Rennet Cheese Research Articles

Cheddar Cheese Made With Bovine Pepsin II. Texture—Microstructure—Composition Relationships

The relationship of texture to microstructure and composition was studied in Cheddar cheese manufactured with calf rennet or bovine pepsin as the coagulating enzyme. Three instrumental parameters of cheese were measured and all were found to correlate closely with sensory evaluations of cheese texture. They did not, however, relate well to trained grader scores. Samples were evaluated over a one year period; aging produced a harder cheese, the greatest change occurring during the first 6 months. Calf rennet cheese was softer than bovine pepsin cheese. A scanning electron microscopical examination of cheese microstructure showed that the major change occurring during the aging process was an increasingly compact appearance. This also was most evident during the first 6 months. Calf rennet cheese was more compact than that made with bovine pepsin. Compositional changes happened early in the ripening process also, with 81% of the increase in acid soluble nitrogen occurring within 6 months. Calf rennet liberated more acid soluble nitrogen than did bovine pepsin. Electrophoretic data showed that the two enzymes produced different proteolytic patterns from three weeks onwards. Protein degradation during ripening resulted in several new bands in the αs1casein fraction which implies that proteolysis is probably greater in this fraction.

Assessment of swine, bovine and chicken pepsins as rennet substitutes for Cheddar cheese-making

SummaryThree enzymes were assessed as rennet substitutes for cheese-making. The bovine and chicken pepsins used were relatively crude extracts of bovine stomach mucosa and chicken proventriculae respectively; the swine pepsin was a partially purified commercial product. The ratios of milk-clotting activity to general proteolytic activity were high for rennet and bovine pepsin and low for swine and chicken pepsins. Both bovine mucosa and chicken stomach gave low milk-clotting activities compared with calf stomach. For all the enzymes the chemical reactions causing milk clotting appeared to be the same. The milk-clotting activity showed a decrease with increase in substrate pH for all the enzymes, although they were all still active at pH 6·81.Duplicate cheeses were made from each of the swine, bovine and chicken pepsins, with rennet as a standard in each trial. The cheese-making process was similar with each enzyme, but differences appeared during ripening. The chicken-pepsin cheeses had poor body and weak Cheddar-cheese flavour, with many and intense off-flavours. The cheeses made with bovine and swine pepsins were only slightly inferior in quality and intensity of Cheddar-cheese flavour to the rennet cheeses. From a simulated cheese-making experiment it was concluded that 30–40 % of the added rennet, bovine pepsin and chicken pepsin was probably inactivated during the cheese-making process and that most or all of the swine pepsin was lost. These results provide an explanation for the variations observed in cheese ripening.It was concluded that chicken pepsin would not prove a suitable rennet substitute for making Cheddar cheese because of the quality of the cheese produced, and that bovine pepsin would not prove suitable because of the cost of preparing a suitable extract. Swine pepsin would appear to be suitable if the ripening time were to be lengthened or if another enzyme were to be added to assist ripening; it is cheaper than rennet and other rennet substitutes.

Cheddar Cheese Manufacture with Pepsin and Rennet

Rennet was compared with a mixture (1:1) of rennet and pepsin in making and curing Cheddar cheese. Eight pairs of vats of cheese were made in each of four factories. Coagulation of milk with the mixture was slower than with rennet in only one factory. Fat losses in the whey in two factories were slightly higher where the mixture was used, but not in the other two factories. Federal graders examined the cheese at 3 weeks, 6 and 12 months of age. The texture of “mixture” cheese was slightly poorer than that of rennet cheese when 3 weeks old. Flavor scores were slightly higher for “mixture” cheese than for rennet cheese when 12 months old. Taste panels revealed only very slight differences in intensities of Cheddar flavor and of bitter flavor when the cheese was 12 months old. “Mixture” cheese was slightly firmer than rennet cheese at 6 and 12 months. Protein hydrolysis was less in “mixture” cheese than in “rennet” cheese made in some factories. Observations are also given for cheese made in four paired vats with rennet and with pepsin only.It was concluded that the mixture (1:1) of rennet and pepsin produced cheese of high quality, essentially equal to that made with rennet, and that pepsin should not be used alone without further trials. The results indicated that cheesemakers should give more attention, when using the mixture, to factors affecting texture of cheese and fat losses in the whey, and that problems might be encountered with slow coagulation of the milk.

Electrophoresis of Milk Proteins II. Some Effects of Methods of Preparation on the Electrophoretic Patterns of Whey Proteins

Paper I of this series (11) reported several small differences in the electrophoretic patterns of whey proteins prepared by two methods. These methods were first, a salt-acid procedure devised by Harland and Ashworth (6) and second, a new salt-lyophylized procedure. Both of these patterns were approximately similar to patterns reported by Smith (10) and Deutsch (3) using whey proteins separated from casein with acid or with rennet. Nitschmann and Lehmann (8) found that a-casein, normally a single component, when treated with rennet produced two electrophoretic peaks. Crystalline fl-lactoglobulin also has been reported to be electrophoretically homogeneous (1) at some pH values, but to contain three peaks at others (7). A more extensive electrophoretic comparison of whey proteins prepared by each of the above four methods seemed justified. A *pH of 6.8 is near the natural pH value of fresh milk. Values of 7.8, 6.8, 5.8 and 3.8, therefore, were chosen for this study. Areas, mobilities and isoelectric points all seemed useful bases for comparison. PROCEDURE To insure that any observed differences would be due to methods of preparation and not to differences in the starting milk, the four procedures were used simultaneously on portions of the same samples of milk. Pooled raw whole milk, cooled as soon as milked, was obtained from the Kansas State College Dairy within 3 to 4 hr. after milking. The cream was separated in a Sharples supercentrifuge. The preparations of whey proteins by the salt-acid method and the salt-lyophilized method were exactly as previously described (11). The acid whey and the rennet whey also were dialyzed, lyophilized and redialyzed in a manner similar to that used for the salt-lyophilized whey. For preparation of the acid whey, a procedure modified from Rowland (9) was used. Five hundred ml. of skimmilk were heated to 40 ° C. and placed in a rectangular fruit jar containing a motor stirrer. Fifty ml. of 10 per cent acetic acid were added dropwise, followed after 10-min. standing by 50 ml. of 1.0 N sodium acetate. The mixture then was cooled to about 5 ° C. and filtered after again standing for 2 hr. Eckles et al. (4) described a commercial method for rennet cheese which was

201. The solubility of Cheddar cheese curd in sodium chloride solutions

Measurements are reported of the solubility, in water and in sodium chloride solution of different concentrations, of the protein of cheese at various times after manufacture. The solubility in 3–10 % sodium chloride solutions reached approximately 100% within 7 days after manufacture of the cheese, both for normal and high rennet cheese, and remained at that value throughout the life of the cheese (8 months). Since the proteins of cheese are thus shown to be equally soluble in sodium chloride solutions corresponding in concentration to those encountered in the whole range of commercial cheese(1), the effect of salt concentration on cheese quality is not to be attributed to a variation in the solubility of the protein in the brine.

180. Alcohol-glycerol rennet preparations in cheese-making

1. Although chemical analysis, bacteriological analysis and graders' reports failed to distinguish the alcohol-glycerol rennet cheese from the brine rennet cheese, the marked qualities in body and texture during making of the alcohol-glycerol rennet curd, and the sterility or low count of the alcoholglycerol extract warrant further trials under practical conditions.2. Where brine rennet may be suspected as the cause of bacterial faults, the alcohol-glycerol rennet could well be used in its place.3. Alcohol-glycerolrennets have superior keeping-qualities to brine rennets.