Effects of two enzymes on qualities of non-fermented dough after freeze-thaw circles

Abstract: In order to explore the effect of enzymes on the quality of non-fermented dough after freeze-thaw cycles, the transglutaminase and xylanase were chosen and their effects on the quality of non-fermented dough after freeze-thaw circles were investigated. The low-field nuclear magnetic resonance (LF-NMR), texture profile analyzer and a rheometer were used to observe the changes of frozen non-fermented dough in quality during freeze-thaw cycles. The water loss rate, water distribution and mobility, protein fraction content, textural and rheological properties of the dough samples were evaluated in the experiment. The results showed that: compared with the control group, the additions of transglutaminase and xylanase could change the contents of different protein fractions. Transglutaminase addition could reduce the gliadin and gluten content (P<0.05), and raise the glutenin macropolymer content in the dough, while adding xylanase could increase the gliadin content but reduce glutenin content. The effect of transglutaminase on water extractable arabinoxylan content was not significant (P>0.05), however, the effect of xylanase was significant (P<0.05) compared with the control group, and with the increase of addition dose, the water extractable arabinoxylan content increased. Though transglutaminase addition could accelerate dehydration of the non-fermented dough after freeze-thaw cycles, xylanase significantly reduced water loss rate (P<0.05). Relaxation time T2(1) remained at 1.75 ms except the addition of 10 g/kg transglutaminase which significantly decreased T2(1) to 1.32 ms, and relaxation timeT2(2) were all reduced with the addition of two enzymes. The addition of transglutaminase gradually increased the relative content of deep bound water of the non-fermented dough after freeze-thaw cycles, and its content became to 33.05% when the addition of transglutaminase was 10 g/kg; while the effect of xylanase was opposite. The firmnness, toughness and hardness of samples were significantly decreased (P<0.05) with the addition of xylanase when compared with the control group. The xylanase improved the sample's texture profile better than the transglutaminase. The transglutaminase improved the sample's adhesiveness, elasticity and cohesiveness, and the xylanase decreased hardness and improved elasticity. To optimize the rheological properties of dough, the transglutaminase significantly increased the storage of moduliand the loss of moduli (P<0.05), and more addition more increased. On the contrary, the xylanase had a negative impact. Therefore, the addition of transglutaminase and xylanase played the roles in different aspects to improve the quality of non-fermented dough after freeze-thaw circles. The results provide the theoretical basis for the two enzymes widely application to the frozen non-fermented flour products.