Simultaneous Quantification of Alcoholic Content and Acidity in Brazilian Commercial Kombuchas by FTIR Spectroscopy...

The growth of the global kombucha market highlights the importance of quality control in production, a crucial factor to ensure consumer safety, regulatory compliance, and product consistency. This study aimed to develop and validate rapid, direct multivariate methods based on Fourier transform infrared (FTIR) spectroscopy combined with partial least squares (PLS) regression to simultaneously quantify alcohol content and acidity. The method requires minimal sample preparation, with no need for extraction or derivatization, allowing spectral acquisition in about 30 s-ideal for high-throughput analysis and aligned with green chemistry principles. Infrared spectra were recorded in the range of 4000-650 cm⁻¹. Reference values were obtained by gas chromatography with flame ionization detection (GC-FID), following validated protocols. Thirty kombucha brands from different regions of Brazil were analyzed, all labeled with an alcohol content of up to 0.5% v/v. However, 60% of the samples exceeded this limit, with levels ranging from 0.10% to 1.70% v/v. Acidity ranged from 17 to 71 mEq/L, with only 50% of the samples meeting the recommended specifications (30-130 mEq/L). The PLS model showed RMSEC and RMSEP values of 0.09% and 0.07% v/v for alcohol, and 3.2 and 3.9 mEq/L for acidity, respectively. Metrics such as precision, bias, and RPD > 2.4 confirmed the robustness of the models. The results reveal discrepancies between declared and measured values, especially for alcohol content, emphasizing the need for stricter regulatory oversight. The method is reliable, efficient, and suitable for routine analyses and regulatory monitoring. PRACTICAL APPLICATIONS: The FTIR-PLS method developed in this study offers a rapid, accurate, and environmentally friendly alternative for routine monitoring of alcohol content and acidity in kombucha. Its application facilitates verification of regulatory compliance and strengthens quality control in the beverage industry, contributing to consumer safety. Moreover, the method can be adopted by regulatory agencies and producers to ensure the conformity of products available on the market.