Supercritical fluid extraction of black cardamom (Amomum subulatum) oleoresin: a sustainable approach for enhanced yield, phytochemical composition, and antioxidant potential

Abstract

Oleoresin extraction from black cardamom is highly valuable due to its rich composition of bioactive compounds, yet it remains underexplored, with no industrial-scale or systematic studies, leaving a critical gap in the valorisation of this underutilised spice. This study addresses the need for an advanced technique by investigating the potential of supercritical fluid extraction (SFE) to efficiently extract high-quality oleoresin. The primary aim is to optimise the SFE process parameters by systematically varying pressure (15–40 MPa), temperature (30–50 °C), and CO₂ flow rate (3–50 g min⁻¹), with ethanol as the cosolvent. The highest oleoresin yield (8.80% ± 0.12%) was achieved at 30 MPa, 50 °C, and 50 g min⁻¹, with increased energy efficiency (2.93 ± 0.03 g kW⁻¹ h⁻¹) and a favourable solvent-to-feed ratio (3 : 1). GC-MS profiling revealed superior retention of aroma-active volatiles (1,8-cineole, terpineol, and α-terpinyl acetate) under SFE, whereas GC-FID analysis revealed a nutritionally beneficial fatty acid profile dominated by oleic and linoleic acids. FTIR analysis confirmed the presence of esters, phenolics, and terpenoids. The extracts obtained under optimal conditions presented the highest total phenolic content (90.61 ± 2.25 mg GAE per g), total flavonoid content (124.96 ± 0.24 mg QE per g), and antioxidant activity (DPPH-88.63% ± 0.02%, ABTS-63.28% ± 0.15%, and FRAP-79.02 ± 0.24 µmol Fe²⁺ per g), significantly outperforming those obtained under all other conditions (p < 0.05). The residual ethanol concentration was within regulatory limits (<12.53 mg kg⁻¹), confirming food-grade applicability. The total volatile and non-volatile contents, colorimetric attributes, and extraction efficiency were significantly influenced by pressure. This green extraction approach offers a sustainable method to increase the bioactive and sensory value of black cardamom oleoresin for food, nutraceutical, and cosmetic applications.