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The Effect of Copper on Lipase Activity in Cheddar Cheese
THE EFFECT
OF C O P P E R ON L I P A S E A C T I V I T Y I N CHEDDAR CHEESE
I. HLYNKA, E. G. HOOD, AND C. A. GIBSON Division of Chemist~'y, the Division of Bacteriology and Dairy Research,l Science Servive, and the Division of Animal Husbandry, Experimental ~arms Service, Department of Agriculture, Ottawa, Canada
A knowledge of the properties and the behavior of milk lipase is necessary in order to u n d e r s t a n d certain lipolytic changes which take place in milk and milk products. I n a previous publication (3) the authors presented evidence to show that active milk lipase is in a reduced chemical state; that mild oxidation such as aeration in the presence of copper inactivates it; and that reactivation of milk lipase is possible b y means of appropriate reducing systems. Although these results were obtained f r o m experiments on raw milk it was possible to draw certain conclusions r e g a r d i n g the probable behavior of milk lipase in r a w milk cheddar cheese in relation to the development of rancid flavor. I t was stated that the effectiveness of oxidative inhibition of milk lipase would be offset by the reducing systems in the cheese. I t was, however, necessary to check our findings with the m a k i n g of experimental cheese. Accordingly, the effect of copper on added pancreatic lipase in cheddar cheese is reported, confirming our previous conclusions. I n all, 10 comparison or duplicate vats of cheese (2) were made. E a c h pair of cheese was identical in every respect and included the same amount of pancreatic lipase added to the cheese milk. The first cheese of each set, however, contained added copper (CuC12 was used), while its mate did not. The level of pancreatic lipase used r a n g e d f r o m 0 to 2.5 gm. per 1000 lbs. milk. This gave both suboptimal and sufficient amounts of lipase necessary to produce a rancid flavor in the cheese. The amounts of copper were 2 and 5 p a r t s Cu per million p a r t s milk, levels which were known to be effective in inhibiting lipase on the basis of our previous experiments. The finished cheese were cured u n d e r the usual conditions and were graded for flavor at suitable intervals. D u r i n g the m a n u f a c t u r e of these cheese a striking difference was noted in the flavor of the curd in the two vats, the difference being most pronounced at the milling stage. The curd in the v a t which contained added copper was less rancid and generally superior in flavor to its mate to which no copper had been added. However, g r a d i n g figures on the cheese a f t e r two weeks and subsequently showed no significant differences in the flavor scores. Detailed data are, therefore, not included. Received for publication lViay 12, 1942. 1 Contribution l~!o. 150 (Journal Series). 923
924
I.
HLYNKA, E. G. HOOD, AND C. A. GIBSON
The results obtained with experimental cheese confirm those previously found with milk. The main conclusion is that copper is not all effective lipase inhibitor in cheddar cheese. That copper does inactivate added lipase follows from the suppression of rancid flavor development while the cheese is in the curd stage. That this effect is not permanent is indicated by the fact that no significant difference in the flavor scores or in the intensity of rancid flavor was found at grading. The explanation for this is to be found in the reactivation of oxidatively inactivated lipase in presence of the reducing systems of cheese. Although copper is known to raise the oxidation-reduction potential of cheese (1) this rise is apparently insufficient to alter the conditions in the cheese appreciably. The potential of the cheese still remains at a sufficiently negative value to be able to reduce any oxidized lipase to its active condition. It is therefore unlikely that slight variations of the oxidation-reduction potential or copper contamination would have any effect on the spontaneous development of rancid flavor under commercial conditions. Two other points may be noted in passing. The behavior of pancreatic lipase is very similar to that of milk lipase and, therefore, the use of the former for experimental purposes in dairy research seems justifiable. Also experiments with milk, used judiciously, are of value in the study of cheese. It is understood, of course, that such experimental expedients as these must ultimately be confirmed on the basis of cheese manufacture. SU M MARY
Although copper inhibits lipase activity in milk under ordinary conditions it is ineffective as a lipase inhibitor in cheddar cheese. This is attributed to the strongly reducing potential of the cheese. ACKNOWLEDGMENT
The authors are indebted to Mr. T. J. Hicks, Senior Dairy Produce Grader, Dairy Products Division, Department of Agriculture, for his services in grading the experimental cheese. REFERENCES
(1) DAVIES, W. L., DAVIS, .I.G., DEARDEN, D. ¥., AND 1VIAT'2ICK, A. T . R . Studies in Cheddar Cheese. I I . The Effect of Controlled Oxidation-Reduction Potential on Ripening. Jour. Dairy Res., 5: 2, 144-148. 1934. (2) HLYNI;A, I., HOOD, E. G., AND GIBSON, C. A. Effect of Proteolysis on Lipase Induced Rancidity in Cheddar Cheese. J o u m DAIRY ScI., 24: 7, 561-565. 1941. (3) HLYNKA, I., AND HOOD, E . G . The Reversibility of Oxidative Inactivation of Milk Lipase in Relation to its Activity in Cheddar Cheese. J o u m DAIRY ScI., 25: 2, 111-115. 1942.
OF C O P P E R ON L I P A S E A C T I V I T Y I N CHEDDAR CHEESE
I. HLYNKA, E. G. HOOD, AND C. A. GIBSON Division of Chemist~'y, the Division of Bacteriology and Dairy Research,l Science Servive, and the Division of Animal Husbandry, Experimental ~arms Service, Department of Agriculture, Ottawa, Canada
A knowledge of the properties and the behavior of milk lipase is necessary in order to u n d e r s t a n d certain lipolytic changes which take place in milk and milk products. I n a previous publication (3) the authors presented evidence to show that active milk lipase is in a reduced chemical state; that mild oxidation such as aeration in the presence of copper inactivates it; and that reactivation of milk lipase is possible b y means of appropriate reducing systems. Although these results were obtained f r o m experiments on raw milk it was possible to draw certain conclusions r e g a r d i n g the probable behavior of milk lipase in r a w milk cheddar cheese in relation to the development of rancid flavor. I t was stated that the effectiveness of oxidative inhibition of milk lipase would be offset by the reducing systems in the cheese. I t was, however, necessary to check our findings with the m a k i n g of experimental cheese. Accordingly, the effect of copper on added pancreatic lipase in cheddar cheese is reported, confirming our previous conclusions. I n all, 10 comparison or duplicate vats of cheese (2) were made. E a c h pair of cheese was identical in every respect and included the same amount of pancreatic lipase added to the cheese milk. The first cheese of each set, however, contained added copper (CuC12 was used), while its mate did not. The level of pancreatic lipase used r a n g e d f r o m 0 to 2.5 gm. per 1000 lbs. milk. This gave both suboptimal and sufficient amounts of lipase necessary to produce a rancid flavor in the cheese. The amounts of copper were 2 and 5 p a r t s Cu per million p a r t s milk, levels which were known to be effective in inhibiting lipase on the basis of our previous experiments. The finished cheese were cured u n d e r the usual conditions and were graded for flavor at suitable intervals. D u r i n g the m a n u f a c t u r e of these cheese a striking difference was noted in the flavor of the curd in the two vats, the difference being most pronounced at the milling stage. The curd in the v a t which contained added copper was less rancid and generally superior in flavor to its mate to which no copper had been added. However, g r a d i n g figures on the cheese a f t e r two weeks and subsequently showed no significant differences in the flavor scores. Detailed data are, therefore, not included. Received for publication lViay 12, 1942. 1 Contribution l~!o. 150 (Journal Series). 923
924
I.
HLYNKA, E. G. HOOD, AND C. A. GIBSON
The results obtained with experimental cheese confirm those previously found with milk. The main conclusion is that copper is not all effective lipase inhibitor in cheddar cheese. That copper does inactivate added lipase follows from the suppression of rancid flavor development while the cheese is in the curd stage. That this effect is not permanent is indicated by the fact that no significant difference in the flavor scores or in the intensity of rancid flavor was found at grading. The explanation for this is to be found in the reactivation of oxidatively inactivated lipase in presence of the reducing systems of cheese. Although copper is known to raise the oxidation-reduction potential of cheese (1) this rise is apparently insufficient to alter the conditions in the cheese appreciably. The potential of the cheese still remains at a sufficiently negative value to be able to reduce any oxidized lipase to its active condition. It is therefore unlikely that slight variations of the oxidation-reduction potential or copper contamination would have any effect on the spontaneous development of rancid flavor under commercial conditions. Two other points may be noted in passing. The behavior of pancreatic lipase is very similar to that of milk lipase and, therefore, the use of the former for experimental purposes in dairy research seems justifiable. Also experiments with milk, used judiciously, are of value in the study of cheese. It is understood, of course, that such experimental expedients as these must ultimately be confirmed on the basis of cheese manufacture. SU M MARY
Although copper inhibits lipase activity in milk under ordinary conditions it is ineffective as a lipase inhibitor in cheddar cheese. This is attributed to the strongly reducing potential of the cheese. ACKNOWLEDGMENT
The authors are indebted to Mr. T. J. Hicks, Senior Dairy Produce Grader, Dairy Products Division, Department of Agriculture, for his services in grading the experimental cheese. REFERENCES
(1) DAVIES, W. L., DAVIS, .I.G., DEARDEN, D. ¥., AND 1VIAT'2ICK, A. T . R . Studies in Cheddar Cheese. I I . The Effect of Controlled Oxidation-Reduction Potential on Ripening. Jour. Dairy Res., 5: 2, 144-148. 1934. (2) HLYNI;A, I., HOOD, E. G., AND GIBSON, C. A. Effect of Proteolysis on Lipase Induced Rancidity in Cheddar Cheese. J o u m DAIRY ScI., 24: 7, 561-565. 1941. (3) HLYNKA, I., AND HOOD, E . G . The Reversibility of Oxidative Inactivation of Milk Lipase in Relation to its Activity in Cheddar Cheese. J o u m DAIRY ScI., 25: 2, 111-115. 1942.