Effect Of Sodium Alginate On Physical Properties Of Rice Starch And Quality Of Fermented Rice-cakes

The fermented rice-cake represents a sort of popular fermented rice product,which has a long processing history and profound cultural deposits.However,it is prone to be rigid in partial structure and be dehydrated with retrogradation in the process of production and storage,which has greatly limited the sustainable development of rice-cake industry.As a kind of natural hydrocolloids with excellent properties,sodium alginate（AG）has been proved to be added in food to improve product quality.However,there are few reports about the application of AG in rice products,and there is no comprehensive and systematic study on the effect of AG on the physical properties of rice starch（RS）,and the interaction between AG and RS molecules is still unclear.In this thesis,the effects of AG on the physicochemical properties of RS were systematically investigated by combining RS with AG,and the possible interactions between AG and RS were preliminarily explored,and AG was applied to improve the quality of the fermented rice-cake.The main research contents and results were presented as follows:Effects of AG on the gelatinization,thermodynamic,rheological,retrogradation and digestive properties of RS.The results of Rapid Viscosity Analyzer（RVA）illustrated that the addition of AG reduced the gelatinization parameters of AG-RS blends in varying degrees,and the breakdown value of the system decreased significantly when the concentration was lower than 0.30%（w/v,the same below）.But when the concentration was higher than 0.30%,the breakdown value increased slightly.The results of Differential Scanning Calorimetry（DSC）suggested that the low concentration（<0.30%）of AG inhibited the gelatinization of RS,while in high concentration（>0.30%）partially promoted the gelatinization process.The rheological experiment results showed that the storage modulus（G’）,the loss modulus（G"）and the loss tangent（tanδ）of the AG-RS blends increased in the range of 0.10%～0.50%,and AG could enhance the toughness,elasticity and stability of RS gel structure.DSC and Texture Profile Analysis（TPA）showed that compared with the control RS,the retrogradation enthalpy of AG-RS blends with 0.30%AG decreased from 2.16 J/g to 1.58 J/g after two weeks,and the hardness decreased from 110.06 g to 54.13 g.AG could effectively retard the retrogradation of RS.The results of in vitro digestion experiment of RS illustrated that the contents of Slow Digestible Starch（SDS）and Resistant Starch（R_eS）increased,indicating that AD could delay the digestion rate of starch in human diet.Interactions between AG and RS molecules.The results of High Performance Size Exclusion Chromatography（HPSEC）suggested that AG increased the weight average molecular weight（M_w）and rotation radius（R_z）of RS.Fourier Transform Infrared Spectroscopy（FTIR）analysis showed that AG and RS in the system had good compatibility,and they were bonded by hydrogen bond interaction.X-Ray Diffraction（XRD）curves illustrated that AG inhibited the exudation of amylose,and impeded the migration of recrystallized water,and finally reduced the relative crystallinity（RC）value of the RS during retrogradation.Low Field Nuclear Magnetic Resonance（LF-NMR）analysis suggested that a new signal peak appeared at 10～60 ms at 7 d of 4℃,which was the peak of semi-binding water.After 14 d of storage,with the concentration of AG increasing from 0.10%to 0.50%,T₂₁moved towards low relaxation,indicating that RS bound more tightly to water molecules.AG could inhibit water molecule migration during starch retrogradation.Scanning Electron Microscope（SEM）observation of the structure for RS and AG-RS blends found that the starch particles were wrapped by the film formed by the combination of AG and water molecules,which resulted in incomplete gelatinization of RS.Effects of AG on the quality of fermented rice-cakes.The results of moisture determination showed that the water content of fermented rice-cakes with 0.50%AG decreased from 50.71%to 50.29%during storage at 4℃for 7 d,indicating that AG improved the water holding capacity of fermented rice-cakes during storage.Sensory evaluation results illustrated that compared with pure fermented rice-cakes stored for 7 d,the score of structure,aroma,color,flavor and taste of fermented rice-cakes added with 0.50%AG increased by 2.1points,0.1 points,0.2 points,4.1 points and 0.9 points,respectively.indicating that the structure,flavor and taste of fermented rice-cakes were improved obviously with the addition of AG,and the score increased with the increase of AG,but it had little effect on the aroma and color of fermented rice-cakes.The results of texture analysis showed that the hardness of fermented rice-cakes decreased from 5897.46 g to 5014.01 g,and the adhesiveness increased from 56.16 g·s to 81.82 g·s with the increase of AG from 0.10%to 0.50%after 7 d of storage,respectively,indicating that AG significantly reduced the hardness and increased the adhesiveness of fermented rice-cakes.As a result,AG could greatly improve the texture and edible quality of fermented rice-cakes,which proved that it could be used as an excellent additive in rice-cake production.