## 4 Discussion
This method more accurately reflects the actual preferences of consumers; on the other hand, it is also susceptible to the subjective factors of evaluators, resulting in deviation in the results [30]. Thus, assistance from instrument detection, which is more accurate, objective, and reproducible, is required for the comprehensive evaluation of flavor quality [31]. In this study, the flavor quality of 30 cucumber cultivars was evaluated, and selected 3 cultivars with distinct flavors as representatives. The evaluation involved sensory evaluation in combination with TSS detection because previous studies have shown a positive correlation between the TSS content and cucumber flavor [32]. Moreover, a total of 163 VOCs were detected in the three cucumber cultivars, which consisted of 13 types of compounds, namely, amines, alcohols, aromatic hydrocarbons, phenols, sulfur-containing compounds, halogenated hydrocarbons, aldehydes, acids, terpenoids, hydrocarbons, ketones, esters, and heterocyclic compounds. Among these VOCs, the contents of (_E_,_Z_)-2,_\(\theta\)_-nonadienal and (_E_)-2-nonenal, which are considered to be the main flavor substances of cucumber [33; 34; 35]; furans are oxygen-containing heterocyclic compounds with a fruity and fresh fragrance [36]; esters are the main type of aromatic compounds and determine the unique fragrance of many fruits and vegetables [37; 38]; terpenoids are the main source of flower fragrance [39], with a pleasant aroma and improve the taste of fruit; acids can regulate fruit acidity, and fatty acids-derived VOCs make significant contributions to tomato fruit flavor and human preferences [40]. Here, in this study, the contents of these important VOCs were found to be higher in YX than in the other two cultivars. This leads us to propose that different varieties of cucumber contain different types and amounts of VOCs, resulting in their taste differences. However, it should be pointed out that the cucumber fruit samples were stored at \(-80\)\({}^{\circ}\)C for 6 days before the HS-SPME/GC-MS analysis, which might have affected the volatile composition. In addition, during SPME sampling, the headspace bottles were placed at 100 \({}^{\circ}\)C for 5 min, which may have changed the chemical structures of cucumber fruits, resulting in altered VOCs. Despite GC is used to separate the volatile and thermally stable substitutes in a sample, further studies with other alternative testing methods are needed to eliminate the potential side effects of thermal processing. It has been reported that there are similar volatile components present in Northern Chinese-type cucumber M13, Southern Chinese-type cucumber Quanzao, and European greenhouse cucumber SW, and the contents of furan compounds in VOCs detected in M13 and Quanzao are higher, while those in SW are relatively lower [41]. Moreover, the Northern Chinese-type cucumber Crete contains higher octadecatrienal and pentadecanol contents, while the European greenhouse cucumber Knossos45 contains higher contents of (_E_,_Z_)-2,6-nonadienal and (_E_)-2-nonenal, which gives the latter a more pleasant flavor [42]. In this study, the main flavor compounds, including (_E_,_Z_)-2,6-nonadienal, (_E_)-2-nonenal, and 2,4-heptadienal, were significantly higher in YX than in KX and GX, which was consistent with previous research conclusions. However, the contents of furans such as 2-n-butyl furan and 2,2\({}^{\prime}\),5,5\({}^{\prime}\)-tetrahydro-2,2\({}^{\prime}\)-bifuran were higher in YX than in the two other cultivars, which may be related to the detection methods and varieties. In the analysis and comparison of differences between the three groups, only three VOCs were detected in all, namely, alpha-cadinol, _N_-(2,3,_A_-trifluorobenzoyl)-l-alanine-methyl ester, and [35-(3-alpha,5-alpha,8-alpha)]-5-azulenemethanol,1,2,3,4,5,6,7,8-octahydro-alpha,alpha,3,8-tetramethyl-acetate. These VOCs have not previously been reported, and how they interact and their metabolic pathways require further study.