THE EFFECTS OF FREEZING ON FLESH PROTEINS

Flesh proteins, in the context of this article, are taken to be the component proteins of the contractile muscle of animals used for food (i.e., meat, poultry, and fish). Attention is given to the similarities and differences between the proteins from these different sources and in particular to the effects on thein of freezing and frozen storage. It is believed that myosin and actin, the main contractile proteins, are largely responsible for the functional properties of flesh foods, and that on frozen storage, myosin, in particular, undergoes aggregation reactions which lead to toughening of the muscle and a loss in water-holding capacity. Variation in stability of flesh of different species on frozen storage can be attributed to some extent to the intrinsic characteristics of the respective myosins. Myosin from fish is generally less stable than its mammalian or avian counterparts and this is reflected in the stability of the flesh on frozen storage. Cryoprotectants, usually in the form of low molecular weight polyhydroxy compounds, are added to some processed products such as surimi to-counter the denaturation process. Theories on the mechanism of protein denaturation and of the action of cryoprotectants are reviewed. The potential.of,using the freezing process to form textures from comminuted flesh or protein dispersions is also discussed.