Study of the effect of freezing rate on banana's polyphenol oxidase and peroxidase activities and its thermodynamics calculation of liquid nitrogen
Taking liquid nitrogen quick-freezing and slow-freezing methods respectively, the effect of freezing rate on banana's polyphenol oxidase (PPO) and peroxidase (POD) activities has been explored in this paper. Meanwhile, simple heat-capacity economical analysis and calculation of liquid nitrogen are conducted. Results are as follows: freezing rate has significant effect on enzyme activities, compared to the fresh sample, the activity of PPO of banana which frozen at -80 ℃, -25 ℃ and liquid nitrogen dropped to 86.84%, 78.86% and 93.42% respectively; and the activity of POD rose to 109.8% and the other two dropped to 69.24% and 90.36%. Taking the enzyme activities'change and the calculation results into account, it is uneconomical to freeze the low affixation fruits and vegetables such as bananas completely with liquid nitrogen, and combined refrigeration methods should be taken into account.