The drying strategy of atmospheric freeze drying apple cubes based on glass transition

• An atmospheric freeze drying (AFD) technique was successfully developed to dry apple cubes.
• After the moisture content of apple decreases below 35% (w.b.), the glass transition temperature increases quickly.
• High air temperature could be adopted during the end stage of AFD, and the product quality could be kept well.
• A step-up temperature program based on the glass transition during AFD process can reduce the drying time by almost half on the premise of keeping product quality.

Freeze drying (FD) yields the best quality of dried apple cubes but at the cost of long drying time and also the overall cost. To achieve economical freeze drying along with a high quality product an atmospheric freeze drying (AFD) technique was developed to dry apple cubes. The effect of different air temperature loading scheme on product quality and drying process was studied during AFD. According to the glass transition temperature of apple, a step-up temperature loading strategy for AFD process was developed to reduce the drying time by almost half and provided a similar good product quality.