Longan (Dimocarpus longan) Concentrate: Bioactive Potential Against Bacterial Strains and Stored Product Insects
Keywords:
Dimocarpus longan; antimicrobial activity; insecticidal activity; stored food protection; natural preservative.Abstract
Longan (Dimocarpus longan Lour.) is a tropical fruit native to southern China and Southeast Asia, traditionally used not only as a food source but also in traditional Chinese medicine. Longan concentrate is a thick yellow brown to dark brown paste with a characteristic aroma, obtained by extraction of plant material using organic solvents. It contains a wide range of bioactive compounds responsible for its antioxidant, antimicrobial, and insecticidal properties. The aim of this study was to evaluate the antimicrobial activity of longan concentrate against selected bacterial strains and its insecticidal activity against two beetle species infesting stored products. Antimicrobial activity was determined using the disc diffusion method and by assessing the minimum inhibitory concentration (MIC50 and MIC90) against six bacterial strains: Bacillus cereus CCM 2010, Enterobacter aerogenes CCM 2531, Klebsiella pneumoniae CCM 2318, Listeria innocua CCM 4030, Staphylococcus epidermidis CCM 4418, and Citrobacter koseri CCM 2535. An antibiotic disc (ABT) was used as a positive control. Insecticidal activity was evaluated against Callosobruchus maculatus and Megabruchidius dorsalis at concentrations ranging from 3.125 % to 100 %. Disc diffusion results showed inhibition zones ranging from 7.67 to 13.67 mm, with the strongest activity observed against S. epidermidis (13.67 mm) and L. innocua (12.67 mm). MIC50 values ranged from 0.188 mg/mL (S. epidermidis) to 2.472 mg/mL (C. koseri), while MIC90 values ranged from 0.468 mg/mL (S. epidermidis) to 3.461 mg/mL (C. koseri). At the highest concentration (100 %), insecticidal activity reached 95.67 % mortality for C. maculatus and 88.67 % for M. dorsalis. Longan concentrate exhibited notable antimicrobial activity, particularly against Gram-positive bacteria, as well as significant insecticidal effects against both tested beetle species. These findings suggest its potential as a natural alternative for the protection of stored food commodities.
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