Phenolics enrichment enhances in vitro antihyperglycaemic activity of sugar-removed water-soluble palm fruit extract

Water-Soluble Palm Fruit Extract (WSPFE) is recovered from oil palm vegetation liquor. WSPFE consists of water-soluble phenolic acids, including protocatechuic acid (PCA), p-hydroxybenzoic acid (p-HBA) and three isomers of caffeoylshikimic acid. WSPFE demonstrated several therapeutic activities in vitro and in vivo; however, its high sugar content relative to the phenolic acids suggests that a large volume would be required to achieve these effects. In this study, various methods were employed to remove sugars and concentrate the phenolic acids in WSPFE, including ethanolic precipitation, alkaline hydrolysis and solid-phase extraction (SPE) using Amberlite XAD-2 and Oasis HLB resins. The most efficient enrichment method was SPE using Oasis HLB, which yielded a total phenolics content of 186.1 ± 0.3 mg g−1 GAE, followed by Amberlite XAD-2 resin at 119.5 ± 1.3 mg g−1 GAE. The highest antioxidant activity, along with the most significant inhibition of alpha-amylase and alpha-glucosidase and the highest glucose uptake in L6 skeletal muscle cells, was observed in sugar-removed WSPFE obtained via SPE. WSPFE demonstrated more pronounced in vitro antihyperglycaemic effects following sugar removal. Compared to ethanol precipitation and alkaline hydrolysis, SPE using Oasis HLB and Amberlite resins was superior at enriching phenolic acids while effectively removing sugar.