Though chemical changes can be detected at 15 seconds, the first 30 seconds of infusion were found to be responsible for the majority of the chemical changes on the surface. Peaks associated with octadecenoic and octadecanoic acids were shown to have a reproducible effect on the positioning of the different infusion times within the PCA plots. The intensity of C3H5O2+ peaks in the spectra increased as infusion time increased, indicating that the waxy cuticle of the leaf surface had been removed revealing the underlying epidermal cell layer. By examining positive and negative ToF-SIMS spectra and using PCA, a change in surface chemistry could be detected from 15 seconds of infusion. SEM revealed structural damage to the leaves from 30 seconds of infusion and this increased with infusion time, resulting in the formation of holes in the cutin on the adaxial surface of the tea leaf. In Chapter 4 the effects of infusion in hot water on the morphology and surface chemistry of the tea leaves are examined. The presence of lipids and epicuticular waxes were observed on the surface of the tea leaves using the ToF-SIMS. SEM images revealed a visual difference between green and black tea leaves, where the black tea leaves had more debris on the surface and greater changes in topography due to the different processing methods. Further experimentation was performed on tea leaves by the addition of diluted samples of aromas, methyl salicylate, trans-2-hexenal and linalool and examining these leaves using depth profiling to discover how far into the leaf the aroma had penetrated and if there was any connection between the chemistry and size of the aromas and how far they penetrated.Ī general characterisation of the tea leaves was performed in Chapter 3 where layers of waxes of a comparable size were observed on both green and black tea leaves with AFM, as were micro-crystals on black tea and areas showing two distinct types of interaction between the cantilever tip and the surface of a green tea leaf indicating different surface properties. Data from the spectra obtained by ToF-SIMS was also analysed using principal component analysis (PCA). The aims of this project were to investigate the surface chemistry and morphology of processed tea leaves the techniques of atomic force microscopy (AFM), scanning electron microscopy (SEM) and time of flight secondary ion mass spectrometry (ToF-SIMS). Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader
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