Development of a Traceability Model for Geographical Origin of Kenya’s Black Teas Based on Principal Component Analysis of FTIR and UV-Vis Spectral Data
Date
2025Author
Waweru, James
Andayi, , Warren Andrew
Mburu, Jane
Kiprotich, Sharon
Kimani, Shadrack
Metadata
Show full item recordAbstract
Authentic tracing of the origins of black tea is important in the tea market as this helps to extrapolate the quality
and thus prices. Tasting on its own can be a misleading test for tea quality and origin tracing since the method
can be compromised by subjectivity of the taster and adulteration. Therefore, there is a need to develop an
analytical chemical method for tracing tea origin that is void of subjectivity. This study presents a traceability
model based on chemical fingerprinting techniques, specifically FTIR and UV-Vis spectroscopy combined with
principal component analysis PCA and heat map analyses that can be applied in distinguishing the geographical
origins of Kenyan black tea. In this study, processed black tea leave samples were collected from seven Kenya
Tea development Authority KTDA, tea factories in tea growing geographical regions in Kenya. The dry black
tea samples were characterized by Fourier transform infrared spectroscopy (FT-IR) at a wavelength range of
400-4000cm-1 whereas the tea aqueous extracts were analysed within 190-600nm range using Ultra violet visible
spectroscopy (UV-vis). The resulting spectral data was subjected to PCA and the heat maps analyses and the
clustering used in model development. The output showed clustering patterns among tea samples based on
similarities in their chemical constituents. The spectral data revealed the presence of phenolic O-H and other OH stretching vibration(3100-3400cm-1
), C-H peak associated with alkane (2850-2950cm-1
, with the asymmetric
and symmetric stretching vibration at 2919cm-1
and 2851cm-1
). The peaks in the range 1590-1620cm-1 were
identified as vibration frequencies of C=O of catechins and flavonoids. The stretching vibration of C-O
associated with carboxylic acids, esters and alcohol was observed at 1032cm-1
. The PCA score plot for the FTIR spectrum showed 82.45% with PC1 (Principal Component 1) contributing 56.15% and PC2 (Principal
Component 2) contributing 26.30%. The tea samples from Kericho, Nyeri, Meru and Vihiga had positive score
in the PC showing greater variation in characteristics. However, teas from Kericho, Meru, Nyeri and Vihiga
exhibited similar characteristics. which were clearly distinct from samples from Bomet, Murang’a, and Kiambu
teas. The intra group variance of samples from Murang’a was low indicating uniformity in the quality. This was
also confirmed using UV-vis spectral data that showed variability index of 0.09 in PC output indicating relatively
low variability compared to neighboring counties. From UV Vis data the samples from Kericho were
predominantly situated at the centre of PC2 axis showing less distinct differences in the chemical properties.
Overall the findings revealed that black tea samples from the same geographical origin clustered together thus
enhancing distinction. The Heat maps from both UV Vis and FT IR data revealed that teas from Vihiga, Nyeri
and Bomet had the lowest levels of phytochemicals and macro elements while those from Meru MERKA, had
the highest levels followed by samples from Kericho, KERTOP and one from Nyeri NYRGA. From the findings,
Meru tea MERKA is a potential standard since has the highest levels of the desired phytochemicals and
macronutrients key to quality and origin tracing
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- Journal Articles (PAS) [301]
