Factors affecting the production of hydrogen sulphide byLactobacillus sakeL13 growing on vacuum-packaged beef

Reflections on food security and smart packaging

Estimating the number of COVID-19 cases in 2020 exacerbated the food contamination and food supply issues. These problems make consumers more concerned about food and the need to access accurate information on food quality. One of the main methods for preserving the quality of food commodities for export, storage, and finished products is food packaging itself. In the food industry, food packaging has a significant role in the food supply which acts as a barrier against unwanted substances and preserves the quality of the food. Meanwhile, packaging waste can also harm the environment; namely, it can become waste in waterways or become garbage that accumulates because it is nonrenewable and nonbiodegradable. The problem of contaminated food caused by product packaging is also severe. Therefore, to overcome these challenges of safety, environmental impact, and sustainability, the role of food packaging becomes very important and urgent. In this review, the authors will discuss in more detail about new technologies applied in the food industry related to packaging issues to advance the utilization of Smart Packaging and Active Packaging.

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.

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.

Volatile and non-volatile metabolite changes in 140-day stored vacuum packaged chilled beef and potential shelf life markers

During storage of vacuum packaged chilled beef (VPCB), lactic acid bacteria become the dominant microflora, facilitating an extended shelf life. However, at some point, (bio)chemical and organoleptic changes render the meat unacceptable. In this investigation we evaluated volatile and non-volatile metabolite changes in VPCB after 84-, 98-, 120- and 140-days storage at ~ - 1 °C. After 140-days storage, the sensory, volatile and non-volatile data did not indicate spoilage. Minimal changes in volatile signatures of collected weep and on raw and grilled steaks were measured. Changes in selected non-volatile components indicated increased proteolysis (free amino acids, carnosine) and changes in organic acids (lactic, succinic) and nucleotide metabolism. Rapid volatile profiling using proton transfer reaction mass spectrometry showed a clear progression of changes in selected compounds over the storage period. An increased concentration of ethanol and other compounds between 120 and 140 days, suggested that volatile changes may be a useful objective indicator of extended storage VPCB quality.

Spoilage characteristics of ground beef with added lactic acid bacteria and rosemary oleoresin packaged in a modified-atmosphere package and displayed at abusive temperatures

Lactic acid bacteria (LAB) can reduce Escherichia coli O157:H7 and Salmonella spp. in ground beef during storage. Furthermore, the addition of rosemary oleoresin (RO), a natural antioxidant, to ground beef has been shown to increase shelf life and is commonly used in modified-atmosphere packaged (MAP) ground beef. This study evaluated the effects of LAB and RO treatment on the shelf life and stability of MAP ground beef displayed at abusive (10°C) temperatures for 36 h. Subjective and objective sensory analyses were conducted to determine spoilage endpoints. Trained and consumer panel responses and Hunter lightness (L*), redness (a*), and yellowness (b*) values were not affected (P = 0.62, 0.66, 0.45) by LAB addition, although RO inclusion improved (P < 0.05) lean color. Ground beef with LAB and RO had significantly less (P < 0.0001) thiobarbituric acid reactive substance values than control ground beef, indicating decreased lipid oxidation. Additionally, RO inclusion reduced (P < 0.0001) off odors, as determined by trained and consumer odor panelists. Overall, the addition of LAB did not negatively affect beef color, odor, or oxidative rancidity, suggesting that LAB can be added to ground beef in MAP packaging as a processing intervention without detrimentally affecting shelf life or stability.

Spoilage of value-added, high-oxygen modified-atmosphere packaged raw beef steaks by Leuconostoc gasicomitatum and Leuconostoc gelidum

Moisture-enhancing and marinating of meats are commonly used by the meat industry to add value to raw, retail products. Recently in Finland, certain value-added beef steak products have proven to be unusually susceptible to microbial spoilage leading to untoward quality deteriorations during producer-defined shelf-life. This study was conducted to evaluate the role of lactic acid bacteria (LAB) in the premature spoilage of value-added beef packaged under high-oxygen modified atmospheres. Spoilage was characterised by green discolouration and a buttery off-odour. The predominant LAB in eight packages of spoiled, marinated or moisture-enhanced beef steaks were identified by reference to a 16 and 23S rRNA gene restriction fragment length polymorphism pattern (ribotype) database. Leuconostoc gasicomitatum, Leuconostoc gelidum, Lactobacillus algidus, Lactobacillus sakei and Carnobacterium divergens were found to predominate in the LAB populations at numbers above 10(8) CFU/g. Inoculation of moisture-enhanced steaks with LAB strains and strain mixtures originating from the spoiled products demonstrated the spoilage potential of L. gasicomitatum and L. gelidum isolates. These two species produced green surface discolouration and buttery off-odours similar to these found in the spoiled, commercial products.

Effect of Lactobacillus-protective cultures with bacteriocin-like inhibitory substances' producing ability on microbiological, chemical and sensory changes during storage of refrigerated vacuum-packaged sliced beef

AIMS

To investigate the effect of applying two different Lactobacillus-protective cultures, with bacteriocin-like inhibitory substances' (BLIS) producing ability, individually or in combination, on microbiological, chemical and sensory changes during storage of refrigerated vacuum-packaged sliced beef meat.

METHODS AND RESULTS

Lactobacillus sakei CECT 4808 and Lactobacillus curvatus CECT 904(T), which were shown to be producers of BLIS, were inoculated individually or in combination on slices of beef M. semitendinosus. The samples were vacuum packaged and stored at 4 +/- 1 degrees C and were assessed during a 28-day storage period for microbiological [Enterobacteriaceae, Pseudomonas spp., lactic acid bacteria (LAB), Brochothrix thermosphacta and yeasts and moulds], chemical (pH, protein hydrolysis degree, lipid oxidation), sensory (abnormal odour) parameters and instrumental colour. Samples inoculated with the Lact. sakei strain and samples inoculated with the combination of the two strains had significantly (P < 0.05) lower spoilage microbial counts than those inoculated with the Lact. curvatus strain alone or the controls, while both chemical parameters (including lipid oxidation) and abnormal odour scores were also significantly (P < 0.05) improved by the former. Moreover, Lact. sakei alone showed a better preserving effect (P < 0.05) than the combination of both strains in the majority of the parameters tested. Instrumental colour measurements changed with storage time, but no treatment effects (P >or= 0.05) were observed during the whole 28-day storage period.

CONCLUSIONS

The BLIS producer Lact. sakei CECT 4808 strain may be used for improving preservation of vacuum-packaged beef slices, as regards spoilage microbial counts and the chemical parameters tested in this study.

SIGNIFICANCE AND IMPACT OF THE STUDY

Inoculation with the BLIS producer Lact. sakei CECT 4808 strain would provide an additional hurdle to improve storage life of refrigerated vacuum-packaged sliced beef. Furthermore, this strain demonstrated limited antioxidative ability, which could make a contribution to the prevention of lipid oxidation in meat and meat products.

Purification and characterisation of acidocin D20079, a bacteriocin produced by Lactobacillus acidophilus DSM 20079

Bacteriocins are natural antimicrobial agents produced by food fermentative bacteria. Lactobacillus acidophilus DSM 20079 produces a small bacteriocin, with a molecular mass of 6.6 kDa, designated acidocin D20079. This antimicrobial peptide was extremely heat-stable (30 min at 121 degrees C) and was active over a wide pH range. It was found to be sensitive to proteolytic enzymes (trypsin, ficin, pepsin, papain, and proteinase K). Acidocin D20079 has a narrow inhibitory spectrum restricted to the genus Lactobacillus which includes L. sakei NCDO 2714, an organism known to cause anaerobic spoilage of vacuum-packaged meat. Maximum production of acidocin D20079 in MRS broth was detected at pH 6.0, and the peptide was purified by ammonium sulphate precipitation followed by sequential cation exchange and hydrophobic interaction chromatography. Purified acidocin D20079 spontaneously formed spherulite crystals during dialysis. As the N-terminus was found to be blocked for sequencing, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was used to determine a partial sequence, and the molecular mass of the bacteriocin in the formed crystals (6.6 kDa). Estimates of the molecular weight of the partially purified peptide, using tricine-SDS-PAGE, in which bacteriocin activity was confirmed by overlayer techniques were in accordance with this value.

Characterization and purification of acidocin CH5, a bacteriocin produced by Lactobacillus acidophilus CH5

AIMS

To characterize and to purify a bacteriocin produced by Lactobacillus acidophilus strain with its activity restricted to Gram-positive bacteria.

METHODS AND RESULTS

Native acidocin CH5, a bacteriocin produced by L. acidophilus CH5 an isolate from a dairy starter culture forms in MRS (Oxoid, Basingstoke, UK) broth high-molecular weight aggregates which can dissociate into smaller units (retained by 5 kDa membrane) with higher activity. Acidocin CH5 was purified using combinations of chromatographic methods based on hydrophobic and cation exchange principles and the N-terminal region was sequenced.

CONCLUSIONS

Based on our results it is evident that acidocin CH5 belongs, according to bacteriocin classification, to the class II bacteriocins with identical N-terminal amino acid sequence described in the literature previously.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study has provided further data on bacteriocin acidocin CH5 from class II with wide spectrum of antimicrobial activity atypical for bacteriocins produced by L. acidophilus sharing the same homology.

Gas formation in ground beef chubs due to Hafnia alvei is reduced by multiple applications of antimicrobial interventions to artificially inoculated beef trim stock

Gas-forming microorganisms were isolated from gas-swollen ground beef chubs obtained from a commercial source and were phenotypically identified as Hafnia alvei. In in situ experiments, the isolated H. alvei strains produced gas in inoculated irradiation-sterilized ground beef chubs. A five-strain cocktail of H. alvei isolates was inoculated on beef trim. The inoculated beef trim samples were treated with either a water wash (W) at 65 psi for five passes (a pass refers to the application of successive multiple antimicrobial treatments to inoculated beef trim on a moving processing conveyor belt at a speed of 1 cm/s under heat ducts or oscillating spray nozzles), W plus a 2% (vol/vol) lactic acid wash (L) at room temperature at 30 psi for three passes (W/L), or a combination treatment (COMB) consisting of W plus 82 degrees C water for three passes plus 510 degrees C hot air for six passes plus L, or were not treated (control). After treatment, the beef trim was ground and vacuum packaged. The numbers of H. alvei were reduced with water alone and with the aforementioned antimicrobial intervention treatments. For the untreated and inoculated control samples, the numbers of H. alvei increased from 7.03 to 8.40 log CFU/g after 7 days of incubation at 4 degrees C. However, the numbers of H. alvei treated by successive antimicrobial interventions (COMB) were initially reduced to 5.25 log CFU/g and increased to just 6.9 log CFU/g after 7 days of incubation at 4 degrees C. Gas was produced in untreated control samples after 3 days at 15 degrees C (15 of 15 inoculated chubs). However, in meat treated with W, W/L, and COMB, gas was produced after 4 to 5, 7 to 8, and 9 to 10 days of storage at 15 degrees C, respectively. These results demonstrate the effectiveness of multiple antimicrobial interventions in reducing H. alvei numbers on beef trim and subsequently delaying gas formation in the resulting ground beef chubs.

Shelf life of ground poultry meat stored under modified atmosphere

The shelf life of ground chicken and turkey meat packaged under a modified atmosphere containing O2 and a high level of CO2 (62% CO2, 8% O2, and 30% N2; gas-1), or a gas mixture without O2 (20% CO2 and 80% N2; gas-2) was evaluated for 20 d at 1 C. Meat packaged under gas-2 maintained a higher a* value (redness) throughout the experiment and generally had a more appealing color than the meat packaged using gas-1. Microbial populations were assessed after 8, 12, and 15 d of storage. Total aerobic mesophilic counts were higher in chicken meat than in turkey throughout storage. Coliforms and Escherichia coli counts were lower in meat packaged under gas-1. After 15 d of storage at 1 C, Brochothrix thermosphacta was detected only in ground chicken meat packaged using gas-2. Meat packaged under the gas mixtures tested had similar counts for presumptive pseudomonads, Staphylococcus aureus, and lactic acid bacteria. These results indicate that an appropriate gas mixture can maintain a desirable color in ground poultry meat but offers no guarantees with respect to the microbial profile of meat.

Using an electronic nose for determining the spoilage of vacuum-packaged beef

The use of an electronic nose in the quantitative determination of the degree of spoilage of vacuum-packaged beef was evaluated. Beef from four different slaughterhouses was sliced, vacuum-packaged and stored at 4 degrees C for 8 weeks. Samples were withdrawn for bacterial (aerobic bacteria, lactic acid bacteria, Brochothrix thermosphacta, Pseudomonas and Enterobacteriaceae) and sensorial analyses and analysis of the volatile compounds during the storage period. A trained panel was used for the sensorial evaluations. The volatile compounds were analysed using an electronic nose containing a sensory array composed of 10 metal oxide semiconductor field-effect transistors, four Tagushi type sensors and one CO2-sensitive sensor. Four of the 15 sensors were excluded due to lack of response or overloading. Partial least-squares regression was used to define the mathematical relationships between the degree of spoilage of vacuum-packaged beef, as determined by the sensory panel, and the signal magnitudes of the sensors of the electronic nose. The mathematical models were validated after 6 months using a new set of samples. The stability of the sensors during this period was examined and it was shown that the sensitivity of five of the 11 sensors used had changed. Using the six remaining sensors, the signal patterns obtained from the meat from the different slaughterhouses did not change over a period of 6 months. It was shown that the degree of spoilage, as calculated using a model based on two Tagushi sensors, correlated well with the degree of spoilage determined by the sensory panel (r2 = 0.94).

Ropy slime-producing Lactobacillus sake strains possess a strong competitive ability against a commercial biopreservative

Aseptically handled Frankfurters were treated with a commercial Lactobacillus alimentarius biopreservative and inoculated with different cell concentrations of four ropy slime-producing Lactobacillus sake strains. The packages were vacuum sealed and kept at 6 degrees C for 28 days, after which the production of ropy slime was evaluated. The inoculation test was controlled by sealing the different control packages containing either aseptically manufactured sausages without any bacterial inoculation, packages containing biopreservative only or packages inoculated only with the four different ropy slime-producing strains. Authenticity of the biopreservative strain after the cold storage period was ascertained by performing EcoRI restriction endonuclease analysis of 30 randomly selected isolates originating from the biopreservative control packages. All patterns were identical to the pattern of the original L. alimentarius biopreservative strain. The biopreservative was found to be ineffective against the four ropy slime-producing L. sake strains. The strongest slime producers inoculated with approximately 1 colony forming units (CFU)/cm2 could compete efficiently with the L. alimentarius inoculated at a level of 10(7) CFU/cm2 on sausage surfaces. This commercial biopreservative failed to occupy the vital niche of the four ropy slime-producing L. sake strains leading to spoilage in almost all packages.

Lactic acid bacteria of foods and their current taxonomy

Application of molecular genetic techniques to determine the relatedness of food-associated lactic acid bacteria has resulted in significant changes in their taxonomic classification. During the 1980s the genus Streptococcus was separated into the three genera Enterococcus, Lactococcus and Streptococcus. The lactic acid bacteria associated with foods now include species of the genera Carnobacterium, Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Oenococcus, Pediococcus, Streptococcus, Tetragenococcus, Vagococcus and Weissella. The genus Lactobacillus remains heterogeneous with over 60 species (ymol% G+C content ranging from 33 to 55), of which about one-third are strictly heterofermentative. However, many changes have been made and reorganization of the genus along lines that do not follow previous morphological or phenotypic differentiation from Leuconostoc and Pediococcus is being studied. Phylogenetically belonging to the Actinomyces branch of the bacteria, Lactobacillus bifidus has been moved to the genus Bifidobacterium also on account of its greater than 50 mol% G+C content. It is therefore no longer considered one of the lactic acid bacteria senso strictu, which form part of the Clostridium branch of the bacteria. The new genus Weissella has been established to include one member of the genus Leuconostoc (Leuc, paramesenteroides) and heterofermentative lactobacilli with unusual interpeptide bridges in the peptidoglycan. Contrary to the clear-cut division of the streptococci, morphological and physiological features of Weissella do not directly support this grouping which now incorporates species that produce D(-)- as well as DL-lactate. The new genus Carnobacterium is morphologically similar to the lactobacilli, but it shares some physiological similarities (e.g. growth at pH 9.5) and a common phylogenetic branch with the genus Enterococcus. The review includes information on the taxonomic changes and the relationship of the bacteria of food fermentation and spoilage.

Bacterial spoilage of meat and cured meat products

The influence of environmental factors (product composition and storage conditions) on the selection, growth rate and metabolic activity of the bacterial flora is presented for meat (pork and beef) and cooked, cured meat products. The predominant bacteria associated with spoilage of refrigerated beef and pork, are Brochothrix thermosphacta, Carnobacterium spp., Enterobacteriaceae, Lactobacillus spp., Leuconostoc spp., Pseudomonas spp. and Shewanella putrefaciens. The main defects in meat are off-odours and off-flavours, but discolouration and gas production also occur. Bacteria associated with the spoilage of refrigerated meat products, causing defects such as sour off-flavours, discolouration, gas production, slime production and decrease in pH, consist of B. thermosphacta, Carnobacterium spp. Luctobacillus spp. Leuconostoc spp. and Weissella spp. Analysis of spoilage as measured by bacterial and chemical indicators is discussed. It is concluded that a multivariate approach based on spectra of chemical compounds, may be helpful in order to analyse spoilage, at least for spoilage caused by lactic acid bacteria. The consequences of bacteria bacteria interactions should be evaluated more.

Chemical/biochemical detection of spoilage

Although sensory and/or microbiological analyses are widely relied on when assigning shelf-life of foods or trouble shooting problems with spoilage under storage, they do have drawbacks. Delay in obtaining results is one of them. The expense of the expert panels required to obtain meaningful sensory evaluations is another, while spoilage is not always of microbial origin. Even when it is, there are an increasing number of situations, including that of meats and fish packaged in modified atmospheres, where the relationships between microbial growth and spoilage onset is poorly defined. Chemical analysis has long been recognized as a means of circumventing at least some of the drawbacks and its potential is reviewed below. From the data presented it can be concluded that chemical characterization of spoilage processes is presently of most value in trouble shooting i.e. establishing the causes of spoilage. Its value in assigning total or remaining shelf-life requires more knowledge of the chemical processes leading to reduced acceptability/spoilage and of their correlations with sensory and microbiological changes.

Biopreservation by lactic acid bacteria

Biopreservation refers to extended storage life and enhanced safety of foods using the natural microflora and (or) their antibacterial products. Lactic acid bacteria have a major potential for use in biopreservation because they are safe to consume and during storage they naturally dominate the microflora of many foods. In milk, brined vegetables, many cereal products and meats with added carbohydrate, the growth of lactic acid bacteria produces a new food product. In raw meats and fish that are chill stored under vacuum or in an environment with elevated carbon dioxide concentration, the lactic acid bacteria become the dominant population and preserve the meat with a "hidden' fermentation. The same applies to processed meats provided that the lactic acid bacteria survive the heat treatment or they are inoculated onto the product after heat treatment. This paper reviews the current status and potential for controlled biopreservation of foods.

Microbial ecology of fresh pork stored under modified atmosphere at -1, 4.4 and 10 degrees C

The prevalent bacteria on fresh pork packaged in modified atmosphere with elevated CO2 were determined by selection of representative colonies from the greatest dilution of meat samples. The pork samples were stored in two packaging films of different oxygen permeability at three storage temperatures. Strains were classified and those identified as lactic acid bacteria were screened for production of inhibitory substances. The types of bacteria isolated from samples stored in the two packaging films were similar. Storage temperature influenced the type of bacteria that dominated the microbial population. At 10 degrees C the prevalent microflora consisted of aeromonads, Enterobacteriaceae and lactic acid bacteria but at 4.4 and -1 degrees C, aeromonads, Brochothrix thermosphacta and lactic acid bacteria dominated. Listeriae were detected as part of the prevalent microflora on samples stored at -1 degree C, but not on samples stored at 4.4 or 10 degrees C. Species of lactic acid bacteria dominating the microflora were influenced by growth medium. The majority of isolates taken from Plate Count agar were carnobacteria whereas those from Lactobacilli MRS agar were homofermentative lactic acid bacteria. Of the 538 lactic acid bacteria isolates screened for production of inhibitory substances, 162 strains showed deferred inhibition toward a range of lactic acid bacteria and nonlactic acid bacteria indicator strains.

Chemical, microbial and sensory changes during the anaerobic cold storage of beef inoculated with a homofermentative Lactobacillus sp. or a Leuconostoc sp

Slices of beef were inoculated with about 3.5 log cfu/cm2 of Lactobacillus sp. 93 SMRICC 235 (homofermentative) or Leuconostoc sp. 89 SMRICC 189 and stored in 5% CO2 + 95% N2 at 4 degrees C. The microbial, chemical (glucose, L-lactate, D-lactate, acetate, formate, ethanol, H2S) and sensory changes of the beef slices were studied. For beef inoculated with Lactobacillus sp. 93 the flavour score started to decrease when the maximum bacterial count was reached. Leuconostoc sp. 89 caused a rapid decrease in the flavour score before reaching the maximum bacterial count. Concentrations of acetate and D-lactate increased while glucose and L-lactate decreased in beef slices inoculated with Lactobacillus sp. 93. In the presence of Leuconostoc sp. 89 ethanol and D-lactate increased while glucose decreased. Lactobacillus sp. 93 formed the highest level of H2S, and a sulphurous off-odour was noted only in the presence of this strain. D-Lactate and acetate indicated high numbers of Lactobacillus sp. 93 on the meat surface, while D-lactate and ethanol indicated high numbers of Leuconostoc sp. 89. More studies are needed in order to correlate levels of D-lactate, acetate and ethanol with sensory changes.