## 2 Results
### OPLS-DA Analysis on Krola Pear Fruit from 12 Orchards  
In order to discriminate Krola pear fruit with different sensory qualities, the GC-MS data including the concentrations of primary metabolites and volatiles were analyzed by using OPLS-DA. As shown in Figure 1, the pear fruit could be classified into two groups, with one corresponding to high sensory quality (sensory ranks: 1-9) and the other corresponding to low sensory quality (sensory ranks: 10-12). As a result, nine metabolites with VIP values higher than 1.5, including l-(+)-tartaric acid, malic acid, p-(-)-fructofuranose, \(\alpha\)-bulnesene, fructose, psicopyranose, l-proline, glucose and l-\(\alpha\)-terpineol, were obtained and listed in the Supplementary Material (Table S9).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Compounds** & **Retention Index (RI)** & **Concentration Range** & \
\begin{tabular}{c} **Average Concentration** \\ **(ug/kg FW)** \\ \end{tabular} &
\begin{tabular}{c} **(\(\mathbf{\mu}\)**g/kg FW)/Percentage** \\ **of Total Volatiles (\%)** \\ \end{tabular} \\ \hline \hline (_E,E_)-2,4-Hexadienal & 911 & 0.00–1045.21 & 206.89/0.68 \\ (_E_)-4-Oxohex-2-enal & 958 & 55.12–1815.23 & 309.67/1.02 \\ Phenol & 980 & 0.00–0.41 & 0.07/- \\ Hexanoic acid & 990 & 0.00–202.81 & 56.68/0.19 \\ \(p\)-Cymene & 1025 & 0.00–60.38 & 11.66/0.04 \\ Benzeneacetaldehyde & 1045 & 2.11–22.32 & 7.34/0.02 \\ (Z)-1-ethoxy-4-methyl-2-Pentene & 3.52–1941.80 & 354.24/1.16 \\
1-methyl-4-(1-methylylidene)-Cyclohexene & 1088 & 0.00–2.22 & 0.23/- \\
2-etherly-1,4-dimethyl-Benzene & 1090 & 0.00–0.37 & 0.03/- \\
2-Nonanone & 1092 & 0.00–156.99 & 31.02/0.10 \\ Undcane & 1100 & 0.00–8.23 & 3.08/0.01 \\
1,2,4,5-tetramethyl-Benzene & 1116 & 0.00–35.93 & 12.78/0.04 \\ Benzoic acid & 1170 & 0.00–103.50 & 12.65/0.04 \\ Naphthalene & 1182 & 2.04–26.36 & 7.28/0.02 \\ Dodecane & 1200 & 9.03–77.73 & 34.46/0.11 \\ (Z)-3,7-dimethyl-2,6-Octadienal & 1240 & 0.00–4.56 & 2.05/0.01 \\ Nonanoic acid & 1273 & 0.00–26.95 & 4.73/0.02 \\
2,6,11-trimethyl-Dodecane & 1275 & 0.00–36.70 & 10.34/0.03 \\ Traceane & 1300 & 7.44–58.40 & 18.34/0.06 \\
2,3,5,8-tetramethyl-Decane & 1318 & 0.00–27.36 & 7.97/0.03 \\ Tetradecane & 1400 & 18.28–91.39 & 35.06/0.12 \\ Pentadecane & 1500 & 0.00–231.63 & 60.09/0.20 \\
2,6,10-trimethyl-Tetradecane & 1539 & 0.00–19.23 & 6.37/0.02 \\
5-methyl-Pentadecane & 1547 & 2.21–45.84 & 7.54/0.02 \\
5,8-Diethyldodecane & 1572 & 3.79–34.53 & 9.61/0.03 \\ Hexadecane & 1600 & 5.84–64.97 & 15.45/0.05 \\
6,9-Heptadecadiene & 1667 & 0.00–2.30 & 0.56/- \\
1-Hydroxycyclohexyl phenyl ketone & 1687 & 9.28–199.96 & 39.17/0.13 \\ Tetradecanoic acid & 1768 & 0.00–1225.67 & 102.14/0.34 \\
2,6,11,15-tetramethyl-Hexadecane & 1792 & 0.19–33.98 & 5.64/0.02 \\ Pentadecanoic acid & 1867 & 0.00–1175.82 & 98.01/0.32 \\ Nonadecane & 1900 & 3.85–94.82 & 18.62/0.06 \\
9-Hexadecenoic acid & 1942 & 0.00–1610.17 & 135.11/0.44 \\ \(n\)-Hexadecanoic acid & 1968 & 0.00–3839.76 & 319.98/1.05 \\ Eicosane & 2000 & 0.00–52.30 & 6.24/0.02 \\ Heptadecanoic acid & 2071 & 0.00–129.25 & 10.77/0.04 \\ Heniccosane & 2100 & 8.04–295.40 & 47.09/0.15 \\ Oleic Acid & 2141 & 0.00–404.28 & 33.69/0.11 \\
**Total** & & **13098.35–79188.69** & **30444.88/100.00** \\ \hline \hline \end{tabular} Note: ‘-’ in the line of the percentage means that the percentage of compounds was lower than 0.005%; bold numbers were the total contents of different kinds of substances; the retention index was acquired on the semi-standard non-polar.  
\end{table}
Table 3: _Cont._