Abstract
Rosemary residue, remaining after the distillation of essential oil, is currently unexploited, while it is a source of phenolic antioxidant components. This raw material was used for the extraction of phenolic compounds by aqueous ethanol or acetone in a continuously stirred reactor. The experimental results were fitted with a two-stage diffusion model. The highest extraction rates, total phenolic content (TPC) recovery, and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity were obtained by acetone 60% and ethanol 60%. Grinding of the raw material enhanced the extraction rate and increased TPC yield and antioxidant capacity as the particle size decreased. Pre-treatment by maceration in water (4 h) dissolved a high amount of TPC and shortened the extraction time, while the combination with the pulsed electric field process did not provide further improvement. The use of ultrasound increased the efficiency of the extraction.
Highlights
Rosemary is the most well-known aromatic plant with antioxidant activity
The residual material from rosemary after the removal of its essential oil proves to be rich in phenolic ingredients with strong overall antioxidant capacity
Extracts with rich phenolic content were recovered by using environmentally friendly solvents, such as aqueous mixtures of ethanol and acetone, and enhancing the extraction process by pretreatment methods such as grinding and maceration. 60% ethanol or acetone in water solution resulted in the highest extraction rates, total phenolic content (TPC) recovery, and antioxidant capacity while increasing temperature from 22 ◦ C to 60 ◦ C resulted in increased extraction efficiency and antioxidant activity
Summary
Rosemary is the most well-known aromatic plant with antioxidant activity. Several researchers have reported radical scavenging and antioxidant properties by using a variety of methods and tests, while extracts of the plant are the only currently approved natural antioxidants in the EU (Directive95/2/EC) and assigned the E number E-392 (European Union Directives 2010/67/EU and 2010/69/EU).According to a new global research study, the worldwide market for rosemary extract is expected to grow at an annual growth rate of roughly 3.7% over the five years and will reach 260 million US$ in 2024 from 210 million US$ in 2019 [1]. Several researchers have reported radical scavenging and antioxidant properties by using a variety of methods and tests, while extracts of the plant are the only currently approved natural antioxidants in the EU In addition to antioxidant properties, rosemary extracts showed antimicrobial, anti-fungal, bio-plaguicide, anti-inflammatory, anti-carcinogenic activities, as well as therapeutic and prophylactic effects on several physiological disorders [2,3,4,5,6,7]. Most of these activities have been associated with the content in total phenolics or, in particular, carnosic and rosmarinic acid, as well as minor flavonoid constituents. Research efforts focus on high-yield extracts rich in Molecules 2020, 25, 4520; doi:10.3390/molecules25194520 www.mdpi.com/journal/molecules
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