Free energy change in collagen hydrolysis
tldr: reaction is exothermic because the heat of reaction is -2.5 Kcal/mol.

(1) Peptides do hydrolize in presence of enzymes. It means that Gibbs energy of hydrolysis is negative. However, Gibbs energy consists of $\Delta$ H and $\Delta$ S*T. $\Delta$ S of hydrolysis is favorable (more disorder), but $\Delta$H can be either lower or higher.  $\Delta$ H is what we are discussing here (the enthalpy of the reaction).

(2) Some endothermic reactions are really very endothermic (like dissolving NH4NO3 in water). Other reactions are mildly endothermic.  Hydrolysis of meat doesn't have a large $\Delta$ H change. "HEATS OF HYDROLYSIS OF AMIDE AND PEPTIDE BONDS" paper has exact value for the reaction: -2.5 Kcal/mol of peptide.  A negative value indicates the reactants have greater enthalpy, or that it is an exothermic reaction. So the reaction is slightly exothermic.