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Biomedical subjects

H Klostermeyer

Publications and source records attributed to H Klostermeyer.

At least 37 records · Page 2Linked to original sources
PubMed1986

Indoxylsulfate in milk.

Indoxylsulfate in 27 individual milk samples ranged from 25.4 to 111 micrograms/l (average 52.3 micrograms/l); pooled milk samples from 12 farms contained 81.1 micrograms/l (46.4-146 micrograms/l); the variation in indoxylsulfate concentration of dried skimmed milk over a period of one year amounted to 23%. This variability is likely attributable to regional and seasonal, and hence to feeding effects. The indoxylsulfate content of milk seems also to be dependent upon the degree of fermentation during processing of milk; yoghurt contained very low amounts of this component (6.4 micrograms/kg). On the other hand, heat treatment of the milk (HTST, UHT, sterilization) apparently does not affect its indoxylsulfate content. Indoxylsulfate concentrations in milk correlated positively with blood-serum indoxylsulfate content (r = 0.752, n = 20) and with the urea content of milk (r = 0.61, n = 12 pooled milks). Further research is suggested on the use of indoxylsulfate determinations as an aid to determine sweet whey added to dried skimmed milk, also as an analytical tool to differentiate bovine and sheep milks.

Animals↗
PubMed1984

[Proteolytic activities of Ps. fluorescens in milk: determination with azocasein in comparison with HPA].

Proteolytic activity of psychotrophie bacteria in milk can be measured in a practical and comparatively sensitive manner using Azocasein as a substrate. The necessary parameters were exemplarily developed and demonstrated with a typical, strongly proteolytic strain of Pseudomonas fluorescens (No. 112). Comparison of the improved Azocasein method with a modified version of the HPA method of Cliffe and Law--they had proposed it for predicting the stability of UHT milk--showed nearly the same sensitivity with six test strains of Pseudomonas fluorescens. The first significant detection of proteolytic activity could be made approximately at the same time except with one strain of the biotype II (miscellaneous strains). It is discussed, whether the demonstrated methods can be judged (by the bacterial counts of detection) as sufficiently sensitive for to prediction of term spoilage during storage of UHT products.

Animals↗
PubMed1984

Heat inactivation of exogenous proteinases from Pseudomonas fluorescens. I. Possibility of inactivation in milk.

The inactivation reaction of the proteinase of a P. fluorescens strain of biotype I in milk was investigated at 130-150 degrees C, also in milk and in buffer with and without added CaCl2 at temperatures below 100 degrees C. The decline in activity corresponded to first order kinetics in the UHT region; Ea = 115 kJ/mol. D values were 290 (130 degrees C), 124 (140 degrees C) and 54 s (150 degrees C); therefore, the usual temperature time combinations of UHT treatment are not sufficient to achieve the required rates of inactivation. At temperatures below 80 degrees C, inactivation corresponded increasingly to second order kinetics with considerably higher reaction rates; at 55 degrees C, an inactivation reaction corresponding to that induced by UHT treatment could be achieved at a thermal stress lower by a factor of 500. This "low temperature inactivation" was observed in a further 20 strains representing the spectrum of P. fluorescens. The average rates of inactivation following heat treatment in milk for 20 min are 47% at 55 degrees C and 44% at 60 degrees C. This can be regarded as the most effective temperature range for the inactivation of the proteinases in milk. Clear connections can be seen between the biotype groups and the optimum temperature for inactivation: biotype group I ca. 55 degrees C, group II (with a few exceptions) less than or equal to 50 degrees C and group III greater than or equal to 60 degrees C. The inactivation reaction is systematically influenced by the proteins and Ca++ ions present in milk.

Animals↗
PubMed1984

A new metalloproteinase from Pseudomonas fluorescens biotype I.

Isolation and purification of a metalloproteinase from Pseudomonas fluorescens Biotype I are described. The molecular mass of the enzyme is 46 kDa, its isoelectric point is 8.1, its activity is trypsin-like. The amino-acid composition of the single chain protein is given. One molecule of the enzyme contains 1 atom of zinc and 9 atoms of calcium.

Amino Acid Sequence↗
PubMed1983

Formation of lysinoalanine during heat treatment of milk.

The heat-induced formation of lysinoalanine (LAL) was studied in raw skim milk that had been subjected to heat treatments as is usual in milk technology. Preheat treatment of milk at temperatures below 100 degrees C up to 20 min resulted in neglectable LAL amounts below 10 ppm i.p. (i.p.=in the protein) if at all. Tests with an UHT pilot plant showed that there was no proven formation of LAL with direct UHT-treatment at 110-130 degrees C for 10-25 min. In indirect UHT-treated milk vert small LAL amouints up to 50 ppm i.p. were detected only in those milk samples that were treated at temperatures high than 145 degrees C and holding times longer than 10 s. Autoclave sterilization in the range of 110-129 degrees C/10-25 min induced LAL amounts of 110 to 710 ppm i.p.. LAL formation in autoclave sterilized milk was almost directly dependent on heating temperature and time. Pre-treatment at temperatures below 100 degrees C induced no further LAL formation in any sterilization processes subsequent to preheating. In the pH range 6,50-6,90 LAL amounts in autoclave-sterilized milk increased directly with higher pH values at all temperatures. The varying degree of LAL formation with pH value was substantially more noticeable at higher than at lower temperatures. Increasing of lactose concentration caused only an insignificant decrease in LAL formation in autoclave-sterilized milk.

Animals↗
PubMed1983

[Detection and determination of protein-bound formaldehyde. II. Improved recovery of formaldehyde by reduction with sodium cyanoborohydride (NaCNBH3)].

When using NaCNBH3 as a reductant, it is possible to recover 70% of added formaldehyde in foods--in this skim milk powder. Formaldehyde is attached to the epsilon-Aminogroups of lysine and is detected after reduction in form of N epsilon-methyllysine in an automated amino acid analyzer system. After addition of N alpha-acetyllysine the reduction is carried out by incubating the skim milk powder at 70 degrees C for 1 h. The best combination of pH, concentration of reductant, time and temperature of incubation is described.

Amino Acids↗
PubMed1980

[Aflatoxin M1 in milk and milk products. A comparison of some determination procedures].

Usual TLC-methods for the determination of Aflatoxin M1 in milk and milk products sometimes do not separate interfering substances with similar optical and chemical properties from Aflatoxin M1, thus leading to considerably incorrect results. Even after an additional clean-up on polystyrene column the solutions contain so many compounds that the identification of Aflatoxin M1 is difficult. The resolving power of HPLC yield pure frations, which may be determined by their MS and UV spectra.

Aflatoxin M1↗
PubMed1977

Gel diffusion--a simple and sensitive technique for the assay of proteinase inhibitors and its use for the determination of the ratio of proteinases in mixtures.

In casein-containing agarose gels, pepsin and chymosin form radial diffusion zones; the diameters of these zones show rectilinear correlations with the logarithm of the enzyme concentration at constant time. The sensitivity for both enzymes is below 1 microgram. Addition of the inhibitor pepstatin A to these enzymes causes a reduction of the diameters of the diffusion zones, with large differences for both the enzymes. With this procedure, the pepsin/chymosin ratio in rennet preparations was assayed with an accuracy of +/- 5%. Identification of the inhibitors allows the determination of amounts in the namomole range. This method is a simple technique for the evaluation of proteinases and their inhibitors in screening systems.

Animals↗
PubMed1977

[Formation of dehydroalanine, lanthionine and lysinoalanine during heat treatment of beta-lactoglobuline A (author's transl)].

Solutions of beta-lactoglobulin A were heated at 97.5 degrees C at pH 6.9 and 9.8 80 min. The formation of dehydroalanine, lanthionine and lysinoalanine as well as changes in the levels of cysteine, cystine and the basic amino acids were recorded. Lanthionine (equal amounts of the 1- and the mesoform) was formed only in small amounts, while the lysinoalanine levels were rather high. Beside this, lysine was converted to unknown compounds. The main sources for the formation of dehydroalanine are the cystine moieties of the protein. Cysteine residues are first oxidized to cystine before beta-elimination occurs.

Alanine↗
PubMed1977

Heat induced crosslinks in milk proteins and consequences for the milk system.

The protein system of milk is rather unusual, there are nearly no interchain crosslinks found. Even intrachain crosslinks, especially disulfide bridges, are present only in about every fourth protein molecule. Heating causes dramatic changes in the structure of milk proteins, resulting in the formation of polymeric networks. The contribution of individual milk proteins, namely the beta-lactoglobulins, alpha-lactalbumin and chi-casein, to the formation of crosslinks is studied with respect to heating temperature and time, pH and atmosphere. Measured are changes in molecular weights and in the SH/SS-levels as well as the formation of dehydroalanine, lysinoalanine, lanthionine and isopeptide bonds. Some practical aspects of crosslinking in milk proteins are discussed.

Animals↗
PubMed1976

[On the occurence of isopeptide bonds in heated milk protein (author's transl)].

Milk, milk products and individual milk proteins were subjected to different heat treatments either as powders or in aquous systems. After complete hydrolysis of the peptide bonds (alpha-amide bonds) by a system of four proteinases or peptidases, respectively, the samples were analysed for isopeptides. For this purpose, two chromatographic ion exchange systems were developed, each of which separates Nepsilon-(beta-aspartyl-)lysine (Asp Lys) as well as Nepsilon-(gamma-glutamyl-)lysine (Glu Lys) from the common amino acids. In samples, heated 24 h for at least 120 degrees C, 2-5% of the lysine residues are incorporated in Glu Lys-bonds. Under the heating conditions used in dairy practice, no isopeptide bonds were formed.

Animals↗
PubMed1976

[Studies on the determination of gelatine in milk products especially in yoghurt (author's transl)].

Gelatine may be determined in yoghurt and similar milk products after total hydrolysis with HCl in the presence of SnCl2 via the content of hydroxyprolin. The high proportion of carbohydrates requires the use of high amounts of SnCl2, since the stannic ions cannot be removed without great lossess of hydroxyprolin. The lossess, however, are well reproducible so that the determination can be performed with an accuracy of +/- 5% by means of calibration curves. Since the gelatine qualities used in the dairy industry are varying in their content of hydroxyprolin by +/- 10%, the determination of the gelatine portion in yoghurt may be performed within a range of 0.05 -- 1.00% with an accuracy of aroung +/- 15%.

Color↗
PubMed1976

[Nepsilon-(beta-Aspartyl)lysine and Nepsilon-(gamma-glutamyl)lysine crosslinkings in bovine colostrum (author's transl)].

In bovine colostrum which was defatted and totally hydrolyzed by proteolytic enzymes, the isopeptides Asp Lys and Glu Lys were identified by ion-exchange chromatography and preparative separation. Isopeptides were identified in two of seven samples of colostrum. It is still to be clarified whether there is a correlation between the amound of gamma-glutamyltransferase and the appearance of these crosslinkings.

Animals↗
PubMed1975

[Polysaccharide additives in foods rich in proteins II. A simple, semi-quantitative technique of estimation (author's transl)].

Samples of foods rich in protein, after removal of lipids and of proteins by enzymatic hydrolysis, are partially demineralized and concentrated. In the concentrate polysaccharides are detected and semi-quantitively estimated by performing the precipitations in graduated tubes, which are especially suitable for this purpose, and the precipitates taken to comparable densities by centrifugation under standard conditions.

Chemical Precipitation↗
PubMed1975

[Polysaccharide additives in foods rich in proteins. i Sample preparation for estimation, especially in fresh cheese (author's transl)].

Published procedures for the isolation of polysaccharides from foods rich in proteins, especially fresh cheese, proved not very useful for the concentration in question (0,01--0.2%). We, instead, propose the following sample preparation: 1. Removal of lipids by an ethanol--ethyl ether--petrol ether mixture; 2. complete hydrolysis of proteins with pepsin, pronase E and a mixture of aminopeptidase M and prolidase; 3. separation of the polysaccharides from the low molecular substances and from enzyme residues by gel filtration on Biogel P-2; 4. concentration of the polysaccharides containing fraction by freeze drying, ultrafiltration or evaporation. --The method was tested with quarg and double cream fresh cheese, it can, however, be adopted to use in other products.

Aminopeptidases↗