Phytochemistry and antimicrobial potential of off-grade white pepper (Piper nigrum L.) essential oils extracted using microwave-assisted hydro-distillation (MAHD)

Abstract

White pepper generally used as spice, has the main component of piperine which gives it a spicy taste and essential oils that determine its aroma. In general trade, only good pepper is traded, while off-grade that does not meet quality requirements will be wasted. This study aims to investigate the effect of extraction methods of essential oils from off-grade white pepper and the potential of its antimicrobial activity against pathogenic bacteria. The results showed that off-grade white pepper essential oils (WPEO) could be isolated by using microwave-assisted hydro-distillation (MAHD) and hydro-distillation (HD). Essential oils produced had physicochemical characteristics in accordance with the ISO 3061:2008 standard. Specifically, MAHD off-grade, MAHD grade-A, and HD WPEO had 13, 11, and 15 components, respectively. The chemical composition showed that all the extracted EO contained the main components of caryophyllene, (+)-3-carene, d-limonene, and β-pinene. The methods showed the extraction ability of monoterpene hydrocarbons by MAHD and sesquiterpene hydrocarbons by HD. In comparison, microwave-extracted essential oils had a higher limonene, while off-grade WPEO contained (+)-3-carene. The FTIR results confirmed the content of the components in the three WPEO that were investigated. All essential oils had antibacterial activity against E. coli and S. typhimurium with zone inhibition values of MAHD off-grade WPEO, MAHD grade-A WPEO, and HD off-grade WPEO against E. coli at 15.44 ± 1.68 mm, 6.72 ± 0.59 mm, and 10.17 ± 0.29 mm, as well as against S. typhimurium at 8.72 ± 1.25 mm, 8.06 ± 0.86 mm, and 8.83 ± 0.87 mm, respectively.