The presence of lactic acid in beer is essential in a certain amount to afford acidity and lactic aromas so it is usually introduced to the wort on purpose. Although lactic acid usually appears as the result of controlled bacteria fermentation, its amount in excess it is considered a defect because it can also appear as result of an infection. Controlling the level of lactic acid is essential not only for the purpose to offer a certain organoleptic properties but to monitor fermentation processes and control food quality/safety. In both cases, miniaturized, portable, low-cost and simple fast-response devices are required which fit perfectly with the use of screen-printing electrodes and miniaturized instruments.

In this publication, a commercial enzymatic sensor based on a Screen-Printed Electrode (Ref. DRP-LACT10) is used to measure this analyte in commercial beers as a proof of concept to its potential application in fermentation monitoring. Determination is based on the detection via mediator of hydrogen peroxide produced by the enzymatic reaction that occurs onto the working electrode. With a sample of 50 µL, this analyte is measured in a range of 0 to 0.4 mM in less than 75 s with an amperometric detection at -0.1 V.

Four different types of beers from a local brewery (Cotoya) were selected to test the availability of these sensors when applied in real samples. To avoid matrix effects, a dilution of 1:10 were made with each beer in Tris-NO₃ 0,1M pH 7,2 aqueous solution before measuring where lactic acid is found as lactate. To validate data obtained, a commercial L-Lactate Assay kit was used. Optical experiments show similar data obtained demonstrating the viability to detect lactate in beer with a portable device without the requirements of complex pretreatments or the use of non-portable optical devices.

In combination to the electrochemical sensing platform, a novel portable potentiostat transducer it is also introduced. DRP-DROPSTATPLUS is a portable user-friendly interface where lactic acid value of the sample can be easily view on its LCD display. This portable equipment is compact and handy and can monitor lactic acid in situ when inserted DRP-LACT10 in its three-electrode connector. Thanks to its small size and its portability, its combination with the lactate biosensor offers a winner combo to acquire in-situ measurement in industrial or household breweries with a simple low-cost setup easy to operate.

Daniel Antuna-Jimenez

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