Effect Of Sucrose Fatty Acid Esters On Physical Properties Of Rice Flour And Quality Of Frozen Rice

In this research, it is aimed to investigate the effect of different types of sucrose fatty acid esters (SE) including S-570, S-970, S-1170and S-1570on the pasting, rheological and retrogradation properties and freeze-thaw stability of rice flour. Meanwhile, the application of SE to quality improvement of frozen rice was studied. The main contents and conclusions of this paper are listed as follows:Effect of different SEs on physical properties of rice flour gel was investigated by the methods of RVA, dynamic rheometer, DSC and colorimeter. It was showed that S-970, S-1170and S-1570with higher HLB values increased viscosity, pasting temperature, gelatinization enthalpy, storage moduli G’, consistency coefficient and the creep retardation time, and decreased loss tangent (tanδ=G"/G’) and thixotropy of rice flour gel. Besides, the corresponding values change increased with the increase of HLB of SEs. However, S-570with a lower HLB value induced that characteristics of rice flour gel showed the opposite trend. All the samples exhibited highly shear-thinning behavior with flow behavior index (n) as low as0.295-0.317. S-1570could improve the whiteness of rice flour gel and this will help improve the eating quality of rice-based food. The higher sucrose ester with higher HLB value can make the gel network structure more solid and enhance entanglements between starch molecular chains. Since sucrose monostearate has better linear structure and smaller steric hindrance, a more robust gel network can be formed. For other sucrose stearates, because larger molecule structure and low HLB cause repulsion, it tends to form a weaker gel network.In term of the chemical composition of SEs used in this study, it could be explained by the fact that the ability of SEs to form inclusion complexes with the helical amylose molecule is in the following order: monostearate> distearate> tristearate> polystearate.This paper investigated the effect of different SEs on the syneresis of rice flour gels during repeated freeze-thaw measurements. Freeze-thaw results demonstrated that four types of SEs addition all enhanced the freeze-thaw stability of rice flour gel and presented a good positive correlation with concentration. The order of effectiveness was S-1570> S-1170> S-970> S-570. Sucrose ester molecules could form strong intermolecular hydrogen bond with the adjacent water molecules, reduced the available water among the system and improved polymer network structure at the same time, therefore SE can enhance the freeze-thaw stability of rice flour gel. Meanwhile, the effectiveness of distilled monoglyceride to improve freeze-thaw stability of rice flour gel was stronger than S-1570, but the lecithin could weaken freeze-thaw stability of rice flour gel.During the process of cold storage for a long time, the storage modulus G’ of rice flour gels with or without different SEs presented obviously rising trend and the loss tangent value tanδ showed a trend of gradual decline. G’ as a retrogradation indicator, which showed that the G’ values of stored gels showed different growth rates which are68.44%,24.26%,18.12%,17.00%, and11.55%for the control, S-570, S-970, S-1170and S-1570samples respectively. Avrami model fitted the process of rice flour gel retrogradation well. Avrami index n showed that rice starch nucleation mode was instantaneous nucleation. The crystallization rate constant k was as follows:0.472.0.396.0.287.0.178�'�0.139d-1for the control, S-570, S-970, S-1170and S-1570group respectively. S-1570exhibited the best ability to inhibit rice flour gel retrogradation process. DSC method determination of retrogradation degree was62.31%、60.15%、58.33%、55.03%�'�48.74%for the control, S-570, S-970, S-1170and S-1570group respectively and in good agreement with the above conclusion. And low field nuclear magnetic results indicated four different SEs changed the water status in rice flour gels after a long cold storage time, limited the mobility of moisture and strengthened the water holding capacity of rice flour gels.The corresponding mechanical indexes of frozen preservation of cooked rice during a long time were determined by TPA and stress relaxation tests. It was showed that mechanical indexes and sensory scores had a different degree of correlation by correlation analysis. A model for evaluating frozen rice quality was established based on principal component analysis of its mechanical indexes. Finally, the application of SE to quality improvement of frozen rice was studied. Results showed that S-1570didn’t impact fresh cooked rice significantly, but the addition of S-1570could delay the eating quality deterioration of frozen rice after a long storage time. Besides, the addition of glucose acid-δ-lactone and S-1570had a synergetic effect on frozen rice.