Solvent-free simultaneous extraction of volatile and non-volatile antioxidants from rosemary (Rosmarinus officinalis L.) by microwave hydrodiffusion and gravity

Abstract

The demand for more efficient environmentally friendly extraction processes is increasing and microwave technology has emerged as remarkable alternative. In this way, microwave hydrodiffusion and gravity (MHG) was purposed as a fast and solvent-free simultaneous extraction of two antioxidant fractions from rosemary (Rosmarinus officinalis L.). The wetted plant material was placed inside the microwave oven, and the extraction conditions optimised using central composite design. The most suitable conditions found for the simultaneous extraction of both volatile and non-volatile fractions from 100 g of plant were 400 W of microwave power, 20 min of extraction and 250 mL of water added for plant wetting. The essential oil yield of 2.32 % was comparable to that obtained by hydrodistillation (HD) of 2.35 %. The profile of extracts obtained by HD and MHG presented differences, with more oxygenated compounds in the essential oil obtained by MHG. In addition, the antioxidant activity of the oil obtained by MHG reached 430 versus 211 μmol Trolox equivalent/g oil for HD. The aqueous extract recovered by MHG presented a total phenolic content similar to 1 h of maceration and also displayed higher antioxidant activity. Phenolic compounds with known antioxidant activity were identified in the aqueous extract from rosemary using high-resolution time-of-flight mass spectrometry with electrospray ionisation. The proposed MHG extraction recovered both volatile and non-volatile fractions in only 20 min and can be considered a clean alternative for antioxidants extraction without the use of solvents.