Sustainable extraction and valorization of grape pomace

RENATA BENCE; NATIVIDAD HERRERA CANO; JORGE URANGA; JOAQUÍN ARATA BADANO; DANIEL A. WUNDERLIN

Congreso; 15th Green Chemistry Postgraduate Summer School; 2023

Green Sciences for Sustainable Development Foundation

After winemaking, red grape pomace (GP) retains significant amounts of anthocyanins (ACNs), phenolic compounds known for their antioxidant activity and their color properties.Due to the prevalent use of synthetic food additives, such as antioxidants and colorants, GP is a promising source of alternative natural additives. Nevertheless, ACNs often exhibit instability during food processing and their desirable properties are influenced by their environment.Pyranoanthocyanins (PACNs) are derivatives of ACNs with enhanced color stability against pH changes, heat, and bleaching. They result from the cycloaddition reaction between ACNs and carbonyl compounds or vinylphenols, with the latter being more reactive. Despite PACNs are naturally found in aged wines, they exist in relatively small quantities and their formation is too slow to hold significant synthetic value in industry. Therefore, the optimization of their production becomes an attractive prospect.In this project, the pH differential method was used to evaluate the ACNs recovery from GP employing conventional solvents (50-70% aqueous ethanol) and NADES (Natural Deep Eutectic Solvent). Interestingly, a novel GdnHCl/1,3-PdiOH NADES (guanidineHCl/1,3-propanediol 1:3) extracted a comparable amount of that achieved by conventional solvents. To further compare the obtained extracts, their radical scavenging capacity was tested using ABTS and DPPH assays. No significant difference was observed between 50% acidified ethanol and NADES extract. Furthermore, the ABTS assay conducted in acidified medium showed approximately 2.5 times higher activity for both extracts than without, consistent with the prevalence of ACNs in their protonated form at pH < 3 (flavylium cation).Biotransformation of caffeic acid into 4-vinylcatechol (4-VC) was successfully achieved (98.4%) by incubation with Lactobacillus plantarum. Subsequently, 4-VC was incubated with a semi-purified GP extract (SPEGP) to enable the formation of PACNs.Visible spectra of the SPEGP extract before and after being incubated with 4-VC suggested the formation of PACNs. A λmax of 504 nm was consistently observed at three different pH values for the derivative extract, thus, its color remained unaffected by environmental pH values from 1 to 7.4.These results contribute to the valorization of grape pomace, a significant byproduct of the wine industry.