Effect of particle size, probe type, position and glassware geometry on laboratory-scale ultrasonic extraction of Citrus maxima flavedo

Laboratory-scale ultrasonic extraction efficiency can be improved by selecting appropriate substrate size, glassware type and hardware configurations. For the first time, effects of using different common glassware shapes and geometries with two common ultrasonic probes on phytochemical extractability in 80 % ethanol were investigated. Citrus maxima peel powder was the model substrate. Smaller particles of 100–150 μm yielded higher mass (51.26 ± 0.25 %), however not consistently enhancing phenolic and flavonoid content owing to thermal effects. 300–500 μm particles exhibited higher antioxidant activities (92.38 ± 0.50 % DPPH reduction and 2.81 ± 0.05 mM/g FRAP). A 3 mm diameter probe gave superior yield (>43 %) and quality (>40 % TPC; >35 % TFC and >28 % FRAP) over a 13 mm probe. Deeper probe placements (50–70 mm) enhanced cavitation effects, improving extraction efficiency and bioactivity (>20 % yield; >10 % TPC and TFC; >21 % FRAP respectively). Curved vessel base was found to be appropriate for generating efficient cavitation effects and extraction zones. Narrow-bodied test tube and falcon tube outperformed wider beakers and conical flasks. Improvements up to 43 %, 40 %, 38 % and 28 % in yield, TPC, TFC and FRAP respectively were achieved in them. Principal component analysis highlighted the synergistic effects. Schemes of ultrasonic activities within the selected set-ups were hence theorized from this study.