## 6 Conclusions and Future Needs  
An overview about PPO has been accomplished, trying to include the main aspects when minimal processing is concerned. Thus, researchers have mainly focused on the following points:  
* The importance of pre-harvest conditions on PPO activity (among other enzymes) and quality deterioration. In that sense, many authors have pointed out the strong influence of these conditions in many aspects related to PPO activity, such as PPO or polyphenol content, firmness, etc.
* The specific characterization of cultivars in order to predict their performance during minimal processing, specifically regarding PPO and polyphenol content. This way, many authors have selected the most suitable fruit or vegetable cultivars to obtain high-quality fresh-cut produce.
* Selection and optimization of treatments to keep quality of minimally processed fruits or vegetables. As explained in previous sections, many works have pointed out the importance of using optimum conditions for each treatment (for instance, the right % CO\({}_{2}\) percentage in MAP or the suitable temperature and time treatment for blanching), both to improve the effectiveness of the treatment to decrease PPO activity and to avoid undesirable effects. It should have noted that, in some cases (especially when different conservation techniques are combined), an intermediary solution should be found.
* The combined use of conservative techniques. As many studies have proved, the use of two or three techniques can present additive or synergistic effects when it comes to PPO inhibition, due to the direct inhibition of the enzyme or indirect positive effects (such as microbial control or turgence promotion, which also results in a decrease in PPO activity). In that sense, the MAP and washing treatments seem to be suitable techniques to be combined with other innovative ones, such as irradiation, the use of active packaging, etc.
* Sustainability and circular economy. In most cases, optimization of operating parameters in most conservative techniques is necessary, not only in order to increase the effectiveness of each method, but also to reduce costs and develop industrial-scale strategies. Thus, the use of hurdle technologies can contribute to mild conditions, implying lower costs (especially concerning temperature or reagent addition). Another interesting aspect is the possible contribution to circular economy, by using some wastes to obtain interesting product for minimal processing (such as natural extracts or essential oils, among others).  
In conclusion, PPO is an important concern for fresh-cut processing, being the developing key for new inhibitory treatments in order to contribute to shelf-life increase. In addition, many studies have been carried out to get further knowledge about PPO's mechanism. Indeed, due to some authors' controversy and probably because of the several matrixes found in fruit and vegetables, the relationship between PPO activity and browning should be cleared up and yet further studies should focus on PPO behavior depending on food matrix.  
Additionally, further studies should be carried out in order to perfect the parameters of some trendy techniques such as HPCD, US or UV treatments.  
Thus, the use of hurdle technology is a promising technique in order to control PPO activity without compromising other quality properties in food. In this case, the use of UV or Gamma radiation or US might be a complementary ally in order to preserve visual quality in fresh-cut produce, as well as the use of mild treatment to avoid any quality change in these products.  
This research received no external funding.  
Not applicable.  
Data Availability StatementData sharing not applicable as no datasets were generated or analysed during this study.  
The author declares no conflict of interest.