| As a green and efficient physical field processing technology,microwave has been used in the field of food processing.Due to the unique mechanism of microwave heating（MHT）,the product quality is difficult to be accepted by consumers in microwave baked food,which limits its application and promotion in the field of microwave baking.Sourdough,as a natural food improver,can improve the quality of fermented foods.However,the application of sourdough in improving the quality of microwave baked food has not been extensively studied.Therefore,in this study,microwaved steamed-cake（MSC）was used as the research object to investigate the effect of adding sourdough on the textural improvement of MSC.The effect of sourdough on moisture content and state,electromagnetic properties and protein/starch during MHT was studied to explore the improvement mechanism of sourdough on the texture of MSC.The main contents and results of this research are as follows:1)The effect of sourdough on the quality characteristics of MSCThe effects of different additions of sourdough on the specific volume,internal structure and texture of MSC were investigated.MSC had higher specific volume,porosity,and resilience compared with steamed-cake,but the hardness and chewiness also increased,resulting a worse texture.With the addition and increase of sourdough content,the p H value of the initial batters and MSCs decreased,the specific volume,porosity and resilience increased,and the hardness and chewiness decreased.However,a reverse effect was observed in the MSC containing 30%sourdough.2)The effect of sourdough on the moisture content and state of the MSC during MHTThe influence of sourdough on the moisture content,moisture distribution and moisture state of the batter during MHT was studied.Adding 20%sourdough result a higher moisture content（39.91%）of the final product.Sourdough decreased the moisture migration rate during MHT.After heating for 120 s,the relaxation time(T22)decreased to 10.72 ms and the amplitude of the proton signal of bound water,semi-bound water and free water increased to 699.64,4128.39 and 68.37,respectively,indicating the water binding capacity of system was enhanced after adding sourdough.3)The effect of sourdough on the electromagnetic characteristics of MSC during MHTThe influence of sourdough on the electromagnetic characteristics and heating rate of the batter during MHT was analyzed.MSC with 20%sourdough（SMSC）had the higher dielectric constant,dielectric loss and loss tangent value than MSC during the whole microwave heating process.The higher impedance matching and lower reflection loss were also observed,which enhanceed the microwave-absorbing ability of the system.The heating curve showed that the adding sourdough improved the heating rate of the middle（k=1.263）and edge parts（k=1.157）of the batter.4)Preliminary study on the mechanism of sourdough improving the quality of MSCBased on the influence of sourdough on the protein aggregation behavior and starch properties of the system,the intervention mechanism of textural improvement was preliminarily analyzed.The results showed that SMSC has a lower glutenin macropolymer（GMP）content and a higher free sulfhydryl group（SH）content,which were 46.46%and 9.78μmol/g（protein）after 120 s,respectively.A lower rate of changes of GMP and SH content was also observed,the results indicated that the sourdough hindered the formation of disulfide bonds and promoted the depolymerization of gluten.In addition,the paste viscosity of SMSC was lower than MSC,and the starch crystallinity analysis showed that SMSC had lower crystallinity in the late heating stage.Scanning electron microscopy（SEM）showed that a more uniform and orderly protein network formed in SMSC,which beneficial to bind starch during MHT. |
