Free Amino Acid Profiles During Ripening of Port Salut Argentino Cheese After Frozen Storage

ABSTRACT: Free amino acid profiles of Port Salut Argentino cheeses at different storage conditions (ripening with and without previous frozen storage), ripening times (1, 6, 13, 27, and 56 d), and cheese zones (central and external) were studied. Derivatization with o-phtaldialdehyde and a C₁₈ column were used for chromatographic separations. Principal component analysis reduced data to 2 dimensions where unripened cheeses (1 to 13 d) were grouped independently of ripening time, sampling zone, and storage condition. Ripened cheeses (27 and 56 d) showed scattering according to ripening time. The contribution of free amino acid profiles to quality in cheeses preserved by frozen storage may be considered similar to that in traditionally ripened cheeses.     

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.     

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.     

Texture Changes During the Ripening of Port Salut Argentino Cheese in 2 Sampling Zones

ABSTRACT: Texture changes during ripening of Port Salut Argentino cheese for different sampling zones were studied. Compression relaxation tests were performed and results were analyzed using both Maxwellian and Peleg's models. Elastic equilibrium modulus obtained from the Maxwellian model decreased from 1.22 to 0.11 10⁴Pa during ripening. The constants derived from Peleg's model, k₁ and k₂, diminished with ripening time from 1.18 to 0.71 min and from 1.27 to 1.12, respectively. Asymptotic equilibrium modulus from Peleg's model decreased from 0.95 to 0.07 10⁴Pa during ripening. Rate parameters derived from a 1st order kinetics applied to both equilibrium moduli showed that the decrease was faster in the external zone (0.0846 d⁻¹) than in the central zone (0.0368 d⁻¹). The correlation between equilibrium moduli, salt concentration, moisture content, and maturation indexes was obtained with a determination coefficient of 0.76.     

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.     

The effect of natural cheddar cheese ripening on the functional and textural properties of the processed cheese manufactured therefrom

ABSTRACT:  Cheddar cheese ripened at 8 °C was sampled at 7, 14, 28, 56, 112, and 168 d and subsequently used for the manufacture of processed cheese. The cheddar cheese samples were analyzed throughout ripening for proteolysis while the textural and rheological properties of the processed cheeses (PCs) were studied. The rate of proteolysis was the greatest in the first 28 d of cheddar cheese ripening but began to slow down as ripening progressed from 28 to 168 d. A similar trend was observed in changes to the texture of the PC samples, with the greatest decrease in hardness and increase in flowability being in the first 28 d of ripening. Confocal scanning laser microscopy showed that the degree of emulsification in the PC samples increased as the maturity of the cheddar cheese ingredient increased from 7 to 168 d. This increased emulsification resulted in a reduction in the rate of softening in the PC in samples manufactured from cheddar cheese bases at later ripening times. Multivariate data analysis was performed to summarize the relationships between proteolysis in the cheddar cheese bases and textural properties of the PC made therefrom. The proportion of α _{s 1}-casein (CN) in the cheddar cheese base was strongly correlated with hardness, adhesiveness, fracturability, springiness, and storage modulus values for the corresponding PC. Degradation of α _{s 1}-CN was the proteolytic event with the strongest correlation to the softening of PC samples, particularly those manufactured from cheddar cheese in the first 28 d of ripening.     

Probiotic Cheddar Cheese: Influence of Ripening Temperatures on Proteolysis and Sensory Characteristics of Cheddar Cheeses

ABSTRACT:  Bifidobacterium longum 1941, B. animalis subsp. lactis LAFTI^® B94, Lactobacillus casei 279, Lb. casei LAFTI L26, Lb. acidophilus 4962, or Lb. acidophilus LAFTI L10 were used as an adjunct in the production of Cheddar cheeses, which were ripened at 4 and 8 °C for 24 wk. Effects of ripening temperatures and probiotic adjuncts on proteolysis and sensory evaluation of the cheeses were examined. Higher ripening temperature increased the level of proteolysis in the cheeses. Product of proteolysis and organic acids released during ripening were shown to be important for the flavor of Cheddar cheeses. There were positive and significant correlations between the levels of soluble nitrogen, lactic, acetic, and butyric acids, percentage hydrolysis of α_s1-CN and β-CN to the scores of cheddary flavor ( P < 0.05). Scores for sour-acid and vinegary flavors were higher in cheeses with the addition of Bifidobacterium sp. or Lb. casei 279 ripened at 8 °C. The scores were positively and significantly correlated to the level of lactic, acetic, and free amino acids in the cheeses ( P < 0.05). The results show that both 4 and 8 °C have potential for use in the ripening of probiotic Cheddar cheeses.     

EFFECT OF SEVERAL EXPERIMENTAL PARAMETERS ON COMBINATION OF RED KIDNEY BEAN (PHASEOLUS VULGARIS) α-AMYLASE INHIBITOR WITH PORCINE PANCREATIC α-AMYLASE

Purified red kidney bean (Phaseolus vulgaris) amylase inhibitor forms a 1:1 stoichiometric complex with porcine pancreatic α-amylase leading to complete loss of enzyme activity on starch. Rate of complex formation is pH dependent and is maximal at pH 5. The rate constants for complex formation, as measured by loss of amylase activity, were 2.85 × 10⁴ M^-1 sec^-1 at pH 6.9 (ionic strength of 0.918) and 2.55 × 10⁵ M^-1 sec^-1 at pH 5 at 30°C. At pH 6.9, rate of complex formation was 4.8 times faster at 0.918 ionic strength as compared with the rate at 0.138 ionic strength. At 30°C, pH 6.9 and ionic strength of 0.168 the dissociation constant of the enzyme-inhibitor complex was determined to be 3.5 × 10^-11 M. The rate constant for dissociation of the complex was calculated to be 8.7 × 10^-8 sec^-1 under the same conditions. The rate constant for complex formation, at ionic strength of 0.168, was 1.1 × 10⁴ M^-1 sec^-1 at 37⁰ and 9.77 × 10² M^-1 sec^-1 at 25.7°C. The calculated activation energy for complex formation is 39.5 kcal/mole suggesting a rate-controlling conformational change. Oxidation of the carbohydrate moiety of the glycoprotein inhibitor caused complete loss of activity. Maltose, a competitive inhibitor of α-amylase, bound as readily to the enzyme-inhibitor complex as to free α-amylase. Trypsinized α-amylase, although still able to bind to Sephadex, did not bind inhibitor. The experiments with maltose and trypsinized amylase suggest the inhibitor may not bind at the active site of α-amylase.     

Ozone treatment of chilled beef

Summary. The initial specific rate of ozone decomposition by muscle was 1.02 ± 0.23 m/hr, for tissue stored at 0.3°C and equilibrium relative humidities (EH) of 99.3, 98.5 or 98.0% in air with ozone concentrations between 0.15 and 38.3 mg/m³, or in air-ozone mixtures containing 11% CO₂. the value was not affected by the presence or absence on the muscle surface of meat spoilage bacteria, yeasts or moulds but considerably lower values were obtained for lean and high fat surface tissues (0.44 and 0.31, respectively).
The slope α of the linear course of the logarithm of reaction velocity-time curves was a power function α= - 9.74 10^-4[O₃]^1.54 for ozone concentrations [O₃] 5 mg/m³. the slope was not significantly different from zero when muscle of EH 98.5% was exposed to 0.7 mg/m³ ozone, but significant values were determined when muscle had an EH of 98.0, and also when tissue (EH 99.3%) was exposed to ozone concentrations > 0.7 mg/m³. Values of α determined for surface tissue and muscle tissue were not significantly different when the same treatment was applied.     

Potassium Sorbate Diffusivity in American Processed and Mozzarella Cheeses

The diffusivity of potassium sorbate in cheeses was determined by using diffusion models and computer programming for examining the residual surface concentration and the penetration of surface-applied potassium sorbate into cheese. To determine diffusivity, the concentration of potassium sorbate in sliced cheese was measured by penetration time and distance from surface. The diffusivity was calculated by nonlinear regression with experimental data based on Fick's law. The diffusivity of potassium sorbate through American processed cheese was 1.31∞10^-6 cm²/sec and for Mozzarella cheese 6.74∞10^-7 cm²/sec. This indicated that Mozzarella cheese would maintain surface concentration of potassium sorbate above the critical fungistatic level two times longer than American processed cheese.     

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.     

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.     

Proteolytic and lipolytic changes during the ripening of León raw cow's milk cheese, a Spanish traditional variety

Proteolytic and lipolytic changes were studied throughout ripening of five batches of León cow's milk cheese, a traditional variety made in the north of Spain. Total soluble nitrogen, non-protein nitrogen, oligopeptides nitrogen, amino nitrogen and ammonia nitrogen fractions increased slightly during the ripening process. The final values of these nitrogen fractions indicate that this cheese undergoes a very slight proteolysis as much in extent as in depth. This weak protein degradation is corroborated when the caseins and their degradation products were quantified by electrophoresis. β-Casein stayed practically intact throughout the ripening process and only 10% of α_s-casein became degraded. The content of total free amino acids increased progressively but in a slightly increased way during ripening, reaching final average values of 592 mg (100 g)⁻¹ of total solids. The most abundant free amino acid at the end of ripening was lysine, followed by leucine, glutamic acid, tryptophan, valine and phenylalanine. The acidity index of the fat values increased during ripening by a factor of 4.39. The final values of this parameter are in the range of those observed in other cow's milk cheeses ripened by bacteria. The content in total free fatty acids underwent an increase throughout ripening reaching final average values of 6669 ppm. The most abundant free fatty acid at the end of ripening was oleic acid followed by butyric and palmitic acids. The high content of short-chain fatty acids is outstanding, specially that of butyric acid.     

Quality of Shredded Carrots as Affected by Packaging Film and Storage Temperature

ABSTRACT: Different packaging films and storage temperatures were used to establish a range of equilibrium modified atmospheres for storage of shredded carrots. Quality and storage-life of the packaged shredded carrots were determined using sensory evaluation, microbial counts, and a range of physical tests. Minimal processing steps such as peeling and shredding caused physical damage, physiological stress, and enhanced microbial growth, leading to a reduced shelf life when compared to the whole vegetable. A P-plus microporous film (CO₂ permeability of 29 X 10³mL.m ^-2.d ^-1.atm ^-1) was the most suitable for the storage of shredded carrots. Findings indicated that deterioration in these products was triggered by the depletion of oxygen more than by the rise in carbon dioxide.     

MEASUREMENT OF THE HARDNESS AND MOUTHFEEL OF CHEESE USING A SLIDING PIN CONSISTOMETER

A sliding pin consistometer (SPC) was used to differentiate between six commercial cheese products, including a hard, mature Cheddar and a soft, cream cheese, at a number of temperatures in the range 0.8 to 25.0°C. Average force values (F_f) decreased with increasing temperature and with decreasing relative cheese hardness. Measurements were also made on six Cheddar cheeses with a range of salt to moisture (s/m) ratio (2.95 × 10^-2 to 5.57 × 10^-2) at a sample temperature of 16°C at maturation periods of 22, 58, 100 and 183 days. A panel of 27 adults scored the hardness and mouthfeel of these samples at these maturation periods using 9-point scoring scales. The SPC discriminated between samples and maturation periods and was more discriminating than the subjective evaluation of panelists. Mean F_f values decreased with maturation and increased linearly with increasing s/m. Panelists' hardness scores increased with s/m but were not influenced significantly by maturation. Mouthfeel increased with maturation and was a maximum at a s/m of between 4.36 × 10^-2 and 4.57 × 10^-2. The SPC provides objective information that could be useful in assessing the effect of treatment on cheese.     

Isolation and Identification of Low-Molecular-Weight Peptides from Emmentaler Cheese

ABSTRACT: Four peptides, derived from the N-terminal fragment of α_sl -casein [CN (1–9), CN (1–12), CN (1–13) and CN (1–14)] were isolated from a low-molecular-weight extract of a commercial Emmentaler cheese (age: approx. 5.5 mo) by gel filtration and RP-FPLC. Capillary zone electrophoresis was used to check the purity of the peptides. Using automatic Edman degradation and MALDI-TOF mass spectrometry, amino acid sequence and molecular mass of the peptides were determined to identify them. The peptide α_sl -CN (1–13) was identified for the first time in Emmentaler cheese. The peptide fraction was shown not to contribute to the characteristic flavor of Emmentaler cheese.     

TEXTURAL PARAMETERS IN COMPRESSION TESTING OF A GEL MADE FROM FRESH AND FROZEN FISH MINCE

The relation between deformability modulus and yield stress is evaluated in compression testing of a model product made from fresh and frozen stored mince of cod. The experiments were performed with a compression rate of 120 mm/min. Preliminary experiments showed decreasing values of yield stress when compression rates were below 50 mm/min. Two moduli were calculated from the slope of the compression curve; α₁, initially (small deformations) and α₂ in a linear part of the curve shortly before rupture of the gel. α₂ was linearly related to yield stress in gels of different water content, and in gels made from fresh and frozen raw material. α₁ showed different relations to yield stress depending on quality of the raw material.     

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).     

Proteolysis of Fynbo Cheese Salted with NaCl/KCl and Ripened at Two Temperatures

Cheeses salted in solutions of 100g NaCl/L and 100g KCl/L and ripened for 90 days at 12°C and 16°C were compared with cheeses salted in brine of 190g NaCl/L and ripened at the same temperatures. Peptides of the water-soluble nitrogen (WSN) fraction were quantified by the Kjeldahl method and analyzed by reverse-phase HPLC. There were no differences (P>0.05) attributable to salt treatments; and the cheeses stored at 16°C showed higher levels of WSN/Total Nitrogen (TN) than cheeses ripened at 12°C. HPLC profiles of WSN extracts showed differences in the hydrophilic zone for cheeses ripened at different temperatures, but profiles were similar for cheeses salted with NaCl and with NaCl/KCl.     

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.