Effect of freezing pretreatment on the quality of juice extracted from Prunus mume fruit by osmosis with sucrose

- Freezing pretreatment improved efficiency of osmotic extraction of Prunus mume.
- Freezing was effective in improving appearance of osmotically extracted juice.
- Slower freezing was more effective in exsudation of organic acids from fruits.

The effects of freezing rate on the efficiency of the subsequent osmotic extraction and the quality of the osmotically extracted juice from Prunus mume fruits were evaluated. Fresh fruits of P. mume were frozen at −20 or −50 °C, thawed, and mixed with sucrose. The juices after osmotic treatment were then prepared from these mixtures. Nonfrozen fruits were used as control. Nominal freezing times were 74 and 28 min for −20 and −50 °C, respectively. Drip loss was higher in fruits frozen at −20 °C than at −50 °C. Clarity and browning index of the juice from frozen fruits were higher and lower, respectively, than those of the nonfrozen fruits. Contents of glucose, fructose, citric acid, tartaric acid, malic acid, and chlorogenic acid in juices ranked in descending order as follows: juice from fruits frozen at −20 °C > juice from fruits frozen at −50 °C > juice from nonfrozen fruits. These results suggest that freezing pretreatment affected the quality of osmotically extracted juice and that slow freezing could be a more useful method in osmotically extracting fruit juice.