3.1. Characterization of freezing curves
Changes in the temperature of P. mume fruits during the freezing process at 20
C and 50
C, called freezing curves, are shown in Fig. 1. The lower freezing temperature led to a faster reduction in temperature. The initial freezing point was about 2.0
C and was observable at the beginning of the freezing plateau, which was longer during freezing at 20
C than at 50
C. The nominal freezing time was used to evaluate freezing rates. The nominal freezing time is defined by the International Institute of Refrigeration as the time needed to decrease the temperature of the thermal center to 10
C below the initial freezing point (International Institute of Refrigeration, 1986, pp. 32e39). The nominal freezing times were about 74 min and 28 min at 20
C and 50
C, respectively. These results suggest that the freezing rate at 20
C