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.     

Combined effect of whey protein and aS1-casein genotype on the heat stability of goat milk

Goat milk is characterized by a very low heat stability, which could be related to compositional factors. In this paper, the role of the heat-induced interaction between whey proteins and casein micelles is considered. The effect of the casein micelle structure is evaluated using milk samples with different α_S1-casein genotypes, and the protein interactions are studied at various pH values in order to take into account the strong pH-dependence of the heat stability. The results suggest that the heat-induced interaction of β-lactoglobulin with κ-casein is of minor importance at natural pH, but is promoted at more elevated pH.     

SURFACE PROPERTIES OF PROTEIN LAYERS ADSORBED FROM MIXTURES OF GELATIN WITH VARIOUS CASEINS

We report surface tensions and surface shear viscosities of protein layers adsorbed from mixtures of gelatin +α_s11-casein, β-casein, k-casein or sodium caseinate. Under conditions where the two protein components carry opposite net charges, the combined experimental data at 25C and neutral pH are consistent with a two-layer model of the mixed protein film. The surface properties of sodium caseinate lie intermediate between those for the two major individual caseins (α_s1 and β).     

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.     

CHANGES IN EQUILIBRIUM MODULUS AND αsl-CASEIN BREAKDOWN DURING THE RIPENING OF PORT SALUT ARGENTINO CHEESE AS AFFECTED BY FROZEN STORAGE

The effect of the freezing, frozen storage and thawing on textural parameters and α_sl-casein breakdown during the ripening of Port Salut Argentino cheese was studied. Moisture content, salt concentration, casein profiles and asymptotic equilibrium modulus were monitored in control cheeses ripened at 5C and in cheeses, stored at -22C for 30 days, thawed and ripened at 5C, for different ripening times (1, 6, 13, 27 and 56 days) and two sampling zones (central and external). The freezing process significantly increased the rate of α_sl-casein and α_sl-I-casein hydrolysis. This process may affect the susceptibility of α_sl-casein to chymosin attack and also the availability of hydrolytic enzymes released by damaged microorganisms, which may contribute to the faster hydrolysis of α_sl-I-casein. The freezing process did not significantly affect the decay rates of asymptotic equilibrium modulus. First order kinetics constants for decay of the asymptotic equilibrium modulus were 3.71 10^-2day^-1 (control cheeses, central zone), 8.48 10^-2 day^-1 (control cheeses, external zone), 4.52 10^-2 day^-1 (frozen cheeses, central zone), and 11.43 10^-2 day^-1 (frozen cheeses, external zone). Significant differences in the decay rates of asymptotic equilibrium modulus were found between central and external zones in control and frozen cheeses primarily due to differences in moisture contents of the sampling zones.     

Acylation and Solubility of Casein Precipitated by Carbon Dioxide

Casein precipitated from milk using carbon dioxide (CO₂-casein) and calcium caseinate were acetylated and succinylated. Aqueous solubility of casein was measured at pH 3, 5, 7, and 9. Acetylation extent was lower for CO₂-casein while both succinylated to similar extents. Solubility between the unmodified caseins was similar except at pH 5 with CO₂-casein being less soluble. Succinylation enhanced solubility for both caseins at pH 5, 7, and 9 with similar solubility between the succinylated caseins at each pH. Acetylation enhanced solubility at pH 5, however CO₂-casein still possessed lower solubility than calcium caseinate. Acylation and solubility behavior indicated structural features in CO₂-casein which were not present in calcium caseinate.     

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.     

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.     

Maribo cheese manufactured with concentrated milk: characteristics, maturation and yield

Research was carried out to study the feasibility of making maribo cheese using milk fortified by the addition of skim milk powder. A control (T-C) with 82 g l^-1 solids-non-fat (SNF) and 32 g l^-1 milk fat was included, along with three treatments with 11.7 (T-1), 14.6 (T-2) and 16.6 g l^-1 SNF (T-3) and standardization of the milk fat. Some chemical characteristics of the cheese milks and of the endproducts were studied and, in addition, cheese yield and the progress of maturation were monitored. It was observed that, as maturation proceeded in all treatments, there was a steady increase in the ripening index (soluble nitrogen/total nitrogen %), which indicates a progressive advance of proteolysis. Nevertheless, there were significant differences (p <.05) between the ripening indices of the control and the rest of the treatments. Furthermore, as the extent of maturation increased, α_sl-casein was degraded more than β-casein. The yield of cheese increased proportionally as the concentration of non-fat-solids in the milk increased.     

Influence of vitamin E supplementation on spontaneous oxidized flavour of milk in dairy buffaloes

Twenty-four Murrah buffaloes (60 days pre-partum) were divided into four equal groups (T ₁ , T ₂ , T ₃ and T ₄ ) and were supplemented with 0, 1000, 1500 and 2000 IU α-tocopheryl acetate per day up to 30 days of lactation, and half of these doses from 30 to 60 days of lactation. Milk samples collected fortnightly were analysed for vitamin E, fat, and development of oxidized flavour, with and without copper addition by a panel of judges, and chemically by the thiobarbituric acid test. Scores for oxidized flavour ranged from 0 to 10 with 0–4 as definite, 5–7 as light and 8–10 having no defect. The α-tocopherol content in milk fat (µg/g) averaged 20.55, 25.56, 29.98 and 31.38 in T ₁ , T ₂ , T ₃ and T ₄ groups, respectively. The addition of Cu in the milk significantly increased milk fat oxidation. Better stability of milk in T ₃ and T ₄ groups was observed, which might be due to a higher level of milk α-tocopherol. Addition of 1500 IU α-tocopheryl acetate in the diet of buffaloes helped in improving the oxidative stability of milk.     

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.     

Effect of technological parameters on the characteristics of kasseri cheese made from raw or pasteurized ewes' milk

Two groups of kasseri cheese (pasta filata type) were manufactured from raw or pasteurized ewes' milk, without starter cultures. Cheeses of each group were divided into two subgroups: the first was ripened and stored at 4°C and packaged in plastic film; the second ripened and stored at 15°C and coated with paraffin wax. Milk pasteurization and technological parameters had a significant effect on the pH ( P  < 0.05), while only technological parameters had an effect on the total solids content. At day 120, the range of mean cfu/g counts for the mesophilic aerobic flora was 9.5 × 10⁷−1.4 × 10⁸; for the thermophilic streptococci, the range was 2.6 × 10⁷−7.6 × 10⁷; and for the thermophilic bacilli, 9.8 × 10⁶−1.7 × 10⁷. Changes in the N fractions became significant after 30 days of ripening. For mature 120-day-old cheeses, the percentage of total N soluble at pH 4.6 was 22.7%–22.9% in raw milk cheeses and 19.0%–21.7% in pasteurized milk cheeses. The percentage of total N soluble at 12% TCA was 10.1%–12.2% in raw milk cheeses and 7.3%–11.5% in pasteurized milk cheeses; the percentages of total N soluble at 5% PTA were 3.1%–4.0% and 2.6%–3.6%, respectively. The residual α_s-casein percentages at day 120 ranged between 63% and 78% of the respective area at day 1; the residual β-casein ranged between 67% and 75%. There were some characteristic differences in the reverse phase-HPLC peptide profiles of the four cheeses. In general, the effect of the different ripening conditions was more pronounced in cheeses made from pasteurized milk.     

Influence of some polyvalent organic acids and salts on the colloidal stability of milk

Fifteen polyvalent organic salts and acids increased, some very markedly, the heat stability of milk progressively with increasing concentration; acetate and mesaconic acid had no effect, and maleate caused destabilization. Citrate, oxalate and EDTA markedly reduced the [Ca⁺] in the milk and increased its ethanol stability by shifting the ethanol/pH profile to lower pH values. These additives ≥ 20 mmol/l prevented the coagulation of milk by rennet, but the other additives caused only slight increases in RCT .
Citrate, EDTA and oxalate disrupted casein micelles and would therefore not be suitable additives: however, the other acids and salts did not alter the appearance of the milk and might be recommended as suitable additives to improve the heat stability. In terms of the response to the level of Ca²⁺ and colloidal calcium phosphate in milk, there appeared to be a correlation between ethanol stability and rennet coagulation time.     

The effects of different cations on the physicochemical characteristics of casein micelles

Physicochemical characterisation of casein micelles suspended in milk ultrafiltrate and enriched with different cations (Fe, Cu, Ca, Zn and Mg) was investigated. After addition of 2.5–8.0 mmol kg⁻¹ of cations, associations of added cation, citrate, inorganic phosphate and calcium with casein micelles were observed. The order of association of cations with casein micelles was Fe³⁺ > Zn²⁺ > Ca²⁺ > Cu²⁺ > Mg²⁺. At the same time, the casein content increased in the casein micelles while the water content decreased. Changes in hydrophobicity and zeta potential of casein micelles were also determined while no variation in the average diameter was detected. In the presence of 8.0 mmol kg⁻¹ of magnesium or ferric iron, heat stability (115 °C for 30 min) of casein micelles was decreased. From these results, a mechanism of cation association with casein micelles is proposed, highlighting the determinant role of ultrafiltrable citrate and inorganic phosphate. This mechanism is discussed in relation to modifications in physicochemical characteristics of casein micelles.     

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.     

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.     

Effects of Lactic Acid Bacteria and Fermented Milks on Eicosanoid Production by Intestinal Epithelial Cells

ABSTRACT: Fermented milk products produced with probiotic lactic acid bacteria (LAB) have attracted interest due to their potential health benefits. Probiotic bacteria have a range of immunomodulatory activity, interacting with a variety of cell types in the immune system. Interactions with intestinal epithelial cells (IEC) are an avenue through which probiotics and their fermented milks can influence production of key immunoregulatory molecules, including cytokines and eicosanoids. The eicosanoids, which include the prostaglandins (PGs), are lipid mediators implicated in both acute and chronic inflammatory processes. The primary objective of this study was to determine the ability of probiotic LAB and their ferments to interact with IEC and influence their eicosanoid production. Effects of LAB and their milk ferments on prostaglandin E₂ (PGE₂) and prostaglandin F_2α (PGF_2α) production by human IEC lines were determined using a competitive enzyme immunoassay. LAB alone did not alter interleukin (IL)-1β-induced prostaglandin production by IEC. However, milk fermented with Lac-tobacillus (L.) rhamnosus strain R0011 significantly suppressed IL-1β-induced levels of PGE₂ and PGF_2α, an effect which was counteracted by the addition of strain R0011. Milk ferments prepared withL. acidophilus strain R0052 were less effective in down-regulation of PG production by IEC. Naltrexone, an opioid receptor antagonist, blocked the suppressive effects of L. rhamnosus R0011 milk ferments on PGF_2α production by IEC, suggesting that the bioactivity the ferments is opioid receptor-mediated. These findings support immunomodulatory potential of fermented food components through interactions with intestinal epithelial cells.     

Influence of the degree of hydration on the thermal expansion of muscle tissue

The variation of expansivity, α, of beef M. semitendinosus with moisture content was determined by measurement of the temperature change induced by adiabatic compression over the moisture content range 2 to 90%, at temperatures (T) of 1, 8 and 15°C. At low levels of hydration, α increased with moisture content, reached a maximum around 35% water, and thereafter decreased. The data suggested that thermal expansivity is related to water binding, and the application of a simple expansivity model based on 'free' water, 'bound' water and dry-solids, gave a value for the expansivity of 'bound' water at 8°C of 8.9±1.7x10-⁴°C-¹, about seventeen times that of 'free' water.     

Changes in the microbiological and chemical characteristics of an artisanal, low-fat cheese made from raw ovine milk during ripening

Changes in the microbial flora of batzos cheese made from raw ovine milk were studied during ripening. Lactic acid bacteria and Enterobacteriaceae were the predominant groups of micro-organisms. Cheeses manufactured in summer had higher microbial counts than those made in spring, with the exception of staphylococci. Nevertheless, Enterobacteriaceae and coliforms decreased more rapidly in cheese made in summer and counts at the end of storage were lower than those in spring cheese.
Enterococci predominated in the ripened curd of cheese made in spring, whereas lactobacilli were the most abundant lactic acid bacteria in cheese made in summer. Enterococcus faecium was the predominant species in spring, and Lactobacillus paracasei ssp. paracasei predominated in cheese made in summer. The pH of the cheeses was > 5.0 throughout ripening, and NaCl-in-moisture content (> 8.0%) permitted the growth and survival of salt-tolerant micro-organisms. α_s1-Casein degraded at a faster rate than β-casein; both caseins were hydrolysed more rapidly in spring than in summer. The free amino acid content became higher in summer cheese (566.24–3460.25 µg/g of glycine equivalent) than in spring cheese because of the progress of ripening. Moreover, the milk fat of the cheese was degraded more in the summer than in the spring. The results suggest that there could be advantages to using starter cultures and improving the level of hygiene during milk and cheese production in order to eliminate undesirable micro-organisms and standardize cheese quality.     

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.