Unveiling the bioactive potential of cashew nut testa shell (Anacardium occidentale L.): a despised by-product

Abstract Cashew nut ( Anacardium occidentale L.) processing generates several by-products that are mostly not managed sustainably and can have environmental and economic impacts. Among these by-products, cashew nut testa shell (CNTS) stands out as an underutilized material despite being a rich source of primary and secondary metabolites. To recover the compounds with bioactive potential present in CNTS, efficient extraction methods aligned with the principles of sustainability are essential. This review explores the paradigm shift towards emerging extraction techniques, aiming to add value to CNTS. Evidence from recent studies highlights that CNTS is particularly rich in polyphenols, tannins, flavonoids, and lipid compounds, which exhibit strong antioxidant, antimicrobial, and anti-inflammatory activities. Alternative methods such as supercritical fluid extraction (SFE), pressurized liquid extraction (PLE), subcritical water extraction (SWE), microwave-assisted extraction (MAE), and ultrasound-assisted extraction (UAE) have demonstrated high selectivity and efficiency compared to traditional methods. Nonetheless, the scalability, cost-effectiveness, and regulatory approvals for food and pharmaceutical uses remain a challenge for the alternative methods. This review synthesizes the current knowledge on CNTS valorization, highlights the potential of green extraction technologies, and points out the main gaps for industrial applications. Graphical abstract