Evaluation of heating uniformity and quality attributes during vacuum microwave thawing of frozen apples

Abstract

This study investigated the effects of air, microwave (MW), and vacuum microwave (VMW) thawing treatments on the physical properties of frozen apples, including weight loss, electrical impedance characteristics for assessment of cellular structure, surface color, and mechanical properties, as well as the heating uniformity in MW and VMW thawing. The results showed that VMW inhibits the localized overheating of the sample during thawing compared to MW thawing. VMW thawing increased the breaking strain of the sample tissues compared to the other samples. The breaking stress and maximum stress, which are indices of the hardness of the tissue, were significantly reduced after freezing–thawing in each thawing method; the phenomenon was thought to be caused by the damage to the cell structure, which was confirmed by the electrical impedance analysis. The level of browning was significantly lower in MW and VMW thawing than in air thawing at 20 °C because they required a relatively short thawing time. This study showed that one of the specific effects of VMW thawing is that it can thaw the sample in a short time by inhibiting excessive heating and localized heating, indicating its potential for application as a high-quality and efficient thawing technology for various foods.