Effect of microbubbles on immersion freezing of grape tomato

Microbubbles (MBs) were incorporated into calcium chloride solution as a novel freezing medium for immersion freezing of grape tomato. The effects of MB size (39, 43, 48 μm mean diameter), entrapped gas (air, N₂, CO₂) and freezing temperature (-10, -15, -20 °C) on the freezing behavior and quality attributes of tomato were investigated. MBs increased the nucleation temperature from -7.4 to -3.5 °C and reduced the onset time of nucleation from 5.8 to 2.9 min at freezing temperature of -20 °C, which facilitated the formation of small ice crystals within tomato. MB-assisted freezing reduced the drip loss by 13.7-17.0% and improved the firmness of tomato, particularly when MB size and freezing temperature decreased. Freezing tomato with air-MBs did not compromise its nutritional quality, using N₂- and CO₂-MBs even increased its lycopene content, by 31% and 23%, respectively. The results proved the preservation effect of MBs on fruit during immersion freezing. This study can benefit the fruit and vegetable industry by providing an efficient freezing technology for producing frozen products with high sensory and nutritional quality.