Analysis of Secondary Metabolites in Citrus swinglei Burkill ex Harms (Jeruk Kunci) Essential Oil and Determination of α-Glucosidase Inhibition Activity

Abstract

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder associated with persistent hyperglycemia. Inhibitors of α-glucosidase play a crucial role in controlling postprandial blood glucose, but the use of synthetic agents such as acarbose is often limited by gastrointestinal side effects. This study aimed to investigate the secondary metabolite profile of jeruk kunci (Citrus swinglei Burkill ex Harms) essential oil and to evaluate its inhibitory activity against α-glucosidase. C. swinglei essential oil was extracted by steam distillation, yielding 0.135% (w/w) of a colorless oil with a characteristic aroma. The chemical composition was analyzed by gas chromatography-mass spectrometry (GC-MS), while thin-layer chromatography (TLC) combined with bioautography was used for qualitative enzyme inhibition screening. The inhibitory activity of the essential oil was quantitatively determined using a microplate reader assay. GC-MS analysis identified 12 major volatile compounds dominated by monoterpenes, particularly bicyclo[3.1.0]hex-2-ene, 4-methyl-1-(1-methylethyl), -Pinene, β-Pinene, -myrcene, 1,3-cyclohexadiene, 1-methyl-4-(1-methylethyl), -cymene, D-limonene, -terpinene, cyclohexene, 1-methyl-4-(1-methylethylidene), linalool, terpinen-4-ol,  and -terpineol.  TLC-bioautography confirmed the presence of active metabolites, indicated by white inhibition zones. The essential oil exhibited significant α-glucosidase inhibition with an IC₅₀ value of 230 0.28 µg/mL. These results support the use of Southeast Asian citrus species as candidates for the development of plant-based antidiabetic agents.