Thermal inactivation kinetics of proteases and polyphenoloxidase in brown shrimp (Crangon crangon)

Abstract

To optimize product quality of the cooked brown shrimp (Crangon crangon), quantitative data on the influence of all relevant process parameters (treatment time and temperature) on several quality attributes is required. Surprisingly, kinetic data and models on heat induced inactivation of important endogenous spoilage enzymes of the brown shrimp are not available today. In this study the thermal inactivation kinetics of the most important spoilage enzymes, proteases and polyphenoloxidase (PPO), were determined from isothermal heat treatments of enzyme extracts of the cephalothorax. For both enzymes, inactivation kinetics showed first order decay(s). Proteases showed two distinct stability fractions. A labile fraction, representing 42±2% of the total activity with kl,60°C=0.94±0.14 min(-1) and Ea,l=178±8.5 kJ/mol, and a stable fraction, representing 58±2%, with ks,60°C=0.020±0.002 min(-1) and Ea,s=155±7.0 kJ/mol. PPO showed a single fraction with k60°C=1.58±0.02 min(-1) and Ea=161±2.2 kJ/mol. Based on these results, the proteolytic activity, in particular the thermostable fraction, should be considered as a target in thermal processing of brown shrimp in relation to enzyme induced product quality changes during storage.

Keywords: Crangon crangon; Kinetics; Polyphenoloxidase; Proteases; Thermal stability.