24 research outputs found
Pilot-scale crossflow-microfiltration and pasteurization to remove spores of Bacillus anthracis (Sterne) from milk
High-temperature, short-time pasteurization of milk
is ineffective against spore-forming bacteria such as
Bacillus anthracis (BA), but is lethal to its vegetative
cells. Crossflow microfiltration (MF) using ceramic
membranes with a pore size of 1.4 μm has been shown
to reject most microorganisms from skim milk; and,
in combination with pasteurization, has been shown to
extend its shelf life. The objectives of this study were
to evaluate MF for its efficiency in removing spores
of the attenuated Sterne strain of BA from milk; to
evaluate the combined efficiency of MF using a 0.8-μm
ceramic membrane, followed by pasteurization (72°C,
18.6 s); and to monitor any residual BA in the permeates
when stored at temperatures of 4, 10, and 25°C
for up to 28 d. In each trial, 95 L of raw skim milk
was inoculated with about 6.5 log10 BA spores/mL of
milk. It was then microfiltered in total recycle mode
at 50°C using ceramic membranes with pore sizes of
either 0.8 μm or 1.4 μm, at crossflow velocity of 6.2 m/s
and transmembrane pressure of 127.6 kPa, conditions
selected to exploit the selectivity of the membrane.
Microfiltration using the 0.8-μm membrane removed
5.91 ± 0.05 log10 BA spores/mL of milk and the 1.4-
μm membrane removed 4.50 ± 0.35 log10 BA spores/
mL of milk. The 0.8-μm membrane showed efficient
removal of the native microflora and both membranes
showed near complete transmission of the casein proteins.
Spore germination was evident in the permeates
obtained at 10, 30, and 120 min of MF time (0.8-μm
membrane) but when stored at 4 or 10°C, spore levels
were decreased to below detection levels (≤0.3 log10
spores/mL) by d 7 or 3 of storage, respectively. Permeates
stored at 25°C showed coagulation and were
not evaluated further. Pasteurization of the permeate
samples immediately after MF resulted in additional
spore germination that was related to the length of
MF time. Pasteurized permeates obtained at 10 min of
MF and stored at 4 or 10°C showed no growth of BA
by d 7 and 3, respectively. Pasteurization of permeates
obtained at 30 and 120 min of MF resulted in spore
germination of up to 2.42 log10 BA spores/mL. Spore
levels decreased over the length of the storage period
at 4 or 10°C for the samples obtained at 30 min of MF
but not for the samples obtained at 120 min of MF.
This study confirms that MF using a 0.8-μm membrane
before high-temperature, short-time pasteurization
may improve the safety and quality of the fluid milk
supply; however, the duration of MF should be limited
to prevent spore germination following pasteurization
Identification of Lactobacillus Strains Capable of Fermenting Fructo-Oligosaccharides and Inulin
Novel probiotic strains that can ferment prebiotics are important for functional foods. The utilization of prebiotics is strain specific, so we screened 86 Lactobacillus strains and compared them to Bifidobacterium breve 2141 for the ability to grow and produce SCFA when 1% inulin or fructo-oligosaccharides (FOS) were provided as the carbon source in batch fermentations. When grown anaerobically at 32 °C, ten Lactobacillus strains grew on both prebiotic substrates (OD600 ≥ 1.2); while Lactobacillus coryniformis subsp. torquens B4390 grew only in the presence of inulin. When the growth temperature was increased to 37 °C to simulate the human body temperature, four of these strains were no longer able to grow on either prebiotic. Additionally, L. casei strains 4646 and B441, and L. helveticus strains B1842 and B1929 did not require anaerobic conditions for growth on both prebiotics. Short-chain fatty acid analysis was performed on cell-free supernatants. The concentration of lactic acid produced by the ten Lactobacillus strains in the presence of prebiotics ranged from 73–205 mM. L. helveticus B1929 produced the highest concentration of acetic acid ~19 mM, while L. paraplantarum B23115 and L. paracasei ssp. paracasei B4564 produced the highest concentrations of propionic (1.8–4.0 mM) and butyric (0.9 and 1.1 mM) acids from prebiotic fermentation. L. mali B4563, L. paraplantarum B23115 and L. paracasei ssp. paracasei B4564 were identified as butyrate producers for the first time. These strains hold potential as synbiotics with FOS or inulin in the development of functional foods, including infant formula
Anti-listerial activity of thermophilin 110 and pediocin in fermented milk and whey
Listeria monocytogenes is a pathogenic bacterium responsible for foodborne illness worldwide. Antimicrobial
peptides, or bacteriocins, produced by food-grade lactic acid bacteria can serve as preservatives to prevent
Listeria’s growth in various foods, including dairy products. This study investigated the anti-listerial activities of
bacteriocin-producing lactic acid bacteria, Streptococcus thermophilus B59671, and Lactobacillus plantarum 076. In
vitro studies showed that the concentration of pediocin produced by L. plantarum 076 (2560 AU/mL) inhibited
the growth of a six-strain cocktail of L. monocytogenes. However, the concentration of thermophilin 110 produced
by S. thermophilus B59671 (320 AU/mL) only delayed the growth by ~2 h. Higher concentrations of thermophilin
110 (≥640 AU/mL) suppressed Listeria growth for up to 22 h. Pasteurized skim milk fermented with a co-culture
of S. thermophilus B59671 and L. plantarum 076 reduced the number of L. monocytogenes cells by > 4 Log CFU/mL
due mainly to the activity of pediocin. The anti-listerial activity was not observed in whey samples collected from
pasteurized skim milk fermented with this co-culture but was detected when raw milk was the substrate. Two
additional whey preparations, the by-products from commercial bovine and goat raw-milk cheeses, also inhibited
Listeria growth and reduced the number of cells following storage at 4 ◦C for one week. This study showed that a
concentrated preparation of thermophilin 110 has potential as an anti-listerial compound. It demonstrated the
prospect of using a co-culture of S. thermophilus B59671 and L. plantarum 076 to prevent Listeria contamination in
dairy foods. Additionally, results showed that metabolites with antimicrobial activities may be generated during
the fermentation of raw milk due to indigenous microflora
Table_1_The quorum sensing peptide BlpC regulates the transcription of genes outside its associated gene cluster and impacts the growth of Streptococcus thermophilus.DOCX
Bacteriocin production in Streptococcus thermophilus is regulated by cell density-dependent signaling molecules, including BlpC, which regulates transcription from within the bacteriocin-like peptide (blp) gene cluster. In some strains, such as S. thermophilus ST106, this signaling system does not function properly, and BlpC must be supplied exogenously to induce bacteriocin production. In other strains, such as S. thermophilus B59671, bacteriocin (thermophilin 110 in strain B59671) production occurs naturally. Here, transcriptomic analyses were used to compare global gene expression within ST106 in the presence or absence of synthetic BlpC and within B59671 to determine if BlpC regulates the expression of genes outside the blp cluster. Real-time semi-quantitative PCR was used to find genes differentially expressed in the absence of chromosomal blpC in the B59671 background. Growth curve experiments and bacteriocin activity assays were performed with knockout mutants and BlpC supplementation to identify effects on growth and bacteriocin production. In addition to the genes involved in bacteriocin production, BlpC affected the expression of several transcription regulators outside the blp gene cluster, including a putative YtrA-subfamily transcriptional repressor. In strain B59671, BlpC not only regulated the expression of thermophilin 110 but also suppressed the production of another bacteriocin, thermophilin 13, and induced the same YtrA-subfamily transcriptional repressor identified in ST106. Additionally, it was shown that the broad-spectrum antimicrobial activity associated with strain B59671 was due to the production of thermophilin 110, while thermophilin 13 appears to be a redundant system for suppressing intraspecies growth. BlpC production or induction negatively affected the growth of strains B59671 and ST106, revealing selective pressure to not produce bacteriocins that may explain bacteriocin production phenotype differences between S. thermophilus strains. This study identifies additional genes regulated by BlpC and assists in defining conditions to optimize the production of bacteriocins for applications in agriculture or human and animal health.</p
Cranberry arabino-xyloglucan and pectic oligosaccharides induce lactobacillus growth and short-chain fatty acid production
Numerous health benefits have been reported from the consumption of cranberry-derived
products, and recent studies have identified bioactive polysaccharides and oligosaccharides from
cranberry pomace. This study aimed to further characterize xyloglucan and pectic oligosaccharide
structures from pectinase-treated cranberry pomace and measure the growth and short-chain fatty
acid production of 86 Lactobacillus strains using a cranberry oligosaccharide fraction as the carbon
source. In addition to arabino-xyloglucan structures, cranberry oligosaccharides included pectic
rhamnogalacturonan I which was methyl-esterified, acetylated and contained arabino-galacto-oligosaccharide
side chains and a 4,5-unsaturated function at the non-reducing end. When grown on
cranberry oligosaccharides, ten Lactobacillus strains reached a final culture density (ΔOD) ≥ 0.50 after
24 h incubation at 32 °C, which was comparable to L. plantarum ATCC BAA 793. All strains produced
lactic, acetic, and propionic acids, and all but three strains produced butyric acid. This study
demonstrated that the ability to metabolize cranberry oligosaccharides is Lactobacillus strain specific,
with some strains having the potential to be probiotics, and for the first time showed these ten
strains were capable of growth on this carbon source. The novel cranberry pectic and arabino-xyloglucan
oligosaccharide structures reported here combined with the Lactobacillus strains that can
metabolize cranberry oligosaccharides and produce short-chain fatty acids, have excellent potential
as health-promoting synbiotics