New insight into quality changes in bread dough under different state/ phase transitions during frozen storage

The mechanisms underlying quality changes in bread dough and baked bread were studied under varying temperature fluctuations (state/phase transitions) over a 4-week frozen storage period. The temperature of frozen bread dough was adjusted from -35 degrees C to facilitate various physical states, namely the thawed state, rubbery state, and glassy state. Rheological properties, rheofermentation properties, short-range ordered structure of starch, mobility of water, microstructures in the dough, and quality of baked bread were analyzed. Findings showed that frozen dough exposed to greater temperature fluctuations above Tm ' (onset of melting) exhibited larger ice crystal sizes, causing more disruption to the gluten network structure and a decline in the short-range molecular order of starch. This led to reduced viscoelasticity and rheofermentation properties in frozen dough, along with a significant decline in quality of baked bread (specific volume reduced by 0.904-38.6%). After 4-week storage, no significant differences were observed between the glassy state without temperature fluctuations (T1) and the glassy state with smaller amplitude of temperature fluctuation (T2) for most dough parameters. T1 had relatively smaller ice crystal sizes, leading to less damage to gluten network structure compared to T2. However, T2 demonstrated relatively higher total released gas volume (Vt) generated by yeast and better short-range molecular order of starch than T1, resulting in significantly improved quality in baked bread (specific volume and texture) from T2. Ice crystal size correlated with the trend of temperature fluctuation amplitude, while rheological properties and water mobility did not, possibly influenced by yeast activity and metabolism.