Application of Subcritical Water Extraction and Enzymatic Hydrolysis as a Combination Green Extraction Technique for Rambutan (Nephelium lappaceum L.) Peel Polyphenol

Abstract

This study aimed to develop a green and efficient technique for extracting rambutan peel polyphenols, while systematically evaluating chemical components, the water solubility, storage stability, in vitro antioxidant activity, and digestive enzyme inhibitory potential of the extracts. Subcritical water (SW) alone and SW followed by enzymatic hydrolysis (SW-EH) were employed to extract rambutan peel polyphenols. The optimal conditions of SW extraction were temperature of 130°C, time of 30 min, and liquid–solid ratio of 80:1 mL/g, which yielded a total phenol content (TPC) of 226.54 mg gallic acid equivalents per gram of dry weight powder. A total of 39 phenolics were identified with ellagic acid as the predominant compound. SW-EH extract maintained similar phenolic profiles but contained less soluble dietary fiber compared to SW extract. The transmittance and polyphenol solubility of SW-EH extract were higher than those of SW extract in the concentration range of 5 to 100 mg/mL. The ellagic acid content in the SW and SW-EH extracts decreased by 19.05% and 1.71%, respectively, after 40 days of storage. Both extracts demonstrated comparable antioxidant activities superior to ascorbic acid, while EH treatment greatly enhanced α-glucosidase inhibitory activity compared to SW extract. With superior water solubility, storage stability, antioxidant activity, and digestive enzyme inhibitory potential, SW-EH extract is a promising product for a wide range of applications.