Effects of liquid nitrogen quick freezing on polyphenol oxidase and peroxide activities, cell water states and epidermal microstructure of wolfberry

Fresh wolfberry has a very short shelf-life and drying is the most common method for preserving wolfberry. For better retention of the quality and nutritional values of wolfberry, effects of liquid nitrogen spray freezing at different temperatures of −60 °C ± 2 °C (NF-60°C), −80 °C ± 2 °C (NF-80°C) and −100 °C ± 2 °C (NF-100°C) on wolfberry were investigated, as compared with air-blast freezing (BF) at −40 °C ± 1 °C and air velocity of 0.75 m/s....