Predicting tea tree oil distillate composition using portable spectrometric technology

Abstract

Commercial tea tree oil (TTO) has to conform chemically to the international standard ISO4730: 2017, which defines acceptable ranges for the 15 main terpenoids therein. Lack of in‐house capacity for the technology typically required for terpenoid quantification (GC‐FID) necessitates that Australian TTO producers outsource the analyses to commercial service providers. This is associated with high cost and slow turnaround times, which have been recognized as limiting factors for TTO process optimization in the areas of quality assurance, distillation and blending. This paper describes the testing of two custom portable Raman devices with different lasers (785 and 1064 nm) for the relative quantification of the 15 main TTO components using model‐based predictions. Initial testing showed that the 1064‐nm device provided superior data for TTO predictions. Machine‐learning algorithms were trained with spectral data from the 1064‐nm device and corresponding GC‐FID data from 214 TTO samples. Hold‐over validation (HV) correlations between actual and predicted values using up to 53 unseen samples showed r2 at or above 0.92 for 10 and at or above 0.95 for 6 of the 15 specified terpenoids. The highly abundant key TTO quality compound terpinen‐4‐ol showed an HV r2 of 0.96 with a root mean square error (RMSE) of 0.37%, whereas the lowly abundant key compound 1,8‐cineole showed an HV r2 of 1.00 with a RMSE of 0.13%. These results indicated a strong potential for Raman spectrometry to provide real‐time product quality data at TTO distillation sites enabling direct feedback control and process optimisations.

Tea Tree Oil: Properties and the Therapeutic Approach to Acne—A Review

“…There are six oil chemotypes in M. alternifolia identified by the presence of distinct percentages of terpinen-4-ol, 1,8-cineole, and terpinelone: terpinen-4-ol chemotype containing 30 to 40% of this monoterpenoid (used in commercial TTO production); terpinolene chemotype; 1,8-cineole chemotype; and three chemotypes all dominated by 1,8-cineole but differing in either terpinen-4-ol or terpinolene content [ 30 , 35 ] According to the International Standard Organization (ISO 4730:2017) [ 36 ], TTO must have a minimum terpinen-4-ol content of 35% and a maximum 1,8-cineole content of 10%, nevertheless market prefers a TTO with the highest terpinen-4-ol (higher than 38%) and the lowest 1,8-cineole content (less than 3%) possible [ 36 , 37 , 38 ]. Ten monoterpene/monoterpenoids and five sesquiterpene/sesquiterpenoids can be found in TTO ( Figure 4 ).…”

“… Chemical structures of the monoterpene/monoterpenoids and sesquiterpene/sesquiterpenoids present in the TTO and their concentrations in percentages [ 37 ]. …”