Black tea differentiation based on caffeine content using an impedimetric multi-sensor system

Black tea flavor is characterized by the oxidization of tea leaves during the stages of fermentation. The secondary polyphenols are oxidized to form derivative polyphenolic compounds such as thearubigins (12-18%), theaflavins (3-6%) and caffeine (2.5-4.5%). Bitterness in black tea is influenced by caffeine, thus estimating the same could help assess tea quality. The objective of the work is to utilize an impedance based multi-sensor system to differentiate black tea according to its caffeine content. Based on the concept of miniaturization, a printed circuit board (PCB) with four sensing units coupled to a multiplexer and impedance analyzer was utilized for measuring the electrical response from samples. As a reference, caffeine content of the samples was determined using high performance liquid chromatography (HPLC), and the values were expressed in milligrams per liter. The data acquired from the multi-sensor system was processed and analyzed using the chemometrics tool i.e., principal component analysis (PCA). The results indicate that the principal component (PC1 and PC2) from score plot help explain 97.58% of the total variation. The samples with higher caffeine content fell on the positive scores of PC1. Contrastingly, samples with lower caffeine content fell on the negative score of PC1. Plotting the PCA bi-plot, helped visualize the contribution of the four sensors i.e., positively correlating to samples with higher caffeine content and negatively for samples with lower caffeine content. The multi-sensor device, in tandem with chemometrics, could be a reliable and cost-efficient tool for quality control of black tea.