Headspace measurement of dimethyl sulfide in beer through paper-based smartphone-colorimetry

Abstract

Beer ranks among the most popular and most widely consumed beverages globally. During its production through brewing and fermentation, its natural characteristic style and inherent flavors are produced. Dimethyl sulfide (DMS) contributes significantly to the flavor profile of beer. Its presence is desirable at low concentration levels. However, it becomes an off-flavor at high concentrations. The concentration of DMS in beer was measured through smartphone-based colorimetry. A paper-based analytical device (PAD) was fabricated by immobilizing a chromogenic reagent phase consisting of alkaline nitroprusside in a gelatin hydrogel. Headspace sampling and subsequent reaction with the immobilized reagent enabled the detection of low levels of DMS. By capturing the digital image of the PAD, the concentration was determined by utilizing the RGB color value. A linear behavior was observed in the Green color value (G value) in the concentration range with 5 to 120 μg DMS L^-1, with a Pearson coefficient of 0.995 and limit of detection was 2.7 μg L^-1. High precision and accuracy were demonstrated, with RSD ranging from 0.79 to 1.36 % (n = 6) and trueness values between 92.5 and 104.4%, respectively which also satisfied AOAC requirements for low levels of analyte. The results of smartphone-based colorimetry agreed well with the results of chromatographic analysis of DMS in lager and all-malt beer samples. This method is an inexpensive alternative to the gas chromatography method for DMS measurement and will allow small-scale brewers and craft beer producers to monitor off-flavor in their products.

Keywords: Beer; Digital imaging colorimetry; Dimethyl sulfide; Headspace measurement; Paper-based analytical device; Smart-phone based colorimetry.