Effect of screw pressing temperature on yield, bioactive compounds, and quality of hemp (Cannabis sativa L.) seed oil.

Background: Screw press extraction is widely used due to its simplicity and efficiency, but the impact of extraction temperature on oil characteristics requires further study. Existing studies highlight that high temperatures can improve yield but compromise oil quality. This study aims to assess the effects of different screw press extraction temperatures on hemp oil yield, composition and quality.

Methods: The study was conducted to examine the influence of screw press extraction temperatures (30, 60, 80, 100, 120 and 140 °C) on hemp oil yield and quality. Extracted oils were analyzed according to key parameters, including oil yield, total phenolic content, tocopherols, oxidation stability index (OSI), pigments, quality indices (free fatty acids (FFA), peroxide value (PV), conjugated diene (K232) and conjugated triene (K270)), fatty acid profiles and color parameters (L*, a*, b*, C*_ab and h_ab). The differences between oils extracted by pressing at different temperatures were evaluated via one-way multivariate analysis of variance.

Results: The temperature played a key role in yield, reaching a maximum of 21.82%, representing an oil recovery of 66.68% at 100 °C, an improvement of approximately 4% over cold pressing (30 °C). Increasing the extraction temperature from 30 °C to 140 °C resulted in an increase in tocopherol content from 410.84 mg/kg to 512.98 mg/kg. On the other hand, temperature had no significant effect on the TPC, which varied from 31.76 mg GAE/kg to 41.89 mg GAE/kg as confirmed by HPLC-DAD/ESI-MS² analysis. On the other hand, oils extracted at higher temperatures were lower in quality, with higher PV, ranging from 6.36 meq O₂/kg at 30 °C to 13.86 meq O₂/kg at 140 °C, accompanied by a slight decrease in OSI. In addition, a decrease in chlorophyll-a content was observed, from 54.60 mg/kg at 30 °C to 36.10 mg/kg at 140 °C, which also led to a reduction in the a* value (green hue). Despite these alterations, the fatty acid profiles remained constant, whatever the thermal regime applied.

Conclusion: Extraction temperature has a significant influence on the yield and quality of hemp oil. Underline the importance of selecting the optimum extraction temperature to balance yield and quality.