## 2 Materials and Methods
### Study of the Use of Resins to Remove Oxidation Aldehydes
#### 2.3.4 Chemical Analysis  
Oenological conventional parameters of colour, total polyphenol index (TPI), pH, total acidity, free sulphur dioxide, total sulphur dioxide, total acetaldehyde and total Strecker aldehydes were determined at time zero and after the treatment with resins.  
Results were processed by means of analysis of variance (ANOVA), whereas mean values were compared by [PERSON]'s test (XLSTAT). The value of \(p\leq 0.05\) was considered statistically significant, and alphabetical letters were used along means in the tables.  
Conventional Oenological Parameters  
The total acidity was determined by acid-base volumetric titration measuring the end of the titration with a pH meter up to pH 7 according to the Organization of Vine and Wine (OIV) [29].  
The pH was determined by potentiometry according to OIV practices [30].  
For free and total sulphur dioxide determination, the aspiration/titration method recommended by the OIV was used [31].  
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Spectrophotometric Measurements  
For colour determination, absorbances at wavelengths 420, 520 and 620 nm of undiluted wine samples were measured using glass cells with optical paths of 1, 2 or 5 mm, taking the measurement which provided absorbance readings between 0.3 and 0.7 as recommended by the OIV [32]. TPI was determined as absorbance at 280 nm as described by [PERSON] et al. [33]. All the absorbance measurements were recorded using an UV\(-\)vis spectrophotometer UV-17000 Pharma Spec from Shimadzu (Kyoto, Japan).  
Total Acetaldehyde Determination  
Total acetaldehyde was determined by gas chromatography with flame ionization detection (GC-FID) by injection of 1 \(\upmu\)L of wine sample spiked with 2-butanol as internal standard. The methodology is based on breaking the adducts directly in the injector port. A GC 8000 series from Fisons Instrument (Ipswich, UK) with a DB-WAX (30 m \(\times\) 0.53 mm of i.d. \(\times\) 2 \(\upmu\)m) capillary column from J&W Scientific (Agilent Technologies, Santa Clara, CA, USA) were used. The injector was kept at 250 \({}^{\circ}\)C and the split ratio was 1:4. Hydrogen was used as carried gas and the pressure was kept at 27.5 kPa. The temperature program was 50 \({}^{\circ}\)C for 5 min and then raised to 220 \({}^{\circ}\)C in 10 min. The FID temperature was 250 \({}^{\circ}\)C. The calibration was obtained by the analysis of synthetic wines (5 g/L tartaric acid, 12% ethanol, 1.5% propane-1,2-diol, 10 g/L glycerin, pH 3.5) containing known amounts of acetaldehyde and plotting the corresponding peak areas (normalized by the internal standard) versus the mass of acetaldehyde. Other validation parameters are detailed elsewhere [24].  
Total Strecker Aldehydes Determination  
Total Strecker aldehydes content was determined as described by [PERSON] et al. [10]. In summary, vials were prepared inside an oxygen free chamber, pouring 10 mL of wine sample into a 20 mL vial. Then samples were spiked with methyl 2-methylbutyrate (187 \(\upmu\)g/L) as internal standard and 6 g/L of glyoxal. Vials were then closed and incubated at 50 \({}^{\circ}\)C for 6 h for ensuring that carbonyl-bisulphite complexes had been broken. Total isobutyraldehyde, 2-methylbutanal, 3-methylbutanal, methanol and phenylacetaldehyde were measured by headspace-solid phase microextraction followed by gas chromatography--mass spectrometry (HS-SPME-GC-MS) using a polydimethylsiloxane/divinylbenzene (PDMS/DVB) fibre from Supelco (Madrid, Spain).  
Data Analysis  
Results were analysed by analysis of variance (ANOVA), and for significant effects post-hoc [PERSON]'s test was calculated (XLSTAT). The value of \(p\leq\) 0.05 was considered statistically significant, and alphabetical letters were used along means in the tables to indicate significant differences.