Effect of pH on potassium metabisulphite biocidic activity against yeast and human cell cultures

Potassium metabisulphite (PMB) is a common antimicrobial additive in the food industry. In aqueous solutions, PMB leads to complex equilibria according to its concentration, pH and temperature, and different chemical species can be present. In winemaking, PMB is used at low pH, suggesting that the biocidic activity is exerted by sulphur dioxide while, in other applications, it is employed at higher pH values with little if any dissociation. This observation leads to the question of which chemical form is biologically active. For this reason, Saccharomyces cerevisiae cells were subjected to PMB solutions at different pH values and analysed with a Fourier transform infrared spectroscopy (FTIR)-based bioassay, to assess the entity and the type of stress. Cell viability was determined and compared to the metabolomics (FTIR) stress indices, which revealed that the metabolomics fingerprint was an effective description of the cell health state. GC–MS metabolite profiles were obtained to describe (in detail) the changes caused by PMB in the fatty acids region. Human dermal fibroblasts (HDF) were also subjected to PMB stress at pH 7.0 and analysed with the FTIR protocol, in order to compare the response spectra of yeast and human cell cultures.