## 4 Discussion
### Impact of Each Equivalent Processing Condition on Physicochemical Parameters  
As mentioned before, AP samples were tested at different processing conditions and physicochemical parameters were analysed for the untreated (control) and treated AP. These results can be found in Figure 2 (for the colour) and Figure 6 (for the other parameters). When comparing the L*a*b* parameters for the HPP treatment to the thermal-based treatments used (BL and CTP), the HPP values either do not show a significant difference or are smaller, apart from a significant effect on the b* variable, when the HPP value was bigger than the CTP, but not BL. These results are comparable to those obtained by [PERSON] and colleagues that found lower a* and b* values for HPP-treated AP (600 MPa, 3 min) than the conventional thermal treatment (35 s at 107 \({}^{\circ}\)C) [37]. However, these results differ from those of another study where the addition of inulin (8% \(w/w\)) to AP, together with thermal processing (a time temperature equivalent of P90 \(\geq\) 10 min to accomplish a procedure similar to a 6-log reduction of vegetative cells), resulted in lower L*a*b* values compared to HPP AP [38]. However, in contrast to the current study where the rise in the L* parameter did not have statistical significance, another study (using Golden Delicious AP) observed a significant increase in that variable (by 4.65) [39]. Other study that measured the effects of heating for 30 min at 90 \({}^{\circ}\)C with or without oxygen noted a decrease in the L* variable for both samples of Fuji AP, a decrease in the a* variable for heating in the presence of oxygen and an increase in the a* variable when samples were heated without oxygen, in comparison to the fresh AP values. These results differ from those seen in the present study for the L* variable (control value of 39.91) but in relation to the CTP value of the a* variable, a decrease was also observed, when compared to the untreated AP sample [23]. In another work, a significant increase in the L* parameter was found for a mild thermal treatment (99 \({}^{\circ}\)C, 1 min) and a standard (92 \({}^{\circ}\)C, 5 min) thermal treatment of 5.52 and 6.68, respectively, when compared to the control (L* of 43.40) [39]. Other thermal treatments like ohmic and microwave have also been tested for AP. A similar trend was observed by [PERSON] and colleagues, which measured the effects of an ohmic treatment on the colour of Golden Delicious AP and observed a decrease in the L* values but no statistically significant change was observed for the a* and b* variables [40]. Other recent ohmic work showed differences between the thermal treatments (conventional and ohmic) and the control, as the thermally treated AP showed lower L* and higher a* values but for the b* parameter, the conventional thermal treatment (35 s at 107 \({}^{\circ}\)C) remained similar to the control, as opposed to the decrease in value observed for the ohmic treatment (flow rate of 2000 L/h, at 107 \({}^{\circ}\)C) [37]. In addition, two studies analysed microwave treatments on different apple varieties and observed similar outcomes. The first study, using Idared and Shampion AP, found significant reductions in the L* and b* variables after a 2 min microwave treatment at 80 \({}^{\circ}\)C, compared to the control group that was heated for 4 min at the same temperature. However, for the a* variable, while Idared AP showed a decrease, Shampion AP exhibited an increase in value [41]. The second study, using Granny Smith AP, applied a shorter treatment (35 s, 652 w with a maximum temperature of 75.3 \({}^{\circ}\)C) and observed changes in colour, including a decrease in L*, an increase in a*, and a non-significant decrease in b*. These results differ from those obtained in the present study using Reineta Parda AP [36].