Simultaneous optimization of microwave- and ultrasound-assisted extractions of bioactive compounds from cashew nut testa shell (Anacardium occidentale L.)

What if the secret to potent antioxidants lies in the discarded shells of cashew nuts? A new study unlocks this potential using green extraction methods.

Cashew nut testa shells are often discarded as waste, but they may hold a treasure trove of bioactive compounds. In this study, researchers compared three green extraction techniques—ultrasound-assisted extraction (UAE), subcritical ethanol (Sbc-EtOH), and supercritical CO2 (ScCO2)—to see which one best unlocks these valuable molecules. They focused on the roots of Rheum cordatum, a plant known for its medicinal properties, and tested the extracts against four bacterial strains: Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa, and Escherichia coli.

The results were striking. Supercritical CO2 extraction, especially at lower pressure (100 bar), proved to be the most effective. It extracted the majority of 53 phenolic compounds, either exclusively or in the highest amounts, and these extracts showed the strongest antioxidant activity. The ScCO2-100 extract also demonstrated powerful antimicrobial effects, with minimum inhibitory concentrations (MIC) ranging from 31.25 to 250 µg/mL.

Among the compounds identified were gallic acid, epicatechin gallate, epigallocatechin gallate, and catechin. Molecular docking studies revealed that epicatechin binds strongly to several target proteins, suggesting potential therapeutic applications. This research highlights the promise of green extraction methods in harnessing nature's chemistry for health benefits.

Key Points

• ScCO2 extraction yielded most phenolic compounds, especially at 100 bar.
• ScCO2 extracts showed highest antioxidant and strong antimicrobial activity.
• Epicatechin showed strong binding in molecular docking studies.