Effect of pectin addition on the drying characteristics of freeze-dried restructured strawberry blocks

Pectin is a commonly used food additive, however, the freeze-drying characteristics of restructured strawberries with pectin addition are currently unclear. This study investigated the effects of 0, 3, 6, and 9 g/kg pectin addition on moisture content, drying date, moisture ratio, water state distribution during the freeze-drying process, as well as water uptake and volatile compounds of freeze-dried restructured strawberry blocks (FRSB). The drying rates at the four levels of pectin addition presented similar early acceleration and later deceleration trends. Moisture content in FRSB was linearly predicted by peak area of low field nuclear magnetic resonance with R2 higher than 0.90 for all the four groups. High pectin addition resulted in higher sulfides response values. Compared with the control group, the water uptake of FRSB samples in 0, 3, 6, and 9 g/kg group decreased by 12, 22, and 31%, respectively, which can be reasoned that pectin addition shielded hydrophilic functional groups from external water molecules. These results provide guidance for improving the drying characteristics, volatile compounds, and water uptake of FRSB by adding pectin.