Freezing by immersion in liquid CO2 at variable pressure: Response surface analysis of the application to carrot slices freezing

• HPCI was firstly studied in the freezing process of fruits and vegetables.
• Optimizing freezing conditions was found by RSM.
• HPCI freezing attains higher residual contents of vitamin C, α- and β-carotene.
• HPCI freezing presents less drip loss and tissue damages than LN or ULTF freezing.

In order to demonstrate the potentials of high pressure carbonic immersion (HPCI) freezing in food fast freezing, effects of HPCI freezing on moisture, drip loss, hardness, nutritional components and microstructure of carrot slices were investigated. Response surface methodology analysis indicated that, the decompression time was the most significant factor affecting the central temperature, followed by pressure and retention time (p < 0.05). HPCI freezing at pressure of 6 MP, initial temperature of 10 °C, retention time of 3 min and decompression time of 5 min produced less drip loss and better nutrition retention, but more moisture loss in samples compared with liquid nitrogen (LN) immersion freezing or − 80 °C Ultra Low Temperature Freezer (ULTF) freezing. The scanning electron microscopy (SEM) images and visual observation indicated that samples in HPCI freezing showed less tissue damage as compared to samples frozen in − 80 °C ULTF freezing or LN immersion freezing. HPCI freezing is a promising way for fast freezing treatment of food.Industrial RelevanceIn the food industry, freezing is one of the common and excellent methods for long term preservation of foods. And it is generally accepted that fast freezing better preserves local structure. High Pressure Carbonic Immersion Freezing (HPCI), named by contrast to the spray-freezing of liquid carbon dioxide, can accelerate the freezing rate and make some quality attributes of food better than those in liquid nitrogen (LN) or liquid carbon dioxide spray freezing. Available data provided in this study will benefit the fast freezing food industry.