Glycolytic and Nucleotide Changes in the Critical Freezing Zone, −0.8 to −5 C, in Prerigor Cod Muscle Frozen at Various Rates

Abstract

Glycolytic and nucleotide changes during freezing at different rates were investigated in prerigor muscle from unexercised cod. Significant changes occurred during freezing as samples 1 cm thick in the center of a 2.8-cm thick pack cooled through the critical temperature zone from −0.8 to −5 C, but little further change occurred after the temperature had fallen below −5 C. The amount of change depended on the thermal arrest time (TAT) (time from −0.8 to −5 C). During rapid freezing with a TAT of 0.22 hr, the most significant change was a 39% dephosphorylation of creatine phosphate; small amounts of glycogen and acid-labile phosphorus were lost. Freezing at an intermediate rate (TAT, 5.4 hr) resulted in a loss of one-half of the initial glycogen and almost all of the creatine phosphate; also about one-third of the initial ATP was converted to IMP. After slow freezing (TAT, 20 hr) only traces of glycogen and high energy phosphorus compounds remained in most samples.Dephosphorylation of creatine phosphate, and degradation of ATP to IMP occurred more rapidly in freezing muscle at −1 C than in unfrozen muscle at 0 C. The rates of glycolysis were similar, but when the temperature dropped below −1 C there was an apparent increase in glycolytic activity.