## 3 Results  
AA concentrations in the six groups of mineral water samples spanned more than two orders of magnitude (Figure 2), ranging from 0.41 to 76.2 \(\mu\)g/L. The highest concentrations (mean \(\pm\) standard deviation) were detected in sparkling carbonated water of 0.5 L (35.1 \(\pm\) 16.8 \(\mu\)g/L), followed by sparkling carbonated water of 1.5 L (27.8 \(\pm\) 15.8 \(\mu\)g/L) and natural effervescent water of 1.5 L (6.05 \(\pm\) 9.90 \(\mu\)g/L); the concentrations were lowest in natural effervescent water of 0.5 L, natural still water of 1.5 L and natural still water of 0.5 L, corresponding to 1.87 \(\pm\) 1.79, 1.51 \(\pm\) 1.77 \(\mu\)g/L and 0.915 \(\pm\) 0.388 \(\mu\)g/L, respectively (Figure 2). ANOVA and the multiple comparison post-hoc test showed significant differences in the AA concentration between the sparkling water (0.5 and 1 L) and the other samples. Characteristics of the samples analyzed, grouped according to volume (0.5 or 1.5 L) and the CO\({}_{2}\) levels in sparkling, natural effervescent and still water are shown in Table 1. The correlation matrix between AA concentrations, volume and sample weight, CO\({}_{2}\) concentration, fixed residues, shelf life and the distance from the point of production showed that AA significantly positively correlated with the CO\({}_{2}\) concentration and the distance from the production site (Table 2). \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample 1**} & \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Weight (g)**} & \multirow{2}{*}{**CO\({}_{2}\) (g/L)**} & \multicolumn{2}{c}{**Fixed Residue**} & \multicolumn{2}{c}{**Shelf Life**} & \multicolumn{2}{c}{**Distance from**} \\  & & & & & & **(mg/L)** & & **(Days)** & & **Production** \\ \hline  & & **Mean** & **SD** & **Mean** & **SD** & **Mean** & **SD** & **Mean** & **SD** & **Mean** & **SD** \\ \hline NW1.5 & 25 & 26.3 & 3.4 & 0.078 & 0.390 & 192 & 148 & 37.1 & 63.6 & 91.5 & 132 \\ NW0.5 & 17 & 13.0 & 1.83 & 0 & 0 & 193 & 133 & 34.0 & 22.3 & 122 & 142 \\ EW1.5 & 4 & 34.1 & 3.13 & 2.11 & 0.643 & 1060 & 308 & 38.3 & 5.50 & 208 & 110 \\ EW0.5 & 4 & 17.7 & 2.87 & 2.11 & 0.643 & 1060 & 308 & 41.2 & 11.3 & 340 & 322 \\ SW1.5 & 22 & 29.4 & 2.96 & 5.86 & 0.895 & 182 & 124 & 30.7 & 20.6 & 87 & 110 \\ SW0.5 & 16 & 14.7 & 1.73 & 6.20 & 0.508 & 194 & 137 & 30.3 & 16.5 & 120 & 128 \\ \hline \hline \end{tabular}  
* NW1.5 = natural still water 1.5L; NW0.5 = natural still water 0.5 L; EW1.5 = natural effervescent water 1.5 L; EW0.5 = natural effervescent water 0.5 L; SW1.5 = carbonated sparkling water 0.5 L.  
\end{table} 
Table 1: Characteristics expressed as mean and standard deviation (SD), of the samples analyzed. Figure 2: Acetaldehyde (AA) concentrations (mean \(\pm\) standard deviation) for each group of water. (* Significantly different from the other groups ([PERSON] one-way analysis of variance and [PERSON]’s multiple comparison post-hoc test, \(P<0.05\)). NW1.5 = natural still water 1.5 L, n = 25; NW0.5 = natural still water 0.5 L, n = 17; EW1.5 = natural effervescent water 1.5 L, n = 4; EW 0.5 = natural effervescent water 0.5 L, n = 4; SW1.5 = sparkling carbonated water 1.5 L, n = 22; SW0.5 = sparkling carbonated water 0.5 L, n = 16). Figure 3 shows the results of the PLS analysis. The PLS score plot (Figure 3a) shows the samples separated mainly according to the CO\({}_{2}\) concentration along the first component. In particular, carbonated sparkling waters samples are positioned on the right side of the plot, the natural still waters samples on the left side, and the natural effervescent waters in an intermediate position. The PLS regression coefficients (Figure 3b), showing the weight of the predictor variables on AA concentration, show that CO\({}_{2}\), and, to a lesser extent, the distance from production to the point of sale, are the main variables directly influencing the AA concentration. The fixed residue, instead, was negatively related to the AA concentration, possibly because these waters generally have higher pH due to the bicarbonates.