight was significantly increased, while no significant change in molecularweight of amylopectin. Water played a crucial role in the inhibition of starch retrogradationprocess. The samples in the presence of Xan had a longer T2than the native RS and wasextremely mobile when stored at4°C for1,3,5,7,14and21days, which has been previouslyascribed to the hydrogen bonding between the leached amylose and Xan that restrained thelosing of water molecules and inhibited the retrogradation of amylopectin. Less amorphousarea was transformed into recrystallization area, thus enabling the water molecules to be moreactive in the RS/Xan mixtures. It showed that Xan filled in the fragments of the starchgranules leading to smaller surface pores, smoother surface and more compact structure by SEM.Finally, the different ratios of Xan were applied to the traditional rice product-MiGAO.The sensory indexes and texture parameters of MiGAO stored in a certain days were analyzedwhich could provide the theoretical basis and technical parameters in industrial production ofMiGAO compared to the modified starch as an anti-aging agent. The results show that withthe increase ratio of Xan, sensory evaluation and texture of the MiGAO were improved. Itshowed that Xan can be widely used in the production of the MiGAO as an anti-aging agent.