# Optimizing Nigella Oil Extraction Temperature for Sustainable Production
## 3 Results and Discussion
### TPC and Antioxidant Capacity  
The results pertaining to the effect of screw press extraction temperatures in TPC and the antioxidant capacity of Nigella oil are summarized in Table 2. As shown in the table, TPC in the oils obtained varied from 81.1 to 90.4 mg GAE/100 g. The lowest TPC was observed at 80 \({}^{\circ}\)C extraction temperature, while the highest was at 40 \({}^{\circ}\)C. Similarly, the CUPRAC values ranged between 380.4 and 417 mg TE/100 g, with the lowest value obtained at 50 \({}^{\circ}\)C and the highest at 80 \({}^{\circ}\)C. However, TPC and CUPRAC values across all five different levels did not show significant differences. Regarding FRAP values, they ranged between 389 and 493.9 mg TE/100 g. The lowest FRAP value was recorded at 80 \({}^{\circ}\)C extraction, whereas the highest was at 60 \({}^{\circ}\)C. The FRAP values of oils extracted at 40 \({}^{\circ}\)C (414.9 mg TE/100 g), 50 \({}^{\circ}\)C (409.1 mg TE/100 g), and 70 \({}^{\circ}\)C (422.1 mg TE/100 g) exhibited no significant difference to those obtained at 80 \({}^{\circ}\)C.  
While previous studies have not specifically explored the effect of screw press temperatures on TPC and antioxidant capacity, numerous investigations worldwide have evaluated these parameters in cold-pressed Nigella oils. The values reported in most of these studies align closely with the findings of the present study [14; 49; 50; 51; 52]. However, variability in TPC values has been noted in the literature. For example, [PERSON] et al. [11] studied cold-pressed oil in Turkey and reported TPC values as low as 3.6 mg GAE/100 g, whereas [PERSON] et al. [53] reported TPC ranging between 96 and 760 mg GAE/100 g for Yemeni and Malaysian Nigella seed oils. Furthermore, the present study observed that the TPC and antioxidant capacity of Nigella oil are comparatively higher compared to the reported values of many other edible oils, including linseed oil, pumpkin oil, milk thistle oil, rapeseed oil, amelina oil, and sunflower oil [54; 55]. These findings highlight the potential of Nigella oil as a rich source of health-promoting compounds. While the present study found no significant difference in the TPC of Nigella oil extracted with the screw press method across five different temperatures, past research on various vegetable oils has reported diverse findings reading the effect of temperature on TPC. For example, [PERSON] et al. [56] investigated almonds, walnuts, and pistachios in Spain, extracting oils from these nuts using the screw press method at temperatures of 50 \({}^{\circ}\)C, 100 \({}^{\circ}\)C, 150 \({}^{\circ}\)C, and 200 \({}^{\circ}\)C. They noted no significant difference in TPC between almond and pistachio oils across the different extraction temperatures but observed a significant increase in TPC in walnut oil as the extraction temperature rose [56]. Similarly, [PERSON] et al. [57] examined TPC in cold-pressed rapeseed oil (pressed at room temperature) versus hot-pressed (pressed at 120 \({}^{\circ}\)C), finding significantly higher TPC in the hot-pressed oil compared to the cold-pressed oil. This irregular trend in TPC across different extraction temperatures may be influenced by factors such as seed moisture content [58], the release of phenolic compounds from bound structures, or chemical alterations of phenolics [59].