Chemical Composition of Turmeric (Curcuma longa L.) Ethanol Extract and Its Antimicrobial Activities and Free Radical Scavenging Capacities

Abstract

Turmeric (<i>Curcuma longa</i> L.) is a perennial tuberous plant from the genus <i>Curcuma</i> (Zingiberaceae) and has been widely used in foods for thousands of years. The present study examined the ethanol extract of turmeric for its chemical composition, antimicrobial activity, and free radical scavenging properties. UHPLC-MS/MS analysis tentatively identified eight compounds in the turmeric extract. Potential antimicrobial effects of 0.1, 1.0, and 10 mg turmeric equivalents (TE)/mL were evaluated in vitro against a variety of Gram-negative bacteria (i.e., <i>Escherichia coli</i>, <i>Klebsiella pneumoniae</i>, and <i>Pseudomonas</i> sp.) and Gram-positive bacteria (i.e., <i>Enterococcus faecalis</i>, <i>Listeria innocua</i>, and <i>Staphylococcus aureus</i>). Concentrations of 0.1 and 1.0 mg TE/mL inhibited the growth of <i>S. aureus</i> and significantly suppressed that of <i>Pseudomonas</i> sp., <i>E. faecalis</i>, and <i>L. innocua</i>. The growth of all strains, including <i>E. coli</i>, was inhibited by 10 mg TE/mL. Moreover, free radical scavenging capacities were determined using HO^●, ABTS^●+, and DPPH^● (HOSC, ABTS, and RDSC, respectively) radicals. The turmeric ethanol extract had a TPC value of 27.12 mg GAE/g, together with HOSC, RDSC, and ABTS values of 1524.59, 56.38, and 1.70 μmol TE/g, respectively. Our results suggest that turmeric extract has potential applications for use in functional foods to reduce microbial burdens and oxidative stress-related health problems.