FATNESS, RATE OF CHILLING AND TENDERNESS OF LAMB

40 lambs were selected to vary in amount of finish for use in determining the mechanism by which fatness affects tenderness. Lambs with thick (n = 10), intermediate (n = 20) or thin (n = 10) finish were slaughtered, chilled at 1 ± 1°C and samples obtained from three muscles for chemical, histological, physical and organoleptic analyses. Subcutaneous fat was removed from one side of each carcass in the intermediate finish group to facilitate comparisons on a within-carcass basis. The data suggest that lamb carcasses which have increased quantities of fat (subjectively determined via live evaluations of finish or objectively determined via subcutaneous fat thickness measurements and marbling scores): (a) chill more slowly; (b) maintain muscle temperatures conducive to autolytic enzyme degradation for greater periods of time postmortem; (c) sustain less shortening of sarcomeres; (d) have muscles with lower ultimate pH values; (e) have less perceptible or softer connective tissue; and (f) are more tender than lamb carcasses which have limited quantities of fat. The data support the hypothesis that deposition of increased quantities of subcutaneous or intramuscular fat (particularly in carcasses with limited quantities of subcutaneous finish) increases tenderness via changes in postmortem chilling rate. An increased quantity of fat decreases the rate of temperature decline (either by insulation or via an increase in carcass mass), enhances the activity (or increases the duration of active proteolysis) of autolytic enzymes in muscle, lessens the extent of myofibrillar shortening and thereby increases the ultimate tenderness of cooked meat from a fatter carcass.