# Changes in Biochemical and Volatile Flavor Compounds of Shine Muscat at Different Ripening Stages
## 1 Introduction  
The composition and distribution of volatile flavor compounds are important characteristics that contribute to the quality of grape berries and wine. The flavors of grape berries and wine can be characterized by complex families of volatile compounds, including terpen, esters, C6-aldehydes and alcohols, and methoxypyrazines, which contribute to fruity, floral, green leafy, and green capsicum flavors, respectively [1]. The development of flavor compounds in grape berries is likely to be affected by various factors, including grape cultivars, growing conditions, and climate [2]. The flavor intensity and aromatic profiles of grape berries are primarily affected by the concentrations and odor thresholds of volatile flavor compounds and their interactions with other compounds [1]. It has been reported that grape berries develop in two successive growth stages: berry formation and ripening [3]. The first stage is characterized by the formation of berry and seed embryos, followed by rapid cell division. During the second stages, berries become softer and start to change color. Furthermore, various secondary metabolites, including volatile aroma compounds, are developed in the berries during this stage [4]. Thus, the changes in biochemical and volatile flavor compounds of grape berries during the second stage are more closely related to consumer's sensory perception than those of the first growth stage. For this reason, the degree of ripening is a crucial factor influencing the development and distribution of volatile compounds, and is closely related to consumer's preferences for grape berries. In recent years, a new grape cultivar called Shine Muscat (_Vitis labruscana_ Baily \(\times\)_Vitis vinifera_ L.), developed in Japan in the late 1980s and commercialized in the early 2000s [5], has been gainingattention as a table grape in Korea. This cultivar has attracted consumer attention due to its unique taste, namely, a strong muscat flavor with excellent sweetness and not much sourness, despite its high price. The muscat flavor of Shine Muscat is the most important attribute in determining consumer preferences. Monoterpene compounds are associated with the distinctive taste and flavor of Muscat grape varieties [6]. In particular, terpenic alcohols, including linalool, geraniol, nerol, citronellol, and \(\alpha\)-terpineol, are known to be the major aroma compounds in Muscat grape varieties [1], and their chemical structures are represented in Figure 1.  
Thus, the development and alteration of flavor compounds in Muscat grape varieties during berry ripening has been widely investigated [1; 7]. [PERSON] et al. [6] investigated the alterations in volatile monoterpene compounds of Muscat of Alexandria during berry ripening and they found that only the concentration of free linalool increased with ripening in parallel to its glycoside, and [PERSON] et al. [8] compared the concentrations of monoterpene compounds among various Muscat grape varieties, such as Muscat of Alexandria, Muscat de Frontignan, Muscat Saint-Vallier, Italia, and Muscat Hamburg, and they found that linalool and geraniol were the most important aroma compounds in Muscat grape varieties. In addition, [PERSON] et al. [9] evaluated the alteration of flavor compounds in Muscat-based wines (Asti Spumante and Moscato d'Asti), and they showed the changes of linalool, \(\beta\)-damascenone, ethyl hexanoate, and ethyl octanoate levels in both two Muscat-based wines. However, to the best of our knowledge, the flavor compound profiles of Shine Muscat grapes during ripening have not yet been extensively investigated. Although several relevant studies have been conducted in China and Japan [10; 11; 12], no such studies have been performed in Korea. Increases in consumer demand for Shine Muscat grapes and higher prices have led many grape growers to harvest and market immature berries, thereby decreasing the quality of Shine Muscat grape and thus consumer demand.