Flow-based titration with a colorimetric detection box using a smartphone for the determination of titratable acidity in coffee

Abstract

Acidity is one of the key components for coffee quality which could be determined by titration. However, the endpoint observation with bare eyes might give error because of the dark color of coffee. Although this problem could be solved by using a pH meter, the calibration and maintenance processes including the cost of the device may be the drawbacks. In this research, a digital image colorimetric detection system was established with economic devices. The caption of image was carried out by a smartphone under the control of light intensity and focus range in a homemade detection box to assess the primitive color (red/green/blue or RGB) data from the color change of an acid-base indicator. In addition, to make process more comfortable and reduce the detection time, the flow-based technique was also applied to the setup for the signal monitoring process. The method was highly reproducible with %RSD less than 1 (n = 11) and detection time of 24 s was achieved. From the analyses of roasted coffee beans, the results obtained agreed well with those from the potentiometric standard method.