## 3 Materials and Methods
### Determination of Organic Acid Contents  
A Thermo Vanquish Flex UHPLC (Thermo Scientific, Sunnyvale, CA, USA) equipped with a Q-Exactive hybrid quadrupole-orbitrap mass spectrometer (Thermo Scientific, San Jose, CA, USA) was used to analyze the organic acid content in durian pulp. The experimental methods and instrument conditions were based on the literature and some optimizations were made ([PERSON] et al., 2016). A total of 100 mg of durian pulp was accurately weighed in a 2.0 mL centrifuge tube, and 300 \(\mathrm{\SIUnitSymbolMicro m}\) extraction solution (methanol: chloroform = 7:3) was added to the centrifuge tube. The solution was mixed thoroughly and left to stand for about 30 min in an ice bath. A total of 200 \(\mathrm{\SIUnitSymbolMicro m}\) of deionized water was added to the system and mixed thoroughly. The mixture was centrifuged at 12,000 rpm for 10 min at 4 \(\mathrm{\SIUnitSymbolMicro C}\), and the supernatant was collected. The centrifugation process was repeated once. After centrifugation, 40 \(\mathrm{\SIUnitSymbolMicro m}\) of the mixture was mixed with 10 \(\mathrm{\SIUnitSymbolMicro m}\) of 0.1M 3-nitrophenylhydrazine (3-NPH) at 40 \(\mathrm{\SIUnitSymbolCelsius}\) for 30 min of incubation to complete the sample derivatization ([PERSON] et al., 2016). Finally, the processed sample solution was diluted 10 times. Separation of organic acid was performed on a UHPLC system equipped with a Waters BEH C18 Column (2.1 mm \(\times\) 50 mm, 1.8 \(\mathrm{\SIUnitSymbolMicro m}\) particle size). The column oven temperature was set to 40 \(\mathrm{\SIUnitSymbolCelsius}\). The mobile phase A was water/0.1% formic acid, and the mobile phase B was ACN/0.1% formic acid. The flow rate was 0.35 mL/min, and the injection volume was 2 \(\mathrm{\SIUnitSymbolMicro m}\). The elution gradient was as follows: 0.0 min A/B (90:10 \(v\)/\(v\)), 2.0 min A/B (90:10 \(v\)/\(v\)), 12.0 min A/B (10:90 \(v\)/\(v\)), 14.0 min A/B (10:90 \(v\)/\(v\)), 14.1 min A/B (90:10 \(v\)/\(v\)) and 16.0 min A/B (90:10 \(v\)/\(v\)). The UHPLC system was coupled to MS equipped with electrospray ionization (ESI) and the MS conditions were as follows: sheatsh gas flow rate 40 arb, auxiliary gas flow rate 10 arb, ion spray voltage \(-\)2800 V at 350 \(\mathrm{\SIUnitSymbolCelsius}\), ion transfer tube temperature 320 \(\mathrm{\SIUnitSymbolCelsius}\). The scan mode was Fullms \(-\)ms2 negative ion. Different durian samples were studied using the same analysis methods and analysis conditions. The standard stock solution of propionic acid, isobutyric acid, butyric acid, oxalic acid, (\(S\))-lactic acid, valeric acid, isovaleric acid, malonic acid, hexanoic acid, 4-methylvaleric acid, fumaric acid, maleic acid, succinic acid, benzoic acid, itaconic acid, glutaric acid, d-(+)-Malic acid, salicylic acid, octanoic acid, adipic acid, d-(-)-Tartaric acid, pimelic acid, shikimic acid, citric acid, dL -isocitricacid and d-(-)-quinic acid were prepared by following concentration gradients of 1 ng/mL, 10 ng/mL, 100 ng/mL, 500 ng/mL, 1000 ng/mL, 5000 ng/mL, 10,000 ng/mL and 20,000 ng/mL, and calibration curves were constructed. According to the calibration curve, the concentration of organic acids in the durian sample were calculated. The chemical standard derivatization method was the same as the sample derivatization method. The software TraceFinder (5.1, San Jose, CA, USA, 2019) was used for data processing. Three parallel determinations were performed under the same conditions.