Effect of water migration on the thermal-vacuum packaged steamed buns under room temperature storage

•The shelf life of the thermal-vacuum packaging steamed buns can be extend at least 90 days at room temperature.•The vacuum degree of steamed buns has an inverse relationship to dough making water amount.•Moisture migration from crust to center in steamed buns.•Deep-bound water content decrease in steamed buns during storage.•Retrogradation process of steamed buns was slowed down with the increasing of WA during dough making.

This study aims to characterize water distribution in thermal-vacuum packaged steamed buns and to investigate the role of water as a mean to control staling during room temperature storage. Therefore, we analyzed vacuum degree (VD), water mobility, and starch retrogradation by using NMR, DSC, X-ray diffraction in the present study. Negative correlation coefficients were observed between water addition (WA) and VD of the package during first 21 h. The VD raised during 1 h, then declined and finally reached stability at 6 h. The initial deep-bound water (DBW) content was also found to be opposite to WA, it ranged from 27.2% to 25.8% as WA increased from 40% to 44% at 0 day. DBW decreased during 42 days of storage, then leveled off. Interestingly, moisture migration from the moist crust and intermediate zone to the dry center. Results from DSC and X-ray indicate that 1) thermal-vacuum packaging significantly inhibited the starch retrogradation of steamed buns; 2) the retrogradation rate of steamed buns was affected by WA during dough-making. Therefore, not only did the thermal-vacuum packaging technology extend the shelf life of the steamed buns by at least 90 days at room temperature, but it also significantly reduced starch retrogradation.