Elsevier

Food Chemistry

Volume 119, Issue 1, 1 March 2010, Pages 69-74
Food Chemistry

Flavour characterisation of fresh and processed pennywort (Centella asiatica L.) juices

https://doi.org/10.1016/j.foodchem.2009.05.072Get rights and content

Abstract

The flavour characteristics of fresh and processed pennywort juices treated by pasteurisation, sterilisation and high pressure processing (HPP) were investigated by using solid-phase micro-extraction combined with gas chromatography–mass spectrometry. Sesquiterpene hydrocarbons comprise the major class of volatile components present and the juices had a characteristic smell due to the presence of volatile compounds including β-caryophyllene, humulene, E-β-farnesene, α-copaene, alloaromadendrene and β-elemene. All processing operations caused a reduction in the total volatile concentration, but HPP caused more volatile acyclic alcohols, aldehydes and oxygenated monoterpenoids to be retained than pasteurisation and sterilisation. Ketones were not present in fresh pennywort juice, but 2-butanone and 3-nonen-2-one were generated in all processed juices, and 2-nonanone and 2-hexanone were present in pasteurised and sterilised juices. Other chemical changes including isomerisation were also reduced by HPP compared to pasteurisation and sterilisation.

Introduction

Asiatic pennywort (C. asiatica), also known as gotu kola and pegapa is one of the herbs grown in Thailand and other Asian countries that is claimed to possess various physiological effects. It has been used for hundreds of years as an anti-inflammatory and a treatment for leprosy and syphilis. It has been included in Thai traditional recipes as a poultice for wound healing (Farnsworth & Buryapraphatsara, 1992) and is commonly used as a vegetable and tonic (Pramongkit, 1995). Moreover, it has been reported that wound and ulcer healing are enhanced by its action in promoting fibroblast proliferation and collagen synthesis (Maquart, Bellon, Gillery, Wegrowski, & Borel, 1990).

Non-thermal methods for juice processing including high pressure have been applied more widely during the past few years. High pressure processing (HPP) is frequently applied in juice processing because it inactivates microorganisms with minimal damage to heat sensitive compounds. This method is capable of maintaining freshness and nutritive value (flavour, colour, vitamin content, biologically active components, etc.). The European Commission has included products processed by high pressure in the group of novel foods regulated by the Novel Foods Legislation.

Herbal plants have commanded special attention due to their value. However, quality control of raw herbs and their products is essential to ensure quality, safety and efficacy. The flavour of herbal plants is due to essential oils which are complex mixtures mainly containing volatile compounds. The most volatile are mono (C10) and sesquiterpenoids (C15) that represent the major components of essential oils. Monoterpenoids may have acyclic, monocyclic and bicyclic structures, and occur in nature as hydrocarbons, alcohols, ketones, aldehydes, ethers, etc. Many literature reports describe the importance of monoterpenoids for the flavour of foods (Perez-Cacho & Rouseff, 2008). However, monoterpenoid chemistry is complex, since they are distinguished by structural characteristics, including the presence of endocyclic and exocyclic carbon–carbon double bonds, which present steric limitations and contribute distinct reactivities; functionalised and substituted skeletons; the presence of highly tensioned rings, and the possibility of bicyclic ring rearrangements.

Chou (2005) identified nineteen compounds in the essential oil from C. asiatica in Taiwan as linalool, p-menth-1-en-8-ol, copaene, elemene, sesquiphellandrene, caryophyllene, thjosene, cadinene, acoradien, humulene, alloaromadendrene, farnesene, selinene, 1,5,5,8-tetramethyl-1,2-oxabicyclo [9,1,0] dodeca-3,7-diene, eudesmene, cuparene, caryophyllene oxide, phytol and hexahydrofarnesylacetone. Ali (2007) reported 23 compounds in this plant from Malaysia including α-pinene (1.2%), germacrene D (1.6%), (+)-cyclosativene (2.3%), β-farnesene (4.8%), β-cubebene (17%), α-caryophyllene (17%), α-humulene (22%), γ-murolene (22%) and various components with concentrations less than 1% including β-pinene, m-cymene, d-limonene, β-trans-ocimene, γ-terpinene, 1-bromoallene, β-linalool, trans-3-nonen-2-one, terpinen-4-ol, ο-menth-8-ene,4-isopropylidene-1-vinyl-α-cubebene, n-decyl acetate, β-cedrene, δ-cadinene and caryophyllene oxide. Oyedeji and Afolayan (2005) also reported that the essential oil extracted from C. asiatica grown in South Africa contained 11 monoterpenoid hydrocarbons (20.20%), 9 oxygenated monoterpenoids (5.46%), 14 sesquiterpenoid hydrocarbons (68.89%), 5 oxygenated sesquiterpenoids (3.90%) and 1 sulphide sesquiterpenoid (0.76%). Components present included sesquiterpenoid hydrocarbons including α-humulene (21.06%), β-caryophyllene (19.08%), bicyclogermacrene (11.22%), germacrene B (6.29%) and myrcene (6.55%). Other reports included trans-β-farnesene and germacrene D as prominent constituents of the essential oil.

The effect of heat treatment and HPP on pennywort juice flavour production has not been reported. In the present studies, we have analysed fresh and processed pennywort juice aroma by gas chromatography–mass spectrometry (GC–MS) using solid-phase micro-extraction (SPME).

Section snippets

Raw material and preparation

The plant sample was freshly harvested, with commercial maturity (2–4 months) obtained from high land, Chiangmai, Thailand. Upon arrival at the laboratory, the sample was washed with running tap water to remove debris and damaged portions. The leaves and petioles of pennywort were stripped from the plant and extracted with water (1:1 w/v) by grinding at room temperature for 15 min. This juice was filled into the double layer of an LDPE Stomacher pouch (Seward Limited, UK) before HPP and filled in

Flavour of fresh juice

The flavour compounds in fresh and processed pennywort juice treated by heat and high pressure treatment are shown in Table 1, Table 2. Fresh juice and high pressure processed juice contained 40 and 39 volatile components that could be identified, respectively, whereas pasteurised and sterilised juice contained 39 and 38 volatile compounds, respectively. Twenty-nine components occurred in all the fresh and processed juice samples, although in some samples only traces of some compounds were

Acknowledgements

The authors thank Mr. Andrew Dodson, Dr. J. Stephen Elmore and Professor Donald Mottram, Department of Food Biosciences, University of Reading, UK for assistance in the GC–MS analysis and the Ministry of Science and Technology, Thailand for the generous financial support through the National Science and Technology Development Agency (NSTDA) grant.

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