Protein in vitro digestion was characterized by pepsin proteolysis of myofibrillar proteins extracted from processed beef samples using 2 descriptors of the kinetics: maximum value (ODmax) and half life time (t 1/2). An experimental fractional factorial design with 32 trials was used to investigate the effect of processes variables; it consists of 5 factors each taking 2 levels (muscle type, mincing, pH, NaCl content, cooking time) and 1 factor taking 4 levels (cooking temperature). The statistical analysis showed that (i) cooking temperature and time have a major effect, (ii) there is interaction between muscle type and NaCl content and (iii) mincing and pH have little effect. The evolutions of the 2 descriptors with cooking time were then analyzed with the 2 muscles at 2% NaCl content, 60 and 90°C. They show that the main changes occur in the first 10 minutes.