Chemometric differentiation of coffee varieties using gas sensors based on polymer-modified piezoelectric quartz crystals
Coffee is the most popular beverage worldwide, enjoyed primarily because of its aroma and flavor. Aroma is commonly used as the basis of coffee quality, and its evaluation is usually carried out by an expert sensory panel. Coffee aroma can also be assessed by means of an electronic nose. The electronic nose generates an electrical signal in the presence of the substances causing the aroma.
This study aimed to apply a self-assembled electronic nose system for the discrimination of the different varieties of coffee in the Philippines. Samples of the four varieties of coffee grown in the Philippines, i.e. Arabica, Robusta, Excelsa, and Liberica, were obtained from several regions in the country. The electronic nose system that was employed was based on six piezoelectric quartz crystals coated (PQC) with sensing elements of different polarities [polyethylene glycol (PEG), polyvinyl chloride (PVC), polymethylacrylate (PMAA), Fluorosil (PVC:Fluor), Silica (PVC:Silica) and Cat-Ex (PVC:CatEx)]. The following parameters involved in the measurement were optimized: weight of sample, flow rate of carrier gas, sample holder, fineness of sample, thickness of sensing elements and incubation time. Distinct radar plot quality profiles were obtained for the different varieties. Chemometric analysis of the responses of the electronic nose were carried out using principal component analysis (PCA) and dendogram cluster analysis. The developed group of sensors was able to categorize the different coffee varieties.