## 3 Results and Discussion
### Optimisation of Volatiles Extraction from Pineapple By-Products by HS-SPME
#### 3.2.3 Determination of Optimal Conditions
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & & & **Area (\%)** \\ \cline{2-5}
**Compound** & **Retention Time** & **Similarity** & **Pineapple** & **Pineapple** \\  & **(Min)** & **(\%)** & **Core** & **Peel** \\ \hline Ethyl acetate & 5.65 & 91 & 7.1 & 40.6 \\ Acetic acid & 7.60 & 91 & 3.9 & 2.1 \\
1-Butanol, 3-methyl & 10.44 & 91 & 12.8 & 2.7 \\ Butanoic acid, 2-methyl, methyl ester & 10.99 & 78 & 3.9 & Nd \\ Silanediol, dimethyl & 11.36 & 91 & 9.6 & 9.3 \\ Octane, 4-methyl & 13.21 & 95 & 0.2 & Nd \\ Isopentyl acetate & 13.60 & 96 & 8.3 & 4.7 \\ Ethlybenzene & 14.00 & 91 & 1.1 & Nd \\ p-xylene & 14.30 & 97 & 4.8 & Nd \\
1-Butanol, 3-methyl, acetate & 14.68 & 90 & 5.1 & 7.8 \\
1-butanol, 2-methyl acetate & 14.78 & 91 & Nd & 1.6 \\ Hexanoic acid, methyl ester & 16.35 & 90 & Nd & 0.9 \\ Hexanoic acid, ethyl ester & 18.89 & 98 & 6.6 & Nd \\ D-limonene & 19.58 & 98 & 0.9 & 9.6 \\
1-octanol & 22.03 & 91 & Nd & 1.1 \\ Heptonacio acid, ethyl ester & 22.16 & 83 & 0.5 & Nd \\
3-(Methylthio)propyl acetate & 23.92 & 89 & Nd & 1.6 \\ Phenylethyl alcohol & 24.41 & 94 & 4.9 & Nd \\ Octanoic acid, ethyl ester & 25.24 & 87 & 14.1 & Nd \\
2-Chloro-4-(4-methoxyphenyl)-6-(4-nitrophenyl)-6-(4-nitrophenyl) & 28.01 & 91 & Nd & 3.5 \\ pyrimidine & & & & \\ Nonanoic acid, ethyl ester & 28.12 & 95 & 1.7 & Nd \\ alpha cubebene & 28.51 & 90 & Nd & 2.8 \\ Decanoic acid, methyl & 28.96 & 98 & 1.7 & Nd \\ alfa copaene & 30.42 & 99 & 5.6 & 2.3 \\ n-Decanoic acid & 31.49 & 98 & 2.6 & Nd \\ alfa muurolene & 33.67 & 99 & 1.7 & 0.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Volatile compounds identification. retention times, percentage of similarity (%) and % area (vs. total area) obtained by HS-SPME–GC–MS in core and peel pineapple wastes. Nd: not detected. acetate are well known for their fruity notes and their low odor thresholds in water [42]. In contrast, volatiles other than esters were only present in small amounts in the pineapple juices [43]. Furthermore, the sweet odor of pineapples is attributed to some alcohols such as phenylethyl alcohol and 3-methyl-1-butanol and the group of ethyl esters [41]. In the case of the core, the volatiles profile is different as it is shown in Table 5, but the ethyl acetate is also an important volatile. In addition, octanoic acid ethyl ester, 3-methyl-1-butanol, silanediol dimethyl and octane were also important in core samples. It is important to highlight the high contribution of the octanoic acid ethyl ester to the volatile profile of core samples which is related to oily, musty, and rancid flavor but, at low concentrations, it has a nice fruity aroma [31]. Quantification of Ethyl Acetate and Isopentyl Acetate Present in Pineapple By-Products by Using HS-SPME-GC-MS  
Since the compounds ethyl acetate and isopentyl acetate, among others, are considered key contributors to the pineapple aroma, their quantification using HS-SPME has been carried out in core and peel pineapple samples [6]. The obtained results are shown in Table 6.  
In general, peel samples showed higher content in ethyl acetate whereas core samples presented higher contents in isopentyl acetate in comparison with peel pineapple samples. In addition, significant differences are observed among all samples related to the content of ethyl acetate, indicating huge variability that can be related to differences in chemical composition, environmental growth conditions, pineapple cultivar, and maturity stage, among others. It has been mentioned previously that the content of ethyl acetate in pineapple samples is the result of the reaction of acetyl CoA with higher alcohols such as isoamyl alcohol that are formed from the degradation of amino acids or carbohydrates [41]. Thus, the composition of the pineapple by-product is directly related to the final content of ethyl acetate quantified. In this sense, the peel is characterized by its high content of cellulose, hemicellulose, lignin, waxes, pectin, and ash.