| Based on reduction of half the fat in the traditional formula,solid oil has gradually been replaced by liquid oil.The purpose of this study was to produce low-fat cake with low solid fat content in a one-step method to obtain a novel high-quality soft low-fat cake.The effects of emulsifier propylene glycol ester on specific density,viscosity,rheology,microstructure of batter and baking characteristics of low-fat cake were investigated.Propylene glycol ester was combined with sucrose ester and monoglyceride,and their mechanism of interaction and effect on batter was explored by analyzing rheological properties(paste density,viscosity,and rheology),bubble structure and baking characteristics.Finally,propylene glycol ester,alpha-amylase and maltose amylase were used to improve the baking quality and storage characteristics of low-fat cakes and their mechanism was studied by texture analysis,low-field NMR,thermal analysis and scanning electron microscopy.Propylene glycol esters added at different concentrations have different effects on the physical properties of oil,rheological properties and microstructure of batter and baking characteristics of cake.The results showed that application of propylene glycol ester in low-fat cake had obvious advantages.Propylene glycol ester reduced the surface tension difference between oil and batter,thereby protecting the bubbles from the effect of oil defoaming,and hence the emulsifying stability of batter were improved.XRD results showed that propylene glycol ester promoted the conversion of oil into alpha crystal form and maintained batter stability.Propylene glycol ester reduced the paste density of low-fat cake by25.2%and increased its viscosity by 3.38 times.Propylene glycol ester also improved the shortcomings such as small specific volume and high hardness of low-fat cake made by one-step method.Compared with the cake group without propylene glycol ester,specific volume of the optimal group increased by 39.4%,while the hardness decreased by 62.2%.Therefore,propylene glycol ester improved the physical properties of oil and batter stability,effectively improving the baking quality and sensory properties of low-fat cake.When propylene glycol ester was combined with sucrose ester and monoglyceride,it was observed that propylene glycol ester increased paste viscosity,while sucrose ester reduced paste density of low-fat cake.The results of Image J software showed that the number of air bubbles and gas phase fraction in batter increased(P<0.05)and the distribution of stomata were uniform with fine pores of the cake.In this combination,propylene glycol ester was able to significantly increase the specific volume of cake(P<0.05).The correlation analysis showed that there was a good correlation between pore area fraction and specific volume(R~2=0.909).Pore area fraction AF(%)=4.425×specific volume(cm~3/g)+9.614.In addition,the combination of propylene glycol ester and sucrose ester reduced cake hardness during storage.Finally,two different amylases(maltose amylase,alpha-amylase)and propylene glycol ester were used to improve the quality of low-fat cake.The results showed that cake with propylene glycol ester and amylase had a reduced hardness and chewiness.Scanning electron microscopy images showed that pore structure of low-fat cake improved when propylene glycol ester and amylase were combined.Starch granules were completely encapsulated by protein network,and bare starch granules could not be observed.Adding maltose amylase and propylene glycol ester had the best effect on delaying the stailing of low-fat cake.After 28days storage,the aging enthalpy of the cake decreased from 0.862 J/g to 0.359 J/g,and the relaxation time of the cake decreased from 4.199 ms to 3.654 ms.The results showed that starch retrogradation in cake slowed down and water holding capacity increased,which delayed the hardness of cake and improved the storage characteristics of low-fat cake.At the same time,the relationship between cake hardness and the fractal dimension of stomatal structure during storage was established,and the non-linear positive correlation between them was obtained.The results showed that the deformation and roughness of stomata affected the hardness of cakes during storage. |
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