# Volatile Compounds of Lemon and Grapefruit IntegroPectin
## 2 Results and Discussion  
A total of 15 volatile compounds were identified in the case of lemon IntegroPectin (Figure 1 and Table 1). Figure 1: GC chromatogram of the volatiles in lemon IntegroPectin. A highly bioactive molecule with antioxidant, anticancer (anti-proliferative and cytostatic), anticonvulsant, antiulcer, antihypertensive, anti-inflammatory, and analgesic (anti-nociceptive) properties [15], \(\alpha\)-terpineol is the most abundant component amid the volatiles found in lemon IntegroPectin. The second most abundant terpene is terpinen-4-ol (21.85%, entry 11 in Table 1), a potent bactericidal [16] and antifungal [17] agent capable of killing _Staphylococcus aureus_ strains and inhibiting azide-resistant human pathogenic _Candida_ species. As the main component of tea tree essential oil, terpinen-4-ol was found in a randomized trial to provide a safe and well-tolerated regimen for the eradication of methicillin-resistant _S. aureus_ carriage in hospitalized patients [18]. 2-methyl-1-butanol (entry 4 in Table 1) and 3-methyl-1-butanol (entry 5) are key components imparting fragrance to grapefruit juice [19] but have been so far unreported in the case of lemon essential oil or juice, thereby indicating the modification of certain volatile molecules during HC-based extraction (see below). Similarly, isoamyl acetate (entry 2 in Table 1) was previously found in orange essential oil [20]. In the case of grapefruit IntegroPectin, 11 volatile compounds were identified (Figure 2 and Table 2). Besides a relatively higher amount of limonene (11.8% vs. 3.39%), the main difference with lemon IntegroPectin is the presence of higher amount of linalool (12% vs. 4.95%) as well as of substantial amounts (16%) of linalool oxide (predominantly the _cis_ isomer, entry 7 in Table 2), which is absent in lemon IntegroPectin. Linalool oxide isomers are well known components of grapefruit essential oil [21]. Due to an ample and diversified spectrum of biological properties, linalool is one of the most widely studied odorant molecules [22]. Found in the essential oils (EOs) of over 200 plants including citrus, linalool exhibits antimicrobial activity against different microorganisms (_Staphylococcus aureus_, _Bacillus subtilis_, _Escherichia coli_, _Pasteurella multocida_), particularly against Gram-positive bacteria, showing activity levels comparable to those of Amoxicillin [23]. Though far less studied due to its relatively minor abundance in EOs, linalool oxide has been recently shown to have (in experiments with mice) even more powerful anticonvulsant and antinociceptive activities than linalool [24]. The low amount of limonene, by far the most abundant terpene in the peel of both lemon [25] and grapefruit [26], points to the formation of \(\alpha\)-terpineol and terpinen-4-ol from their precursors \(d\)-limonene and linalool in the cavitation microbubbles, in accordance with what happens in orange [27] and mandarin [28] juices (rich in citric acid) after storage. Following fast protonation likely taking place in the cavitation microbubbles (Figure 3), both linalool and limonene are readily converted into \(\alpha\)-terpineol and terpinen-4-ol, with linalool being even more reactive than limonene [27]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Entry** & **Compound** & **RT (min)** & **\%Area** \\ \hline
1 & 1-Butanol, 3-methyl-acetate (isoamyl acetate) & 8.26 & 0.67 \\
2 & Limonene & 8.31 & 11.77 \\
3 & 2-Methyl-1-butanol & 8.54 & 12.91 \\
4 & 3-Methyl-1-butanol & 8.6 & 15.17 \\
5 & 1-Hexanol & 9.94 & 3.24 \\
6 & 3-Hexen-1-ol & 10.33 & 1.28 \\
7 & _cis_-Linalool oxide & 11.26 & 14.4 \\
8 & _trans_-Linalool oxide & 11.66 & 1.76 \\
9 & \(\alpha\)-Linalool & 11.71 & 12.01 \\
10 & Terpinen-4-ol & 12.88 & 9.37 \\
11 & \(\alpha\)-Terpineol & 13.73 & 17.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Volatile organic compounds in grapefruit IntegroPectin. Figure 3: Molecular pathway from linalool and limonene to \(\alpha\)-terpineol in the hydrodynamic cavitation microbubbles (adapted from Ref. [27]).