The effect of thermal pasteurization and high pressure processing at cold and mild temperatures on the chemical composition, microbial and enzyme activity in strawberry purée

Abstract

The impact of high pressure processing (HPP) at 300 or 500 MPa for 1, 5 or 15 min at 0 or 50 °C and thermal processing (TP) at 90 °C for 15 min on the quality of strawberry purée was studied. TP caused the highest degradation of polyphenols (14%), anthocyanins (43%), vitamin C (61%) and color (dE > 3) but only this method effectively decreased the activity of polyphenol oxidase — PPO (97.7%), peroxidase — POD (99.5%) and microorganism count (< 1 log cfu/g). The highest decrease of the mentioned nutrients (4%, 14%, 30%, respectively) in HPP-treated samples was noticed at 500 MPa/15 min/50 °C, whereas color changes were unnoticeable (dE < 3) and enzymes were inactivated only in 72% (PPO) and 50% (POD). Counts of yeasts and molds were reduced to < 1 log cfu/g only after TP and HPP at 500 MPa. HPP preservation at 0 °C affects the content of nutrients and color to the least extent. This study demonstrated that the nutritional and sensory qualities of strawberry purée after high pressure processing were much better than after thermal pasteurization. Purée treated with HPP at 0 °C did not show significant difference compared to fresh strawberry purée. Greater inactivation of PPO and POD was observed after thermal pasteurization, but this treatment caused also slightly more degradation of anthocyanins, vitamin C and sensory quality. The results showed that HPP might be a useful method for preservation of strawberry products. However, considering the residual enzyme activity, it will be a very important point to check the stability of the products during storage. • Nutrients depended on temperature whereas pressure and time were inappreciable. • HPP of strawberry purée at 0 °C had minimal impact on its quality. • The pressure, temperature and time of HPP influenced the enzyme and microbial count. • Chemical and sensory qualities of the purée were reduced more by TP than HPP system.