As a result of earlier studies by two of the present authors and other workers, the fact seemed well established that the temperature of freezing has an important bearing on tenderness and on the drip loss of meat in thawing. To determine the basic cause of these effects was an obvious need. The purpose of the studies reported here was to throw light on the relation between the histological characteristics of beef frozen at different temperatures, on one hand, and tenderness and drip loss of the product, on the other.
REVIEW OF LITERATUREIn a study of ice formation, &loran (1931) found that in meat frozen a t -2Q°C. (--4"F.) large crystals were formed in the center of the sample, whereas on the outside layer, where the time required for freezing was short, the ice crystals were very small. Moran (1932) also reported that approximately 82 per cent of the water in meat was frozen a t -5°C. (23°F.). A t lower temperatures more of the water was frozen, but it was of smaller percentage in relation to the reduction in temperature. Koonz and Ramsbottom (1939), using a modification of the Altmann-Gersh freezing-drying technic, studied frozen sections of chicken muscle and reported that ice crystals formed externally to the muscle fibers when freezing was done at -26.1°C. (-150F.) or above. The ice formations became larger, fewer in number, and the component fibers and bundles of fibers were forced into compact groups when freezing was slow. At -75.6"C. (-104°F.) a sample several millimeters in thickness froze in a few seconds, and water separated from the fiber protoplasm so that the ice crystals were extremely small but numerous. On histological examination the fibers closely resembled those of fresh, unfrozen tissue. A whole bird frozen a t --48.3"C. (-55"F.) showed a different picture, owing to slower freezing. The fibers appeared distorted and were characterized by jagged outer surfaces. The longitudinal sections of 'these fibers showed ice within the sarcolemma, which formed parallel to the long axis of the fiber, and extended its full length. The diameter of these ice columns increased in proportion to temperature increase. DuBois, Tressler, and Fenton (1940, 1942) and Tressler and DuBois (1940) report that boned, rolled beef rib roasts, frozen in still air at -31.7 or -23.3"C. (-25 or -1O0F.), or in an air blast a t -17.8"C. (O'F.), showed some cell disruption, whereas those frozen in still air at -16.7"C. (2°F.) showed considerable breakdown in the tissue. The same conditions were observed in case of chicken flesh. Shrewsbury and co-312