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Irradiated Milk: The Reflecting Properties and Antirachitic Activation as Affected by the Impingment Angle of the Incident Radiation
I R R A D I A T E D M I L K : T H E R E F L E C T I N G P R O P E R T I E S AND A N T I R A C H I T I C ACTIVATION AS A F F E C T E D BY T H E IMPINGMENT ANGLE OF T H E I N CID E N T RADIATION G. C. S U P P L E E
The Dry Mille Company I~esearch Laboratories, Bainbridge, New Yorl~ AND M. J . DORCAS
The 2Vational Carbon Company, Cleveland, Ohio
The relationship between the character and intensity of the ultra-violet radiation applied to milk films and the antirachitic potency imparted to the milk during momentary periods of exposure has been previously reported (1--4). Milk films 0.11 ram. thick transmit less than 5 per cent of the radi.ation below 2850 X ineident to the surface at an angle of 90 ° (2). Since the incident radiation may be transmitted, absorbed or reflected, the difference between the amount of energy applied and that transmitted does not necessarily indicate the amount absorbed. According to Drothus' law only absorbed radiation can cause photochemical change. It does not necessarily follow, however, that all the energy absorbed brings about photochemical reactions; much of the absorbed energy may be manifested as heat. If data are to be developed which will more adequately show the eharacter and the amount of radiant energy necessary for the most effective and efficient antirachitic activation of milk, it is necessary to know the degree to which the activating rays are reflected from milk surfaces. Such data are recorded in the present paper. EXPERIMENTAL
Vertical flowing milk films of known characteristics were formed with the apparatus described in an earlier paper (2). The carbon arc burning C type eleetl~odes at 60 amperes and 50 volts was used for supplying the beam of ultra-violet radiation. The speetroradiometer previously used was placed in such a position that a beam of the radiation reflected from the milk surface was reflected into the instrument. The amount of radiation received by the speetroradiometer compared with that received by the instrument placed in such a position that it received the same beam from the same source at the same optical distance without the intervening milk film, permitted the calculation of the percentage of energy reflected. Spectral or mirror refleetion from the surface of flowing milk films receiving the radiation at different an#es of incidence is shown by the curves in Chart I. (The angle of incidence as referred to in this paper is to be interpreted as Received for publication February 10, 1934.
6O7
608
0. C. SUPPLEE AND M. J. DORCAS
the angle between the surface of the milk and the incident radiation; a beam parallel to the milk surface being zero degrees and a beam intersecting the milk at right angles being indicated as 90 °.) In presenting these data it is recognized that in the visible portion of the spectrum there would be a certain degree of diffuse reflection originating at some distance below the
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CHART I The reflection of ultra-violet radiation from the surface of milk.
immediate surface of the milk. However, in view of the transmission data previously obtained, ~nd in view of the resul'ts shown by preliminary measurements, wherein it was found that diffuse reflection of the wave lengths under consideration were too weak to be measured with the apparatus
IRRADIATED MI LK
609
available, it is believed that the effect of this factor has been slight or even negligible in the results obtained. The reflection measurements shown by the graphs are the average of three separate determinations from whole milk films 0.11 ram. thick. Similar measurements from skimmed milk films were made for the 15 ° and 30 ° angle of incidence. The results showed that throughout the 2550-3000 -~ range the reflection from skim milk, although tending to parallel that of whole milk was from 1 to 2 per cent lower between 2550 and 2800 A, and from 2 to 8 per cent lower in the 2800 to 3000 /~ region. The reflection from the milk films compared with the reflection from the surface of water, calculated for the range of wave lengths and angles of incidence u n d e r consideration, shows that the reflection from both substances is of the same order of magnitude. However, the calculated reflection from water, as well as actual measurements from vertical flowing water films, shows that the water surface does not exhibit the selective reflection shown by milk. Since the transmission data has indicated a selective absorption of ultraviolet radiation by milk, selective reflection may be expected. In order to determine the possible significance of the reflection of ultraviolet radiation from milk surfaces on the antirachitic potency, milk films of known thickness and" flow characteristics were irradiated by radiation of known intensity impinging at different angles of incidence. The carbon arc of the same characteristics as was used for obtaining the reflection data was used for irradiating the milk films. The arc was placed 43 cm. from the center of the milk films having a width of 10 cm. The films were formed on the flow board mounted on a vertical central axis which permitted accurate change of the plane of flow with reference to the projected beam of radiation. Milks containing 1.2 per cent and 3.6 per cent butter fat were used. The biological assays were made by the usual methods, and the results recorded in the manner heretofore used (1-5). These results as well as those showing the amount of energy applied per cc. of milk are recorded in table 1. In determining the amount of energy applied to the milk film, the effect of the difference in angle of impingment was taken into consideration. Since the data do not p u r p o r t to show the amount of energy absorbed, that which was reflected has not been considered in the calculations. However, an approximation of the amount of energy absorbed m a y be calculated from the transmission data (2) in conjunction with that shown herein. An analysis of the reflection data shows that at an impingment angle of 75 ° from parallel, an average of 3.1 per cent of the incident radiation between 2550 and 3000 A is reflected; at an impingment angle of 45 ° from parallel an average of 2.9 per cent is reflected; at 30 ° , the average is 6.1 per cent; at 20 ° , 13.4 per cent is reflected; at 15 ° , 28 per cent; and at 10 °, 34 per cent.
610
G. C. C. SUPPLEE AND AND M. J. DORCAS DORCAS G.
resu}ts show that the reduction in intensity of the inciThe biological results dent radiation resulting from impinging impinging the energy at angles of incidence as low as 30° 30 ° from parallel parallel does not cause a reduction in antirachitic antir~chitic potency of the milk milk treated treated under the conditions used in these tests. At At potency impingmen¢ angles angles -of ,of 15° 15 ° there is definite evidence evidence of a reduction in antiimpingmenrt TABLE 1 TABLE
The vitamin D concentration concentration of milk mille a.s as affected by film thickness, thickness, film capacity, capacity, tat fat impi.ngment of incident incident 1'adiati
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3A190 3A175 3A160 3A145 3A130 3Al15 3A115
Milk,,, 1.2 1.2%,, Fat,, 34.02 34~02 Milk, % Fat
6A190 6A175 6A160 6A14-5 6Al45 6A130 6Al15 6A115
Milk,,, 1.2%,, :Pat,, 192178 Milk, 1.2% Fat 192.78
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Milk, 3.6% Fat
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8,945 8,945 8,640 8,640 7,746 6,325 4,472 2,282
11,851 11,851 11,446 11,446 10,103 10,].03 8,379 5,925 3,067 3,067
90 75 60 45 30 15
3,769 3,640 3,640 3,284 2,665 1,884 1,884 975
4,994 4,823 4,325 4,325 3,531 3,531 2,497 1,292 1,292
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Milk, 1.2% Fat
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1A190 1A190 IA175 1A175 IA160 1A160 IA145 1A145 1AI30 1A130 IAII5 1A115
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90 75 60 45 30 15
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90 75 60 45 30 15
3,769 3,769 3,640 3,640 3,284 3,284 2,665 2,665 1,884 I 1,884 975 I 975
90 75 60 45 30 15
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225 225 225 225 75 75
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80
90 9O
-
90
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56
30
150
30 3-0 30 30 70
150 150 150 64
4,994 4,994 4,823 4,823 4,325 4,325 3,531 3,531 2,497 2,497 1,292 1,292
20 26 20 20 20 20
225 225 225 225 225 225 225 225
30 30
150
1,288 1,288 1,244 1,244 1,115 1,115 910 644 644 333
35 35 35 35 35 35 35 35 50 5 O
128 128
11,851 11,851 11,446 11,446 10,103 10,103 8,379 8,379 5.925 5,925 3,067 31067
-
-
128 128 128 128 128 128 !28 90 90
IRRADIATED MILK
611
raehitie potency. The d a t a as a whole are considered as f u r t h e r confirmat o r y evidence s u p p o r t i n g the conclusion t h a t the synthesis of V i t a m i n D d u r i n g the irradiation of milk is essentially a surface reaction and t h a t in the practical t r e a t m e n t of milk with ultra-violet rays, conditions which facilitate the reaction at the surface are to be preferred. SUMMARY
1. The reflection of ultra-violet radiation f r o m the surf, ace of milk films is of the same order of m a g n i t u d e as the reflection of such radiation f r o m the surface of w a t e r ; the degree of reflection increases as t h e angle of incidence decreases. 2. Ultra-violet radiation between 2550 and 3000 A when impinged on milk surfaces ,at 75 ° and 45 ° f r o m parallel are reflected to about the same degree---approximately 3 per cent; the average percentage reflection f r o m a 30 ° angle of incidence is about 6 per cent; f r o m a 20 ° angle of incidence, 13.4 per cent; f r o m a 15 ° angle, 28 per cent; and f r o m a 10 ° angle, about 34 per cent. 3. Milk films show the p r o p e r t y of selective reflection of ultra-violet radiation, especially througtmut the range 2550 to 3300 2~. This p r o p e r t y is most pronounced at angles of incidence of 30 ° or less. 4. The antirachitic potency of milk irradiated with ultra-violet radiation ~triking milk films a t angles of incidence less than 90 ° and as low as 30 ° is the same as that obtained when the angle of incidence is 90 ° , other things being equal. REFERENCES
(1) SUPPhEE, G. C., BECK, H. I:[., AND DORCAS, .-V[. J. (2)
(3)
(4)
(5)
Irradiated milk: The influence of the intensity and character of the radiations on the antirachitie potency. Jour. Biol. Chem. 98: 769. 1932. SUPPLEE, G. C., AND DORCAS, :~[. J. Irradiated milk: The transmission and antirachitic activation of milk films by ultra-violet radiations. Joum DAIRY SCL 17: 433. 1934. S u P t ' ~ , G. C., FLAgmAN, G. E., BENDZIt, R. C., ASD DORCAS, M. 5. Irradiated milk: The influence of f a t content and time of exposure on the antirachitic potency. JouR. DAIRY ScI. 17: 483. 1934. S u e P ~ z , G. C., A~) DORCAS, M . J . Irradiated milk: Characteristics of the flowing film required for optinmm efficiency of antirachitic activation. Joum DAIRY S ~ . 17: 5~4. 1934. SO'PrL~, G. C., HArtfORD, Z. M., DORCAS, M. J., AND BECK, H . H . Irradiated milk: The amount of vitamin D and its rate of formation. Jour. Biol. Chem. 95: 687. 1932.
The Dry Mille Company I~esearch Laboratories, Bainbridge, New Yorl~ AND M. J . DORCAS
The 2Vational Carbon Company, Cleveland, Ohio
The relationship between the character and intensity of the ultra-violet radiation applied to milk films and the antirachitic potency imparted to the milk during momentary periods of exposure has been previously reported (1--4). Milk films 0.11 ram. thick transmit less than 5 per cent of the radi.ation below 2850 X ineident to the surface at an angle of 90 ° (2). Since the incident radiation may be transmitted, absorbed or reflected, the difference between the amount of energy applied and that transmitted does not necessarily indicate the amount absorbed. According to Drothus' law only absorbed radiation can cause photochemical change. It does not necessarily follow, however, that all the energy absorbed brings about photochemical reactions; much of the absorbed energy may be manifested as heat. If data are to be developed which will more adequately show the eharacter and the amount of radiant energy necessary for the most effective and efficient antirachitic activation of milk, it is necessary to know the degree to which the activating rays are reflected from milk surfaces. Such data are recorded in the present paper. EXPERIMENTAL
Vertical flowing milk films of known characteristics were formed with the apparatus described in an earlier paper (2). The carbon arc burning C type eleetl~odes at 60 amperes and 50 volts was used for supplying the beam of ultra-violet radiation. The speetroradiometer previously used was placed in such a position that a beam of the radiation reflected from the milk surface was reflected into the instrument. The amount of radiation received by the speetroradiometer compared with that received by the instrument placed in such a position that it received the same beam from the same source at the same optical distance without the intervening milk film, permitted the calculation of the percentage of energy reflected. Spectral or mirror refleetion from the surface of flowing milk films receiving the radiation at different an#es of incidence is shown by the curves in Chart I. (The angle of incidence as referred to in this paper is to be interpreted as Received for publication February 10, 1934.
6O7
608
0. C. SUPPLEE AND M. J. DORCAS
the angle between the surface of the milk and the incident radiation; a beam parallel to the milk surface being zero degrees and a beam intersecting the milk at right angles being indicated as 90 °.) In presenting these data it is recognized that in the visible portion of the spectrum there would be a certain degree of diffuse reflection originating at some distance below the
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CHART I The reflection of ultra-violet radiation from the surface of milk.
immediate surface of the milk. However, in view of the transmission data previously obtained, ~nd in view of the resul'ts shown by preliminary measurements, wherein it was found that diffuse reflection of the wave lengths under consideration were too weak to be measured with the apparatus
IRRADIATED MI LK
609
available, it is believed that the effect of this factor has been slight or even negligible in the results obtained. The reflection measurements shown by the graphs are the average of three separate determinations from whole milk films 0.11 ram. thick. Similar measurements from skimmed milk films were made for the 15 ° and 30 ° angle of incidence. The results showed that throughout the 2550-3000 -~ range the reflection from skim milk, although tending to parallel that of whole milk was from 1 to 2 per cent lower between 2550 and 2800 A, and from 2 to 8 per cent lower in the 2800 to 3000 /~ region. The reflection from the milk films compared with the reflection from the surface of water, calculated for the range of wave lengths and angles of incidence u n d e r consideration, shows that the reflection from both substances is of the same order of magnitude. However, the calculated reflection from water, as well as actual measurements from vertical flowing water films, shows that the water surface does not exhibit the selective reflection shown by milk. Since the transmission data has indicated a selective absorption of ultraviolet radiation by milk, selective reflection may be expected. In order to determine the possible significance of the reflection of ultraviolet radiation from milk surfaces on the antirachitic potency, milk films of known thickness and" flow characteristics were irradiated by radiation of known intensity impinging at different angles of incidence. The carbon arc of the same characteristics as was used for obtaining the reflection data was used for irradiating the milk films. The arc was placed 43 cm. from the center of the milk films having a width of 10 cm. The films were formed on the flow board mounted on a vertical central axis which permitted accurate change of the plane of flow with reference to the projected beam of radiation. Milks containing 1.2 per cent and 3.6 per cent butter fat were used. The biological assays were made by the usual methods, and the results recorded in the manner heretofore used (1-5). These results as well as those showing the amount of energy applied per cc. of milk are recorded in table 1. In determining the amount of energy applied to the milk film, the effect of the difference in angle of impingment was taken into consideration. Since the data do not p u r p o r t to show the amount of energy absorbed, that which was reflected has not been considered in the calculations. However, an approximation of the amount of energy absorbed m a y be calculated from the transmission data (2) in conjunction with that shown herein. An analysis of the reflection data shows that at an impingment angle of 75 ° from parallel, an average of 3.1 per cent of the incident radiation between 2550 and 3000 A is reflected; at an impingment angle of 45 ° from parallel an average of 2.9 per cent is reflected; at 30 ° , the average is 6.1 per cent; at 20 ° , 13.4 per cent is reflected; at 15 ° , 28 per cent; and at 10 °, 34 per cent.
610
G. C. C. SUPPLEE AND AND M. J. DORCAS DORCAS G.
resu}ts show that the reduction in intensity of the inciThe biological results dent radiation resulting from impinging impinging the energy at angles of incidence as low as 30° 30 ° from parallel parallel does not cause a reduction in antirachitic antir~chitic potency of the milk milk treated treated under the conditions used in these tests. At At potency impingmen¢ angles angles -of ,of 15° 15 ° there is definite evidence evidence of a reduction in antiimpingmenrt TABLE 1 TABLE
The vitamin D concentration concentration of milk mille a.s as affected by film thickness, thickness, film capacity, capacity, tat fat impi.ngment of incident incident 1'adiati
"z .."'Ill'"
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3A190 3A175 3A160 3A145 3A130 3Al15 3A115
Milk,,, 1.2 1.2%,, Fat,, 34.02 34~02 Milk, % Fat
6A190 6A175 6A160 6A14-5 6Al45 6A130 6Al15 6A115
Milk,,, 1.2%,, :Pat,, 192178 Milk, 1.2% Fat 192.78
1AWl90 1AW190 1AWl75 1AW175 1AW160 1AW160 1AW145 1AW145 1AW130 1AW130 1AWll5 1AW115
Milk, 3.6% Fat
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11,851 11,851 11,446 11,446 10,103 10,].03 8,379 5,925 3,067 3,067
90 75 60 45 30 15
3,769 3,640 3,640 3,284 2,665 1,884 1,884 975
4,994 4,823 4,325 4,325 3,531 3,531 2,497 1,292 1,292
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Milk, 1.2% Fat
"
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90 75 60 45 30 15
8,945 8,945 8,640 8,640 7,746 6,325 6,325 4,472 4,472 2,282
90 75 60 45 30 15
3,769 3,769 3,640 3,640 3,284 3,284 2,665 2,665 1,884 I 1,884 975 I 975
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972 972 939 939 841 687 687 486 123
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20 20 20 20 60 60
225 225 225 225 75 75
50
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80
90 9O
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90
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56
30
150
30 3-0 30 30 70
150 150 150 64
4,994 4,994 4,823 4,823 4,325 4,325 3,531 3,531 2,497 2,497 1,292 1,292
20 26 20 20 20 20
225 225 225 225 225 225 225 225
30 30
150
1,288 1,288 1,244 1,244 1,115 1,115 910 644 644 333
35 35 35 35 35 35 35 35 50 5 O
128 128
11,851 11,851 11,446 11,446 10,103 10,103 8,379 8,379 5.925 5,925 3,067 31067
-
-
128 128 128 128 128 128 !28 90 90
IRRADIATED MILK
611
raehitie potency. The d a t a as a whole are considered as f u r t h e r confirmat o r y evidence s u p p o r t i n g the conclusion t h a t the synthesis of V i t a m i n D d u r i n g the irradiation of milk is essentially a surface reaction and t h a t in the practical t r e a t m e n t of milk with ultra-violet rays, conditions which facilitate the reaction at the surface are to be preferred. SUMMARY
1. The reflection of ultra-violet radiation f r o m the surf, ace of milk films is of the same order of m a g n i t u d e as the reflection of such radiation f r o m the surface of w a t e r ; the degree of reflection increases as t h e angle of incidence decreases. 2. Ultra-violet radiation between 2550 and 3000 A when impinged on milk surfaces ,at 75 ° and 45 ° f r o m parallel are reflected to about the same degree---approximately 3 per cent; the average percentage reflection f r o m a 30 ° angle of incidence is about 6 per cent; f r o m a 20 ° angle of incidence, 13.4 per cent; f r o m a 15 ° angle, 28 per cent; and f r o m a 10 ° angle, about 34 per cent. 3. Milk films show the p r o p e r t y of selective reflection of ultra-violet radiation, especially througtmut the range 2550 to 3300 2~. This p r o p e r t y is most pronounced at angles of incidence of 30 ° or less. 4. The antirachitic potency of milk irradiated with ultra-violet radiation ~triking milk films a t angles of incidence less than 90 ° and as low as 30 ° is the same as that obtained when the angle of incidence is 90 ° , other things being equal. REFERENCES
(1) SUPPhEE, G. C., BECK, H. I:[., AND DORCAS, .-V[. J. (2)
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Irradiated milk: The influence of the intensity and character of the radiations on the antirachitie potency. Jour. Biol. Chem. 98: 769. 1932. SUPPLEE, G. C., AND DORCAS, :~[. J. Irradiated milk: The transmission and antirachitic activation of milk films by ultra-violet radiations. Joum DAIRY SCL 17: 433. 1934. S u P t ' ~ , G. C., FLAgmAN, G. E., BENDZIt, R. C., ASD DORCAS, M. 5. Irradiated milk: The influence of f a t content and time of exposure on the antirachitic potency. JouR. DAIRY ScI. 17: 483. 1934. S u e P ~ z , G. C., A~) DORCAS, M . J . Irradiated milk: Characteristics of the flowing film required for optinmm efficiency of antirachitic activation. Joum DAIRY S ~ . 17: 5~4. 1934. SO'PrL~, G. C., HArtfORD, Z. M., DORCAS, M. J., AND BECK, H . H . Irradiated milk: The amount of vitamin D and its rate of formation. Jour. Biol. Chem. 95: 687. 1932.