The Effect of Microwaves on Essential oils of White and Black Pepper (Piper nigrum L.) and their Antioxidant Activities

Abstract

White and black peppers were subjected to conventional roasting as well as microwave heating in order to study the effects of such techniques on the volatile constituents of each spice oil and its antioxidative activity. Hydrodistillation oil of each spice was analyzed using Gas Chromatography (GC) and Gas chromatography-Mass spectrometry (GC-MS). Twenty six compounds were identified in essential oil of white pepper, whereas, twenty compounds were detected in black pepper essential oil. ô-Carene, limonene, (X - and ß-pinene and ß-caryophyllene were the major components in both. Due to heating treatments, increase in sesquiterpenes and drastic increase in oxygenated terpenes were observed in comparison to the raw samples. Such changes affected the antioxidant activity of the treated samples using 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging as well as ß-carotene bleaching test against tert-Butylhydroquinone (TBHQ). The strongest effect for reduction of DPPH radical was by white pepper microwave heated sample which exhibit 78.2 % ± 2.1), followed by conventionally roasted black pepper sample, (75.2 % ± 1.9) compared to TBHQ (98.8 % ± 2.1) at the same concentration 400 µg/ml. However, conventionally roasted black pepper recorded the highest inhibiting effect for the oxidation of linoleic acid and the subsequent bleaching of ß-carotene (78.2 % ± 2.3), followed by white pepper microwave heated sample (76.2 % ± 1.9) in comparison to TBHQ (98.8 % ± 2.1).