Concentration Of Β-lactoglobulin Research Articles

Interactions between methyl ketones and beta-lactoglobulin: sensory analysis, headspace analysis, and mathematical modeling.

Interaction of flavor compounds with proteins is known to have an influence on the release of flavor from food. Hydrophobic interactions were found between beta-lactoglobulin and methyl ketones; the affinity constant increases by increasing the hydrophobic chain. Addition of beta-lactoglobulin (0.5 and 1%) to aroma solutions (12.5, 50, and 100 microL L(-)(1)) of three methyl ketones induces a significant decrease in odor intensity. The chosen methyl ketones were 2-heptanone (K(b) = 330), 2-octanone (K(b) = 950), and 2-nonanone (K(b) = 2440). The release of these flavor compounds (50 microL L(-)(1)) was studied by static headspace in water solution (50 mM NaCl, pH 3) with different concentrations of beta-lactoglobulin (0, 0.5, 1, 2, 3, and 4%). Increasing the concentration of protein increases the retention of volatiles, and this effect is greatest for 2-nonanone, the compound with the highest affinity constant, and lowest for 2-heptanone. A mathematical model previously developed to describe flavor release from aqueous solutions containing flavor-binding polymers (Harrison, M.; Hills, B. P. J. Agric. Food Chem. 1997, 45, 1883-1890) was used to interpret the data. The model assumes that the polymer-flavor interaction is reversible and the rate-limiting step for release is the transfer of volatiles across the macroscopic gas-liquid interface. This model was used to predict the equilibrium partitioning properties and the rate of release of the three methyl ketones. Increasing the affinity constant leads to decreased release rates and a lower final headspace aroma concentration.

Rheological influence of non-gelling amylopectins on β-lactoglobulin gel structures

The effect of non-gelling potato amylopectin on the gel properties of a particulate β-lactoglobulin gel was studied by small and large deformation rheology and by light microscopy. Two different techniques using small deformations, one measuring the modulus in shear and the other measuring the modulus in compression, have been compared. The fracture tests of the gels were performed in tension. The concentration of β-lactoglobulin was kept constant at 6 wt%, and the amount of potato amylopectin was varied from 0 to 2 wt%. Two preparations of potato amylopectin, with different rheological behaviour, were used. The results illustrate the importance of a full rheological characterisation, since small and large deformation tests responded different to the structure. Both the viscoelastic and the failure properties of β-lactoglobulin gels changed on addition of potato amylopectin even at low concentrations. The effect of the potato amylopectin concentration on the rheological properties of the mixed system varied with the properties of the potato amylopectin. The higher viscosity (HV) potato amylopectin had a shear-thinning behaviour and a small yield stress, while the lower viscosity (LV) potato amylopectin had a lower viscosity with a Newtonian behaviour. The gels containing the LV potato amylopectin increased in the modulus of small deformations with increasing potato amylopectin concentration, while the stress at fracture was constant up to a concentration of 0.5 wt% potato amylopectin and then increased with increasing potato amylopectin concentration. For the gels containing the HV potato amylopectin the modulus of small deformations reached a maximum at 0.25 wt% potato amylopectin and then decreased with increasing potato amylopectin concentration. The stress at fracture was constant up to 0.5 wt% potato amylopectin and decreased at higher concentrations. The state of aggregation of β-lactoglobulin was influenced both by concentration and properties of potato amylopectin. The higher the potato amylopectin concentration the larger the pores in the β-lactoglobulin gel.

Identification of the human β-casein C-terminal fragments that specifically bind to purified antibodies to bovine β-lactoglobulin

The presence of foreign proteins in human milk after the ingestion of bovine dairy products is thought to be one of the possible causes of allergic sensitization in exclusively breast-fed predisposed infants. The immunologic determination of bovine β-lactoglobulin (LG) concentration in human milk has been reported by several researchers, but the results are conflicting. Moreover, a strong cross-reactivity between antibodies to bovine β-LG and human milk proteins and peptides was reported, throwing doubt on the reliability of radioimmunoassay and enzyme-linked immunosorbent assay detection and quantification assays for bovine β-LG in human milk. Thus, the goal of this study was to isolate human milk peptides with a molecular mass ≥ 1,000 Da cross-reactive with antibodies to bovine β-LG in order to identify possible common epitopes between human and bovine milk proteins. The proteins were first isolated by affinity chromatography with purified polyclonal antibodies to bovine β-LG, followed by gel filtration fast phase liquid chromatography and reverse phase-high performance liquid chromatography purification of the components specifically bound in the affinity separation step. Affinity-bound peptides were identified by determining their amino acid sequence. All the sequenced peptides belonged to the C-terminal part of human β-casein, which confirms the cross-reactivity of human milk proteins and peptides with antibodies to bovine β-LG and allows the identification of possible common epitopes between the two proteins. No bovine β-LG peptides with a molecular mass ≥ 1,000 Da were found in our milk samples from healthy mothers on a diet rich in bovine milk and dairy products.

Purification of goat beta-lactoglobulin from whey by an ultrafiltration membrane enzymic reactor.

This paper presents a novel contribution to the purification of goat beta-lactoglobulin by using an ultrafiltration membrane enzymic reactor. The basis of the purification process was the enzymic hydrolysis of contaminating proteins, alpha-lactalbumin and traces of serum albumin, by pepsin at 40 degrees C and pH 2, conditions under which beta-lactoglobulin is resistant to peptic digestion. Simultaneously, beta-lactoglobulin and peptides were separated by ultrafiltration. beta-Lactoglobulin was retained in the reactor while peptides generated by hydrolysis from alpha-lactalbumin and serum albumin permeated through the membrane. The process was made continuous by the addition of fresh whey to replace the lost permeate. Three mineral membranes with 10, 30 and 50 kDa molecular mass cut-off were tested and the 30 kDa membrane was selected for the continuous process. The simultaneous purification and concentration of beta-lactoglobulin from clarified goats' whey was achieved in a single step. The ultrafiltration membrane enzymic reactor could treat eight reactor volumes of clarified whey. The recovery of beta-lactoglobulin was 74%, its purity was 84% and its concentration 6.6-fold that in the initial clarified whey.

Use of different thermal indices to assess the quality of pasteurized milks

Lactoperoxidase activity and lactulose, furosine and undenatured whey protein contents were determined in Spanish commercial milks labelled as pasteurized (group A) and high-temperature pasteurized (group B), in order to assess their quality. Three samples of group A and all of the samples of group B were lactoperoxidase negative. Most samples of group A had measurable amounts of lactulose, even though their concentrations of undenatured β-lactoglobulin were higher than 2600 mg/l. In general, samples of group B showed higher lactulose and furosine and lower undenatured whey protein contents. High levels of furosine and lactulose accompanied by high levels of undenatured β-lactoglobulin could indicate the addition of milk heated at high temperatures, whereas high levels of furosine and relatively low levels of lactulose may have been due to the presence of reconstituted milk powder.

Intestinal barrier function and cow's milk sensitization in guinea pigs fed milk or fermented milk.

The respective effect of milk and fermented milks on intestinal barrier capacity and on sensitization to beta-lactoglobulin was studied using a guinea pig model of cow's milk allergy. Guinea pigs were fed a control diet or the same diet supplemented with milk, fermented milk (Streptococcus thermophilus and Bifidobacterium breve), or dehydrated fermented milk. Intestinal barrier capacity to macromolecules was assessed in an Ussing chamber, and sensitization to cow's milk proteins was measured by systemic anti-beta-lactoglobulin immunoglobulin G1 titers and by intestinal anaphylaxis, the latter assessed by the beta-lactoglobulin-induced increase in short-circuit current of jejunal fragments (deltaIsc(beta-LG)). The electrical resistance of jejunum was similar in the four groups (approximately 80 omega/cm2) suggesting the same paracellular permeability. The transport of 14C-beta-lactoglobulin from mucosa to serosa was significantly decreased in the animals fed dehydrated fermented milk (403+/-131 ng / hr x cm2) compared with that in control animals or animals fed milk (767+/-250 ng / hr x cm2 and 749+/-475 ng / hr x cm2, respectively; p < 0.05). Milk fermentation did not modify native beta-lactoglobulin concentration but anti-beta-lactoglobulin immunoglobulin G1 titers were higher in fermented milk and dehydrated fermented milk (log10 titer = 2.86 and 2.79, respectively) than in guinea pigs fed milk (log10 titer = 2.5; p < 0.007). However, beta-lactoglobulin-induced intestinal anaphylaxis remained the same in the three groups (deltaIsc(beta-LG), 9.6+/-4.1 microA/cm2, 8.5+/-4.3 microA/cm2, and 8.5+/-3.4 microA/cm2 in milk-fed, fermented milk-fed, and dehydrated fermented milk-fed guinea pigs, respectively). The intestinal barrier capacity to milk proteins seems to be reinforced by dehydrated fermented milk, but milk and fermented milks are equally efficient in inducing cow's milk allergy in guinea pigs.

Effect of milk coagulation properties of herd bulk milks on yield and composition of Emmental cheese

Tutkimuksessa selvitettiin tankkimaidon juoksettumis-ominaisuuksien vaikutusta Emmental-juuston määrään sekä juuston ja juustoheran koostumukseen ja laatuun.Juustokoetta varten kerättiin 2–6 lypsykerran tankkimaidot yhteensä kahdeksasta karjasta,jotka muodostivat kaksi neljän karjan ryhmää .Ryhmän A karjat olivat tuottaneet kohtalaisen hyvin juoksettuvaa maitoa ja ryhmän B karjat huonosti juoksettuvaa maitoa.Hyvin juoksettuvaa maitoa tuottaneessa ryhmässä A a s1 -kaseiinin C-alleeli,ß -kaseiinin A 1 -ja B-alleelit sekä . K-kaseiinin B-alleeli olivat yleisem- piä ,friisiläislehmien suhteellinen osuus oli suurempi ja maidon . K-kaseiinin,a -laktalbumiinin ja ß -lak- toglobuliinin pitoisuudet olivat korkeammat kuin ryh- mässä B. Kummankin karjaryhmän tuottamasta maidosta valmistettiin kaksi Emmental-juustoa.Kunkin juuston valmistamiseen käytettiin noin 740 l maitoa.Ryhmä A hyvin juoksettuneesta maidosta saatiin keskimäärin 2 kiloa enemmän juustoa kuin ryhmän B huonosti juoksettuneesta maidosta.Tämä johtui pääosin siitä, että hyvin juoksettuneen maidon heraan hukkaantui vähemmän kaseiinia ja rasvaa kuin huonosti juoksettuneen maidon. Tankkimaidon juoksettumisominaisuuksissa esiintyy runsaasti vaihtelua karjojen välillä .Tankkimaitojen juoksettumisominaisuuksilla oli vaikutus maidon käyttö kelpoisuuteen juuston valmistuksessa. Tämän vuoksi maidon juoksettumisominaisuuksien pysyvä parantaminen on yksi edellytys juustontuotannon tehostumiselle.;

A Rapid Fluorimetric Method to Estimate the Heat Treatment of Liquid Milk

A rapid and sensitive fluorimetric method is proposed to evaluate the heat treatment of commercial milk. This method is based on the simultaneous determination of protein denaturation by Trp fluorescence (λexc 290 nm; λem 340 nm) and formation of fluorescent advanced Maillard products (λexc 350 nm; λem 440 nm) in the milk fraction soluble at pH 4.6. The first reaction characterizes low heat treatments such as pasteurization or direct UHT sterilization and the second one becomes significant for indirect UHT treatments and for in bottle sterilization. Trp fluorescence of 80 commercial milk samples was correlated well with the soluble protein concentration evaluated by the Lowry method as well as the concentration of β-lactoglobulin quantified by HPLC. The advanced Maillard products were poorly correlated to the furosine content. Furosine, formed during acid hydrolysis of the Amadori product, increased linearly with time for a constant temperature, while the fluorescence of the advanced Maillard products progressed exponentially. This method allows a wide characterization of heat processes and gives a rapid evaluation of the nutritional quality of milk proteins.

Competitive adsorption between egg yolk lipoproteins and whey proteins on oil-in-water interfaces

Adsorption characteristics of mixtures of egg yolk lipoproteins and whey protein isolate (WPI) were studied in emulsions (20% oil, v/v 0.5% protein, w/v pH 7.0) made with pure triolein or n-tetradecane. Emulsions stabilized by granule lipoproteins (GLP) or low-density lipoproteins (LDL) had smaller particle sizes than emulsions stabilized by WPI. In protein mixtures containing egg yolk lipoproteins and WPI, there was a decrease in particle size with increased concentration of the yolk lipoproteins. The reduction in particle size of emulsions was greater when WPI was mixed with LDL than with GLP, for both n-tetradecane and triolein. Emulsions made with triolein had smaller particle sizes than those made with n-tetradecane, irrespective of the type or ratio of lipoproteins used. Therefore, the protein concentration per unit area of the interface was greater for emulsions containing n-tetradecane than for triolein. In displacement experiments, emulsions made with only WPI were mixed with 0.1 and 0.5% GLP or LDL for a given period of time and the relative concentrations of β-lactoglobulin and α-lactalbumin determined. Displacement of β-lactoglobulin by LDL increased with time and was greater in emulsions made with n-tetradecane than with triolein. However, displacement of β-lactoglobulin by GLP was greater in emulsions made with triolein than with n-tetradecane. α-lactalbumin was completely displaced from the interface within 1 min of addition of either 0.5% GLP or LDL, whereas addition of 0.1% GLP or LDL resulted only in a partial displacement. The results suggest that egg yolk lipoproteins are more surface active than WPI and that LDL penetrates the n-tetradecane–water interface more than GLP, while GLP penetrates the triolein–water interface more than LDL.

Effects of composite casein and β-lactoglobulin genotypes on renneting properties and composition of bovine milk by assuming an animal model

The effects of κ-β-casein genotypes and β-lactoglobulin genotypes on the renneting properties and composition of milk were estimated for 174 and 155 milk samples of 59 Finnish Ayrshire and 55 Finnish Friesian cows, respectively. As well as the random additive genetic and permanent environmental effects of a cow, the model included the fixed effects for parity, lactation stage, season, κ-β-casein genotypes and κ-lactoglobulin genotypes. Favourable renneting properties were associated with κ-β-casein genotypes ABA1A2, ABA1A1 and AAA1A2 in the Finnish Ayrshire, and with ABA2B, AAA1A3, AAA2A3, ABA1A2 and ABA2A2 in the Finnish Friesian. The favourable effect of these genotypes on curd firming time and on firmness of the curd was partly due to their association with a high κ-casein concentration in the milk. The effect of the κ-casein E allele on renneting properties was unfavourable compared with that of the κ-casein B allele, and possibly with that of the A allele. The β-lactoglobulin genotypes had no effect on renneting properties but they had a clear effect on the protein composition of milk. The β-lactoglobulin AA genotype was associated with a high whey protein % and β-lactoglobulin concentration and the BB genotype with a high casein % and casein number.

5. Differences in β-lactoglobulin concentrations between morning and afternoon milkings at early, mid and late stages of lactation

5. Differences in β-lactoglobulin concentrations between morning and afternoon milkings at early, mid and late stages of lactation

Molecular Mass Distributions of Heat-Induced β-Lactoglobulin Aggregates

The aggregates in heated bovine β-lactoglobulin solutions were separated by high-performance size-exclusion chromatography, and molecular characteristics were measured on-line using multiangle laser-light scattering detection (SEC-MALLS). This technique was proven to be a very useful and valuable approach for characterization of heat-induced β-lactoglobulin aggregates. Using TSK G2000 SWXL and TSK G4000 SWXL silica gel columns connected in series, aggregates up to a molecular mass of 4 × 106 Da could be separated, and complete molecular mass distributions were derived. Up to a molecular mass of 1.5 × 106 Da the molecular masses calculated by the MALLS agreed very well with the results obtained by conventional calibration. The measured molecular mass distributions of the heat-induced β-lactoglobulin aggregates varied strongly with experimental heating conditions (β-lactoglobulin concentration, pH, heating temperature, ionic strength). The results obtained with several β-lactoglobulin concentrations at neutral pH were consistent with a kinetic aggregation model based on thiol/disulfide exchange reactions. The average molecular mass and the radius of gyration of the heat-induced β-lactoglobulin aggregates increased with increasing initial β-lactoglobulin concentration. Keywords: β-Lactoglobulin; aggregation; size-exclusion chromatography; light scattering; molecular size

Isothermal and Scanning Calorimetry Measurements on β-Lactoglobulin

The denaturation and aggregation of β-lactoglobulin was studied by isothermal calorimetry. Experiments with several β-lactoglobulin concentrations (15−100 g/L) were performed at temperatures in the range 62−68.5 °C. Even a small change in temperature had a tremendous effect on the shape of the thermograms, depending also very strongly on the β-lactoglobulin concentration used. The measured thermograms were modeled using the kinetic model for the denaturation and aggregation of β-lactoglobulin recently developed by Roefs and De Kruif. In this kinetic model we recognize four consecutive steps: dissociation, unfolding, exchange of disulfide bonds, and aggregation. The numerical calculations yielded results that were in qualitative and quantitative agreement with typical experimental isothermal calorimetry curves. DSC curves and the decrease in concentration of native β-lactoglobulin as a function of time could also be reproduced well. We think that isothermal calorimetry, in combination with this kinetic mo...

Differentiation between 15 whole milk powders in relation to oxidative stability during accelerated storage: Analysis of variance and canonical variable analysis

Abstract The colour of powder and reconstituted milk (Hunter's L-, a- and b-values), fluorescent oxidation products, and two peak areas (corresponding to β-lactoglobulin and α-lactalbumin) from size exclusion chromatography were measured 9 times during accelerated storage at 50 °C and a water activity of 0.31 on 15 medium-heat whole milk powders manufactured at the same production plant. The powder and reconstituted milk gradually turned darker and more yellow with increasing storage time, but the Hunter a-value (redness value) was ambiguous, suggesting that during lactose crystallization, β-carotene migrates with free fat to the surface of the powder particles. Fluorescent oxidation products were formed at a constant rate from carbonyl compounds and protein amino groups. β-Lactoglobulin and α-lactalbumin were subject to progressive denaturation. Using canonical variable analysis, milk powders were best distinguished by their colour and by their content of β-lactoglobulin and α-lactalbumin. Age classification of powders of unknown origin should follow two different strategies: fresher powders (corresponding to accelerated storage times up to 25 days) should be distinguished by the amount of fluorescent oxidation products, the content of α-lactalbumin and powder brightness, whereas for older powders (accelerated storage times from 25 to 43 days), the colour of the reconstituted milk should be measured also. An interaction was found between storage time and powder which indicated a more erratic behaviour of the powders as storage time was prolonged.

Effect of milk fractions on survival of equine spermatozoa

Milk-based semen diluents are known to be practical and effective in protecting equine spermatozoa during storage. Due to complex composition of milk, the components which are beneficial or harmful to spermatozoa are unknown. To address these unknowns the effect of various milk fractions on motility of stallion spermatozoa was evaluated. The fractions tested were native phosphocaseinate (NPPC), β-casein, whey protein concentrate (WPC), α-lactalbumin, β-lactoglobulin, microfiltrate, and ultrafiltrate. The standard reference diluents were INRA 82, commercial skim milk, and Hank's salts solution supplemented with Hepes, glucose, lactose (HGLL) supplemented with BSA. After 48 and 96 h storage at 4 or 15 °C some milk fractions (ultrafiltrate, microfiltrate, and α-lactalbumin fraction) decreased spermatozoal survival. Others (β-lactoglobulin (BL) and native phosphocaseinate) were protective. Native phosphocaseinate (NPPC) at milk concentration afforted better protection than did the standard reference diluents. The optimal concentration of β-lactoglobulin afforted significantly better protection than did BSA. The protection afforded by native phophocaseinate was not synergistic with β-lactoglobulin. This implies a similar mechanism of protective action of these two components. Semen diluted in HGLL supplemented with NPPC (HGLL-NPPC) or in INRA 82 and stored 24 h at 15 °C or 4 °C, respectively, produced no difference of spermatozoal motility. However, fertility of semen stored in HGLL-NPPC (60%) was higher (p < 0.05) than that stored in INRA 82 (36%).

Heat-Induced Aggregation of β-Lactoglobulin: Role of the Free Thiol Group and Disulfide Bonds

The heat-induced aggregation of bovine β-lactoglobulin, dispersed in water at neutral pH and in different concentrations (10, 30, or 50 g of dry matter/L), was studied at 65 °C, and the results are related to a kinetic model. Native PAGE and SDS−PAGE analysis under nonreducing and reducing conditions showed that on heating disulfide-linked aggregates were formed and that the average size of these aggregates increased with increasing initial β-lactoglobulin concentration. In the presence of the thiol-blocking agent N-ethylmaleimide (NEM), at a molar ratio of NEM/β-lactoglobulin monomer of 1, all thiol groups were blocked and no disulfide-linked aggregates were formed, although with native PAGE high molecular mass noncovalently linked aggregates were observed. The formation of these aggregates accelerated with increasing NEM concentration until a molar ratio of NEM/β-lactoglobulin monomer of 1 was reached. In separate experiments we studied the effect of pH (in the range pH 6.0−8.0) on the aggregation of β-...

Behaviour of droplets in simple shear flow in the presence of a protein emulsifier

The effect of two structurally diverse protein emulsifiers, β-lactoglobulin and β-casein, upon the break-up behaviour of a single aqueous droplet in a Couette flow field has been studied over a wide range of protein concentrations for bulk viscosity ratios between 8 × 10 −5 and 0.05. It has been found that β-casein and low concentrations (⩽10 −2 g l −1) of β-lactoglobulin cause the droplets to be at least as stable as expected from conventional theories on the basis of their equilibrium interfacial tension. In such cases the presence of the emulsifier at the deforming interface is thought to enhance the interfacial elasticity. This effect can be characterized by an effective interfacial tension, which is higher than the equilibrium value. High concentrations of β-lactoglobulin (⩾ 10 −1 g l −1), on the other hand, have been shown to cause droplets to be less stable than would have been predicted from the equilibrium interfacial tension. It is thought that an interfacial protein network is formed, which limits the droplet deformation and makes the droplet interface rigid with respect to tangential stresses. As a result, the critical deformation and capillary number are found to be essentially independent of the viscosity ratio. It is proposed that the interfacial structure may be probed using a combination of interfacial shear and dilational rheological measurements. From this type of analysis it may be possible to predict the break-up stability of droplets.

Comparison of .BETA.-Lactoglobulin Content in Dairy Products by Inhibition ELISA and Immunoblotting.

To estimate the effect of food processing on allergen content in dairy products, β-lactoglobulin (β-LG) contents of 4 milks, 5 yogurts and 6 cheeses were compared using inhibition ELISA (enzyme-linked immunosorbent assay), SDS-PAGE and immunoblotting. Results of the inhibition ELISA suggested that low temperature-pasteurized milk contained several times higher levels of β-LG than high temperature-pasteurized milk, and that yogurts contain a lower amount of β-LG than milks. On the contrary, results of SDS-PAGE and immunoblotting suggested that the degradation of milk proteins including β-LG during yogurt manufacturing was not very extensive. These results suggest that yogurts contain factor(s) which interfere some reactions of inhibition ELISA. β-LG was also detected in cheeses, though the level was lower than that of milks. Though milk proteins were degraded most extensively in Roquefort cheese, its β-LG level was the highest. Among them, processed cheese had the lowest amount of β-LG, followed by Emmental cheese. These results suggest that an appropriate application of specific bacteria is useful for the preparation of low allergenic dairy products.

Aggregation of β-lactoglobulin studied by in situ light scattering

SummaryIn situ light scattering, where light scattered from a sample is measured directly while the sample is heated in the instrument, is presented as a simple and effective technique for studying the heat-induced aggregation of β-lactoglobulin. This technique was shown to be applicable not only to monitoring the initial aggregation steps, but to following the overall aggregation process with time. The experiments gave results similar to measurements carried out after a heat-quench treatment, but were more informative. From experiments on a standard NIZO β-lactoglobulin sample, a strongly desalted standard NIZO sample, different genetic variants of β-lactoglobulin and a mixture of these, we concluded that the standard NIZO sample was suitable for studying heat-induced aggregation. This sample has been investigated more extensively. Results with β-lactoglobulin (10–100 g/1) at 65 °C fitted a kinetic model for the denaturation and aggregation of β-lactoglobulin. This model, which held for β-lactoglobulin dissolved in water at near neutral pH and at 60–75 °C, recognizes an initiation, propagation and termination reaction, by analogy with polymer radical chemistry. It gave a quantitatively correct description of the dependence of the scattering intensity on the initial β-lactoglobulin concentration. Salt composition, pH and temperature strongly influenced the aggregation of β-lactoglobulin. Particle size increased with salt concentration in the range studied (up to 20 mM-NaCl and 1·0 mM-CaCl2). When the pH increased from 6°9 to 8·0 particle size was strongly reduced, whereas it strongly increased when pH was lowered to 6·2. Between 61·5 and 70 °C temperature did not affect particle size, whereas aggregation rate strongly increased. These effects could be incorporated in the kinetic model via the reaction constants of the reaction kinetic pathway.

Different amounts of β-lactoglobulin A and B in milk from heterozygous AB cows

Abstract The concentrations of total protein, casein and whey protein were determined in milk samples derived from 1278 Ayrshire, 718 Jersey, 396 Brown Swiss and 271 Canadienne cows which were all heterozygous β-lactoglobulin AB. The mean values for the respective components were: 3.40, 2.69 and 0.70% for Ayrshire, 3.82, 3.08 and 0.74% for Jersey, 3.54, 2.80 and 0.74% for Brown Swiss and 3.60, 2.88 and 0.72% for Canadienne. Polyacrylamide gel electrophoresis, followed by densitometric scanning, was used to quantify the relative proportions of β-lactoglobulin A and β-lactoglobulin B in the whey protein fraction. For the four breeds studied, a higher proportion of β-lactoglobulin was produced as the A variant than as the B variant. In the heterozygous β-lactoglobulin AB, the A form was present in higher amounts of 49, 41, 40 and 31% when compared to the B form of the protein in Jersey, Canadienne, Brown Swiss, and Ayrshire, respectively. These results support previous observations that the concentrations of β-lactoglobulin in milk are associated with the genetic variants of the protein and are in the following decreasing order of magnitude, according to phenotypes: AA > AB > BB.