*2.6. Principal Component Analysis (PCA)*

To better understand the correlations between all the evaluated parameters, a chemometric analysis was performed integrating all the data (Figure 6). The PCA based on the correlation matrix standardizes the data and this analysis was performed using a correlation matrix (Corr-PCA). In this analysis, the first two factorial axes (PC1 and PC2) represent 95.04% of the total variance, with factor 1 the one that presents the higher weight (82.81%).

**Figure 6.** Principal component analysis using the whole dataset of two sweet cherry cultivars (Early Bigi and Lapins). Analyzed parameters: WC—wax content; ERF—epidermis rupture force; FF—flesh firmness; pH; CI—cracking index; FW—fruit weight; FS—fruit size (width); TA—titratable acidity; TSS—total soluble solids; MI—maturity index.

The CI as well as the most of the analyzed parameters (fruit size, fruit weight, total soluble solids, titratable acidity, and maturity index) were together in the right PCA quadrant as well as flesh firmness, epidermis rupture force, and pH, although the latter were further away from the remaining parameters. On the other hand, the wax content was spatially separated and placed in the left PCA quadrant, corroborating the negative correlation between this parameter and the CI.

#### **3. Material and Methods**

#### *3.1. Experimental Design and Sweet Cherry Raw Material*

The experiment was conducted in 2019 in a 10 year-old sweet cherry orchard located in São João de Fontoura, Resende (Viseu district, Northern Portugal; latitude 41◦120 N, longitude 7◦930 W, altitude 149 m).

Weather data were recorded by a weather station located near the experimental site. The daily minimum temperature in March, when the first flowers appeared in the trees, ranged between 3.7 and 12.2 ◦C and the daily maximum temperature ranged between 11.9 and 22.6 ◦C. The total precipitation in that month was 4.1 mm, with day 6 as the rainiest. April was a very rainy month, with a total rainfall of 8.1 mm throughout the month. The daily minimum temperature ranged between 2.0 and 14.3 ◦C and the daily maximum temperature varied between 10.9 and 26.0 ◦C. The hottest days were 29 and 30 April. May was the warmest month (daily minimum temperature ranged between 6.4 and 17.4 ◦C

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and daily maximum temperature fluctuated between 16.2 and 32.9 ◦C) and the least rainy month (only 0.3 mm of total precipitation).

For this study, ten trees of each sweet cherry cultivar (Early Bigi and Lapins, grafted on 'Saint Lucie 640 rootstock) were used. Trees were spaced 3.0 m between rows and 2.5 m from each other in the row. Fruits were hand-picked at their commercial ripening stage, which was on 2 May and 27 May 2019 for cv. Early Bigi and cv. Lapins, respectively. The commercial ripening stage for each cultivar was defined by the producer. In fact, the fruits to analyze were collected at the same time that the producer harvested it to send to the market. Within each cultivar, about 500 g samples of fruit were collected randomly from all trees and two fruits per tree were additionally collected to determine the wax content. In the field, collected fruits were kept on ice and placed in the refrigerator upon reaching the laboratory. There, fruits were randomly divided into two sub batches. The first sub batch (150 sweet cherries without visual defects) was assigned to the evaluation of the cracking index (CI), while the second sub batch, consisting of 30 sweet cherries, was assigned for fruit weight (FW), size (FS), epidermis rupture force (ERF), flesh firmness (FF), total soluble solids (TSS), titratable acidity (TA), maturity index (MI), and pH measurements.
