D.M. Irvine

A comparison of microstructures of Cheddar cheese curd manufactured with calf rennet, bovine pepsin, and porcine pepsin

Calf 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.

Precipitation and Recovery of Whey Proteins: A Review

Abstract The economic feasibility of recovering whey protein is dependent upon the efficiency of the process and the utilization of the protein isolate. Heat processing is an efficient method of recovering whey proteins which can be used in process cheese spreads. Chemical precipitation of whey proteins yields functional isolates which promote gelation, whipping and emulsification, but residual precipitants are retained. Co-precipitation of casein and whey protein as occurs in the manufacture of Queso Blanco is the simplest method of recovering whey proteins. Membrane processing offers great potential for whey protein recovery. Required conditions and selected processes for the precipitation and recovery of whey proteins are discussed.

Manufacturing Parameters of Queso Blanco Made from Milk and Recombined Milk

Abstract 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.

Cheddar Cheese Made with Chicken Pepsin

Abstract 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.

Microstructure of Cheddar cheese: sample preparation and scanning electron microscopy

Three 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.

Separation and Quantification of Whey Proteins by Size Exclusion Chromatography

Abstract 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