Definition of the optimum freezing rate—1. Investigation of structure and ultrastructure of beef M. longissimus dorsi frozen at different freezing rates

The influence of freezing rate on location, shape and size of ice crystals formed during freezing of beef M. longissimus dorsi, as well as its influence on ultrastructure, were investigated. Muscle samples were frozen at different rates: 0·22 cm/h and 0·39 cm/h (cooling agent was chilled air), and 3·33 cm/h, 3.95 cm/h, 4·92 cm/h and 5·66 cm/h (cooling agent was liquid carbon dioxide which expanded in the sucking-pipe of the tunnel freezer). It was found that by slow freezing (freezing rates 0·22 cm/h and 0·39 cm/h) 30·00 μm). An increase in the freezing rate was followed by a change in ice crystal location. In this case they had also been formed intracellularly. The number of crystals increased while their size decreased. The most intensive fibre damage was found in samples frozen at a rate of 0·22 cm/h, and the least in samples frozen at a rate of 3·95 cm/h with a freezing temperature of -50°C.