Age Of Cheese Research Articles

Survey For Detection and Determination of Aflatoxins M1 and B1 in local Milk and Certain Dairy Products by Thin Layer Chromatographic Method.

90 different type of milk samples, 10 Yogurt Samples, 110 different type of cheese samples and 10 ice cream samples were collected randomly from Giza Governorate during the summer of 1998 – 1999, for detection and determination of Aflatoxins M1& B1 by using thin layer chromatographic method. Results revealed that the average range of Aflatoxin M1 in milk samples amounted from 0.144 to 0.378 ng/ml. About 20 % of cows and buffaloes milk samples contained form 0.378 to 0.342 ng/ml of AFM1, whereas about 10% of other milk samples were contaminated with 0.162, 0.288, 0.324, 0.234, 0.144 and 0.162 ng/ml for skim , Pasteurized , sterilized, UHT, powder, and baby milk, in the same order. Concentrations of AFM1 detected in cheese samples, furthermore, varied due to the type and age of cheese being examined. 20% of cheese samples were contaminated with AFM1 being 5.1, 3.2, 2.99, 2.099, and 2.34 ng/gm for fresh Domiati, aged Domiati, Processed and Karish cheese, respectively, whereas, 30% of the other types of cheese contained 5.88, 6.3 and 3.4 ng/gm for Roquefort, fresh Romi, and Cheddar cheese, respectively. The lowest concentration of AFM1, of 0.116 ng/gm was detected, however, in 10% of yogurt samples. Meanwhile, 20% of ice cream samples were found to be contaminated with 2.7 ng/ml, and 10% of Feta cheese samples contained 3.3 ng/gm. It could also be appeared from results that both of cream and spread cheese were found completely free from this Aflatoxin, the lowest content of Aflatoxin detected in all of the above examined samples was 0.116, 0.162, 0.162 and 0.216 (ppb) in yogurt, skim, baby milk and cream, respectively. On the other hand, results also indicated that all milk samples were free from Aflatoxin B1 except one sample of skim milk (out of 10) which gave positive result.

Impact of Milk Preacidification with CO2 on Cheddar Cheese Composition and Yield

Preacidification of milk for cheese making may have a beneficial impact on increasing proteolysis during cheese aging. Unlike other acids, CO2 can easily be removed from whey. The objectives of this work were to determine the effect of milk preacidification on Cheddar cheese composition, the recovery of individual milk components, and yield. Carbon dioxide was injected inline after the cooling section of the pasteurizer. Cheeses with and without added CO2 were made simultaneously from the same batch of milk. This procedure was replicated 3 times. Carbon dioxide in the cheese milk was about 1600ppm, which resulted in a milk pH of about 5.9 at 31°C. The starter culture and coagulant addition rates were the same for both the CO2 treatment and the control. The whey pH at draining of the CO2 treatment was lower than the control. Total make time was shorter for the CO2 treatment compared with the control. Cheese manufactured from milk acidified with CO2 retained less of the total calcium and fat than the control cheese. The higher fat loss was primarily in the whey at draining. Preacidification with CO2 did not alter the crude protein recovery in the cheese. The CO2 treatment resulted in a higher added salt recovery in the cheese and produced a cheese that contained too much salt. Considering the higher added salt retention, the salt application rate could be lowered to achieve a typical cheese salt content. Cheese yield efficiency of the CO2 treated milk was 4.4% lower than the control due to fat loss. Future work will focus on modifying the make procedure to achieve a normal fat loss into the whey when CO2 is added to milk.

Impact of Milk Preacidification with CO2 on the Aging and Proteolysis of Cheddar Cheese

To determine the influence of milk preacidification with CO2 on Cheddar cheese aging and proteolysis, cheese was manufactured from milk with and without added CO2. The experiment was replicated 3 times. Carbon dioxide (approximately 1600ppm) was added to the cold milk, resulting in a milk pH of 5.9 at 31°C in the cheese vat. The starter and coagulant usage rates were equal for the control and CO2 treatment cheeses. The calcium content of the CO2 treatment cheese was lower, but no difference in moisture content was detected. The higher CO2 content of the treatment cheeses (337 vs. 124ppm) was maintained throughout 6 mo of aging. In spite of having almost one and a half times the salt-in-moisture, proteolysis as measured by pH 4.6 and 12% trichloroacetic acid soluble nitrogen expressed as percentages of total nitrogen, was higher in the CO2 treatment cheeses throughout aging. The ratio of αs-casein (CN) to para-κ-CN decreased faster in the CO2 treatment cheeses than in the control cheeses, especially before refrigerated storage. No difference was detected in the ratio of β-CN to para-κ-CN between the control and CO2 treatment cheeses. Intact αs- and β-CN were found in the expressible serum (ES) from the CO2 treatment cheese as well as αs1-I-CN, but they were not detected in the ES from the control cheese. No CN was detected in the ES from the curd before the salting of either the control or CO2 treatment cheese. Higher proteolysis in the cheese made from milk preacidified with CO2 may have been due to increased substrate availability in the water phase or increased chymosin activity or retention in the cheese.

Chemometric Analysis of Proteolysis During Ripening of Ragusano Cheese

Chemometric modeling of peptide and free amino acid data was used to study proteolysis in Protected Denomination of Origin Ragusano cheese. Twelve cheeses ripened 3 to 7 mo were selected from local farmers and were analyzed in 4 layers: rind, external, middle, and internal. Proteolysis was significantly affected by cheese layer and age. Significant increases in nitrogen soluble in pH 4.6 acetate buffer and 12% trichloroacetic acid were found from rind to core and throughout ripening. Patterns of proteolysis by urea-PAGE showed that rind-to-core and age-related gradients of moisture and salt contents influenced coagulant and plasmin activities, as reflected in varying rates of hydrolysis of the caseins. Analysis of significant intercorrelations among chemical parameters revealed that moisture, more than salt content, had the largest single influence on rates of proteolysis. Lower levels of 70% ethanol-insoluble peptides coupled to higher levels of 70% ethanol-soluble peptides were found by reversed phase-HPLC in the innermost cheese layers and as the cheeses aged. Non-significant increases of individual free amino acids were found with cheese age and layer. Total free amino acids ranged from 14.3 mg/g (6.2% of total protein) at 3 mo to 22.0 mg/g (8.4% of total protein) after 7 mo. Glutamic acid had the largest concentration in all samples at each time and, jointly with lysine and leucine, accounted for 48% of total free amino acids. Principal components analysis and hierarchical cluster analysis of the data from reversed phase-HPLC chromatograms and free amino acids analysis showed that the peptide profiles were more useful in differentiating Ragusano cheese by age and farm origin than the amino acid data. Combining free amino acid and peptide data resulted in the best partial least squares regression model (R2 = 0.976; Q2 = 0.952) predicting cheese age, even though the peptide data alone led to a similarly precise prediction (R2 = 0.961; Q2 = 0.923). The most important predictors of age were soluble and insoluble peptides with medium hydrophobicity. The combined peptide data set also resulted in a 100% correct classification by partial least squares discriminant analysis of cheeses according to age and farm origin. Hydrophobic peptides were again discriminatory for distinguishing among sample classes in both cases.

Use of dyed solutions to visualize different aspects of vacuum impregnation of Minas cheese

The process of salting Minas cheese (a Brazilian cheese) was studied using salt solutions dyed with methylene blue, in order to visualize different aspects of the salting. Vacuum impregnation experiments were carried out in a hermetic chamber, where cheese samples were immersed in the salt solutions, after the manufacturing pressing stage, under absolute pressure ranging from 16 to 21.3kPa. Impregnation experiments were carried out under continuous and intermittent vacuum conditions. After 1, 2 or 3h, the chamber was opened, the impregnated cheese was withdrawn and cut, and the sections were analysed with respect to salt concentration and photographed. The pictures indicated that solute impregnation increased with the vacuum intensity and with the impregnation time. Solute penetration decreased with the force applied during the pressing step and as the cheese aged. These results could be associated with the decrease in the average size and number of the interconnected pores. The experiments showed that intermittent vacuum salting promoted a greater cheese impregnation, which can be explained by the action of deformation–relaxation mechanisms. Despite their qualitative nature, dyed solutions can be useful to study impregnation of porous foods. The experimental results for salt concentration showed that vacuum salting of Minas cheese is a simple and effective procedure for obtaining products with more homogeneous salt concentration.

Reduced-fat cheddar cheese manufactured using a novel fat removal process.

Normally, reduced-fat Cheddar cheese is made by removal of fat from milk prior to cheese making. Typical aged flavor may not develop when 50% reduced-fat Cheddar cheese is produced by this approach. Moreover, the texture of the reduced-fat cheeses produced by the current method may often be hard and rubbery. Previous researchers have demonstrated that aged Cheddar cheese flavor intensity resides in the water-soluble fraction. Therefore, we investigated the feasibility of fat removal after the aging of Cheddar cheese. We hypothesized the typical aged cheese flavor would remain with the cheese following fat removal. A physical process for the removal of fat from full-fat aged Cheddar cheese was developed. The efficiency of fat removal at various temperatures, gravitational forces, and for various durations of applied forces was determined. Temperature had the greatest effect on the removal of fat. Gravitational force and the duration of applied force were less important at higher temperatures. A positive linear relationship between temperature and fat removal was observed from 20 to 33 degrees C. Conditions of 30 degrees C and 23,500 x g for 5 min removed 50% of the fat. The removed fat had some aroma but little or no taste. The fatty acid composition, triglyceride molecular weight distribution, and melting profile of the fat retained in the reduced-fat cheeses were all consistent with a slight increase in the proportion of saturated fat relative to the full-fat cheeses. The process of fat removal decreased the grams of saturated fat per serving of cheese from 6.30 to 3.11 g. The flavor intensity of the reduced-fat cheeses were at least as intense as the full-fat cheeses.

Probing protein hydration and aging of food materials by the magnetic field dependence of proton spin-lattice relaxation times

Most cheeses can be considered as solid emulsions of milk fat in a matrix of water and proteins. Regions of each of the phases can be liquid during processing and maturation. Identifying these regions and monitoring changes in them is important as a prelude to controlling the structure of the final cheese. We concentrate on the behavior of water in the vicinity of proteins as a function of cheese aging. Our method utilizes nuclear magnetic relaxation dispersion (NMRD) associated with the frequency dependence of water spin-lattice relaxation rates using the field cycling NMR technique. This method provides insight into the dynamical behavior of water molecules on a very large time scale. Moreover, we can distinguish between molecular motion in bulk and motion in the vicinity of a source of relaxation, such as proteins. A fit of our dispersion data using a theory developed by J.-P. Korb and R.G. Bryant (J. Chem. Phys. 115 (2001) 23) allowed us to determine the degree of hydration of proteins as a function of aging. In particular, we find that protein hydration increases with ripening.

Effect of feeding treatments and lactation stages on composition and organoleptic quality of goat milk Domiati cheese

To investigate the effect of pasture feeding with different levels of concentrate on the milk composition and quality of Domiati cheese, a total of 20 lactating Alpine goats were randomly allocated into four groups. Group A was confined and fed alfalfa hay with 0.66 kg per day of concentrate mixture per 1.5 kg of milk (conventional confinement system with feeding). Groups B, C, and D were rotationally grazed and received 0.66, 0.33, and 0 kg per day of concentrate, respectively. Milk from each group was processed into Domiati cheese twice monthly for a 6-month lactation period. Cheeses were sampled fresh and at 1 and 2 months of pickling in whey. Results of the present study indicate that feeding systems of dairy goats with different levels of concentrate supplementation did not affect the composition (fat, protein and total solids) of Domiati cheese. The pasture-grazing without concentrate supplementation (group D) resulted in a lower short-chain fatty acids content and a higher flavor score of Domiati cheese than the confined feeding system (group A). Cheese age during pickling did not change flavor score but increased the total sensory score due to a smoother, creamier body and texture of cheese. As lactation advanced, the contents of total, short- and long-chain fatty acids and the sensory scores of the cheese fluctuated markedly. Further research is needed to investigate the effect of fatty acids in diets on the profile of fatty acids in goat milk and cheese, and to correlate the individual fatty acids in diet, milk and cheese to establish the sensory quality of goat cheese.

Impact of Low Concentration Factor Microfiltration on the Composition and Aging of Cheddar Cheese

The effect of microfiltration (MF) on proteolysis, hardness, and flavor of Cheddar cheese during 6 mo of aging was determined. Raw skim milk was microfiltered twofold in two cheese making trials. In trial 1, four vats of cheese were made in 1 d using unconcentrated milk (1X), 1.26X, 1.51X, and 1.82X concentration factors (CF). Casein-(CN)-to-fat ratio was constant among treatments. Proteolysis during cheese aging decreased with increasing CF due to either limitation of substrate availability for chymosin due to low moisture in the nonfat substance (MNFS), inhibition of chymosin activity by high molecular weight milk serum proteins, such as α2-macroglobulin, retained in the cheese or low residual chymosin in the cheese. Hardness of fresh cheese increased, and cheese flavor intensity decreased with increasing CF. In trial 2, the 1X and 1.8X CF were compared directly. Changes made in the cheese making procedure for the 1.8X CF (more chymosin and less cooking) increased the MNFS and made proteolysis during aging more comparable for the 1X and 1.8X cheeses. The significant difference in cheese hardness due to CF in trial 1 was eliminated in trial 2. In a triangle test, panelists could not differentiate between the 1X and 1.8X cheeses. Therefore, increasing chymosin and making the composition of the two cheeses more similar allowed production of aged Cheddar cheese from milk concentrated up to 1.8X by MF that was not perceived as different from aged Cheddar cheese produced without MF.

STRESS RELAXATION CHARACTERISTICS OF CHEDDAR CHEESE

Stress relaxation experiments were conducted by heating a cheese sample (22 mm diameter and 17.5 mm height) at 40, 50 and 60°C in an aluminum cup whose inner diameter and depth were 22 mm and 17.5 mm, respectively. A plunger of 18 mm diameter, which was attached to an Instron type machine, was allowed to compress the cheese instantaneously to 10% deformation. The relaxation of stress was recorded as a function of time. Cheddar cheeses with four different fat content (15.3, 22.8, 37.3 and 45.6% fat dry matter – FDM) and two different moisture content (58.1 and 62.4% moisture in non fat portion – MNFP) at 2, 4, 12 and 24 weeks were used in this study. Generalized Maxwell and empirical Peleg models were used to characterize the stress relaxation behavior of melted cheese. The effect of fat content, moisture content, and age of cheese on stress relaxation behavior was studied. Peleg model well described the stress relaxation behavior of melted cheese (cheeses above 50°C) and eight element Maxwell model predicted better than three element Maxwell and six element Maxwell models. The stress relaxation experiment differentiated the viscoelastic nature of different cheeses due to reduction of fat content, increase in moisture, increase in melting temperature and age of cheese. Stress relaxation test can be used as a tool to systematically study cheese functionality.

THERMAL PROPERTIES OF CHEDDAR CHEESE: EXPERIMENTAL AND MODELING

Thermal properties (thermal conductivity, thermal diffusivity and heat capacity) of Cheddar cheese were measured as a function of cheese age and composition. The composition ranged from 30–60% moisture, 8–37% fat, and 22–36% protein (wet basis). The thermal conductivity and heat capacity ranged from 0.354–0.481 W/m °C and from 2.444–3.096 kJ/kg °C. Both thermal conductivity and heat capacity increased with moisture and protein content and decreased with fat content. The thermal diffusivity ranged from 1.07×10−7 − 1.53 × 10−7 m2/s. There was no significant relationship between thermal diffusivity and moisture, fat and protein content of cheese. No statistically significant effect (at the 10% level) of age (0 to 28 wk) on thermal properties was observed. Models predicting thermal properties as a function of cheese composition were developed and their predictive ability was compared with that of empirical models available in the literature. In addition, several theoretical thermal conductivity models were evaluated for their usefulness with Cheddar cheese. Published thermal conductivity models cannot accurately predict (mean error was from 3.4 to 42%) the thermal conductivity of Cheddar cheese.

Accumulation of Free L-Glutamic Acid in Full- and Reduced-fat Cheddar Cheese Ripened at Different Time/temperature Conditions

Influence of ripening conditions on accumulation of free L-glutamic acid (FGA) in full (FF)- and reduced-fat (RF) Cheddar cheese was investigated. Cheeses were ripened isothermally at 5 and 8°C for 6 months; aged at 5 and 8°C for 1 and 2 months and then at 8 and 5°C, respectively, for 5 and 4 months, respectively; or aged for 1 and 2 months at the latter temperatures and then again at 5 or 8°C for 4 and 3 months, respectively. In all cases, accumulation of FGA correlated well with accumulation of soluble nitrogen-containing fractions of cheese and, for isothermally aged cheeses, was linearly related to cheese age. Results suggested that level of FGA might be considered a ripening index in both FF and RF Cheddar. Level of FGA in cheese ripened at 8°C was significantly higher than that in cheese ripened at 5°C and, at a given aging conditions, level of FGA in FF cheese was significantly lower than that in RF cheeses. Increasing or decreasing aging temperature by 3°C at different cheese ages resulted in cheese-specific FGA levels that differed significantly from those obtained with cheeses ripened isothermally at 8°C or 5°C. Accumulation of FGA was influenced by effects of aging conditions and cheese composition on cheese-age-specific proteolytic activities in cheese. Results suggested that small changes in aging temperature, at desired stages during aging, may offer opportunities in controlling and modulating rate and extent of proteolytic activities during cheese aging and thus provide tools to better modulate the development of cheese quality attributes.

Proteolysis and Lipolysis of Goat Milk Cheese

Numerous varieties of goat milk cheeses are produced worldwide. Maturation or ripening of goat and other species milk cheeses is governed by interplay of many different factors. Proteolysis and lipolysis are two major biochemical processes in the multifaceted phenomenon of cheese aging, which involves a variety of chemical, physical, and microbiological changes under controlled environmental conditions. Proteolysis of cheeses in general is influenced by several factors including plasmin, chymosin, protease from starter and nonstarter bacteria, pH and moisture levels of the curds, storage temperature and time, salt content, salt-to-moisture ratio, and humidity. Primary factors affecting lipolysis in cheeses are fatty acid composition, lipolytic enzymes, lipolytic microorganisms, moisture, temperature, storage time, oxygen, and surface area, etc. Several analytical techniques have been used to measure proteolysis of goat and (or) cow milk cheeses during ripening, such as solubility of peptides and amino acids in various solvents or precipitants, liberation of reactive functional groups, various forms of chromatography, and different forms of electrophoresis. Lipolysis of goat milk cheeses has been estimated by acid degree value (ADV), acid value, and free fatty acid concentration, while lipid oxidation of dairy goat products can be determined by peroxide value, thiobarbuturic acid value (TBA). Recent reports have shown that goat cheeses had greater rates of protein degradation than cow counterparts, and that aging time and temperature synergistically elevated most of proteolytic and lipolytic indices in goat cheeses. This paper will further discuss proteolytic and lipolytic characteristics of goat milk cheeses.

Proteolysis in reduced sodium Kefalograviera cheese made by partial replacement of NaCl with KCl

Abstract Kefalograviera cheeses (five trials) of different sodium content were made from split lots of curd by varying the salting processes, i.e. brine — and dry — salting, with NaCl (control) or a mixture of NaCl/KCl (3:1 or 1:1, w/w basis). The extent and characteristics of proteolysis in the cheeses were monitored during aging by Kjeldahl determination of soluble nitrogen fractions (water-soluble nitrogen [WSN], trichloroacetic acid [TCA]-SN, phosphotungstic acid [PTA]-SN), the cadmium-ninhydrin method for the determination of total free amino acids (FAA), urea-polyacrylamide gel electrophoresis of cheese proteins, followed by densitometric analysis of the αs1- and β-casein fractions, reverse-phase high-performance liquid chromatography (HPLC) analysis of the water-soluble extracts of cheeses, and ion-exchange HPLC analysis of FAA. The results showed that proteolysis was similar in control and experimental cheeses at all sampling ages, indicating that the partial substitution of NaCl by KCl in the manufacture of Kefalograviera cheese did not significantly influence the extent and characteristics of proteolysis during cheese aging.

Lipolysis in reduced sodium Kefalograviera cheese made by partial replacement of NaCl with KCl

Abstract Kefalograviera cheeses (five trials) of different sodium content were made from split lots of curd by varying the salting processes, i.e. brine — and dry — salting, with NaCl (control) or a mixture of NaCl/KCl (3:1 or 1:1, w/w basis). The extent and characteristics of proteolysis in the cheeses were monitored during aging by Kjeldahl determination of soluble nitrogen fractions (water-soluble nitrogen [WSN], trichloroacetic acid [TCA]-SN, phosphotungstic acid [PTA]-SN), the cadmium-ninhydrin method for the determination of total free amino acids (FAA), urea-polyacrylamide gel electrophoresis of cheese proteins, followed by densitometric analysis of the αs1- and β-casein fractions, reverse-phase high-performance liquid chromatography (HPLC) analysis of the water-soluble extracts of cheeses, and ion-exchange HPLC analysis of FAA. The results showed that proteolysis was similar in control and experimental cheeses at all sampling ages, indicating that the partial substitution of NaCl by KCl in the manufacture of Kefalograviera cheese did not significantly influence the extent and characteristics of proteolysis during cheese aging.

Formation of Biogenic Amines in Raw Milk Hispánico Cheese Manufactured with Proteinases and Different Levels of Starter Culture

Two proteinases, a neutral proteinase from Bacillus subtilis and a cysteine proteinase from Micrococcus sp., were used to accelerate the ripening process of raw cow's milk Hispánico cheese, a semihard variety. Two levels (0.1% and 1%) of a commercial starter culture containing Lactococcus lactis subsp. lactis and L. lactis subsp. cremoris were added for cheese manufacture. The influence of both factors, proteinase addition and level of starter culture, on the growth of amino acid–decarboxylating microorganisms and on the formation of biogenic amines during cheese ripening was investigated in duplicate experiments. The population of tyrosine decarboxylase–positive bacteria, which represented less than 1% of the total bacterial population in most cheese samples, and tyrosine decarboxylase–positive lactobacilli was not influenced by proteinase addition or level of starter culture. Tyramine was detected in all batches of cheese from day 30. Its concentration was significantly (P < 0.05) influenced by proteinase addition but not by the level of starter culture and increased with cheese age. After 90 days of ripening, 103 to 191 mg/kg of tyramine was found in the different cheese batches. Histamine was not detected until day 60 in cheese with neutral proteinase and 1% starter culture and until day 90 in the rest of the cheeses. The concentration of this amine did not exceed 20 mg/kg in any of the batches investigated. Phenylethylamine and tryptamine were not found in any of the samples.

Immunochemical evaluation of bovine beta-casein and its 1-28 phosphopeptide in cheese during ripening.

Polyclonal antibodies raised against the plasmin-released 1-28 phosphopeptide from bovine beta-casein [i.e., beta-CN(f1-28)4P] specifically recognized the tryptic beta-casein 1-25 and 2-25 peptides, whatever the degree of phosphorylation, but were unresponsive to the shortened beta-casein 16-22 phosphopeptide. These antibodies were able to recognize the parent bovine beta-casein as well as the homologous water buffalo protein, but they could not detect the homologous counterparts from ovine and caprine milks. Such antibodies were used in competitive enzyme-linked immunosorbent assays to monitor the plasmin-mediated release of the 1-28 phosphopeptide from beta-casein and to evaluate the residual native beta-casein in bovine cheese sampled during ripening. Applications of these polyclonal antibodies are suggested mainly for estimating the age of hard cheeses and, possibly, for tracing the presence of bovine casein in fresh ovine and caprine cheeses.

The effect of exposure to pressure of 50 MPa on Cheddar cheese ripening

The possibility of acceleration of commercial Cheddar cheese ripening by exposure to a high pressure (HP) treatment of 50 MPa for 3 days at 25°C at different stages of ripening was investigated. Proteolysis was examined in the treated and untreated cheeses by measurement of pH 4.6 water soluble nitrogen, expressed as g/100 g total N (pH 4.6 SN/TN), urea-PAGE, reverse phase (RP) HPLC, analysis of molecular mass distribution by gel permeation and measurement of free amino acids (FAA) in the pH 4.6 SN. There was an immediate increase in pH 4.6 SN/TN and FAA in cheese HP-treated at 2 days of age, although this effect decreased with cheese age. Urea-PAGE analysis of cheese samples indicated that HP treatment accelerated degradation of α s1-casein and accumulation of α s1-I-casein (f 24-199). RP-HPLC profiles indicated quantitative but not qualitative differences between treated and non-treated samples. Confocal laser scanning microscopy did not indicate any gross structural changes in the cheese matrix as a result of exposure to 50 MPa for 3 days at 25°C. It was concluded that the enhancement of proteolysis observed may be attributed to a combination of the temperature and pressure used in the treatment.

Influence of ripening temperature on the volatiles profile and flavour of Cheddar cheese made from raw or pasteurised milk

Cheddar cheeses were made from raw (R1, R8) or pasteurised (P1, P8) milk and ripened at 1°C (P1, R1) or 8°C (P8, R8). Volatile compounds were extracted from 6 month-old cheeses and analysed, identified and quantified by gas chromatography-mass-spectrometry. A detailed sensory analysis of the cheeses was performed after 4 and 6 months of ripening. The R8 cheeses had the highest and P1 the lowest concentrations of most of the volatile compounds quantified (fatty acids, ketones, aldehydes, esters, alcohols, lactones and methional). The R8 and P8 cheeses contained higher levels of most of the volatiles than R1 and P1 cheeses. Ripening temperature and type of milk influenced most of the flavour and aroma attributes. Principal component analysis (PCA) of aroma and flavour attributes showed that P1 and R1 had similar aroma and flavour profiles, while R8 had the highest aroma and flavour intensities, highest acid aroma and sour flavour. The age of cheeses influenced the perception of creamy/milky and pungent aromas. PCA of the texture attributes separated cheeses on the basis of ripening temperature. The R8 and P8 cheeses received significantly higher scores for perceived maturity than P1 and R1 cheeses. The P1 and R1 cheeses had similar values for perceived maturity. In a related study, it was found that concentrations of amino acids and fatty acids were similar in R1 and P1 during most of the ripening period, and R1 and P1 cheeses had low numbers of non-starter lactic acid bacteria (NSLAB). The panel found that ripening temperature, type of milk and age of cheeses did not influence the acceptability of cheese. It is concluded that NSLAB contribute to the formation of volatile compounds and affect the aroma and flavour profiles and the perceived maturity of Cheddar cheese.

Proteolysis in reduced sodium Feta cheese made by partial substitution of NaCl by KCl

Abstract Feta cheeses (five trials) of different sodium content were made, using ewes’ milk, from split lots of curd by varying the salting procedure, i.e. dry salting with NaCl (control) or mixtures of NaCl/KCl (3:1 or 1:1, w/w basis) and filling the cans with brine made with NaCl or the above NaCl/KCl mixtures, respectively, in order to study the influence of the partial substitution of NaCl by KCl on the proteolysis during cheese ripening. The extent and characteristics of proteolysis in the cheeses were monitored during aging by using Kjeldahl determination of soluble nitrogen fractions (water-soluble nitrogen, trichloroacetic acid-soluble nitrogen, phosphotungstic acid-soluble nitrogen), the cadmium–ninhydrin method for the determination of total free amino acids (FAA), urea–polyacrylamide gel electrophoresis of cheese proteins followed by densitometric analysis of the α s1 - and β -casein fractions, reverse-phase HPLC analysis of the water-soluble extracts of cheeses, and ion-exchange HPLC analysis of FAA. The results showed that proteolysis was similar in control and experimental cheeses at all sampling ages, indicating that the partial substitution of NaCl by KCl in the manufacture of Feta cheese had no significant effect on the extent and characteristics of proteolysis during cheese aging.