Abstract

During the malolactic fermentation of red wines, l-malic acid is mainly converted to l-lactic acid. Both acids should be precisely measured during the entire process to guarantee the quality of the final wine, thus making real-time monitoring approaches of great importance in the winemaking industry. Traditional analytical methods based on laboratory procedures are currently applied and cannot be deployed on-site. In this work, we report on the design and development of a bi-parametric compact analytical flow system integrating two electrochemical biosensors that could be potentially applied in this scenario. The developed flow-system will allow for the first time the simultaneous measurement of both acids in real scenarios at the real-time and in remote way. Miniaturized thin-film platinum four-electrode chips are fabricated on silicon substrates by standard photolithographic techniques and further implemented in a polymeric fluidic structure. This includes a 15 µL flow cell together with the required fluidic channels for sample and reagent fluid management. The four-electrode chip includes counter and pseudo-reference electrodes together with two working electrodes. These are sequentially modified with electropolymerized polypyrrole membranes that entrap the specific receptors for selectively detecting both target analytes. The analytical performance of both biosensors is studied by chronoamperometry, showing a linear range from 5 × 10−6 to 1 × 10−4 M (LOD of 3.2 ± 0.3 × 10−6 M) and from 1 × 10−7 to 1 × 10−6 M (LOD of 6.7 ± 0.2 × 10−8 M) for the l-lactate and the l-malate, respectively. Both biosensors show long-term stability, retaining more than the 90% of their initial sensitivity after more than 30 days, this being a prerequisite for monitoring the whole process of the malolactic fermentation of the red wines (time between 20 and 40 days). The flow system performance is assessed with several wine samples collected during the malolactic fermentation process of three red wines, showing an excellent agreement with the results obtained with the standard method.

Highlights

  • During the malolactic fermentation of red wines, l-malic acid is mainly converted to l-lactic acid

  • Millimetre-sized electrodes show suitable dimensions to work in a compact flow system like the one shown in this work with the electrode distance and electrochemical cell layout being adequate to avoid any electrochemical cross-talk due to the reactions taking place at the counter electrode on the biosensor devices and Ohmic drop

  • The pseudo-reference electrode was placed upstream the biosensors to avoid any potential changes caused by the enzymatic reaction

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Summary

Introduction

During the malolactic fermentation of red wines, l-malic acid is mainly converted to l-lactic acid. The bi-parametric fluidic system was applied to the monitoring of l-lactic and l-malic in samples collected along the MLF process of three different red wines and the results were compared with those recorded with the standard methods.

Results
Conclusion
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