## 3 Results and Discussion
Differences between Solid Waste Hydroalcoholic Extracts (TWE and FEW) and Distillation Wastewaters (LEACH) in the Relative Composition of Single Phenolic and Flavonoid Compounds  
The analysis of the HPLC profiles for phenolic and flavonoid compounds revealed clear differences in the number and relative abundance of single compounds depending on the type of extract considered (Figure 3A-C). Overall number of chromatographed compounds ranged between 29 and 30 (Table 3). At the qualitative level, distillation wastewaters were characterized by the absence of p-coumaric acid and two non-polar unidentified flavonoids, likely aglycones. In turn, TWE samples were apparently lacking syringe acid, rutin and an unidentified polar flavonoid. These were the three most abundant compounds in LEACH samples, suggesting that steam distillation was a relatively efficient extraction method for some abundant compounds in the selected lavender cultivar. Syringic acid, rutin and the abovementioned flavonoid were present instead in the FEW samples, likely due to a concentration effect resulting from discarding the stem and the few leaves usually present in floral spikes used for essential oil distillation. The presence of flavonoid glycosides is very variable within the subgenus _Lavandula_, resulting in flavonoid profiles that may differ between groups of species [46]. There is little information of flavonoid variation at the cultivar level, although our results suggest that PUAE of distillation by-products may also contribute to lavender characterization at this level. The most abundant compound in TWE samples was the phenol gentisic acid (2,5-dihydroxybenzoic acid), accounting for more than 40% of the polyphenic fraction obtained by PUAE (Table 3). Figure 3: Chromatographic profiles of distillation wastewaters and hydroalcoholic extracts of distilled straws obtained after essential oil distillation from flowers of _Lavandula angustifolia_ cultivar Rosa. (**A**): distillation wastewater (LEACH); (**B**): PUAE of dry distillation straws (TWE) in 70:30 ethanol:water; (C): PUAE of dry petals from distillation straws (FWE) in 70:30 ethanol:water. Chromatograms were obtained at 280 nm wavelength after RP-HPLC. Note that retention times may vary for the same compounds depending on the specific laboratory conditions during the analysis. Numbers within square brackets indicate unidentified compounds. Peak numbers correspond to those reported in Table 3. The studied compounds differed in molecular weight and structure and not all of them showed maximum absorbance at 280 nm wavelength; therefore, observed peak areas and/or peak heights do not necessarily match calculated concentrations. This is indicative of the fact that polar phenolic compounds were more abundant in TWE than in FWEs, likely due to the relatively higher concentrations of phenolic compounds (about four times higher in the case of gentisic acid) in leaves and/or stem tissues. Other phenolic compounds, such as caffe, chlorogenic and \(p\)-coumaric acids were also present in the studied extracts, although their relative abundance significantly depended on the type of extract (Table 3). In general, as in the case of gentisic acid, the proportion of these compounds was higher in TWE than in the other two extracts. Regarding the identity of the chromatographed phenolics, the occurrence of caffe and p-coumaric acids was already reported in lavender distilled straws [1] as typical phenolic constituents of this kind of distillation by-product. Besides simple phenols, [PERSON] et al. [45] showed that lavender distilled straws are characterized by the presence of numerous glycosylated forms, which renders unlikely their identification using common external standards, as we tried to do in this study. In addition, distilled straws are a source  
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**No.