Spoilage Lactic Acid Bacteria Research Articles

Multivariate Analysis of the Influence of Microfiltration and Pasteurisation on the Quality of Beer during Its Shelf Life.

Gas chromatography-mass spectrometry (GC-MS), physicochemical and microbiological analyses, sensory descriptive evaluation, and multivariate analyses were applied to evaluate the efficiencies of microfiltration and pasteurization processes during the shelf life of beer. Samples of microfiltered and pasteurised beer were divided into fresh and aged groups. A forced ageing process, which consisted of storing fresh samples at 55° C for 6 days in an incubator and then keeping them under ambient conditions prior to analysis, was applied. Physicochemical analysis showed that both microfiltered and pasteurised samples had a slight variation in apparent extract, pH, and bitterness. The samples that underwent heat treatment had lower colour values compared with those that were microfiltered. Chromatographic peak areas of vicinal diketones increased in both fresh and aged samples. The results of the microbiological analysis revealed spoilage lactic acid bacteria (Lactobacillus) and yeasts (Saccharomyces and non-Saccharomyces) in fresh microfiltered samples. In the GC-MS analysis, furfural, considered by many authors as a heat indicator, was detected only in samples that underwent forced ageing and not in samples that were subjected to thermal pasteurisation. Finally, sensory analysis found differences in the organoleptic properties of fresh microfiltered samples compared with the rest of the samples.

The Effect of Commonly Used Organic Acids on the Microbiota of Cured Deli-Style Turkey Breast

The purpose of this study was to investigate changes in the microbial community structure consisting of spoilage lactic acid bacteria (LAB) when sodium lactate (SL) and SL + sodium diacetate (SD) are included in RTE meat product formulations at concentrations commonly used for controlling Listeria monocytogenes. Sliced cooked, vacuum-packaged turkey breast samples containing no SD or SL (control [C]), 0.125% SD, and the combination of 2.5% SL + 0.125%SD (SLSD) were inoculated with a target of 3 log colony-forming units (CFU)/g of 5 different LAB species (Lactobacillus sakei, Leuconostoc mesenteroides [bacon and deli-shaved ham isolates], Lactococcus lactis, and Enterococcus faecium) and stored at 4°C for 35 d. Microbial community changes were analyzed utilizing 16S ribosomal RNA (rRNA) gene sequencing for the V4 region from the samples collected at days 0, 7, 14, 21, and 35. No significant difference (P>0.05) was observed between the richness of microbial community for all treatments. According to Bray-Curtis dissimilarity matrix and permutational analysis of variance, a significant difference in β-diversity was observed only between C and SLSD (P<0.05) because of the antimicrobial effect of the addition of SL that slowed down changes in microbial community composition until day 14. L. sakei remained a dominant strain throughout 35 d of storage regardless of treatment, whereas L. mesenteroides existed with a very low abundance. Two of the five strains were not seen after day 7. No significant effect (P>0.05) was observed for the SD treatment compared with C in the microbiota. According to the results from this study, only SLSD affected the microbial community structure at the beginning of the storage. This study demonstrated that the incorporation of SL in the formulation slowed down the microbial spoilage and the changes in the microbiota of RTE meat products.

Effect of high pressure processing and water activity on pressure resistant spoilage lactic acid bacteria (Latilactobacillus sakei) in a ready-to-eat meat emulsion model

The main use of High Pressure Processing (HPP) in food processing is microorganism inactivation, and studies demonstrated that the characteristics of matrix and microorganisms can interfere on it. As the behavior of lactic acid bacteria exposed to different water activity (aw) levels in a meat product is still unclear, this study aimed to determine the effect of pressure, time, and aw to inactivate Latilactobacillus sakei, a pressure resistant lactic acid bacteria (LAB) in a meat emulsion model through a response surface methodology. The meat emulsion model was designed with adjusted aw (from 0.940 to 0.960) and was inoculated with a pressure resistant LAB and processed varying pressure (400-600 MPa) and time (180–480 s), following the Central Composite Rotational Design (CCRD). The inactivation of the microorganism ranged from 0.99 to 4.12 UFC/g depending on the applied condition. At studied conditions, according to the best fitting and most significant polynomial equation (R2 of 89.73 %), in a meat emulsion model, aw had no influenced on HPP inactivation on LAB (p > 0.05) and only pressure and holding time had significative impact on it. The results of experimental validation of the mathematical model were satisfactory, confirming the suitability of the model. The information obtained in the present study stands out the matrix, microorganism and process effects at HPP efficiency. The answers obtained support food processors in product development, process optimization and food waste reduction.

Wine Microbial Consortium: Seasonal Sources and Vectors Linking Vineyard and Winery Environments

Winemaking involves a wide diversity of microorganisms with different roles in the process. The wine microbial consortium (WMC) includes yeasts, lactic acid bacteria and acetic acid bacteria with different implications regarding wine quality. Despite this technological importance, their origin, prevalence, and routes of dissemination from the environment into the winery have not yet been fully unraveled. Therefore, this study aimed to evaluate the WMC diversity and incidence associated with vineyard environments to understand how wine microorganisms overwinter and enter the winery during harvest. Soils, tree and vine barks, insects, vine leaves, grapes, grape musts, and winery equipment were sampled along four seasons. The isolation protocol included: (a) culture-dependent microbial recovery; (b) phenotypical screening to select fermenting yeasts, lactic acid, and acetic acid bacteria; and (c) molecular identification. The results showed that during all seasons, only 11.4% of the 1424 isolates presumably belonged to the WMC. The increase in WMC recovery along the year was mostly due to an increase in the number of sampled sources. Acetic acid bacteria (Acetobacter spp., Gluconobacter spp., Gluconoacetobacter spp.) were mostly recovered from soils during winter while spoilage lactic acid bacteria (Leuconostoc mesenteroides and Lactobacillus kunkeii) were only recovered from insects during véraison and harvest. The fermenting yeast Saccharomyces cerevisiae was only isolated from fermented juice and winery equipment. The spoilage yeast Zygosaccharomyces bailii was only recovered from fermented juice. The single species bridging both vineyard and winery environments was the yeast Hanseniaspora uvarum, isolated from insects, rot grapes and grape juice during harvest. Therefore, this species appears to be the best surrogate to study the dissemination of the WMC from vineyard into the winery. Moreover, the obtained results do not evidence the hypothesis of a perennial terroir-dependent WMC given the scarcity of their constituents in the vineyard environment along the year and the importance of insect dissemination.

Growth and Biocontrol of Listeria monocytogenes in Greek Anthotyros Whey Cheese without or with a Crude Enterocin A-B-P Extract: Interactive Effects of the Native Spoilage Microbiota during Vacuum-Packed Storage at 4 °C.

Effective biopreservation measures are needed to control the growth of postprocess Listeria monocytogenes contamination in fresh whey cheeses stored under refrigeration. This study assessed growth and biocontrol of inoculated (3 log10 CFU/g) L. monocytogenes in vacuum-packed, fresh (1-day-old) or ‘aged’ (15-day-old) Anthotyros whey cheeses, without or with 5% of a crude enterocin A-B-P extract (CEntE), during storage at 4 °C. Regardless of CEntE addition, the pathogen increased by an average of 2.0 log10 CFU/g in fresh cheeses on day 15. Gram-negative spoilage bacteria also increased by an average of 2.5 log10 CFU/g. However, from day 15 to the sell-by date (days 35–40), L. monocytogenes growth ceased, and progressively, the populations of the pathogen declined in most cheeses. This was due to an unmonitored, batch-dependent natural acidification by spoilage lactic acid bacteria, predominantly Leuconostoc mesenteroides, which reduced the cheese pH to 5.5, and finally to ≤5.0. The pH reductions and associated declines in pathogen viability were greater in the CEntE-treated samples within each batch. L. monocytogenes failed to grow in cheeses previously ‘aged’ in retail for 15 days. Overall, high population levels (>7.5 log10 CFU/g) of psychrotrophic Enterobacteriaceae, particularly Hafnia alvei, were associated with an extended growth and increased survival of L. monocytogenes during storage.

Development of Culture-Independent Detection Method for Beer Spoilage Lactic Acid Bacteria

In microbiological quality control of final beer products, 100–400 ml beer samples are traditionally filtered on a membrane filter, followed by a lengthy culturing process in/on a laboratory medium that usually requires 3–14 days. This study aims to detect beer spoilage lactic acid bacteria (LAB) in a culture-independent fashion, using a direct polymerase chain reaction (PCR) approach. In order to detect a trace level of spoilage LAB in beer products, pressure cycling technology was evaluated to determine if this technology could improve the direct recovery of DNA from membrane filters for PCR detection. In this study, a mixed cellulose ester filter was adopted to allow a larger volume of beer to be filtrated. As a result of the optimization of the DNA extraction process that minimizes the loss of DNA and the effect of PCR inhibitors, 100 (1–10) cells/300 ml beer were successfully detected for beer spoilage LAB. Furthermore, a challenge test using 3,000 ml beer showed that 100 cells of Levilactobacillus (Lactobacillus) brevis were detectable without the negative effects of beer-originated PCR inhibitors, indicating that a trace level of contamination, corresponding to 1 cell in 300 ml of beer products, is detectable. It was also shown that the test was completed in approximately 8 hours. Therefore, this newly developed method is considered to be useful for the culture-independent direct detection of an extremely low level of beer spoilage LAB without a traditional culturing process. Supplemental data for this article is available online at at.

Applications of the Third-Generation DNA Sequencing Technology to the Detection of Hop Tolerance Genes and Discrimination of Saccharomyces Yeast Strains

To expand the applicability of the third-generation DNA sequencing technologies for the brewing industry, the new experimental protocols for quality control (QC) brewery laboratories have been developed, using the MinION system. Firstly, the hop tolerance genes, horA and horC, were amplified with multiplex PCR, and the PCR amplicons were sequenced by the MinION system. As a result, all of the beer spoilage lactic acid bacteria (LAB) strains carrying horA and/or horC were positively identified. Secondly, STA1, SbKEX2 and GEX1, were evaluated as diagnostic marker genes (DMGs) for discriminating Saccharomyces cerevisiae and S. pastorianus strains that possess essentially indistinguishable nucleotide sequences of the rDNA and internal transcribed spacer (ITS) regions. As a consequence of multiplex PCR specific to STA1, SbKEX2 and GEX1, these DMGs were shown to separate these hard-to-discriminate strains into four groups, namely top-fermenting ale yeast strains (S. cerevisiae), bottom-fermenting lager yeast strains (S. pastorianus), non-brewing S. cerevisiae wild yeast strains, and S. cerevisiae var. diastaticus. This study also demonstrated that the multiplexed PCR amplicons are independently recognized and correctly identified by the MinION system. Taken together, the newly developed methods using the MinION system are applicable to the identification and discrimination of important brewery microorganisms for microbiological QC. It was also shown that the concurrent applications of the rDNA-sequencing-based species identification and DMG approaches by the MinION system are useful for the breweries that now manufacture both traditional beers and non-traditional beverages. Supplemental data for this article is available online at https://doi.org/10.1080/03610470.2021.1939606 .

Assessment of the spoilage microbiota in minced free-range chicken meat during storage at 4 C in retail modified atmosphere packages

This study assessed the evolution of spoilage microbiota in association with the changes in pH and concentrations of lactic and acetic acids in retail oxygen-free modified atmosphere (30:70 CO2/N2) packages (MAP) of minced free-range chicken meat during storage at 4 °C for 10 days. MAP retarded growth of spoilage lactic acid bacteria (LAB) below 6.5 log cfu/g and fully suppressed growth of pseudomonads, enterobacteria, enterococci, staphylococci and yeasts. Two distinct Latilactobacillus sakei strain biotypes were predominant and Leuconostoc carnosum, Carnobacterium divergens, Latilactobacillus fuchuensis and Weissella koreensis were subdominant at spoilage. The chicken meat pH ranged from 5.8 to 6.1. l-lactate (832 mg/100 g on day-0) decreased slightly on day-7. d-lactate remained constantly below 20 mg/100 g, whereas acetate (0–59 mg/100 g) increased 5-fold on day-7. All MAP samples developed off-odors on day-7 and a strong ‘blown-pack’ sulfur-type of spoilage on day-10. However, neither the predominant Lb. sakei nor other LAB or gram-negative isolates formed H2S in vitro, except for C. divergens.

Study of Beer Spoilage Lactobacillus nagelii Harboring Hop Resistance Gene horA

Lactic acid bacteria (LAB) cause the majority of beer spoilage incidents in the brewing industry. Previous studies revealed that the hop resistance genes, horA and horC, are applicable to the species-independent determination of beer spoilage ability of LAB. However, novel beer spoilage LAB species are occasionally emerging, and their insights should be shared in the industry to prevent spoilage incidents by these unknown species. In this study, Lactobacillus nagelii ABBC668 strain, isolated from spoiled pilsner-type beer, was investigated, as L. nagelii has been poorly characterized as a beer spoiler. The beer spoilage ability and hop resistance genes of L. nagelii ABBC668 were examined. Results showed that L. nagelii ABBC668 harbored hop resistance gene horA and exhibited beer spoilage ability. Also, it was considered that horA harbored by ABBC668 was acquired via horizontal gene transfer and had an unstable nature compared to that of Lactobacillus brevis. The unstable nature may account for the less frequent encounter of beer spoilage L. nagelii strains in the brewing industry. Furthermore, ABBC668 showed similar motility to other L. nagelii strains. To our knowledge, this is the first report of L. nagelii as a beer spoilage species.

Preceding Subculture Conditions Affect Growth Characteristics of Beer Spoilage Lactic Acid Bacteria in Quality Control Culture Media: Comparative Study on Hard-to-Culture and Culturable Secundilactobacillus (Lactobacillus) paracollinoides Strains

Beer spoilage lactic acid bacteria (LAB) often display hard-to-culture characteristics and fail to grow on conventional quality control (QC) laboratory media, while retaining growth capability in beer. This phenomenon is at least partly due to profound adaptation of spoilage LAB to the brewing environments, where multifactorial antibacterial hurdles and low temperature stress are encountered. In this study, changeable culturability of Secundilactobacillus (Lactobacillus) paracollinoides strains, JCM 11969T and JCM 15729, has been evaluated by comparing the variants obtained under various preceding subculture conditions. Sodium acetate substantially inhibited the growth of hard-to-culture S. paracollinoides variants, with smaller negative impacts for growth observed with yeast extract, peptone, and manganese sulfate. Growth inhibition was also observed at values higher than pH5.3 for hard-to-culture JCM 11969T variants and higher than pH5.0 for hard-to-culture JCM 15729 variants, respectively. In contrast, culturable S. paracollinoides variants exhibited sensitivities to low pH and grew well at pH 5.6 or even higher. Strikingly, the addition of sodium acetate led to increased colony forming units for culturable JCM 15729 strains, suggesting that sodium acetate exerts both positive and negative effects on the growth of S. paracollinoides strains. It has been also demonstrated that hard-to-culture and culturable states are reversible for S. paracollinoides JCM 11969T and JCM 15729, depending on the preceding subculture conditions. Taken together, it has been suggested that culturability of S. paracollinoides strains is easily changeable, and brewing microbiologists must ensure their culturability is maintained as observed upon primary isolation.

Evaluation of the antibacterial activity of allyl isothiocyanate, clove oil, eugenol and carvacrol against spoilage lactic acid bacteria

In recent years, the antibacterial properties of essential oils (EOs) and EO components have attracted attention, but only few studies have investigated their effect against spoilage lactic acid bacteria (LAB). To collect knowledge of antimicrobial effect of EO and EO components against spoilage LAB, the ability of allyl isothiocyanate (AITC), clove oil, eugenol, and carvacrol to control the growth of 6 types of spoilage-causing LAB was evaluated. Carvacrol, at 500 mg/L, and eugenol and AITC, at 2000 mg/L, could suppress the growth of all LAB. Susceptibility to clove oil varied among strains. Finally, the effect of carvacrol on the growth of 2 types of selected LAB in fresh sausage was evaluated. The number of LAB in sausages treated with 5000 or 10,000 mg/kg of carvacrol was lower than that in the control sausages (to which EO had not been added), and the growth of LAB was significantly suppressed at 20,000 mg/kg (P < 0.01). In this study, it was found that EO and EO components were effective in suppressing the growth of LAB, thus suggesting its application in preservation of food in the future.

Transcriptomic time-series analysis of cold- and heat-shock response in psychrotrophic lactic acid bacteria

BackgroundPsychrotrophic lactic acid bacteria (LAB) species are the dominant species in the microbiota of cold-stored modified-atmosphere-packaged food products and are the main cause of food spoilage. Despite the importance of psychrotrophic LAB, their response to cold or heat has not been studied. Here, we studied the transcriptome-level cold- and heat-shock response of spoilage lactic acid bacteria with time-series RNA-seq for Le. gelidum, Lc. piscium, and P. oligofermentans at 0 °C, 4 °C, 14 °C, 25 °C, and 28 °C.ResultsWe observed that the cold-shock protein A (cspA) gene was the main cold-shock protein gene in all three species. Our results indicated that DEAD-box RNA helicase genes (cshA, cshB) also play a critical role in cold-shock response in psychrotrophic LAB. In addition, several RNase genes were involved in cold-shock response in Lc. piscium and P. oligofermentans. Moreover, gene network inference analysis provided candidate genes involved in cold-shock response. Ribosomal proteins, tRNA modification, rRNA modification, and ABC and efflux MFS transporter genes clustered with cold-shock response genes in all three species, indicating that these genes could be part of the cold-shock response machinery. Heat-shock treatment caused upregulation of Clp protease and chaperone genes in all three species. We identified transcription binding site motifs for heat-shock response genes in Le. gelidum and Lc. piscium. Finally, we showed that food spoilage-related genes were upregulated at cold temperatures.ConclusionsThe results of this study provide new insights on the cold- and heat-shock response of psychrotrophic LAB. In addition, candidate genes involved in cold- and heat-shock response predicted using gene network inference analysis could be used as targets for future studies.

Beer spoilage lactic acid bacteria from craft brewery microbiota: Microbiological quality and food safety

Craft beer is more susceptible to microbial spoilage because it does not have a pasteurization or filtration process, with lactic acid bacteria (LAB) being the most common beer spoilage microorganism. The aim of this study was to isolate LAB in a craft brewery and their characterization from a food safety and microbiological quality perspective, with a special focus on their abilities to produce biogenic amines (BA) and spoil the beer. The results of 60 monitored points inside the craft brewery showed that LAB associated with the craft brewing processes belonged to Lactobacillus, Pediococcus, and Leuconostoc genera, and most of them were detected in the filling area, which can lead to secondary contamination. Two isolates of L. brevis showed the most significant beer spoilage ability because they could grow in more acidic conditions, at a higher hop and alcohol content, and they displayed horA, horC, and hitA genes, which spoiled the vast majority of the tested beers. In addition, the aforementioned L. brevis isolates showed the highest BA production.

Antimicrobial efficacy of nisin-loaded bacterial cellulose nanocrystals against selected meat spoilage lactic acid bacteria

This study aimed to explore the potential of bacterial cellulose nanocrystals (BCNs) loaded with nisin against selected meat spoilage lactic acid bacteria (LAB) in vitro. BCNs were produced by H2SO4 hydrolysis, and nisin-loaded BCNs were produced through the complexation method. All nanocrystals were assessed for their zeta-potential, encapsulation efficiency and antimicrobial activity. Different nisin concentrations were tested and the most effective nanocrystals were further characterised. BCNs had an average zeta-potential of - 43 mV and all nisin-loaded BCNs produced with 5 mg/ml BCNs suspension had zeta-potential values ≥− 30 mV. The encapsulation efficiency of nisin varied from 80.5 to 93.3 % and crystallinity of BCNs was not influenced by nisin encapsulation. Microbial inactivation was achieved by BCN loaded with 2.0 and 2.5 mg/ml nisin. Therefore, nisin-loaded BCNs may be used as antimicrobial agents in active food packaging.

Spoilage Lactic Acid Bacteria in the Brewing Industry.

Lactic acid bacteria (LAB) have caused many microbiological incidents in the brewing industry, resulting in severe economic loss. Meanwhile, traditional culturing method for detecting LAB are time-consuming for brewers. The present review introduces LAB as spoilage microbes in daily life, with focus on LAB in the brewing industry, targeting at the spoilage mechanism of LAB in brewing industry including the special metabolisms, the exist of the viable but nonculturable (VBNC) state and the hop resistance. At the same time, this review compares the traditional and novel rapid detection methods for these microorganisms which may provide innovative control and detection strategies for preventing alcoholic beverage spoilage, such as improvement of microbiological quality control using advanced culture media or different isothermal amplification methods.

Effective use of nisin to control lactic acid bacterial spoilage in sliced cooked ham

Cooked ham is one of the most consumed meat products in Brazil. It is sensitive to the deterioration caused by the growth of lactic acid bacteria (LAB). The objective of this study was to evaluate the antimicrobial activity of nisin over the naturally present LAB on sliced cooked ham stored at 8°C. For this, nisin was added to the cooked ham at two different stages of processing: Injected together with the brine (assay 1) and added during tumbling (assay 2). Results from assay 1 showed LAB inhibition for 2 days, whereas, results from assay 2 showed LAB inhibition for up to 10 days. These results demonstrated that 12.5 mg/kg (dosage approved in Brazil for dairy products) of nisin significantly inhibited LAB growth, suggesting its effectiveness as an appropriate barrier in the control of LAB spoilage in cooked ham. Practical applications When evaluating the antimicrobial activity of nisin for its biopreservation capacity, it is important to consider that meat products are complex systems with several factors influencing the microbial growth and subsequent metabolite production. Therefore, the influence of the medium formulation and technology on the process needs to be tested. Addition of nisin at the tumbling step had a better inhibitory effect against LAB. Thus, it can deliver an important contribution to improve food quality by optimizing the storage management.

Control of Autochthonous Spoilage Lactic Acid Bacteria in Apple and Orange Juices by Sensorially Accepted Doses of Citrus Spp. Essential Oils Combined with Mild Heat Treatments.

This study assessed the compromised acceptance threshold (CAT) and rejection threshold (RT) of Citrus lemon (CLEO) and Citrus reticulata essential oil (CREO) in apple and orange juices. The efficacy of CLEO and CREO concentrations below the RT were evaluated alone and combined with mild heat treatment (MHT) (54 °C, up to 12 min) to inactivate the autochthonous spoilage bacteria Lactobacillus brevis, Lactobacillus plantarum, and Leuconostoc mesenteroides in apple and orange juices. The CAT of CLEO and CREO varied from 0.15 to 0.17μL/mL in orange and apple juices. The RT of CLEO was approximately 0.58μL/mL in apple and orange juices, and the RT of CREO was 0.68μL/mL in both juices. When CLEO and CREO were assayed alone, the highest concentration (0.50μL/mL) decreased counts of all strains approximately 2 log10 CFU/mL after 12 min of exposure to 54 °C. All concentrations of CLEO or CREO in combination with MHT acted synergistically against L. brevis, L. plantarum, and L. mesenteroides. Decreases in counts varied with the strain, CLEO and CREO concentrations, juice type, and exposure time to the combined treatment. CREO was more effective than CLEO in combination with MHT against the strains in apple and orange juices. Effective combinations of CLEO or CREO with MHT to control the autochthonous spoilage bacteria did not compromise the quality parameters (°Brix, pH, and titratable acidity) that characterize unsweetened juices. These results indicate CLEO or CREO at concentrations below the sensory RT in combination with MHT as a feasible technology to control autochthonous spoilage bacteria in fresh fruit juices. PRACTICAL APPLICATION: The present study provides novel information concerning the efficacy of sensorially accepted doses of CLEO and CREO combined with MHT against autochthonous spoilers in fruit juice. The valuable synergistic effects that can be observed when combining CLEO and CREO with MHT reveal a feasible preservation technology and alternative to traditional treatments that are successful because they help reduce treatment intensity, thereby avoiding adverse effects on the sensory, physicochemical, and nutritional properties of these products.

Dipstick Assay for Rapid Detection of Beer Spoilage Organisms

Background: Beer spoilage caused by wild yeast and bacteria is a major concern to both commercial and home brewers. Objective: To address this problem, Molecular Epidemiology Inc. (MEI, Seattle, WA) has developed a beer spoilage organism detection kit consisting of an enrichment media (BSE) and a multiplex PCR DNA dipstick that simultaneously detects these organisms within 2h following enrichment. Methods: The kit was tested by using samples obtained from breweries located in the Greater Seattle area. Samples were spiked with the target microbes, when necessary, and used for assessing the performance characteristics of the DNA dipstick assay. Microbial enumerations were performed as per the standard microbiological plating methods. The suitability of the BSE medium to support the growth of beer spoilage microbes was compared with the industry-approved NBB-C medium (Dohler, Darmstadt, Germany). Results: Inclusivity (a panel of 50 isolates) and Exclusivity (a panel of 92 isolates) testing indicated that the dipstick assay can exclusively detect the indicated target beer spoilage microbes. When compared with the NBB-C medium (Dohler, Darmstadt, Germany) approved by the European Brewers Convention for beer spoilage organisms, the BSE medium supported faster growth of critical spoilage lactic acid bacteria such as Lactobacillus brevis, L. lindneri, and Pediococcus damnosus. Conclusions: The beer spoilage organism detection kit has a detection limit of 10 cells/mL. Highlights: The kit can be used at different stages of the brewing process, thus offering a convenient, cost effective, and faster test system for brewers interested in monitoring the quality of their product.

Определение и подсчет молочнокислых бактерий порчи в продуктах в ROP-упаковке с помощью тест-пластины 3M™ PETRIFILM™ LAB

Определение и подсчет молочнокислых бактерий порчи в продуктах в ROP-упаковке с помощью тест-пластины 3M™ PETRIFILM™ LAB

Hop bitter acids inhibit carbohydrate metabolism, enhance biogenic amine metabolism and alter L‐malic acid, glutamic acid and arginine metabolism of Lactobacillus brevis 49

SummaryBeer contains only limited amounts of readily fermentable carbohydrates and amino acids. Beer spoilage lactic acid bacteria have to come up with metabolic strategies in order to deal with selective nutrient content. The research was performed to investigate the influence of iso‐α‐acids on the metabolism of organic acids, biogenic amines (BAs), off‐flavour compounds, carbohydrates and amino acids of Lactobacillus brevis 49. Only glyoxylic acid and ethyl formate in de man, rogosa, sharpe broth was consumed, and multiple organic acids, BAs and off‐flavour compounds were produced. By supplementing a series of concentrations of hop iso‐α‐acids, consumption of L‐malic acid, glutamic acid and arginine and generation of BAs were found benefit for bacteria to develop hop‐resistance. In the metabolism of carbohydrates, glucose was preferred over maltose and maltriose, and hops significantly inhibited the utilisation of carbohydrates. The results provide comprehensive information of metabolites of L. brevis 49 under various concentrations of hop stress.