Studies On Prefermented Frozen Dietary Fiber Dough And Its Application In Steamed Bread Making

In this paper, the dietary fiber and prefermented frozen dough process has been applied in the steamed bread making, and the research included: effects of dietary fiber and transglutaminase (TGase) on thermo-mechanical properties; effects of dietary fiber and TGase on specific volume, texture and lightness of steamed bread; cryoprotective impact of glycerol on the dietary fiber containing prefermented frozen dough; and effects of dietary fiber, TGase, glycerol, water addition ,prefermentation time and their interactions on the rheofermentometer parameters and steaming quality of prefermented frozen dough after 30 days of frozen storage using response surface methodology.Results from Mixolab showed that different levels (2, 5, 8%) of dietary fiber addition increased water absorption, and 8% of dietary fiber could enhance the water absorption of dough by 18.75%. The addition of dietary fiber improved the stability of dough, but did not reduce gluten weakening. TGase addition (0, 0.5, 1.0%) in further enhanced the stability of dough, and significantly reduced alpha absolute value, as well as lowered gluten weakening. dietary fiber had an decrease impact on starch pasting rate, and reduced the C3 value at the same time. While TGase could increase starch pasting rate and the C3 value as well. Compared to the sample without dietary fiber, the samples containing dietary fiber had lower retrogradation values. While TGase increased the retrogradation value slightly.The results of steamed bread showed that, dietary fiber had a great minus impact on specific volume, but the addition of TGase could improve the specific volume of steamed bread. The specific volume of the sample with 1.0% of TGase addition containing 5% dietary fiber was still kept at 2.3 mL/g. With the increasing level of dietary fiber addition, the hardness, chewiness of steamed bread increased significantly, springiness and resilience decreased, but the addition of TGase led to a decrease in hardness, chewiness of steamed bread and a rise in springiness and resilience. However, dietary fiber and TGase did not affect the crust lightness significantly.The differential scanning calorimetry (DSC) measurements showed that, the ratio of freezable water content to total water content increased from 44.86% to 93.74% during 4 weeks of frozen storage. When glycerol was added the freezable water content was much lower than the control one. The melting peak temperature of dietary fiber frozen dough increased from around 0oC to around 6oC during frozen storage. The addition of glycerol made the transfer shift to a lower temperature, and the melting peak temperature of samples with glycerol kept around 0oC after 4 weeks of frozen storage.The yeast survival rate at -18o C condition decreased by 29.27% after 4 weeks of frozen storage compared with fresh samples. The addition of glycerol moderated the downward trend.The response surface plots indicated that, dietary fiber inserted minus effects on maximum dough height (Hm), specific volume and hardness of prefermented frozen dough steamed bread after 30 days of frozen storage. Prefermentation time affected significantly the maximum height of gas release (H'm), retention coefficient of gas release, steamed bread specific volume and hardness. While glycerol and TGase could improve Hm, H'm and steamed bread specific volume. Glycerol could also ease the negative influence from prolonged fermentation. Dietary fiber and prefermentation time reduced the lightness of steamed bread crust significantly, and glycerol and water content also had an slight negative influence on crust lightness. The optimization result (maximum specific volume) was as follows: the additions of dietary fiber, TGase, glycerol and water were 5.75%, 1.0%, 4% and 61.77% respectively, and the prefermentation time was 40 min.