Optimization of oil yield and oil total phenolic content during grape seed cold screw pressing

• Grape seed oil expression on screw press enables high oil yield.
• Raw material is the major factor affecting oil expression.
• Oil polyphenols content is independent of seed polyphenols content.
• Playing on process parameter an increase in oil polyphenol content can be reached.

Grape seed oil being industrially obtained by solvent extraction, in this study we investigate oil extraction from grape seeds by cold screw pressing, as an alternative extraction process.Effect of raw material and process parameters were evaluated using a 12 experiments Taguchi experimental design. Variables were (1) type of grape seeds, (2) preheating temperature (90 and 120 °C), (3) screw rotation speed (40 and 70 rpm) and (4) die diameter (10 and 15 mm). The type of grape seed was the most influencing parameter on the studied responses. Screw rotation speed and die diameter only affected the oil yield. Maximum oil yield was observed for type 1 grape seeds (64.3%, o/o). Total oil polyphenol content was also maximal for type 1 seeds with up to 121 mg GAE/kg of oil. Maximum oil yield was 57.3% and 58.8% (o/o) for type 2 and type 3 grape seed respectively and total polyphenol oil content was below 90 mg GAE/kg for these two types of seeds. Additional experiments were carried out on type 1 seeds to enhance oil yield and oil polyphenol content. Maximal oil yield achieved was 73% (o/o) and total oil polyphenol content was increased up to 26% (153 mg/kg of oil) on the maximum yield obtained with Taguchi design.