Study On The Mechanism Of Microwave Improving Gel Property Of Low Acyl Gellan With Calcium Ions Addition

Low acyl gellan gum is often used in the starch food industry.However,low acyl gellan gum is sensitive to cations.The presence of cations hinders the hydration of low acyl gellan gum,thereby inhibiting the formation of the gel network structure and leading to the collapse of the texture properties of the products.As a typical anionic polysaccharide,low acyl gellan gum contains many microwave-sensitive hydroxyl groups.It undergoes molecular polarization to convert electromagnetic energy into heat energy under the microwave field.The gelation mechanism of colloids under the microwave field has not been extensively studied.Therefore,in this study,the effect of different heating methods on the quality of steamed cakes with calcium ions and low acyl gellan mixture was explored.Then,low acyl gellan gum aqueous solutions with calcium ions were used as the research object to investigate the effect of microwave irradiation on gel properties.The effect of microwave irradiation on the conformation and hydration properties of low acyl gellan gum was studied to reveal the mechanism using experimental methods and molecular dynamics simulations.The main contents and results of this research are as follows:(1)Study on the quality of microwave-steamed cakes with calcium ions and low acyl gellan mixtureThe effects of different heating methods on the texture,specific volume and internal texture characteristics of steamed cakes with calcium ions and low acyl gellan mixture were investigated.Microwave-steamed cakes were characterized by higher specific volume(1.98m L/g),chewiness,and resilience than steamed cakes with low acyl gellan and baking powder mixture.The average stomatal area and porosity of microwave-steamed cakes were higher,which were 0.27 mm~2 and 30.10%,respectively.The density and uniformity of pores of microwave-steamed cakes were significantly improved.Therefore,microwave processing can still maintain good quality of steamed cakes with one-time addition of calcium ions and low acyl gellan.(2)Effect of microwaves on gel properties of low acyl gellan gum with calcium ions additionThe similarities and differences of water bath and microwave heating on the gel properties,molecular conformational transition,spiral aggregation and hydration of low acyl gellan gum were studied.Compared with water bath-induced gels,microwave heating dramatically enhanced the gel strength,hardness,and water holding capability of low acyl gellan.Moreover,the gelation point and coil-helix transition temperatures of the microwave-heated induced gels were significantly higher than those for water bath heating.the circular dichroism and small-angle X-ray scattering spectra of the microwave-heated and water bath-induced gellan gum solutions showed no significant differences,indicating that the gellan chain was unchanged under microwave irradiation.The relaxation time of microwave-heated induced gels decreased,which reduced the degree of freedom of water molecules.The ratio of bound water,immobilized water,and free water changed.Compared with water bath-induced gels,the proportion of bound water increased by 34.13%～109.36%,indicating that microwaves promoted the hydration of low acyl gellan gum.(3)Preliminary study on the mechanism of microwave improving the properties of low acyl gellanMolecular dynamic simulations were employed to reveal the microscopic mechanism of microwave improving the gel properties.Results of root-mean-square deviation and root-mean-square fluctuation showed that microwave irradiation had little impact on the structural conformation of the low acyl gellan molecule.The microwave energy is partially converted into the interaction energy between low acyl gellan gum and water molecules,which promotes the formation of hydrogen bonds between them,thus forming a stable hydration layer.