Effect of Different Thawing Methods on Quality of Prunes

To study the effects of different thawing methods on prune quality, five thawing methods (hot water, microwave, ultrasound, high hydrostatic pressure and room temperature) were applied to treat quick-frozen prunes by liquid nitrogen. The juice loss rate, microstructure, enzyme activity, nutrient contents and sensory quality of prunes were determined. The results showed that compared to room temperature thawing, ultrasonic and 30 °C hot water treatment could accelerate the thawing process, but the juice loss rate was higher (2%~3%). Microwave thawing led to uneven heating but with less juice loss (1.08%), good microstructure and texture. High hydrostatic pressure (100 MPa) had the shortest thawing time (60 s), which could improve the hardness, chewiness and sensory evaluation acceptance, but it had caused 5% juice loss rate with severe separation and rupture in cells. Except for ultrasound thawing, different thawing methods significantly decreased the pectinase activity, soluble solid content (SSC) and vitamin C content of prunes. Among them, high hydrostatic pressure thawing could reduce the pectinase activity by 96.60%, while the loss of SSC and vitamin C by microwave thawing was the least, which were 9.17% and 44.70%, respectively. Thus, this study could provide some references for the application of various thawing technologies in the preservation and processing of prunes.