Occurrence of Pectinatus and Megasphaera in the Major UK Breweries

The two faces of microorganisms in traditional brewing and the implications for no- and low-alcohol beers

The production of alcoholic beverages is intrinsically linked to microbial activity. This is because microbes such as yeast are associated with the production of ethanol and key sensorial compounds that produce desirable qualities in fermented products. However, the brewing industry and other related sectors face a step-change in practice, primarily due to the growth in sales of no- and low-alcohol (NoLo) alternatives to traditional alcoholic products. Here we review the involvement of microbes across the brewing process, including both their positive contributions and their negative (spoilage) effects. We also discuss the opportunities for exploiting microbes for NoLo beer production, as well as the spoilage risks associated with these products. For the latter, we highlight differences in composition and process conditions between traditional and NoLo beers and discuss how these may impact the microbial ecosystem of each product stream in relation to microbiological stability and final beer quality.

Microbial Biofilms in the Food Industry-A Comprehensive Review

Biofilms, present as microorganisms and surviving on surfaces, can increase food cross-contamination, leading to changes in the food industry’s cleaning and disinfection dynamics. Biofilm is an association of microorganisms that is irreversibly linked with a surface, contained in an extracellular polymeric substance matrix, which poses a formidable challenge for food industries. To avoid biofilms from forming, and to eliminate them from reversible attachment and irreversible stages, where attached microorganisms improve surface adhesion, a strong disinfectant is required to eliminate bacterial attachments. This review paper tackles biofilm problems from all perspectives, including biofilm-forming pathogens in the food industry, disinfectant resistance of biofilm, and identification methods. As biofilms are largely responsible for food spoilage and outbreaks, they are also considered responsible for damage to food processing equipment. Hence the need to gain good knowledge about all of the factors favouring their development or growth, such as the attachment surface, food matrix components, environmental conditions, the bacterial cells involved, and electrostatic charging of surfaces. Overall, this review study shows the real threat of biofilms in the food industry due to the resistance of disinfectants and the mechanisms developed for their survival, including the intercellular signalling system, the cyclic nucleotide second messenger, and biofilm-associated proteins.

Pectinatus spp. - Unpleasant and recurrent brewing spoilage bacteria

Traditionally, beer has been recognised as a beverage with high microbiological stability because of the hostile growth environment posed by beer and increasing attention being paid to brewery hygiene. However, the microbiological risk has increased in recent years because of technological advances toward reducing oxygen in beers, besides the increase in novel beer styles production, such as non-pasteurised, flash pasteurised, cold sterilised, mid-strength, and alcoholic-free beer, that are more prone to spoilage bacteria. Moreover, using innovative beer ingredients like fruits and vegetables is an added cause of microbial spoilage. To maintain quality and good brand image, beer spoilage microorganisms are a critical concern for breweries worldwide. Pectinatus and Megasphaera are Gram-negative bacteria mostly found in improper brewing environments, leading to consumer complaints and financial losses. Because of the lack of compiled scientific knowledge on Pectinatus spoilage ability, this review provides a comprehensive overview of the occurrence, survival mechanisms, and the factors affecting beer spoilage Pectinatus species in the brewing process.

Comparative genetic and physiological characterisation of Pectinatus species reveals shared tolerance to beer-associated stressors but halotolerance specific to pickle-associated strains

Obligate anaerobic bacteria from the genus Pectinatus have been known to cause beer spoilage for over 40 years. Whole genome sequencing was performed on eleven beer spoilage strains (nine Pectinatus frisingensis, one Pectinatus cerevisiiphilus and one Pectinatus haikarae isolate), as well as two pickle spoilage species (Pectinatus brassicae MB591 and Pectinatus sottacetonis MB620) and the tolerance of all species to a range of environmental conditions was tested. Exploration of metabolic pathways for carbohydrates, amino acids and vitamins showed little difference between beer spoilage- and pickle spoilage-associated strains. However, genes for certain carbohydrate- and sulphur-containing amino acid-associated enzymes were only present in the beer spoilage group and genes for specific transporters and regulatory genes were uniquely found in the pickle spoilage group. Transporters for compatible solutes, only present in pickle-associated strains, likely explain their experimentally observed higher halotolerance compared to the beer spoilers. Genes involved in biofilm formation and ATP Binding Cassette (ABC) transporters potentially capable of exporting hop-derived antimicrobial compounds were found in all strains. All species grew in the presence of alcohol up to 5% alcohol by volume (ABV) and hops extract up to 80 ppm of iso-α-acids. Therefore, the species isolated from pickle processes may pose novel hazards in brewing.

Rapid separation and identification of beer spoilage bacteria by inertial microfluidics and MALDI-TOF mass spectrometry

Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS), in combination with Biotyper software, is a rapid, high-throughput, and accurate method for the identification of microbes. Microbial outbreaks in a brewery present a major risk for companies as it can lead to cost-intensive recalls and damage to the brand reputation. MALDI-TOF MS has been implemented into a brewery setting for quality control practices and the identification of beer spoilage microorganisms. However, the applicability of this approach is hindered by compatibility issues associated with mixed cultures, requiring the use of time-consuming selective cultivation techniques prior to identification. We propose a novel, low-cost approach based on the combination of inertial microfluidics and secondary flows in a spiral microchannel for high-throughput and efficient separation of yeasts (Saccharomyces pastorianus and Saccharomyces cerevisiae) from beer spoilage microorganisms (Lactobacillus brevis and Pediococcus damnosus). Flow rates were optimised using S. pastorianus and L. brevis, leading to separation of more than 90% of the L. brevis cells from yeast. The microorganisms were then identified to the species level using the MALDI-TOF MS platform using standard sample preparation protocols. This study shows the high-throughput and rapid separation of spoilage microorganisms (0.3-3 μm) from background yeast (5 μm) from beer, subsequent identification using MALDI Biotyper, and the potential applicability of the approach for biological control in the brewing industry.

The chemistry of sour taste and the strategy to reduce the sour taste of beer

The contributions of free hydrogen ions, undissociated hydrogen ions in protonated acid species, and anionic acid species to sour taste were studied through sensory experiments. According to tasting results, it can be inferred that the basic substance producing a sour taste is the hydrogen ion, including free hydrogen ions and undissociated hydrogen ions. The intensity of a sour taste is determined by the total concentration of free hydrogen ions and undissociated hydrogen ions. The anionic acid species (without hydrogen ions) does not produce a sour taste but can intensify or weaken the intensity of a sour taste. It seems that hydroxyl or conjugated groups in anionic acid species can intensify the sour taste produced by hydrogen ions. The following strategy to reduce the sensory sourness is advanced: not only reduce free hydrogen ions, namely elevate pH value, but also reduce the undissociated hydrogen ions contained in protonated acid species.

Development of a species-specific PCR assay for identification of the strictly anaerobic bacterium Selenomonas lacticifex found in biofilm-covered surfaces in brewery bottling halls

AIMS

In recent years, beer-spoilage cases from strictly anaerobic bacteria have risen in frequency, in connection with the production of non-pasteurized, non-alcohol and low-alcoholic beers and with the lowering of dissolved oxygen in the packaged beer. Selenomonas lacticifex, found in brewer's yeast and in biofilms covering some surfaces in brewery bottling area, is considered to be a beer-spoilage organism. This study aims to develop S. lacticifex-specific PCR assay. The objective of this study was also evaluation of the specificity and reproducibility of the developed PCR assay in real brewery samples.

METHODS AND RESULTS

Three primers (one forward and two reverse) were designed for identification of the strictly anaerobic bacterium S. lacticifex on the basis of the species-specific sequences of the 16S rDNA region. The specificity of the primers was tested against 44 brewery-related non-target micro-organisms that could potentially occur in the same brewery specimens. None of the primer pairs amplified DNA from any of the non-S. lacticifex strains tested including genera from the same family (Pectinatus, Megasphaera, Zymophilus) and the closely related species Selenomonas ruminantium, showing thus 100% specificity.

CONCLUSIONS

The PCR assay developed in this study enables the detection of the strictly anaerobic bacterium S. lacticifex in real brewery samples including pitching yeast.

SIGNIFICANCE AND IMPACT OF THE STUDY

Selenomonas lacticifex-specific PCR assay developed in this study allows for the extension of the spectra of detected beer-spoilage micro-organisms in brewing laboratories and thus lowering the risk of contamination of the final product.

Identification of beer-spoilage bacteria using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Applicability of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for identification of beer-spoilage bacteria was examined. To achieve this, an extensive identification database was constructed comprising more than 4200 mass spectra, including biological and technical replicates derived from 273 acetic acid bacteria (AAB) and lactic acid bacteria (LAB), covering a total of 52 species, grown on at least three growth media. Sequence analysis of protein coding genes was used to verify aberrant MALDI-TOF MS identification results and confirmed the earlier misidentification of 34 AAB and LAB strains. In total, 348 isolates were collected from culture media inoculated with 14 spoiled beer and brewery samples. Peak-based numerical analysis of MALDI-TOF MS spectra allowed a straightforward species identification of 327 (94.0%) isolates. The remaining isolates clustered separately and were assigned through sequence analysis of protein coding genes either to species not known as beer-spoilage bacteria, and thus not present in the database, or to novel AAB species. An alternative, classifier-based approach for the identification of spoilage bacteria was evaluated by combining the identification results obtained through peak-based cluster analysis and sequence analysis of protein coding genes as a standard. In total, 263 out of 348 isolates (75.6%) were correctly identified at species level and 24 isolates (6.9%) were misidentified. In addition, the identification results of 50 isolates (14.4%) were considered unreliable, and 11 isolates (3.2%) could not be identified. The present study demonstrated that MALDI-TOF MS is well-suited for the rapid, high-throughput and accurate identification of bacteria isolated from spoiled beer and brewery samples, which makes the technique appropriate for routine microbial quality control in the brewing industry.