bluuebunny/crossref_metadata_2025_split huggingface dataset:
Properties of aseptically packed ultra-high-temperature milk: II. Molecular weight changes of the casein components during storage
Authors: Andrews A. T. , Cheeseman G. C. 
Published: June 2009

SummaryStorage of aseptically packed ultra-high-temperature (UHT) milk has been shown to be accompanied by pronounced changes in the molecular weight distribution of the pH 4·6 insoluble casein. These changes were both time-dependent and temperature-dependent, proceeding much more rapidly at 37 °C than at 30 °C, but even at 4 °C the changes were considerable. The proportions of high molecular weight material present before and after storage have been studied by gel filtration in dissociating solvents using Sephadex G-200. Measurements have also been made on casein material isolated from in-bottle sterilized milks and canned evaporated milk for comparison. The results of gel filtration have been compared with sedimentation coefficients recorded by ultracentrifugation and with changes in the content of amino groups titratable with trinitrobenzene-sulphonic acid. The results are compatible with the suggestion that the Maillard reaction occurred at ambient temperatures, and over a period of several months led to browning and sediment formation due to covalent cross-linking of polypeptide chains. The implications of this are discussed with reference to spoilage of UHT milk on storage and the phenomenon of gelation.
Volatile compounds in butter oil: III. Recovery of added fatty acids and δ-lactones From volatile-free butter oil by cold-finger molecular distillation
Authors: Stark W. , Urbach Gerda , Hamilton Janet S. , Forss D. A. 
Published: June 2009

SummaryMore than 90% of the C2,4,6,8,10fatty acids and C8,10, δ-lactones added at quantities between 0·5 and 40 ppm were recovered from volatile-free butter oil by cold-finger molecular distillation at 35°C, while approximately 65% of the C12fatty acid and of the C12δ-lactone was recovered. Cold-finger molecular distillation at 50°C increased the recovery of the C12compounds to more than 90%. The acids and lactones were estimated quantitatively as the free compounds by gas chromatography on a mixture of Carbowax 20 M and isophthalic acid as the stationary phase.
Some properties of frozen concentrated starters produced by continuous culture
Authors: Lloyd G. T. , Pont E. G. 
Published: June 2009

SummaryFrozen concentrated cheese starters were prepared from 7Streptococcus cremorisand 2Str. lactisstrains by continuous culture. pH control with NH4OH and Ca(OH)2increased the yield ofStr. cremorisstrains as compared with NaOH, but the resultant cells were smaller and less active. Maximum yields for both species were obtained at a dilution rate of 0·6 and pH 6·3, but withStr. cremoriscell activity was reduced above pH 6·0.Degeneration in continuous culture was observed in the 2Str. lactisstrains, due apparently in one case to the action of a bacteriophage and in the other possibly to selection or to loss of adaptive enzymes.Concentrated starters retained full viability and activity when stored for 10–12 weeks at −110°C, and 94% activity after storage for 4 weeks at −40°C.Cheese made with the concentrated starters ripened normally and was comparable in quality with control cheese made with normal bulk starter.
Metabolite levels and enzyme activities in the bovine mammary gland in different stages of lactation: II. Some metabolite levels and enzyme activities of the citric acid cycle
Authors: Waldschmidt Marianne , Rilling S. 
Published: June 2009

SummarySamples of the mammary gland were obtained by the freeze-clamping technique from heifers, lactating and dry cows. Levels of acetyl CoA, citrate, isocitrate and α-oxoglutarate were determined in extracts of the samples and calculated per g fresh gland and per mg DNA. All mammary metabolite levels were significantly higher in lactating cows than in heifers or dry cows. The accumulation in the lactating gland increased in the sequence acetyl CoA–α-oxoglutarate–isocitrate–citrate. NADP/NADPH ratios in cytoplasm, as calculated from the equilibrium of isocitrate dehydrogenase, were lowest in lactating glands. The activities of some enzymes were also determined in the cytoplasm and calculated per g fresh gland, per mg protein and per mg DNA. Mammary citrate synthase activity did not vary significantly between different groups of cattle, whereas mammary isocitrate dehydrogenase activity was higher in lactating cows than in heifers or dry cows. No activity of ATP citrate lyase was detected.
Further studies on the estimation of diacetyl by the methods of Prill and Hammer and Owades and Jakovac
Authors: Walsh B. , Cogan T. M. 
Published: June 2009

SummaryBoth the rate of formation and the total amount of dimethylglyoxime formed from diacetyl in the presence of hydroxylamine were increased on omission of phosphate from the Owades & Jakovac (1963) hydroxylamine reagent. Sodium acetate was also unnecessary and slightly decreased the rate of dimethylglyoxime formation. The optimum concentration of hydroxylamine lay between 0·5 and 0·75 M. The heating time necessary for formation of dimethylglyoxime can be reduced from 60 to 20min at 75°C. Based on these findings a shortened and more sensitive method for the estimation of diacetyl is recommended.
Formation of methyl ketones during ripening of Cheddar cheese
Authors: Walker N. J. , Keen A. R. 
Published: June 2009

SummaryCheddar cheeses made using single strains AM2 and HP of Streptococcus cremoris as starter were analysed for methyl ketones during ripening at 7°C. The level of odd-numbered C3–C15 methyl ketones increased very slowly in all cheeses and at maturity represented only 15–20% of the level potentially available from the degradation of esterified β-ketoalkanoic acids of milk fat in cheese. The potential for formation of the methyl ketones in unripened cheese curd was similar to the sum of free and potentially available ketones in mature cheese which suggests that the oddnumbered ketones once formed are not reduced or otherwise degraded by the normal cheese microflora. Significant variations were observed in the level of 2-butanone, which, in some cases, far exceeded the quantity which could be formed by breakdown of β-ketovaleric acid. Organoleptic evaluations and comparison of the levels of methyl ketones present in mature cheese with published threshold data suggest that while the methyl ketones may contribute to flavour they do not in their own right impart a typical mature Cheddar flavour to cheese.
Some physico-chemical properties of porcine milk
Authors: Hoynes M. C. T. , Fox P. F. 
Published: June 2009

SummaryThe principal results of an investigation of the major physico-chemical properties of porcine milk were:Heat stability: all individual porcine milks examined had poor heat stability and some coagulated in 2 min at 95°C; the Q10°Cwas high and variable and was 40 for some samples. Dialysis of porcine milk against bulk bovine milk did not influence its heat stability; removal of colloidal calcium phosphate (CCP) from porcine milk increased its heat stability 4-fold, but it was still very unstable. Unlike bovine milk, porcine milk did not exhibit a maximum-minimum in the heat stability-pH curve, but rather resembled bovine casein micelles suspended in milk dialysate. Addition of isolated bovine β-lactoglobulin to porcine milk did not influence its heat stability-pH curve.Rennet coagulation: under similar conditions, porcine milk coagulated about 4 times faster than bovine milk and the resultant curd was about twice as soft. Dialysis of porcine milk against a large excess of bulk bovine milk did not influence its rennet coagulability nor did removal of 50% of its CCP, but complete removal of the CCP rendered porcine milk non-coagulable by rennin. Porcine milk was readily coagulated by rennin down to 5°C; its second-stage coagulation was independent of temperature – a characteristic due mainly to its high level of CCP.Alcohol stability: porcine milk was coagulated by 66–68% (v/v) ethanol, as compared with 74% (v/v) for bovine milk.Calcium stability: porcine milk was stable to at least 300 mM-CaCl2at both 2 and 37°C.Solvation: porcine milk contained significantly less water of hydration than bovine milk, 1·7g H2O/g casein compared with 2·0g H2O/g casein.
Acid phosphatase activity in cheese and starters
Authors: Andrews A. T. , Alichanidis E. 
Published: June 2009

SummaryThe acid phosphatase activity levels in a number of Greek cheeses and in Cheddar cheeses were found to be unaffected by storage for up to 18 months and 12 months respectively. In Cheddar cheese, starter organisms made an insignificant contribution to this activity. Studies of acid phosphatase prepared fromStreptococcus cremoris-lactisNCDO 762 starter cultures showed that the enzyme was of high molecular weight and largely particle-bound. The pH of optimum activity was 5·2 and the enzyme was inhibited by F−, Al3+, a number of heavy metals, oxidizing agents and sulphydryl-modifying reagents. Kinetic measurements at pH 5·2 gave aKmvalue for p-nitrophenyl phosphate of 1·2 mM. Orthophosphate, pyrophosphate and isoelectrically precipitated casein behaved as competitive inhibitors to the hydrolysis of p-nitrophenyl phosphate withK1values of 1·2 mM, 1·0 mM and 1·1 mM respectively. In spite of this binding to the enzyme, casein provided a very poor substrate for the starter acid phosphatase. The properties of acid phosphatase present in Cheddar cheese made withStr. cremorisNCDO 924 starter were consistent with the enzyme being exclusively of milk origin and small differences between this and the acid phosphatase previously isolated from bovine milk were attributable to the binding of peptides produced during the cheese maturation to the enzyme molecules. It was concluded that in cheese, phosphatase action was due largely to the enzyme of milk origin, with that provided by the starter being of minor importance.
Formation of acetaldehyde from threonine by lactic acid bacteria
Authors: Lees G. J. , Jago G. R. 
Published: June 2009

SummaryGroup N streptococci were found to cleave threonine to form acetaldehyde and glycine. Threonine aldolase, the enzyme catalysing this reaction, was found in all strains exceptStreptococcus cremorisZ8, an organism which had been shown previously to have a nutritional requirement for glycine. The enzyme was strongly inhibited by glycine and cysteine. The inhibition showed characteristics of allosteric inhibition and was pH-dependent. Inhibition by glycine, but not by cysteine, was highly specific. Analogues and derivatives of cysteine which contained a thiol group and a free amino group inhibited the activity of threonine aldolase. The presence of a carboxyl group was not necessary for inhibition. The cleavage of threonine by wholecell suspensions was stimulated by either an energy source to aid transport, or by rendering the cells permeable to substrate with oleate. Threonine did not appear to be degraded by enzymes other than threonine aldolase, as threonine dehydratase activity was low and NAD- and NADP-dependent threonine dehydrogenases were absent.
A comparison of microstructures of Cheddar cheese curd manufactured with calf rennet, bovine pepsin, and porcine pepsin
Authors: Eino M. F. , Biggs D. A. , Irvine D. M. , Stanley D. W. 
Published: June 2009

SummaryCalf rennet, bovine pepsin, and porcine pepsin were used to produce cheese curd, using the same milk and lactic culture for each. Specimens were prepared for scanning electron microscope examination by a modified critical-point drying technique.From examination of the micrographs, the curd made with bovine and porcine pepsin were similar in structure and in orientation of the coagulated protein, whereas the curd produced with rennet was different, having a more compact and organized structure.
The effect of non-starter bacteria on the chemical composition and the flavour of Cheddar cheese
Authors: Law B. A. , Castañón Marisi , Sharpe M. Elisabeth 
Published: June 2009

SummaryDifferences in flavour scores and in the concentrations of free fatty acids, methyl ketones and H2S were measured in Cheddar cheeses containing various groups of non-starter bacteria or starter streptococci alone, made under controlled bacteriological conditions by the aseptic vat technique. The non-starter bacteria were made up of lactobacilli, leuconostocs, pediococci, micrococci and Gram-negative rods isolated in commercial creameries from raw milk or fresh cheese curd. These were added to the experimental cheese as single groups or as complete floras (reference floras). Several bacterial groups influenced the measured concentrations of the flavour compounds, but flavour differences were not correlated with these chemical differences. Only cheese containing a curd-derived whole reference flora or cheese made in open vats in the N.I.R.D. Experimental Dairy had significantly better flavour than starter-only cheese, but this improvement was not attributable to any particular group of bacteria.
Heat-induced changes in sulphydryl and disulphide levels of β-lactoglobulin A and the formation of polymers
Authors: Watanabe K. , Klostermeyer H. 
Published: June 2009

SummaryThe effects of heat and pH on sulphydryl (–SH) and disulphide (–SS–) groups of β-lactoglobulin (β-lg) A have been studied by heating at different temperatures and pH values in air and at pH 6·9 in the absence of air. At pH 6·9 under aerobic conditions a decrease of –SH groups and an increase of –SS– groups was observed with increasing time and temperature. Only small changes were found under anaerobic conditions. At pH from 3·0 to 9·8 the –SH level decreased while the –SS– level increased up to pH 6·9 and then dropped rapidly. In addition to –SH/–SS– interchange there were reactions to other sulphur-containing compounds as seen from the losses in the total amount of –SH plus –SS– sulphur. The results of gelchromatographic investigations suggest that –SH-initiated –SS– exchange-reactions play an important role in the formation of high molecular weight polymers of β-lg A during heat treatment, and that the formation of intermediates depends on the presence of air.
The effect of diet on the γ- and δ-lactone and methyl ketone potentials of caprine butterfat
Authors: Stark William , Urbach Gerda , Cook Leonard J. , Ashes John R. 
Published: June 2009

SummaryWhen caprine butterfat was heated in the presence of water vapour and the absence of air, γ- and δ-lactones and methyl ketones were produced which were qualitatively the same as those from bovine butterfat. The saturated δ-lactone and methyl ketone potentials of the caprine butterfat were of the order of one third those of bovine butterfat when the goats and cows received similar rations. γ-Dodecanolactone, γ-dodec-cis-6-enolactone, δ-tetradec-cis-8-enolactone and δ-tetradec-trans-8-enolactone potentials of the caprine butterfat were in the same range as for bovine butterfat when the animals were on similar diets. The γ- and δ-lactone and methyl ketone potentials and the fatty acid composition of caprine butterfat varied with the diet of the goat. Supplementing the diet with polyunsaturated fat, whether or not protected against biohydrogenation in the rumen, lowered the saturated δ-lactone and methyl ketone potentials as well as the proportion of C10,12,14,16fatty acids in the caprine butterfat. Inclusion of crushed oats in the diet increased the γ-dodecanolactone potential. The γ-dodecanolactone and they γ-dodec-cis-6-enolactone potentials were also enhanced by feeding seed oil supplements which were not protected against ruminal hydrogenation. To prevent the development of the sweet off-flavour associated with γ-dodecalactones in heated, ruminant-derived meat and butterfat with elevated levels of linoleic acid, it appears that oats should be excluded from the basal ration of the ruminant and the polyunsaturated oil supplement should have the highest possible degree of protection against biohydrogenation in the rumen.
Metabolism of [14C]bicarbonate byStreptococcus lactis: the synthesis, uptake and excretion of aspartate by resting cells
Authors: Hillier Alan J. , Rice Garry H. , Jago G. Richard 
Published: June 2009

SummaryResting cells ofStreptococcus lactisC10 were able to synthesize aspartic acidde novobut could not actively transport aspartic acid into the cell. Intracellular aspartate was excreted from the cell in the presence of glucose but did not exchange with any extracellular amino acids. The results indicated thatStr. lactisC10 obtains the aspartic acid it requires for growth by bicarbonate fixation instead of by the utilization of extracellular aspartic acid.
Natural variations in the average size of bovine casein micelles: II. Milk samples from creamery bulk silos in south west Scotland
Authors: Holt Carl , Muir D. Donald 
Published: June 2009

SummarySamples of bulk silo milk from 5 creameries in the south west of Scotland were taken over a 16-month period. The average radii of casein micelles were determined by measuring the wavelength dependence of the turbidity of skim-milk diluted with its own ultrafiltrate. In addition, the concentrations of casein, soluble and colloidal Ca and P1 were measured. The average size of casein micelles followed a pronounced seasonal trend with smaller average sizes in the summer compared to the winter period, confirming earlier observations made on milks from individual cows. The average size of casein micelles correlated positively (r = +0·777, P < 0·001) with the amount of colloidal P1 per unit weight of casein and negatively (r = −0·77, P < 0·001) with casein-bound Ca. Average micelle radius was negatively correlated with heat stability at the natural pH of milk (r = −0·61, P < 0·001), but there did not appear to be any causal relation between these 2 variables.
Storage of lactose-hydrolysed dried milk: effect of water activity on the protein nutritional value
Authors: Burvall Anders , Asp Nils-Georg , Bosson Agneta , José Carmen San , Dahlqvist Arne 
Published: June 2009

SummaryThe retention of the protein nutritional value during storage of lactosehydrolysed dried milk at different water activities (aw) was studied and compared with that of ordinary milk. In the lactose-hydrolysed milk biologically available lysine decreased much more rapidly than in the ordinary milk at all the different aw studied. Thus, at conditions normally accepted for ordinary dried milk (aw ~0·2; moisture ~ 4 %) there was an available lysine loss in the hydrolysed milk of about 25 % after 2 months and about 40 % after 6-months storage at room temperature. This occurred without any visible browning. It is concluded that drying to very low aw (≦ 0·11) is necessary to obtain good stability of the protein nutritional value (PNV) in lactose-hydrolysed milk. The drying, however, must be done so that losses in nutritional value are minimal during that process. It should also be noted that fat oxidation might be a problem at such low aw. A chemical method for available lysine assay (guanidination and assay of homoarginine) gave values in good agreement with the biological evaluations with rats.
A frequency response of the dairy cow's teat
Authors: Reitsma Sybren Y. , Scott Norman R. 
Published: June 2009

SUMMARYA frequency response of the cow's teat has been determined by applying sinusoidal changes in vacuum level to the teat. Twelve frequencies were applied ranging from 0.06 to 12 Hz. The responses investigated were the external teat end diameter and the teat milk flow-rate. The measured variables were: (1) frequency of applied pressure and teat end diameter, (2) peak-to-peak pressure and teat end diameter, (3) average vacuum level and teat end diameter, (4) time delay between maxima of vacuum level and teat end diameter, (5) time delay between minima of vacuum level and teat end diameter, and (6) teat milk flow-rate. The results showed that within the range of the investigation milk flow-rates were lower between 0.8 and 2.5 Hz than at frequencies both below and above this range. A statistical analysis of the flow rate and teat end diameter data supports the common practice of applying the same frequency to both front and rear teats during milking. Other findings show good agreement with results reported previously on dynamic responses of the teat to step changes in pressure.
Metabolism of [U-14C; 2, 3-3H]-L-valine by the isolated perfused goat udder
Authors: Roets Eddy , Massart-LeëN Anne-Marie , Verbeke Roger , Peeters Georges 
Published: June 2009

SUMMARYTwo lactating mammary glands excised from 2 goats were perfused for several hours in the presence of [U-14C; 2,3-3H]-L-valine and received adequate quantities of glucose, acetate and amino acids. In the synthesized milk 96 and 89% respectively of the casein valine was derived from free plasma valine. Valine was extensively catabolized by mammary tissue, resulting in a considerable14CO2production and in the incorporation of14C into milk citric acid and to a lesser extent into casein aspartic acid and glutamic acid. About 30% of the valine molecules which were taken up by the mammary gland were oxidized to CO2and 70% were incorporated in casein as valine residues. About 10% of the plasma valine molecules were reversibly transaminated during one passage through the udder. An important amount of radioactivity of plasma was present in unknown metabolites. Only 7% of this activity was localized in isobutyrate. The radioactivity of total milk fat was very low. Mainly iso-14:0, iso-16:0 and 15:0 were labelled.
Proteolytic activity in UHT-sterilized milk
Authors: Corradini Cesare , Pecis Paola Panini 
Published: June 2009

SUMMARYThe proteolytic activity in UHT-sterilized milk of a proteinase-containing fraction, prepared from the milk, is reported. The proteinase fraction was isolated from casein micelles as described by Reimerdes & Klostermeyer (1974).The fraction was added to UHT milks and the proteolysis in the samples, measured as the liberation of non-protein nitrogen, compared with that in control samples without added proteinases. The increase in proteolytic activity and deterioration in samples containing added proteinases indicated that an enzyme process occurred in UHT-sterilized milk which could influence gel formation.
On the size of monomers and polymers of β-casein
Authors: Buchheim Wolfgang , Schmidt Daniël G. 
Published: June 2009

SUMMARYThe size and number average molecular weight have been determined for β-casein monomers and polymers from electron micrographs using the freeze-etching procedure with spray-frozen specimens. For the spherical β-casein monomers we found a mol. wt of 22600 and a diam. about 10 nm, which compared quite well with data obtained from ultracentrifugation, light scattering and viscosity measurements. Polymer sizes were in agreement with molecular weight determinations from ultracentrifugation and light scattering, assuming that the volume and weight of the particles are proportional.
Structure of β-casein
Authors: Arima Shunrokuro , Niki Ryoya , Takase Kenji 
Published: June 2009

SUMMARYThe temperature and concentration dependent association of β-casein was studied by means of viscometry, gel filtration chromatography, electron microscopy, analytical ultracentrifugation and UV difference spectrophotometry. Degrees of polymerization of 12, 22 and 49 and free energies of association of –21, –23 and – 25 kJ/mole monomer were found at temperatures of 10, 15 and 20 °C respectively in 0·2 M Na phosphate buffer pH 6·7.Monomeric β-casein was not a completely random coil but became more compact with increasing temperature, due to hydrophobic interactions.