Studies On Effects Of Anti-freezing Additives On Fermentation And Baking Properties Of Frozen Dough

This paper mainly studied the effects of anti-freezing additives including trehalose(TR), ice structuring proteins(ISP), locus bean gum(LBG) and transglutaminase(TG) on cell viability and gas production of yeast,the state of water,fermentational,baking characteristics and microstructure of frozen dough.The results of microscope and rheofermentometer experiments showed that: pretreatment of anti-freezing additives effectively improved the anti-freezing property of yeast. The addition of ISP or TR could effectivly improve the cell viability and gas production of yeast, and combination of ISP and TR was better. Pretreatment of cold or heat treatment didn't significantly affect viability of yeast solution that contained ISP and TR, but decreased the gas production.SEM pictures indicated that ISP could protect the microstructure of frozen dough effectively. For the control dough, the gluten was completed destroyed and the starch granules were seperated after 105d long-term frozen storage, while gluten network could also be seen in the dough added with ISP at 0.5% level. For the different amount of water addition, the gluten network was protected better when the water addition was 60.5% Fermentation and baking results showed that the addition of ISP improved the proofing time and specific volume of frozen dough bread. The proofing time decreased from 153 min to 130 min and the specific volume increased from 4.05 mL/g to 4.71 mL/g, when 0.5% ISP was added to the dough after 105d frozen storage. The ISP also had positive impact on firmness of bread.In order to understand the physico-chemical properties of frozen dough and the staling process of bread during storage, in particular the role of water in this process, it is necessary to investigate changes in the states of water over a wider spectrum. The two-component model was found to well represent the states of water in the frozen dough and bread using NMR. The results showed that the amount of T22 state water of frozen dough increased with increasing time, indicating the capability of holding water of frozen dough system decreased as storage time increased, TR didn't affect the water state, but ISP could reduce water mobility of frozen dough, and the combination of TR and ISP was better. In compared dough, amount of water addition had only slight effect on the bound water, but less amount of water addition could help to hold the stability of free water; In ISP dough, less water addition helped to hold the stability of both the bound and free water. During bread staling in 7d storage, intensities of protons of T21 effectively increased while T22 decreased, indicating the retrogradation of amylum and the evaporation of water.We used response surface method to study the combinational effects of anti-freezing additives including TR, TG and LBG on fermentational, baking characteristics of frozen dough. The results show that TR decreased CO2 production of fresh dough, but increased Hm and CO2 production of frozen dough after 18 weeks frozen storage, and it significantly improved the specific volume of the fresh dough bread. LBG significantly decreased CO2 production of fresh dough and frozen dough,whlie improved the hardness of frozen dough. The addition of TG in frozen dough could increase Hm, decrease the hardness, and the influence in fresh dough was different because it depended on the amount of TG.