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Title: Quality evaluation of Terpinen-4-ol type Australian Tea Tree oils and commercial products: An integrated approach using conventional and chiral GC/MS combined with chemometrics

Author
item WANG, MEI - University Of Mississippi
item ZHAO, JIANPING - University Of Mississippi
item AVULA, BHARATHI - University Of Mississippi
item WANG, YAN-HONG - University Of Mississippi
item CHITTIBOYINA, AMAR - University Of Mississippi
item PARCHER, JON - University Of Mississippi
item KHAN, IKHLAS - University Of Mississippi

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2015
Publication Date: 2/28/2015
Publication URL: https://handle.nal.usda.gov/10113/62321
Citation: Wang, M., Zhao, J., Avula, B., Wang, Y., Chittiboyina, A.G., Parcher, J.F., Khan, I.A. 2015. Quality evaluation of Terpinen-4-ol type Australian Tea Tree oils and commercial products: An integrated approach using conventional and chiral GC/MS combined with chemometrics. Journal of Agricultural and Food Chemistry. 63:2674-2682.

Interpretive Summary: This investigation was initiated at the request of the Australian Tea Tree Industry Association (ATTIA) to develop new analytical methods for the detection of substandard, adulterated, or otherwise unacceptable commercial products claiming to contain Australian tea tree oils. Over 100 samples were provided to give a comprehensive data set. ATTIA was concerned because tea tree oils are a significant agricultural product and represent a significant commercial investment for the manufacturers and growers in Australia. The submitted manuscript describes a series of analytical methods, viz., conventional GC/MS, chiral GC/MS, and chemometrics, that were used to investigate 104 samples of known provenance pure Australian tea tree oils (57) along with a variety of commercial products purported to contain tea tree oils (47). Classical GC/MS methods were used to detect samples that did not meet the standards set by ISO-4730-2004. The chiral GCMS results are original and supplement the GC data with new standards for the enantiomeric ratio (+)/(-) of four probe solutes observed in tea tree oil samples. For the first time, chemometric analyses were used to correlate the outlier samples discovered by the two chromatographic techniques.

Technical Abstract: Conventional GC/MS, chiral GC/MS and chemometric techniques were used to evaluate a large set of tea tree oils (TTO) and commercial products purported to contain tea tree oils. Fifty-seven known provenance pure Australian tea tree oils and forty-seven commercial TTO products were investigated. Twenty components (monoterpenes, sesquiterpenes along with associated alcohols and ethers) were determined in each sample and compared with the standards specified by ISO-4730-2004. Several of the oil samples that were ISO compliant when distilled did not meet the ISO standards primarily due to the presence of excessive p-cymene and/or depletion of terpinenes. This variation was possibly due to auto-oxidation of the oil samples. Twenty-five of the commercial samples (excluding 2 synthetics) did not meet the ISO standards. Every terpene was present at levels outside the ISO standards for at least one sample for these twenty-five commercial samples. In summary, 48% of the commercial products did not meet the ISO specifications for commercially-produced tea tree oil products. Four chiral components, viz., a-pinene, limonene, terpinen-4-ol and a-terpineol, present in tea tree oils with the (+) isomer predominant were measured by chiral GC/MS. The results clearly indicated that 28 commercial products contained excessive (+) isomer or contained the (+) isomer in concentrations below the norm of the known provenance tea tree oils data set. Of the 28 outliers determined by chiral analysis, 8 met the ISO standards. So there was a substantial subset of commercial products that met ISO standards but displayed unusual enantiomeric (+)/(-) ratios. In order to determine if the abnormal chiral distribution was an indicator of substandard tea tree oils products, chemometric analysis was used for the conventional GC/MS data. A class predictive model based on the oils samples that met ISO standards was constructed, validated and used to evaluate the remainder of the samples in the tea tree oil data set. The outliers identified by the class predictive model coincided with the samples that displayed an abnormal chiral ratio for chiral analysis. Thus, the two tests, i.e., chiral and chemometric analysis, could be used to confirm the identification of substandard commercial products including those that met all of the ISO standards.