High pressure thermal processing of pears: Effect on endogenous enzyme activity and related quality attributes

The effect of high pressure-thermal (HPT) processing (600 MPa, 20-100 degrees C) on the activity of pear enzymes and related quality attributes was investigated. HPT processing at 20 degrees C for 5 min resulted in 32%, 74% and 51% residual activities of polyphenol oxidase (PPO), peroxidase (POD) and pectin methylesterase (PME), respectively. Increasing processing temperature to 40 and 60 degrees C reduced the level of PPO and POD inactivation, with the maximum residual activities of 64% and 123%, respectively observed after 3-min treatments at 40 and 60 degrees C. Overall, HPT at 20 to 60 degrees C had minimal effect on quality, although enzymatic browning was observed upon air exposure. HPT at 80 to 100 degrees C caused almost complete inactivation of PPO and POD with 90% and 92% inactivation respectively after 3-min processing at 100 degrees C, which reduced browning upon air exposure. Nevertheless, the lowest texture retention of 22% was observed under this condition. Industrial relevance: The study examined the effects of combined high pressure thermal processing on quality related pear enzymes and related instrumental quality attributes such as colour and texture. The study enabled identification of processing regimes for enzyme inactivation and quality retention. The excellent quality retention following HPP at 20 to 40 degrees C makes this condition suitable for 'fresh-like' small portion products for immediate consumption after unpacking that do not require complete PPO and POD inactivation. On the other hand, the almost complete inactivation of oxidative enzymes PPO and POD at 100 degrees C makes this condition more appropriate for the production of bulk products for food service applications or pureed ingredients for baby food, or pear pieces for yoghurt, that require PPO inhibition but not necessarily high firmness retention. (C) 2015 Elsevier Ltd. All rights reserved.