Effects of different heat treatments on the quality of wheat flour and its steamed cakes

Steamed cakes can usually adopt as the traditional hot water dough. Among them, the boiled water and wheat flour are required to be fully mixed instantaneously for the uniform and stable quality of dough. The complex procedure has seriously hindered the large-scale production of steamed cake. It is particularly necessary to explore the suitable treatment for the industrial production of steamed cake. In this study, the steam, microwave and dry heat treatments were used to treat the wheat flour. A systematic investigation was implemented to explore the effects of different treatments on the gelatinization, thermal mechanical properties, and microstructure indicators of wheat flour. The processed wheat flour was also added into the untreated to make the steamed cake. The water distribution, texture and sensory quality of steamed cakes were investigated . The results indicated that three heat treatments caused the different degrees of binding between protein and starch in wheat flour, where free damaged starch was observed. The damaged starch content of wheat flour increased significantly (P<0.05) after microwave and dry heat treatments, compared with the untreated. Besides, the appropriate treatment time of three heat treatments improved the peak viscosity, through viscosity, final viscosity and retrogradation of wheat flour (P<0.05). The increase of peak viscosity indicated that the thermal stability of starch was enhanced in the wheat flour. The increase of retrogradation value means that the gel stability of wheat flour was enhanced. In terms of thermomechanical properties, the three types of heat-treated wheat flour were improved the water absorption and starch gelatinization in the mixed flour doughs (P<0.05); The steam treated wheat flour was reduced the kneading resistance of dough but improved the cooking stability (P<0.05); The microwave- and dry heat-treated wheat flour also increased the kneading resistance and stability of the internal structure in the mixed dough (P<0.05). The addition of three heat-treated wheat flour was significantly promoted the bound water content of steamed cakes, while also improving their hardness, elasticity, and chewiness P< 0.05). However, the addition of wheat flour with different heat treatments also shared the different effects on the firmness of steamed cakes. Especially, the firmness of steamed cakes made of wheat flour treated with steam was significantly reduced (P<0.05). The suitable treatment time was then screened out in each heat treatment, particularly for the high quality of steamed cake. An optimal combination of wheat flour treatment with 40-min steam, 2-min microwave and 30-min dry heat was achieved in the relatively moderate strength and toughness, high bound water content and sensory scores. It was feasible to produce the steamed cake with the high quality. The steamed cake was then prepared to add the heat-treated wheat flour, instead of the traditional hot water dough. The finding can also provide the basic data and theoretical foundation for the industrial production of steamed cake. The processing parameters can be adjusted in actual production, according to the product requirements. In addition to steamed cake, the heat-treated wheat flour can be expected to realize the industrial production of staple food products that made of hot water dough in future.