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Preparation of Products from Milk Treated with Cationic Resin for Removing Radionuclides from Milk
Preparation of Products from Milk Treated with Cationic Resin for Removing Radionuclides from Milk G. K. MURTHY Environmental Control Administration, Department of Health, Education, and Welfare Cincinnati, Ohio 45202 Experimental Procedures
Abstract
Standard procedures were employed to make cultured milk, butter, and Cheddar cheese from resin-treated milk that had been acidified to p t I 5.35 with citric acid, passed through IR-120 (Ca :3/fg :K :Na) resin, and neutralized to p i t 6.8 with K O t t . A portion of the untreated milk served as the control. When Cheddar cheese was prepared from the treated milk, the proeedure varied: About 6 ml of ~ CaC12 per liter of milk were added and the curd cooked at 36.5 C. Comparison of test results for the treated samples with those for the controls showed that because of excess citric acid, proper selection of cultures is necessary to obtain good-quality cultured milk having comparable diacetyl content and flavor. A shortterm test on keeping" quality of butter stored at room temperature revealed that resintreated samples had better keeping quality. This is attributed to a slight depletion of copper content of milk as a result of resin treatment and presence in the butter sera of excess citric acid, which behaves like a synergist. Other than a slight improvement in the flavor, no significant differences in some of the observed physical and chemical properties of Cheddar cheese were noted. Previously we reported (8) that when milk was subjected to a cationic radionuclide removal process, the distribution of calcium, phosphorus, and nitrogen between the casein micelles and the serum phases was drastically altered. The milk was not coagulable by rennin and alcohol. Therefore, modification of calcium content and manufacturing procedures of certain milk products may be necessary to obtain satisfactory end products. The present investigation was undertaken to determine the feasibility of using milk treated with cationic resin to p r e p a r e such products as butter, cultured milk, and Cheddar cheese. Some of the properties of the control and the experimental samples were compared. ~eceived for publication October 18, 1968. 629
Materials. The milk samples were obtained on the Cincinnati, Ohio, market. The buttermilk and cheese cultures were of commercial s origin (Meyer-Blanke Co. St. Louis, Missouri). Before using the dry cultures, they were activated by two to three transfers in sterile skimmilk incubated at 21 C for 16 hr. Procedure. Treatment of milk with the cation exchange resin [IR-120 ( C a : S f g : K : N a ) ] has been described (10). Portions of the control and the resin-treated samples of milk were separated into 30% cream and skimmilk. Whole milk, skimmilk, and cream were used to standardize milk of known fat and solids content. All smnples were pasteurized at 62.8 C for 30 rain before preparing the products. Butter. Cream was adjusted to 10.5 C and churned in a W a r i n g Blendor to separate the butter. The butter was washed twice in cold, previously boiled, deionlzed water, and the excess water removed by worldng with a stainless steel spatula. The butter sample was divided into portions, placed in a l l 2 - g sterile jars, and stored in the dark at 21 C and in normM light at 23.5 to 25 C. Aliquots of butter were removed at intervals and analyzed for peroxide value and organoleptic quality. Cultured mille. The cultured milk was prepared from whole milk according to the method described by Foster et al. (5), using active cultures at 1 and 2% levels. These cultures were initially prepared from dlw cultures as indicated before. Before determining diacetyl content and organoleptic quality, the samples were stored at 4 C. Cheddar cheese. Cheddar cheese was prepared from milk showing negative penicillinase activity. After standardizing milk for proper fat and casein content., the rennet coagulation test was made to determine the amount of CaC12 required to obtain a coagulum similar to that obtained with the control sample (8). F o u r liters of milk were used for cheese making as per standard procedure (12). The milk, after pasteurization, was brought to
1 Mention of a commercial product does not imply endorsement by the Department of Health, Education, and Welfare.
630
MURTHY
30 C, or if the milk was held in the refrigerator, it was warmed to 40 C and then cooled to 30 C before adding the culture to avoid losses of fat during processing. The resin-treated sample was modified; the appropriate amount, as indicated by test, of ~ CaCI 2 p e r liter of milk was added just before adding the culture, and the cooking temperature of curd was 36.5 instead of 38.5 C. A f t e r salting, the curd was placed in a plunger-equipped Leucite cylinder (6.5 by 2.5 cm) with a perforated bottom. There it was left overnight with a 9-kg lead brick weighing down on top of the plunger. Next day the cheese was removed from the cylinder, a portion of horizontal section cut out for analyses, and the remainder dressed, paraffined, and cured in the refrigerator at 10 to 12 C. The initial analyses included moisture, acidity, fat, total solids, calcium, total phosphorus, and citric acid. A t the end of the six-month curing period, the cheese samples were analyzed for acidity, organoleptic quality, p H , and acetic, butyric, eaproic, and total higher f a t t y acids. Analytical methods. Throughout this investigation the following methods were used: for the pH, a Beckman Model Zeromatic p H meter; for the titratable acidity, milk fat, moisture, and total solids contents, methods described in Standard Methods for the Examination of Dairy Products ( 1 ) ; for the cationic and anionic composition of milk and its products, previously described methods (1, 2, 4, 7, 9) ; for the casein content of milk, Walker's titration method (13); for the diacetyl content, the colorimetrie method of Prill and Hammer (11) ; for the peroxide value, a determination according to Hills and Thiel ( 6 ) ; and for acetic, butyric, caproie, and total higher f a t t y acids of cheese samples, the method of Bills and Day (3). Results and Discussion
Cultured milk. Table 1 presents data on titratable acidity and diacetyl content of cultured milk prepared from control and resintreated milks. The diaeetyl content of samples varied slightly with the type of culture used. Control samples prepared with Cultures B-1 and B-2 showed diacetyl contents of 1.70 to 2.18 and 3.18 to 3.23 ppm, respectively, and treated samples, contents of 0.91 to 1.52 and 1.94 to 2.16 ppm, respectively. They had good flavor and taste. Control samples prepared with Cultures B-3 showed diacetyl contents of 1.74 to 2.28 p p m and treated samples, 10.96 to 11.25 ppm. High diacetyl contents of the treated samples resulted in frothing because of carbon g. DAIRY SCIEI~CE VOL. 52, NO.
TABLE 1. Titratable acidity and diacetyI content of cultured milk made from control and resin-treated milks, a
Sample
Cnlture b
Control
B-1
Treated
B-1
Control
B-2
Treated
B-2
Control
B-3
Treated
B-3
TitratInocu- able lure acidity c 1 2 1 2 1 2 1 2 1 2 1 2
(%) 0.77 0.84 0.80 0.83 0.80 0.81 0.82 0.84 0.82 0.85 0.85 0.87
Diacetyl c (ppm) 1.70 2.18 0.91 1.52 3.18 3.23 1.94 2.16 2.28 1.74 11.25 10.96
a Milk fat, 3.4%; total solids, 11.5%. b Source: Meyer-Blanke Co., St. Louis, Missouri. ¢ Average of two samples. dioxide. The samples were not palatable and exhibited a strong aroma. Normally, the resintreated milk contained 3.8 to 4.0 g citric acid per liter, whereas, the control had 1.6 to 1.8 g. I f the culture contained citrate-fermenting bacteria, the high citrate, naturally, was responsible for the increased diaeetyl and carbon dioxide. Unfortunately, the microbial floras of the cultures used in these studies were not ascertainable from the manufacturer and no attempt was made to identify the cultures in the laboratory. The data, however, indicate that with properly selected cultures, cultured milk can be prepared satisfactorily from the resin-treated milk. Butter. I n Fig. 1, averaged data (two samples) are presented of the keeping quality of butter stored at room temperature. There was no significant difference between the peroxide value of salted butter made from the control and from the resin-treated milks. Flavor defect was observed after five and seven days of storage, respectively. I n unsalted samples, the peroxide of control butter increased from 0.12 to 1.90 in 13 days and the off-flavor was evident after two days; whereas, with the treated sample, the peroxide increased from 0.16 to 0.80 during the same period and the off-flavor was evident after five days. Analyses of butter sera showed citric acid content of 58 mg per ]00 g of butter for the control sample and 180 mg for the treated sample. The
RESIN-TREATED MILK
631
TABbE 2. Some of the chemical and physical properties of laboratory-prepared milk and cheese, a Sample
Tests
Control
Treated
Milk
pH Titratable acidity (%) F a t (%) Casein ( % )
6.81 0.16 3.20 2.23
6.88 0.19 3.20 2.24
Cheese culture b
Titratable acidity (%)
0.75
0.75
Whey
Titratable acidity after cutting curd ( % ) Temperature of cooking (C) p H at milling F a t (%)
0.11 38.5 5.30 0.18
0.15 36.5 5.37 0.22
Green cheese
Total phosphorus (%) Total calcium ( % ) Citric acid (%)
Cured cheese
Age (months) pH Moisture ( % ) Titratable acidity (%) Fat (%) Acetic acid (meqfkg) Butyric acid (meq/kg) Caproic acid (meq/kg) Total higher fatty acids (meq/kg)
0.486 0.712 0.193 6 5.O9 36.0 1.15 33.3 2.74 1.78 0.35 7.65
0.380 0.545 0.277 6 5.24 37.8 1.19 31.0 2.72 1.90 0.50 8.05
a Average of two samples. b Source: Meyer-Blanke Co., St. Louis, Missouri. copper content of corresponding control and resin-treated milk samples was 0.046 and 0.037 ppm, respectively. A plausible explanation for the better keeping quality of butter from the resin-treated milk is related to a slight depletion in the copper content of the milk and to the presence of excess citric acid, which probably acts like a synergist. Butter samples stored in the dark at 21 C had peroxide values of less than 0.21 and there were no significant differences among samples over a period of 16 days. Some flavor defect was noticed at the end of ten days. These data indicate that butter samples of satisfactory quality may be prepared from resin-treated nfilk. Cheddar cheese. Several trials were made to determine the step modification necessary to obtain satisfactory product from the resintreated milk. When cheese was made according to the standard procedure, including adding CaC12 after cooking the curd and draining the whey, there was slight toughness and shrinkage of curd. Attempts to correct the curd toughness were ineffective until the cooking temperature was reduced from 38.5 to
36.5 C. With this modification, the resulting curd was comparable to that obtained from the control sample cooked at 38.5 C. Two sets of cheese samples were prepared, and some of their physical and chemical properties are presented in Table 2. When compared with the control cheese, the treated sample showed about 2% loss in fat, based on total solids content. In green cheese, the decreases of total calcium and phosphorus contents were from 71.2 to 54.5 mg and 48.6 to 38.0 rag, respectively. These decreases are small compared with the previous finding that resin treatment of milk drastically increa,ses the serum calcium and phosphorus contents (8). Addition of CaC12 to milk causes some binding" of calcium with the casein. The citric acid content increased from 19.3 to 27.7 rag, and this exists possibly as a Ca-eitrate-proteinate complex. No significant differences were observed in the acetic, butyric, caproie, and total higher fatty acids content of eontrol and the treated samptes. The acetic acid content was rather low compared with the data published in the literature (3). Laboratory conditions for preff. DAII~Y SCIENCE VOL, 52, NO,. 5
632
MURTHY 2.0
I
i
References
I
(1)
A
(2) (3) (4) (5)
(6)
o.o
I 4
I 8
I 12
16
(7)
DAYS
PIG. 1. Keeping quality of butter at room temperature. A, Control, unsalted; B, Treated, unsalted; C, Control, salted; D, Treated, salted; E, all samples at 21 C in dark. p a r i n g a n d c u r i n g cheese samples, however, a r e n o t ideal, a n d the m a i n p u r p o s e of this s t u d y was to find i f s a t i s f a c t o r y cheese could be p r e p a r e d f r o m r e s i n - t r e a t e d milk. O r g a n o leptic e x a m i n a t i o n s indicated t h a t t h e samples of cheese were mild in flavor a n d taste. The flavor of cheese f r o m t r e a t e d milk was p r e f erable to the control sample.
(8) (9) (10)
(11)
(12) Acknowledgment
The author is grateful to Dr. J. E. Campbell for his interest in the problem and to A. J. Wehby for his technical help.
J. D A Z R Y S C I E N C E VOW. 52, NO. 5
(13)
American
Public
Health
Association.
1960.
Standard Methods for the Examination of Dairy Products. l l t h ed. New York. Association of Official Agricultural Chemists. 1955. Official Methods of Analyses. 8th ed., p. 8. Washington, D.C. Bills, D. C., and E. A. Day. 1964. Determination of the major free f a t t y acids of Cheddar cheese. J. Dairy Sci., 47: 733. Fiske, C. H., and Y. Subbarow. 1925. Colorimetric determination of phosphorus. J. Biol. Chem., 66: 375. Poster, E. M., P. E. Nelson, M. L. Speck, R. N. Doetsch, and J. C. Olson. 1961. Dairy Microbiology. 2nd ed., p. 321. Prentice-Hall Inc., New Jersey. Hills, G. L., and C. C. Thieh 1946. The ferric thiocyanate method of estimating peroxide in the f a t of butter, milk and dried milk. J. Dairy Res., 14: 340. Marier, J. R., and M. Boulet. 1958. Direct determination of citric acid in milk with an improved pyridine-aeetie anhydride method. J. Dairy Sci., 41: 1683. Murthy, G. K. 1967. Effect of ion exchange resins o~ composition of milk and its fractions. J. Dairy Sci., 50: 809. Murthy, G. K., and R. McL. Whitney. 1956. A plan for the rapid determination of major cations in milk. J. Dairy Sci., 39: 364. Murthy, G. K., E. B. Masurovsky, J. E. Campbell, and L. P. Edmundson. 1961. Method for removing cationic radionuclides from milk. J. Dairy Sci., 44: 2158. Prill, E. A., and B. W. Hammer. 1937-38. A colorimetric method for the microdetermination of biacetyl. Iowa State Coll. J. Sci., 12 : 385. Yar~ Slyke, L. L., and W. V. Price. 1952. Cheese. pp. 156-261. Orange J u d d Publ. Co., New York. Walker, W. O. 1914. A rapid method for determining the percentage of casein in milk. Ind. Eng. Chem., 6: 131.
Abstract
Standard procedures were employed to make cultured milk, butter, and Cheddar cheese from resin-treated milk that had been acidified to p t I 5.35 with citric acid, passed through IR-120 (Ca :3/fg :K :Na) resin, and neutralized to p i t 6.8 with K O t t . A portion of the untreated milk served as the control. When Cheddar cheese was prepared from the treated milk, the proeedure varied: About 6 ml of ~ CaC12 per liter of milk were added and the curd cooked at 36.5 C. Comparison of test results for the treated samples with those for the controls showed that because of excess citric acid, proper selection of cultures is necessary to obtain good-quality cultured milk having comparable diacetyl content and flavor. A shortterm test on keeping" quality of butter stored at room temperature revealed that resintreated samples had better keeping quality. This is attributed to a slight depletion of copper content of milk as a result of resin treatment and presence in the butter sera of excess citric acid, which behaves like a synergist. Other than a slight improvement in the flavor, no significant differences in some of the observed physical and chemical properties of Cheddar cheese were noted. Previously we reported (8) that when milk was subjected to a cationic radionuclide removal process, the distribution of calcium, phosphorus, and nitrogen between the casein micelles and the serum phases was drastically altered. The milk was not coagulable by rennin and alcohol. Therefore, modification of calcium content and manufacturing procedures of certain milk products may be necessary to obtain satisfactory end products. The present investigation was undertaken to determine the feasibility of using milk treated with cationic resin to p r e p a r e such products as butter, cultured milk, and Cheddar cheese. Some of the properties of the control and the experimental samples were compared. ~eceived for publication October 18, 1968. 629
Materials. The milk samples were obtained on the Cincinnati, Ohio, market. The buttermilk and cheese cultures were of commercial s origin (Meyer-Blanke Co. St. Louis, Missouri). Before using the dry cultures, they were activated by two to three transfers in sterile skimmilk incubated at 21 C for 16 hr. Procedure. Treatment of milk with the cation exchange resin [IR-120 ( C a : S f g : K : N a ) ] has been described (10). Portions of the control and the resin-treated samples of milk were separated into 30% cream and skimmilk. Whole milk, skimmilk, and cream were used to standardize milk of known fat and solids content. All smnples were pasteurized at 62.8 C for 30 rain before preparing the products. Butter. Cream was adjusted to 10.5 C and churned in a W a r i n g Blendor to separate the butter. The butter was washed twice in cold, previously boiled, deionlzed water, and the excess water removed by worldng with a stainless steel spatula. The butter sample was divided into portions, placed in a l l 2 - g sterile jars, and stored in the dark at 21 C and in normM light at 23.5 to 25 C. Aliquots of butter were removed at intervals and analyzed for peroxide value and organoleptic quality. Cultured mille. The cultured milk was prepared from whole milk according to the method described by Foster et al. (5), using active cultures at 1 and 2% levels. These cultures were initially prepared from dlw cultures as indicated before. Before determining diacetyl content and organoleptic quality, the samples were stored at 4 C. Cheddar cheese. Cheddar cheese was prepared from milk showing negative penicillinase activity. After standardizing milk for proper fat and casein content., the rennet coagulation test was made to determine the amount of CaC12 required to obtain a coagulum similar to that obtained with the control sample (8). F o u r liters of milk were used for cheese making as per standard procedure (12). The milk, after pasteurization, was brought to
1 Mention of a commercial product does not imply endorsement by the Department of Health, Education, and Welfare.
630
MURTHY
30 C, or if the milk was held in the refrigerator, it was warmed to 40 C and then cooled to 30 C before adding the culture to avoid losses of fat during processing. The resin-treated sample was modified; the appropriate amount, as indicated by test, of ~ CaCI 2 p e r liter of milk was added just before adding the culture, and the cooking temperature of curd was 36.5 instead of 38.5 C. A f t e r salting, the curd was placed in a plunger-equipped Leucite cylinder (6.5 by 2.5 cm) with a perforated bottom. There it was left overnight with a 9-kg lead brick weighing down on top of the plunger. Next day the cheese was removed from the cylinder, a portion of horizontal section cut out for analyses, and the remainder dressed, paraffined, and cured in the refrigerator at 10 to 12 C. The initial analyses included moisture, acidity, fat, total solids, calcium, total phosphorus, and citric acid. A t the end of the six-month curing period, the cheese samples were analyzed for acidity, organoleptic quality, p H , and acetic, butyric, eaproic, and total higher f a t t y acids. Analytical methods. Throughout this investigation the following methods were used: for the pH, a Beckman Model Zeromatic p H meter; for the titratable acidity, milk fat, moisture, and total solids contents, methods described in Standard Methods for the Examination of Dairy Products ( 1 ) ; for the cationic and anionic composition of milk and its products, previously described methods (1, 2, 4, 7, 9) ; for the casein content of milk, Walker's titration method (13); for the diacetyl content, the colorimetrie method of Prill and Hammer (11) ; for the peroxide value, a determination according to Hills and Thiel ( 6 ) ; and for acetic, butyric, caproie, and total higher f a t t y acids of cheese samples, the method of Bills and Day (3). Results and Discussion
Cultured milk. Table 1 presents data on titratable acidity and diacetyl content of cultured milk prepared from control and resintreated milks. The diaeetyl content of samples varied slightly with the type of culture used. Control samples prepared with Cultures B-1 and B-2 showed diacetyl contents of 1.70 to 2.18 and 3.18 to 3.23 ppm, respectively, and treated samples, contents of 0.91 to 1.52 and 1.94 to 2.16 ppm, respectively. They had good flavor and taste. Control samples prepared with Cultures B-3 showed diacetyl contents of 1.74 to 2.28 p p m and treated samples, 10.96 to 11.25 ppm. High diacetyl contents of the treated samples resulted in frothing because of carbon g. DAIRY SCIEI~CE VOL. 52, NO.
TABLE 1. Titratable acidity and diacetyI content of cultured milk made from control and resin-treated milks, a
Sample
Cnlture b
Control
B-1
Treated
B-1
Control
B-2
Treated
B-2
Control
B-3
Treated
B-3
TitratInocu- able lure acidity c 1 2 1 2 1 2 1 2 1 2 1 2
(%) 0.77 0.84 0.80 0.83 0.80 0.81 0.82 0.84 0.82 0.85 0.85 0.87
Diacetyl c (ppm) 1.70 2.18 0.91 1.52 3.18 3.23 1.94 2.16 2.28 1.74 11.25 10.96
a Milk fat, 3.4%; total solids, 11.5%. b Source: Meyer-Blanke Co., St. Louis, Missouri. ¢ Average of two samples. dioxide. The samples were not palatable and exhibited a strong aroma. Normally, the resintreated milk contained 3.8 to 4.0 g citric acid per liter, whereas, the control had 1.6 to 1.8 g. I f the culture contained citrate-fermenting bacteria, the high citrate, naturally, was responsible for the increased diaeetyl and carbon dioxide. Unfortunately, the microbial floras of the cultures used in these studies were not ascertainable from the manufacturer and no attempt was made to identify the cultures in the laboratory. The data, however, indicate that with properly selected cultures, cultured milk can be prepared satisfactorily from the resin-treated milk. Butter. I n Fig. 1, averaged data (two samples) are presented of the keeping quality of butter stored at room temperature. There was no significant difference between the peroxide value of salted butter made from the control and from the resin-treated milks. Flavor defect was observed after five and seven days of storage, respectively. I n unsalted samples, the peroxide of control butter increased from 0.12 to 1.90 in 13 days and the off-flavor was evident after two days; whereas, with the treated sample, the peroxide increased from 0.16 to 0.80 during the same period and the off-flavor was evident after five days. Analyses of butter sera showed citric acid content of 58 mg per ]00 g of butter for the control sample and 180 mg for the treated sample. The
RESIN-TREATED MILK
631
TABbE 2. Some of the chemical and physical properties of laboratory-prepared milk and cheese, a Sample
Tests
Control
Treated
Milk
pH Titratable acidity (%) F a t (%) Casein ( % )
6.81 0.16 3.20 2.23
6.88 0.19 3.20 2.24
Cheese culture b
Titratable acidity (%)
0.75
0.75
Whey
Titratable acidity after cutting curd ( % ) Temperature of cooking (C) p H at milling F a t (%)
0.11 38.5 5.30 0.18
0.15 36.5 5.37 0.22
Green cheese
Total phosphorus (%) Total calcium ( % ) Citric acid (%)
Cured cheese
Age (months) pH Moisture ( % ) Titratable acidity (%) Fat (%) Acetic acid (meqfkg) Butyric acid (meq/kg) Caproic acid (meq/kg) Total higher fatty acids (meq/kg)
0.486 0.712 0.193 6 5.O9 36.0 1.15 33.3 2.74 1.78 0.35 7.65
0.380 0.545 0.277 6 5.24 37.8 1.19 31.0 2.72 1.90 0.50 8.05
a Average of two samples. b Source: Meyer-Blanke Co., St. Louis, Missouri. copper content of corresponding control and resin-treated milk samples was 0.046 and 0.037 ppm, respectively. A plausible explanation for the better keeping quality of butter from the resin-treated milk is related to a slight depletion in the copper content of the milk and to the presence of excess citric acid, which probably acts like a synergist. Butter samples stored in the dark at 21 C had peroxide values of less than 0.21 and there were no significant differences among samples over a period of 16 days. Some flavor defect was noticed at the end of ten days. These data indicate that butter samples of satisfactory quality may be prepared from resin-treated nfilk. Cheddar cheese. Several trials were made to determine the step modification necessary to obtain satisfactory product from the resintreated milk. When cheese was made according to the standard procedure, including adding CaC12 after cooking the curd and draining the whey, there was slight toughness and shrinkage of curd. Attempts to correct the curd toughness were ineffective until the cooking temperature was reduced from 38.5 to
36.5 C. With this modification, the resulting curd was comparable to that obtained from the control sample cooked at 38.5 C. Two sets of cheese samples were prepared, and some of their physical and chemical properties are presented in Table 2. When compared with the control cheese, the treated sample showed about 2% loss in fat, based on total solids content. In green cheese, the decreases of total calcium and phosphorus contents were from 71.2 to 54.5 mg and 48.6 to 38.0 rag, respectively. These decreases are small compared with the previous finding that resin treatment of milk drastically increa,ses the serum calcium and phosphorus contents (8). Addition of CaC12 to milk causes some binding" of calcium with the casein. The citric acid content increased from 19.3 to 27.7 rag, and this exists possibly as a Ca-eitrate-proteinate complex. No significant differences were observed in the acetic, butyric, caproie, and total higher fatty acids content of eontrol and the treated samptes. The acetic acid content was rather low compared with the data published in the literature (3). Laboratory conditions for preff. DAII~Y SCIENCE VOL, 52, NO,. 5
632
MURTHY 2.0
I
i
References
I
(1)
A
(2) (3) (4) (5)
(6)
o.o
I 4
I 8
I 12
16
(7)
DAYS
PIG. 1. Keeping quality of butter at room temperature. A, Control, unsalted; B, Treated, unsalted; C, Control, salted; D, Treated, salted; E, all samples at 21 C in dark. p a r i n g a n d c u r i n g cheese samples, however, a r e n o t ideal, a n d the m a i n p u r p o s e of this s t u d y was to find i f s a t i s f a c t o r y cheese could be p r e p a r e d f r o m r e s i n - t r e a t e d milk. O r g a n o leptic e x a m i n a t i o n s indicated t h a t t h e samples of cheese were mild in flavor a n d taste. The flavor of cheese f r o m t r e a t e d milk was p r e f erable to the control sample.
(8) (9) (10)
(11)
(12) Acknowledgment
The author is grateful to Dr. J. E. Campbell for his interest in the problem and to A. J. Wehby for his technical help.
J. D A Z R Y S C I E N C E VOW. 52, NO. 5
(13)
American
Public
Health
Association.
1960.
Standard Methods for the Examination of Dairy Products. l l t h ed. New York. Association of Official Agricultural Chemists. 1955. Official Methods of Analyses. 8th ed., p. 8. Washington, D.C. Bills, D. C., and E. A. Day. 1964. Determination of the major free f a t t y acids of Cheddar cheese. J. Dairy Sci., 47: 733. Fiske, C. H., and Y. Subbarow. 1925. Colorimetric determination of phosphorus. J. Biol. Chem., 66: 375. Poster, E. M., P. E. Nelson, M. L. Speck, R. N. Doetsch, and J. C. Olson. 1961. Dairy Microbiology. 2nd ed., p. 321. Prentice-Hall Inc., New Jersey. Hills, G. L., and C. C. Thieh 1946. The ferric thiocyanate method of estimating peroxide in the f a t of butter, milk and dried milk. J. Dairy Res., 14: 340. Marier, J. R., and M. Boulet. 1958. Direct determination of citric acid in milk with an improved pyridine-aeetie anhydride method. J. Dairy Sci., 41: 1683. Murthy, G. K. 1967. Effect of ion exchange resins o~ composition of milk and its fractions. J. Dairy Sci., 50: 809. Murthy, G. K., and R. McL. Whitney. 1956. A plan for the rapid determination of major cations in milk. J. Dairy Sci., 39: 364. Murthy, G. K., E. B. Masurovsky, J. E. Campbell, and L. P. Edmundson. 1961. Method for removing cationic radionuclides from milk. J. Dairy Sci., 44: 2158. Prill, E. A., and B. W. Hammer. 1937-38. A colorimetric method for the microdetermination of biacetyl. Iowa State Coll. J. Sci., 12 : 385. Yar~ Slyke, L. L., and W. V. Price. 1952. Cheese. pp. 156-261. Orange J u d d Publ. Co., New York. Walker, W. O. 1914. A rapid method for determining the percentage of casein in milk. Ind. Eng. Chem., 6: 131.