The determination of in vitro digestibility of acid proteases in the digestive gland (DG) of adult O. vulgaris (>1,2 Kg) was performed, using four different preys (Mackrel, Scomber scombrus; Green crab, Carcinus maenas; Swimming crab, Necora puber; Shortfin squid, Illex coindetti). For each prey, four treatments were applied: 1) Frozen, 2) boiled at 100ºC for 1 minute, 3) Lyophilized and 4) Oven dried at 70ºC. A pH-Stat was used to determine in vitro digestibility at pH 3. Results showed that digestibility was higher (p0.05), compared to the other two treatments that suffered heating (boiled and oven dried), regardless of the diets tested. Regarding acid proteases metabolism, which is the most important for O. vulgaris, results indicate that heat treatments close and/or higher than 70ºC promote changes in the different diets that prevent their assimilation by the DG of O. vulgaris.