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The analysis of β -lactoglobulin (β-LG) and α -lactalbumin (α-LA) in whey by size exclusion chromatography was rapid (25 min/run) and quantitative. Standard curves (0.025 — 0.20% protein; r > 0.99) of β-LG and α-LA were prepared at pH 4.8 and 7.0. In agreement with literature values, the method indicated concentrations of 0.38% β-LG and 0.14% of α-LA in a whey sample prepared from 10% reconstituted skim milk powder. Studies with standard mixtures of β-LG and α-LA at pH

Effects of pH, heat treatment, concentration of solids and mechanics of processing on separation of proteins from whey concentrated by reverse osmosis were studied. Acidification of whey to yield a protein concentrate of pH less than 5.5 decreased protein recovery in laboratory experiments, but increased recovery of protein in pilot plant experiments. Ash content of heat precipitated whey proteins decreased with acidification. Maximum protein recovery was obtained by heating to 95° C for 5 min before acidification with citric acid and drainage through 16 mesh/cm metal screen. Whey from the manufacture of 10 kg of semisoft cheese of 49% moisture yielded 8 kg protein concentrate.

Titration and buffer capacity curves of Mozzarella, Cheddar and Cottage cheese-type wheys were studied at concentrations of 6–24% solids. Buffer maxima due to lactate and phosphate occurred at pH 3.2 – 4.0 and 5.6 – 7.0, respectively, and were dependent on the type and concentration of whey. Titration curves of all whey varieties intersected at pH 3.7. An equation was developed to define whey pH as a function of pH at dipping, concentration and level of HCI or NaOH (r = 0.99, p < 0.01). The pH of Mozzarella and Cheddar cheese-type whey decreased during concentration but the pH of Cottage cheese whey increased. This difference is explained by calcium-phosphate equilibria in whey.

The effects of pH, calcium chloride, milk supply and levels of milk solids on the yield, composition and quality of Queso Blanco cheese were studied. The optimum pH of experimental cheese made from whole and reconstituted milk was in the range 5.2 to 5.3 with respect to flavour and body. Recovery of solids was higher from whole milk than from reconstituted milk of similar composition. Levels of acid indicated no effect on the recovery of solids in the range pH 5.5 to 4.9. Equations were developed to predict the amount of citric acid required to produce a desired pH in milk of a given protein content, and the optimum amount of citric acid for cheese manufacture. The use of more than 0.05% calcium chloride increased cheese moisture and solids recovery, and produced bitter flavoured cheese. Lesser amounts of calcium chloride increased solids recovery but did not affect other parameters. Cheese lactose content and protein recovery increased with increasing milk solids. Recombined milk of 15% solids-not-fat and 4.5% fat resulted in acceptable Queso Blanco. Eighty-six percent of milk protein was recovered and cheese yield was 20 to 22% of milk weight.

This study investigated and compared the effects of heating system and residence times on the physicochemical properties and interactions of casein and whey proteins in heated milk. Milk was processed by vat heating (85°C for 10 to 40min), HTST heating (98°C for .5 to 1.87min), UHT heating (140°C for 2 to 8s), cooled, and fractionated into casein and whey by isoelectric precipitation. β -Lactoglobulin A and B variants were partially denatured by HTST and UHT heating and totally denatured by vat heating. Increasing residence time caused significant ( P β -lactoglobulin variants in UHT and HTST heating systems and of α-lactalbumin in the vat heating system. Surface hydrophobicity and sulfhydryl content were negatively correlated with whey protein denaturation. Sodium dodecyl sulfate electrophoresis of the casein fraction of heated milk indicated the presence of a high molecular weight component that would not enter the gel. Addition of 2-mercaptoethanol to heated casein samples dissociated this component, with the concurrent appearance of β -lactoglobulin and α -lactalbumin bands. In HTST and UHT heating systems, ratio of β -lactoglobulin to κ -casein increased linearly from the complex with increasing residence time.

Dilute citric acid (1 to 2%) for the manufacture of Queso Blanco produced a cohesive curd that was easily drained and exhibited improved body and texture compared to curd coagulated with 10% acidulant containing the same amount of citric acid. A manufacturing procedure employing such dilute acidulants has been developed and successfully tested in pilot plant trials and in a commercial facility using up to 3000kg of milk. Pilot plant yields from standardized milk containing between 3.69 and 4.41% protein (52% moisture corrected) ranged from 14.89 to 17.89%. Commercial yields did not show a significant correlation ( P = .05) with predicted yields based on pilot plant data (.70 P Optimum moisture was approximately 52% for overall texture and sliceability. Cheese pH was between 5.4 and 5.5. Typical protein and fat contents for a 52% moisture cheese were about 22 and 19%, respectively.

Commercial chicken pepsin was compared to calf rennet and a mixture of calf rennet and porcine pepsin as coagulating enzymes for the production of pilot plant quantities (25 kg) of Cheddar cheese. Yield data indicated that a significantly lower yield of cheese may be expected using chicken pepsin. Acid soluble nitrogen levels were considerably higher in the chicken pepsin cheese at both the 3 week and 3 month sampling periods, indicating a higher level of proteolysis with this enzyme. Instrumental and sensory texture analyses showed the chicken pepsin cheese lacked firmness compared to the other cheeses. The sensory panel also perceived a high and objectionable level of bitterness in cheese prepared with the chicken enzyme. Scanning electron microscopy revealed a more open, less compact protein network in chicken pepsin cheese that is probably responsible for its poorer texture. Electrophoresis of the respective cheese caseins showed a larger beta casein peak for calf rennet cheese. The alpha S peak was composed of four separate bands and their relative proportions were influenced by enzyme source. It is concluded that the chicken pepsin enzyme used in this study does not produce an acceptable Cheddar cheese either from quality or yield considerations. This is considered due to extensive proteolysis that led to defects in flavor and texture. A more highly purified enzyme preparation should be evaluated in the future.

The effects of temperature (85° and 95°C) and holding time (0, 5, 15 and 30 min) were investigated in factorial combination on recombined milk (15% SNF, 4% B.F.) for Queso Blanco manufacture. Temperature was not significant with respect to yield, fat or protein content (expressed on a dry basis) or recovery of fat, protein or solids. Protein recovery significantly (P 2 values of 0.42 and 0.34, respectively. In laboratory experiments, heat treatment at 85°C for 5 min produced acceptable, sliceable and bland-flavoured cheese with pH of 5.3. The feasibility of homogenizing milk (0 to 140 kg/cm 2 ) for making Queso Blanco was investigated. Cheese of acceptable organoleptic quality was produced in laboratory trials. Fat recoveries for unhomogenized control milk and milk homogenized at 140 kg/cm 2 were 69.81 and 93.38%, respectively in laboratory trials. However, slow drainage of curd from homogenized milk would discourage larger production trials.

Instrumental evaluation of Queso Blanco texture as influenced by several factors was carried out using the Instron testing machine. Variables investigated were salting temperature of the curd, moisture content, and age of the cheese. Cheese hardness (maximum force) increased linearly with age over a 17-day period and was inversely related to moisture content. Hardness was not significantly affected by salting temperature of the curd. Stress decay under constant strain was greater with curd that had been salted at low temperatures. These observations are of value in process control.

Anion exchange chromatography was used to measure residual α-lactalbumin (α-LA), β-lactoglobulin A (β-LG A), and β-lactoglobulin B (β-LG B) in isoelectric supernatants of heated wheys. A study of the effects of dipping pH (6.7 and 4.6) corresponding to sweet and acid wheys, respectively, and the pH (2.4–6.8) of heating (85°C, 10 min) revealed the following: (1) Precipitation of α- LA in sweet whey was greater after heating at pH 4.6–6.8 than in acid whey probably due to stabilization of α-LA by increased levels of Ca + + in acid whey. There was no effect of whey variety on precipitation of α-LA after heating at pH 2.4–3.5; (2) Precipitation of β-LG A at isolelectric pH in both acid and sweet wheys was greater than that of β-LG B. In acid whey at pH below the isoelectric region, precipitation of β-LG A was greater than that of β-LG B; (3) Precipitation of α-LA after heat treatment at pH 2.4–3.5 was greater than that of β-LG but the reverse was true at pH 5.7–6.8.

The Mark II Pro-Milk Tester was evaluated for its accuracy, repeatability, reliability, and operational limitations. During 1 yr the instrument calibration was checked continually with preanalyzed calibration milks prepared by combining individual cow milks at specific fat contents. Protein ranged from 2.96 to 4.24% by a semi-micro Kjeldahl method. Plant milk samples (833) were analyzed with the instrument and protein of these samples was from 2.75 to 3.65% by the Kjeldahl method. From regression analysis calibration maintained with calibration milks was unsuitable for use with the plant milks. For the 1 yr the standard deviation of difference between Kjeldahl and Pro-Milk results for calibration milks was .031 whereas for the plant milks it was .074. Repeatability of the Pro-Milk test (±.0110) was about the same as with the Kjeldahl (± .0114), and mean difference between Kjeldahl and Pro-Milk were small both for calibration milks (.0007) and plant milks (.0049). The larger standard deviation of difference with plant milks, therefore, was the result of a different requirement for calibration slope. Six adjustments of calibration were required during the year, three with changing from one dye lot to another and three with the same dye lot. As there was no noticeable drift in instrument read-out at any time, changes in calibration could be required because of differences in purity of dye or because of seasonal changes in mean dye binding capacity of milk proteins. Calibration of the Pro-Milk Tester needs to be monitored continually and its results adjusted to conform to those of an official method for the type of milk to be analyzed routinely with the instrument.

Summary The factors which alter the rate of rennet action and curd tension of non-homogenized milk have a similar action on rate of coagulation but very little or no effect on the curd tension obtained by rennet action on homogenized milk. Practically normal curd-making properties were restored to homogenized’ milk by concentrating it or by adding to it low-heat, nonfat dry milk solids or low-heat concentrated skimmilk. The treatments may have practical commercial applications. These data suggest that reduction of curd tension by homogenizing may be caused by adsorption of casein on the newly created surfaces of fat.

Weekly milk samples from 24 selected dairy plants in Ontario were analyzed for protein for 12 months in 1971 and early 1972. Samples from selected dairy plants proportionally represented the industrial milk production of eastern, southern and northern Ontario. The data showed a significant difference in amounts of casein, whey protein and non-protein nitrogen between milks from different areas as well as between seasons. There was also a significant difference in the expected composition of the total protein in the Ontario milk supply and these results. Historically, protein components are for casein 76.6%, serum protein 18% and nonprotein nitrogen 5.5%. Results for protein were 74.76% casein, 19.1% serum protein, and 6.16% nonprotein nitrogen. Eastern Ontario had the lowest casein and the highest serum protein, followed by northern Ontario and southern Ontario respectively. The highest casein occurred in January and February, 77.08 and 77.19% with the lowest standard deviations of ± 2.36 and ± 2.28. This coincided with the lowest serum protein of 17.98 and 17.79% with the lowest standard deviations of ± .97 and ± 1.18. Casein fluctuated most in May with a standard deviation of ± 5.89%. The lowest casein occurred in August, September, and October, 73.41, 73.07 and 73.09%. This coincided with the highest nonprotein nitrogen of 6.99, 7.59 and 7.09%.

The enzyme complex from a mutant of Bacillus subtilis revealed less proteolytic activity on milk proteins when pH of the milk was lowered by addition of acid. Nonprotein N in whey was much lower when milk was acidified before addition of milk clotting enzyme. Canadian Cheddar cheese was made from milk adjusted to pH 6.63 to 5.86 with additions of Bacillus subtilis proteases as coagulants. During manufacture the firmest curd resulted from the most acid milk. Protein recovery was greatest in cheese from milk acidified to the lowest pH. Cheese yields were significantly increased by acidification of milk. The best cheese was made from milk acidified to pH 6.3 to 6.0.

Properties of proteases of a mutant of Bacillus subtilis were compared with those of calf rennet. Clotting ability of proteases was affected less by addition of Calcium ++ , pH, and temperature changes than rennet. During manufacture of Canadian Cheddar cheese, proteolysis by bacterial proteases singly or together was continuous, resulting in a softer curd with more protein in whey (1.08 to 1.14%) than in the control (.95%). Fat in whey from protease lots was higher (.26 to .38) than from rennet control (.19). More proteolysis by bacterial proteases lowered cheese yield by 10%. Cheese made with proteases from a mutant of Bacillus subtilis revealed more and different proteolytic activity than did cheese made with calf rennet.

A stable, nontoxic, 15% sunflower oil emulsion containing 65% linoleic acid was formulated for intravenous infusion into a cow. An infusion of 500ml of this emulsion into a Jersey cow caused a parallel increase in the fat and protein of the milk and a decrease in lactose. The correlations obtained, between the percentages of fat-protein (morning's milk, r=0.99; evening's milk, r=0.85), and fat-lactose (r = −0.71) and yields of fat-protein (r = 0.98) and fat-lactose (r = 0.98) indicated the existence of some control mechanism in the cow, relating fat, protein, and lactose synthesis. There was an increase of 5% in linoleic acid at the second post-infusion milking. Consequently, the unsaturation of the milk fat was increased which, in turn, improved its fixation by osmium tetroxide for electron microscopy. The appearance of large extraalveolar fat droplets, 3 to 85 μ in diameter, and the prolonged effect of the infusion on the milk fat composition is indicative that the emulsion was cleared from the blood stream and stored as milk fat precursors until they could be used in the formation of milk fat by the secreting alveolar cells.

Typical commercial lactic cultures were grown at 100°F. in reconstituted nonfat dry milk containing varied concentrations of salt up to 5%. Acid development was stimulated by small amounts of salt, but was definitely inhibited at levels of 2.5% salt and over. When comparable starters were used in making curd by the Dariworld process, the curd was taken at dipping at pH 6.1 to 6.0 and covered with brine at 100°F. Acid development continued more rapidly in brines with 3% salt than in identical curd covered with water. Most rapid acid development in the curd was found at salt concentrations approximating 2%.

Summary Protein stability in reconstituted skimmilk is adversely affected by high calcium and magnesium levels in the reconstituting water. The heat stability, as measured by the Storrs stability test, is a function of total hardness, and is not changed by varying the calcium-to-magnesium ratio. The effect of magnesium ions can be balanced by sequestration with equivalent quantities of sodium hexametaphosphate, but with calcium more than equivalent quantities of this sequestering agent are needed. Sequestration of a portion of the hardness of very hard waters is suggested as a possible method for avoiding premature protein coagulation during heat processes used in the manufacture of cottage cheese and in the preparation of media for propagation of cheese starters.

SummaryThree techniques were used for preparing Cheddar cheese specimens for examination by scanning electron microscopy. Resulting micrographs prepared from fresh cheese made with calf rennet revealed that while all the techniques were satisfactory, different structural features were observed depending upon the method used. A modified critical point drying technique and a freeze-drying method displayed surface features whereas trypsin hydrolysis showed internal microstructure. The surface microstructure of the cheese was found to be formed of protein aggregated and fused into structural units of 1·5 μm. The internal microstructure appeared to be formed of thin compact walls. Cross sections prepared by freeze-drying displayed arrays in the protein matrix and locations where fat globules had been embedded.

SummaryCalf rennet, bovine pepsin, and porcine pepsin were used to produce cheese curd, using the same milk and lactic culture for each. Specimens were prepared for scanning electron microscope examination by a modified critical-point drying technique.From examination of the micrographs, the curd made with bovine and porcine pepsin were similar in structure and in orientation of the coagulated protein, whereas the curd produced with rennet was different, having a more compact and organized structure.

The time required to make cheese by the Dariworld process from addition of 1% starter to hooping is about six hours. By using 2.5 or 4% starter, and adding rennet immediately after the starter, the total making time can be reduced 16 or 25%. The usual acidity of about pH 6.0 at dipping and pH 5.4 at second heating are observed. Curd making, cheese composition, and grades are not significantly altered by increased starter and rate of acid development.