Biomedical subjects

F M Rombouts

Publications and source records attributed to F M Rombouts.

At least 73 records · Page 4Linked to original sources

PubMed1995

The effects of processing on the availability of lysine in kenkey, a Ghanaian fermented maize food.

The effects of processing steps such as soaking, fermentation, cooking and drying on the availability of lysine in kenkey were investigated. Soaking increased lysine availability by 21% and 22% for maize and maize-cowpea mixtures, respectively. Cooking of soaked samples further improved lysine availability by 68% and 31% for maize and maize-cowpea mixtures, respectively. Further significant improvements in lysine availability were effected by fermentation and cooking and values of 3.42 and 4.43 g/16 g N were recorded, respectively for maize and maize-cowpea doughs fermented for 4 days and cooked for 3 h. Cabinet drying had no significant effect on lysine availability, but drum drying of fermented maize and maize-cowpea doughs significantly lowered lysine availability in the resulting kenkey. A 1:1 mixture of cabinet and drum dried flours gave a product with higher available lysine content than the drum dried flour.

Biological Availability↗

PubMed1994

2-O-methyl-D-mannose residues are immunodominant in extracellular polysaccharides of Mucor racemosus and related molds.

In this study, the structure of the immunodominant carbohydrate epitope of the extracellular polysaccharides from mold species belonging to the order Mucorales reactive with rabbit IgG antibodies was elucidated. An exo-alpha-D-mannanase which was able to abolish the antigenicity of these polysaccharides completely was purified and characterized, and the activity was compared with that of an alpha-D-mannosidase. Analysis of the monomeric reaction products after enzymatic treatment revealed the presence of 2-O-methyl-D-mannose residues. This compound is a constituent of the polysaccharides from the mold genera Mucor, Rhizopus, Rhizomucor, Absidia, Syncephalastrum, and Thamnidium, and its occurrence in fungi has not been reported until now. Two mannan fractions which are highly reactive with rabbit IgG were isolated from the extracellular polysaccharides of Mucor racemosus and characterized with ethylation analysis. The role of the newly found 2-O-methyl-D-mannose residues in the immunoreactivity was assessed by specific degradation of these mannans with the exo-alpha-D-mannanase and subsequent ethylation analysis. It was concluded that the immunodominant carbohydrates reactive with rabbit IgG are chains composed of a single terminal non-reducing 2-O-methyl-D-mannose residue, alpha (1-2)-linked to a short sequence of alpha(1-2)-linked D-mannose residues.

Antibodies, Fungal↗

PubMed1994

Modelling growth rates of Listeria innocua as a function of lactate concentration.

The effect of sodium lactate (NaL) concentration on growth of Listeria innocua in a yeast-extract/peptone broth at pH 5.5, 6.0, 6.5 and 7.0 at 4, 10, 20 and 30 degrees C was modelled with the modified Gompertz model. NaCl was used as a reference to distinguish between the water activity effect and the specific inhibitory effect of NaL. Minimum inhibitory concentrations (MIC) of NaCl appeared to be significantly higher than MIC values of NaL, indicating that NaL had a specific inhibitory effect on growth of L. innocua. The MIC values of NaL and NaCl were not much influenced by the temperature. The pH of the growth medium was shown to have influence on the MIC values of NaL but not on the MIC values of NaCl. Total growth inhibition of L. innocua at low pH (5.5) took place at lower NaL concentrations (217 mM) than at neutral pH (1071-1339 mM), indicating that the undissociated lactic acid plays a role in the mechanism of inhibition. However, MIC values for undissociated acid increased with decreasing pH from 0.8 mM at pH 7 to 5 mM at pH 5.5. It is therefore likely that besides acidification of the cytoplasm due to diffusion of undissociated acid into the cell, other mechanisms are involved. Growth rates at NaL concentrations between 0 and the MIC value decreased progressively with increasing concentrations down to 0 at the MIC value, and were strongly influenced by both temperature and pH. Growth rates in the presence of NaCl were influenced by the temperature only. It was shown that a modified Monod equation with three parameters was effective for description of growth rates of L. innocua at NaL and NaCl concentrations over the whole experimental range.

Cell Division↗

PubMed1994

Effect of exogenous proline, betaine, and carnitine on growth of Listeria monocytogenes in a minimal medium.

Three Listeria monocytogenes strains isolated from food or food-processing environments were used to assess the response of this species to salinity in a chemically defined minimal medium. Growth in a minimal medium containing five essential amino acids and glucose as a carbon and energy source was comparable to growth in a rich medium (brain heart infusion broth). In the absence and presence of 3% NaCl the final cell numbers reached in minimal medium were 10(9) and 10(7) CFU/ml, respectively. Growth under the latter conditions could not be detected by spectrophotometry by measuring A660. Apparently, this technique was not suitable for these experiments since the detection level was > 10(7) CFU/ml. Exogenously added proline (10 mM), trimethylglycine (betaine) (1 mM), and beta-hydroxy-gamma-N-trimethyl aminobutyrate (carnitine) (1 mM) significantly stimulated growth under osmotic stress conditions in minimal medium at both 37 and 10 degrees C. Betaine and carnitine are present in foods derived from plants and animals, respectively. Therefore, these compounds can contribute significantly to growth of L. monocytogenes in various foods at high osmolarities.

Amino Acids↗

PubMed1994

Energy-dependent, carrier-mediated extrusion of carboxyfluorescein from Saccharomyces cerevisiae allows rapid assessment of cell viability by flow cytometry.

Carboxyfluorescein diacetate is a nonfluorescent compound which can be used in combination with flow cytometry for vital staining of yeasts and bacteria. The basis of this method is the assumption that, once inside the cell, carboxyfluorescein diacetate is hydrolyzed by nonspecific esterases to produce the fluorescent carboxyfluorescein (cF). cF is retained by cells with intact membranes (viable cells) and lost by cells with damaged membranes. In this report, we show that Saccharomyces cerevisiae extrudes cF in an energy-dependent manner. This efflux was studied in detail, and several indications that a transport system is involved were found. Efflux of cF was stimulated by the addition of glucose and displayed Michaelis-Menten kinetics. A Km for cF transport of 0.25 mM could be determined. The transport of cF was inhibited by the plasma membrane H(+)-ATPase inhibitors N,N'-dicyclohexylcarbodiimide and diethylstilbestrol and by high concentrations of tetraphenylphosphonium ions. These treatments resulted in a dissipation of the proton motive force, whereas the intracellular ATP concentration remained high. Transport of cF is therefore most probably driven by the membrane potential and/or the pH gradient. The viability of S. cerevisiae was determined by a two-step procedure consisting of loading the cells with cF followed by incubation at 40 degrees C in the presence of glucose. Subsequently, the fluorescence intensity of the cells was analyzed by flow cytometry. The efflux experiments showed an excellent correlation between the viability of S. cerevisiae cells and the ability to translocate cF. This method should prove of general utility for the rapid assessment of yeast vitality and viability.

Adenosine Triphosphatases↗

PubMed1994

Mode of Action of Nisin Z against Listeria monocytogenes Scott A Grown at High and Low Temperatures.

Nisin Z, a natural nisin variant, was recently isolated from Lactococcus lactis subspecies lactis NIZO 22186. The gene for this lantibiotic, designated nisZ, has been cloned, and its nucleotide sequence was found to be identical to that of the precursor nisin gene with the exception of a single mutation resulting in the substitution of Asn-27 for His-27 in the mature polypeptide (J. W. M. Mulders, I. J. Boerrigter, H. S. Rollema, R. J. Siezen, and W. M. de Vos, Eur. J. Biochem. 201:581-584, 1991). A K electrode was used to investigate the effect of various environmental parameters on the action of nisin Z against Listeria monocytogenes. Addition of nisin Z resulted in immediate loss of cell K, depolarization of the cytoplasmic membrane, inhibition of respiratory activity, and hydrolysis and partial efflux of cellular ATP. The action of nisin Z was optimal at pH 6.0 and was significantly reduced by di- and trivalent cations. The lanthanide gadolinium (Gd) was an efficient inhibitor and prevented nisin Z activity completely at a concentration of 0.2 mM. Nisin Z-induced loss of cell K was reduced at low temperatures, presumably as a result of the increased ordering of the lipid hydrocarbon chains in the cytoplasmic membrane. In cells grown at 30 degrees C, the action of nisin Z was prevented below 7 degrees C, whereas in cells grown at 4 degrees C nisin Z was able to induce K leakage at this low temperature.

Journal Article↗

PubMed1993

Characterization and frequency distribution of species of lactic acid bacteria involved in the processing of mawè, a fermented maize dough from Benin.

Lactic acid bacteria involved in the natural fermentation of both home-produced and commercial mawè were investigated during a 72 h fermentation period. Lactobacillus spp. constitute the majority (94%) of the strains of the lactic acid bacteria isolated, among which 89% represent the Betabacterium group. They include L. fermentum (biotype cellobiosus) (41%), L. fermentum or L. reuteri (19%), L. brevis (26%), L. confusus (less than 2%), L. curvatus (less than 1%) and L. buchneri (less than 1%). Other isolated lactic acid bacteria were L. salivarius, Lactococcus lactis, Pediococcus pentosaceus, Pediococcus acidilactici and Leuconostoc mesenteroides. Several species were detected at the early stage of fermentation, but the final stage was dominated by L. fermentum (biotype cellobiosus) and L. fermentum or L. reuteri totalling 90% of the isolated strains. The trend was the same for both home-produced and commercial mawè. No strains of L. plantarum, generally reported as dominating lactic acid bacteria at the final stage of fermentation of most plant foods, were isolated.

Benin↗

PubMed1993

Minimum inhibitory concentration (MIC) of sodium lactate for pathogens and spoilage organisms occurring in meat products.

Pathogens and spoilage organisms occurring in meat products were screened in laboratory media, according to a method of Eklund (1983), in order to determine the specific inhibitory effect of lactate on growth of these microorganisms under optimum growth conditions (pH 6.5, 20 degrees C). In general, Gram-positive bacteria were more sensitive towards lactate than Gram-negative bacteria. It was shown especially, that strains that were able to grow at water activities of 0.95 and below in the presence of NaCl (Staphylococcus aureus, Listeria monocytogenes, Brochothrix thermosphacta) were inhibited by sodium lactate (NaL). It appeared, that yeasts were resistant to large amounts of NaL (> 10% w/v). However, NaL had a specific inhibitory effect on growth of these organisms when compared to the effect of NaCl. These results indicate that lactate addition to food products with a pH near neutrality offers good prospects for shelf life prolongation.

Animals↗

PubMed1993

Inhibition of the growth of yeasts in fermented salads.

Salads composed of vegetables and/or meat in an oil-in-water emulsion were prepared by fermentation for 7 h at 42 degrees C or 45 degrees C with strains of Lactobacillus spp. Their stability towards spoilage yeasts was studied using Saccharomyces cerevisiae, Saccharomyces exiguus and Torulaspora delbrueckii, isolated from salads, as well as Pichia membranaefaciens and Zygosaccharomyces bailii. Salads fermented with good lactic starters usually had pH values of < or = 4.2 and lactic acid concentrations of 0.28 to 0.43% (w/w). High numbers of spoilage yeasts (and production of large volumes of CO2) were not attained in these salads, provided the initial concentration of spoilage yeasts was sufficiently low (< or = 100 CFU/g). Inhibition of spoilage yeasts in lactic fermented salads is probably due to lactic acid, the low storage temperature and the low residual oxygen concentration.

Animals↗

PubMed1993

The production and partial characterization of a monoclonal IgG antibody specific for moulds belonging to the order Mucorales.

A monoclonal antibody (mAb) was raised against extracellular polysaccharides from Mucor racemosus after intrasplenic immunization of mice. An indirect ELISA and a dot-blot assay were developed with this mAb. The IgG antibody was found to be very specific for all mould species tested belonging to the order of Mucorales, except species belonging to the genus Mortierella sensu stricto. No cross-reactions were observed with other moulds or yeasts. The immunoreactivity of the polysaccharides of these moulds with this mAb is based on carbohydrate epitopes, in which fucose residues probably play an important role. The mAb may be suited for specific detection of species of the genera Mucor, Rhizopus, Rhizomucor, Thamnidium, Absidia, Syncephalastrum and species belonging to the Mortierella isabellina group in food, and possibly for diagnosis of mucormycosis in humans.

Animals↗

PubMed1992

Detection of fungal carbohydrate antigens by high-performance immunoaffinity chromatography using a protein A column with covalently linked immunoglobulin G.

Fungal carbohydrate antigens were analysed by high-performance immunoaffinity chromatography (HPIAC) with immunoglobulin G (IgG) antibodies raised against extracellular polysaccharides of Mucor racemosus. The protein A-IgG complex was covalently bound with dimethyl pimelimidate, which enabled the use of strong acidic buffers to release the tightly bound antigens from the column. Prior to pulsed-amperometric detection, an anion-micromembrane suppressor was used to raise the pH of the effluent to above 12 without dilution. The HPIAC system provides a sophisticated method for the rapid and sensitive detection of antigenic oligomeric carbohydrates in biological samples and is proposed as an alternative to quantitative enzyme-linked immunosorbent assay techniques.

Antigens, Fungal↗

PubMed1992

Carbohydrate analysis of water-soluble uronic acid-containing polysaccharides with high-performance anion-exchange chromatography using methanolysis combined with TFA hydrolysis is superior to four other methods.

Sulfuric acid hydrolysis according to the Saeman procedure, TFA hydrolysis, and methanolysis combined with TFA hydrolysis were compared for the hydrolysis of water-soluble uronic acid-containing polysaccharides originating from fungi, plants, and animals. The constituent sugar residues released were subsequently analyzed by either conventional GLC analysis of alditol acetates or high-performance anion-exchange chromatography with pulsed-amperometric detection. It was shown that TFA hydrolysis alone is not sufficient for complete hydrolysis. Sulfuric acid hydrolysis of these polysaccharides resulted in low recoveries of 6-deoxy-sugar residues. Best results were obtained by methanolysis combined with TFA hydrolysis. Methanolysis with 2 M HCl prior to TFA hydrolysis resulted in complete liberation of monosaccharides from pectic material and from most fungal and animal polysaccharides tested. Any incomplete hydrolysis could be assessed easily by HPAEC, by the detection of characteristic oligomeric products, which is difficult using alternative methods currently in use. Methanolysis followed by TFA hydrolysis of 20 micrograms water-soluble uronic acid containing polysaccharides and subsequent analysis of the liberated sugar residues by HPAEC allowed us to determine the carbohydrate composition of these polysaccharides rapidly and accurately in one assay without the need for derivatization.

Animals↗

PubMed1992

Formation of antigenic extracellular polysaccharides by selected strains of Mucor spp., Rhizopus spp., Rhizomucor spp., Absidia corymbifera and Syncephalastrum racemosum.

In this study, polyclonal IgG antibodies raised against extracellular polysaccharides (EPS) of Mucor racemosus were characterised as almost specific for moulds belonging to the order of Mucorales. Cross-reactivity in the ELISA could be observed only towards the yeast Pichia membranaefaciens. EPS were isolated from various cultures of M. hiemalis growing on six different carbon sources and two nitrogen sources, with ratios varying from 0.13 to 0.44 relative to the amount of biomass. Other strains including Mucor spp., Rhizopus spp., Rhizomucor spp., Absidia corymbifera and Syncephalastrum racemosum also excreted EPS, with ratios varying from 0.05 to 0.23. In all cases, the excreted EPS had similar antigenic properties as determined by ELISA. No enzymatic degradation of the antigenic parts of the polysaccharides could be observed upon prolonged incubation. Considering that all tested strains formed similar amounts of antigenic EPS there might be scope for the specific detection of biomass of Mucoralean moulds using ELISA techniques for example in food.

Antibodies, Fungal↗

PubMed1992

Detection of Aspergillus and Penicillium extracellular polysaccharides (EPS) by ELISA: using antibodies raised against acid hydrolysed EPS.

Species of the fungal genera Aspergillus and Penicillium produce immunologically active extracellular polysaccharides (EPS) in which galactofuranose residues are immunodominant. The antigenic determinant of the EPS of A. fumigatus, A. niger and P. digitatum could be removed by acid hydrolysis. Due to the hydrolysis of the EPS the immunological reaction between IgG anti-native EPS and hydrolysed EPS disappeared. Antibodies raised in rabbits against the acid hydrolysed EPS revealed new antigenic determinants that were exposed as a result of the acid hydrolysis. Immunological inhibitory experiments showed that the antibodies were no longer directed to galactofuranose residues. Enzyme Linked Immunosorbent Assay, carried out with antibodies raised against the acid hydrolysed EPS showed that the antibodies against the acid hydrolysed EPS were more species specific in comparison with the antibodies against the native EPS.

Animals↗

PubMed1992

Mycological condition of maize products.

Maize and maize-related products were investigated in a collaborative study for viable moulds and antigenic extracellular polysaccharides (EPS) produced by Aspergillus and Penicillium species. In addition, the samples were tested for the presence of aflatoxin B1. All maize products, with the exception of the heat processed products, contained viable moulds on an average of (log10 values) 3.3 +/- 0.7 colony-forming units per gram. In most samples a mixed mould flora was present. Species of the genus Fusarium were dominant, followed by Aspergillus, Eurotium and Penicillium. The mould colony count correlated positively with the presence of antigenic extracellular polysaccharides produced by species of Aspergillus and Penicillium. Gamma irradiation did not affect the detection of antigenic extracellular polysaccharides. Aflatoxin B1 was detected in two out of 35 samples; these contained 0.6 and 0.8 microgram/kg. From one of these aflatoxin B1-containing samples, Aspergillus flavus was isolated.

Aflatoxin B1↗

PubMed1992

Comparison of definitions of the lag phase and the exponential phase in bacterial growth.

Different definitions for the lag time and of the duration of the exponential phase can be used to calculate these quantities from growth models. The conventional definitions were compared with newly proposed definitions. It appeared to be possible to derive values for the lag time and the duration of the exponential phase from the growth models and differences between the various definitions could be quantified. All the different values can be calculated from the growth parameters microm, lambda and alpha. Therefore, it appeared to be unnecessary to use complicated mathematical equations; simple equations were adequate. For the Gompertz model the conventional definition of the lag time did not differ appreciably from the newly proposed definition. The end-point of the exponential phase and thus the duration of the exponential phase differed considerably for the two definitions. For the logistic model the two definitions lead to considerable differences for all quantities. It is recommended that the conventional definition is used for calculating the lag time. For the duration of the exponential phase it is recommended that the new definition is used. The value can be calculated, however, directly from the conventional growth parameters.

Bacteria↗

PubMed1992

New structural features of the antigenic extracellular polysaccharides of Penicillium and Aspergillus species revealed with exo-beta-D-galactofuranosidase.

To study the structures of the epitopes of the extracellular polysaccharides from Penicillium and Aspergillus species, an exo-beta-D-galactofuranosidase was purified from a commercial crude enzyme preparation from Trichoderma harzianum. Analysis of ring size and linkage position of the galactose residues of the extracellular polysaccharide of Penicillium digitatum, before and after enzymatic treatment, was determined by the reductive-cleavage technique. In addition to terminal and beta (1-5)-linked galactofuranosides, beta (1-6)-linked and beta (1,5,6)-linked branched galactofuranose residues could be identified. After degradation with the purified exo-beta-D-galactofuranosidase, all initial linkages of the galactofuranose residues were still present, but the amount of beta (1-5)-linked galactofuranose residues had decreased considerably. Treatment of the extracellular polysaccharides of Penicillium and Aspergillus species with the purified exo-beta-D-galactofuranosidase resulted in complete disappearance of the enzyme-linked immunosorbent assay reactivity of these polysaccharides, using immunoglobulin G antibodies raised against P. digitatum. Therefore, with the use of this enzyme, it was proved that the beta (1-5)-linked galactofuranosyl residues only are responsible for the antigenicity of the extracellular polysaccharides of Penicillium and Aspergillus molds. A new structural model for the antigenic galactofuranose side chains of the galactomannan from P. digitatum is proposed.

Aspergillus↗

PubMed1992

Faecal micro-organisms on the hands of carriers: Escherichia coli as model for Salmonella.

To evaluate the public health hazard caused by Salmonella carriers as food handlers, a study was carried out to gather more quantitative data about faecal contamination of hands after stools. Faecal E. coli was used as a model bacterium for Salmonella. In total 92 subjects cooperated in this study. The hand was sampled before toilet use, and also after stools, with or without washing of the hands. Besides E. coli the number of Enterobacteriaceae was also determined. It appeared that hands may be contaminated with Enterobacteriaceae, regardless of toilet use, for a well before as after stools about 60% of the sampled hands carried a detectable number of Enterobacteriaceae. That is why the presence of Enterobacteriaceae on hands is not a good indicator for toilet hygiene. In 4% of the samples before stools and in 25% of the samples taken after stools E. coli could be detected (> 20 CFU/sample). The average 10log CFU of E. coli in the positive samples taken before and after stools were about the same: 2.30 per sample. Hand washing after stools reduced the numbers of Enterobacteriaceae and E. coli on the hands. It was concluded that symptomless Salmonella excretors in the period starting two weeks after infection form only a low risk in carrying over Salmonella by their hands to food. Especially if normal hygiene is practiced like washing hands after stools, the number of contaminated hands will be very low and furthermore the number of faecal micro-organisms will be very small.(ABSTRACT TRUNCATED AT 250 WORDS)

Carrier State↗