A preliminary multistep combination of pulsed electric fields and supercritical fluid extraction to recover bioactive glycosylated and lipidic compounds from exhausted grape marc

This article reports the first multistep combination of pulsed electric field (PEF; 3 kV/cm, 100 kJ/kg, 2 Hz, 100 ms) and supercritical fluid extraction (SFE) with CO2 (10-20 MPa, 25 mL/min [10% EtOH], 50 degrees C, 60 min) for exhausted grape marc (EGM). This current protocol was mainly created to recover bioactive glycosylated and lipidic compounds. In this regard, total antioxidant capacity (TAC) was enhanced up to 68% after PEF treatment compared to conventional soaking. However, re-extracting PEF-treated EGM after the application of SFE (PEF + SFE) boosted the efficiency by up to 87%. Several polyphenols (kaempferol, luteolin, scutellarin, and resveratrol, among others), together with other glycosylated structures, were identified by liquid chromatography coupled with mass spectrometry analysis. The bioactive lipidic compounds extracted by SFE, along with the carbohydrate fraction (free sugars) favourably extracted by PEF pre-treatment (mainly glucose, but also fructose and sucrose), were concurrently detected by nuclear magnetic resonance. The remaining solid fraction after treatment was also characterised. Different microscopic morphology was observed by scanning electron microscopy (SEM) on untreated, PEF, and PEF + SC-CO2-treated EGM. Differential thermogravimetric (DTG) curves determined by thermogravimetric analysis (TGA) also suggested alternative and potential means for the valorisation of this matrix.

Automated summary

This article reports the first combination of pulsed electric field (PEF) and supercritical fluid extraction (SFE) for exhausted grape marc (EGM) to recover bioactive compounds. PEF treatment enhanced the total antioxidant capacity (TAC) of EGM by 68% compared to conventional soaking. Re-extracting PEF-treated EGM after SFE further increased the efficiency by up to 87%. Polyphenols and other glycosylated structures were identified, and bioactive lipidic compounds and carbohydrate fraction were concurrently detected. The remaining solid fraction was characterized, and alternative valorization methods were suggested.