Chemometrics and essential oil analysis: Chemical polymorphism in two Thymus species

Application of chemometrics in authentication of herbal medicines: a review

INTRODUCTION

Herbal medicines (HM) and their preparations have been widely used for hundreds of years all over the world. However, they have not been officially recognised due to a lack of adequate or accepted research methodology for their evaluation.

OBJECTIVE

To present a concise overview of the recent applications of chemometrics in solving the ambiguity of herbal medicine authentication during the last two decades.

METHODOLOGY

Studies involving the applications of chemometric analysis in combination with different analytical methods were classified according to the method of analysis used including chromatographic (HPLC, GC and CE), spectroscopic (NMR, IR, UV and ICP) and genetic analysis (RAPD). The purpose of each of these studies was classified into one of three main categories: taxonomic discrimination, quality assessment or classification between plants of different geographic origins.

RESULTS

This review comprises over 150 studies, covering the past two decades, emphasising the significance of chemometric methods in the discrimination of many herbs from closely related species and from adulterants, based on the principal bioactive components and phytochemical diversity. Furthermore, the differentiation between varieties and hybrids was achieved in addition to the prediction of the active components by quantitative methods of analysis. Discrimination according to geographical origin and localities, processing methods, DNA profiling and metabolomics were also efficiently investigated.

CONCLUSION

Chemometric methods have provided an efficient and powerful tool for the quality control and authentication of different herbs.

Antimicrobial activity of essential oils isolated from Portuguese endemic species of Thymus

AIMS

Thymus species are wild species mostly found in the arid lands of Portugal. Possible antimicrobial properties of Thymus essential oils have been investigated. The chemical composition of the essential oils and the antimicrobial activity of Thymus mastichina (L) L. subsp. mastichina, T. camphoratus and T. lotocephalus from different regions of Portugal were analysed.

METHODS AND RESULTS

Hydrodistillation was used to isolate the essential oils and the chemical analyses were performed by gas chromatography (GC) and GC coupled to mass spectrometry. The antimicrobial activity was tested by the disc agar diffusion technique against Candida albicans, Escherichia coli, Listeria monocytogenes, Proteus mirabilis, Salmonella spp. and Staphylococcus aureus. Pure linalool, 1,8-cineole and a mixture (1 : 1) of these compounds were included. Linalool, 1,8-cineole or linalool/1,8-cineole and linalool/1,8-cineole/linalyl acetate were the major components of the essential oils, depending on the species or sampling place. The essential oils isolated from the Thymus species studied demonstrated antimicrobial activity but the micro-organisms tested had significantly different sensitivities.

CONCLUSIONS

The antimicrobial activity of essential oils may be related to more than one component.

SIGNIFICANCE AND IMPACT OF THE STUDY

Portuguese endemic species of Thymus can be used for essential oil production for food spoilage control, cosmetics and pharmaceutical use. Further studies will be required to elucidate the cell targets of the essential oil components.

Genetic diversity of Ocimum gratissimum L. based on volatile oil constituents, flavonoids and RAPD markers

Morphological, chemical and genetic differences of 12 tree basil (Ocimum gratissimum L.) accessions were studied to determine whether volatile oils and flavonoids can be used as taxonomical markers and to examine the relationship between RAPDs to these chemical markers. Eugenol, thymol, and geraniol were the major volatile oil constituents found in Ocimum gratissimum. Xantomicrol and cirsimaritin were the major external flavones. The accessions morphologically described as O. gratissimum var. gratissimum contained eugenol as the major volatile oil constituent, and cirsimaritin as the major flavone. Ocimum gratissimum var. macrophyllum accessions contained thymol as the major volatile oil constituent, and xantomicrol as the major flavone. A distinct essential oil and flavone chemotype (producing geraniol and a mixture of the flavones cirsimaritin, isothymusin, xanthomicrol, and luteolin) was found in an accession genetically more distant from the other two groups when analyzed by molecular markers. The accessions could be divided based on volatile oil constituents into six groups: (1) thymol: alpha-copaene (ot24, ot25, ot26, and ot28); (2) eugenol:spathulenol (ot17, ot63, and ot52); (3) thymol:p-cymene (ot65); (4) eugenol:gamma-muurolene (ot27 and ot29); (5) eugenol:thymol: spathulenol (ot85); and (6) geraniol (ot84). Cluster analysis of RAPD markers showed that there are three groups that are distinct genetically and highly correlated (r=0.814) to volatile oil constituents.