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.