Ultrasound-assisted extraction of clove buds using batch- and flow-reactors: A comparative study on a pilot scale

• Flow plant extraction: process intensification at high-power density ultrasound
• Dry clove buds have been extracted in a multiple-horns ultrasonic flow reactor.
• Flow extraction gave higher phenolic content and free-radical scavenging activity.
• Flow and batch extractions gave a comparable aromatic profile (headspace-GC/MS).

This study will assess the efficiency of both batch and flow ultrasonic reactors (20 L in 45 min) in carrying out the ultrasound-assisted extraction of dry clove buds and compare these more recent methods with classic maceration. Flow ultrasound-assisted extraction was carried out in a new multi-horn reactor working in continuous flow mode (450, 900, 1350 mL/min) and at high power density (about 700 W/L vs 18 W/L in batch). The specific energy input was a slightly lower in flow procedure 47.2 kJ/L vs 48.6 kJ/L in batch reactor. Total phenolic compound content ranged from 191 ± 1 to 215 ± 3 mg gallic acid equivalents/L of extract. The best results were obtained under flow ultrasound-assisted extraction operating at 1350 mL/min (highest phenolic content and best radical scavenging activity). Clove bud volatiles from hydroalcoholic extracts were separated and identified using hyphenated headspace gas chromatography and mass spectrometry. We herein show that the development of large-scale multiple transducer flow reactors operating at high power density allows noteworthy process intensification.Industrial relevanceThis piece of work was carried out thanks to the investment of Pernod-Richard Italia, an international company worldwide known in the field of liqueurs and wines. Considering the huge amount of plant extracts required by this type of production, only flow systems may be suitable for scaling up. The results of this investigation on pilot reactors pave the road for the set up of an industrial plant.