4. Conclusions
Although there seems to be limited information on HPP treatment effects during shelf life specifically in apple juice, in general terms the results observed in this project agree with previous research findings. The trends reported may well confirm the suitability of HPP as an alternative to conventional, thermal methods of apple juice treatment. In this study, HPP processing decreased PPO activity to undetectable levels, although a resistant fraction recovered up to 20% of its activity during the shelf life period. Such recovery in PPO activity did not cause, however, browning of the stored juice. Physicochemical characteristics, sensory attributes and nutritive quality of the HPP-treated apple juice remained practically unchanged in the shelf life period studied. Extending the shelf life of high quality HPP-treated apple juice is an important aspect for its wider distribution and commercialisation. The exercise of optimising HPP operating variables by response surface methodology resulted in moderate values of 430 MPa for 7 min at room temperature, so that scaling to industrial capacity may result in a cost-effective preservation option