# Profiling Taste and Aroma Compound Metabolism during Apricot Fruit Development and Ripening
## 1 Introduction  
Apricot (_Prunus armeniaca_ L.) is an important Rosaceae family fruit crop, and its fruits contain many nutrients and phytochemicals that contribute to a healthy diet. Generally, apricots are appreciated by consumers for their unique flavor. In fact, flavor is not only a fruit quality factor that determines consumer preference, but also serves as a crucial clue to signal nutrient makeup to humans [1]. Fruit flavor is derived from a combination of taste and aroma [2, 3]. The taste of apricot primarily depends on sugars and organic acids, whereas the aroma depends on a large number of volatile organic compounds (VOCs).  
Flavor compound accumulation during fruit development has been widely studied in different species. The composition and content of sugars, organic acids and aroma volatiles usually changes with fruit development. Soluble sugars reach the peak at maturation or ripening [4]. Organic acids usually accumulate at the early stages of fruit development and are used as respiratory substrates during fruit ripening, and subsequently to their lowest levels in ripe fruit [5, 6]. For aroma compounds, the fruityodor compounds such as esters will increase significantly during the late fruit development, while the green odor such as hexenal rapidly decrease. In most fruit, glucose and fructose form the major portion of soluble sugars, whereas in peach, litchi and mandarin, sucrose is the predominant sugar. Fructose is by far the major sugar in apple. For organic acids, malic acid and citric acid predominate quantitatively in most fruits. The final organic acid concentration in ripe fruit is determined by the balance of organic acid biosynthesis, degradation and vacuolar storage.  
However, flavor compounds accumulation patterns and concentrations differ between species even cultivars. To date, the effect of development and ripening on flavor compound accumulation has been extensively investigated in tomato [7], peach [8,9] plum [10], strawberry [11], goijberry [12], sweet orange [13], melon [14], pineapple [15] and grape [16]. So far, the current studies on fruit flavor have focused on specific flavor compounds, one developmental stage, individual enzymes, or a single variety. Only a few detailed studies addressing sugars, organic acids and aromas as a whole and as a dynamic system are available in the literature. Up to now, chemical changes [17] and aroma-related genes during ripening of apricot fruit [18], as well as a rapid method of determination of sugars and organic acids [19] have been mentioned, however, the flavor profile of apricot is not fully clear. The knowledge about how flavor compounds shape underlying development remains to be unraveled. As the indispensable information for improvement strategies of flavor quality, the main flavor compounds in apricot fruit are still not yet identified.  
Thus, in the study, we intended to firstly integrate sugars, organic acids and aroma volatile information and to provide a unique, extensive vision of developmental dynamics of flavor compound metabolism in apricot. To this end, a large fraction of the metabolites and enzymes involved in metabolism of these flavor compounds were assayed within five genotypes at different times of fruit development to delineate the complex process of flavor shaping and to reveal the mechanism underlying this process. Additionally, the key taste and aroma components in fruit were identified. These results will provide a powerful resource for uncovering key components in the regulation of metabolic networks and give the important information for consumer-oriented breeding.