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.     

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.     

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.     

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.     

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.     

Natural preservative ingredient from marine alga Ulva lactuca L.

The contents of total chlorophyll (T-Chl), carotenoids and phenolics compounds were quantified in the biomasses of Ulva lactuca grown either in normal or artificial sea water under indoor conditions. The antioxidant and antibacterial activities of U. lactuca crude organic extracts ( Ulva- COEs) were determined. Thirty-four compounds in Ulva- COEs were characterised by thin layer chromatography and high-performance liquid chromatography. The major compounds were chlorophyll a (Chl a ) (15.60–30.90%) and b (Chl b ) (12.20–14.89%) , 9-cis β-carotene (13.12–14.47%), α-carotene (11.44–11.47%) and all-trans β-carotene (6.16–29.70%, of total carotenoids).The Ulva- COEs exhibited remarkable antioxidant activity, with an IC₅₀ (concentration which causes a 50% of DPPH radical scavenging activity) values ranged from 16.5 and 18.7 μg mL⁻¹, which could be compared with the synthetic antioxidants: α-tocopherol (14.4 μg mL⁻¹), butylated hydroxyanisol (13.1 μg mL⁻¹) and butylated hydroxyltoluene (13.1 μg mL⁻¹). Also, Ulva- COEs exhibited great potential antibacterial activities against six bacterial strains, with minimal inhibitory concentration values ranged from 0.40 to 0.35 mg mL⁻¹.     

Fate of Aflatoxin M1 during Manufacture and Storage of Feta Cheese

ABSTRACT:  The effect of feta cheese manufacture on aflatoxin M₁ (AFM₁) content was studied using an enzyme immunoassay technique. Feta cheese was made from milk spiked with 1 and 2 μg AFM₁ per kilogram milk. Pasteurization at 63 °C for 30 min caused <10% destruction of AFM₁. During cheese making, the remaining AFM₁ in milk was partitioned between curd and whey with two-thirds retained in the curd and one-third going into the whey. Cheeses were then stored for 2 mo in 8%, 10%, and 12% brine solutions at 6 and 18 °C. There was a 22% to 27% reduction of AFM₁ during the first 10 d of storage, with slightly more loss as salt concentration increased and when the cheese was stored at 18 °C. Further storage caused only slight decrease in AFM₁ and after 30 d of brining there was no difference in AFM₁ content of the cheese based upon salt concentration of the brine. At 18 °C, no further losses of AFM₁ occurred after 30 d, and at 6 °C, there was continued slight decrease in AFM₁ levels until 50 d. After 60 d of brining, there was a total loss of 25% and 29% of the AFM₁ originally present for cheese brined at 6 and 18 °C, respectively. Thus, the combination of pasteurization, conversion of milk into feta cheese, and at least 50 d storage of cheese in brine caused a total loss of about 50% of the AFM₁ originally present in the raw milk.     

Production of hard cheese from caprine milk by the use of two types of probiotic cultures as adjuncts

Hard cheeses (Kefalotyri-like) were manufactured from caprine milk with yoghurt as a starter (A), and with its partial replacement with the probiotic adjuncts Lactobacillus rhamnosus LC 705 (B) and/or Lactobacillus paracasei ssp. paracasei DC 412 (C). Both adjuncts retarded the growth of enterococci, and the environment in cheese B did not favour the recovery of lactic acid bacteria (LAB) on Rogosa agar. However, better recovery of the LAB population on M17 agar from cheeses B and C made with adjuncts was recorded early in ripening, and this was accompanied by a greater decrease in pH. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of whole-cell protein demonstrated that cheese C, made with Lb. paracasei ssp. paracasei as adjunct, is a better vehicle for delivery of live probiotic cells (10 ⁷   cfu/g) to the gastrointestinal tract than cheese B, made with Lb. rhamnosus ; the latter did not belong to the predominant microflora of one out of the two B cheeses. Urea-PAGE electrophoresis results indicated that adjunct lactobacilli enhanced the degradation of both α _S -casein (α _S -CN) and β-casein (β-CN). In the fresh cheese, hydrolysis of α _S -CN was more rapid than β-CN, and the free amino acid content of B and C was higher than in A. Lipolysis products were also higher in B and C than in A as ripening progressed, and the organoleptic characteristics of these cheeses resulted in higher scores, in the order C > B > A. Thus, making Kefalotyri-like cheese from caprine milk with probiotic lactobacilli, particularly Lb. paracasei ssp. paracasei, as adjunct can be considered an effective way of producing a cheese with a large number of probiotic cells.     

Optimisation of the medium composition for production of protease and soybean peptides by Bacillus subtilis SHZ using response surface methodology

Responses surface methodology was employed to enhance the production of protease and soybean peptides by Bacillus subtilis SHZ. For screening of medium composition significantly influencing protease and soybean peptides yield, the two-level Plackett–Burman design was used. Among thirteen variables tested; KH₂PO₄, glucose and defatted soybean flour (DSF) were selected based on their high significant effect on both protease activity and soybean peptides yield. Then, a three-level Box–Behnken design was employed to optimise the medium composition for the production of the protease and soybean peptides in submerged fermentation. Mathematical models were then developed to show the effect of each medium composition and their interactions on the production of protease and soybean peptides. The model estimated that, the maximal protease activity (320 ± 1 U mL⁻¹) could be obtained when the concentrations of glucose, KH₂PO₄, DSF were set at 8–9 g L⁻¹, 2–3 g L⁻¹, 55–65 g L⁻¹, respectively; while a maximal yield of soybean peptides (8.5 ± 0.1 g L⁻¹) could be achieved when the concentrations of glucose, KH₂PO₄, DSF were set at 7–9 g L⁻¹, 3–4 g L⁻¹ and 55–58 g L⁻¹, respectively. These predicted values were also verified by validation experiments.     

KINETICS OF NONENZYMATIC BROWNING IN CHEDDAR CHEESE POWDER DURING STORAGE

Nonenzymatic browning (NEB) in Cheddar cheese powder during storage was investigated in the water activity (a_w) and temperature ranges of 0.48–0.85 and 20–40C, respectively. The NEB obeyed zero-order reaction kinetics during storage. Activation energies and Q₁₀ values were in the range of 15.1–22.3 kcal/mole and 2.2–3.5, respectively. The NEB increased with increasing temperature and storage time. There was an a_w maxima at 0.63 for NEB at 20C. At 30 and 40C, NEB decreased with increasing a_w. A generalized NEB model for Cheddar cheese powder during storage was developed based on Arrhenius equation to describe NEB as a function of a_w and temperature. Powders stored at 20 and 30C were evaluated for quality aspects. Maximum storage stability was obtained in powders stored at a_w of 0.54 at 20C for five months based on an overall desirability score of 3.5 on a 7-point scale. The average score of fresh powders were 4.7 throughout the storage study 7.     

Reduction of Streptococcus thermophilus in a whey protein isolate by low moisture extrusion cooking without loss of functional properties

A whey protein isolate powder (WPI) (4–5% water) inoculated with 5x10⁵ viable Streptococcus thermophilus per g, was continuously processed in a twin screw extruder under the following conditions (barrel length = 500 or 1000 mm; screw profile = forward transport and compression elements; moisture content during extrusion = 4–5%; feed rate = 10 kg h^-1; barrel temperature ( T_b ) = 80–204°C; speed of screw rotation = 50 r.p.m.). The minimum residence time determined by pulse injection of erythrosin was 20–25 s (500 mm barrel) or 35–40 s (1000 mm barrel).
Reduction values of viable Streptococcus thermophilus of 10^4.2-fold (500 mm barrel, T_b = 143°C) or 10^4.9-fold (1000 mm barrel, T_b = 133°C) were obtained without any modification of protein solubility or gelling properties. WPI extruded at the highest barrel temperatures (182–204°C) underwent limited browning and reduction of protein solubility. Gel permeation and hydrophobic interaction chromatography of the soluble constituents did not show any aggregates of β-lactoglobulin or α-lactalbumin.
Gels prepared from control or extruded WPI ( T_b 143°C with a barrel length = 500 mm or T_b 133°C with a barrel length = 1000 mm) were identical, as judged by scanning electron microscopy and rheological evaluations.     

PRELIMINARY OBSERVATIONS ON EFFECTS OF FAT CONTENT AND DEGREE OF FAT EMULSIFICATION ON THE STRUCTURE-FUNCTIONAL RELATIONSHIP OF CHEDDAR-TYPE CHEESE

Cheddar type cheeses of different fat contents were produced and denoted: full-fat (FFC), 306g/kg; half-fat (HFC), 174 g/kg; and low fat (LFC, 13 g/kg). Full-fat Cheddar cheese (FFCH) was also prepared from milk which had been homogenized at first and second stage pressures of 25 and 5 MPa, respectively. The cheeses were held at 4C for 30 days and at 7C for the remainder of the 190-day ripening period. Reducing the fat level from 174 to 13 g/kg resulted in decreases in contents of moisture in nonfat substance and pH 4.6 soluble N as a percentage of total N (pH4.6SN), and increases in the contents of moisture, protein and intact casein. Homogenization of cheesemilk resulted in a slight increase in moisture content and an increase in pH4.6SN. Confocal laser scanning microscopy revealed that the extent of fat globule clumping and coalescence in both the unheated and heated (to 95C) cheeses decreased with homogenization of the cheesemilk and with fat reduction. Homogenization of the cheesemilk and reducing the fat content of the cheese resulted in a decrease in the flowability and stretchability of the melted cheese. Dynamic measurement of the viscoelastic changes on heating the cheese from 20 to 90C showed that reduction of fat content resulted in a decrease in the magnitude of the phase angle, δ, at temperatures >50C. At temperatures<∼60C, the storage modulus, G', increased on reducing the fat content from 306–174 g/kg to 13 g/kg. Homogenization resulted in a marked decrease in δ at temperatures>45–50C, with δ_max typically decreasing from ∼65–70° in the FFC to ∼35° in the FFCH.     

Colour loss during extrusion cooking of β-carotene-wheat flour mixes as an indicator of the intensity of thermal and oxidative processing

The thermal and/or oxidative colour loss from a wheat flour/all-trans β-carotene (20–80 mg kg⁻¹) mix during extrusion cooking follows first order kinetics. The intensity of processing in extrusion is reflected in the overall rate constant ( K ) of colour loss. K -values were in the range 3–20x10⁻³ s⁻¹. They increased markedly with decreasing water content of the mix (24–14%), and with increasing barrel temperature (100–220°C). Results were independent of the type of twin-screw extruder (Werner-Pfleiderer Continua 37 or Clextral BC-45). Modelling of the overall rate constant K and of the 'equivalent plug flow' residence time was used to define 'iso-destructive' extrusion conditions giving approximately the same residence time and the same mean product temperature. Extrusion under N₂ or O₂, or in the presence of 1 mg BHT per g of β-carotene, slightly affected colour loss. Adsorption chromatography on alumina indicated that within a barrel temperature range of 125–200°C, 38–73% of the initial all-trans β-carotene was destroyed, and that 2/3 to 1/2 of this loss corresponded to the formation of 9-cis plus 13-cis β-carotene isomers. The formation of smaller amounts of unknown β-carotene derivatives may be responsible for the colour loss.     

Separation of Immunoglobulin G from Cheddar Cheese Whey by Avidin-Biotinylated IgY Chromatography

High-purity immunoglobulins (Ig), which may be useful for immunologic supplementation of food products, were isolated from Cheddar cheese whey in a one-step process using avidin-biotinylated yolk immunoglobulin (IgY) column chromatography. Yolk antibodies specific to bovine IgG (IgY_IgG) were biotinylated with biotinyl amido-hexanoic acid-N-hydroxy-sulfo-succinimide ester without any notable effect on antigen-binding activity, and coupled to immobilized avidin columns. The resulting avidin-biotinylated IgY_IgG columns, with binding capacity of 50–55% (w/w percent ratio of IgG to immobilized IgY_IgG), were used for specific binding of IgG from cheese whey. Elution with a commercially available eluent (Actisep) or 0.1 M glycine-HCl buffer at pH 2.8 yielded IgG with purity of 99% by radial immunodiffusion.     

EFFECT OF WATER ACTIVITY ON THE GROWTH OF STAPHYLOCOCCUS AUREUS AT MEAT-CHEESE INTERFACES

There is increased marketing of ready-to-eat nonrefrigerated snack foods which consist of meat or sausage products with low or intermediate moisture levels combined with high moisture food products, i.e., cheese products. Packaging the intermediate moisture meat in direct contact with a high moisture food might change the water activity (a_w) of the products sufficiently to support growth of Staphylococcus aureus at contaminated interfaces. To evaluate this possibility, sterile sausage slices (a_w= 0.60 to 0.82) were surface inoculated with log 2-3 CFU/g of S. aureus, interfaced with processed cheese slices (a_w= 0.94), vacuum packaged, and incubated at 19, 28, 37C and at cyclic temperature of 19–37–19C. S. aureus levels and water activities were determined weekly for 0 to 9 weeks. The a_w at the interface changed rapidly and reached an a_w that supported S. aureus growth. Growth of S. aureus occurred under all test conditions when the samples were stored at 28 and 37C. At 19C storage S. aureus remained viable for the length of the study.     

Effect of pan-frying in extra-virgin olive oil on odour profile, volatile compounds and vitamins

Changes in odour of Arauco (ARA) and Arbequina (ARB) extra-virgin olive oil (OO) were monitored during frying by electronic nose (EN) and solid-phase microextraction–gas chromatography methodologies. Degradation of α- and γ-tocopherols was monitored by HPLC. Electronic nose data and volatile compounds were analysed at intervals of 15 min ( t ₁₅) during 60 min of frying ( t ₆₀). α- and γ-tocopherols were determined at intervals of 5 min ( t ₅) during 30 min of frying ( t ₃₀). Principal components analysis applied to EN data showed one component, PC₁ which accounted 96.6% of the total odour variation. SnO₂ sensors had a positive correlation with PC₁. ARA variety corresponding to frying t ₆₀ had the highest positive correlation with PC_1. Analysis of variance results for volatile compounds showed an increase on production for: 3-methyl butanal, n -pentanal, n -hexanal, n -heptanal and n -nonanal at 15 min of frying for ARB OO and at 30 min for ARA OO. α-tocopherol and γ-tocopherol showed an important decrease after the first 5 min of frying for ARB OO and at 15 min for ARA OO.     

STUDY OF SAGO STARCH (METROXYLON SAGU) GELATINIZATION BY DIFFERENTIAL SCANNING CALORIMETRY

Differential scanning calorimetry (DSC), at various heating rates (1–30C/min) and water:starch ratios (0.1:1–4:1), was used to study gelatinization phenomena of sago starch. The results showed that the gelatinization temperature and enthalpy (Δ H) of starches in excess water were 60–77C and 15.5–15.8 J/g, respectively. Δ H of gelatinization remained substantially the same at excess water contents, but decreased significantly beyond a water:starch ratio of 1.3:1. A single endothermic transition (G) that transformed into a double endotherm (G and M₁) and only M₁ occurred, respectively, at excess, intermediate and limited water contents. At 50% water content, evidence of the M₁ endotherm was observed, and 85C represented the effective conclusion temperature (T_m) at the end of melting for sago starch. The experimental data were treated thermody-namically by applying an equation describing phase transitions of semi-crystalline polymers. The calculated value for the melting point of the undiluted polymer (T_m) was 432 K (R²= 0.96).     

The Contribution of Water to the Specific Heat Change at the Glass-to-Rubber Transition of the Ternary System BSA-Water-NaCl

ABSTRACT: We studied the glass-to-rubber transition of a BSA-water-NaCl system using DSC. The T_g was 178–187 K and decreased with increasing NaCl content from 1:9 to 6:4 NaCl:BSA. The specific heat change (ΔC_p*, J/((g BSA)K)) at T_g increased as the weight ratio increased from 1:9 to 5:5 NaCl:BSA, as did the change in calculated unfrozen water (UFW). The UFW was also correlated with the amount of NaCl in the glassy region with a correlation coefficient of approx. 6 (mol H₂O)/ (mol NaCl), which is comparable to the hydration number of Na⁺. These results suggest that UFW could contribute to the ΔC at T_g of the BSA-water system.     

Aflatoxin levels in dried figs, nuts and paprika for export from Turkey

Three hundred and thirteen of 2643 dried fig, two of eighty hazelnut, sixteen of twenty-eight pistachio, five of ten peanut and nineteen of twenty-three paprika samples for export from Turkey were contaminated with total aflatoxins in the range of 0.2–162.76, 5.46–6.55, 2.31–63.11, 0.75–26.36 and 1.79–6.55 μg kg⁻¹, respectively. Samples were collected from January to August 2007 and tested for aflatoxins (B₁, B₂, G₁ and G₂) by immunoaffinity column extraction using RP-HPLC. Fifty-six of the 313 dried fig, all of the contaminated hazelnut and pistachio, two of the sixteen peanut and three of the nineteen paprika samples exceeded the regulatory limits of the European Union. The ratio of the different types of aflatoxin present in each sample exhibited great variability. For example, of 313 contaminated fig samples, 159 contained only aflatoxin B₁, eighty-five contained B₁ (49.7%) + G₁ (50.3%), twenty-two contained only G₁, twenty contained B₁ (89.4%) + B₂ (10.6%), thirteen contained B₁ (73.7%) + B₂ (10.8%) + G₁ (15.5%) and fourteen contained all four types, B₁ (26%) + B₂ (2.5%) + G₁ (66.5%) + G₂ (5%).