Effect of Time and Storage Conditions on Vitamin A in Instantized Nonfat Dry Milk

Effect of Time and Storage Conditions on Vitamin A in Instantized Nonfat Dry Milk M. deBOER, L. d e M A N , and J. M. deMAN Department of Food Science University of Guelph Guelph, Ontario, Canada N1G 2W1

ABSTRACT

Instantized nonfat dry" milk was obtained directly from the manufacturer. Analysis of nine bags taken from the packaging line demonstrated considerable variability of vitamin A content. Vitamin A stability was measured over 16 wk at 21, 26, and 32°C in the dark and at 21°C under fluorescent light exposure at 3500 lx. Data were analyzed by regression analysis. Samples kept in the dark lost from 20 to 38% of the original vitamin A. Loss from samples exposed to iight was as high as 70%. Most vitamin loss occurred during the first 10 wk of storage. Random samples of instantized nonfat dr), milk were obtained from local supermarkets. Seven of 17 samples failed to meet the minimum required for vitamin A. INTRODUCTION

Thompson and Erdody (7) demonstrated that added vitamin A in milk is less stable than the native vitamin. This was confirmed by deMan (3), who showed that light exposure of whole milk in plastic pouches for 48 h caused 32.2% loss of vitamin A, 74.4% loss from 2% milk, and 95.8% loss from skim milk. The reason of this difference in stability has not been determined. However, added vitamin A is in fewer dispersed particles than native vitamin A and is also in these particles in a much higher concentration. Any breakdown reaction, therefore, would be expected to occur at a greater rate in dispersed particles of the added vitamin A than in the original fat globules. This phenomenon is related to the difficulty of dispersing a lipid soluble substance in a large volume of nonlipid material.

Received September 12, 1983. 1984 J Dairy Sci 67:2188-2191

The Canadian F o o d and Drug Act requires fortification of instantized nonfat dry' milk with vitamin A. According to section B.08.014 of the act, the added vitamin A shall be in such amount that a reasonable daily intake of the milk contains not less than 1200 IU and not more than 2500 IU of vitamin A. A reasonable daily intake is defined in schedule K of the a c t as 852 ml. This would correspond to a range of addition of vitamin A in instantized nonfat dry milk of 1408 to 2933 IU/100 g. Vitamin A fortification is also important for food aid programs. At the 20th meeting of the Protein Advisory Group (1), it was recommended that instantized nonfat dry milk (NDM) be fortified to 5000 IU/100 g. This is important because populations receiving food aid also have high incidence of xerophthalmia. Protein supplements without vitamin A rapidly deplete vitamin A in the liver and increase the incidence of xerophthalmia. The basic information on vitamin enrichment of nonfat dry milk was published by Bauernfeind and Allen (2). Because added vitamin A in instantized nonfat dry milk would be subject to the same instability as that in milk, we decided to determine the effect of light and storage temperature on instantized nonfat dry milk. A limited number of retail samples were analyzed also to determine whether these samples contained vitamin A within the recommended range. MATERIALS AND METHODS

Nine consecutive 2.5-kg plastic bags of instantized nonfat dry milk were taken from the packaging line at Stacey Brothers Dairy in Mitchell, Ontario. Addition of vitamin in this plant was immediately after steam injection of the instantizing process. This is a commonly used procedure in the industry. The preparation was Vitex A-D (Diamond Shamrock Corp., St. Louis, MO), which is a liquid vitamin supplement containing vitamin A palmitate in

2188

VITAMIN A IN NONFAT DRY MILK

2189

TABLE 1. Vitamin A content of nine consecutive 2.5-kg bags of instantized nonfat dry milk analyzed in quadruplicate. ~9

Vitamin A, IU/100 g Bag no.

Range

Mean

SD

1 2 3 4 5 6

1450 1419 1650 1403 1234 1512

1459 1465 1672 1415 1249 1520

8.2 33.4 16.9 15.0 11.0 15.0 17.8 17.3 19.3 121.5

1465 1496 1697 1434 1265 1542 1 2 9 5 - - 1342 1373 - 1403 1373 1419

7

8 9 Overall

-----

1317

1383 1392 1430

IE tU O2 gSO

z_

~as >

0

I

I

I

I

I

I

I

I

2

4

6

8

I0

12

14

16

STORAGE

TIME

-

WEEKS

Figure 1. Vitamin A for 16 wk in the dark at 21°C (A), at 26°C (B), at 32°C (C), and at 21°C under 3500 lx of fluorescent light (D). Points represent concentrations by regression analysis from the analytical data. r e c o n s t i t u t e d NDM and b u t t e r oil. Sampies were t r a n s p o r t e d in the dark to the I a b o r a t o r v and k e p t in t h e refrigerator until analyzed. The vitamin A c o n t e n t o f the i n s t a n t i z e d n o n f a t d r y milk in each bag was d e t e r m i n e d to o b t a i n information about uniformity of incorporation. F o r stability e x p e r i m e n t s , t h r e e lots o f instantized n o n f a t dry milk were p r e p a r e d by m i x e d c o n t e n t s o f t w o 2.5-kg bags. Samples were m i x e d b y shaking for 20 min in a covered plastic pail. F r o m each o f these m i x e d samples, lO0-g p o r t i o n s were placed in clear p o l y e t h y l e n e bags and closed w i t h twist ties. F o r vitamin A analysis, 100 g of i n s t a n t i z e d n o n f a t dry milk and 400 ml of w a t e r were m i x e d in a b l e n d e r at m e d i u m s p e e d for 1 min.

F i f t y grams o f this solution was diluted with 50 ml o f w a t e r and 100 ml o f a 1% s o l u t i o n o f pyrogalloi in e t h a n o l . This m i x t u r e was sap o n i f i e d w i t h 20 ml o f 37.5% p o t a s s i u m h y d r o x i d e for 20 rain in a w a t e r b a t h at 80°C. T h e saponified s o l u t i o n was cooled and t h e n t r a n s f e r r e d to a 250-ml v o l u m e t r i c flask and b r o u g h t to the m a r k with 50% e t h a n o l . V i t a m i n A c o n t e n t was d e t e r m i n e d a c c o r d i n g to the m e t h o d o f S e n y k et al. (6) w i t h a GK T u r n e r A s s o c i a t e s mode1 110 f l u o r o m e t e r . The ins t r u m e n t was s t a n d a r d i z e d daily with a s t a n d a r d quinine sulfate solution.

TABLE 2. Results of regression analysis of vitamin A data obtained in the stability experiment. Variable

Regression term

Mean square

r2

Temp 21°C -- light

Time - linear Time quadratic

63893 38139

.57 .34

Temp 21°C -- dark

Time - linear Time -- quadratic

7150 3223

.50 .22

Temp 26°C -- dark

Time linear Time -- quadratic

12690 3854

.66 .20

Time 32°C

Time - linear Time quadratic

28479 4445

.73 .11

CV a × 100

29 11

dark

16 a

.

.

.

.

Coefficient of vananon. Journal of Dairy Science Vol. 67, No. 10, 1984

2190

deBOER ET AL.

The stability experiment consisted of a 4 x 7 factoral arrangement in three replications. The first factor consisted of four storage conditions: 2 I°C and fluorescent light exposure of 3500 lx, 21°C and darkness, 26°C and darkness, 32°C and darkness. The second factor consisted of seven storage times; 0, 2, 4, 6, 8, 12, and 16 wk. Statistical analysis was by CMS statistical analysis system of the University of Guelph, Institute of Computer Science. Data were fitted by a regression equation of the form:

O'~

r)

~

~e~

O

~

eq ,.-a

O

y=a+btxl

+b2

X1 2

wh ere : y x a b

-- IU of vitamin A = storage time = regression intercept = partial regression coefficients

% ~.

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m."

. ~ .eqeq

,,--~ ,..~

r~

A separate regression equation was developed for each storage condition.

E O

RESULTS A N D DISCUSSION

A 100-g portion of NDM from each of nine 2.5-kg bags was suspended in 400 ml of water and analyzed for vitamin A content in quadruplicate. Results of these analyses are in Table 1. The data indicate the reliability of the method and the considerable variation of vitamin A content between bags of the same lot (range of means 123.4 to 169.7 IU/100 g). Analysis of variance indicated that the difference between bags was significant. This demonstrates the difficulty in homogeneously incorporating vitamin concentrate into the powder. Effects of storage temperature and light were investigated in the stability experiment. Vitamin A content was determined for up to 16 wk at three storage temperatures, 21, 26, and 32°C, and at 21°C and 3500 lx of fluorescent light. The data were analyzed as described under Materials and Methods. Predictions by the regression equations are in Figure 1. Increasing storage temperature in the absence of light increased loss of vitamin A. At the end of the 16 wk, the powder stored at 21°C lost 20%; at 26°C the loss was 28%, and at 32°C the loss was 38%. Most of the loss occurred during the first 10 wk of storage. The product stored at 21°C under fluorescent light suffered more Journal of Dairy Science Vol. 67, No. 10, 1984

6

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VITAMIN A IN NONFAT DRY MILK extensive loss of vitamin A than those stored in the dark. Conditions of temperature and light were chosen to represent conditions that may be encountered in a supermarket. Up to 70% of vitamin A was lost at the end of 12 wk of storage. There was an increase of vitamin A during the last 4 wk of this part of the experiment. Although analysis of the data involving a quadratic term partially may explain the upward turn of the curve, there is no obvious explanation for the higher vitamin A during the last week of this experiment. Such upturns of vitamin A have been observed in several experiments in our laboratory and in the work of others (5). The pertinent data from the regression analysis of this experiment are in Table 2. The r 2 indicate that a greater portion of variability was accounted for by the quadratic term for samples exposed to light than for samples kept in the dark. A number of samples of instantized nonfat dry milk were obtained from local supermarkets. Seventeen samples of seven brands were analyzed. Results are in Table 3. For those packages with identifiable code dating, the mean age of products varied from 12 to 15 wk. All packages had claimed vitamin A in the product. These claims varied from 1400 IU/100 g, the lowest permitted by the Canadian Food and Drug Act, to a high of 2370 1U/100 g. Of the three brands of which more than one sample were anaiyzed, two (A and C) had widely different vitamin A contents, whereas brand B was more uniform between samples. Of the 17 samples only 1 exceeded the amount claimed on the label. Most samples met the minimum required by the Canadian Food and Drug Act, but 7 of the 17 samples failed to reach this concentration. Mol (4) found that stability of vitamin A in stored instantized nonfat dry milk was satisfactory when vitamin A was added to milk or mixed with powder in the form of small beadlets.

2191

Nakai et aI. (5) found that 27% of instantized nonfat dry milk samples analyzed had vitamin A less than the accepted minimum. They found that dry blending vitamin A beadlets with the powder or addition of beadlets at the agglomeration chamber during the instantizing process were the best fortification methods. In this work vitamin A loss of instantized nonfat dry milk stored at 21°C was not excessive. However, exposure to light may greatly increase the loss. Because it is difficult to incorporate vitamin A uniformly, there is a possibility of a considerable number of samples at retail being below the prescribed content. ACKNOWLEDGMENT

Financial support for this research was provided by the Ontario Milk Marketing Board and the Ontario Ministry of Agriculture and Food. G. C. Ashton assisted with experimental design and analysis of data.

REFERENCES

1 Anonvmous. 1976. Fortification of skimmilk powder with vitamins A and D. PAG Bull. 6(4):2. 2 Bauernfeind, J. C., and L. E. Allen. 1963. Vitamin A and D enrichment of nonfat dry milk. J. Dairy Sci. 46:245. 3 deMan, J. M. 1981. Light induced destruction of vitamin A in milk. J. Dairy Sci. 64:2031. 4 Mol, J. J., A. J. Damman, and J. Eisses. 1976. Her vitamineren van ordermelkpoeder. Zuivelzicht 68:802, 5 Nakai, S., G. Amantea, K. Eugster, L. Jung, C. Y. Ma, K. Nillson, K. Suyama, and D. Emmons. 1983. Vitamin A and haylike flavour in nonfat dry milk and pasteurized low fat milks. Can. Inst. Food Sci. Technol. J. 16:116. 6 Senyk, G, F., J. F. Gregory, and W. F. Shipe. 1975. Modified fluorometric determination of vitamin A in milk. J. Dairy Sci. 58:558. 7 Thompson, J. N., and P. Erdody, 1974. Destruction by light of vitamin A added to milk. Can. Inst. Food Sci. Technol. J. 7:157,

Journal of Dairy Science Vol. 67, No. 10, 1984