A new ultrasound-assisted bleaching technique for impacting chlorophyll content of cold-pressed hempseed oil

• Extraction of hempseed oil chlorophyll is most efficient with diethyl ether.
• Significant reduction in hempseed chlorophyll upon ultrasonic bleaching with clays.
• Ultrasonic bleaching with clays reduced total phenolic content and peroxide value.
• Ultrasonic bleaching is a novel method to modify the color of hempseed oil.

Ultrasonic treatment was applied to reduce chlorophyll of cold-pressed hempseed oil in conjunction with various clays. Bleaching clays such as bentonite (activated/non-activated), sepiolite and clay from a canola oil refining industry (industrial clay) were used. Ultrasonic bleaching of hempseed oil for 20 min at 20, 40 and 60% power (expressed as ultrasound amplitude) with bleaching clays (40 g/kg) reduced chlorophyll in decreasing order of effectiveness from industrial clay > activated bentonite > sepiolite > non-activated bentonite together with an increase in ultrasound power to 40%. At 20% ultrasound power, chlorophyll reduction (%) was found to be 99.4% (industrial clay) > 97.8% (activated bentonite) > 82.7% (sepiolite) > 47.1% (non-activated bentonite). The reduction in total phenolic content was 27.3%, 33.4%, 27.9% and 34.7% when treated at 20% ultrasound power with 40 g/kg clay from canola industry, activated bentonite, non-activated bentonite and sepiolite, respectively. The corresponding reduction in the peroxide value for the oil samples, due to the adsorptive nature of the clay, followed the trend of industrial clay > sepiolite > non-activated bentonite. This process proved promising for impacting hempseed oil color through reduction of chlorophyll.