Pulsed ultrasound-assisted transcritical CO₂ improves the freezing characteristics of fruit and vegetable gel models via ice crystal inhibition.

This study constructed a novel green freezing technology by coupling low-frequency pulsed ultrasound with transcritical CO₂ refrigeration (UTCF). Pectin-sucrose-gelatin gel models (PSGMs) with different moisture contents and fresh fruits and vegetables (FVs) were used to evaluate its freezing characteristics and quality-preserving effects. Results showed that UTCF-40 outperformed RF-40 (traditional refrigerator freezing), it significantly shortened transition time and total freezing time by 18.46-21.79%, thus improving freezing efficiency and decreasing drip loss. Moreover, compared with RF-40, UTCF-40 also exhibited better texture, minimized microstructural damage, and improved moisture-holding capacity. This was mainly attributed to the modulation of ice crystal morphology and size during freezing, with UTCF-40 decreased the ice crystal area by 29.68-35.45% relative to RF-40. Finally, its efficacy was further validated in fresh FVs (blueberry, kiwifruit, citrus, radish). These observed benefits mainly stem from rapid heat transfer of transcritical CO₂ (0 ODP and 1 GWP) and uniform small ice crystals induced by ultrasound. This study confirms that UTCF is a promising green technology for FVs processing.