Innovative and Conventional Valorizations of Grape Seeds from Winery By-Products as Sustainable Source of Lipophilic Antioxidants

Abstract

The aim of this study was to valorize the oil recovery from red and white grape seeds (Vitis vinifera L.) that remains as by-product after the winemaking process. Oils were extracted by modern techniques, ultrasound assisted (UAE), microwave assisted (MAE) and supercritical fluid extraction (SFE), and compared to the Soxhlet extraction (SE). Firstly, SFE was optimized at different operating conditions: pressure (250-350 bar), temperature (40-60 °C), CO₂ flow rate (0.2, 0.3 and 0.4 kg h^-1), and particle size (315-800 µm and >800 µm). The highest extraction yields were achieved by SFE at the optimal conditions: 350 bar, 60 °C, 0.4 kg h^-1. Afterwards, SFE was compared to SE, UAE and MAE with respect to oil extraction yields, and analyzed for fatty acid composition and antioxidant capacity. Considering the general classification of fatty acids, it was found that samples had high content of polyunsaturated fatty acids, regardless of extraction technology. Tocopherol content was significantly influenced by all extraction methods, whereas UAE and MAE resulted in extracts richer with lipophilic antioxidants. In conclusion, modern extractions that are suited for industrial applications had better performance as compared to SE, as judging by the oil yield and quality.

Keywords: Soxhlet; antioxidant activity; grape seed oil fatty acid; microwave assisted; novel extraction; supercritical fluid; tocopherol; ultrasound assisted.

Figure 1

Influence of supercritical fluid extraction (SFE) extraction parameters on total extraction yield of grape seed oil: (a) Influence of pressure at fixed temperature (40 °C) and CO₂ flow rate (0.3 kg/h), (b) Influence of temperature at fixed pressure (350 bar) and CO₂ flow rate (0.3 kg/h), (c) Influence of CO₂ flow rate at fixed pressure (350 bar) and temperature (60 °C), and (d) Influence of particle size at 350 bar, 60 °C and 0.4 kg CO₂/h. * Different letters indicate significant difference (p ≤ 0.05) between total extraction yields of grape seed oil with respect to sources of variation.

Figure 2

Total extraction yield for grape seed oils recovered by conventional and modern extraction techniques. * Different lowercase letters indicate significant difference (p ≤ 0.05) between extraction techniques, while different uppercase letters indicate significant difference between red grape seeds (RGS) and white grape seeds (WGS).

Figure 3

Antioxidant capacity of grape seed oils recovered by conventional and modern extraction techniques (µM Trolox g⁻¹). * Different lowercase letters indicate significant difference (p ≤ 0.05) between extraction techniques, while different uppercase letters indicate significant difference between RGS and WGS.