*4.5. Phenolic Content Extraction and Analysis*

The phenolic content was determined from the apple powder and leaf powder gained from grounding in the mortar with the help of liquid nitrogen. The extraction and determination of phenolics was made following the protocol of Vrhovsek et al. [38]. Two grams of apple powder were extracted using aqueous 80% methanol (Honeywell, LC-MS Chromasolv). For leaves, a slight modification was made, 1 g of lyophilized leaf powder was used and extracted with 4.8 mL of MeOH:H2O (2:1) and 3.2 mL of chloroform (Honeywell, LC-MS Chromasolv). An ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used for the analysis. Two µL of samples were injected and processed through 100 × 2.1 mm, 1.8 µm column (Acquitiy HSS T3, Waters), maintained at 40 ◦C, with the flow rate of 0.4 mL min−<sup>1</sup> . The gradient profile of mobile phases was as described in Vrhovsek et al. [38]. The mass spectrometry detection was performed on Waters Xevo TQMS (Milford, MA, USA), equipped with an electrospray (ESI) source in positive and negative modes [38]. Results are presented in mg kg−<sup>1</sup> of fresh weight (FW) for flesh and mg kg−<sup>1</sup> of dry weight for leaves.

#### *4.6. Glutathione (GSH, GSSH), Cystein and Methionine Extraction, and Analysis*

The frozen apple flesh (−80 ◦C storage) was ground under cryogenic conditions (−196 ◦C) using AK11 mill (IKA), rapidly weighted into ice cold MeOH with sample weight to solvent volume (*w*/*v*) ratios of 1:4, shaken at room temperature for 15 min, and centrifuged (10,000× *g*, 4 ◦C) for 10 min. The volume was adjusted, samples were filtered through a 0.2 µm PVDF filter (Agilent technologies) into dark vials and directly injected onto UHPLC-MS/MS (Agilent technologies), and analyzed as described [39].
