Ultrasound Extraction Unlocks Higher Antioxidant Yields From a Medicinal Mushroom
- Gauri Khanna
- 23 minutes ago
- 4 min read
Researchers at Jilin Agricultural University optimised an ultrasound-assisted extraction process for Inonotus hispidus, achieving a total polyphenol yield of 25.46 mg/g, a 35.86% improvement over unoptimised conditions.
Acoustic cavitation, the rapid collapse of microscopic bubbles generated by ultrasound waves, physically disrupts fungal cell walls and accelerates the release of polyphenols without the thermal degradation associated with conventional heat-based extraction.
The method consumed roughly 4.4 times less energy than heat reflux extraction and earned an environmental greenness score of 0.76 out of 1.0, pointing to its potential as a scalable, sustainable route for producing medicinal fungal extracts.
Inonotus hispidus, a bracket fungus traditionally used in Chinese medicine, has long attracted scientific interest for the polyphenols concentrated in its fruiting bodies. These plant-like compounds, also found in many mushrooms, are associated with antioxidant, anti-inflammatory, and antiproliferative effects in laboratory studies. Despite that promise, efficient and environmentally responsible methods for extracting them at useful concentrations have remained elusive. A new study published in Ultrasonics Sonochemistry by researchers at Jilin Agricultural University and the China Academy of Chinese Medical Sciences sets out to close that gap, using sound itself as the extraction tool.
What Ultrasound-Assisted Extraction Does Differently
Conventional methods for pulling bioactive compounds from fungal material, including heat reflux extraction and stirring-assisted extraction, rely on elevated temperatures or mechanical agitation. Both approaches carry penalties: prolonged heat can chemically degrade the very compounds being targeted, while stirring alone lacks the force needed to fully breach rigid fungal cell walls. Ultrasound-assisted extraction (UAE) works through a different mechanism. At a frequency of 50 kHz, ultrasound generates acoustic cavitation: the rapid formation and violent collapse of microscopic bubbles within the liquid. That collapse produces localised shear forces, high-velocity microjets, and shock waves that physically disrupt cell walls and drive solvent deep into the fungal matrix. The result is faster, more complete extraction at milder temperatures.
In an initial head-to-head comparison, UAE produced a total polyphenol content (TPC) of 18.74 mg/g from I. hispidus dried powder, exceeding heat reflux extraction by 8.70% and stirring-assisted extraction by 14.62%. Energy consumption told a similarly clear story: the UAE required 1.62 × 10⁶ joules, compared with 4.80 × 10⁶ joules for stirring and 7.20 × 10⁶ joules for heat reflux, making it 3.0 and 4.4 times more energy-efficient, respectively.
Tuning the Process: Finding the Optimal Conditions
The research team then systematically varied six extraction parameters, including sonication time, temperature, ethanol concentration, ultrasonic power, solid-to-liquid ratio, and the number of extraction cycles, before applying response surface methodology (RSM) with a Box-Behnken design to identify the optimal combination. RSM is a statistical modelling technique that maps how multiple variables interact and jointly affect an outcome, allowing researchers to locate a true optimum rather than simply testing one factor at a time.
The final optimised protocol called for 95 minutes of sonication, 60% ethanol as the solvent, 150 W of ultrasonic power, and a temperature of 65°C. Under these conditions, the experimental TPC reached 25.46 mg/g, a 35.86% improvement over the pre-optimised baseline. The result closely matched the model's prediction of 25.23 mg/g, confirming the reliability of the approach. A single extraction cycle proved sufficient: additional cycles yielded negligible gains while consuming more solvent and energy.
The choice of 150 W power was deliberate. Beyond that threshold, an overly dense cloud of cavitation bubbles begins to scatter the acoustic field and generates excess hydroxyl radicals that can oxidatively degrade the polyphenols being extracted. Temperature followed a similar biphasic pattern: 65°C optimised both solvent penetration and cell wall disruption, while 70°C caused a measurable decline in yield.
Antioxidant Activity and Compound Profile
The optimised extract was then tested across four antioxidant assays, measuring its capacity to scavenge DPPH radicals, ABTS radical cations, ferric ions (FRAP assay), and hydroxyl radicals. All four showed concentration-dependent responses, with the optimised extract performing significantly better than the unoptimised version, suggesting that the improved extraction conditions not only raised yield but also preserved the structural integrity of the polyphenols responsible for that activity.
HPLC-MS/MS analysis identified 60 individual polyphenolic compounds in total, including hispidin, luteolin, caffeic acid, ferulic acid, kaempferol, and isorhamnetin. Hispidin, a compound specific to I. hispidus and already noted for a range of bioactivities in fungal research, was the most prominent. The environmental sustainability of the optimised method was quantified using the AGREE metric, a standardised greenness scoring tool grounded in green analytical chemistry principles, and returned a score of 0.76 out of 1.0, comfortably above the 0.6 threshold considered environmentally acceptable.
Limitations and the Road Ahead
The authors are transparent about what remains to be done. The entire study was conducted at laboratory scale, and pilot-scale validation is required before any industrial application can be considered. Biological activity was assessed only through in vitro antioxidant assays, meaning no claims can be made about how these compounds might behave in living systems or at therapeutic concentrations. The acoustic power measurements relied on calorimetric approximation under a single set of conditions, and the mechanistic interpretations around cavitation remain inferential without direct sonochemical measurement.
Whether the polyphenol profile of I. hispidus translates into the wider therapeutic potential suggested for fungal compounds more broadly is a question this study does not address. What it does establish is a reproducible, energy-efficient, and chemically characterised extraction protocol, a necessary foundation for whatever comes next.