A review of extraction methods, geographic variation in chemical composition and identification of marker compounds in bud, leaf and stem clove oil

Clove (Syzygium aromaticum) is one of the most precious spices that has been used since ages. Cloves are well-known for their many medicinal properties. It is also widely used in food, flavours and cosmetics industry. One of the main usage of cloves is in the dentistry field to treat bad odour, toothache etc. Though it is native to Indonesia, it has been cultivated in several parts of the world. Clove oil is the richest source of phenolic compounds such as eugenol, eugenyl acetate. It is most powerful source of antioxidant as per oxygen radical absorption capacity. Many review articles had already been published on clove oil which elucidate its morphology, biological and pharmacological benefits. The characteristics of this review study is the exploration and elaborate discussion about extraction methods, discrepancies between the chemical composition due to geographic conditions and identification of marker compounds in leaf, stem and bud clove oil. The comprehensive review revealed that the clove oil mainly consists of phenolic compounds such as eugenol, eugenyl acetate followed by sesquiterpene namely beta-caryophyllene.

Enzymatic Synthesis of Eugenyl Acetate from Essential Oil of Clove Using Lipases in Liquid Formulation as Biocatalyst

In this research, eugenyl acetate, a compound with flavoring, antioxidant and antimicrobial properties, was obtained from essential oil of clove (Syzygium aromaticum) via liquid lipase-mediated acetylation. Clove essential oil was extracted by drag water vapor from dry flower buds and its physic-chemical characteristics were analyzed. For the enzymatic synthesis, an extensive evaluation of reaction parameters was accomplished through employment of distinct reaction temperatures, acetic anhydride to eugenol molar ratios, enzyme loads and three different lipases (a lyophilized enzyme produced by solid-state fermentation of sunflower seed with Penicillium sumatrense microorganism and others two commercial lipases – Lipozyme TL 100L and CALB L). Characterization by Infrared Spectroscopy and Nuclear Magnetic Resonance (1H NMR and 13C) was used to confirm the presence of eugenyl acetate in the samples. Through optimized conditions (55 °C, acetic anhydride to eugenol molar ratio of 1:1, 10 wt% of Lipozyme TL 100L), 91.80 % of conversion after 2 h was achieved to the eugenyl acetate production. With the results obtained, it was possible to conclude that the use of lipases in liquid formulation is a promising alternative for the synthesis of essential esters largely applied on food, cosmetic and pharmaceutical industries.

Optical Investigation of Essential Oils Using Absorbance and Photoluminescence

Essential oils are complex mixtures of organic substances with large commercial importance in the pharmaceutical, food, fragrance, and cosmetic industries due to their organoleptic and biological properties. Also, these materials are also luminescent what has taken several studies about its potential uses for the detection and quality control of essential oils, imaging, and for the investigation of the synergies of their constituents. Concerning this, the present work is dedicated to studying the optical properties of selected essential oils: citronella ( Cymbopogon winterianus), Japanese mint ( Mentha arvensis), clove bud ( Syzygium aromaticum), and bergamot ( Citrus bergamia). We carried out a comparative study of the photoluminescence and the UV–Vis optical absorption (abs-UV–Vis) of these essential oils with their typical constituents. To inspect the effects of the intermolecular interactions on the optical response of these systems, mixtures between the essential oils constituents following the expected average percent mass fraction were also studied. From these experiments, the main results were bathochromic effects in the abs-UV–Vis spectra; excimer formation in citral, isopulegol, isomenthone, eugenol, and eugenyl acetate; excimer emission enhancing and specific solvent effect in the essential oils photoluminescence spectra. These results contribute to the knowledge of essential oils’ applications, especially in the evaluation of components’ interactions through a simple abs-UV–Vis assay.

Synthesis of Solid Acid Catalyst from Fly Ash for Eugenol Esterification

A series of fly ash-based heterogeneous acid catalysts were prepared by chemical and thermal treatment. Fly ash was chemically activated using sulfuric acid and followed by thermal activation. Characterization methods of XRD, BET, SEM-EDX, and the performance in esterification of eugenyl acetate production was carried out to reveal the physical and chemical characteristics of prepared catalysts. Activated catalyst showed high silica content (96.5%) and high BET surface area of 70 m2.g-1. The catalyst was proven to be highly active solid acid catalyst for liquid phase esterification of eugenol with acetic acid yielding eugenyl acetate. A yield of 43-48% was obtained with activated fly ash catalysts for 90 minutes reaction. These catalysts may replace beneficially the conventional homogenous liquid acid to the eco-friendly heterogeneous one. Copyright © 2019 BCREC Group. All rights reserved

Acetylation of Eugenol over 12-Molybdophosphoric Acid Anchored in Mesoporous Silicate Support Synthesized from Flint Kaolin

A new prepared catalyst, 12-molybdophosphoric acid (HPMo) anchored to the mesoporous aluminosilicate AlSiM, synthesized from Amazon kaolin, was characterized and used as a heterogeneous acid catalyst for the production of eugenyl acetate by acetylation of eugenol with acetic anhydride. The effect of various reaction parameters, such as catalyst concentration, eugenol/acetic anhydride molar ratio, temperature and reaction time, was studied to optimize the conditions of maximum conversion of eugenol. The kinetics studies showed that in eugenol acetylation, the substrate concentration follows a first order kinetics. The results of activation energy was 19.96 kJ mol−1 for HPMo anchored to AlSiM. The reuse of the catalyst was also studied and there was no loss of catalytic activity after four cycles of use (from 99.9% in the first cycle to 90% in the fifth cycle was confirmed), and an excellent stability of the material was observed. Based on catalytic and kinetic studies, HPMo anchored to AlSiM is considered an excellent catalyst.