Changes

Another antimicrobial mechanism resulting from oxidative stress has been attributed to both iso-α-acids and humulinic acids<ref name="Schurr et al, 2015"> [http://www.sciencedirect.com/science/article/pii/S0740002014002470 Schurr et al., (2015)] </ref>. Humulinic acids are either not bitter tasting or much less bitter than iso-α-acids but are similar in structure to and are formed from the degradation of iso-α-acids. This oxidative stress-driven antimicrobial activity is due to potential for oxidation-reduction (redox) reactions within bacterial cells between Mn2+ ions and these specific hop acids. The redox potential is due to different conditions inside (higher pH, higher Mn2+) and outside (lower pH, lower Mn2+) of the bacterial cell<ref name="Behr and Vogel, 2010"> [http://aem.asm.org/content/76/1/142.short Behr and Vogel, (2010)] </ref><ref name="Schurr et al, 2015"/>. Iso-α-acids or humulinic acids passing into the cell, form complexes with Mn2+ and transfer electrons out of the cell<ref name="Behr and Vogel, 2010"/>. By targeted molecular modifications [http://www.sciencedirect.com/science/article/pii/S0740002014002470 Schurr et al. (2015)] determined that the Mn oxidative stress-driven antimicrobial effect of iso-α-acids was more important than antimicrobial effect of the ionophore proton transfer discussed above in the overall antimicrobial activity of hops<ref name="Schurr et al, 2015"/>.

===Bacterial Resistance to Hop Compounds===