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Preliminary Observations on the Effect of Slight Proteolysis of Fluid Milk on Wettability of the Resulting Dried Milk1
444
Z O U a N A L OF D A I R Y S C I E N C E
P R E L I M I N A R Y OBSERVATIONS ON T H E E F F E C T OF SLIGHT P R O T E O L Y S I S OF F L U I D MILK ON W E T T A B I L I T Y OF T H E RESULTING D R I E D MILK 1 I n 1898 Bachaus (2) described a procedure for the production of soft curd milk, which involved treatment of the milk with proteolytie enzymes. Conquest et al. (3) and others (7, 10) have also carried out further work in this connection. Tarassuk and Nury (11) subjected evaporated milk to a limited enzymatic proteolysis and observed a marked increase in the viscosity of the milk after subsequent sterilization. The increase in the viscosity was found to be directly related to the lowering of the stability of the milk towards heat. Several workers have shown that mild treatment of milk with proteolytic enzymes before pasteurization gives some protection against the development of oxidized flavors (1, 4, 5). This paper reports the results of preliminary experiments on the effects of treating fluid milk with proteolytic enzymes, prior to drying, on the wettability of whole milk powder. The fat content of freshly drawn milk (3.8% milkfat) was adjusted to 3.3% with skimmilk. Three 500-ml. portions of this milk were treated with Rhozyme P l l (Rhom and Haas) under the following conditions: The temperatures of samples 1, 2, and 3 were adjusted to 60 ° C., 65 ° C., and 70 ° C., respectively, before the addition of the enzyme (0.17 g; 1% of milk protein). The temperatures were then increased at the rate of one degree per minute until a temperature of 75 ° C. was reached. This temperature was maintained for 15 minutes. A fourth sample, which served as a control, was heated to 60 ° C., and the temperature was raised to 75 ° C. at the rate of one degree per minute and was maintained at this temperature for 15 minutes before cooling. The viscosity of the four samples did not differ appreciably. A taste panel (9) showed a slight preference for the milk that had been treated at 60 ° C. (Sample 1). This prefer-
ence indicated that Sample 1 had a more creamlike flavor. The tyrosine values (6, 10) expressed as milligrams tyrosine per liter were as follows: control, 24; Sample 1, 54; Sample 2, 46; Sample 3, 32. One hundred pounds of milk was divided into two equal portions. One was heated to 60 ° C., Rhozyme P l l (7.94 g.) was added to one 50-lb. portion (treated milk) and no enzyme was added to the other portion. The milk was heated by the same procedure as that followed with Sample 1 of the previous experiment. After the heating period, the milk was cooled to 60 ° C. and was homogenized at 2,300 lb. pressure, before condensing it in a vacuum pan to approximately 36% solids. The milk was dried in a laboratory-type, Niro Spray Drier operated under the following conditions: air pressure on the atomizer 6.0-6.5 kg/cm2; inlet air temperature, 190°-200 ° C.; outlet temperature, 850-95 ° C. Table 1 shows the moisture content (8), the solubility index (ADMI), the tyrosine value, and the taste rating of the two samples. The following procedure was used to check the wettability of the two samples: 10 g. of milk powder was placed on the surface of water at 25 ° C. in a 250-ml. cylinder. Photographs were taken immediately after the addition of the powder (Figure l a ) , 30 minutes after the addition (Figure l b ) , and 1 hour after the addition (Figure le). The photographs show that the treated ~ample was appreciably more wettable than the untreated sample. The results of this experiment were confirmed in detail by complete repetition of the work on two other occasions. The results of this investigation show that the wettability of milk powder may be improved by treatment of the milk, prior to dryrag, with proteolytic enzymes. The mild enzyme treatment would affect primarily the 1Contribution from the Faculty of Agriculture, surface of the protein molecule (10). Such McGill University, Macdonald College, Que., changes in the surface of the molecule would Canada. Journal Series No. 396. be likely to alter its hydrophilic properties, and TABLE 1
The effects of enzyme treat~nent on the properties of whole ,milk powder Moisture content
Solubility index (ADMI)
Tyrosine value (Mg. Tyrosine/ liter)
Taste criticism
Treated
2.1
0.4 ml.
55
Untreated
2.0
0.3 ml.
23
1. Less chalky tasting and more creamy than untreated sample 2. Taste indistinguishable from that of freshly prepared, commercial whole milk powder
Dried milk
TECHNICAL NOTES
(a) Immediately
(b) 30 minutes
445
(e) One hour
Fro. 1. The effect of enzymic treatment on the wettability of whole milk powder. The cylinder on the left in each photograph contains the untreated sample, and the one on the right, the treated sample. the p r e s e n t observations suggest t h a t , of these p r o p e r t i e s , the w e t t a b i l i t y is a p p r e c i a b l e a n d a d v a n t a g e o u s l y nmdified. ACKNOWLEDGMENTS The a u t h o r s wish to t h a n k the Quebec Research Council a n d t h e D e p a r t m e n t of N a t i o n a l Defense f o r r e s e a r c h g r a n t s which have def r a y e d p a r t of the expense of this investigation. One of the a u t h o r s ( J . P . J . ) wishes to t h a n k the G r a n b y Co-op., P. Q., f o r a fellowship. J. P. JULIEN
Dairy School, St. Hyacinthe, P. Q., Canada AND B. E. BAKER
Department of Agricultural Chemistry, Macdonald College, P. Q., Canada REFERENCES (1) ANDERSON, E. O. Preventing Development of Oxidized Flavour in Milk. Milk Dealer, 29, 3: 32. 1939. (2) ]~ACHAUS, ALI~XANDER. P r e p a r i n g Cow's Milk for I n f a n t s . U. S. P a t e n t 597, 378, Jan. 18, 1898. (3) CONQUZST, V., TURNER, A. W., AND RI~YNOLDS, H. J. Soft Curd Milk Produced with Pancreatic Concentrate. J. Dairy Sei., 21: 361. 1938.
(4) CORBETT, W. J., .eND T~CY, P. H. Experiments on the Use of Certain Antioxidants for Control of Oxidizing Flavor in Dairy Products. Food Research, 5: 445. 1941. (5) FORSTF~R, T. L., JENSEN, C., AND PLATHE~ EMILY. Influence of Protein Hydrolysis on the Susceptibility of Milk ~o Oxidized Flavor Development. J. Dairy Sci., 36: 98. 1953. (6) HULL, M. E. Studies on Milk Proteins. I I . Colorimetric Determination of the Partial Hydrolysis of the Proteins in Milk. J. Dairy Sci., 30: 881. 1947. (7) KEIL, H. a., AND ROUNDY, Z. D. Studies on Milk Proteins. I. Conditioning of Milk Proteins with Pancreatic Enzymes. J. Dairy Sci., 30: 877. 1947. (8) MARTIN, G., AND JULIEN, J. P. D~termination Rapide de l'Humidit6 dans la Poudre de Lair au Moyen des Rayons Infrarouges. Le Quebec Laitier, 13, 3: 14. 1954. (9) MURI~AY, T. K., AND BAKER, B. E. Studies on Protein Hydrolysis. I. Preliminary Observations on the Taste of Enzymic Protein-Hydrolysates. J. Sci. Food and Agriculture, 3: 470. 1952. (10) STolms, A. B. Studies on Milk Proteins. I I I . The Modification of Milk by Pancreatic Enzymes. J. Dairy Sci., 30: 885. 1947. (]1) TAR.A-SSUK, N. P., AND NURY, M. S. Effect of Incipient Enzymatic Proteolysis on the Viscosity and Heat Stability of Evaporated Milk. J. Dairy Sei., 35: 857. 1952.
Z O U a N A L OF D A I R Y S C I E N C E
P R E L I M I N A R Y OBSERVATIONS ON T H E E F F E C T OF SLIGHT P R O T E O L Y S I S OF F L U I D MILK ON W E T T A B I L I T Y OF T H E RESULTING D R I E D MILK 1 I n 1898 Bachaus (2) described a procedure for the production of soft curd milk, which involved treatment of the milk with proteolytie enzymes. Conquest et al. (3) and others (7, 10) have also carried out further work in this connection. Tarassuk and Nury (11) subjected evaporated milk to a limited enzymatic proteolysis and observed a marked increase in the viscosity of the milk after subsequent sterilization. The increase in the viscosity was found to be directly related to the lowering of the stability of the milk towards heat. Several workers have shown that mild treatment of milk with proteolytic enzymes before pasteurization gives some protection against the development of oxidized flavors (1, 4, 5). This paper reports the results of preliminary experiments on the effects of treating fluid milk with proteolytic enzymes, prior to drying, on the wettability of whole milk powder. The fat content of freshly drawn milk (3.8% milkfat) was adjusted to 3.3% with skimmilk. Three 500-ml. portions of this milk were treated with Rhozyme P l l (Rhom and Haas) under the following conditions: The temperatures of samples 1, 2, and 3 were adjusted to 60 ° C., 65 ° C., and 70 ° C., respectively, before the addition of the enzyme (0.17 g; 1% of milk protein). The temperatures were then increased at the rate of one degree per minute until a temperature of 75 ° C. was reached. This temperature was maintained for 15 minutes. A fourth sample, which served as a control, was heated to 60 ° C., and the temperature was raised to 75 ° C. at the rate of one degree per minute and was maintained at this temperature for 15 minutes before cooling. The viscosity of the four samples did not differ appreciably. A taste panel (9) showed a slight preference for the milk that had been treated at 60 ° C. (Sample 1). This prefer-
ence indicated that Sample 1 had a more creamlike flavor. The tyrosine values (6, 10) expressed as milligrams tyrosine per liter were as follows: control, 24; Sample 1, 54; Sample 2, 46; Sample 3, 32. One hundred pounds of milk was divided into two equal portions. One was heated to 60 ° C., Rhozyme P l l (7.94 g.) was added to one 50-lb. portion (treated milk) and no enzyme was added to the other portion. The milk was heated by the same procedure as that followed with Sample 1 of the previous experiment. After the heating period, the milk was cooled to 60 ° C. and was homogenized at 2,300 lb. pressure, before condensing it in a vacuum pan to approximately 36% solids. The milk was dried in a laboratory-type, Niro Spray Drier operated under the following conditions: air pressure on the atomizer 6.0-6.5 kg/cm2; inlet air temperature, 190°-200 ° C.; outlet temperature, 850-95 ° C. Table 1 shows the moisture content (8), the solubility index (ADMI), the tyrosine value, and the taste rating of the two samples. The following procedure was used to check the wettability of the two samples: 10 g. of milk powder was placed on the surface of water at 25 ° C. in a 250-ml. cylinder. Photographs were taken immediately after the addition of the powder (Figure l a ) , 30 minutes after the addition (Figure l b ) , and 1 hour after the addition (Figure le). The photographs show that the treated ~ample was appreciably more wettable than the untreated sample. The results of this experiment were confirmed in detail by complete repetition of the work on two other occasions. The results of this investigation show that the wettability of milk powder may be improved by treatment of the milk, prior to dryrag, with proteolytic enzymes. The mild enzyme treatment would affect primarily the 1Contribution from the Faculty of Agriculture, surface of the protein molecule (10). Such McGill University, Macdonald College, Que., changes in the surface of the molecule would Canada. Journal Series No. 396. be likely to alter its hydrophilic properties, and TABLE 1
The effects of enzyme treat~nent on the properties of whole ,milk powder Moisture content
Solubility index (ADMI)
Tyrosine value (Mg. Tyrosine/ liter)
Taste criticism
Treated
2.1
0.4 ml.
55
Untreated
2.0
0.3 ml.
23
1. Less chalky tasting and more creamy than untreated sample 2. Taste indistinguishable from that of freshly prepared, commercial whole milk powder
Dried milk
TECHNICAL NOTES
(a) Immediately
(b) 30 minutes
445
(e) One hour
Fro. 1. The effect of enzymic treatment on the wettability of whole milk powder. The cylinder on the left in each photograph contains the untreated sample, and the one on the right, the treated sample. the p r e s e n t observations suggest t h a t , of these p r o p e r t i e s , the w e t t a b i l i t y is a p p r e c i a b l e a n d a d v a n t a g e o u s l y nmdified. ACKNOWLEDGMENTS The a u t h o r s wish to t h a n k the Quebec Research Council a n d t h e D e p a r t m e n t of N a t i o n a l Defense f o r r e s e a r c h g r a n t s which have def r a y e d p a r t of the expense of this investigation. One of the a u t h o r s ( J . P . J . ) wishes to t h a n k the G r a n b y Co-op., P. Q., f o r a fellowship. J. P. JULIEN
Dairy School, St. Hyacinthe, P. Q., Canada AND B. E. BAKER
Department of Agricultural Chemistry, Macdonald College, P. Q., Canada REFERENCES (1) ANDERSON, E. O. Preventing Development of Oxidized Flavour in Milk. Milk Dealer, 29, 3: 32. 1939. (2) ]~ACHAUS, ALI~XANDER. P r e p a r i n g Cow's Milk for I n f a n t s . U. S. P a t e n t 597, 378, Jan. 18, 1898. (3) CONQUZST, V., TURNER, A. W., AND RI~YNOLDS, H. J. Soft Curd Milk Produced with Pancreatic Concentrate. J. Dairy Sei., 21: 361. 1938.
(4) CORBETT, W. J., .eND T~CY, P. H. Experiments on the Use of Certain Antioxidants for Control of Oxidizing Flavor in Dairy Products. Food Research, 5: 445. 1941. (5) FORSTF~R, T. L., JENSEN, C., AND PLATHE~ EMILY. Influence of Protein Hydrolysis on the Susceptibility of Milk ~o Oxidized Flavor Development. J. Dairy Sci., 36: 98. 1953. (6) HULL, M. E. Studies on Milk Proteins. I I . Colorimetric Determination of the Partial Hydrolysis of the Proteins in Milk. J. Dairy Sci., 30: 881. 1947. (7) KEIL, H. a., AND ROUNDY, Z. D. Studies on Milk Proteins. I. Conditioning of Milk Proteins with Pancreatic Enzymes. J. Dairy Sci., 30: 877. 1947. (8) MARTIN, G., AND JULIEN, J. P. D~termination Rapide de l'Humidit6 dans la Poudre de Lair au Moyen des Rayons Infrarouges. Le Quebec Laitier, 13, 3: 14. 1954. (9) MURI~AY, T. K., AND BAKER, B. E. Studies on Protein Hydrolysis. I. Preliminary Observations on the Taste of Enzymic Protein-Hydrolysates. J. Sci. Food and Agriculture, 3: 470. 1952. (10) STolms, A. B. Studies on Milk Proteins. I I I . The Modification of Milk by Pancreatic Enzymes. J. Dairy Sci., 30: 885. 1947. (]1) TAR.A-SSUK, N. P., AND NURY, M. S. Effect of Incipient Enzymatic Proteolysis on the Viscosity and Heat Stability of Evaporated Milk. J. Dairy Sei., 35: 857. 1952.