Research trends in selected blanching pretreatments and quick freezing technologies as applied in fruits and vegetables: A review

This paper presents a comprehensive review of recent developments in thermal (radio frequency, microwave and ohmic), non-thermal (high pressure, ultrasound and infrared) methods in blanching pretreatment. Recent developments in quick freezing technology (high pressure, dehydrofreezing and ultrasound-assisted) as applied to freezing of fruits and vegetables are also reviewed. The thermal and non-thermal blanching methods provide rapid and uniform heating; reduce the loss of soluble nutrients and minimize thermal damage compared to conventional hot water blanching. High pressure freezing seems to promote instantaneous and homogeneous ice nucleation in fruits and vegetables. Dehydrofreezing is capable of reducing the damage to plant texture by removal partial of water before freezing. Ultrasound-assisted freezing is found to be effective in the initiation of nuclei and subsequent growth of crystals. More fundamental researches are needed for better design and scale up, so that these technologies can be transferred from laboratory to industry.