605. Preparation of a cheese with crystalline rennin

Abstract

Kizer, Hankin, Speck & Aurand(i) have observed that the impurities associated with proteolytic enzymes are stimulating to lactic acid bacteria, and they have suggested that these substances may accelerate the ripening of dairy products. In view of these observations and suggestions an experiment begun in March 1954, on the preparation of cheese with crystalline rennin, is reported below. The results are in agreement with the suggestions of Kizer et al.Three 30 lb. Cheddar cheese were made from a single batch of milk. One control cheese was made with ordinary commercial rennet. The second cheese was made with crystalline rennin and the third with rennin plus impurities which are discarded during the preparation of crystalline rennin.The crystalline rennin was made according to the method of Berridge & Woodward (2). The impurities were prepared as follows; the filtrate obtained after saturating commercial rennet with sodium chloride was acidified to pH 1-8. A copious precipitate was formed. This precipitate was removed by filtration and stored in the refrigerator until needed. It had a low but definite activity, consequently when the amount of enzyme needed for 30 gal. of milk was calculated from the activity of the precipitate a much larger quantity of adventitious material than is present in commercial extracts accompanied the rennin. The crystalline enzyme was free from adventitious material.Parallel experiments indicate that the acid precipitate contained about 10% of the active enzyme present in the parent solution and about 80 % of the crude protein, making it about one-fifth of the specific activity of commercial rennet, on a dry-weight basis. The crystalline rennin had about ten times the specific activity of commercial extracts.Both crystals and precipitate were prepared for addition to the milk by dissolving in dilute phosphate buffer of pH 6*8.During making the control cheese behaved normally in every respect. The milk with crystalline rennin clotted very quickly (3 min.), but the curd remained soft for a relatively long time. In a small-scale parallel experiment similar curd was no firmer after half an hour than a curd produced by commercial rennet clotting in 9 min.The curd formed by crystalline rennin developed less acidity than the control; on applying the hot iron test threads only J in. long were formed in place of the normal 1 | in. threads. After pressing, the acidity, though sufficient, was less than that in the control, and the curd was softer.The curd formed with the preparation containing excess of adventitious material, when subjected to the hot iron test, formed a small number of threads which were both stouter and longer than normal.When the cheese were tasted after ripening for 4 months, the control was of normal pleasant flavour. The cheese made with adventitious material had a similar but stronger,

Cheddar cheesemaking with recombinant calf chymosin synthesized in Escherichia coli

“…No evidence was found to suggest that cheeses made with recombinant chymosin would be measurably different in quality from those made with rennet. This result is unexpected in view of a previous observation that Cheddar cheese made with crystalline calf chymosin did not develop a typical flavour (Berridge, 1955) and the recombinant chymosin used in this study was electrophoretically pure (Marston et al 1984). This suggests that there was more proteolysis in the cheese than could be explained by the known proteolytic agents present.…”