In the master’s thesis, we used acid whey (KS), a by-product of quark production, to formulate four functional whey beverages (FSN). At the company Arhel d.o.o., the KS was microfiltered, pasteurized and fermented with kefir grains (KZ). The product was named spent growth medium (IG). After ultrafiltration of the IG, we got spent growth medium retentate (IGR), which was not further processed and spent growth medium permeate (IGP), which we used as the base for the beverages. The IGP was mixed with bottled water and supplemented with various ingredients. The beverages were pasteurized and filled into pasteurized bottles. The final product was stored for 105 days in the refrigerator, at room temperature in the light and dark. We assessed the antimicrobial activity of the IGP against potentially pathogenic bacteria and the chemical composition of the beverages, which was determined at the Institute for Dairy and Probiotics. We monitored the effect of storage conditions on microbiological stability, which was evaluated by measuring total viable counts, yeasts and molds, Enterobacteriaceae, staphylococci, Salmonella spp. and Listeria monocytogenes, as well as on sensory stability (turbidity, sediment, changes in color, smell and taste). At the beginning and end of the study, we analysed vitamin content and monitored changes in phenolic compounds and antioxidant activity during storage. We found that IGP did not show antimicrobial activity against any of the nine indicator strains included in the study. We found that the stability of the measured parameters changed the most during storage at room temperature with exposure to light and that low temperatures were the most optimal storage condition.
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