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Flavor of Milk One Week After Addition of Iron Complex1
Flavor of Milk One Week After Addition of Iron Complex 1 R. E. B A L D W I N , D. S. S H E L L E Y , and R. T. M A R S H A L L Department of Food Science and Nutrition University of Missouri Columbia 65211
ABSTRACT
Reduced iron, complexed with citric and phosphoric acids and containing potassium hydroxide, was added 100 mg/ liter to milk before and after pasteurization at combinations of comparatively low and high times and temperatures. Milk was stored 1 wk at 3°C, then analyzed for sensory attributes by an experienced panel and for degree of oxidation by the thiobarbituric acid test. The additive containing iron reduced the intensity of cooked flavor in milk heated at 80°C for 25 s and produced a slight but significant increase in oxidized flavor when it was added after pasteurization to milk heated at 72°C for 17 s. Thiobarbituric acid tests showed higher aldehyde concentrations in treated than in control samples, and the highest thiobarbituric acid value was associated with adding iron after pasteurization at 72°C for 17 s. The additive showed promise for fortification of milk with minimal risk of oxidized flavor.
INTRODUCTION
Milk contains less than 1 mg of iron per liter. Thus, a 232 ml serving provides only about .2% of the maximal US Recommended Dietary Allowance for iron. Because milk is an excellent source of other nutrients and is widely consumed, it is a logical vehicle for iron supplementation. It could provide an effective means of combating iron deficiency, particularly in children.
Received July 29, 1981. Contribution from the University of Missouri Experiment Station, Journal Series No. 8924. 1982 J Dairy Sci 65:1390-1393
A deterrent to iron supplementation of milk is the phenomenon of metal-catalyzed oxidation accompanied by undesirable changes of flavor. The catalytic effect of iron on oxidation in milk is greater if the iron is in the ferrous rather than the ferric iron (4, 5). Iron and copper that occur naturally in milk do not affect oxidation because they are complexed with proteins and are not dialyzable at the normal pH of milk (7). Scanlan and Shipe (9) reported that oxidized flavor was induced by steam-vacuum treatment in multivitamin mineral milk containing soluble ferric pyrophosphate. However, flavor was not affected when the milk was pasteurized at 76°C for 16 s before homogenization at 12,000 kPa. They suggested that steam-vacuum treated milk had a higher reducing capacity than did normally pasteurized milk. Thus, it had a greater capacity to reduce ferric iron to the stronger prooxidant ferrous form. This is in contrast to numerous reports that high heat treatment retards onset of oxiized flavor (10). This study was to evaluate the potential of a proprietary compound, Bio-PlexTM Fe, as an iron supplement for milk. The compound was added to milk before and after pasteurization under conditions simulating m i n i m u m and near maximum heat treatments for the high-temperature short-time process. Oxidative, cooked, and feed flavors were examined as characteristics that were most likely to vary in milk. The thiobarbituric acid (TBA) test was applied to assess oxidative changes. MATERIALS AND METHODS Milk
Grade A raw milk was collected from three or more Holstein cows for each experimental replication. It was no more than 48-h old when processed. The milk for each of the five replications was from different groups of cows.
1390
FLAVOR OF MILK WITH IRON Processing
Within each replicate, milk was divided into six aliquots. Bio-PlexT M Fe, 2 an iron additive, was mixed with two aliquots before and two aliquots after pasteurization. The remaining two aliquots were negative controls (no iron additives). Pasteurization was in an APV plate type heat exchanger. Milk was preheated to 60°C, then homogenized at pressures of 14,000 and 3500 kPa on first and second stage valves, respectively. After passage through the holding tube, milk immediately was cooled to below 10°C in a plate heat exchanger. Samples were collected aseptically in hypochlorite sanitized glass bottles, then stored in the dark at 3°C. Aliquots to which iron was added after pasteurization were kept outside the refrigerator no longer than the other aliquots, and mixing was with thoroughly sanitized utensils. Bio-PlexTM Fe was added at 100 rag/liter, which provided 3.5 mg of iron per 232 ml. This concentration was 20% the US Recommended Dietary Allowance. Treatments of milk were: 1) pasteurized at 72°C for 17 s with a) no iron added (control1), b) iron added after pasteurization, c) iron added before pasteurization; 2) pasteurized at 80°C for 25 s with a) no iron added (control2), b) iron added after pasteurization, c) iron added before pasteurization. Milk was stored 7 days (3°C) prior to evaluation. Standard plate counts (8) of bacteria were at the time of sensory analysis. Sensory Evaluation
The sensory panel was 10 individuals (staff and students) with considerable experience and expertise in evaluating dairy products. Orientation consisted of evaluations-of samples of milk with slight and definite oxidative flavors induced by light. These samples were discussed, and agreement on intensity ratings was achieved. Two replications were completed on each of 3 days of testing. Each replication included one
2Bio_PlexTM Fe, R.G.B. Laboratories, Inc., Kansas City, MO 64108. Contains citric acid, potassium hydroxide, phosphoric acid, and reduced iron (15%).
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sample representing each of the six treatments. There was a 15 min rest between replications. The first set of samples evaluated on the 1st day served as practice. Milk was removed from the refrigerator (4°C) and brought to 18°C + 1° in a water bath. Twenty milliliter samples were poured into randomly coded odorless plastic cups (100 ml capacity) and served immediately in a separate random order to each panelist, one sample at a time. Panelists evaluated each sample on a 5-point scale ranging from none to intense for oxidized, cooked, and feed flavors. If other flavors were observed, a descriptor and intensity rating were recorded. Panelists expectorated samples and cleansed their palates with tap water at room temperature. Sensory panels were in an air-conditioned facility equipped with individual booths. Twoway signal lights provided communication between panelist and researcher. Thiobarbiturie Acid (TBA) Analyses
The TBA analyses were on milk from all treatments on the morning following sensory tests. These determinations were by the method of Dunkley and Jennings (3) as modified by Hegenauer et al. (5). Results are molar concentration of malonaldehyde (x 10 - l ° ) with 1,1, 3,3-tetramethoxypropane (TMP) as the standard. Statistical Analysis
Data were treated by analysis of variance (11) and Duncan's (1) new multiple range test was applied to locate significant (P<.05) differences among means. These analyses required assigning numbers to sensory ratings for intensity of flavors. One denoted none and five denoted a rating of intense for each characteristic. Correlation coefficients (11) were computed for sensory scores and TBA values. Off-flavor descriptors, which were recorded by panelists, were tallied and classified as terms related to oxidative changes or as terms denoting other undesirable characteristics. Chi square analyses (11) were applied to these two classes of descriptors. RESULTS AND DISCUSSION
Mean sensory scores (Table 1) suggested that all of the milk had very slight oxidized and Journal of Dairy Science Vol. 65, No. 8, 1982
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BALDWIN ET AL.
TABLE 1. Mean I sensory scores and malonaldehyde concentration (TBA analysis) for milk with Bio-PlexT M Fe added before and after pasteurization at two temperatures.
Flavor description s
Malonaldehyde (molar concentration × 10 -1° )
Treatment
Oxidized
Cooked
Feed
Pasteurized 72°C, 17 s Control 1 Bio-PlexT M Fe added after pasteurization Bio-PlexT M Fe added before pasteurization
1.4 B 1.9 A 1.6 AB
2.2 B 1.9 B 2.0 B
1.7 A 1.6 A 1.8 A
1.89 C 7.85AB 5.65 B
Pasteurized 80°C, 25 s Control 2 Bio-PlexT M Fe added after pasteurization Bio-PlexT M Fe added before pasteurization
1.4 B 1.6 AB 1.6 AB
3.0 A 2.1B 2.2 B
1.6 A 1.8 A 1.7 A
1.60 C 8.92 A 8.77 A
A'B'CMeans within a column with different superscripts are significantly different (P<.05). 1 N = 5 replications (10 judges each). 2 Range of flavor scores, 1 = none to 5 = intense.
feed-like flavors. I n t e n s i t y o f feed flavor did n o t differ a m o n g t r e a t m e n t s . O x i d i z e d flavor was significantly m o r e i n t e n s e in m i l k to w h i c h Bio-PlexWM Fe was a d d e d a f t e r p a s t e u r i z a t i o n at 7 2 ° C f o r 17 s t h a n it was in e i t h e r c o n t r o l . Each of t h e o t h e r a l i q u o t s w i t h a d d e d BioPlexTM Fe h a d i n t e r m e d i a t e s e n s o r y scores t h a t were n o t significantly h i g h e r t h a n scores o f c o n t r o l s w i t h o u t a d d e d iron. N e i t h e r were t h e s e i n t e r m e d i a t e scores significantly lower t h a n t h a t of t h e m i n i m a l l y p a s t e u r i z e d s a m p l e (72°C, 17 s) w i t h iron a d d e d a f t e r pasteurization. C o o k e d flavor was significantly m o r e intense, as e x p e c t e d , in t h e m a x i m a l l y h e a t e d c o n t r o l 2 milk t h a n in t h e m i n i m a l l y h e a t e d controI1 milk. A d d i t i o n of Bio-Plex t o t h e m a x i m a l l y h e a t e d milk was associated w i t h significantly less i n t e n s e c o o k e d flavor t h a n was in t h e c o n t r o l 2 (Table 1). V a r i a n c e also was a n a l y z e d o f d a t a g r o u p e d a c c o r d i n g to t i m e of a d d i n g Bio-Plex T M Fe ( b e f o r e or a f t e r p a s t e u r i z a t i o n ) . No e f f e c t in oxidized, c o o k e d , or feed flavors was signific a n t f o r this variable. A l t h o u g h d e t e c t a b l e b y t h e highly experie n c e d p a n e l in this s t u d y , t h e m a g n i t u d e o f oxidized flavor was small even w h e r e t h e difference was significant. In milk p a s t e u r i z e d at Journal of Dairy Science Vol. 65, No. 8, 1982
80°C (25 s), t h e d i f f e r e n c e in c o o k e d flavor b e t w e e n c o n t r o l 2 m i l k a n d t h a t c o n t a i n i n g BioPlexTM Fe also was small. However, BioPlex TM Fe a p p e a r e d t o m a s k or r e d u c e i n t e n sity o f t h e c o o k e d flavor (Table 1). Because d i f f e r e n c e s in b o t h o x i d i z e d a n d c o o k e d flavors were so small, it is n o t likely t h a t i n e x p e r i e n c e d panelists or c o n s u m e r s w o u l d b e aware of t h e m . It is h i g h l y u n l i k e l y t h a t m i c r o b i a l l y i n d u c e d o f f flavors were in t h e s e samples, b e c a u s e o n l y grade A fresh raw m i l k was u s e d as r a w m a t e r ial, a n d b a c t e r i a c o u n t s o f p a s t e u r i z e d samples never e x c e e d e d 103/ml.
Thiobarbituric Acid (TBA) Analyses D u n k l e y (2) p o i n t e d o u t t h a t p e r o x i d e n u m bers, fat a l d e h y d e , i o d i n e n u m b e r s , a n d o t h e r tests have o n l y l i m i t e d a p p l i c a t i o n to dairy p r o d u c t s a n d are n o t s u f f i c i e n t l y sensitive to assess o x i d a t i v e changes associated w i t h flavor d e t e r i o r a t i o n in milk. C o r r e l a t i o n o f data f r o m t h e T B A test w i t h s e n s o r y scores f o r o x i d i z e d flavor o f m i l k a n d r e p r o d u c i b i l i t y o f t h e d a t a have b e e n d o c u m e n t e d (2, 3, 6). T h e r e f o r e , t h e T B A test was selected f o r a p p l i c a t i o n in this investigation. T h e test is based o n a r e a c t i o n b e t w e e n m a l o n a l d e h y d e , p r o d u c e d d u r i n g oxidative b r e a k d o w n o f u n s a t u r a t e d f a t t y acids,
FLAVOR OF MILK WITH IRON and TBA that forms a red color measurable by s p e c t r o p h o t o m e t r i c m e t h o d s (12). Oxidative r a n c i d i t y , as m e a s u r e d b y T B A test, was significantly less in b o t h c o n t r o l s t h a n in milk w i t h a d d e d Bio-PlexTM F e ( T a b l e 1). Also, t h e t r e n d in T B A d a t a for m i l k past e u r i z e d at 72°C (17 s) s u p p o r t s findings o f t h e s e n s o r y p a n e l t h a t o x i d a t i o n was g r e a t e s t in samples to w h i c h Bio-PlexTM Fe was a d d e d a f t e r p a s t e u r i z a t i o n . However, w h e n all d a t a were g r o u p e d a c c o r d i n g t o t i m e of a d d i n g BioPlexTM Fe, t h e r e was n o significant d i f f e r e n c e in m a l o n a l d e h y d e c o n c e n t r a t i o n . This, too, s u p p o r t s t h e t r e n d in d a t a of s e n s o r y tests. CONCLUSIONS
Bio-PlexTM Fe is p o t e n t i a l l y a g o o d iron s u p p l e m e n t for milk. T h e additive has an att e n u a t i n g e f f e c t o n c o o k e d flavor a n d exerts little i n f l u e n c e o n o x i d i z e d flavor in m i l k past e u r i z e d u n d e r h i g h - t e m p e r a t u r e s h o r t - t i m e processing c o n d i t i o n s . T h e l i k e l i h o o d o f o x i d i z e d flavor w o u l d be increased if t h e c o m p o u n d were a d d e d a f t e r p a s t e u r i z a t i o n a t t h e m i n i m a l t e m p e r a t u r e a n d time. Even u n d e r this c i r c u m stance, t h e p r o b a b i l i t y of c o n s u m e r s discrimin a t i n g against t h e m i l k is small. This s h o u l d be verified b y tests w i t h a c o n s u m e r panel. ACKNOWLEDGMENTS
A p p r e c i a t i o n is e x p r e s s e d to A h m e d S h a h i n for assistance w i t h T B A tests a n d t o J i m m i e D. B r e c h b u h l e r f o r assistance w i t h p r e p a r a t i o n o f samples.
1393 REFERENCES
1 Duncan, D. B. 1955. New multiple range and multiple F tests. Biometrics 11:1. 2 Dunkley, W. L. 1951. Evaluation of the thiobarbituric acid test as a measure of oxidized flavor in milk. Food Technol. 5:342. 3 Dunkley, W. L., and W. G. Jennings. 1951. A procedure for application of the thiobarbituric acid test to milk. J. Dairy Sci. 34:1064. 4 Greenback, G. R. 1940. Variation in the oxidationreduction potential as cause for the oxidized flavor in milk. J. Dairy Sci. 23:725. 5 Hegenauer, J., P. Saltman, D. Ludwig, L. Ripley, and P. Bajo. 1979. Effects of supplemental iron and copper on lipid oxidation in milk. I. Comparison of metal complexes in emulsified and homogenized milk. J. Agric. Food Chem. 27:860. 6 King, R. L. 1962. Oxidation of milk fat globule membrane material. I. Thiobarbituric acid reaction as a measure of oxidized flavor in milk and model systems. J. Dairy Sci. 45:1165. 7 King, R. L., J. R. Luick, I. I. Litman, W. G. Jennings, and W. L. Dunkley. 1959. Distribution of natural and added copper and iron in milk. J. Dairy Sci. 42:780. 8 Marth, E. H., ed. 1978. Standard methods for the examination of dairy products. 14th ed. Am. Publ. Health Assoc., Washington, DC. 9 Scanlan, R. A., and W. F. Shipe. 1962. Factors affecting the susceptibility of multivitamin mineral milk to oxidation. J. Dairy Sci. 45:1449. 10 Shipe, W. F. 1964. Oxidations in the dark. J. Dairy Sci. 47:221. 11 Snedecor, G. W., and W. G. Cochran. 1967. Statistical methods. 6th ed. Iowa State Univ. Press, Ames. 12 Tarladgis, B. E., A. M. Pearson, and L. R. Dugan, Jr. 1964. Chemistry of the 2-thiobarbituric acid test for determination of oxidative rancidity in foods. II. Formation of the TBA-malonaldehyde complex without acid-heat treatment. J. Sci. Food Agric. 15:602.
Journal of Dairy Science Vol. 65, No. 8, 1982
ABSTRACT
Reduced iron, complexed with citric and phosphoric acids and containing potassium hydroxide, was added 100 mg/ liter to milk before and after pasteurization at combinations of comparatively low and high times and temperatures. Milk was stored 1 wk at 3°C, then analyzed for sensory attributes by an experienced panel and for degree of oxidation by the thiobarbituric acid test. The additive containing iron reduced the intensity of cooked flavor in milk heated at 80°C for 25 s and produced a slight but significant increase in oxidized flavor when it was added after pasteurization to milk heated at 72°C for 17 s. Thiobarbituric acid tests showed higher aldehyde concentrations in treated than in control samples, and the highest thiobarbituric acid value was associated with adding iron after pasteurization at 72°C for 17 s. The additive showed promise for fortification of milk with minimal risk of oxidized flavor.
INTRODUCTION
Milk contains less than 1 mg of iron per liter. Thus, a 232 ml serving provides only about .2% of the maximal US Recommended Dietary Allowance for iron. Because milk is an excellent source of other nutrients and is widely consumed, it is a logical vehicle for iron supplementation. It could provide an effective means of combating iron deficiency, particularly in children.
Received July 29, 1981. Contribution from the University of Missouri Experiment Station, Journal Series No. 8924. 1982 J Dairy Sci 65:1390-1393
A deterrent to iron supplementation of milk is the phenomenon of metal-catalyzed oxidation accompanied by undesirable changes of flavor. The catalytic effect of iron on oxidation in milk is greater if the iron is in the ferrous rather than the ferric iron (4, 5). Iron and copper that occur naturally in milk do not affect oxidation because they are complexed with proteins and are not dialyzable at the normal pH of milk (7). Scanlan and Shipe (9) reported that oxidized flavor was induced by steam-vacuum treatment in multivitamin mineral milk containing soluble ferric pyrophosphate. However, flavor was not affected when the milk was pasteurized at 76°C for 16 s before homogenization at 12,000 kPa. They suggested that steam-vacuum treated milk had a higher reducing capacity than did normally pasteurized milk. Thus, it had a greater capacity to reduce ferric iron to the stronger prooxidant ferrous form. This is in contrast to numerous reports that high heat treatment retards onset of oxiized flavor (10). This study was to evaluate the potential of a proprietary compound, Bio-PlexTM Fe, as an iron supplement for milk. The compound was added to milk before and after pasteurization under conditions simulating m i n i m u m and near maximum heat treatments for the high-temperature short-time process. Oxidative, cooked, and feed flavors were examined as characteristics that were most likely to vary in milk. The thiobarbituric acid (TBA) test was applied to assess oxidative changes. MATERIALS AND METHODS Milk
Grade A raw milk was collected from three or more Holstein cows for each experimental replication. It was no more than 48-h old when processed. The milk for each of the five replications was from different groups of cows.
1390
FLAVOR OF MILK WITH IRON Processing
Within each replicate, milk was divided into six aliquots. Bio-PlexT M Fe, 2 an iron additive, was mixed with two aliquots before and two aliquots after pasteurization. The remaining two aliquots were negative controls (no iron additives). Pasteurization was in an APV plate type heat exchanger. Milk was preheated to 60°C, then homogenized at pressures of 14,000 and 3500 kPa on first and second stage valves, respectively. After passage through the holding tube, milk immediately was cooled to below 10°C in a plate heat exchanger. Samples were collected aseptically in hypochlorite sanitized glass bottles, then stored in the dark at 3°C. Aliquots to which iron was added after pasteurization were kept outside the refrigerator no longer than the other aliquots, and mixing was with thoroughly sanitized utensils. Bio-PlexTM Fe was added at 100 rag/liter, which provided 3.5 mg of iron per 232 ml. This concentration was 20% the US Recommended Dietary Allowance. Treatments of milk were: 1) pasteurized at 72°C for 17 s with a) no iron added (control1), b) iron added after pasteurization, c) iron added before pasteurization; 2) pasteurized at 80°C for 25 s with a) no iron added (control2), b) iron added after pasteurization, c) iron added before pasteurization. Milk was stored 7 days (3°C) prior to evaluation. Standard plate counts (8) of bacteria were at the time of sensory analysis. Sensory Evaluation
The sensory panel was 10 individuals (staff and students) with considerable experience and expertise in evaluating dairy products. Orientation consisted of evaluations-of samples of milk with slight and definite oxidative flavors induced by light. These samples were discussed, and agreement on intensity ratings was achieved. Two replications were completed on each of 3 days of testing. Each replication included one
2Bio_PlexTM Fe, R.G.B. Laboratories, Inc., Kansas City, MO 64108. Contains citric acid, potassium hydroxide, phosphoric acid, and reduced iron (15%).
1391
sample representing each of the six treatments. There was a 15 min rest between replications. The first set of samples evaluated on the 1st day served as practice. Milk was removed from the refrigerator (4°C) and brought to 18°C + 1° in a water bath. Twenty milliliter samples were poured into randomly coded odorless plastic cups (100 ml capacity) and served immediately in a separate random order to each panelist, one sample at a time. Panelists evaluated each sample on a 5-point scale ranging from none to intense for oxidized, cooked, and feed flavors. If other flavors were observed, a descriptor and intensity rating were recorded. Panelists expectorated samples and cleansed their palates with tap water at room temperature. Sensory panels were in an air-conditioned facility equipped with individual booths. Twoway signal lights provided communication between panelist and researcher. Thiobarbiturie Acid (TBA) Analyses
The TBA analyses were on milk from all treatments on the morning following sensory tests. These determinations were by the method of Dunkley and Jennings (3) as modified by Hegenauer et al. (5). Results are molar concentration of malonaldehyde (x 10 - l ° ) with 1,1, 3,3-tetramethoxypropane (TMP) as the standard. Statistical Analysis
Data were treated by analysis of variance (11) and Duncan's (1) new multiple range test was applied to locate significant (P<.05) differences among means. These analyses required assigning numbers to sensory ratings for intensity of flavors. One denoted none and five denoted a rating of intense for each characteristic. Correlation coefficients (11) were computed for sensory scores and TBA values. Off-flavor descriptors, which were recorded by panelists, were tallied and classified as terms related to oxidative changes or as terms denoting other undesirable characteristics. Chi square analyses (11) were applied to these two classes of descriptors. RESULTS AND DISCUSSION
Mean sensory scores (Table 1) suggested that all of the milk had very slight oxidized and Journal of Dairy Science Vol. 65, No. 8, 1982
1392
BALDWIN ET AL.
TABLE 1. Mean I sensory scores and malonaldehyde concentration (TBA analysis) for milk with Bio-PlexT M Fe added before and after pasteurization at two temperatures.
Flavor description s
Malonaldehyde (molar concentration × 10 -1° )
Treatment
Oxidized
Cooked
Feed
Pasteurized 72°C, 17 s Control 1 Bio-PlexT M Fe added after pasteurization Bio-PlexT M Fe added before pasteurization
1.4 B 1.9 A 1.6 AB
2.2 B 1.9 B 2.0 B
1.7 A 1.6 A 1.8 A
1.89 C 7.85AB 5.65 B
Pasteurized 80°C, 25 s Control 2 Bio-PlexT M Fe added after pasteurization Bio-PlexT M Fe added before pasteurization
1.4 B 1.6 AB 1.6 AB
3.0 A 2.1B 2.2 B
1.6 A 1.8 A 1.7 A
1.60 C 8.92 A 8.77 A
A'B'CMeans within a column with different superscripts are significantly different (P<.05). 1 N = 5 replications (10 judges each). 2 Range of flavor scores, 1 = none to 5 = intense.
feed-like flavors. I n t e n s i t y o f feed flavor did n o t differ a m o n g t r e a t m e n t s . O x i d i z e d flavor was significantly m o r e i n t e n s e in m i l k to w h i c h Bio-PlexWM Fe was a d d e d a f t e r p a s t e u r i z a t i o n at 7 2 ° C f o r 17 s t h a n it was in e i t h e r c o n t r o l . Each of t h e o t h e r a l i q u o t s w i t h a d d e d BioPlexTM Fe h a d i n t e r m e d i a t e s e n s o r y scores t h a t were n o t significantly h i g h e r t h a n scores o f c o n t r o l s w i t h o u t a d d e d iron. N e i t h e r were t h e s e i n t e r m e d i a t e scores significantly lower t h a n t h a t of t h e m i n i m a l l y p a s t e u r i z e d s a m p l e (72°C, 17 s) w i t h iron a d d e d a f t e r pasteurization. C o o k e d flavor was significantly m o r e intense, as e x p e c t e d , in t h e m a x i m a l l y h e a t e d c o n t r o l 2 milk t h a n in t h e m i n i m a l l y h e a t e d controI1 milk. A d d i t i o n of Bio-Plex t o t h e m a x i m a l l y h e a t e d milk was associated w i t h significantly less i n t e n s e c o o k e d flavor t h a n was in t h e c o n t r o l 2 (Table 1). V a r i a n c e also was a n a l y z e d o f d a t a g r o u p e d a c c o r d i n g to t i m e of a d d i n g Bio-Plex T M Fe ( b e f o r e or a f t e r p a s t e u r i z a t i o n ) . No e f f e c t in oxidized, c o o k e d , or feed flavors was signific a n t f o r this variable. A l t h o u g h d e t e c t a b l e b y t h e highly experie n c e d p a n e l in this s t u d y , t h e m a g n i t u d e o f oxidized flavor was small even w h e r e t h e difference was significant. In milk p a s t e u r i z e d at Journal of Dairy Science Vol. 65, No. 8, 1982
80°C (25 s), t h e d i f f e r e n c e in c o o k e d flavor b e t w e e n c o n t r o l 2 m i l k a n d t h a t c o n t a i n i n g BioPlexTM Fe also was small. However, BioPlex TM Fe a p p e a r e d t o m a s k or r e d u c e i n t e n sity o f t h e c o o k e d flavor (Table 1). Because d i f f e r e n c e s in b o t h o x i d i z e d a n d c o o k e d flavors were so small, it is n o t likely t h a t i n e x p e r i e n c e d panelists or c o n s u m e r s w o u l d b e aware of t h e m . It is h i g h l y u n l i k e l y t h a t m i c r o b i a l l y i n d u c e d o f f flavors were in t h e s e samples, b e c a u s e o n l y grade A fresh raw m i l k was u s e d as r a w m a t e r ial, a n d b a c t e r i a c o u n t s o f p a s t e u r i z e d samples never e x c e e d e d 103/ml.
Thiobarbituric Acid (TBA) Analyses D u n k l e y (2) p o i n t e d o u t t h a t p e r o x i d e n u m bers, fat a l d e h y d e , i o d i n e n u m b e r s , a n d o t h e r tests have o n l y l i m i t e d a p p l i c a t i o n to dairy p r o d u c t s a n d are n o t s u f f i c i e n t l y sensitive to assess o x i d a t i v e changes associated w i t h flavor d e t e r i o r a t i o n in milk. C o r r e l a t i o n o f data f r o m t h e T B A test w i t h s e n s o r y scores f o r o x i d i z e d flavor o f m i l k a n d r e p r o d u c i b i l i t y o f t h e d a t a have b e e n d o c u m e n t e d (2, 3, 6). T h e r e f o r e , t h e T B A test was selected f o r a p p l i c a t i o n in this investigation. T h e test is based o n a r e a c t i o n b e t w e e n m a l o n a l d e h y d e , p r o d u c e d d u r i n g oxidative b r e a k d o w n o f u n s a t u r a t e d f a t t y acids,
FLAVOR OF MILK WITH IRON and TBA that forms a red color measurable by s p e c t r o p h o t o m e t r i c m e t h o d s (12). Oxidative r a n c i d i t y , as m e a s u r e d b y T B A test, was significantly less in b o t h c o n t r o l s t h a n in milk w i t h a d d e d Bio-PlexTM F e ( T a b l e 1). Also, t h e t r e n d in T B A d a t a for m i l k past e u r i z e d at 72°C (17 s) s u p p o r t s findings o f t h e s e n s o r y p a n e l t h a t o x i d a t i o n was g r e a t e s t in samples to w h i c h Bio-PlexTM Fe was a d d e d a f t e r p a s t e u r i z a t i o n . However, w h e n all d a t a were g r o u p e d a c c o r d i n g t o t i m e of a d d i n g BioPlexTM Fe, t h e r e was n o significant d i f f e r e n c e in m a l o n a l d e h y d e c o n c e n t r a t i o n . This, too, s u p p o r t s t h e t r e n d in d a t a of s e n s o r y tests. CONCLUSIONS
Bio-PlexTM Fe is p o t e n t i a l l y a g o o d iron s u p p l e m e n t for milk. T h e additive has an att e n u a t i n g e f f e c t o n c o o k e d flavor a n d exerts little i n f l u e n c e o n o x i d i z e d flavor in m i l k past e u r i z e d u n d e r h i g h - t e m p e r a t u r e s h o r t - t i m e processing c o n d i t i o n s . T h e l i k e l i h o o d o f o x i d i z e d flavor w o u l d be increased if t h e c o m p o u n d were a d d e d a f t e r p a s t e u r i z a t i o n a t t h e m i n i m a l t e m p e r a t u r e a n d time. Even u n d e r this c i r c u m stance, t h e p r o b a b i l i t y of c o n s u m e r s discrimin a t i n g against t h e m i l k is small. This s h o u l d be verified b y tests w i t h a c o n s u m e r panel. ACKNOWLEDGMENTS
A p p r e c i a t i o n is e x p r e s s e d to A h m e d S h a h i n for assistance w i t h T B A tests a n d t o J i m m i e D. B r e c h b u h l e r f o r assistance w i t h p r e p a r a t i o n o f samples.
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1 Duncan, D. B. 1955. New multiple range and multiple F tests. Biometrics 11:1. 2 Dunkley, W. L. 1951. Evaluation of the thiobarbituric acid test as a measure of oxidized flavor in milk. Food Technol. 5:342. 3 Dunkley, W. L., and W. G. Jennings. 1951. A procedure for application of the thiobarbituric acid test to milk. J. Dairy Sci. 34:1064. 4 Greenback, G. R. 1940. Variation in the oxidationreduction potential as cause for the oxidized flavor in milk. J. Dairy Sci. 23:725. 5 Hegenauer, J., P. Saltman, D. Ludwig, L. Ripley, and P. Bajo. 1979. Effects of supplemental iron and copper on lipid oxidation in milk. I. Comparison of metal complexes in emulsified and homogenized milk. J. Agric. Food Chem. 27:860. 6 King, R. L. 1962. Oxidation of milk fat globule membrane material. I. Thiobarbituric acid reaction as a measure of oxidized flavor in milk and model systems. J. Dairy Sci. 45:1165. 7 King, R. L., J. R. Luick, I. I. Litman, W. G. Jennings, and W. L. Dunkley. 1959. Distribution of natural and added copper and iron in milk. J. Dairy Sci. 42:780. 8 Marth, E. H., ed. 1978. Standard methods for the examination of dairy products. 14th ed. Am. Publ. Health Assoc., Washington, DC. 9 Scanlan, R. A., and W. F. Shipe. 1962. Factors affecting the susceptibility of multivitamin mineral milk to oxidation. J. Dairy Sci. 45:1449. 10 Shipe, W. F. 1964. Oxidations in the dark. J. Dairy Sci. 47:221. 11 Snedecor, G. W., and W. G. Cochran. 1967. Statistical methods. 6th ed. Iowa State Univ. Press, Ames. 12 Tarladgis, B. E., A. M. Pearson, and L. R. Dugan, Jr. 1964. Chemistry of the 2-thiobarbituric acid test for determination of oxidative rancidity in foods. II. Formation of the TBA-malonaldehyde complex without acid-heat treatment. J. Sci. Food Agric. 15:602.
Journal of Dairy Science Vol. 65, No. 8, 1982