Casein diversity in caprine milk and its relation to technological properties: heat stability

Caprine milk is characterized by a genetically linked diversity in casein content. Of particular importance is the genetic polymorphism of α_s1-casein, which is under the influence of seven known alleles controlling the level of α_s1-casein expression in milk. In this article, the effect of α_s1-casein genotype on milk composition and heat stability is considered. Two different types of caprine milk were used: milk high in α_s1-casein from animals heterozygous AE or BE with respect to α_s1-casein genotype and milk low in α_s1-casein from animals homozygous FF. Milk high in α_s1-casein was less stable upon heating than milk low in α_s1-casein. Unlike bovine milk there was no recovery in heat stability at pH values greater than 7.0. These differences were associated with factors in the serum rather than the casein fraction and could not be explained by the variation in the protein composition, /3–lactoglobulin to casein ratio or the small variation in Ca²⁺ and lactose levels between the two milks. On the other hand, milk low in α_s1-casein had a higher urea content, which had a significant stabilizing effect.     

Stability of β-lactoglobulin/micellar casein mixtures on heating in simulated milk ultrafiltrate at pH 6.0

The stability of β-lactoglobulin (β-lg)/micellar casein (MC) mixtures was examined on heating at pH 6.0 in increasing levels of lactose-free simulated milk ultrafiltrate (SMUF). Heated β-lg associated with MC to form stable particles (up to 771 nm in size in SMUF × 0.5). Higher levels of SMUF induced reductions in the charge on particles, resulting in greater aggregation and precipitation. Results indicated that the nonthiol-containing α_s1- and β-casein fractions showed greater interaction with β-lg on heating than the thiol-containing fractions (α_s2-casein and κ-casein). Casein proteins and their fractions have potential application in the development of heat-stable dairy-based beverages.     

Sodium caseinates — composition and properties of different preparations

A number of samples of commercially available spray-dried and roller-dried caseinates have been compared with freshly prepared caseinate from the laboratory. The compositions of the materials were measured using chromatography, and their calcium susceptibilities were determined using turbidity measurements. The chromatographic analysis showed that the commercial caseinates differed substantially from the fresh material, especially in the regions where α-casein and α_s2-caseins were eluted. The fresh caseinate was more affected by the presence of calcium ions than the others, and there were also differences between the individual spray-dried caseinates in this respect. The roller-dried caseinates were very insensitive to the presence of calcium ions.     

ISOLATION OF β2-CHACONINE, A POTATO BITTERNESS FACTOR

The 4-rhamnoglucoside of alkaloid solanidine, β₂-chaconine, was isolated from a mixture of α-solanine with β₂-chaconine by fractionation from hot ethyl acetate. The mixture of the two glycoalkaloids is obtained by endogenous enzyme action in a homogenate of potato berries and blossoms within a 24–36 h incubation at 37° C, pH 6.00. The identity of β₂-chaconine was ascertained by m.p., [α]D° IR spectrum, TLC of sugar components and reference to partial acid hydrolysis products of α-chaconine.     

SEPARATION OF STEROLS AND TRITERPENE ALCOHOLS FROM UNSAPONIFIABLE FRACTIONS OF THREE PLANT SEED OILS

Preparative HPLC was used to separate sterols and triterpene alcohols from the unsaponifiable matters in plant oils from Camellia weiningensis L., Brassica juncea L. and Microula sikkimensis . The isolated sterols and triterpene alcohols were acetylated and further purified by AgNO₃ impregnated silica gel preparative thin layer chromatography (TLC). The isolated acetyl derivatives of sterols and triterpene alcohols were identified by melting point, specific rotation, infrared and mass spectrometry. The sterols were brassicasterol, campesterol, stigmasterol, β-sitosterol and Θ⁵-avenasterol, Θ⁷-avenasterol, Θ⁷-stigmastenol and α-spinasterol. The triterpene alcohols were cycloartanol, cycloartenol, 24-methylenecycloartanol, cyclobranol, dammaradienol, tirucalla-7,24-dienol, butyrospermol, β-amyrin, germanicol, α-4-taraxasterol and lupeol.     

Influence of the Coagulant Level on Early Proteolysis in Ovine Cheese-like Systems Made with Sterilized Milk and Cynara cardunculus

ABSTRACT: The effect of coagulant level on the quality and quantity of protein breakdown during the first 24 h of ripening of cheese-like systems, manufactured with sterilized ovine milk using crude aqueous extracts of Cynara cardunculus as coagulant, was experimentally assessed. Urea-polyacrylamide gel electrophoresis was performed on both water-soluble and water-insoluble cheese extracts to monitor the casein degradation pattern; the ripening extension index and the ripening depth index were thus calculated. Peptides from the water-soluble fraction were isolated by reverse-phase, high-performance liquid chromatography and partially sequenced by Edman degradation. Higher residual coagulant levels in curdled milk led to earlier breakdown of caseins, as expected. The primary cleavage sites were Phe105-Met106 in k-casein, Phe23-Val24 in α_s1-casein, and Leu127-Thr128, Ser142-Trp143, Leu165-Ser166, and Leu190-Tyr191 in β-casein.     

THE MOLECULAR WEIGHT OF α-AMYLASE INHIBITOR FROM WHITE BEAN cv 858B (PHASEOLUS VULGARIS L.) IS 56 kDa, NOT 20 kDa

The molecular weights (M_rs) of α-amylase inhibitors (αAIs)fiom 18 (Ah) bean cultivars estimated by Superose 12 gelfiltration chromatography were 22–62% smaller than those determined by Sephadex G-100 gel filtration and by polyacrylamide gel electrophoresis (PAGE) methods. αAI-4 from WKB cultivar 858B was purified and the Mr was shown to be 51.0 kDa based on Sephadex G-100 gel filtration chromatography and by PAGE. A M_r for aAI-4 of 56.714 kDa was determined by laser-assisted time-of-flight mass spectrometry and appears to be the true M_r of the mature glycosylated active aAI-4. The results show that Superose 12 gelfiltration chromatography is not usefulfor M_r determination of some proteins. Sodium dodecyl sulfate electrophoresis (SDS-PAGE) showed that the 56.7 kDa aAI-4 molecule dissociated into 45.0, 33.6,15.2 and 12.4 kDa submolecules, with only the two small subunits, a and β, present at high SDS concentration. This provides evidence that the aAI-4 molecules composition is α₂β².     

Evaluation of Serpa cheese proteolysis by nitrogen content and capillary zone electrophoresis

Proteolysis of Serpa cheese produced traditionally (B) and semi-industrially (C) was evaluated for the first time by determination of nitrogen content and capillary zone electrophoresis (CZE). A citrate dispersion of cheese was fractionated to determine the nitrogen in pH 4.4, trichloroacetic and phosphotungstic acid soluble fractions (pH 4.4-SN, TCA-SN and PTA-SN, respectively). The pH 4.4-SN was significantly higher for B ( P  < 0.001), while TCA-SN was significantly higher for C ( P  < 0.001). PTA-SN was also higher for C but at 60 days ripening no significant difference was found between B and C. Degradation of α_s1- and β-caseins evaluated by CZE was in good agreement with the maturation index (pH 4.4-SN/TN).     

RHEOLOGICAL AND CHEMICAL PROPERTIES OF MOZZARELLA CHEESE

Dynamic viscoelastic parameters and chemical properties of Mozzarella cheese produced using a "no-brine" cheese making method with 3 different cooking temperatures (38, 41, and 44C) were determined. Samples were stored for 3 weeks at 4C before dynamic mechanical analysis at 22C. G', G" and tan δ were 5.8 – 6.4 × 10⁵ dyne/cm², 1.9 – 2.1 × 10⁵ dyne/cm², and 0.33 – 0.35, respectively, at 1% strain and 10 rad/s. The percentage of intact α_s-casein and β-casein were 38–40% and 33–35% of total protein in the cheese, respectively. The range of cooking temperatures used in this experiment had little effect on dynamic viscoelastic properties or the amount of intact protein for the cheese.     

Changes in rheological and viscoelastic properties and protein breakdown during the ripening of 'Port Salut Argentino' cheese

Changes in the rheological behaviour and viscoelastic properties during ripening at 10°C of a soft cheese (Port Salut Argentino) packaged in a plastic film (EVA-EVA) were analysed. Casein degradation was measured by electrophoresis slab gels; α_s1 casein degradation was rapid and striking compared with that of β casein. Rheological parameters obtained from uniaxial compression tests changed during ripening: hardness decreased, adhesiveness and cohesiveness increased.
An exponential decay equation with two maxwellian elements and one elastic in parallel was fitted to characterize stress relaxation curves. Viscoelastic parameters (elastic moduli and relaxation times) were obtained using non-linear regression analysis. The elastic equilibrium modulus decreased 80% during the ripening period and the viscosity of the element with the highest relaxation time decreased 20%. These parameters represented the changes observed in cheese hardness and elasticity during ageing time and were related to the extent of casein breakdown.     

Proteolysis in ultra-filtered and conventional Iranian white cheese during ripening

Conventional and ultra-filtered (UF) Iranian white cheeses were made with almost identical gross chemical composition and the extent and characteristics of proteolysis were studied during ripening. UF cheeses exhibited a lower rate of development of pH 4.6-soluble nitrogen than conventional cheeses. The rates of degradation of α_s1-casein and particularly β-casein were lower in UF cheeses than in conventional cheeses. Plasmin activity was lower in UF cheeses than that in conventional cheese, whereas coagulant activity was higher in the former. Noticeable qualitative and quantitative differences were observed in reverse-phase high performance liquid chromatography (RP-HPLC) peptide profiles between UF and conventional white cheeses and chemometric analysis of peak height data distributed the cheeses into two separate groups. The levels of free amino acids in UF cheeses were lower than in conventional cheeses. Lower peptide degradation and production of amino acids suggested slower ripening, which may have been associated with the weak aroma development characteristic of UF cheeses.     

Fractionating Soybean Storage Proteins Using Ca2+ and NaHSO3

ABSTRACT:  Individual soybean storage proteins have been identified as having nutraceutical properties, especially β-conglycinin. Several methods to fractionate soy proteins on industrial scales have been published, but there are no commercial products of fractionated soy proteins. The present study addresses this problem by using calcium salts to achieve glycinin-rich and β-conglycinin-rich fractions in high yields and purities. A well-known 3-step fractionation procedure that uses SO_2, NaCl, and pH adjustments was evaluated with CaCl₂ as a substitute for NaCl. Calcium was effective in precipitating residual glycinin, after precipitating a glycinin-rich fraction, into an intermediate fraction at 5 to 10 mM CaCl₂ and pH 6.4, eliminating the contaminant glycinin from the β-conglycinin-rich fraction. Purities of 100%β-conglycinin with unique subunit compositions were obtained after prior precipitation of the glycinin-rich and intermediate fractions. The use of 5 mM SO₂ in combination with 5 mM CaCl₂ in a 2-step fractionation procedure produced the highest purities in the glycinin-rich (85.2%) and β-conglycinin-rich (80.9%) fractions. The glycinin in the glycinin-rich fraction had a unique acidic (62.6%) to basic (37.4%) subunit distribution. The β-conglycinin-rich fraction was approximately evenly distributed among the β-conglycinin subunits (30.9%, 35.8%, and 33.3%, for α', α, and β subunits, respectively). Solids yields and protein yields, as well as purities and subunit compositions, were highly affected by pH and SO₂ and CaCl₂ concentrations.     

PREPARATION OF ENRICHED FRACTIONS OF α-LACTALBUMIN AND β-LACTOGLOBULIN FROM CHEESE WHEY USING CARBON DIOXIDE

A new process for preparing enriched fractions of α-lactalbumin (α-La) and β-lactoglobulin (β-Lg) from whey protein concentrate was developed. To prepare the fractions, solutions containing from 7% (w/w) to 25% (w/w) whey protein concentrate (WPC75) were sparged with carbon dioxide (CO₂) in a batch reactor. The effects of pressure, temperature, concentration, and residence time on the distribution of the individual whey proteins in each fraction were investigated. Best results were obtained for 7% (w/w) WPC75 solutions, at reactor fill pressures of 4140 kPa and 5520 kPa, temperature of 64C and reactor residence time of 10 min. Gel electrophoresis of unpurified enriched samples showed that recovery of α-La was approximately 55% and that of β-Lg was 78%. The resulting fractions have a pH of 6.0 and contain no added salts.     

Evaluation of changes during storage of probiotic dahi at 7°C

Low-fat probiotic dahi (an Indian traditional fermented milk product like yogurt) prepared with lactococci starter and two adjunct probiotic cultures of Lactobacillus acidophilus and Lactobacillus casei was stored at 7°C. The survival of bacterial species was affected during storage of dahi, in which viable counts increased up to 2 days and gradually decreased from 2 days, up to 8 days. The quality of refrigerated dahi was assessed by a panel of trained judges. On storage, pH significantly decreased over storage time, indicating that the dahi samples did not develop much acidity under the storage conditions of the study. However, after 8 days of storage, the samples were disliked by the panel, which reported slight bitterness, which may have been due to proteolysis. Proteolysis increased during storage. More α_s1-casein was degraded than β-casein. On the basis of the results of this study we can conclude that dahi stored up to 8 days may be acceptable to consumers.     

Elimination of β-Lactoglobulin from Whey to Simulate Human Milk Protein

When the pH of cottage cheese whey was adjusted to 4.5 in the presence of 6.7 mM FeCI³, β-lactoglobulin was eliminated from the whey as a precipitate. However, the majority of immunoglobuhns were also coprecipitated. To recover immunoglobulins together with α-lactalbumin, the whey pH was adjusted to 3.0 in the presence of 4.0 mM FeCI³. After centrifugation of the whey, the supernatant contained exclusively β-lactoglobulin; other whey proteins were found in the precipitate. Excess Fe₊₊₊ in the precipitate was removed by ion exchange or by ultrafiltration. This protein concentrate had a protein composition much more similar to that of human milk whey than that of ultrafiltered whey protein concentrate.     

FLOW PROPERTIES OF BABACO (CARICA PENTAGONA) PUREES AND CONCENTRATES

A power law model describes adequately the rheological behaviour of Babaco purees and concentrates while a Herschel-Bulkley model describes concentrates only. A single equation η_a=α x cβ x exp (E_a/RT), combining the effects of temperature and concentration on apparent viscosity (η_a100), was used to describe rheological behaviour.     

Emulsifying and foaming properties of protein isolates prepared from heated milks

Surface activities at the air-water interface and the emulsifying and foaming properties of sodium caseinate, conventional casein-whey protein co-precipitate prepared from milk heated at 90°C × 15 min at pH 6.6 and milk protein isolates prepared from milks heated at 90°C × 15 min at pH 7.5 or at 60°C × 3 min at pH 10.0 were determined. The surface activities of the four proteins at the air-water interface were similar, while the emulsifying capacity and emulsion stabilizing ability of casein was less than that of the milk protein isolates or the conventional co-precipitate. Fat surface areas formed on emulsification with the four proteins were similar and increased with increasing power input. Total protein adsorbed at the interface and protein load (mg protein/m₂ fat) for the emulsions stabilized by sodium caseinate and the milk protein isolate prepared from the milk heated at 90°C × 15 min at pH 7.5 were similar and lower than those for emulsions stabilized by the other two proteins. Foam overruns followed the order: sodium caseinate > milk protein isolate prepared from milk heatedat90°C × 15min, pH 7.5 > milk protein isolate prepared from milk heated at 60°C × 3 min, pH 10.0 > conventional co-precipitate, while foam stabilities followed the reverse order.     

PROTEIN DEGRADATION IN CHEDDAR CHEESE SLURRIES

SUMMARY— Preferential degradation of caseins was noted in the ripening of Cheddar curd slurries, with the degradation generally being in the order of para-K, β-, α_s-caseins. The addition of reduced glutathione to the slurry caused an immediate release of peptides from the protein mass and decreased the initial rate of β-casein degradation. The peptides appeared to be preferentially utilized during the first 4 days of ripening; thereafter rapid degradation of β-casein occurred. In quiescent slurries, α_s-casein degradation exceeded that of β-casein, whereas periodic agitation reversed the degradation rate of the two caseins. The rate and extent of characteristic flavor development appeared to be related directly to β-casein degradation, but not to changes in concentration of pare-K or α_s-caseins.     

ADSORPTION BEHAVIOR OF β-LACTOGLOBULIN ONTO STAINLESS STEEL SURFACES

Nonporous stainless steel particles with an average diameter of 25.5 μm and an average surface area of 215 cm²/g were used to study the adsorption of β-lactoglobulin (β-lg). Scanning electron microscopy of stainless steel particle surfaces with adsorbed β-lg showed an obvious eradication of crevices as protein was adsorbed. The adsorption process for β-lg was very rapid in the first 5 min and essentially reached equilibrium within 10 min. Precipitation of calcium phosphate onto the stainless steel surface was very slow compared to monolayer deposition of β-lg. A monolayer of β-lg adsorbed very tightly to the stainless steel surface and a significant fraction of the protein was irreversibly adsorbed. The amount of adsorbed protein decreased with increasing ratio of surface area to reaction volume. pH in the range 6.0–6.8 did not significantly affect the amount of adsorbed protein.     

RHEOLOGY OF SODIUM CASEINATE-CARRAGEENAN MIXTURES

The main effects and interactions of mixtures of sodium caseinate, k- or t- carrageenan, sodium chloride, calcium chloride and hydrogen ions on the rheological properties in aqueous systems cooled to 5 C were quantified. Response surface methodology was used to display the results for five different response variables: gelation temperature, consistency index (k*), dynamic power law factor (n*), critical strain (γ_c), and syneresis. The gelation profiles observed for both k- and t-carrageenan systems demonstrated that the sol-gel transition in sodium caseinate-carrageenan mixtures was due to electrostatic interactions of free carrageenan loops or tails with the intervention of cations. Caseinate molecules did not play a major role in this process. The electrostatic nature of the interactions was further demonstrated by the significant influence of salts and pH on the consistency and brittleness of the gels (represented by k*and γ_c, respectively). Consistency and brittleness were inversely related as well as consistency and syneresis. Syneresis was negligible in t-carrageenan gels and was reduced by sodium caseinate and sodium chloride in the k-carrageenan systems.