Comparative analysis of four hop cultivars grown in Brazil and the USA by GC-MS-based metabolomics

2024-11-06T02:47:32-08:00

Why was the work done: Although the third largest beer producer in the world, Brazil currently imports the majority of its hops. A recent development is the cultivation of hops (Humulus lupulus L.) in Brazil. In addition to genetic factors, the chemical composition of hops can exhibit variations due to conditions of cultivation. Accordingly, it is of value to characterise and differentiate hop cultivars grown in Brazil with the same cultivars grown in a long established location such as the United States of America.

How was the work done: Centennial, Chinook, Columbus, and Nugget cultivars grown in Brazil or in the USA were compared by metabolomic analyses of the chemical profiles using gas chromatography coupled to mass spectrometry. Principal component analysis showed sample grouping according to where the hops were grown. Partial Least Squares Discriminant Analysis allowed the characterisation of the main metabolites that discriminated hop samples from the two countries. A total of 31 metabolites were putatively identified, including monoterpenes, sesquiterpenes, oxygenated mono- and sesquiterpenes, esters, alcohols, and ketones.

What are the main findings: There were clear metabolic differences between the same hop varieties grown in Brazil or the USA. The metabolites with the greatest discriminating power for Brazilian hops were trans-α-bergamotene, 2-decanone, and ι-gurjunene, while American hops presented β-copaene, humuladienone, and isopentyl isobutyrate. Notably, trans-α-bergamotene was present in Brazilian hops but absent from American hops.

Why is the work important: This study sheds light on the differences in the chemical composition of hops cultivated in Brazil compared those cultivated in the USA. This knowledge may stimulate new producers and contribute to the development of hop cultivation in Brazil.

Survival of Escherichia coli O157, Salmonella Enteritidis, Bacillus cereus and Clostridium botulinum in non-alcoholic beers

2024-10-17T01:19:52-07:00

Why was the work done: To (i) determine whether microbial pathogens were present in packaged alcohol-free and low alcohol beers, (ii) to assess whether pathogens can survive or grow in non-alcoholic beers, and (iii) to determine the impact of pH and bitterness on their growth and survival of pathogens in alcohol-free beer.

How was the work done: : 50 alcohol-free and low alcohol beers, available in the UK, were screened for pathogens and analysed for ABV, pH and bitterness (IBU). One of the alcohol-free beers (with the lowest IBU) was adjusted to 25 and 50 IBU and pH 3.8, 4.2, 4.6 and 4.9. Challenge testing of these beers was performed with Escherichia coli O157, Salmonella Enteritidis, Bacillus cereus and Clostridium botulinum. In addition, the heat resistance (D₆₀ value) of the pathogens, spoilage bacteria and Saccharomyces cerevisiae ascospores in these beers was determined.

What are the main findings: Salmonella, E. coli, Enterobacteriaceae, Bacillus cereus and sulphite reducing clostridia were not found in any of the 50 beers. However, two emerging opportunistic pathogens (Cupriavidus gilardii and Sphingomonas paucimobilis) were found in the low alcohol keg beers. None of the pathogens used in this study could grow in the alcohol-free beer at low pH (pH 3.8). E. coli O157 was unable to grow at pH 4.2 but could grow at pH 4.6 but only with reduced levels of carbon dioxide and increased oxygen. Salmonella Enteritidis was able to grow at pH 4.2 and 4.6 but also with reduced levels of CO₂ and increased O₂. Although Bacillus cereus and C. botulinum were unable to grow in any of the tested conditions, both pathogens were able to survive. Survival and/or growth of the microorganisms was impacted by pH; bitterness had no effect.

Why is the work important: Salmonella Enteritidis and E. coli O157 only grew in alcohol free beer at a higher pH (4.2 and 4.6 for Salmonella and 4.6 for E. coli) together with with reduced levels of CO₂ and increased O₂. This suggests that packaged beer with appreciable levels of carbon dioxide and negligible levels of oxygen will not support the growth of pathogens. However, draught alcohol free beer may be vulnerable to pathogens.

Journal of the Institute of Brewing

Comparative analysis of four hop cultivars grown in Brazil and the USA by GC-MS-based metabolomics

Survival of Escherichia coli O157, Salmonella Enteritidis, Bacillus cereus and Clostridium botulinum in non-alcoholic beers