Title: The Effect of Added Amino Acids on the Flavor of Cheddar Cheese Made from Pasteurized Milk
Abstract: The protein in cheese curd has been shown to undergo a series of chemical changes during the ripening process, until amino acids and ammonia are present in some quantities, in addition to the more complicated degradation products.Whether certain protein decomposition products, materials produced by action upon butterfat or products resulting from changes in other components of the cheese curd are responsible for the characteristic Cheddar flavor has not been established satisfactorily, partly because of the complexity of the system in which the changes are occurring. Davies et al.(2) added, at the time of salting, various chemical compounds which might affect the growth and metabolism of bacteria or the activity of rennet enzymes.Cystine was added in concentrations of 0.01 and 0.02 per cent, but it had no significant effect on the rate of ripening, even though the flavor score of the cheese made with cystine was slightly higher than that of the control cheese.No differences were noted in the amounts of the various nitrogen fractions.After the present investigation had been completed, Harper and Swanson (4) indicated that mixtures of amino acids may contribute to the flavor of Cheddar cheese.The purpose of the present study was to test the possibility that the addition of various amino acids to cheese curd made from pasteurized milk might contribute to production of the typical flavor and aroma characteristic of a fine rawmilk Cheddar cheese ripened properly, either directly or as substrata upon which microorganisms or enzymes might act. METHODS Manufacture of Cheddar cheese.The mi]k used in all cheese was mixed herd milk with a fat content varying from 3.1 to 3.8 per cent.It was pasteurized at 143 ° F. for 30 minutes in a spray-vat pasteurizer.For lots 1 through 8, 170 lb. of milk were used and for lots 9 through 12, 125 lb. of milk were used.In all lots the method of manufacture was essentially that of Wilson (7), with the modification that after the curd was salted, it was weighed into separate 2.5-1b.quantities.Lots 1 through 8 required six separate quantities from each quantity of curd, while lots 9 through 12 required five quantities.The amino acid-salt mixture described later then was incorporated into the 2.5-1b.quantities of curd and allowed to dissolve for approximately 10 minutes before the curd was placed in small wooden hoops.The hoops were used to produce a cheese 5 inches in diameter and 2.5 inches thick, weighing approximately 2.5 lb.The pressure was.applied slowly in the press to minimize the amount of whey expressed from the cheese until the