Indicador colorimétrico natural para avaliação do desempenho da fermentação de kombucha: aplicação de antocianinas de Phaseolus vulgaris L. (feijão preto)

Abstract

The growing demand for safe, high quality food has driven the development of technologies for monitoring critical parameters during food processing, especially in fermentation, where even small variations can compromise product yield and quality. Among these parameters, pH stands out for its importance in controlling the fermentation process. However, conventional methods for determining pH require equipment that demands maintenance, periodic calibration, and higher operating costs, which can limit their use by small-scale producers and in home-based preparations. In this context, natural anthocyanin-based indicators represent a promising alternative, as they change color in response to pH and are non-toxic, renewable, and readily available. Thus, the objective of this study was to develop a colorimetric pH indicator using anthocyanins extracted from Phaseolus vulgaris L. (black beans), incorporated into filter paper, for monitoring pH during the kombucha fermentation process. To this end, a colorimetric scale was developed in solution and on filter paper, followed by the application of the indicator at the start of fermentation, after seven days, and at the end of fifteen days. The pH values determined by a pH meter during the fermentation process were 4.4, 3.0, and 2.5, respectively. The indicator exhibited color changes consistent with the developed scale, both to the naked eye and after digital image processing, as well as with the instrumentally obtained values, demonstrating its ability to track pH changes during fermentation. Although the indicator cannot distinguish pH values below 2.7, this limitation does not compromise its application for monitoring kombucha fermentation, since the pH range considered suitable for consumption, according to Normative Instruction No. 41 of September 17, 2019, is between 2.5 and 4.2. Thus, the developed indicator shows potential as a practical, low cost, and easy to use alternative for monitoring pH in small scale production and homemade preparations, and can complement conventional instrumental methods.