Inhibitory Effects of Iso-alpha and beta Hop Acids Against Pediococcus pentosaceus

The goal of the research was to assess the inhibitory effects of hop extracts, iso-alpha and beta acids, against Pediococcus pentosaceus bacteria, during a short incubation period, both in liquid selective media (high pH values) and beer wort fermentation (low pH values) and testing if the identified iso-alpha acid stress changes the activity of S. cerevisiae boulardii yeast and ethanol production. Flow cytometry analysis was used for bacterial and yeast cell viability. In relation to the antibacterial activity of beta-acids, a lower viability of Pediococcus pentosaceus cells was observed after a short incubation period in selective media, under iso-alpha acid stress. In beer wort, for a mixed culture with P. pentosaceus bacteria and S. cerevisiae boulardii yeast, under iso-alpha acid stress conditions at pH 4.0-5.0, Pediococcus pentosaceus exhibited lower cell viability (20.7%) than in selective media (61.4%). Regarding iso-alpha hop acid on S. cerevisiae boulardii yeast, the results showed that iso-alpha does not change the S. cerevisiae activity but prevents the culture from being contaminated by Pediococcus pentosaceus. The results highlighted reliable inhibitory effects of iso-alpha and beta-acids against P. pentosaceus, both at pH 6.0-7.0 and pH 4.0-5.0, which open the possibility of hops being used as a supplement to prevent beverage contamination with spoilage microorganisms.