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The dioxane lignin was isolated from extractives-and suberin-free cork (Quercus suber L.) by a modified acidolytic procedure and submitted to structural analysis by permanganate oxidation, analytical pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC-MS), liquid-and solid-state nuclear magnetic resonance (NMR) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The molecular weight (M w = 2500 Da) was assessed by size exclusion chromatography (SEC). The results obtained show that the cork lignin is of syringyl (S)/guaiacyl (G) type with a small proportion of p-hydroxyphenyl (H) units (S:G:H molar ratio of 23:72:5). Among a dozen detected lignin structures, those linked by ether bonds, such as β-O-4′ (38 mol %) and 4-O-5′ (5 mol %), were the most abundant. The frequency of occurrence of β-5′, β-β′, 5-5′, tetrahydrofuran type, and structures arising from the condensation with concomitant procyanidins was assessed. Ferulates were the only cinnamic structure detected in the cork dioxane lignin.

Reactive washing (RW) is a key process for disinfecting, purifying, and bleaching of cork stoppers to seal bottles with alcoholic beverages. Excessively severe treatment conditions deteriorate the surface properties of cork stoppers and must be strictly controlled. In this study, the conventional RW of natural cork stoppers was optimized employing a fractional factorial design. The RW variables (H 2 O 2 and NaOH concentrations, oxidation time, and washing water volume) were correlated with the final ISO brightness of the stoppers. A three-level and four-factor fractional factorial design within the response surface methodology approach allowed a quadratic model to predict the process response, where the H 2 O 2 concentration is the variable with the highest response (ISO brightness), followed by the NaOH concentration. The model obtained was validated, allowing the optimization of the process with savings of 37% in the concentration of H 2 O 2 and 33% in the concentration of NaOH and volume of washing water, without deteriorating the final appearance of the stoppers. In addition, the less severe treatment of stoppers under optimized conditions led to less degradation of their surface, thus favoring the receptivity to functional coatings.