title: Degradation of spent craft brewer's yeast by caprine rumen hyper ammonia-producing bacteria.
abstract: Spent yeast from craft beers often includes more hops (Humulus lupulus L.) secondary metabolites than traditional recipes. These compounds include α- and β- acids, which are antimicrobial to the rumen hyper ammonia-producing bacteria (HAB) that are major contributors to amino acid degradation. The objective was to determine if the hops acids in spent craft brewer's yeast (CY; ~ 3·5 mg g(-1) hops acids) would protect it from degradation by caprine rumen bacteria and HAB when compared to a baker's yeast (BY; no hops acids). Cell suspensions were prepared by harvesting rumen fluid from fistulated goats, straining and differential centrifugation. The cells were re-suspended in media with BY or CY. After 24 h (39°C), HAB were enumerated and ammonia was measured. Fewer HAB and less ammonia was produced from CY than from BY. Pure culture experiments were conducted with Peptostreptococcus anaerobiusBG1 (caprine HAB). Ammonia production by BG1 from BY was greater than from CY. Ammonia production was greater when exogenous amino acids were included, but similar inhibition was observed in CY treatments. These results indicate that rumen micro-organisms deaminated the amino acids in CY to a lesser degree than BY.
  
  
  CONCLUSIONS
  Spent brewer's yeast has long been included in ruminant diets as a protein supplement. However, modern craft beers often include more hops (Humulus lupulus L.) than traditional recipes. These compounds include α- and β- acids, which are antimicrobial to the rumen hyper ammonia-producing bacteria (HAB) that are major contributors to amino acid degradation. This study demonstrated that hops acids in spent craft brewer's yeast protected protein from destruction by HABin vitro. These results suggest that the spent yeast from craft breweries, a source of beneficial hops secondary metabolites, could have value as rumen-protected protein.
authors.affiliation: Department of Animal and Food Sciences, University of Kentucky, Lexington, KY, USA.
authors.forename: B E
authors.initials: BE
authors.lastname: Harlow
authors.affiliation: Asheville Flavor Innovations, LLC, Asheville, NC, USA.
authors.forename: R W
authors.initials: RW
authors.lastname: Bryant
authors.affiliation: Fermentation Sciences, Appalachian State University, Boone, NC, USA.
authors.forename: S D
authors.initials: SD
authors.lastname: Cohen
authors.affiliation: Department of Biology, Western Carolina University, Cullowhee, NC, USA.
authors.forename: S P
authors.initials: SP
authors.lastname: O'Connell
authors.affiliation: Department of Animal and Food Sciences, University of Kentucky, Lexington, KY, USA. michael.flythe@ars.usda.gov.|Agricultural Research Service, Forage-Animal Production Research Unit, USDA, Lexington, KY, USA. michael.flythe@ars.usda.gov.
authors.forename: M D
authors.identifier: http://orcid.org/0000-0002-8868-9169
authors.initials: MD
authors.lastname: Flythe
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D001515:Beer / Q000382:microbiology*; D003641:Deamination / Q000502:physiology; D004032:Diet; D006041:Goats; D027582:Humulus / Q000737:chemistry*; D010462:Peptostreptococcus / Q000378:metabolism*; D010936:Plant Extracts / Q000494:pharmacology*; D012417:Rumen / Q000382:microbiology*; D012418:Ruminants; D012441:Saccharomyces cerevisiae / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D000890:Anti-Infective Agents; D010936:Plant Extracts; D000641:Ammonia
keywords: brewer's yeast; bypass protein; goat; hops; micro-organism; phyto-ionophore; ruminant