Phytochemical composition and antibacterial activity of calamansi (Citrus microcarpa L.) rind essential oil against Bacillus cereus and Serratia marcescens

Abstract

Calamansi <i>(Citrus microcarpa L.),</i> a citrus fruit widely cultivated in the Philippines and Southeast Asia, generates significant agricultural waste as its rind is typically discarded despite its potential value. This study evaluated the antibacterial activity of calamansi rind essential oil against two food spoilage bacteria, <i>Bacillus cereus</i> and <i>Serratia marcescens, </i> to explore its utility as a natural preservative. Extraction was done using rotary evaporation, and characterized through phytochemical analysis which identified terpenoids, flavonoids, glycosides, and phenols/tannins—compounds with known antimicrobial and antioxidant properties. Antibacterial efficacy was assessed via disk diffusion and microdilution methods. Disk diffusion revealed moderate activity, with average inhibition zones of 7.93 mm and 9.13 mm against <i>B. cereus</i> and <i>S. marcescens</i> respectively, though smaller than ampicillin and gentamicin controls. Microdilution assays, used to determine minimum inhibitory concentrations (MIC), yielded inconsistent results due to interference from the extract’s dark pigmentation, highlighting a methodological limitation. Despite lower efficacy than synthetic antibiotics, results suggest that calamansi rind essential oil has potential as a sustainable, natural antimicrobial agent for food or agricultural applications.