Laboratory-Scale Optimization of Hemp Seed Roasting Temperature and Time for Producing a High-Quality Pressed Oil

Abstract

Roasting is widely applied in oil processing to improve the extraction yield and desired sensory characteristics. The current study is aimed at optimizing roasting conditions (time and temperature) of hemp (Cannabis sativa L.) seeds prior to seed pressing to improve the oil yield and antioxidant capacity, using response surface methodology based on central composite design (CCD). Hemp seeds were roasted at five temperatures (132, 140, 160, 180, and 188°C) and for five duration times (9, 15, 30, 45, and 51 min). Mathematical models have shown that roasting conditions significantly affected response variables ( $p<0.05$ ), including oil yield, total phenolic content (TPC), radical scavenging activity, and oxidative stability index (OSI). The CCD led to the following optimum roasting conditions: 163°C for 15 min, which improved the extraction yield by 45% and oxidative stability by 80%. Thus, the oil produced under these conditions showed a yield of 23.09%, TPC of 121.21 mg GAE kg-1, and OSI of 21.37 hours. In addition, roasting hemp seeds under optimal conditions did not negatively influence the oil quality. Only chlorophylls, tocopherols, and palmitic acid slightly decreased ( $p<0.05$ ) after roasting (from 39.10 to 36.54 mg kg-1, 483.06 to 469.77 mg kg-1, and 7.65 to 7.29%, respectively). Furthermore, the concentrations of most volatile compounds identified in unroasted hemp seeds decreased after roasting under optimal conditions, with the formation of new compounds sought for their positive attributes, such as pyrazines and aldehydes derived from the Strecker degradation, responsible for the roasted, nutty, and almond odors. The main volatile compounds in raw and roasted hemp seeds were β-myrcene (3170.30 and 1177.69 ng g-1, respectively) and D-limonene (1347.25 and 470.35 ng g-1, respectively). The results obtained in this study could provide valuable information for the food industry to produce hemp seed oil with high nutritional quality that meets consumer demands.