The use of glass electrodes in food industry is the standard for pH and acidity levels determination in direct samples, being the dairy industry one of the most important sectors linked. It is known that the glass electrodes becomes fouled due to protein and lipid adsorption on the electrode surface and their brittle nature; so, it has made necessary to look for other kind of ion selective electrode in order to determine the [H<sup>+</sup>] in aqueous solution. For this work, solid-state sensors based on tungsten oxides were designed, built and characterized. The electrodes were anodized using an optimized methodology in a controlled aqueous media. Some of them were coated with Nafion®, with the purpose to protect the pH sensible film. The performance of these electrodes was evaluated in terms of their sensibility in the process of calibration using controlled buffer solution. The response of the electrodes in presence of potassium and sodium as interference ions was determined.<br/>The procedures used to determine the acidity in milk were based on the Mexican standards NOM-155-SCFI-2003 (analysis of direct samples) and NOM-155-SCFI-2012 (analysis of diluted samples). To get the equivalence point during the acid-base titration, diverse methodologies were used, and those different values of acidity obtained are attributable to the fouling of glass electrodes in the characteristic of the samples. Typical acid-base titrations shown several problems, as difficulty to see the change of color in the pH indicator. The Gunnar Gran functions (using the data obtained from tungsten sensors) gave the most repeatable and trustworthy results and a similar parameter to an acid dissociation constant was obtained in the milk titrations, which is attributed to the caseins. Such fact was later confirmed with the ones obtained from the titration of pure casein. Finally, in the titration of yogurt, the contribution of acidity given by the caseins and the one given by the lactic acid, formed in the fermentation process of yogurt, can be differentiated using G. Gran functions.<br/>

Construction and characterization of solid-state sensors based on tungsten oxides used for the determination of acidity in dairy samples

256th National Meeting (2018)

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