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The Effects of Season and Fortification on Variations in the Vitamin A Activity of Saskatoon Market Milk
Can. Inst. Food Sei. TeehnoJ. J. Vo\. 15, No. I, pp. 041-
The Effects of Season and Fortification on Variations in the Vitamin A Activity of Saskatoon Market Milk J. Kikafunda and J. P. Olson College of Home Economics University of Saskatchewan Saskatoon, Saskatchewan S7N OWO
cette etude indiquent que pour obtenir des niveaux uniformes de vitamine A dans les laits ecreme et partiellement ecreme, il est necessaire de faire des controles periodiques du lait it l'usine et d'ajuster la fortification en accord avec les fluctuations saisonnieres en vitamine A du lail.
Abstract The effect of seasonal variation on vitamin A and l3-carotene content of raw bulk milk was investigated using commercial milk produced in Saskatoon over the period of June 1977 to June 1978. Pronounced seasonal variations were observed, with spring milk having the highest and winter milk the lowest vitamin A activity. Average values for spring, summer, fall and winter milk were 40.2, 37.0,33.6 and 31.5 retinol equivalent of vitamin A activity (vitamin A plus l3-carotene) per 100 mL, respectively. Overall, spring and summer milk contained significantly more vitamin A than winter and fall milk. Vitamin A levels in unfortified skim, 2% butterfat, and 3.25% butterfat milk and fortified skim and 2% butterfat milk were investigated simultaneously throughout the same period. The levels of vitamin A in the unfortified milk products followed the same seasonal trend as in the raw bulk milk samples, being highest in summer and lowest in winter. Fortification, in the processing plant, of the skim and 2% butterfat milk products resulted in highly variable vitamin A levels in the milk samples. The results of the study indicate that, in order to obtain uniform levels of vitamin A in skimmed and partly skimmed milk, periodic on-line monitoring and periodic alterations in the level of fortification at the processing plant will be necessary to make up for seasonal fluctuations in the vitamin A levels of milk.
Introduction Vitamin A, the first of the vitamins to be discovered, was initially identified as a growth promoting factor isolated from animal fats and oils (McCollum and Davis, 1915). Vitamin A and its derivatives are exclusively of animal origin (Roels, 1967). The carotenoids of plants, of which l3-carotene is the most biologically active, are converted to vitamin A in the intestinal mucosa of almost all animal species (Moore, 1957) by the enzyme l3-carotene 15-15' dioxygenase (Goodman and Huang, 1965). Dietary vitamin A is required for the maintenance of the normal processes of vision (Wald, 1960), growth (Olson, 1969), bone development (Roels, 1967), reproduction (Thompson, 1970) and synthesis and maintenance of the mucus-secreting membranes (De Luca and Wolf, 1969). Hypovitaminosis A is a major nutritional problem in many developing countries (Srikantia, 1975; Pereira and Begum, 1976), particularly affecting post-weaning, preschool children. In North America, dietary vitamin A has been identified as one of the three essential nutrients supplied in marginal amounts (Sauberlich et al., 1976). Results of a Canadian survey (Hoppner et al., 1969) and of an American survey (Underwood et al., 1970) reveal that 15-34% of the Canadian and 35% of the American subjects tested had less than adequate hepatic reserves of vitamin A. Milk is one of the best dietary sources of vitamin A (Roels, 1967) and contains, on average, 150 IV of vitamin per 100 mL (Hartman and Dryden, 1974). The healthy mammary gland has the capacity of transferring large amounts of retinyl palmitate and small quantities of retinol and l3-carotene from blood into
Resume Cette etude porte sur I'influence des saisons sur les teneurs en vitamine A et en beta-carotene du lait cm en vrac avec du lait commercial produit it Saskatoon au cours de la periode dejuin 1977 it juin 1978. Les variations saisonnihes observees furent tres fortes. Les activites de vitamine A (vitamine A plus beta-carotene) les plus elevees furent trouvees dans le lait de printemps et les moins elevees, dans le lait d'hiver. Les valeurs moyennes des activites en vitamine A furent 40,2,37,0,33,6 et 31,5 equivalent retinol respectivement pour le printemps, l'ete, I'automne et I'hiver. Dans l'ensemble les laits de printemps et d'ete furent significativement plus riches en vitamine A que les laits d'hi~er et d'automne. On a aussi etudie au cours de la meme periode les niveaux de vitamine A dans les laits non fortifies de types ecreme, 2% m.g. et 3,25% m.g., et dans les laits fortifies de types ecreme et 2% m.g. Les memes variations saisonnieres en vitamine A furent observees dans les laits non fortifies que pour le lait cru en vrac, les valeurs etant plus fortes en ete et plus faibles en hiver. La fortification it l'usine des produits ecreme et it 2% m.g. a cause des variations tres fortes dans les teneurs en vitamine A des echantillons de lail. Les resultats de
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03 J5-5463 / 82 /0 I 004 J-06$3.00/ 0 1982 Canadian Institute of Food Science and Technology
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milk (Hartman and Dryden, 1974). Milk, as a carrier of vitamin A, is superior to other foods because the other ingredients of milk, particularly milk protein and fat, enhance the utilization of the vitamin in the body (Mahadevan et al., 1965; Thompson, 1968). However, the vitamin A content of milk is not stable as the level fluctuates under the influence of seasonal, dietary, metabolic and processing factors. The seasonal variations generally observed in the vitamin A and f3-carotene content of milk reflect the responsc to different levels of I3-carotene in the feed at different times of the year. Summer milk has been found to contain 1.5 to fifteen times more vitamin A activity than winter milk (Hartman and Dryden, 1974). Searles and Armstrong (1970) reported a total activity for Alberta (Canada) butter of 22.6 IV I g butterfat (BF) in winter and 30.5 IV I g BF in summer. Results of pooled milk samples from Halifax, Montreal, Toronto, Winnipeg and Vancouver generally indicate a higher vitamin A content in summer than in winter milk (Thornpson et al., 1972). The efficiency of utilization of vitamin A and 13carotene provided by milk and milk products is superior to that provided by any other food (Thompson, 1968). Milk is a good vehicle for fortification of vitamin A as it is consumed by infants and children who require more vitamin A for growth. When BF is removed from milk, the fat soluble vitamins are also removed. These nutrients need to be returned to skim milk (nonfat milk), partly skimmed milk (2% BF) and dry skim milk powder (DSMP). Fortification of milk with v~amin A is accomplished by using either a water dispersible, stabilized beadlet carrier of synthetic retinyl palmitate or a retinyl palmitate emulsified concentrate (Hartman and Dryden, 1974). The degree of fortification of skimmed and partly skimmed milk products largely determines the overall vitamin A level of these products. In view of the importance of milk as a dietary source of vitamin A, the present study was undertaken to investigate and determine the existence and extent of seasonal influences and the effect of fortification on variations of the vitamin A activity of Saskatoon market milk.
Materials and Methods Five bulk samples were obtained monthly, from the Dairy Producers' Co-operative, Saskatoon, which originated from five representative areas of the Saskatoon milk shed during the period of June 1977 to June 1978. Pooled samples were taken from dairy farms in the Rosthern, Warman, Waldheim, Viscount, Gurnsey and Asquith regions situated within a fifty mile radius in the northeastern, northern, northwestern, southeastern and western sections about the city of Saskatoon. One monthly bulk sample, taken from the University of Saskatchewan dairy herd, was used as a control as these cows are maintained indoors throughout the year. From these bulk samples, I L samples were obtained for analytical purposes. To study the ~ffects of fortification, samples of unfortified skim, % BF and 3.25% BF milk and fortified skim and 2% 42/Kikafunda and Olson
BF milk were also obtained monthly, during the same period, from the Dairy Producers' Co-operative, Saskatoon. The milk samples were refrigerated immediately upon receipt and analyzed on the same or following day. The vitamin A and f3-carotene contents of the milk samples were determined using a modification of the trifluoroacetic acid methods of Neeld and Pearson (1963) and Dugan et al. (1964) as adapted by the Saskatchewan Feed Testing Laboratory, University of Saskatchewan. Modifications of the vitamin A assay included a 1.5 h saponification of 50 mL of milk with 10 mL of propylene glycol, 25 mL of I % pyrogallol in ethanol (wl v) and 10 mL of 50% potassium hydroxide (wl v), followed by ether extraction. Following saponification, the samples were extracted with three 50 mL volumes of ethyl ether and then washed with three 50 mL volumes of distilled water. Extract volume was brought to 200 mL with ethyl ether immediately prior to analysis. Aliquots of the ether extracts (10 mL) were taken to dryness at 40° C and color was developed by the sequential addition of three drops of acetic anhydride, 0.3 mL of chloroform and 3.0 mL of trifluoroacetic acid:chloroform (1:2 v I v). Absorbance was measured at 620 nm using a Unicam SP 1750 spectrophotometer. Vitamin A levels of the samples were determined using a standard curve obtained from the absorbance, using the above colorimetric method, of several dilutions, three replicates, of a known solution (5 retinol equivalent (RE)I mL) of pure alltrans retinol (Eastman Kodak Co., Rochester, N.Y.). f3-carotene was measured by the addition of 3.0 mL of petroleum ether to dried ether-extract aliquots and the absorbance was measured at 450 nm. The BF content of the milk samples was measured using a Milko-tester MK Ill. f3-carotene levels of the samples were determined using a standard curve obtained from the absorbance, using the above method, of several dilutions, three replicates, of a known solution (5 REI mL) of pure all-trans-f3-carotene (Eastman Kodak Co., Rochester, N. Y.). All reagents used were reagent grade. Concentrations of vitamin A and f3-carotene were expressed as REI 100 mL or as REI g BF. One retinyl equivalent was expressed as I p.g retinol or 6 p.g of 13carotene (Dietary Standard for Canada, 1975). The vitamin A activity of the milk samples was calculated as the sum of the vitamin A and f3-carotene concentrations and was expressed as REI 100 mL or as REI g BF. Analysis of variance was used to determine the extent of seasonal variations on the vitamin A and 13carotene and vitamin A activity of milk. Significant differences between seasons were determined by the Student-Newman-Keuhl's range test (Rohlf and Sokal, 1969).
Results Seasonal Effects For the purposes of this work, the 12 mo were grouped into four equal seasons: winter comprised of December to February; spring, March to May; sumJ. Inst. Can. Sci. Technol. Aliment. Vol. IS. No. I, 1982
mer, June to August; and fall, September to November. The levels of vitamin A, /3-carotene and vitamin A activity (vitamin A plus /3-carotene) in the milk are expressed as REI 100 mL and REI g BF (Table 1). Results were also expressed as monthly and seasonal mean values of milk for samples drawn from the five representative areas of the Saskatoon milk shed. The vitamin A and /3-carotene contents of the milk samples rose sharply in the spring, reaching a maximum of 41.0 RE vitamin A and 3.3 RE /3-carotene I 100 mL in May (Table 1 and Figure 1). Early summer milk maintained an average of 37.2 RE vitamin A and 2.8 RE /3-carotenel 100 mL, but declined to a low of 29.3 RE vitamin A and 1.8 RE /3-carotene/lOO mL by the end of the season. The vitamin A content of milk rose slightly in early fall, reaching an average of 33.2 RE vitamin AI 100 mL, but by the end of the season had reached a low level of 29.2 RE vitamin AI 100 mL. These low levels were maintained throughout the winter months. The vitamin A activity of monthly and seasonal samples when expressed as REI g BF, showed
the same seasonal trend described above but to a lesser degree. A comparison of the vitamin A activity of the milk over the four seasons indicated that spring milk contained 27.7%, 19.3% and 8.6% more vitamin A activity than winter, fall and summer milk, respectively. Summer milk contained 17.5% and 9.8% more vitamin A activity than that of winter and fall milk, respectively. Fall milk had 7.1% more vitamin A activity than winter milk. Statistical analysis revealed that spring milk had significantly higher amounts (P < 0.05) of total vitamin A activity than winter milk (TaWe I). The vitamin A activity of summer milk was not significantly different from spring and fall milk but was significantly higher than winter milk. The vitamin A activity of fall and winter milk was not significantly different. The milk of the control herd (University of Saskatchewan dairy herd) contained vitamin A and /3carotene levels and vitamin A activity that did not fluctuate with seasons as did the milk of the experimental herds (Table 2, Figure I).
Table I. Seasonal variations in the vitamin A, l3-carotene content and vitamin A activity of Saskatoon market milk. Vitamin A RE/lOO mL
Season Winter Spring Summer Fall
29.9a ± 37.7b ± 34.6ab ± 31.8a ±
0.4' 2.9 4.7 2.3
Vitamin A activity
l3-carotene RE/g BF
8.5 ± 10.6 ± 9.5 ± 8.9 ±
0.2 0.9 1.5 0.6
RE/g BF J.5a ±O.I 2.5b ±0.8 2.4ab ± 0.6 1.8ab ± 0.3
RE/g BF 0.5 0.7 0.7 0.5
± ± ± ±
0.1 0.3 0.2 0.1
RE/lOO mL 31.5a ± 40.2c ± 37.0bc ± 33.6ab ±
0.4 2 3.4 5.2 2.4
RE/g BF 9.0 11.3 10.2 9.4
± ± ± ±
0.3 0.2 1.4 0.6
'Each value is a mean of fifteen samples ± standard deviation of seasonal samples. 2Values calculated from summation of vitamin A and l3-carotene contents of milk samples. a,b,c Means sharing the same letter are not significantly different. Table 2. Seasonal variations in the vitamin A and l3-earotene, and vitamin A activity of bulk milk produced by the University of Saskatchewan dairy herd.
40
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Mean seasonal values I 35 ::;
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Fig. I. The Vitamin A and l3-carotene contents of monthly samples from commercial (e, A) and university (0,6.) dairy herds. Can. Inst. Food Sci. Technol. J. Vol. 15, No. I, 1982
Vitamin A
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l3-carotene
Vitamin A activitl
Winter Spring Summer Fall Winter Spring Summer Fall Winter Spring Summer Fall
RE/lOO mL 28.7 ± 1.5 2 29.1 28.5 28.6 1.8 1.7 1.6 1.7 30.4 30.8 30.1 30.2
± ± ± ± ± ± ± ± ±
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lEach value is a mean of three samples. 2Mean ± standard deviation of the samples. )Values calculated from sum of vitamin A and l3-earotene concentrations.
Effect of Fortification The effect of fortification with synthetic vitamin A on the vitamin A concentration in 2% BF and skim milk was studied for a period of I year. The vitamin A content of 3.25% BF (unfortified), unfortified 2% BF and skim milk and fortified 2% BF and skim milk are shown in Table 3. Kikafunda and 0lson/43
Table 3. Vitamin A content of unfortified skim, 2% BF and 3.25% BF milk and fortified skim and 2% BF milk. Vitamin A concentration in milk' 3.25% BF milk Month of sample collection
2% BF milk
Skim milk
No vitamin A added 2
No vitamin A added 3
Vitamin A added'
29.2 28.7 34.8 33.6 35.2 37.3 38.1 33.6 33.6 33.6 28.3
19.8 23.1 23.1 21.5 24.2 27.4 28.0 26.3 25.9 26.3 27.1 23.5
68.8 23.9 30.8 61.1 57.1 45.4 86.6 30.4 73.7 71.3 87.1 65.2
33.3 ± 3.3
24.7 ± 2.6
58.5 ± 21.5
December January February March April May June July August September October November Mean ± SD
No vitamin A added 3
Vitamin A added'
2.8
50.2 31.7 67.6 65.2 28.3 27.5 67.2
4.5
3.8
69.8 66.4 65.2
3.7 ± 0.9
53.9 ± 17.9
'Vitamin A concentration expressed as REI lOO mL. 23.25% BF milk is not fortified with vitamin A. 'Samples were taken from the separator before vitamin A was added. 'Samples taken after pasteurization, before marketing.
The process of removing fat from milk is accompanied by a loss of vitamin A. As a result, partly skimmed or wholly skimmed milk has lower vitamin A levels than 3.25% BF milk. The vitamin A content of the unfortified 2% BF milk was found to be low with
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slightly elevated levels during spring and summer (Table 3, Figure 2). Unfortified skim was found to haye a very low vitamin A content with little apparent seasonal variation (Table 3, Figure 3). The vitamin A content of skimmed milk (whole or partly skimmed) can be replaced by fortification with synthetic vitamin A. In Canada skimmed milk products are required to be fortified, with synthetic vitamin A, to have a total vitamin A content of 141 to 293 IVI 100 mL (42 to 88 REI 100 mL) (Food and Drug Act, 1979, Sections 8.08.004 and 8.08.005). Fortified 2% BF milk was found to contain, on the average, 137% more vitamin A than the unfortified 2% BF milk and 76% more vitamin A than 3.25% BF milk (Table 3, Figure 2). However, the vitamin A content of fortified 2% BF milk was found to fluctuate, ranging from 23 to 87 REI 100 mL. Fortified skim milk had about fifteen times as much vitamin A as unfortified skim milk and 62% more vitamin A than 3.25% BF milk (Table 3, Figure 3). However, the vitamin A content of fortified skim milk was found to fluctuate, ranging from 27 to 70 REI 100 mL. No apparent trends were found in the vitamin A content of the fortified skimmed products (Table 3, Figures 2 and 3).
Discussion
30
20 10
o
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F
M
A M
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A
SON
TIME (months) Fig. 2. The vitamin A content of 3.25% BF milk (A), unfortified 2% BF milk (0) and fortified 2% BF milk (e).
441 Kikafunda and Olson
There was no evidence that seasonal changes in metabolism in the cow had an effect on the vitamin A activity of milk. Season, however, affects the amount of fj-carotene in the feed, thus affecting, indirectly, the vitamin A activity of the milk. This observation is confirmed by the fact that the vitamin A content of milk of stall-fed cows was stable throughout the year while that of stall-fed cows put out to pasture in summer fluctuated with the seasons (Figure I). On the average, spring and summer milk contained 1.2 times more vitamin A activity than winter and fall milk, a figure close to that of 1.5 times reported by Hartman and Dryden (1974). Seasonal variations reported for some regions of Canada (Searles and ArmJ. Inst. Can. Sei. Teehnol. Aliment. Vo!. 15, No. I, 1982
80 70 :::;
E 60
0 0
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~ 30 ~
... >
20
10 -0-
0-
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M
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0
A
5
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TIME (months) Fig. 3. The vitamin A content of 3.25% BF milk (A), unfortified skim milk (0) and fortified skim milk (e).
strong, 1970; Thompson et al., 1972), the United States (Dornbush et al., 1940) and Great Britain, Denmark, Sweden and Holland (Greenhalgh, 1969) agree with the results of the present study in that there is more vitamin A activity in summer than in winter milk. However, in New Zealand, as the green winter pastures ensure better grazing than the relatively dry summer pastures, winter milk has more vitamin A activity than summer milk (McGillivray, 1960; Thompson, 1968). The observed increase in vitamin A activity of Saskatoon milk in late spring and early summer (Figure I) could have been due to the transfer of cattle from winter feeds to pastures. Fresh spring and summer pastures contain high levels of ~-carotene. Kirchgessner et al. (1967) reported mean values of 40-100 mg ~-carotene per kg fresh foliage, which is greater than the amount of ~-carotene required to produce average vitamin A levels in milk. The decline in the vitamin A and ~-carotene levels of milk in late summer could have been due to the maturation and drying of pastures. The stage of maturity of a forage crop significantly influences the seasonal variation in the vitamin A activity of milk. McDowall and McGillivray (1963) observed a higher vitamin A activity in the milk of cows fed immature rye grass than in the milk of cows fed mature rye grass. The slight increase in the vitamin A activity of early fall milk was also reported by Dornbush et al. (1940) and could have been due to early fall rains. The steady decline of vitamin A and ~-carotene levels of milk in late fall and throughout winter was possibly due to transfer of cattle from Can. Inst. Food Sci. Technol. J. Vol. 15. No. I. 1982
pasture to conserved forages. Conserved forages contain much less ~-carotene than green forage due to extensive oxidative breakdown and loss of ~-carotene in harvested forages (Kirchgessner et al., 1967). The vitamin A activity of late winter milk was much less than that of early winter milk because the oxidative loss of ~-carotene in feeds is increased by the length of storage time (Morrison, 1961). In addition to the low level of ~-carotene in winter foods, the reduced vitamin A activity in winter milk could be attributed to the high percentage of inactive carotenoids reportedly present in winter feeds (McDowall and McGillivray, 1963; Thompson, 1968). ~-carotene levels in milk were observed to rise slowly in spring and decline slowly in fall (Figure l) in accordance with the observations ofThompson (1968). These findings are in contrast to the reports of Smith (1959) and Searles and Armstrong (1970) who noted a sudden increase and a sudden decline in the ~-carotene l_evels of spring and fall milk, respectively. The ~ carotene contribution to the total activity of the milk was 20% in summer and 14.5% in winter. These values are comparable to values of 23.7% for summer and 13.8% for winter reported by Searles and Armstrong (1970) for pooled milk samples from Manitoba, Saskatchewan and Alberta. The process of skimming milk is performed to obtain skim milk (0.05% BF) and partly skimmed milk (2% BF) which are required by people incapable of digesting fat and those who are on calorie reduced diets. Unfortunately, the skimming process results in the loss of the fat soluble vitamins, particularly vitamin A. The vitamin A potency of whole (3.25% BF) milk and fortified and unfortified 2% BF and skim milk samples was analyzed for a period of I year. The results (Table 3, Figures 2 and 3) show that 88.9% and 25.8% of the vitamin A content of whole milk was lost upon complete and partial (2% BF) skimming of milk, respectively. Rakes and Potts (1965) reported a loss of 88.5% of the vitamin A of whole milk upon complete skimming. More recently, Thompson et al. (1972) observed a vitamin A loss of 33.4% in pooled samples of 2% BF milk from five Canadian cities. The vitamin A content of skim milk and 2% BF milk can be restored by fortification of the milk with synthetic vitamin A. Commercially fortified skim milk and 2% BF milk were found to contain 14.6 and 2.4 times more vitamin A, respectively, than the corresponding unfortified samples (Table 3). Thompson et al. (1972) reported that fortified 2% BF milk had 2.3 times more vitamin A than a corresponding unfortified sample. Both fortified skim and 2% BF milk appear to be better sources of vitamin A than pasteurized whole (3.25% BF) milk (Table 2, Figures 2 and 3). However, three of the twelve samples of fortified skim milk, and three of the twelve fortified 2% BF milk samples were found to contain less than the minimal level of vitamin A required by the Food and Drug Act (1979). Either no fortification occurred or inadequate amounts of vitamin A were added to the milk in the dairy plant on the days the milk samples were taken. As milk samples were taken monthly, the extent of this problem on a Kikafunda and Olson/45
day to day basis is not known. This emphasizes a need for proper managerial and personnel control in the procedures for the fortification of skimmed milk products. The dairy producer in Canada, being required to fortify skimmed milk products to a specific total vitamin A level range (Food and Drug Act, 1979), has four problems: (i) the original vitamin A level in whole milk is not accurately known for each region. (ii) the vitamin A level in milk fluctuates seasonally. (iii) few dairy plants have the analytical capacity to monitor vitamin A levels on a continuing basis. (iv) fortification procedures presently used do not give consistent vitamin A levels in the fortified products. Obviously, dairy producers are encountering difficulty in complying with federal fortification regulations. As whole milk contains, on the average, about 100 IV (33.3 RE)/100 mL and the seasonal fluctuations are not of large magnitude, at least for Saskatchewan and perhaps the Prairie Provinces, compliance with federal regulations by smaller dairy plants could be met by adding 150 IV (45 RE)/100 mL and 180 IV (54 RE)/100 mL of vitamin A to 2% BF and skim milk products, respectively. Larger plants, with on-line vitamin A pumps, could make periodic adjustments to the rate of fortification to account for season. If possible, periodic monitoring of vitamin A levels of skimmed milk products should be done to ensure that fortification procedures are correct.
Acknowledgements We wish to extend thanks to the Canadian International Development Agency, the College of Home Economics, Feed Testing Laboratories, the University of Saskatchewan and the Dairy Producers' Co-operative, Saskatoon, for the help provided with equipment, methodology and samples.
References De Luca, L. and Wolf, G. 1969. Vitamin A and protein synthesis in mucous membranes. Am. J. Clin. Nutr. 22: 1050. Dietary Standard for Canada. 1975. Department of National Health and Welfare, Ottawa, ON. Dornbush, A. c., Peterson, W. H. and' Olson, F. R. 1940. The carotene and vitamin A of market milk. J. Am. Med. Assoc. 114:1748. Dugan, R.E., Frigerio, N. A. and Siebert, J. M. 1964. Colorimetric determination of vitamin A and its derivatives with trifluoroacetic acid. Anal. Chem. 36: 114. Food and Drug Act. 1979. Department of National Health and Welfare, Ottawa, ON. Goodman, D. S. and Huang, H. S. 1965. Biosynthesis of Vitamin A with rat intestinal enzymes. Science 149:879. Greenhalgh, J. F. D. 1969. Nutrition of the dairy cow. In.' Nutrition
46/ Kikafunda and Olson
of Animals of Agricultural Importance. D. Cuthbertson (Ed.). p. 717. Pergamon Press, London, England. Hartman, A. M. and Dryden, L. P. 1974. The vitamins in milk and milk products. In: Fundamentals of Dairy Chemistry. B. H. Webb, A. H. Johnson and J. A. Alford (Eds.). p. 261. AVI Publishing Company, Inc., Westport, CT. Hoppner, K., Phillips, W. E. J., Erdody, P., Murray, T. K. and Perrin, D. K. 1969. Vitamin A reserves of Canadians. Can. Med. Assoc. J. 101:84. Kirchgessner, M., Friesecke, H. and Koch, G. 1967. Nutrition and the Composition of Milk. J. B. Lippincott Co., Philadelphia, PA. Mahadevan, S., Malaltin, P. and Ganguly, J. 1965. Influence of proteins on absorption and metabolism of vitamin A. World Rev. Nutr. Dietet. 5:209. McCollum, E. V. and Davis, M. 1915. The nature of the dietary deficiency of rice. J. BioI. Chem. 23: 181. McDowall, I. F. and McGillivray, W. A. 1963. Effect of stage of maturity of rye grass fed cows on characteristics of butterfat and its f3-carotene and vitamin A contents. J. Dairy Res. 30:49. McGillivray, W. A. 1960. The role of carotene and vitamin A in animal feeding. World Rev. Nutr. Dietet. 2: 133. Moore, T. 1957. Vitamin A. Elsevier Publishing Co., Amsterdam, The Netherlands. Morrison, F. B. 1961. Feeds and Feeding. 9th Edition. The Morrison Publishing Co., Clinton, lA. Neeld, J.B. and Pearson, W. N. 1963. Macro and micro methods for the determination of vitamin A using trifluoroacetic acid (TFA). J. Nutr. 79:454. Olson, J. A. 1969. Metabolism and functions of vitamin A. Fed. Proc. 28: 1670. Pereira, S. M. and Begum, A. 1976. Vitamin A deficiency in Indian children. World Rev. Nutr. Dietet. 24:192. Rakes, J. M. and Potts, D. F. 1965. Vitamin A content of whole and skim milk. J. Dairy Sci. 48:793. Roels, O. A. 1967. Vitamin A: Biochemical systems. In: The Vitamins. Volume I. W. H. Sebrell and R. S. Harris(Eds.). p. 167. Academic Press, New York, NY. Rohlf, F. J. and Sokal, R. R. 1969. Statistical Tables. Freeman and Co., San Francisco, CA. Sauberlich, H. E., Dowdy, R. P. and Skala, J. H. 1976. Laboratory Tests for the Assessment of Nutritional Tests. CRC Press, Inc., Cleveland, OH. Searles, S. K. and Armstrong, J. C. 1970. Vitamin E, vitamin A and carotene contents of Alberta butter. J. Dairy Sci. 53: 150. Smith, V. R. 1959. Physiology of Lactation. 5th Edition. Iowa State University Press, Ames, lA. Srikantia, S. G. 1975. Human vitamin A deficiency. World Rev. Nutr. Dietet. 20:184. Thompson, J. N. 1970. Role of vitamin A in reproduction. In: The Fat Soluble Vitamins. H. F. De Luca and J. W. Suttie (Eds.). p. 267. University of Wisconsin Press, Madison, WI. Thompson, J. N., Erdody, P., Maxiwell, W. B. and Murray, T. K. 1972. Fluorimetric determination of vitamin A in dairy products. J. Dairy Sci. 55: 1077. Thompson, S. Y. 1968. Nutritive value of milk and milk products: Fat soluble vitamins. J. Dairy Res. 35:149. Underwood, B. A., Siegel, H., Weisell, R. C. and Dolinski, M. 1970. Liver stores of vitamin A in a normal population dying suddenly from unnatural causes in New York City. Am. J. Clin. Nutr. 23:1037. Wald, G. 1960. The visual functions of vitamin A. Vitam. Horm. 18:417. Accepted May I, 1981
J. Inst. Can. Sci. Technol. Aliment. Vo!. 15. No. 1.1982
The Effects of Season and Fortification on Variations in the Vitamin A Activity of Saskatoon Market Milk J. Kikafunda and J. P. Olson College of Home Economics University of Saskatchewan Saskatoon, Saskatchewan S7N OWO
cette etude indiquent que pour obtenir des niveaux uniformes de vitamine A dans les laits ecreme et partiellement ecreme, il est necessaire de faire des controles periodiques du lait it l'usine et d'ajuster la fortification en accord avec les fluctuations saisonnieres en vitamine A du lail.
Abstract The effect of seasonal variation on vitamin A and l3-carotene content of raw bulk milk was investigated using commercial milk produced in Saskatoon over the period of June 1977 to June 1978. Pronounced seasonal variations were observed, with spring milk having the highest and winter milk the lowest vitamin A activity. Average values for spring, summer, fall and winter milk were 40.2, 37.0,33.6 and 31.5 retinol equivalent of vitamin A activity (vitamin A plus l3-carotene) per 100 mL, respectively. Overall, spring and summer milk contained significantly more vitamin A than winter and fall milk. Vitamin A levels in unfortified skim, 2% butterfat, and 3.25% butterfat milk and fortified skim and 2% butterfat milk were investigated simultaneously throughout the same period. The levels of vitamin A in the unfortified milk products followed the same seasonal trend as in the raw bulk milk samples, being highest in summer and lowest in winter. Fortification, in the processing plant, of the skim and 2% butterfat milk products resulted in highly variable vitamin A levels in the milk samples. The results of the study indicate that, in order to obtain uniform levels of vitamin A in skimmed and partly skimmed milk, periodic on-line monitoring and periodic alterations in the level of fortification at the processing plant will be necessary to make up for seasonal fluctuations in the vitamin A levels of milk.
Introduction Vitamin A, the first of the vitamins to be discovered, was initially identified as a growth promoting factor isolated from animal fats and oils (McCollum and Davis, 1915). Vitamin A and its derivatives are exclusively of animal origin (Roels, 1967). The carotenoids of plants, of which l3-carotene is the most biologically active, are converted to vitamin A in the intestinal mucosa of almost all animal species (Moore, 1957) by the enzyme l3-carotene 15-15' dioxygenase (Goodman and Huang, 1965). Dietary vitamin A is required for the maintenance of the normal processes of vision (Wald, 1960), growth (Olson, 1969), bone development (Roels, 1967), reproduction (Thompson, 1970) and synthesis and maintenance of the mucus-secreting membranes (De Luca and Wolf, 1969). Hypovitaminosis A is a major nutritional problem in many developing countries (Srikantia, 1975; Pereira and Begum, 1976), particularly affecting post-weaning, preschool children. In North America, dietary vitamin A has been identified as one of the three essential nutrients supplied in marginal amounts (Sauberlich et al., 1976). Results of a Canadian survey (Hoppner et al., 1969) and of an American survey (Underwood et al., 1970) reveal that 15-34% of the Canadian and 35% of the American subjects tested had less than adequate hepatic reserves of vitamin A. Milk is one of the best dietary sources of vitamin A (Roels, 1967) and contains, on average, 150 IV of vitamin per 100 mL (Hartman and Dryden, 1974). The healthy mammary gland has the capacity of transferring large amounts of retinyl palmitate and small quantities of retinol and l3-carotene from blood into
Resume Cette etude porte sur I'influence des saisons sur les teneurs en vitamine A et en beta-carotene du lait cm en vrac avec du lait commercial produit it Saskatoon au cours de la periode dejuin 1977 it juin 1978. Les variations saisonnihes observees furent tres fortes. Les activites de vitamine A (vitamine A plus beta-carotene) les plus elevees furent trouvees dans le lait de printemps et les moins elevees, dans le lait d'hiver. Les valeurs moyennes des activites en vitamine A furent 40,2,37,0,33,6 et 31,5 equivalent retinol respectivement pour le printemps, l'ete, I'automne et I'hiver. Dans l'ensemble les laits de printemps et d'ete furent significativement plus riches en vitamine A que les laits d'hi~er et d'automne. On a aussi etudie au cours de la meme periode les niveaux de vitamine A dans les laits non fortifies de types ecreme, 2% m.g. et 3,25% m.g., et dans les laits fortifies de types ecreme et 2% m.g. Les memes variations saisonnieres en vitamine A furent observees dans les laits non fortifies que pour le lait cru en vrac, les valeurs etant plus fortes en ete et plus faibles en hiver. La fortification it l'usine des produits ecreme et it 2% m.g. a cause des variations tres fortes dans les teneurs en vitamine A des echantillons de lail. Les resultats de
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milk (Hartman and Dryden, 1974). Milk, as a carrier of vitamin A, is superior to other foods because the other ingredients of milk, particularly milk protein and fat, enhance the utilization of the vitamin in the body (Mahadevan et al., 1965; Thompson, 1968). However, the vitamin A content of milk is not stable as the level fluctuates under the influence of seasonal, dietary, metabolic and processing factors. The seasonal variations generally observed in the vitamin A and f3-carotene content of milk reflect the responsc to different levels of I3-carotene in the feed at different times of the year. Summer milk has been found to contain 1.5 to fifteen times more vitamin A activity than winter milk (Hartman and Dryden, 1974). Searles and Armstrong (1970) reported a total activity for Alberta (Canada) butter of 22.6 IV I g butterfat (BF) in winter and 30.5 IV I g BF in summer. Results of pooled milk samples from Halifax, Montreal, Toronto, Winnipeg and Vancouver generally indicate a higher vitamin A content in summer than in winter milk (Thornpson et al., 1972). The efficiency of utilization of vitamin A and 13carotene provided by milk and milk products is superior to that provided by any other food (Thompson, 1968). Milk is a good vehicle for fortification of vitamin A as it is consumed by infants and children who require more vitamin A for growth. When BF is removed from milk, the fat soluble vitamins are also removed. These nutrients need to be returned to skim milk (nonfat milk), partly skimmed milk (2% BF) and dry skim milk powder (DSMP). Fortification of milk with v~amin A is accomplished by using either a water dispersible, stabilized beadlet carrier of synthetic retinyl palmitate or a retinyl palmitate emulsified concentrate (Hartman and Dryden, 1974). The degree of fortification of skimmed and partly skimmed milk products largely determines the overall vitamin A level of these products. In view of the importance of milk as a dietary source of vitamin A, the present study was undertaken to investigate and determine the existence and extent of seasonal influences and the effect of fortification on variations of the vitamin A activity of Saskatoon market milk.
Materials and Methods Five bulk samples were obtained monthly, from the Dairy Producers' Co-operative, Saskatoon, which originated from five representative areas of the Saskatoon milk shed during the period of June 1977 to June 1978. Pooled samples were taken from dairy farms in the Rosthern, Warman, Waldheim, Viscount, Gurnsey and Asquith regions situated within a fifty mile radius in the northeastern, northern, northwestern, southeastern and western sections about the city of Saskatoon. One monthly bulk sample, taken from the University of Saskatchewan dairy herd, was used as a control as these cows are maintained indoors throughout the year. From these bulk samples, I L samples were obtained for analytical purposes. To study the ~ffects of fortification, samples of unfortified skim, % BF and 3.25% BF milk and fortified skim and 2% 42/Kikafunda and Olson
BF milk were also obtained monthly, during the same period, from the Dairy Producers' Co-operative, Saskatoon. The milk samples were refrigerated immediately upon receipt and analyzed on the same or following day. The vitamin A and f3-carotene contents of the milk samples were determined using a modification of the trifluoroacetic acid methods of Neeld and Pearson (1963) and Dugan et al. (1964) as adapted by the Saskatchewan Feed Testing Laboratory, University of Saskatchewan. Modifications of the vitamin A assay included a 1.5 h saponification of 50 mL of milk with 10 mL of propylene glycol, 25 mL of I % pyrogallol in ethanol (wl v) and 10 mL of 50% potassium hydroxide (wl v), followed by ether extraction. Following saponification, the samples were extracted with three 50 mL volumes of ethyl ether and then washed with three 50 mL volumes of distilled water. Extract volume was brought to 200 mL with ethyl ether immediately prior to analysis. Aliquots of the ether extracts (10 mL) were taken to dryness at 40° C and color was developed by the sequential addition of three drops of acetic anhydride, 0.3 mL of chloroform and 3.0 mL of trifluoroacetic acid:chloroform (1:2 v I v). Absorbance was measured at 620 nm using a Unicam SP 1750 spectrophotometer. Vitamin A levels of the samples were determined using a standard curve obtained from the absorbance, using the above colorimetric method, of several dilutions, three replicates, of a known solution (5 retinol equivalent (RE)I mL) of pure alltrans retinol (Eastman Kodak Co., Rochester, N.Y.). f3-carotene was measured by the addition of 3.0 mL of petroleum ether to dried ether-extract aliquots and the absorbance was measured at 450 nm. The BF content of the milk samples was measured using a Milko-tester MK Ill. f3-carotene levels of the samples were determined using a standard curve obtained from the absorbance, using the above method, of several dilutions, three replicates, of a known solution (5 REI mL) of pure all-trans-f3-carotene (Eastman Kodak Co., Rochester, N. Y.). All reagents used were reagent grade. Concentrations of vitamin A and f3-carotene were expressed as REI 100 mL or as REI g BF. One retinyl equivalent was expressed as I p.g retinol or 6 p.g of 13carotene (Dietary Standard for Canada, 1975). The vitamin A activity of the milk samples was calculated as the sum of the vitamin A and f3-carotene concentrations and was expressed as REI 100 mL or as REI g BF. Analysis of variance was used to determine the extent of seasonal variations on the vitamin A and 13carotene and vitamin A activity of milk. Significant differences between seasons were determined by the Student-Newman-Keuhl's range test (Rohlf and Sokal, 1969).
Results Seasonal Effects For the purposes of this work, the 12 mo were grouped into four equal seasons: winter comprised of December to February; spring, March to May; sumJ. Inst. Can. Sci. Technol. Aliment. Vol. IS. No. I, 1982
mer, June to August; and fall, September to November. The levels of vitamin A, /3-carotene and vitamin A activity (vitamin A plus /3-carotene) in the milk are expressed as REI 100 mL and REI g BF (Table 1). Results were also expressed as monthly and seasonal mean values of milk for samples drawn from the five representative areas of the Saskatoon milk shed. The vitamin A and /3-carotene contents of the milk samples rose sharply in the spring, reaching a maximum of 41.0 RE vitamin A and 3.3 RE /3-carotene I 100 mL in May (Table 1 and Figure 1). Early summer milk maintained an average of 37.2 RE vitamin A and 2.8 RE /3-carotenel 100 mL, but declined to a low of 29.3 RE vitamin A and 1.8 RE /3-carotene/lOO mL by the end of the season. The vitamin A content of milk rose slightly in early fall, reaching an average of 33.2 RE vitamin AI 100 mL, but by the end of the season had reached a low level of 29.2 RE vitamin AI 100 mL. These low levels were maintained throughout the winter months. The vitamin A activity of monthly and seasonal samples when expressed as REI g BF, showed
the same seasonal trend described above but to a lesser degree. A comparison of the vitamin A activity of the milk over the four seasons indicated that spring milk contained 27.7%, 19.3% and 8.6% more vitamin A activity than winter, fall and summer milk, respectively. Summer milk contained 17.5% and 9.8% more vitamin A activity than that of winter and fall milk, respectively. Fall milk had 7.1% more vitamin A activity than winter milk. Statistical analysis revealed that spring milk had significantly higher amounts (P < 0.05) of total vitamin A activity than winter milk (TaWe I). The vitamin A activity of summer milk was not significantly different from spring and fall milk but was significantly higher than winter milk. The vitamin A activity of fall and winter milk was not significantly different. The milk of the control herd (University of Saskatchewan dairy herd) contained vitamin A and /3carotene levels and vitamin A activity that did not fluctuate with seasons as did the milk of the experimental herds (Table 2, Figure I).
Table I. Seasonal variations in the vitamin A, l3-carotene content and vitamin A activity of Saskatoon market milk. Vitamin A RE/lOO mL
Season Winter Spring Summer Fall
29.9a ± 37.7b ± 34.6ab ± 31.8a ±
0.4' 2.9 4.7 2.3
Vitamin A activity
l3-carotene RE/g BF
8.5 ± 10.6 ± 9.5 ± 8.9 ±
0.2 0.9 1.5 0.6
RE/g BF J.5a ±O.I 2.5b ±0.8 2.4ab ± 0.6 1.8ab ± 0.3
RE/g BF 0.5 0.7 0.7 0.5
± ± ± ±
0.1 0.3 0.2 0.1
RE/lOO mL 31.5a ± 40.2c ± 37.0bc ± 33.6ab ±
0.4 2 3.4 5.2 2.4
RE/g BF 9.0 11.3 10.2 9.4
± ± ± ±
0.3 0.2 1.4 0.6
'Each value is a mean of fifteen samples ± standard deviation of seasonal samples. 2Values calculated from summation of vitamin A and l3-carotene contents of milk samples. a,b,c Means sharing the same letter are not significantly different. Table 2. Seasonal variations in the vitamin A and l3-earotene, and vitamin A activity of bulk milk produced by the University of Saskatchewan dairy herd.
40
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Fig. I. The Vitamin A and l3-carotene contents of monthly samples from commercial (e, A) and university (0,6.) dairy herds. Can. Inst. Food Sci. Technol. J. Vol. 15, No. I, 1982
Vitamin A
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l3-carotene
Vitamin A activitl
Winter Spring Summer Fall Winter Spring Summer Fall Winter Spring Summer Fall
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lEach value is a mean of three samples. 2Mean ± standard deviation of the samples. )Values calculated from sum of vitamin A and l3-earotene concentrations.
Effect of Fortification The effect of fortification with synthetic vitamin A on the vitamin A concentration in 2% BF and skim milk was studied for a period of I year. The vitamin A content of 3.25% BF (unfortified), unfortified 2% BF and skim milk and fortified 2% BF and skim milk are shown in Table 3. Kikafunda and 0lson/43
Table 3. Vitamin A content of unfortified skim, 2% BF and 3.25% BF milk and fortified skim and 2% BF milk. Vitamin A concentration in milk' 3.25% BF milk Month of sample collection
2% BF milk
Skim milk
No vitamin A added 2
No vitamin A added 3
Vitamin A added'
29.2 28.7 34.8 33.6 35.2 37.3 38.1 33.6 33.6 33.6 28.3
19.8 23.1 23.1 21.5 24.2 27.4 28.0 26.3 25.9 26.3 27.1 23.5
68.8 23.9 30.8 61.1 57.1 45.4 86.6 30.4 73.7 71.3 87.1 65.2
33.3 ± 3.3
24.7 ± 2.6
58.5 ± 21.5
December January February March April May June July August September October November Mean ± SD
No vitamin A added 3
Vitamin A added'
2.8
50.2 31.7 67.6 65.2 28.3 27.5 67.2
4.5
3.8
69.8 66.4 65.2
3.7 ± 0.9
53.9 ± 17.9
'Vitamin A concentration expressed as REI lOO mL. 23.25% BF milk is not fortified with vitamin A. 'Samples were taken from the separator before vitamin A was added. 'Samples taken after pasteurization, before marketing.
The process of removing fat from milk is accompanied by a loss of vitamin A. As a result, partly skimmed or wholly skimmed milk has lower vitamin A levels than 3.25% BF milk. The vitamin A content of the unfortified 2% BF milk was found to be low with
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slightly elevated levels during spring and summer (Table 3, Figure 2). Unfortified skim was found to haye a very low vitamin A content with little apparent seasonal variation (Table 3, Figure 3). The vitamin A content of skimmed milk (whole or partly skimmed) can be replaced by fortification with synthetic vitamin A. In Canada skimmed milk products are required to be fortified, with synthetic vitamin A, to have a total vitamin A content of 141 to 293 IVI 100 mL (42 to 88 REI 100 mL) (Food and Drug Act, 1979, Sections 8.08.004 and 8.08.005). Fortified 2% BF milk was found to contain, on the average, 137% more vitamin A than the unfortified 2% BF milk and 76% more vitamin A than 3.25% BF milk (Table 3, Figure 2). However, the vitamin A content of fortified 2% BF milk was found to fluctuate, ranging from 23 to 87 REI 100 mL. Fortified skim milk had about fifteen times as much vitamin A as unfortified skim milk and 62% more vitamin A than 3.25% BF milk (Table 3, Figure 3). However, the vitamin A content of fortified skim milk was found to fluctuate, ranging from 27 to 70 REI 100 mL. No apparent trends were found in the vitamin A content of the fortified skimmed products (Table 3, Figures 2 and 3).
Discussion
30
20 10
o
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A M
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A
SON
TIME (months) Fig. 2. The vitamin A content of 3.25% BF milk (A), unfortified 2% BF milk (0) and fortified 2% BF milk (e).
441 Kikafunda and Olson
There was no evidence that seasonal changes in metabolism in the cow had an effect on the vitamin A activity of milk. Season, however, affects the amount of fj-carotene in the feed, thus affecting, indirectly, the vitamin A activity of the milk. This observation is confirmed by the fact that the vitamin A content of milk of stall-fed cows was stable throughout the year while that of stall-fed cows put out to pasture in summer fluctuated with the seasons (Figure I). On the average, spring and summer milk contained 1.2 times more vitamin A activity than winter and fall milk, a figure close to that of 1.5 times reported by Hartman and Dryden (1974). Seasonal variations reported for some regions of Canada (Searles and ArmJ. Inst. Can. Sei. Teehnol. Aliment. Vo!. 15, No. I, 1982
80 70 :::;
E 60
0 0
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0
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5
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TIME (months) Fig. 3. The vitamin A content of 3.25% BF milk (A), unfortified skim milk (0) and fortified skim milk (e).
strong, 1970; Thompson et al., 1972), the United States (Dornbush et al., 1940) and Great Britain, Denmark, Sweden and Holland (Greenhalgh, 1969) agree with the results of the present study in that there is more vitamin A activity in summer than in winter milk. However, in New Zealand, as the green winter pastures ensure better grazing than the relatively dry summer pastures, winter milk has more vitamin A activity than summer milk (McGillivray, 1960; Thompson, 1968). The observed increase in vitamin A activity of Saskatoon milk in late spring and early summer (Figure I) could have been due to the transfer of cattle from winter feeds to pastures. Fresh spring and summer pastures contain high levels of ~-carotene. Kirchgessner et al. (1967) reported mean values of 40-100 mg ~-carotene per kg fresh foliage, which is greater than the amount of ~-carotene required to produce average vitamin A levels in milk. The decline in the vitamin A and ~-carotene levels of milk in late summer could have been due to the maturation and drying of pastures. The stage of maturity of a forage crop significantly influences the seasonal variation in the vitamin A activity of milk. McDowall and McGillivray (1963) observed a higher vitamin A activity in the milk of cows fed immature rye grass than in the milk of cows fed mature rye grass. The slight increase in the vitamin A activity of early fall milk was also reported by Dornbush et al. (1940) and could have been due to early fall rains. The steady decline of vitamin A and ~-carotene levels of milk in late fall and throughout winter was possibly due to transfer of cattle from Can. Inst. Food Sci. Technol. J. Vol. 15. No. I. 1982
pasture to conserved forages. Conserved forages contain much less ~-carotene than green forage due to extensive oxidative breakdown and loss of ~-carotene in harvested forages (Kirchgessner et al., 1967). The vitamin A activity of late winter milk was much less than that of early winter milk because the oxidative loss of ~-carotene in feeds is increased by the length of storage time (Morrison, 1961). In addition to the low level of ~-carotene in winter foods, the reduced vitamin A activity in winter milk could be attributed to the high percentage of inactive carotenoids reportedly present in winter feeds (McDowall and McGillivray, 1963; Thompson, 1968). ~-carotene levels in milk were observed to rise slowly in spring and decline slowly in fall (Figure l) in accordance with the observations ofThompson (1968). These findings are in contrast to the reports of Smith (1959) and Searles and Armstrong (1970) who noted a sudden increase and a sudden decline in the ~-carotene l_evels of spring and fall milk, respectively. The ~ carotene contribution to the total activity of the milk was 20% in summer and 14.5% in winter. These values are comparable to values of 23.7% for summer and 13.8% for winter reported by Searles and Armstrong (1970) for pooled milk samples from Manitoba, Saskatchewan and Alberta. The process of skimming milk is performed to obtain skim milk (0.05% BF) and partly skimmed milk (2% BF) which are required by people incapable of digesting fat and those who are on calorie reduced diets. Unfortunately, the skimming process results in the loss of the fat soluble vitamins, particularly vitamin A. The vitamin A potency of whole (3.25% BF) milk and fortified and unfortified 2% BF and skim milk samples was analyzed for a period of I year. The results (Table 3, Figures 2 and 3) show that 88.9% and 25.8% of the vitamin A content of whole milk was lost upon complete and partial (2% BF) skimming of milk, respectively. Rakes and Potts (1965) reported a loss of 88.5% of the vitamin A of whole milk upon complete skimming. More recently, Thompson et al. (1972) observed a vitamin A loss of 33.4% in pooled samples of 2% BF milk from five Canadian cities. The vitamin A content of skim milk and 2% BF milk can be restored by fortification of the milk with synthetic vitamin A. Commercially fortified skim milk and 2% BF milk were found to contain 14.6 and 2.4 times more vitamin A, respectively, than the corresponding unfortified samples (Table 3). Thompson et al. (1972) reported that fortified 2% BF milk had 2.3 times more vitamin A than a corresponding unfortified sample. Both fortified skim and 2% BF milk appear to be better sources of vitamin A than pasteurized whole (3.25% BF) milk (Table 2, Figures 2 and 3). However, three of the twelve samples of fortified skim milk, and three of the twelve fortified 2% BF milk samples were found to contain less than the minimal level of vitamin A required by the Food and Drug Act (1979). Either no fortification occurred or inadequate amounts of vitamin A were added to the milk in the dairy plant on the days the milk samples were taken. As milk samples were taken monthly, the extent of this problem on a Kikafunda and Olson/45
day to day basis is not known. This emphasizes a need for proper managerial and personnel control in the procedures for the fortification of skimmed milk products. The dairy producer in Canada, being required to fortify skimmed milk products to a specific total vitamin A level range (Food and Drug Act, 1979), has four problems: (i) the original vitamin A level in whole milk is not accurately known for each region. (ii) the vitamin A level in milk fluctuates seasonally. (iii) few dairy plants have the analytical capacity to monitor vitamin A levels on a continuing basis. (iv) fortification procedures presently used do not give consistent vitamin A levels in the fortified products. Obviously, dairy producers are encountering difficulty in complying with federal fortification regulations. As whole milk contains, on the average, about 100 IV (33.3 RE)/100 mL and the seasonal fluctuations are not of large magnitude, at least for Saskatchewan and perhaps the Prairie Provinces, compliance with federal regulations by smaller dairy plants could be met by adding 150 IV (45 RE)/100 mL and 180 IV (54 RE)/100 mL of vitamin A to 2% BF and skim milk products, respectively. Larger plants, with on-line vitamin A pumps, could make periodic adjustments to the rate of fortification to account for season. If possible, periodic monitoring of vitamin A levels of skimmed milk products should be done to ensure that fortification procedures are correct.
Acknowledgements We wish to extend thanks to the Canadian International Development Agency, the College of Home Economics, Feed Testing Laboratories, the University of Saskatchewan and the Dairy Producers' Co-operative, Saskatoon, for the help provided with equipment, methodology and samples.
References De Luca, L. and Wolf, G. 1969. Vitamin A and protein synthesis in mucous membranes. Am. J. Clin. Nutr. 22: 1050. Dietary Standard for Canada. 1975. Department of National Health and Welfare, Ottawa, ON. Dornbush, A. c., Peterson, W. H. and' Olson, F. R. 1940. The carotene and vitamin A of market milk. J. Am. Med. Assoc. 114:1748. Dugan, R.E., Frigerio, N. A. and Siebert, J. M. 1964. Colorimetric determination of vitamin A and its derivatives with trifluoroacetic acid. Anal. Chem. 36: 114. Food and Drug Act. 1979. Department of National Health and Welfare, Ottawa, ON. Goodman, D. S. and Huang, H. S. 1965. Biosynthesis of Vitamin A with rat intestinal enzymes. Science 149:879. Greenhalgh, J. F. D. 1969. Nutrition of the dairy cow. In.' Nutrition
46/ Kikafunda and Olson
of Animals of Agricultural Importance. D. Cuthbertson (Ed.). p. 717. Pergamon Press, London, England. Hartman, A. M. and Dryden, L. P. 1974. The vitamins in milk and milk products. In: Fundamentals of Dairy Chemistry. B. H. Webb, A. H. Johnson and J. A. Alford (Eds.). p. 261. AVI Publishing Company, Inc., Westport, CT. Hoppner, K., Phillips, W. E. J., Erdody, P., Murray, T. K. and Perrin, D. K. 1969. Vitamin A reserves of Canadians. Can. Med. Assoc. J. 101:84. Kirchgessner, M., Friesecke, H. and Koch, G. 1967. Nutrition and the Composition of Milk. J. B. Lippincott Co., Philadelphia, PA. Mahadevan, S., Malaltin, P. and Ganguly, J. 1965. Influence of proteins on absorption and metabolism of vitamin A. World Rev. Nutr. Dietet. 5:209. McCollum, E. V. and Davis, M. 1915. The nature of the dietary deficiency of rice. J. BioI. Chem. 23: 181. McDowall, I. F. and McGillivray, W. A. 1963. Effect of stage of maturity of rye grass fed cows on characteristics of butterfat and its f3-carotene and vitamin A contents. J. Dairy Res. 30:49. McGillivray, W. A. 1960. The role of carotene and vitamin A in animal feeding. World Rev. Nutr. Dietet. 2: 133. Moore, T. 1957. Vitamin A. Elsevier Publishing Co., Amsterdam, The Netherlands. Morrison, F. B. 1961. Feeds and Feeding. 9th Edition. The Morrison Publishing Co., Clinton, lA. Neeld, J.B. and Pearson, W. N. 1963. Macro and micro methods for the determination of vitamin A using trifluoroacetic acid (TFA). J. Nutr. 79:454. Olson, J. A. 1969. Metabolism and functions of vitamin A. Fed. Proc. 28: 1670. Pereira, S. M. and Begum, A. 1976. Vitamin A deficiency in Indian children. World Rev. Nutr. Dietet. 24:192. Rakes, J. M. and Potts, D. F. 1965. Vitamin A content of whole and skim milk. J. Dairy Sci. 48:793. Roels, O. A. 1967. Vitamin A: Biochemical systems. In: The Vitamins. Volume I. W. H. Sebrell and R. S. Harris(Eds.). p. 167. Academic Press, New York, NY. Rohlf, F. J. and Sokal, R. R. 1969. Statistical Tables. Freeman and Co., San Francisco, CA. Sauberlich, H. E., Dowdy, R. P. and Skala, J. H. 1976. Laboratory Tests for the Assessment of Nutritional Tests. CRC Press, Inc., Cleveland, OH. Searles, S. K. and Armstrong, J. C. 1970. Vitamin E, vitamin A and carotene contents of Alberta butter. J. Dairy Sci. 53: 150. Smith, V. R. 1959. Physiology of Lactation. 5th Edition. Iowa State University Press, Ames, lA. Srikantia, S. G. 1975. Human vitamin A deficiency. World Rev. Nutr. Dietet. 20:184. Thompson, J. N. 1970. Role of vitamin A in reproduction. In: The Fat Soluble Vitamins. H. F. De Luca and J. W. Suttie (Eds.). p. 267. University of Wisconsin Press, Madison, WI. Thompson, J. N., Erdody, P., Maxiwell, W. B. and Murray, T. K. 1972. Fluorimetric determination of vitamin A in dairy products. J. Dairy Sci. 55: 1077. Thompson, S. Y. 1968. Nutritive value of milk and milk products: Fat soluble vitamins. J. Dairy Res. 35:149. Underwood, B. A., Siegel, H., Weisell, R. C. and Dolinski, M. 1970. Liver stores of vitamin A in a normal population dying suddenly from unnatural causes in New York City. Am. J. Clin. Nutr. 23:1037. Wald, G. 1960. The visual functions of vitamin A. Vitam. Horm. 18:417. Accepted May I, 1981
J. Inst. Can. Sci. Technol. Aliment. Vo!. 15. No. 1.1982