Effects of pulsed-vacuum and ultrasound on the osmodehydration kinetics and microstructure of apples (Fuji)

The influence of pulsed-vacuum (PV) and ultrasound on the osmodehydration kinetics and microstructure of apples (Fuji) was investigated. Apple cylinders (15 mm height × 15 mm diameter) immersed in a 60% (w/w) high-fructose corn syrup solution were subjected to shaking (55 rpm), PV (13 MPa vacuum for 5 min + atmospheric pressure for 5 min + same vacuum for 5 min, then atmospheric pressure), or ultrasound treatment (50/60 Hz and 185 W) for 3 h. Changes in water loss, solid gain, and firmness of apples were measured, and the data were fitted using Weibull and Peleg models. In addition, microstructure was observed using scanning electronic microscopy (SEM). The high regression coefficients (R2 > 0.96) and low percent mean relative deviations (E < 6.37%) indicated the acceptability of Weibull model for predicting both water loss and solid gain under all treatments. The Peleg model well described the sample firmness changes with a R2 ∼ 0.98 and E ∼ 3.24–6.14%. PV resulted in the lowest shape parameter α value (0.74) for solid gain and the greatest rate constant k1 (40.98 s) for firmness loss, indicating the largest amount of solid gain (3.02%) and the least firmness loss of samples, while ultrasound led to the lowest α value (0.45) for water loss and k1 value (33.42 s) for firmness loss: the highest water and firmness losses (56.3% and 22.3%, respectively) in samples among three treatments. SEM showed that cell deformation and cell structure collapse were the most severe in ultrasound treated samples, but moderate in PV samples. SEM also revealed a larger amount of solute uptake in the cells of PV and ultrasound treated samples.