bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of proteolytic raw milk psychrotrophs on Cheddar cheese-making with stored milk
Authors: Law Barry A. , Andrews Anthony T. , Cliffe Allan J. , Sharpe M. Elisabeth , Chapman Helen R. 
Published: June 2009

SummaryThe effect of proteolytic, psychrotrophic strains of Pseudomonas fluorescens, Ps. putida and Acinetobacter spp. on cheese-making with stored milk has been investigated. Ps. fluorescens and Ps. putida growing for 72 h in raw milk at 7·5 °C to levels of approx. 107 colony-forming units/ml caused a low degree of β- and к-casein breakdown detectable by gel electrophoresis, but this was insufficient to affect N losses in whey or cheese yields. Variations in cheese-making times with pasteurized milks were not attributable to the counts of psychrotrophs in the corresponding raw milks. The water-soluble and TCA-soluble N fractions of maturing cheeses were unaffected by psychrotroph counts in raw milks, but small differences in levels of casein fractions of cheeses made from milks stored for 72 h were detected by quantitative polyacrylamide gel electrophoresis. The incidence of casein breakdown in raw milk and subsequently in cheese were not necessarily related. None of the cheeses developed off flavour related to excessive protein breakdown but many became lipolytically rancid, despite the selection of strains with low lipolytic activity on a diagnostic medium. It is concluded that the numbers of psychrotrophic bacteria likely to occur in stored raw milk under commercial conditions are unlikely to cause significant changes in the yields or quality of Cheddar cheese through their proteolytic activity.
The conductivity of milk—the effect of the volume and degree of dispersion of the fat
Authors: Prentice J. H. 
Published: June 2009

SummaryThe conductivity of raw and homogenized milks was measured using apparatus capable of high precision. The effect of fat content was examined and found to conform to the established behaviour for a polydisperse suspension of nonconductors in a homogeneous conducting medium. Homogenization of the milk over a range of pressures was found to have no measurable effect on the conductivity.
A modified method for the determination of glyceride glycerol
Authors: Moore J. H. 
Published: June 2009

SummaryA routine method giving accurate results was required for the determination of the glyceride content of eluate fractions obtained in the silicic acid chromatography of lipid mixtures. The technique of determining glyceride glycerol by saponification, oxidation of the liberated glycerol to formaldehyde, reaction of the formaldehyde with chromotropic acid and measurement of the resulting chromogen at 570 mμ has been investigated. Procedures based on this principle have appeared in the literature but none of these has been found to be entirely satisfactory. Accordingly, a modification of the method has been developed that is capable of giving results of a high degree of accuracy.
A compound responsible for metallic flavour in dairy products: I. Isolation and identification
Authors: Stark W. , Forss D. A. 
Published: June 2009

SummaryThe ‘metallic compound’ previously reported as an important cause of off-flavour in oxidized dairy products has been identified as oct-l-en-3-one. The compound was found to have a flavour threshold value of one part in 109 in butterfat and one part in 1010 in water. This compound was also isolated from oxidized safflower oil.
The free and masked sulphydryl groups of heated milk and milk powder and a new method for their determination
Authors: Lyster R. L. J. 
Published: June 2009

SummaryA new method is described for the determination of the free and masked sulphydryl (-SH) groups in heated milk and milk products. The procedure is based on the use of the specific -SH reagent p-chloromercuribenzoate, and utilizes another specific -SH reagent, 5,5' -dithiobis(2-nitrobenzoate), as an indicator producing yellow colours which are matched with the aid of standard glasses in the Lovibond Comparator.The method was applied to heated skim-milks and a series of commercially prepared milk powders. Measurements were made in particular of the -SH content of UHT-treated milk. The changes in the -SH content of such milks on storage were studied; these changes could not be explained by a reversal of the denaturation of the whey proteins, although evidence was obtained that small amounts of heatdenatured whey protein can revert to the native state.
Histochemical study on the ripening of Parmesan cheese
Authors: Bolcato V. , Pallavicini C. , De Felice M. 
Published: June 2009

SummaryThe results reported suggest that it is possible to follow the ripening of Parmesan cheese by means of histochemical reactions for proteins, glycoproteins, acid mucopolysaccharides and lipids containing choline.The blue colour, formed when the proteins of the curd were stained with Bonhag's reagent, slowly turned to violet and then to red as ripening progressed.Glycoproteins and acid mucopolysaccharides, although present in very small amounts, appeared to be a constant characteristic of the cheese.Lipids containing choline, which were absent from the curd, were clearly visible in 3 to 7-month-old cheese. They then decreased and were absent in the ripened cheese.
A compound responsible for mushroom flavour in dairy products
Authors: Stark W. , Forss D. A. 
Published: June 2009

SummaryThe ‘mushroom compound’ previously reported as a gas chromatographic fraction of oxidized dairy products has been identified as oct-l-en-3-ol. The alcohol was found to have a flavour threshold value of 1 part in 109 in water, 1 part in 108 in skim-milk, and 1 part in 107 in butterfat. A mechanism for the formation of oct-1- en-3-ol is discussed.
Analysis of milk by infra-red absorption
Authors: Goulden J. D. S. 
Published: June 2009

SummaryThe infra-red, absorption of milk and its main constituents has been recorded and it has been found possible to determine quantitatively the fat, protein and lactose contents from measurements of the intensities of the respective absorption peaks at 5·73, 6·46 and 9·6 μm. Solids-not-fat (SNF) content can be obtained from a single intensity measurement at 7·9 μm where the fat shows no attenuation and where the protein and lactose extinction coefficients are approximately equal. Photometric errors due to natural variations in fat globule size distribution can be eliminated by prior homogenization. Based on these observations, an automatic infra-red milk analyser (IRMA) has been constructed, which can determine the fat, protein, lactose and SNF in a pre-warmed milk sample in under 1 min. Preliminary tests carried out on 50 milk samples from individual cows, representing 3 different breeds, gave standard deviations from the chemical analyses for the percentages of fat, protein, lactose and SNF of 0·10, 0·07, 0·07 and 0·19, respectively. The standard deviations for the percentages of fat and SNF on 60 farm bulk milk samples were found to be 0·08 and 0·12.
Mechanics of machine milking: I. Pressures in the teatcup assembly and liner wall movement
Authors: Thiel C. C. , Clough P. A. , Akam D. N. 
Published: June 2009

SummaryA method is described of measuring pressures in a teatcup assembly using strain gauge transducers and simultaneously following movement of the liner wall by means of a cine camera. In preliminary experiments with a narrow bore type liner it was found that pressures below the teat could vary during a single pulsation cycle from a few inches of mercury below atmospheric pressure (inHg vacuum) to as high as 25 inHg vacuum in the absence of an airbleed. Bleeding air into the barrel of the liner or into the clawpiece considerably reduced fluctuation in pressure, and the vacuum barely rose above the nominal milking vacuum of 15 inHg. Reducing the rate of change of pressure in the pulsation chamber did not greatly affect the maximum vacuum obtained. Opening and closing of the liner by pressure change in the pulsation chamber was under some conditions considerably delayed by the pressure conditions existing inside the liner.It is suggested that inertia effects of milk in the cluster and the natural frequency of the system are largely responsible for the observed pressure changes under the teat.
The effect of antioxidants on the keeping quality of whole milk powder: II. Tocopherols
Authors: Abbot J. , Waite R. 
Published: June 2009

SummarySpray-dried whole milk powders were prepared containing 0·01% of γ-tocopherol and of a mixture of α-γ- and δ-tocopherols. Control powders and powders containing 0·01% of dodecyl gallate, an antioxidant of known effectiveness, were also made. The powders were stored at 37°C and examined at intervals for taste, peroxide value and absorbed oxygen. The protection against oxidation afforded by both the tocopherol additions was small, although γ-tocopherol was more effective than the mixture of tocopherols. Dodecyl gallate was again found to be a good antioxidant for whole milk powder.
Survival of strains of lactic streptococci during frozen storage
Authors: Gibson C. A. , Landerkin G. B. , Morse Pamela M. 
Published: June 2009

SummarySixteen single-strain cultures, 10 ofStreptococcus cremoris, 3 ofStr. lactisand 3 ofStr. diacetilactiswere examined for their ability to withstand freezing and storage at –17·8 and –23·3°C. The numbers of surviving bacteria decreased as storage time increased. For the majority of strains, the survival rate was greater at the lower temperature. At both storage temperatures there were differences between the percentages of surviving bacteria for different strains.The results suggest that the relative proportion of strains in mixed cultures would not remain constant under frozen storage.
The effect of silage made from grass at different stages of maturity on the yield and composition of milk
Authors: Murdoch J. C. 
Published: June 2009

SummaryIn cross-over experiments it has been established that milk yield increased and the fat solids-not-fat (SNF) contents of the milk decreased when cows were given approximately 15 lb dry matter/day of early-cut silage compared with the values obtained by giving the same amount of silage made from herbage cut at a later stage of maturity.Increasing the proportion of concentrates to silage in the cow's diet so that the milk yield remained unchanged increased the SNF content of the milk but had no effect on the fat content.Supplementing early-cut silage with 5 lb hay/day increased the fat content of the milk, but had no effect on either milk yield or the SNF content of the milk.Compared with a silage to which molasses had been added, untreated silage decreased milk yield, and increased the fat content without affecting the SNF content of the milk.
The effect of incomplete milking or of an extended milking interval on the yield and composition of cow's milk
Authors: Wheelock J. V. , Rook J. A. F. , Dodd F. H. 
Published: June 2009

SummaryThe effect of incomplete milking or of an extended milking interval on the yield and composition of cow's milk has been investigated. At the 1st milking after either treatment, the yield of milk was augmented by a carry-over of milk but at the 2nd milking the yield was invariably depressed and then increased until the original yield, or slightly less, was recovered within 5 days. The concentration of lactose and potassium decreased and of sodium, chloride, whey proteins and casein increased during the period of the treatment, and on the resumption of normal milking the original composition was rapidly recovered. The changes in the composition of fat were less clearly defined because of residual milk effects but over the period of the treatment and the succeeding 6 milkings the effect was invariably to increase fat percentage. The differing effects on composition resulted in a more marked effect on the yields of lactose, potassium and casein than on those of sodium, chloride or the whey proteins throughout the treatment and recovery periods. When milk was removed in portions after an extended milking interval there were decreases in the concentrations of lactose and potassium and increases in those of sodium and chloride throughout normal milking. When the residual milk was obtained after an injection of oxytocin the composition of the portions of milk resembled that of the first portions of milk removed from the udder. The possible effects of the treatments on the secretory cells and the permeability of the udder tissue are discussed.
Studies on the laboratory soiling of milking equipment
Authors: Bačić Branca , Cousins Christina M. , Clegg L. F. L. 
Published: June 2009

SummaryA laboratory method has been developed for studying the action of chemical disinfectants on milking equipment using a wet film and both metal and rubber surfaces. It was shown that milking machines may be soiled as effectively with fresh milk of low bacterial content as with aged milk of high bacterial content. When a single heat treatment preceded the soiling with milk and subsequent treatment with detergent and chemical disinfectant, a build-up of bacteria began on the third day. However, when the surfaces were heat treated daily 18 h before soiling, followed by cleaning and disinfection, no build-up occurred. These findings support the hypothesis that contamination of milk results from bacteria developing on the milking equipment and not merely from those added to it at each milking. The sites of bacterial contamination were shown to be the under surfaces of lid gaskets and the joints of the short milk tubes and the metal clawpiece nipples.
Some properties of the extracellular proteolytic enzymes of the milk-spoiling organismPseudomonas aeruginosaATCC 10145
Authors: Juffs H. S. , Doelle H. W. 
Published: June 2009

SummaryThe proteolytic enzymes present in the culture supernatant ofPseudomonas aeruginosaATCC 10145 were active in the pH range 5·5–9·0 with a maximum activity at pH 7·3. Heating for 15 sec at 72°C resulted in a 36% loss of proteolytic activity whereas heating for 30 min at 63°C resulted, in a 6% loss. Boiling for 2 min completely inactivated the proteolytic enzymes. At 2°C the proteolytic enzymes were stable for at least a month and casein was readily hydrolysed at this temperature.
Microcalorimetry applied to certain species of bacteria growing in sterilized separated milk
Authors: Berridge N. J. , Cousins Christina M. , Cliffe A. J. 
Published: June 2009

SummaryThe heat produced per colony-forming unit (CFU) of growing bacteria was found to depend on the species and was greater the younger the culture. With the exception of 2 determinations out of 13, with 6 species the results show that it should be possible to detect < 5×105CFU/ml by the heat produced. A seventh species, a micrococcus, could be detected at a lower level of CFU presumably because the unit was a clump of several cells. Gross variations which occurred with fullcream milk await investigation.
A quantitative gel-filtration method for analysis of the proteinaceous fraction of Cheddar cheese
Authors: Foster P. M. D. , Green Margaret L. 
Published: June 2009

SummaryMethods are described for the solubilization of the nitrogenous portion of cheese in a dissociating solvent system and separation of the solution into fractions on a Sephadex G-100 column under conditions where the proteins and peptides would be expected to be split into monomeric units. TheE280measurement of the fractions, expressed as a percentage of the total material eluted, followed a reproducible pattern, both with duplicate runs on the same sample and comparative runs on non-identical samples of the same type. With cheese curd, a small peak of undissociated material was obtained at the void volume of the column; this was followed by a main peak and a minor third peak, with a small quantity of material being eluted at larger volumes. A qualitatively similar pattern was obtained with 43-day-old cheese as the sample, but the main peak was smaller, the third peak was larger, and a relatively larger amount of material was eluted at greater volumes. There was only partial separation of the proteins on the column; the main peak contained β- and αs-caseins, their larger breakdown products and some para-κ-casein, and the third peak contained smaller breakdown products of the main casein fractions and para-κ-casein. Although the resolution was considerably inferior to that obtained by gel electrophoresis, the method has the advantage over this and other methods in that it gives a quantitative analysis of the sample based on molecular size. Thus, it is suggested that it may find use in analysing protein breakdown in cheese during ripening.
A method of diagnosing intramammary infection in dairy cows for large experiments
Authors: Griffin T. K. , Dodd F. H. , Neave F. K. , Westgarth D. R. , Kingwill R. G. , Wilson C. D. 
Published: June 2009

SummaryDiagnosis of microbial infections in the udders of cows in commercial dairy farms for large experiments cannot be without error. Limitations of sampling method and routine prevent collection of the necessary information for sure diagnosis. However, with an organized method of repeated bacteriological examinations using consistent and proven methods of aseptic sampling the errors were shown to be very low. A method based on bacteriological tests on aseptic milk samples was used in 32 herds (approximately 2000 cows) for a 3-year period. This is described and examined in terms of other criteria to validate its use in experimental work. With this method it was not difficult to differentiate between those quarters which regularly shed pathogens and those which did not. Other evidence indicated that it was reasonable to assume that this classification accurately distinguished between infected and uninfected quarters. The errors using this method were quite small: when measuring the state of infection of all quarters in the herds the errors did not exceed 1 %. Some small modifications to the method described are suggested to improve further its diagnostic accuracy.
The theory of branching processes applied to milk proteins: I. Heat-induced coagulation of whole milk
Authors: Parker T. G. , Dalgleish D. G. 
Published: June 2009

SummaryThe theory of branching processes is used to present a unified kinetic model for the heat induced coagulation of milk. Nitrogen depletion curves for the overall reaction are fitted to a theoretical curve to demonstrate that the reaction is a single process and that the idea of a lag phase up to the coagulation time, followed by the aggregation reaction proper, is an unnecessary complication. Coagulation times as a function of temperature are then used to determine the activation energy of the reaction; the average value of 126 kJ/mol agrees with that found from analysis of the post-coagulation reaction.
Quantitative analysis of food products by pulsed nuclear magnetic resonance II. Simultaneous analysis of water and fat in milk powder and cottage cheese
Authors: Hester R. E. , Quine D. E. C. 
Published: June 2009

SummaryA small process analyser employing the pulsed nuclear magnetic resonance technique has been used to determine both water and fat contents of milk powder and cottage cheese samples. The procedures used for establishing and eliminating cross-interferences in these analyses are described. For milk powders, water and fat contents in the ranges 1–5 and 0·5–25 % respectively were determined with standard deviations of 0·20 % water and 0·64 % fat. Cottage cheese samples with water and fat contents in the ranges 77–81 and 2–7 % respectively were determined with standard deviations of 0·30 % water and 0·16 % fat.
Selective denaturation of milk coagulants in 5 M-urea
Authors: Mulvihill D. M. , Fox P. F. 
Published: June 2009

SummaryPorcine and bovine pepsins were very stable in 5·0 M-urea at pH 2·0 or 2·5 at 30 °C while chymosin and Mucor miehei and M. pusillus proteases were rapidly denatured under these conditions. These differences may provide the basis of a quantitative assay of the complement of individual milk clotting enzymes in a coagulant and a possible scheme is suggested.
Effect of diet and stage of lactation on bovine milk lipolysis
Authors: Salih Amer M. A. , Anderson Malcolm 
Published: June 2009

SummaryThe effect of lactation and diet on milk lipoprotein lipase activity (LPL), cell count, serum albumin concentration and free fatty acid levels, expressed in terms of acid degree value (ADV), was examined in 2 experiments. In addition, the ability of blood plasma from cows on different diets to activate LPL was also investigated.Changes in ADV were not consistently associated with changes in LPL, cell count or serum albumin throughout lactation, although results indicated that ADV appeared to be influenced by cell count in early lactation, and by the amount of blood plasma proteins reaching the milk during the remainder of lactation. LPL activity was low in colostrum, but increased rapidly between d 2 and 12 post-partum, reaching a peak at 5 months. Activity was unaffected by diet.There was no effect on ADV of feeding concentrate: hay ratios of 75:25 and 60:40, but ADV was higher in cows fed a low protein diet (crude protein 9%) between 10 and 60 d post-partum, than in cows fed a high protein diet (crude protein 18 %) during the same period. In addition, the blood plasma for cows on the low protein diet had a greater ability to activate LPL although, on the basis of the millk: blood serum albumin ratio, a smaller proportion of blood constituents had reached the milk. The ability of blood plasma to activate LPL was also found to increase with increasing levels of lipoprotein lipid in the blood.
Proteolytic specificity of chymosin on bovine αs1-casein
Authors: Mulvihill Donald M. , Fox Patrick F. 
Published: June 2009

SummaryIn dilute buffers ⋟ pH 5·8, chymosin hydrolysed bovine αs1-casein to αs1-I, αs1-II and αs1-III/αs1-IV in a sequential manner while at pH 4·6 αs1-casein was hydrolysed to αs1-I which was then hydrolysed to αs1-V. In the presence of 5 % (w/v) NaCl at pH 5·2, αs1-casein was hydrolysed to αs1-I which was then hydrolysed to αs1-VII and αs1-VIII. αs1-I, αs1-II and αs1-III/αs1-IV were isolated by chromatography on cellulose phosphate followed by preparative slab-gel electrophoresis; αs1-V was isolated by repeated preparative slab-gel electrophoresis and αs1-VII by gel filtration on Sephadex G-150 followed by preparative slab-gel electrophoresis. The mol. wts of the peptides, estimated by gel filtration on Sephadex G-100, were 21000, 17600, 15600, 19900 and 14600 for αs1-I, αs1-II, αs1-III/αs1-IV and αs1-V and αs1-VII respectively. Characterization of the peptides by amino acid, phosphorus and terminal residue analysis showed that they probably consisted of segments of the αs1-casein chain as follows: αs1-I: residues 24/25–199; αs1-II: residues 24/25–169; αs1-III/αs1-IV: residues 24/25–149–150; αs1-V: residues 29/33–199; αs1-VII: residues 56–179. Peptide bonds close to phosphate residues on the αs1-casein chain were not hydrolysed by chymosin at high pH values (⋟ 5·8) when the phosphate groups were charged, but became available for hydrolysis when the reaction pH was reduced. Proteolytic specificity was also modified by NaCl.