title: Importance of tetrahydroiso alpha-acids to the microbiological stability of beer.
abstract: While beer provides a very stable microbiological environment, a few niche microorganisms are capable of growth in malt, wort, and beer. The production of off-flavors and development of turbidity in the packaged product are due to the growth and metabolic activity of wild yeast, certain lactic acid bacteria (LAB) and anaerobic Gram-negative bacteria. Beer also contains bitter hop compounds, which are toxic to Gram-positive and Gram-negative bacteria, and contribute to preventing the spoilage of this beverage. In the boiling process, the hop alpha-acids (humulones) are isomerized into iso alpha-acids. These products are responsible for the bitter taste of beer, but they also play an essential role in enhancing foam stability. Antibacterial activity of iso alpha-acids and their hydrogenated derivates (rhoiso alpha-acids and tetrahydroiso alpha-acids) in MRS broth and beer have been evaluated against different LAB (Lactobacillus and Pediococcus) for the determination of their beer-stabilizing capabilities. Besides this, we have determined the minimum inhibitory concentration and the bacteriostatic effect of each compound against Pediococcus. We found that tetrahydroiso alpha-acids (added directly to beer during production processes) are the compounds that present the greatest antibacterial activity against the main agents implicated in beer spoilage.
authors.affiliation: Universidad de Valladolid, Dpto. Ingeniería Agrícola y Forestal, Area de Tecnologia de los Alimentos, E.T.S. Ingeniarías Agrarias, 34004 Palencia, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Caballero
authors.forename: Montserrat
authors.initials: M
authors.lastname: Agut
authors.forename: Alicia
authors.initials: A
authors.lastname: Armentia
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Blanco
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000494:pharmacology*; D001515:Beer / Q000382:microbiology*; D002264:Carboxylic Acids / Q000737:chemistry* / Q000494:pharmacology*; D003470:Culture Media; D027582:Humulus / Q000737:chemistry*; D007778:Lactobacillus / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D010376:Pediococcus / Q000187:drug effects*
chemical_list: D000900:Anti-Bacterial Agents; D002264:Carboxylic Acids; D003470:Culture Media