Advantages of immersion freezing for quality preservation of litchi fruit during frozen storage

Abstract

The effects of immersion freezing (IF) followed by microwave thawing on the quality of frozen litchis were investigated after frozen storage for various time periods and compared with traditional air-blast freezing (AF). The freezing rate of IF samples was 10 times higher than that of AF samples. The average size of ice crystals in IF and AF samples was determined as: AF > 200 μm > IF. Consequently, there was good integrity of the fruit microstructure, hardly any drip loss and high retention (80%) of texture, quality and nutrient content in IF samples. Moreover, the IF samples retained their red color, with texture and taste that were difficult to distinguish from fresh litchis after being thawed and placed at room temperature for 3 h. In contrast, the AF litchis showed significant degradation in their quality, including loss of firmness, 4% drip loss and rapid browning. Compared with the AF method, the IF technology improved the quality of frozen litchis overall and greatly extended their shelf-life to at least 6 months. Therefore, IF should be considered as a promising novel technology for long-term storage of litchis.