Effects Of Recombinant Rhizopus Chinensis Lipase And Transglutaminase On The Anti-freezing Properties Of Frozen Dough Systems

The overall objective of this research was to study the effect of recombinant rhizopus chinensis lipase (RCL) and transglutaminase (TG) at optimum amount on frozen dough properties. First response surface central composite experimental analysis method was used to obtain the optimum amount of RCL and TG on dough with different frozen storage. Based on the optimum amount of RCL and TG, we studied the effect of RCL and TG on dough proofing time, bread specific volume, crumb cell structure parameters, and sensory evaluation; at the same time, comparing the effect of RCL and FBG on bread system. Dynamic rheometer, scanning electron microscopy, and chemical method (e.g. free thiol group content) were used to study the effect of RCL and TG on dough gluten structure. The mechanisms of RCL and TG on anti-freezing and fermentation properties of frozen dough during storage were investigated by using differential scanning calorimetry (DSC), F3 rheofermentometer, and viable yeast cell count determination.Response surface plots experiments, different amounts of RCL and TG as the variable and bread crumb specific volume as the reference, showed that the optimum amount of RCL and TG on frozen dough were 700 U/kg and 100 U/kg (flour weight basis), respectively. The bread crumb specific volume of frozen dough with 35 days of frozen storage and with RCL and TG addition were larger than that of dough without any enzyme addition.Based on the optimum amount of RCL and TG, we compared the effect of RCL and FBG on bread system. Results showed that dough proofing time prolonged and bread crumb specific volume decreased with frozen storage increasing. After 35 days of frozen storage, dough proofing time without enzyme increased by 3.06% and bread specific volume decreased by 5.63% compared with that of the dough with RCL and TG. Cell density (CD) and area fraction (AF) of bread crumb without enzyme decreased as time in frozen storage increased; by contrast, CD and AF of bread crumb with RCL and TG increased during frozen storage. After 35 days of frozen storage, AF of bread crumb with RCL and TG increased by 22% compared with that of crumb without enzyme. Results of sensory evaluation showed that there were significant difference in bread appearance, color, and overall acceptance when compared bread with RCL and TG with that of without enzyme. Compared to FBG, RCL showed a similar or better than FBG for improving the dough proofing time, bread specific volume, and crumb cell structure parameters.Results of the effect of RCL and TG on dough gluten structure showed that RCL and TG could improve the viscoelastic properties, strength the gluten structure of frozen dough, promote cross-linking of gluten proteins, which resulted in repaired gluten protein that damaged by frozen storage. And after 35 days of frozen storage, RCL and TG could decrease the free thiol group content by 29.75%. RCL and TG could also improve the emulsion ability and emulsion stability of dough with different frozen storage time. Results of the effect of RCL and TG on anti-freezing and fermentation properties of frozen dough showed that RCL and TG could increase significantly glycerol content of frozen dough. During 35 days of frozen storage, the increased amplitude of freezing water enthalpy value of dough with RCL and TG was 28.39% smaller than that of without enzyme. And RCL and TG could significant increase the viable yeast cell count of frozen dough. Meanwhile, rheoferment characteristics was determined using F3 rheofermentometer, results showed that RCL and TG could significant increase the maximum fermentation height (Hm) and the maximum gas production height (H'm) of frozen dough; RCL and TG could increase the total volume of CO2 production and stability of dough during fermentation; improve the anti-freezing and fermentation characteristics.