Production, identification, and quantification of antioxidants from torrefaction and pyrolysis of grape pomace

• Published in: Fuel processing technology 2021-01, Vol.211, p.106602, Article 106602
• Main Authors: del Pozo, Cristina, Bartrolí, Jordi, Alier, Santi, Puy, Neus, Fàbregas, Esteve
• Format: Article
• Language: English
• Subjects: Acetic acid; Antioxidants; Bio-oil; Composition; Devolatilization; Drying; Grape pomace; Grapes; Phenolic compounds; Pyrolysis; Sugar; Torrefaction
• ISSN: 0378-3820; 1873-7188
• DOI: 10.1016/j.fuproc.2020.106602

Wine production generates huge amounts of residues, with grape pomace (GP) being the main solid waste. This work attempted to determine whether the use of thermochemical treatments (pyrolysis (400 °C) and torrefaction (225 °C)) are suitable processes to transform GP to a value-added compounds source, paying special attention to phenolics. GP management through thermochemical treatments could then provide ecological and economic benefits. Composition of the liquid fractions was determined by GC–MS. Phenolic quantification was performed using Folin-Ciocalteu (FC) and DPPH assay. Firstly, the suitability of these methods was discussed: DPPH assay was used to quantify phenolics in all the samples; however, in FC method, reducing sugars could interfere in the measurement. The results showed that phenolics were mainly concentrated in the non-aqueous phase of bio-oil (pyrolysis process). It was also observed that these compounds not only came from the GP composition, but from lignin devolatilization during the thermochemical process. Apart from phenolics, bio-oil was also composed of other products, such as acetic acid or levoglucosan. Therefore, this study showed that intermediate pyrolysis is a suitable treatment to add value to GP within a biorefinery concept, turning the winemaking waste into a potential source of antioxidants, together with other value-added compounds. [Display omitted] •Intermediate pyrolysis (400 °C) is a suitable method to obtain phenolics from GP.•Non-aqueous phase of bio-oil was the richest fraction in phenolic compounds.•DPPH and Folin-Ciocalteu methods were used to quantify antioxidants from GP bio-oil.•Antioxidant from GP torrefaction liquid should be quantified through DPPH assay.•Revalorisation of GP allows coming closer towards circular economy in wine industry.