Improving the quality of Ras-type cheese made from recombined milk containing high levels of total solids

Ras type cheese was made from recombined milk (RM) containing normal (12·5%) or high levels of Total Solids (TS) (25%, 32% or 40%) using fresh or recombined cream. Cheese curds obtained from RM containing high TS levels were moulded directly or after washing with warm water (50°C) for 10 min before moulding. The cheeses were matured at 7°C or 15°C. Cheese made from fresh milk was better in flavour and consistency than any of the cheeses made from RM. Use of RM in which fresh cream was used gave cheeses of better quality than those made from RM containing recombined cream. Washing the curd made from all RMs resulted in cheeses with better flavour and body characteristics than those made from unwashed curd. Cheese made from RM containing 25% TS with or without washing of the curds was of better quality than those made from RM containing 32% or 40% TS.The changes of nitrogenous fractions, degradation of α_sI- and β-caseins, accumulation of free amino acids and the formation of free fatty acids were reduced as the level of TS in RM was increased. All cheeses made from washed RM curd showed greater proteolysis and lipolysis compared with those made from unwashed curd. Storage of RM cheese at 15°C accelerated its ripening and improved cheese quality compared with ripening at 7°C.     

Sterigmatocystin: Incidence,fate and production by Aspergillus versicolor in Ras cheese

The occurrence, distribution, and stability of sterigmatocystin (STG) in Ras cheese were investigated. An incidence value for STG in market samples of Ras cheese was 35% with a mean value of 22.2 μg/kg. In experimental Ras cheese from milk contaminated with STG, 80% of the toxin was retained in the curd while 20% was found in the whey. The temperature for cheese ripening affected the toxin content. At 6 °C the toxin concentration was hardly affected, but at 20 °C the concentration was reduced by 16% after 90 days. In Ras cheese contaminated with spores of Aspergillus versicolor, toxin production started after 45 days of the ripening, reached a maximum after 90 days, and declined thereafter. Cow's milk favoured toxin formation in comparison with buffaloe's milk. Aged cheese (more than 6 months) inhibited toxin production.     

Microstructure and chemical changes in Twarog cheese made from ultrafiltrated milk and from lactose-hydrolysed milk

Twarog cheese was manufactured from fresh milk, lactose-hydrolysed milk and retentate. Microstructure, chemical composition, protein breakdown, amino acid distribution and organoleptic properties were studied during ripening.Inoculation of the milk with β-galactosidase, before cheese processing, reduced the clotting time, enhanced the protein breakdown and enhanced amino acid accumulation during ripening. Concentrating the milk, by ultrafiltration, prolonged the coagulation time and resulted in a cheese with greater amounts of moisture, fat, total nitrogen and higher pH than other cheeses.Essential free amino acids are considered to constitute more than half of the total free amino acids of Twarog cheese and glutamic acid, leucine and phenylalanine are the major free amino acids in the ripened cheese.Quality of the cheese was improved either by ultrafiltration or by lactose hydrolysis and the acceptable flavour was more pronounced in β-galactosidase-treated cheese.Microstructure of the protein in young cheeses does not differ in all treatments. The disintegration and fusion of casein advanced during ripening in the outer protein matrix more than internally. The appearance of the cheese matrix was similar in both control and ultrafiltrated cheeses while the casein in β-galactosidase-treated cheese fused faster than in other treatments.     

Proteolysis in goat cheese made from raw,pasteurized or pressure-treated milk

Primary and secondary proteolysis of goat cheese made from raw (RA), pasteurized (PA; 72 °C, 15 s) and pressure-treated milk (PR; 500 MPa, 15 min, 20 °C) were examined by capillary electrophoresis, nitrogen fractionation and HPLC peptide profiles. PA milk cheese showed a more important hydrolysis (P<0.05) of α_s1-casein than RA milk cheese at the first stages of ripening (15 days), while PR milk cheese had a level between those seen in PA and RA milk cheeses. Degradation of β-casein was more important (P<0.05) in PA and PR than in RA milk cheeses at 15 days of ripening. However, from thereon β-casein in PR and RA milk cheeses was hydrolyzed at essentially similar rates, but at lower rates (P<0.05) than in PA milk cheeses. Pressure treatment could induce proteolysis of β-casein in a way, which is different from that produced by heat treatment. There was an increase in 4.6-soluble nitrogen (WSN) and in trichloroacetic acid (TCASN) throughout ripening in cheeses, but higher contents (P<0.05) in PA and PR milk cheeses at the end of ripening were observed. PR milk cheeses contained considerably higher content (P<0.05) of free amino acids than RA or PA milk cheeses. In general, heat and pressure treatments had no significant effect on the levels of hydrophobic and hydrophilic peptides.     

Utilization of freeze-shocked lactobacilli for enhancing flavour development of Ras cheese

Freeze-shocked cultures of Lactobacillus helveticus or Lactobacillus casei were added at levels of 1% and 2% to Ras cheese milk prior to renneting as an adjunct starter to enhance flavour development of cheese. These additives did not affect the gross chemical composition of the cheeses but increased the formation of soluble nitrogenous compounds, free volatile fatty acids, the flavour intensity and improved the body characteristic. Also, the counts of bacterial groups (total, proteolytic and lipolytic) of the cheese treated with freeze-shocked lactobacilli were higher than in the control. Moreover, the ripening period was reduced to be 2 months compared with 4 months required for the control cheese. Also, using freeze-shocked culture of L. helveticus was the most effective in this respect.     

Evolution of Free Amino Acids during the Ripening of Cheddar Cheese Containing Added Lactobacilli Strains

Cheddar cheese was produced with different lactobacilli strains added to accelerate ripening. The concentration of proteolytic products was determined as free amino acids in the water-soluble fraction at two, four, seven and nine months of aging and at two different maturation temperatures (6°C, 15°C). All amino acids increased during ripening and were higher in the Lactobacillus- added cheeses than in the control cheese, and higher in cheeses ripened at 15°C than at 6°C. Glutamic acid, leucine, phenylalanine, valine and lysine were generally in higher proportion in all cheeses. The cheeses with added L. casei-casei L2A were classified as having a “strong Cheddar cheese” flavor after only seven months of ripening at 6°C.     

Microbiological,chemical, textural and sensory characteristics of Hispánico cheese manufactured using frozen ovine milk curds scalded at different temperatures

Hispánico cheese is a semi-hard variety, manufactured in Spain from a mixture of pasteurized bovine and ovine milk. To study one strategy for overcoming a seasonal shortage of ovine milk in summer and autumn, curds made from ovine milk, scalded at 32, 35 or 38 °C, were pressed for 30 min and frozen at ?24 °C for 4 months. After thawing, they were added to fresh bovine milk curd for the manufacture of experimental Hispánico cheeses. Control cheese was made from a mixture of pasteurized bovine and ovine milk in the same (80:20) proportion. No significant effect of the addition of frozen ovine milk curd or scalding temperature was found for lactic acid bacteria counts, dry matter content, hydrophilic and hydrophobic peptides, 45 out of 65 volatile compounds, texture, and sensory characteristics throughout a 60-day ripening period. Differences between cheeses, of low magnitude and little practical significance, were found for pH value, aminopeptidase activity, proteolysis, free amino acids, free fatty acids, and the remaining 20 volatile compounds. Thus, the addition of frozen ovine milk curd to fresh bovine milk curd does not alter the main physicochemical and sensory characteristics of Hispánico cheese.     

Ripening changes of Ras cheese made from recombined milk as affected by certain additives

An attempt has been made to accelerate the ripening of Ras cheese made from recombined milk (RM). RM cheese was made from curd with either a mixture of Fromase 100 (fungal rennet) and Kapalase L (an animal lipase) at concentrations of 0·025 and 0·05% or a slurry of fully ripened cheese at concentrations of 1 and 2%. These treatments enhanced flavour development, body characteristics, formation of soluble nitrogen compounds and free fatty acids. The proteinase/lipase mixture was the most effective. A rancid flavour and bitter taste were developed in 3–4-month-old RM cheese made with the higher concentration enzyme mixture.     

Immobilization of β-galactosidase by bioaffinity adsorption on concanavalin A layered calcium alginate–starch hybrid beads for the hydrolysis of lactose from whey/milk

Aspergillus oryzae β-galactosidase was immobilized on the surface of a novel bioaffinity support: concanavalin A layered calcium alginate–starch beads. The maximum activity of the immobilized β-galactosidase was obtained at 60 °C, approximately 10 degrees higher than that of the free enzyme. The immobilized β-galactosidase exhibited significantly higher stability to heat, urea, MgCl₂, and CaCl₂ than the free enzyme. An enhancement of the activity of immobilized β-galactosidase by up to 5.0% MgCl₂ was seen, whereas the activity of the free enzyme decreased above 3.0% MgCl₂. Immobilized β-galactosidase retained 61%, 50% and 43% activity in the presence of 5% CaCl₂, 5% galactose and 4 m urea, respectively, when incubated for 1 h at 37 °C. The immobilized β-galactosidase had a much higher K_iapp value than the free enzyme, which indicated less susceptibility to product inhibition by galactose. The immobilized β-galactosidase preparation was superior to the free enzyme in hydrolysing lactose in whey or milk in a batch process: it hydrolyzed 89% of the lactose in whey in 3 h and 79% of the lactose in milk in 4 h. The immobilized β-galactosidase retained 61% of its original activity after 2 months storage at 4 °C, while the soluble enzyme showed only 37% of the initial activity under identical conditions.     

Manufactore of Ras cheese from ultrafiltered milk supplemented with caseinates

Whole cow's milk was ultrafiltered (conc. Factor 5), sodium and calcium caseinate were added to the milk retentate at the rate of 0.5 and 0.75% (w/w) of the milk. Ras cheese was made from milk retentate supplemented with different levels of caseinate salts, as well as unsupplemented retentates, and compared with Ras cheese made by the traditional method. Retentate supplemented with 0.5% Na and Ca caseinate was suitable for Ras cheese-making with limited whey drainage, supplementation of retentate with 0.75% Ca caseinate gave defective cheese at the end of ripening, while Na caseinate increased soluble N and free fatty acids in the cheese. Organoleptic scoring showed that supplementation with Na caseinate enhanced cheese ripening.     

The effect of ripening and cooking temperatures on proteolysis and lipolysis in Manchego cheese

The influence of ripening temperature on proteolysis and lipolysis was studied on four lots of raw ewe's milk Manchego cheese held for 60 days at 5, 10, 15 or 20°C. Mean levels of pH 4·6, trichloroacetic acid and phosphotungstic acid soluble N in 20°C cheeses were 52%, 78% and 95% higher than the respective levels in 5°C cheeses at the end of the ripening period. Free fatty acids content after 60 days was 90% higher in 20°C cheeses than in 5°C cheeses. Significant effects of the cooking temperature of the curd (30, 36, 38 or 40°C) on pH, moisture and NaCl content were recorded, but levels of nitrogenous fractions or free fatty acids in 60-day cheeses were not affected.     

Effect of ripening temperature on the growth and significance of non-starter lactic acid bacteria in Cheddar cheese made from raw or pasteurised milk

Two cheese-making trials were conducted, each involving four cheeses, two made from raw milk (R1, R8) and two from pasteurised milk (P1, P8), and ripened at 1°C (R1, P1) or 8°C (R8, P8). The 1-day-old R1 and R8 cheese in trials 1 and 2 contained ∼10⁴ non-starter lactic acid bacteria (NSLAB) g⁻¹. In trial 1, no NSLAB were detected in 1-day-old P1 and P8 cheeses while those in trial 2 contained 10² cfu g⁻¹. In both trials, the maximum differences between the number of NSLAB in the cheeses ripened at 1 or 8°C were observed at 4 months, when the number of NSLAB in cheeses ripened at 8°C were 3 log cycles higher than in those ripened at 1°C. At the end of ripening (6-months), the number of NSLAB in P8 and R8 were ∼2 log cycles higher than in P1 and R1 cheeses, respectively. Primary proteolysis in the cheeses was markedly affected by ripening temperature, but not by pasteurisation of the cheese milk. Urea-polyacyrlamide gel electrophoretograms and reverse-phase (RP)-HPLC of the water-soluble fraction showed differences between cheeses made from raw or pasteurised milk and between cheeses ripened at 1 or 8°C. The concentration of amino acids and fatty acids were in the order R8>P8>R1>P1. Commercial graders awarded highest flavour scores to the R1 cheeses during gradings at 4, 5 and 6 months. A sensory panel found that most flavour and aroma attributes and maturity were in the order of R8>P8>R1=P1. The results of this study suggest that NSLAB play an important role in the development of flavour in Cheddar cheese by contributing to the production of amino acids and fatty acids.     

Using High-Pressure Processing for Reduction of Proteolysis and Prevention of Over-ripening of Raw Milk Cheese

High-pressure-processing (HPP) at 400 or 600 MPa was applied to cheeses made from ewe raw milk, on days 21 or 35 after manufacturing, to reduce proteolysis and prevent over-ripening. The characteristics of HPP and non-pressurized (control) cheeses were compared during ripening at 8 °C until day 60 and further storage at 4 °C until day 240. HPP and control cheeses showed similar pH values throughout ripening, but on day 240 pH values remained 0.4–0.6 units lower for HPP cheeses than for the control cheeses. Casein degradation was significantly retarded in the 600 MPa cheeses. Their α-casein concentration was 48–52 % higher on day 60 and 30–33 % higher on day 240 than in the control cheeses while β-casein concentration was 25–26 % higher on day 60 and 100–103 % higher on day 240. No significant differences in para-κ-casein concentration between cheeses were found on day 60, but on day 240, it was 22–35 % higher in the 600 MPa cheeses than in the control cheese. Hydrophilic peptides, hydrophobic peptides and total free amino acids evolved similarly in HPP and control cheeses during the 60-day ripening period. However, on day 240 hydrophilic peptides were at 34–39 % lower levels in the 600 MPa cheeses than in the control cheeses, hydrophobic peptides at 7–16 % lower levels and total free amino acids at 25–29 % lower levels. Flavour intensity scores increased at a slower rate in HPP cheeses than in the control cheese. Flavour quality declined markedly in the control cheeses during refrigerated storage while it did not vary significantly in 600 MPa cheeses.     

Effects of heating milk and accelerating ripening of low fat Ras cheese on biogenic amines and free amino acids development

Two experiments were conducted to study the effects of heating milk and, consequently, incorporation of whey proteins into cheese curd, fat content, accelerating cheese ripening by attenuated lactobacilli, species of bacteria and method of attenuation on formation of biogenic amines and liberation of free amino acids. Total biogenic amines and total free amino acids increased as ripening period progressed in all cheese treatments. Total biogenic amines and total free amino acids decreased as the fat content was decreased. Heating of 3% fat milk up to 70°C caused a significant (p<0.05) increase in total biogenic amines and total free amino acid concentrations, while raising the temperature of heat treatment up to 75 and 80°C decreased them. However, heating of 2% fat milk up to 75°C caused a definite (p<0.05) increase in total biogenic arnines and total free amino acids; conversely raising heat treatment temperature to 80°C decreased them. These results indicate that there is a positive correlation between total biogenic amines and total free amino acids; moisture and salt contents affected the formation of biogenic amines, while incorporation of whey proteins had no significant effect on biogenic amines development. In a second experiment, addition of attenuated lactobacilli as adjunct bacteria caused a pronounced (p<0.05) increase in free amino acids and biogenic amines. Addition of either freeze- or heat-shocked Lactobacillus helviticus was more effective in promoting the build-up of biogenic amines and free amino acids in the resultant cheeses than in cheeses made with addition of freeze- or heat-shocked Lactobacillus casei, respectively. There was a positive correlation between free amino acids and biogenic amine contents. The type of bacteria and prolongation of ripening period significantly affected the development of biogenic amines. Tyramine was the highest biogenic amine followed by histamine, while spermidine was the lowest.     

The manufacture of Ras cheese from gamma irradiated milk

Cheese milk exposed to gamma irradiation at a dose of 0·5 Mrad was used in the manufacture of Ras cheese. Quality and ripening of cheese made from irradiated milk were compared with those of cheese made from heat-treated milk.Gamma irradiation of cheese milk reduced the total bacterial count and spore formers by 98·98% and 95·77%, respectively, and eliminated the coliform and pathogenic bacteria. This treatment slightly increased the acid and peroxide values of milk fat, as well as the time required for complete coagulation of milk.An oxidized flavour in the fresh and 1-month-old gamma-irradiated milk (GIM) cheese disappeared during ripening. At the end of ripening, GIM cheese had a better consistency and increased flavour compared with cheese made from heated milk.Ras cheese made from GIM differed little in gross chemical composition but contained higher concentrations of soluble nitrogen compounds and of Free Fatty Acids than the control. Irradiation had a stimulating effect on the total, proteolytic and lipolytic bacterial counts during cheese ripening.     

A gas chromatography-mass spectrometry untargeted metabolomics approach to discriminate Fiore Sardo cheese produced from raw or thermized ovine milk

Thermization is a sub-pasteurization heat treatment of cheese milk (at 57–68°C for 15–30 s) aimed to reduce the number of undesirable microbial contaminants with reduced heat damage to the indigenous milk enzymes. In this work, the effects of milk thermization on the compositional parameters, proteolysis indices, free fatty acid levels, and low molecular weight metabolite profiles of ovine cheese were studied. Cheese samples at different ripening stages and produced in 2 different periods of the year were analyzed. While the effects of milk thermization on cheese macro-compositional parameters and free fatty acid levels were not evident due to the predominant effects of milk seasonality and cheese ripening stage, the gas chromatography-mass spectrometry based metabolomics approach of ovine cheese produced from raw and thermized milk highlighted strong differences at the metabolite level. Discriminant analysis applied to gas chromatography-mass spectrometry data provided an excellent classification model where cheese samples were correctly classified as produced from raw or thermized milk. The metabolites that mostly changed due to the thermization process belonged to the classes of free amino acids and saccharides. Gas chromatography-mass spectrometry-based metabolomics has proven to be a valid tool to study the effect of mild heat treatments on the polar metabolite profile in ovine cheese.     

Texture and flavour development in Ras cheese made from raw and pasteurised milk

Texture, proteolysis and flavour development in Ras cheeses made from raw or pasteurised milk with two different thermophilic lactic cultures were monitored during ripening. Results showed that at day 1 of manufacture, the moisture content and pH were lower in raw milk cheese than in pasteurised milk cheeses. Levels of water-soluble nitrogen, casein breakdown, free amino groups and free fatty acids were higher in cheese made from raw milk than in that made from pasteurised milk. Textural characteristics, such as hardness, cohesiveness and chewines, increased in all treatments during the first 60 days of ripening due to the reduction in the moisture level during the second stage of salting (dry salting during the first 60 days of ripening). Cheese made from raw milk received the highest texture and flavour scores by panellists.     

Determination of lipase activity in cheese using trivalerin as substrate

Lipolysis during cheese ripening is usually assessed by the accumulation of free fatty acids (FFA). An assay to determine total lipolytic activity present in a cheese during ripening was established. Finely grated cheese (1 g) was directly incubated with trivalerin (204 mg) as a substrate at 35 °C for 4 h. Free valeric acid was extracted and quantified by gas chromatography. The assay was linear with time up to 24 h and up to 0.11 Lipase Units g⁻¹ cheese. The total amount of lipolytic activity determined with this assay was consistent with the total amount of FFA present in 5 types of cheese. In Idiazabal cheese samples manufactured with or without lipase added, the total lipolytic activity determined during ripening remained constant up to 6 months of ripening. In addition to trivalerin, other possible substrates investigated were triolein, triundecanoin and the endogenous butyric acid-containing triacylglycerols present in the cheese sample. Activities measured with these substrates were considerably lower than values obtained with trivalerin due to the high levels of oleic acid present in cheese, or to difficulties in mixing triundecanoin (solid at 35 °C) with the grated cheese sample. Endogenous triacylglycerols gave increasingly lower activity values as ripening time progressed due to substrate depletion.     

Microstructure,free amino acids and free fatty acids in Domiati cheese treated with β-galactosidase

Domiati cheese was made from partially lactose hydrolyzed fresh milk and examined for the microstructure, the free amino acids, and the free fatty acids when young and after two months. The addition of β-galactosidase to cheese milk before renneting enhanced the fusion of protein and the formation of more homogenious structure of submicelles compared to control, as well as produced a good quality cheese of 1.5–2.5 fold free amino acids and free fatty acids as much as those of control. The differences were particularly great in respect of serine, phenylalanine, aspartic acid, glutamic acid, myristic acid, palmatic acid and oleic acid.     

The accelerated ripening of cholesterol-reduced Cheddar cheese by crosslinked β-cyclodextrin

This study was carried out to investigate the influence of salt content on cholesterol-reduced Cheddar cheese obtained by a treatment with crosslinked β-cyclodextrin (β-CD) and to find if the ripening process was accelerated in cholesterol-reduced cheese. The crosslinked β-CD used was made by adipic acid. A primary study indicated that the chemical and rheological properties were not changed by the salt addition and the composition of Cheddar cheese treated with crosslinked β-CD was similar to untreated Cheddar cheese. Approximately 91 to 92% cholesterol reduction was observed in the cheeses that were treated using β-CD. In a subsequent study, we found accelerated ripening by the crosslinked β-CD based on the productions of short-chain free fatty acids and free amino acids. In rheological properties, elasticity, cohesiveness, and gumminess scores in the cholesterol-reduced Cheddar cheese were significantly greater at 5 wk ripening than those in the control at 4 mo ripening. At the early stage of ripening, most flavor properties such as rancidity, bitterness, and off-flavor in the cholesterol-reduced cheese were greater. With ripening, however, those scores changed to similar or lower scores than those in the control. The present study indicated that the crosslinked β-CD treatment for cholesterol removal showed accelerated ripening effect on the properties of Cheddar cheese.