Hop resistance mechanisms in beer-spoilage

Figure 7.3 Complex hop resistance mechanisms in beer-spoilage Lactobacillus brevis. Hop...

The hop resistance mechanisms described above are summarized in Figure 7.3. However, it should be noted that hop resistance mechanisms are more complex than previously assumed. Presumably these multiple layers of defense systems in beer-spoilage LAB have been acquired progressively through centuries of brewing... 

The antimicrobial effect of hop resins is mainly derived from the isomerised alpha-acids. Though beta-acids also have antimicrobial effects, their low solubility means they contribute little to this in beer. The isomerised alpha-acids cause the cell membranes of many Gram-positive bacteria to leak, dissipate the transmembrane pH gradient, deplete the proton motive force, inhibit the uptake of nutrients, deplete divalent cations and cause oxidative stress. However, beer spoilage bacteria have a number of mechanisms to resist these effects. 

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