## 3 Results and Discussion
### Principal Component Analysis (PCA) of the Volatile Organic Compounds (VOCs)  
To explore the relationship between the volatile organic compounds profiles of samples from the various durian genotypes, principal component analysis (PCA) was performed to identify the grouping of the genotypes based on the correlation matrix. The finding revealed the first two principal components (PCs), PC1 (33.32%) and PC2 (29.20%), together accounted for 62.93% of the data variance. The result of PCA reveals that the seven genotypes were classified into five groups which can be seen in Figure 3. From the case projection on the factor plane (PC1 versus PC2), the PC1 axis distinguished _D. dulcis_ that constituted a cluster on the positive side, while _D. gravelens_ (yellow-fleshed), _D. gravelens_ (orange\(-\)fleshed), _D. gravelens_ (red-fleshed), _D. kutejensis, D. axleynus_, and _D. zibethinus_ (Terung iban) spread at the negative side of PC1 axis.  
Group 1 consists of _D. dulcis_ alone on the positive side of the PC1 axis, as it has a high amount of aldehyde, ketone, and ether compounds. The ester compounds such as (E)-2-butenoic acid, ethyl ester; 2-methyl-2-butenoic acid, ethyl ester; 2-hydroxy-2-methyl-butanoic acid, methyl ester; [R-(R*, R*)]-2,3-bis(acetyloxy), butanediotic acid; octanoic acid, ethyl ester, and methoxyacetic acid, 2-pentadecyl ester compounds were only present in _D. dulcis_. The presence of (E)-2-butenoic acid, ethyl ester, and octanoic acid, ethyl ester, which describe as having a pungent and sulfury odor, respectively, could explained the most ill-smelling of all _Durio_ species that can be smelled for miles as stated by [PERSON] [8]. Moreover, _D. dulcis_ also recorded the highest amount of 2-Furanmenthanol compound among the genotypes, where the compound gave a burnt odor. The two genotypes of _D. gravelens_, yellow-fleshed and orange-fleshed, were grouped on the positive side of PC2 (Group 2). This group was characterized as both genotypes having a similar presence of compounds such as alcohol, ester, and a small amount of ether, ketone, and sulfur but amine is not present in the yellow-fleshed genotype. Butanoic acid, heptyl ester, and butanoic acid, butyl ester had the highest relative amount in yellow- and orange-fleshed genotypes, which give a fruity odor [27; 28].  
_Durio graveolens_ (red-fleshed), _D. kutejensis_, _D. oxleyanus_, and _D. zibethinus_ located in negative PC2, were grouped into three groups. _Durio graveolens_ (red\(-\)fleshed) in Group 3 was characterized by a mixture of mild aroma from alcohol, ester, and sulfur compounds and high relative amount of ketone and ether. The presence of ketone, ester, and ether compounds gives the durian a floral, fruity, and sweet odor. _Durio kutejensis_ and _D. oxleyanus_ grouped in Group 4 as they both perceived almost the same compounds. Alpha.\(-\)Aminooxy-propionic acid and ethyl ester compounds were only present in both genotypes of this group. However, _D. oxleyanus_ has a high relative amount of nitrogen-containing compounds, such as tetramethylhydrazine and 2\(-\)ethyl\(-\)5-methyl-pyrazine,  
Figure 3: Principal Component Analysis (PCA) biplot of wild edible durians in Sarawak. The code of the volatile organic compounds was referred to in the list of the volatile organic compounds in Table 4.  
which might be responsible for the ammonia-like and nutty odor, respectively. This supports the report by [PERSON] [8] as they stated that _D. axleganus_ was slightly fragrant but had a very tasty aril with a strong odor. _Durio zibethinus_ alone, in Group 5, was characterized by a higher amount of sulfur-containing compound than other genotypes. Ethanol, diethyl disulfide, disulfide ethyl 1-methylethyl, trisulfide diethyl, and 3,5-dimethyl-1,2,4-Trithiolane were reported to be responsible for overpowering and roasty odor [28]. Thiol and sulfur were generally the most odorous aroma compounds and were found to be relatively high in all durian clones [19].