## 1 Introduction
The first evaluation regards the pulp, which usually has a yellow/white color and can be crunchy, pasty or floury, based on the percentage of pectin and cellulose [15]. The crunchiness or meshowness of the apple is affected by the water content, too, which is generally around the 85%. By varying this percentage, greater or less juiciness results [6]. The flavor that distinguishes the various apples species depends on the quantity of organic acids and sugars present in the pulp [16]. All the qualitative, physical and organoleptic parameters characterizing the existing apple varieties are listed in Table 1.  
In addition to the apple fruit varieties listed in Table 1, some other types result from crosses between them [17]. Moreover, it should be considered that some small variations in each apple variety could occur, due to grafts and environmental conditions [16]. All the existing varieties of apple fruits show a characteristic profile of phytochemical components [18]. Like all fruits, apples have to meet commercial-quality parameters established by the European Commission Regulation (CE) N. 85/2004 15 January 2004. In detail, an apple fruit must be whole, healthy, clean, free of pathogens and free of flavors or odors other than usual, in order to be considered qualitatively relevant, from a commercial point of view. In general, the phytochemical profile of apple fruits strongly correlates with most of their peculiar characteristics, such as taste, flavor and color. As previously said, it is difficult to estimate the number of the existing apple varieties among the world, due to the continuous changes and hybridizations performed [6]. However, it is possible to determine the phytochemical profile of apples to provide the real quantities of all natural compounds [19]. At the same time, new bioactive molecules could be identified as markers of a specific apple variety. Thus, an investigation of the complete metabolic profile of these fruits is mandatory. In this review, a discussion on the main analytical methods, differing in their extraction and detection protocols, developed in the last ten years for the investigation of primary and secondary metabolites occurring in apple fruits is provided. Particular attention is given to the more recent and cutting-edge techniques, thus making the readers could easily choose the methods that best suit their needs. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Apple Variety** & **Color** & **Dimension** & **Pulp** & **Flavor** \\ \hline Renetta & Yellow, tending to the green & Medium & Soft and pasty & Acid, medium sweetened \\ \hline Golden Delicious & Gold yellow & Large & Crunchy and juicy & Very sweet \\ \hline Stark Delicious & Bright red & Large & Crunchy and juicy & Sweet, little acidic \\ \hline Gramny Smith & Green & Medium & Crunchy & Acid \\ \hline Fuji & Reddish with yellow-green streaks & Large & Crunchy and juicy & Sweet, little acidic \\ \hline Pink Lady & Reddish/red & Medium & Crunchy & Sweet \\ \hline Annurca & Bright red & Small & Crunchy & Acid \\ \hline Royal Gala & Red with streaks & Small & Crunchy and juicy & Very sweet \\ \hline Kanzi & Intense red or yellow & Medium & Hard and crunchy & Medium sweet and acid \\ \hline Braeburn & Brown red & Medium-large & Crunchy & Medium sweet/acid \\ \hline Morgenduft & Red with clear patches & Medium & Hard and juicy & Sweet and slightly acid \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Qualitative, physical and organoleptic parameters characterizing all the existing apple fruit varieties.