Determination of Hop Alpha-Acids by Semi-Automatic Conductometric Titration

Morgan, K. J.; Rees, T. C.

doi:10.1002/j.2050-0416.1968.tb03146.x

Cited by 4 publications

(1 citation statement)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In order to investigate the impact of the α-acids on the overall antimicrobial activity of the methanol extracts, fractions enriched with these compounds were prepared. A specific reaction of α-acids with a methanolic solution of lead (II) acetate has been described in the literature [2,[31][32][33]. The precipitate was washed with distilled water and centrifuged and dissolved in sulfuric acid.…”

Section: Acquisition Of α-Acid-enriched Fraction (α-Aef)mentioning

confidence: 99%

Anti-Coccal Activity and Composition of the Essential Oils and Methanolic Extracts Obtained from Brewing Quality Humulus lupulus L. Hop Pellets

2023

View full text Add to dashboard Cite

This study examined the chemical composition and anti-coccal properties of essential oils and methanolic extracts of six different Humulus lupulus L. varieties from Poland: Iunga, Marynka, Sybilla, Magnum, Tradition and Chinook. The activity of an α-acid-enriched fraction of methanolic extracts was also studied. The chemical composition of essential oils and extracts was determined by gas chromatography–mass spectrometry (GC/MS) and liquid chromatography–mass spectrometry (LC/MS) techniques. The compounds characteristic to H. lupulus extracts include xanthohumol, α-acids, β-acids, and prenylated flavonoids. Essential oil compositions showed a high prevalence of monoterpene hydrocarbon, myrcene and sesquiterpene hydrocarbons, α-humulene and β-caryophyllene. The antimicrobial activity was investigated against eight human cocci pathogenic strains: Staphylococcus aureus MRSA (ATCC 43300), S. aureus MRSA (29213), S. aureus MSSA (ATCC 29213), S. epidermidis (ATCC 12228), Enterococcus faecalis (ATCC 29212), E. faecalis VRE (ATCC 51299), E. faecium (ATCC 19434) and Micrococcus luteus (ATCC 10240). The lowest minimum inhibitory concentrations (MIC) were obtained for extracts and essential oils from Iunga hop samples. Extracts were significantly more active than essential oils. The most susceptible strain to both essential oils and extracts was M. luteus, whilst the least susceptible was E. faecium. The antimicrobial activity correlated with a high concentration of xanthohumol of active extracts rather than with the content of α-acids. Xanthohumol showed considerable activity against MRSA with an MIC value of 3.9 µg/mL. The activity of the α-acid-enriched fraction was mediocre compared to the results of all extracts.

show abstract

Section: Acquisition Of α-Acid-enriched Fraction (α-Aef)mentioning

confidence: 99%

Anti-Coccal Activity and Composition of the Essential Oils and Methanolic Extracts Obtained from Brewing Quality Humulus lupulus L. Hop Pellets

2023

View full text Add to dashboard Cite

show abstract

ENZYMIC DEGRADATION OF Α-Acids IN HOPS

Menary

Williams

Doe

1983

Journal of the Institute of Brewing

View full text Add to dashboard Cite

Evidence is presented for the biological oxidation of a-acids in hop cones by an enzyme having molecular weight 17,000 daltons, Km 6-0 and Mn as the active metal ion. The enzyme is located in bracts and bracteoles and not in lupulin glands. The presence of an endogenous inhibitor was dem onstrated. The specific activity of protein in hop cones increased with maturity and this was probably associated with release of a-acids from lupulin glands.

show abstract

Some morphological and chemical changes in hops during maturation

Menary

Doe

1983

J Sci Food Agric

View full text Add to dashboard Cite

The surface topography of lupulin glands was studied at various stages of maturity using scanning electron microscopy. Maximum gland filling coincided with maximum alpha-acid concentration and dry matter yield. The percentage of the different components of oil remained constant after maximum gland filling had occurred. Dry matter content of hops at maximum gland filling varied from year to year and was not an accurate guide to optimum harvest date.

show abstract

Determination of Hop Alpha-Acids by Semi-Automatic Conductometric Titration

Abstract: The conductometric method for determination of α‐acids in hops consists of extraction of the hops with organic solvent, followed by conductometric titration of α‐acids in the extract. A method is now described for semi‐automatic conductometric titration of the extracts.

Cited by 4 publications

References 0 publications

Anti-Coccal Activity and Composition of the Essential Oils and Methanolic Extracts Obtained from Brewing Quality Humulus lupulus L. Hop Pellets

Anti-Coccal Activity and Composition of the Essential Oils and Methanolic Extracts Obtained from Brewing Quality Humulus lupulus L. Hop Pellets

ENZYMIC DEGRADATION OF Α-Acids IN HOPS

Some morphological and chemical changes in hops during maturation

Contact Info

Product

Resources

About