Aims
This study aimed to explore the discriminatory power of MALDI‐TOF MS as a high‐throughput method to monitor growth dynamics of meat‐spoiling bacteria on modified atmosphere packaged (MAP) beef ...and to differentiate psychrophilic and psychrotrophic spoilage‐associated strains.
Methods and Results
MAP beef steaks were incubated for 21 days at constant 4 and 10°C. Development of headspace gas composition, pH, CFU and spoilage‐associated microbial composition were monitored. MALDI‐TOF MS exhibited high discriminatory power for reliable, high‐throughput identification of spoilage‐associated, psychrotrophic microbiota. Microbiota development was highly dependent on initial abundance of specific species. Organoleptic onset of spoilage was concomitant with an alteration of headspace atmosphere and pH. Screening for psychrophiles at 4°C on beef revealed the abundance of Leuconostoc gelidum subsp. gelidum TMW2·1998 with characteristic psychrophilic growth behaviour.
Conclusions
We suggest that control of initial contaminants is crucial to predict the onset of spoilage and that headspace atmosphere and pH are important parameters with spoilage‐indicative potential.
Significance and Impact of the Study
MALDI‐TOF MS proved suitable for high‐resolution monitoring of psychrotrophic and psychrophilic spoilage‐associated microbiota and enables improved insights in the spoilage progress. The presence of psychrophilic strains on beef is the likely causative for unexplained spoilage events.
Aims
The aim of this study was to analyse the bacterial microbiota of water kefir using culture‐independent methods.
Methods and Results
We compared four water kefirs of different origins using 16S ...rDNA amplicon sequencing and ARDRA. The microbiota consisted of different proportions of the genera Lactobacillus (Lact.), Leuconostoc (Leuc.), Acetobacter (Acet.) and Gluconobacter. Surprisingly, varying but consistently high numbers of sequences representing members of the genus Bifidobacterium (Bif.) were found in all kefirs. Whereas part of the bifidobacterial sequences could be assigned to Bifidobacterium psychraerophilum, a majority of sequences identical to each other could not be assigned to any known species. A nearly full‐length sequence of the latter exhibited a beyond‐species similarity (96·4%) with the sequence from the closest relative species Bif. psychraerophilum. A Bifidobacterium‐specific ARDRA analysis reflected the abundance of the novel Bifidobacterium species by revealing its unique MboI restriction profile. Attempts to isolate the bifidobacteria were successful for Bif. psychraerophilum only.
Conclusions
The complexity of the water kefir microbiota has been underestimated in previously studies. The occurrence of bifidobacteria as part of the consortium is novel.
Significance and Impact of the Study
These data give new insights into the understanding of the complexity of food fermentations and underline the need for approaches detecting noncultivable organisms.
In the present study we investigated the influence of heat treatment of lupin-based (LB) milk alternatives and different exopolysaccharide (EPS)-producing lactic acid bacteria on the physical ...characteristics of set-type LB yogurt alternatives. LB milk alternatives, obtained from protein isolate of Lupinus angustifolius cv. Boregine, were either pasteurized at 80°C for 60s or ultra-high temperature (UHT) heated at 140°C for 10s and was fermented with Lactobacillus plantarum TMW 1.460 and 1.1468, Pediococcus pentosaceus BGT B34 and Lactobacillus brevis BGT L150. Fermentation duration was strongly affected by heat treatment: different strains needed between 25 to 35h in UHT LB milk alternative to reach a pH of 4.5 compared to 14 to 24h in pasteurized LB milk alternative. EPS extraction revealed slightly higher amounts of EPS for UHT LB yogurt alternatives (~0.5–0.9g/l; pasteurized: ~0.4–0.7g/l). The more intensive heat treatment (UHT) resulted also in better rheological (apparent viscosity, hysteresis loop area, flow point, elastic, viscous and complex modulus) and textural properties (firmness, consistency, cohesiveness and index of viscosity) of the investigated LB yogurt alternatives. Furthermore, LB yogurt alternatives out of UHT milk alternative revealed a lower tendency to syneresis, measured with siphon and centrifugation method. This work contributes to the fundamental knowledge of the textural properties of LB yogurt alternatives.
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•Ultra-high temperature (UHT) treatment of lupin-based (LB) milk alternatives improved physical properties of respective yogurts compared to pasteurization.•Fermentation duration was longer in UHT than in pasteurized LB milk alternative.•Microorganisms produced more exopolysaccharides in UHT than in pasteurized LB milk alternative.
During storage of modified atmosphere packaged (MAP) meat, the initial microbiota grows to high cell numbers, resulting in perceptible spoilage after exceeding a specific threshold level. This study ...analyses, whether elevated oxygen consumption in the headspace of MA‐packages would enable a prediction method for meat spoilage. We monitored the growth of single spoiling species inoculated on high‐oxygen MAP beef and poultry, performed sensorial analysis and determined oxygen concentrations of the headspace via a non‐invasive sensor spot technology. We detected microbial headspace oxygen consumption occurring prior to perceptible meat spoilage for certain species inoculated on beef steaks. However, headspace oxygen consumption and cell counts at the onset of spoilage were highly species‐dependent, which resulted in a strong (Brochothrix thermosphacta) and moderate (Leuconostoc gelidum subspecies) decrease of the headspace oxygen content. No linear decrease of the headspace oxygen could be observed for Carnobacterium divergens and Carnobacterium maltaromaticum inoculated on poultry meat. We demonstrate the applicability of an incorporated oxygen sensor spot technology in MAP meat packages for detection of spoilage in individual packages prior to its perceptible onset. This enables individual package evaluation and sorting within retail, and consequently reduces meat disposal as waste.
Significance and Impact of the Study: This study demonstrates applicability of an incorporated oxygen sensor spot to non‐invasively determine microbial headspace oxygen consumption in high oxygen modified atmosphere packages (MAP). Furthermore, exploitation of this technology for the prediction of the onset of meat spoilage prior to human perception is demonstrated. Thus, this study provides proof of concept for a novel rapid and easily implementable method, which can be used to reduce meat disposal as waste in retail by individual assessment of single high oxygen MAP.
Aims
This study aimed to monitor development of spoilage‐associated microbiota on high‐oxygen modified atmosphere packaged (MAP) minced beef, assess diversity of Pseudomonas sp. therein employing a ...polyphasic approach and probe their ability to grow anaerobically in the presence of carbon dioxide.
Methods and Results
Headspace atmosphere and total viable count of MAP minced beef were monitored, and spoilage‐associated microbiota was identified using matrix‐assisted laser desorption/ionization time of flight mass spectrometry (MALDI‐TOF MS). Pseudomonas spp. represented a major part of the spoilage‐associated microbiota throughout the spoilage process and were characterized with a polyphasic approach including MALDI‐TOF, randomly amplified polymorphic DNA biotyping, 16S rDNA and rpoD sequence analysis, and carA multiplex polymerase chain reaction. Pseudomonas isolates displayed high diversity and varying assertiveness under conditions employed in MAP minced beef with P. fragi, P. lundensis and P. weihenstephanensis as dominant species.
Conclusions
The polyphasic approach enabled high‐throughput characterization of Pseudomonas sp. Their adapted capability to grow anaerobically and resistance to high levels of CO2 is suggested to be a general feature within the genus, which is hitherto underexplored.
Significance and Impact of the Study
This study shows that diverse Pseudomonas generally regarded as strict aerobes and CO2‐sensitive appear well adapted to grow under MAP conditions, leading to high cell counts in minced beef and ultimately contribute to spoilage of the product.
Latilactobacillus sakei comprises a biodiversity of strains, which display different assertiveness upon their application as starter cultures in raw sausage fermentation. While the assertiveness of ...winning partner strains has been referred to competitive exclusion based on genomic settings enabling occupation of multiple niches of the sausage habitat, single strain assertiveness of L. sakei remained unexplained. In this study we assessed the impact of the expression of a glycosyltransferase enabling the production of a glucan from sucrose to the assertiveness of L. sakei TMW 1.411, which expresses a plasmid-encoded glycosyltransferase (gtf). In a sausage fermentation model wild type L. sakei TMW 1.411 and its plasmid-cured mutant were employed in competition with each other and with other Latilactobacillus sakei strains. To differentiate any effects resulting from general sugar utilization from those of glucan formation, the experiments were carried out with glucose, fructose, and sucrose, respectively. It was shown that the type of sugar affects the individual strains behaviour, and that the wild type was more competitive than the mutant in the presence of any of these sugars. In direct competition between wild type and mutant, a clear competitive advantage could also be demonstrated for the strain possessing the plasmid with the glycosyltransferase. Since this competitive advantage was observed with all sugars, not just sucrose, and Gtf expression has been shown as independent of the employed sugar, it is suggested that possession of the gtf gene-carrying plasmid confers a competitive advantage. It appears that the Gtf contributes to competitive exclusion and the establishment of colonization resistance, to a larger extent by an adhesive functionality of the Gtf on the cellular surface than by the production of glucan. Hence, gtf genes can be used as a possible additional marker for the selection of assertive L. sakei starter strains in sausage fermentation.
•The choice of sugar affects strain performance in sausage fermentation.•Cell wall-bound L. sakei dextransucrase confers a competitive advantage.•Above dextran formation the gtf protein confers colonization resistance.
In situ annealing within a neutron beam line and ex situ annealing followed by transmission electron microscopy were used to study the thermal stability of the texture, microstructure, and bi-metal ...interface in bulk nanolamellar Cu/Nb composites (h = 18 nm individual layer thickness) fabricated via accumulative roll bonding, a severe plastic deformation technique. Compared to the bulk single-phase constituent materials, the nanocomposite is two orders of magnitude higher in hardness and significantly more thermally stable, e.g., no observed recrystallization in Cu at temperatures as high as 85% of the melting temperature. The nanoscale h = 18 nm individual layer thickness is maintained up to 500°C, the lamellar structure thickens but is maintained up to 700°C, and recrystallization is suppressed even up to 900°C. With increasing temperature, the texture sharpens, and among the interfaces found in the starting material, the {112}
Cu
|| {112}
Nb
interface with a Kurdjumov-Sachs orientation relationship shows the greatest thermal stability. Our results suggest that thickening of the individual layers under heat treatment coincides with thermally driven removal of energetically unfavorable bi-metal interfaces. Thus, we uncover a temperature regime that maintains the lamellar structure but alters the interface distribution such that a single, low energy, thermally stable interface prevails.
In this study lupin-based milk alternative (LBMA), obtained from protein isolate of Lupinus angustifolius cv. Boregine, was homogenized and was subjected to different heat treatments (unheated; ...pasteurized: 80°C, 60s; ultra-high temperature heating (UHT): 140°C, 10s). Upon thermal treatment, lupin proteins, namely β-conglutin and α-conglutin, were stepwise denatured, which was accompanied by the exposure of masked sulfhydryl groups, the decrease of free sulfhydryl groups and reoxidation to disulfide bridges. Moreover, quaternary structure of lupin proteins was influenced upon heat treatment displayed with molecular weight distribution (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Further, particle size distribution showed that heat treatment promoted the formation of smaller particles. Differently heated LBMA were additionally fermented to lupin-based yogurt alternatives (LBYA) with different lactic acid bacteria (Lactobacillus plantarum TMW 1.460 and 1.1468, Pediococcus pentosaceus BGT B34 and Lactobacillus brevis BGT L150) and microstructural observations (Confocal Laser Scanning Microscopy, cryo-Scanning Electron Microscopy) were performed. Micrographs showed that harsher thermal treatments of LBMA (UHT heating) led to more close-meshed microstructures of respective LBYA. Further, the choice of microorganisms seemed to play a decisive role in microstructural appearance of respective LBYA as the composition of the networks were fundamental different.
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•Upon heating of lupin-based milk alternatives, proteins were stepwise denatured.•Heating caused the exposure of sulfhydryl groups and oxidation to disulfide bridges.•Harsher heating led to more close-meshed networks of lupin-based yogurt alternatives.•Microstructural appearance of lupin-based yogurt alternatives was strain-dependent.
Aims
This study aimed to investigate intraspecies assertiveness of meat‐borne Lactococcus piscium isolates, inhibitory effects on unwanted and harmful meat spoilers, and the prevalence on beef ...deliberately inoculated with Lc. piscium.
Methods and Results
Co‐inoculation of Lc. piscium isolates and spoilers (Brochothrix thermosphacta, Leuconostoc gelidum subsp. gasicomitatum, Carnobacterium divergens, Pseudomonas weihenstephanensis, Serratia liquefaciens, Hafnia alvei) were conducted in sterile meat simulation medium. Differentiation of Lc. piscium strains was carried out with colony‐based RAPD‐PCR. Selective cultivation was used to differentiate spoilers from Lc. piscium. Intraspecies assertiveness revealed Lc. piscium TMW2.1614 as most assertive strain. Co‐inoculation of selected Lc. piscium strains caused substantial growth reduction of spoilers while the extent was strain‐ and spoiler dependent. Monitoring the microbiota on beef steaks deliberately inoculated with Lc. piscium revealed prevalence over the endogenous microbiota while maintaining a ripened sensory impression without undesired alterations.
Conclusions
This study reveals Lc. piscium strains TMW2.1612/2.1614/2.1615 as highly competitive against spoilers in vitro while beef deliberately inoculated with these strains maintained acceptable organoleptics.
Significance and Impact of the Study
Selected Lc. piscium strains exhibit high potential for application as bioprotective cultures for competitive exclusion on beef in order to extend minimum shelf life and enhance product safety of meat.
Crop residues such as corn (
Zea mays L.) stover are viewed as an abundant and inexpensive source of biomass that can be removed from fields to produce bioenergy. Assumptions include that with ...minimum or no-tillage farming methods, there will be no deleterious production or environmental effects. A long-term field study was established in eastern Nebraska, USA, to compare the switchgrass managed as a biomass energy crop versus no-till corn on a non-irrigated site, marginal for row-crop production, in the western Corn Belt. Our objective in this paper is to report on corn stover removal effects on corn grain yields and potential ethanol production in both cropping systems. Corn, under no-till management, and switchgrass were grown at three N fertilizer levels. In the first 5 years (2001–2005), removal of half the available stover significantly reduced corn yields. During that same time period, the potential ethanol yield for switchgrass was equal to or greater than the potential total ethanol yield of corn grain and harvested stover fertilized at the same optimum N rate. The effect of crop residue removal on crop productivity needs to be investigated in other agro-ecosystems and the potential use of dedicated perennial biomass energy crops should remain a viable renewable energy option on non-irrigated marginal croplands.
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