Abstract: Differential scanning calorimetry (DSC), low-field nuclear magnetic resonance (NMR) and in situ Raman spectroscopy were used to explore the cryoprotective effect of enzymatic hydrolysates of flaxseed meal proteins obtained at different hydrolysis times on dough. The results showed that the thermal hysteresis activity of the 60 min hydrolysate, with a 13.62% degree of hydrolysis (DH), was highest (0.83 ℃), and the ice recrystallization inhibitory activity was also highest, minimizing the proportion of large ice crystals. It was found that addition of the hydrolysate had the most significant cryoprotective effect on dough. Compared with the control group, the proportion of strongly bound water in dough increased by 13.2%, and the proportions of weakly bound water and free water decreased by 0.7% and 7.9%, respectively. The maximum fermentation height, the final height and the onset time of CO2 leakage increased by 18.5%, 24.4% and 34.4%, respectively. Protein structure analysis showed that the relative α-helix content of gluten proteins in dough with the hydrolysate was highest and increased by 35.3% compared with the control group, and the relative random coil content decreased by 28.9%. The intensity (I760) of tryptophan band at 760 cm-1 increased by 282.3%, and the ratio (I850/I830) between the intensities of tyrosine bands at 850 and 830 cm-1 decreased by 59.6%. The relative contents of disulfide bond configurations g-g-g and g-g-t were increased by 8.8% and 9.8%, respectively. In conclusion, enzymatic hydrolysates of flaxseed meal proteins improved the water-holding capacity of dough, shortened dough proofing time, and weakened the damage of ice crystals to the network structure of dough, and the effect of the hydrolysate with DH of 13.62% was most pronounced.

Key words: protease hydrolysate; frozen dough; thermal hysteresis activity; molecular structure; cryogenic protection