# Changes in Biochemical and Volatile Flavor Compounds of Shine Muscat at Different Ripening Stages
## 3 Results and Discussion
### Free Volatile Aroma Compounds
The presence of hortienol in the RS3 group may be derived from the thermal degradation of dienediol-1 during analysis [6]. The total concentration of monoterpene compounds was 136.9, 123.0, and 260.5 \(\mu\)g/kg in the RS1, RS2, and RS3 groups, respectively (Table 2)  
As mentioned in the introduction, the major volatile compounds composing the muscat flavor arelinal, geraniol, nerol, citronellol, and \(\alpha\)-terpineol. Our volatile aroma profile result also indicated that the linalool was the most abundant volatile compound, possibly having a strong influence on the muscat flavor of Shine Muscat grape. Furthermore, [PERSON] et al. [30] reported that cis-rose oxide, linalool, citral, and geraniol were the only volatile monoterpene compounds present above their odor activity value (OAV) in the Muscat Hamburg grape berries during the period of ripening. Thus, regarding the relative concentrations of those monoterpene compounds detected in Shine Muscat berries, the change in the linalool concentration could be a good indicator for determining the ripening degree and timing of harvests of Shine Muscat grape. Figure 5: Total ion chromatograms of Shine Muscat grape berry extracts at different ripening stages: RS1, ripening stage 1; RS2, ripening stage 2; and RS3, ripening stage 3. The increasing numbers behind the abbreviation RS indicate the degree of ripening. (1) 3-Methyl butanal, (2) Pentanal, (3) Sabinene, (4) Hexanal, (5) \(\alpha\)-Phellandrene, (6) \(\alpha\)-Terpinene, (7) Limonene, (8) \(\beta\)-Myrcene, (9) \(\gamma\)-Terpinene, (10) 3-Methyl-1-butanol, (11) \(\beta\)-Ocimene, (12) 1-Hexanol, (13) Rose oxide, (14) Ethyl octanoate, (15) Linalool oxide, (16) 1-Octen-3-ol, (17) 2-Ethyl-1-hexanol, (18) Benzaldehyde, (19) Linalool, (20) Linalyl acetate, (21) Terpinen-4-ol, (22) Hotrienol, (23) Phenyl acetaldehyde, (24) \(\alpha\)-Terpineol, (25) \(\beta\)-Citronellol, (26) Damascenone, (27) Geraniol, (28) Nerol, (29) 1-Dodecanol, and (30) 2-Methyl-\(\beta\)-ionone. Peaks without a number correspond to the contaminants from the column and septa bleedings. Nevertheless, using the linalool concentration as a quality index for Shine Muscat grape is challenging because it requires a special equipment, i.e., gas chromatograph to determine the concentration of linalool in the grape berries. Thus, in the economic aspect, an easier way to evaluate the quality of Shine Muscat grape, in particular flavor acceptability, is necessary. The determination of sugar content and acidity of grape berries is much easier than that of volatile aroma compounds profile. For this reason, in this study, the correlations of the \({}^{\circ}\)Brix/acid ratio with total monoterpene and linalool content were determined. The highest correlation was observed between the linalool content and \({}^{\circ}\)Brix/acid ratio (\(r\) = 0.9981), followed by the monoterpene content and \({}^{\circ}\)Brix/acid ratio (\(r\) = 0.9933) (Figure 6). The linalool and monoterpene content and \({}^{\circ}\)Brix/acid ratio were found to increase suddenly in the RS1 group (Figure 6). The balance of sugar and acidity partially corresponded to the development of flavor compounds in table grapes [31]. Further study on the investigation of the relationship between linalool content and \({}^{\circ}\)Brix/acid ratio accompanied with a sensory evaluation is  
Figure 6: Dual axes bar and scatter overlay plots for (**a**) the monoterpenes content and \({}^{\circ}\)Brix/acid ratio and (**b**) the linalool content and \({}^{\circ}\)Brix/acid ratio of Shine Muscat grape berry extracts at different ripening stages: RS1, ripening stage 1; RS2, ripening stage 2; and RS3, ripening stage 3; TTC, total monoterpenes content. The increasing numbers behind the abbreviation RS indicate the degree of ripening. All data represent mean \(\pm\) SD. necessary to provide more scientific and reliable evidence on their relationships to evaluate the quality of Shine Muscat grape.