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Analysis of volatiles from the New Zealand scented plant - Mairehau (Leionema nudum)
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New Zealand native scented plants may possess potential industry value as perfume ingredients. To provide the overall impression of New Zealand scented plant resource and to guide the future researches in this area, this submission begins with a literature review on chemical and sensory studies of several commonly found New Zealand scented plants. A New Zealand scented plant, mairehau (Leionema nudum) was chosen for compositional analysis of volatiles. First, during the 15 days natural dehydration after cutting from plants, mairehau twigs decreased in weight, but increased in the number of volatile compounds and their concentration. A negative linear regression with R2=75.2% was observed between twigs weight and the number of volatile compounds. It was found that the metabolic change significantly altered the volatile characteristics from day 5 to day 9 during natural dehydration. The total 71 volatile compounds were grouped into 5 clusters in multivariate analysis according to their similarity in behaviour during 15 days of natural dehydration. For comparison between volatiles from different mairehau parts, a total of 33 (3 unidentified) and 37 (4 unidentified) compounds were found in samples of fresh mairehau twigs and mairehau flowers, respectively, and there were 15 compounds found in both. For the volatiles of homogenized mairehau samples, there were 99 and 92 compounds found in fresh samples and dry samples, with 73 and 55 compounds identified, respectively. Adding liquid Nitrogen during homogenization of fresh mairehau would give the volatiles a different dynamic status from those prepared under room condition; however, the number of volatile compounds did not significantly vary. The volatiles were sampled by SPME. In this study, the 100 µm PDMS fibre showed the best reproducibility and was chosen for the experiment. The regression models of adsorption amount on fibre predicted by adsorption time (at 25°C and 35°C) agreed with the theoretic ones. In addition, increasing the adsorption temperature from 25°C to 35°C would promote the adsorption amount on the fibre. GC-MS and NIST MS Database similarity searching were used for the qualitative and quantitative analysis of mairehau volatile compounds. To overcome the peak overlapping problem in GC-MS and improve the accuracy of the results, a chemometric algorithm, MCR-ALS coupled with EFA was applied. The algorithm showed a better efficiency in volatile samples with low complexity. The whole algorithm was successfully coded and ran in R software, suggesting this open-source software was capable for carrying out chemometric process, as well as MATLAB (a mathematic tool that most of publications used for carrying out chemometrics). R scripts were supplied in appendixes of this submission, providing a good reference to those who want to apply this technique with R software, in processing their GC-MS data.