The obtained results indicated that the cathepsin activity was higher by about 60% in the extract from thigh than from breast muscles. Freezing and defrosting (not stored) of chicken meat did not influence the breast muscle cathepsin activity while they caused a decrease of activity of about 20% in the case of thigh muscles. The increase in cathepsin activity was noticed in both kinds of muscles during storage at -20 "C up to 4 months (45.6% and 19.4% for thigh and breast muscles respectively). The activity of cathepsin in extract from 5 months stored meat reached 80% in case of breast muscles and 83% in case of thigh muscles in relation to control sample respectively.
The cathepsin activity significantly increased during heating of breast muscles up to 60 "C, but in case of thigh muscles it was slightly higher than at 50 "C. The heating of cured chicken breast muscles up to 60 "C caused a non significant growth in cathepsin activity opposite to raw muscles. The cathepsin activity from all cured samples heated up to 70 "C were several times lower in relation to control samples. The cathepsin activity of both thigh and breast muscles were resistant to gamma radiation.
The investigated factors caused changes in the activity of cathepsin but none of them caused its total inactivation. The changes of cathepsin activity depended on the kind of muscles and the kind and the value of acting factors.