| Youtiao is desired by consumers due to its special taste and flavor.With increasing demand of healthy foods,however,high oil content brings consumers a negative impact on youtiao.Therefore,a study on the mechanism of oil absorption,reducing the oil content,and improving the quality of Youtiao is very crucial.In this study,a hydrophilic colloid(hydroxypropyl methyl cellulose,HPMC)was applied to the processing of Youtiao,and the effects of HPMC on the processing properties of flour and dough,the oil content,the specific volume,texture and other properties of Youtiao were investigated.Meanwhile,the related mechanism of HPMC in reducing oil content of Youtiao was also explored.(1)The results of farinograph and extensogragh showed that the water absorption of flour increased significantly while the development time of dough decreased with the addition of HPMC.When HPMC was added less than 1%,the stability time of dough with HPMC was higher than that of the control.Moreover,addition of HPMC could improve the tensile properties of dough,resulting in an increase in extensibility and a decrease in the resistance and ratio of extensibility.Furthermore,the results of dynamic rheology indicated that addition of HPMC could enhance the elastic modulus and viscous modulus of dough whereas decline the loss tangent of dough.The results of the content of gluten and free sulfhydryl,as well as p H value manifested that proper addition of HPMC could increase the wet gluten and dry gluten content of dough whereas decrease the content of free sulfhydryl and p H value of dough.Electrophoresis results further showed that HPMC combined with proteins to form complexes with high molecular weight.Meanwhile,the pictures of dough indicated that addition of HPMC had an adverse effect on the microstructure and porosity of dough,resulting in a denser microstructure and a decrease in the porosity of dough after fermentation.(2)The results of physicochemical indexes,textural properties,and evaluation scores of Youtiao showed that the oil content and the specific volume of Youtiao decreased with increasing additioin of HPMC content.Adding appropriate amount of HPMC improved the texture properties,some sensory quality,and the L * and b * values of Youtiao.When 0.5% HPMC was added,the overall sensory quality of the samples was better than that of the control.Moreover,the addition of HPMC could also reduce the content of acrylamide and starch digestibility of Youtiao;a reduction in the moisture loss and a delay in the increase in hardness of Youtiao during storage(1-5d)were also observed.(3)Thermogravimetric analysis of dough showed that the addition of HPMC enhanced the water holding capacity of dough,and within a certain range,the water holding capacity of dough increased with the increase of HPMC addition.The results of mass transfer kinetics indicated that the mass transfer coefficient of oil absorption and dehydration of Youtiao gradually decreased with the increase of HPMC addition.The superficial microstructure of Youtiao manifested that HPMC could improve the surface texture and reduce the roughness and porosity of Youtiao.In addition,the study also found that with the increase of HPMC addition,the fractal dimension of Youtiao surface decreased and oil content of Youtiao surface also declined.Sudan red B dyeing experiments showed that the oil in Youtiao was mainly distributed in the surface structure but less in the core of Youtiao.The results obtained showed that HPMC could be used as an additive in the production of Youtiao to reduce the oil content and improve the quality of Youtiao. |
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