pH-driven mechanistic segmentation and enzyme-assisted deconstruction for the selective release of centelloids from Centella asiatica

Abstract

The effect of pre-extraction treatment of Centella asiatica (L.) using different pre-treatment parameters, namely, pH (4.0–6.0) and treatment time (15–105 min), in combination with enzymatic pretreatment, on centelloid extracts obtained by ultrasound-assisted extraction was investigated. It was observed that the pre-extraction treatment of plant samples at all tested pH values in combination with enzymatic deconstruction led to distinct synergistic effects. Liberation of centelloids was found to occur mainly at two different pretreatment regimes, namely, Phase I (Proton-induced pectin relaxation and rapid glycoside liberation), which led to maximum glycoside yield at pH 4.0 within 15 min (18.20 ± 0.15 mg/g madecassoside and 8.51 ± 0.15 mg/g asiaticoside), and Phase II (Enzyme-mediated collapse and aglycone re-adsorption), in which, at pH 5.0–6.0, the role of enzymatic contribution in enhancing the extraction of aglycones was found to be negligible. Optimum yields and quality of centelloid aglycones were achieved at pH 6.0, where maximal yields were obtained at 60 min and declined thereafter. The observed decline in centelloid aglycone yields at prolonged treatment time could be attributed to the extensive enzymatic fragmentation and subsequent collapse of the disrupted plant matrix, leading to non-specific re-adsorption of the bioactive triterpenes. This study provides a sustainable and cost-effective framework for optimizing extract composition through precise pH and temporal control, offering an efficient methodology for the green separation of bioactive centelloids.