- Email: [email protected]
An Assessment of Light-Induced Off-Flavors in Retail Milk
An Assessment of Light-Induced Off-Flavors in Retail Milk J. R, OLSEN and S. H. ASHOOR Division of Agriculture Arizona State University Tempe 85287 ABSTRACT
Samples of whole and skim milk from two local dairy plants that were packaged in 3.8-L plastic containers (nonreturnable high density polyethylene) and 1.9, .95, and .48-L fiberboard containers and displayed in the dairy cases of four local grocery stores under normal fluorescent light were analyzed for light-induced changes in flavor and riboflavin content. Milk samples were analyzed daily for flavor, odor, appearance, and riboflavin content. Sensory evaluation was by 25 untrained panelists, and riboflavin was determined by HPLC method. Milk samples were analyzed first in summer, then repeated in winter. Data indicated that under typical production and storage conditions in the area, type and size of container, fat content, and season of production had no major damaging effects on flavor, odor, appearance, or riboflavin content of retail milk. INTRODUCTION
Light-induced off-flavors in milk have been well-documented and discussed in several reviews (5, 9, 21, 24, 26). The development of these off-flavors in milk has been associated with the photodegradation of riboflavin, vitamin C, and recently, added vitamin A (1, 3, 8, 10, 14, 15, 23, 24). Therefore, the exposure of milk to sunlight or fluorescent light not only affects the flavor quality but decreases its nutritional value as well. Riboflavin loss is most significant in milk without vitamin A fortification since milk is not a good source of vitamin C and naturally occurring vitamin A is less susceptible to photodegradation (23). There are several factors that play a role in the photodegradation of vitamins and light-
Received September 12, 1986. Accepted March 16, 1987. 1987
J Dairy Sci 70:1362-1370
induced flavor changes in milk. Dimick (9) indicated that a major factor is the type and composition of the container in which milk is packaged and stored. Fiberboard and plastic containers are most widely used in the market today. Over 50% of all milk is sold in plastic containers at the present time (18) due to convenience and desirable appearance. Plastic containers, however, are more detrimental than fiberboard containers to the quality of lightexposed milk (6, 8, 13, 20) because they transmit more light than fiberboard containers (17). Recently, pigmented plastic containers, which reduce light transmittance and lightdamaging effects in milk, were found acceptable by consumers (25). Fat content of milk is another factor affecting photodegradation reactions in milk. Photodegradation of riboflavin and vitamin A was greater in skim milk than in whole milk (1, 23). Light-induced changes in milk are also dependent on the size of the container. Bradfield and Duthie (4) found that milk in .95-L containers developed light-induced off-flavors 6 h sooner than the same milk packaged in 1.9-L containers under similar conditions. They attributed this finding in part to less light transmission by the 1.9-L containers. Hedrick and Glass (14) pointed out that both size and shape of container influence light-induced vitamin losses in milk. Season of production affects light-induced changes in milk. Herreid et al. (15) and Dillman et al. (7) reported a greater incidence of light activated flavor in milk during the winter months, possibly due to seasonal differences in feeding conditions. However, Herreid et al. (15)also found greater photodegradation of riboflavin in milk during summer. Light-induced changes in milk are dependent on the intensity and wavelength of the light to which the milk is exposed. Sattar et al. (22) reported that the spectral wavelength range of 350 to 510 nm was generally damaging to riboflavin in solution and that the wavelengths of 415 to 455 nm were responsible for its destruction. This finding was
1362
LIGHT-INDUCED OFF-FLAVORS IN MILK of interest since most retail dairy cases are equipped with white fluorescent lamps, which have maximum emission at 450 to 500 nm (9, 11). Use of yellow fluorescent lamps or fluorescent lamps with yellow shields was effective to reduce off-flavor development in milk since these lighting systems show minimum energy emitted at wavelengths below 540 nm (5, 13). Most studies dealing with light-induced changes in milk were conducted under simulated store conditions and very few were under actual display conditions (7, 12, 18). Because studies in which milk was sampled from the market place were not comprehensively designed and did not fully clarify the effects of milk exposed to display lights in the dairy case, the National Dairy Council (16) called for further studies on the vitamin content and flavor quality of market milks to establish the significance of light exposure. This research was done to comprehensively investigate the effects of type and size of container, fat content, season of production, and store conditions on the flavor quality and riboflavin content of retail milk in the local market place. MATERIALS A N D METHODS Samples
Batches of whole milk and skim milk commercially packaged in 3.8-L plastic containers 1.9-L, .95-L, and .48-L fiberboard containers were followed from production in two local dairy plants to purchasing by consumer in four local retail stores (stores 1 and 2 for the first plant and stores 3 and 4 for the second plant. Stores 1 and 3 were large volume stores 34,200 L of milk/wk), whereas stores 2 and 4 were small volume stores (950 L of milk/wk). In atl stores, milk in various containers was displayed in the dairy case under white fluorescent light 24 h/d. In each dairy plant, samples were obtained of the raw milk from storage tanks, after pasteurization and homogenization, and immediately after packaging in different containers (control samples). Milk containers were then followed, by code date and brand, to the particular supermarkets, and samples of all containers were randomly taken daily from the same batch until the milk was sold out. The light intensity in the dairy case of each store
1363
was measured daily at center and sides of display shelves using a triple range light meter type 214 (General Electric, Cleveland, OH). The temperature inside the dairy case was also measured daily at different locations with a thermometer. Two samples were taken of each treatment. All samples were transported in ice immediately to the laboratory and were kept in a dark refrigerator at 4°C until further analysis. To study the effect of season of production, sampling was in September (summer run) and January (winter run). Sensory EvaLuation
Refrigerated milk samples were analyzed for flavor, odor, and appearance on the day of sampling. Twenty-five untrained panelists evaluated the milk samples for preference using a nine-point hedonic scoring system (from 1, dislike extremely, to 9, like extremely). Each panelist was given, on the average, eight samples to evaluate at a time, and enough water to rinse mouth after each evaluation. Riboflavin Analysis
Milk samples were analyzed for riboflavin content following the HPLC method of Ashoor et al. (2). The newly developed method was simple, rapid, and compared favorably with the AOAC official method (2). Statistical Analysis
Means obtained from flavor scores and riboflavin determinations were subjected to analysis of variance according to the Statistical Analysis System (SAS) (19). RESULTS AND DISCUSSION
The four stores chosen for this study were representative of local grocery stores. Display conditions of the dairy cases of these stores are given in Table 1. Light intensities in the dairy cases of the stores were generally lower than reported intensities in other dairy cases. In a 1974 nationwide survey, the average illumination in the dairy cases of 105 supermarkets was 2001 lx (8). In another survey, Sattar and deMan (20) indicated that the intensity of fluorescent lighting in milk display cases ranged from 269 to 5380 lx with values of 1076 to 2152 Ix being most common. Three of the four Journal of Dairy Science Vol. 70, No. 7, 1987
1364
OLSEN AND ASHOOR
stores chosen for this study had a light intensity in their dairy cases much lower than the national average, and although one of the stores (store 3) had higher light intensity, it had the fastest milk turnover and the shortest display time (Table 1). The milk display time in the dairy case of each store was monitored closely, because milk photodegradation is a function of light intensity and exposure time. The actual display time, time o f milk exposure to fluorescent light in the dairy case, was very difficult to determine. Therefore, the milk shelf-life (time after milk left the dairy plant until sold out in each store) was easier to record and was considered the "display time". Of course, this milk display time included the storage time in the dark cooler before milk was displayed in the dairy case under fluorescent light. The best estimate of the time an average milk container was exposed to fluorescent light in any of the dairy cases was 5 to 10% o f the display time. The temperature o f each dairy case at the time milk samples were picked up for evaluation was also reported (Table 1). In every store, the temperature range of the dairy case was always higher in the summer than in winter. Data obtained from evaluation of summer whole and skim milk in all containers available in our area (during this study, the only plastic containers available in the market place were the 3.8-L containers) are presented in Tables 2 and 3. This part of the study was planned for July and August; however, it could not be carried out until September. In our location, the average daytime temperature during September was 38.3°C, which is hotter than the
summer months of many other locations. Statistical analysis of the flavor scores in Table 2 indicated that all b u t two scores 3.8-L and .48-L after a display time of 1 d were not significantly different (P<.05). The riboflavin content (Table 2) varied slightly among whole milk samples, but the variation did not follow a pattern. F o r example, the riboflavin content of whole milk packaged in .95-L and .48-L fiberboard containers did not change after display times of 4 and 7 d (Table 2). Riboflavin content of the same milk in 1.9-L fiberboard containers decreased by 12.0% after display time of 4 d, whereas whole milk packaged in 3.8-L plastic containers lost only 7.9% of its riboflavin during the same display time. Similar conclusions can be derived from the data in Table 3 resulting from evaluating summer skim milk. In general, flavor scores for skim milk were lower than for whole milk, whereas skim milk had higher riboflavin content. Data in Table 3 did not include skim milk in 3.8-L plastic containers because they were not available for the same milk from the same dairy plant. Tables 2 and 3 indicate that flavor quality and riboflavin content o f marketplace milks were not significantly affected by type of container (plastic vs. fiberboard), size of container (3.8, 1.9, .95, and .48 L), or fat content (whole milk vs. skim milk). In order to study the effect o f season and to confirm the data obtained in the summer, a winter evaluation of market place milks in January (the average daytime temperature was 18.3°C) was performed under similar conditions. Data obtained from winter samples are presented in Tables 4 and 5. These results
TABLE 1. Display conditions of the dairy cases at local grocery stores.
Store
Light intensity
1
(Ix) 215-1076
2
215-1076
3 4
915--4304 129-1076
Temperature range Summer Winter (°C) 4-13 5-15 6-I0 4-12
(-1)--3 4-8 3-9 3-6
Display time I (d) 5 4--5 3--4 3-7
1Includes storage time in dark cooler prior to display. An average container was exposed to light for approximately 5 to 10% of display time. Journal of Dairy Science Vol. 70, No. 7, 1987
T A B L E 2. F l a v o r s c o r e a n d r i b o f l a v i n c o n t e n t o f s u m m e r w h o l e m i l k . ~
Flavor score 3
Display time 2
3.8L s
Riboflavin content 4
.95 L 6
1.9 L 6
.48 L 6
3.8 L s
1.9 L 6
.95 L 6
.48 L 6
(~g/ml) (d)
R
SD
0 1 2 3 4 5 6 7
7.0 4.9 6.8 6.8 6.6 , . .7 . . . . . .
1.2 a 2.5 b 1.3 a 1.8 a 1.8 a
6.9 6.0 7.3 7.1 7.2
SD
X
SD
1.0 a 1.8 a 1.1 a 1.5 a 1.2 a
5.7 4.2 4.8 5.2 5.0
2.0 a 2.2 a 2.7 a 2.3 a 2.2 a
6.1 4.9 5.4 6.1 5.1 5.7 6.2 5.5
SD
X
SD
2.1 a 2.0 b 1.8 a 1.7 a 1.9 a 2.2 a 1.9 a 1.9 a
1.40 1.34 1.23 1.22 1.29 ... . .. . . .
.03 a .02 b .01 c .02 c .02 c
1.34 1.18 1.15 1.21 1.18
SD
X
SD
.02 a .03 b .03 b .03 b .03 b
1.28 1.29 1.22 1.25 1.29
.05 a .05 a .03 a .02 a .03 a
SD 1.25 1.20 1.21 1.15 1.21 1.27 1.33 1.25
.07 a .04 a .07 a .04 b .03 a .04 a .01 a .04 a
Z t~
t~ O
-h t"
> < 0
a'b'CMeans within columns with unlike superscripts differ (P<.05). ~a
1 P l a n t 2, s t o r e 4.
o
2 I n c l u d e s s t o r a g e t i m e in d a r k c o o l e r .
N
3 M e a n o f 25 s c o r e s . 4 Mean of 6 determinations. t~
s High d e n s i t y p o l y e t h y l e n e (plastic) container. 6 Fiberboard container.
< o .,a 9 Z 9
M
7 Sold o u t .
ox Ln
1366
OLSEN AND ASHOOR
TABLE 3. Flavor score and riboflavin content of skim milk in summer) Flavor score 3
Display time 2
Riboflavin content 4
1.9 L s
1.9 L s
.95 L s
(d)
.95 L s (/~g/ml)
SD
X,
SD
2.1 a 1.9 a
4.5 2.7
2.1 a 1.5 b 2.2 a 2.3 a
0 1
4.9 4.1
2 3
4.6
1.9 a
3.9
5.3 . . .~
2.1 a
4.3 4.4
4
SD 1,59 1.51 1.48 1.33
2.1 a
.07 a .05 a .08 a .02 b
SD 1.42 1.65 1.32 1.33 1.26
.07 a .05 b .02 c .01 c .01 c
a b,c .
'
. . . . Means wlmm columns with unlike superscripts differ (P<.05).
1Plant 2, store 3. 2 Includes storage time in dark cooler. aMean of 25 scores. a Mean of 6 determinations. s Fiberboard container. 6 Sold out.
confirm the s u m m e r data and indicate that season of p r o d u c t i o n does n o t have a significant effect on the flavor quality or riboflavin stabilit y of retail milk. Flavor scores o f winter whole milk and skim milk presented in Tables 4 and 5 were n o t significantly different (P<.05), indicating no significant effect o f type, size o f container, o r fat c o n t e n t on flavor quality o f milk. Loss in riboflavin c o n t e n t in winter whole m i l k (Table 4) was 8.1% in 3.8 13.6% in and (1.9-L) c o n t a i n e r milks during 4 d of display. In w i n t e r skim m i l k (Table 5), the only loss in riboflavin was in 3.8-L milk (9.7%). However, t h e riboflavin c o n t e n t o f b o t h whole milk and skim milk was generally lower in winter than in summer. Tables 6 and 7 were c o n s t r u c t e d for easier c o m p a r i s o n of flavor scores and riboflavin c o n t e n t o f w i n t e r w h o l e milk o b t a i n e d f r o m t w o dairy plants in 3.8-L plastic containers and 1.9-L fiberboard containers and stored and displayed in three stores u n d e r different lighting and handling conditions. O n c e again the flavor scores were n o t significantly different (P<.05), and t h e variation in riboflavin c o n t e n t was within the e x p e r i m e n t a l variation o f the analytical m e t h o d with no definite pattern. Similar results were o b t a i n e d for s u m m e r milks. U n d e r typical p r o d u c t i o n and display c o n d i t i o n s in local dairy plants and grocery Journal of Dairy Science Vol. 70, No. 7, 1987
stores, neither flavor quality nor riboflavin c o n t e n t o f retail milk was significantly damaged by the t y p e or size of containers, fat content, season of p r o d u c t i o n , handling, or s t o r a g e conditions. The data therefore disagree with previous reports, especially t h o s e concluding t h a t plastic containers are m o r e detrimental to retail milk t h a n fiberboard containers (6, 8, 13, 18, 19). The data also contradict studies showing that retail skim milk is m o r e susceptible to p h o t o d e g r a d a t i o n t h a n whole milk (1, 23). One reason for the disagreement is because m o s t previous studies were done u n d e r controlled l a b o r a t o r y conditions. A n o t h e r reason may be t h e lower light intensities used in t h e dairy cases of the local stores. Reif et el. (18) studied the quality o f retail milk in California and f o u n d no difference in the riboflavin c o n t e n t of milks purchased in paper or plastic containers; however, t h e y r e p o r t e d that milk samples in plastic containers were criticized for light-induced flavor over 10 times as freq u e n t l y as those packaged in paper containers. T h e light intensity and display t i m e o f the dairy cases and the previous history o f the milk samples used in the study of R e i f et al. (18) were n o t given. Optimal m i l k quality is essential for cons u m e r acceptance, and the milk industry has always encouraged studies on p r o b l e m s related
T A B L E 4. F l a v o r score a n d r i b o f l a v i n c o n t e n t o f s u m m e r w h o l e m i l k . I ,,,,
,
Display time 2
Riboflavin content 4
F l a v o r scor e S _ . ~ 3.8 L s
1.9 L 5
3.8 L s
.48 L 6
.95 L 5
.95 L 6
1.9 L 6
.48 L*
(~g/ml)
(d) SD 0 1 2 3 4
5.9 6.7 6.8 6.7 6.5
1.7 a 1.3 b 1.3 a 1.6 a 1.9 a
.~ 5.7 6.8 6.3 6.8 6.7
SD 1.8 a 1.5 a 2.0 a 1.4 a 1.3 a
X 4-.2 4.8 5.1 5.0 ...7
SD
R
SD
"X
SD
2.0 a 2.4 a 2.2 a 2.1 a
4.2 5.0 5.9 5.4 5.7
2.0 a 2.0 a 2.0 a 1.9a 1.7 a
1.24 1.15 1.17 1.17 1.14
.01 a .02 b .01 b
a'bMeans w i t h i n c o l u m n s w i t h u n l i k e s u p e r s c r i p t s d i f f e r ( P < . 0 5 ) .
.01b .01 b
SD 1.25 1.12 1.16 1.14 1.08
.01 a .01 b .01 b .olb .03 b
1.13 1.12 1.12 1.13
SD
.~
SD
.01 a .01 a .02 a .01 a
1.16 1.13 1.14 1.13 1.12
.O2 a .01 a .01 a .01 a .01 a
C
O *lq
O
1 P l a n t 2, s t o r e 4. C
I n c l u d e s storage t i m e in d a r k cooler.
ga
3 Mean of 25 scores.
t"
4 Mean of 4 d e t e r m i n a t i o n s .
,9
s High d e n s i t y p o l y e t h y l e n e (plastic) c o n t a i n e r . 6 Fiberboard container. Sold o u t .
< O .,...
o X .0 O~
1368
OLSEN AND ASHOOR
T A B L E 5. F l a v o r s c o r e a n d r i b o f l a v i n c o n t e n t o f w i n t e r s k i m m i l k )
Flavor s c o r e 3
Display time 2
Riboflavin content 4
3.8 L ~
3.8 L s
1.9 L 6
1.9 L 6
(d)
(/~g/ml)
0 1 2 3 4
4.8 4.9 4.9 4.3 5.4
SD
X
SD
2.0 a 2.2 a 2.2 a 2.0 a 1.8 a
5.1 5.6 4.8 4.9 ...
2.0 a 1.9 a 1.7 a 1.7 a
so 1.24 1.24 1.16 1.14 1.I2
SD
.01 a .01 a .01 b .03 b .02 b
1.25 1.25 1.21 1.24
.01 a .01 a .02 a .01 a
a'bMeans within columns with unlike superscripts differ (P<.05). i P l a n t 2, s t o r e 3. 2 I n c l u d e s s t o r a g e t i m e in d a r k c o o l e r . ZMean of 25 scores. 4Mean of 4 determinations. s High density polyethylene (plastic) container. 6Fiberboard container. 7 Sold out.
T A B L E 6. F l a v o r s c o r e a n d r i b o f l a v i n c o n t e n t o f w i n t e r w h o l e m i l k in 3 . 8 - L p l a s t i c c o n t a i n e r s f r o m d i f f e r e n t grocery stores) Flavor score 3
Display time 2
Store 1
Riboflavin content 4
Store 2
Store 4
Store 1
Store 2
(d)
0 1 2 3 4 5
Store 4
(/zg/ml) .X
SD
X
SD
.~
SD
X
SD
X
SD
X
SD
6.9 6.9 6.5 5.3 6.6 6.1
1.1 a 1.4 a 2.1 a 2.1 a 1.4 a 1.7 a
6.9 6.3 5.2 6.1 6.6 . . .s
1.1 a 1.7 a 2.0 a 1.9 a 1.5 a
5.9 6.7 6.8 6.7 6.5 . . .
1.7 a 1.3 a 1.3 a 1.6 a 1.9 a
1.09 1.08 1.14 1.11 1.11 1.08
.01 a .01 a .01 a .01 a .02 a .01 a
1.09 1.09 1.14 1.07 1.12 . . .
.01 a .02 a .01 a .01 a .01 a . .
1.24 1.15 1.17 1.17 1.14
.01 a .02 b .01 b .01 b .01 b
.
a'bMeans within columns with unlike superscripts differ (P<.05). W h o l e m i l k in g a l l o n p l a s t i c c o n t a i n e r s f r o m t h i s b a t c h w a s n o t a v a i l a b l e in s t o r e 3. V o l u m e w a s a p p r o x i m a t e l y 3 4 , 2 0 0 L / w k f o r s t o r e I a n d 9 5 0 L / w k f o r s t o r e s 2 a n d 4. 2 I n c l u d e s s t o r a g e t i m e in d a r k c o o l e r . 3Mean of 25 scores. 4 Mean of 4 determinations. s Sold out.
J o u r n a l o f D a i r y S c i e n c e Vol. 70, N o . 7, 1 9 8 7
1369
LIGHT-INDUCED O F F - F L A V O R S IN MILK
T A B L E 7. Flavor score and riboflavin c o n t e n t of winter whole milk in 1.95-L fiberboard containers from different grocery stores.a Flavor score 3
Display time 2
Store 1
Riboflavin c o n t e n t 4
Store 2
Store 4
Store 1
Store 2
(d) 0 1 2 3 4 5
Store 4
(/~g/ml) R
SD
R
SD
X
SD
R
SD
.X
SD
X"
SD
6.4 6.6 5.8 6.0 6.0 6.4
1.5 a 1.4 a 2.2 a 1.5 a 2.1 a 1.47 a
6.4 6.1 5.4 5.9 6.5
1.5 a 1.8 a 2.2 a 1.9 a 1.8 a
5.7 6.8 6.3 6.8 6.7 ...s
1.8 a 1.5 a 2.0 a 1.4 a 1.3 a
1.12 1.12 1.13 1.12 1.07 ...
.01 a .02 a .02 a .04 a .04 a
1.12 1.10 1.13 1.09 1.13 1.09
.01 a .01 a .02 a .02 a .02 a .01 a
1.25 1.12 1.16 1.14 1.08 ...
.01 a .01 b .01 b .01 b .03 b
a'bMeans within c o l u m n s with unlike superscripts differ (P<.05). 1Whole milk in 1.9-L fiberboard containers f r o m this batch was n o t available in store 3. V o l u m e was approximately 34,200 L of milk per wk for store 1 and 950 L of milk/wk for stores 2 and 4. 2 Includes storage time in dark cooler. 3Mean of 25 scores. 4 Mean of 4 determinations. s Sold out. t o m i l k q u a l i t y . It is h o p e d t h a t t h i s s t u d y h a s shed some light on the quality of market milks in o u r a r e a a n d t h a t s i m i l a r s t u d i e s in o t h e r areas with different production and display c o n d i t i o n s will t a k e p l a c e s o o n .
ACKNOWLEDGMENTS The authors thank the Arizona Society of Dairy Technologists, local dairy plants, and l o c a l s t o r e s f o r t h e i r c o o p e r a t i o n in c a r r y i n g out this study. REFERENCES 1 Allen, C., and O. W. Parks. 1979. Photodegradation of riboflavin in milks exposed to fluorescent light. J. Dairy Sci. 6 2 : 1 3 7 7 . 2 Ashoor, S. H., M. J. Knox, J. R. Olsen, and D. A. Deger. 1985. Improved liquid chromatographic determination of riboflavin in milk and dairy products. J. Assoc. Offic. Anal. Chem. 68:693. 3 Aurand, L. W., J. A. Singleton, and B. W. Noble. 1966. P h o t o o x i d a t i o n reactions in milk. J. Dairy Sci. 50:138. 4 Bradfield, A., and A. H. Duthie. 1965. Protecting milk f r o m fluorescent light. A m . Dairy Rev. 27:110. 5 Bradley, R. L., Jr. 1980. Effect of light on alteration o f nutritional value and flavor o f milk: review. J. Food Prot. 43:314. 6 Coleman, W. W., G. H. Watrous, Jr., and P. S. Dimick. 1976. Organoleptic evaluation o f milk in various containers exposed to fluorescent light. J.
Milk Food Technol. 39:551. 7 Dillman, W. F., E. O. Anderson, and L. Hankin. 1971. An assessment o f the flavor quality of whole milk available at commercial outlets. J. Milk Food Technol. 34:244. 8 Dimick, P. S. 1973. Effect of fluorescent light on t h e flavor and selected nutrients of h o m o g e n i z e d milk held in conventional containers. J. Milk Food Technol. 36: 383. 9 Dimick, P. S. 1978. Photochemical effects o n constituents of milk. Page 32 in Proc. 32nd A n n u . Prod. Conf. Pennsylvania Manuf. Conf. Assoc., Lancaster, PA. 10 Dunkley, W. L., J. D. Franklin, and R. M. Pangborn. 1962. Effects o f fluorescent light on flavor, ascorbic acid and riboflavin in milk. Food Technol. 16:112. 11 Gregory, M. E., A. P. Hansen, and L. W. Aurand. 1972. Controlling light-activated flavor in milk. A m . Dairy Rev. 34:10. 12 Hankin, L., and W. F. Dillman. 1972. Further studies on the flavor quality of retail milk in Connecticut. J. Milk Food Technol. 35:710. 13 Hansen, A. P., L. G. Turner, and L. W. Aurand. 1975. Fluorescent light-activated flavor in milk. J. Milk F o o d Technol. 38:388. 14 Hedrick, T. I., and L. Glass. 1975. Chemical changes in milk during exposure to fluorescent light. J. Milk Food Technol. 38:129. 15 Herreid, E. O., B. Ruskin, G. L. Clark, and T. B. Parks. 1952. Ascorbic acid and riboflavin destruction and flavor development in milk exposed to t h e s u n in amber, clear paper and r u b y bottles. J. Dairy Sci. 35:772. 16 National Dairy Council's Statement. 1984. Effect of light on milk's n u t r i e n t c o n t e n t and flavor. Natl. Journal of Dairy Science Vol. 70, No. 7, 1987
1370
OLSEN AND ASHOOR
Dairy Counc., Rosemont, IL. 17 Nelson, K. H., and W, M. Cathcart. 1984. Transmission o f light through pigmented polyethylene milk bottles. J. Food Prot. 47:346. 18 Reif, G. D., A. A. Franke, and J. C. Bruhn. 1983. Retail dairy foods quality - an assessment o f the incidence o f off-flavors in California milk. Dairy Food Sanit. 3:44. 19 Statistical Analysis System. 1982. SAS User's guide: statistics. SAS Insti., Inc., Cary, NC. 20 Sat-tar, A., and J. M. deMan. 1973. Effect of packaging material on light induced quality deterioration of milk. J. Inst. Can. Sci. Technol. 6:170. 21 Sattar, A., and J. M. deMan. 1975. Photooxidation
Journal o f Dairy Science Vol. 70, No. 7, 1987
22
23 24
25 26
of milk and milk productS: a review. CRC Crit. Rev. Food Sci. Nutr. 7:13. Sattar, A., J. M. deMan, and J. C. Alexander. 1977. Light-induced degradation of vitamins I. Kinetic studies on riboflavin decomposition in solution. Can. Inst. F o o d Sci. Technol. J. 10:61. Senyk, G. F., and W. F. Shipe. 1981. Protecting your milk from nutrient losses. Dairy Field. 64:81. Stull, J. W. 1983. The effect of light on activated flavor development and on the constituents of milk and its products: a review. J. Dairy Sci. 36:1153. White, C. H. 1985. Consumer reaction to colored plastic milk jugs. J. Dairy Sci. 68:261. Wishner, L. A. 1964. Light induced oxidations in milk. J. Dairy Sci. 47:216.
Samples of whole and skim milk from two local dairy plants that were packaged in 3.8-L plastic containers (nonreturnable high density polyethylene) and 1.9, .95, and .48-L fiberboard containers and displayed in the dairy cases of four local grocery stores under normal fluorescent light were analyzed for light-induced changes in flavor and riboflavin content. Milk samples were analyzed daily for flavor, odor, appearance, and riboflavin content. Sensory evaluation was by 25 untrained panelists, and riboflavin was determined by HPLC method. Milk samples were analyzed first in summer, then repeated in winter. Data indicated that under typical production and storage conditions in the area, type and size of container, fat content, and season of production had no major damaging effects on flavor, odor, appearance, or riboflavin content of retail milk. INTRODUCTION
Light-induced off-flavors in milk have been well-documented and discussed in several reviews (5, 9, 21, 24, 26). The development of these off-flavors in milk has been associated with the photodegradation of riboflavin, vitamin C, and recently, added vitamin A (1, 3, 8, 10, 14, 15, 23, 24). Therefore, the exposure of milk to sunlight or fluorescent light not only affects the flavor quality but decreases its nutritional value as well. Riboflavin loss is most significant in milk without vitamin A fortification since milk is not a good source of vitamin C and naturally occurring vitamin A is less susceptible to photodegradation (23). There are several factors that play a role in the photodegradation of vitamins and light-
Received September 12, 1986. Accepted March 16, 1987. 1987
J Dairy Sci 70:1362-1370
induced flavor changes in milk. Dimick (9) indicated that a major factor is the type and composition of the container in which milk is packaged and stored. Fiberboard and plastic containers are most widely used in the market today. Over 50% of all milk is sold in plastic containers at the present time (18) due to convenience and desirable appearance. Plastic containers, however, are more detrimental than fiberboard containers to the quality of lightexposed milk (6, 8, 13, 20) because they transmit more light than fiberboard containers (17). Recently, pigmented plastic containers, which reduce light transmittance and lightdamaging effects in milk, were found acceptable by consumers (25). Fat content of milk is another factor affecting photodegradation reactions in milk. Photodegradation of riboflavin and vitamin A was greater in skim milk than in whole milk (1, 23). Light-induced changes in milk are also dependent on the size of the container. Bradfield and Duthie (4) found that milk in .95-L containers developed light-induced off-flavors 6 h sooner than the same milk packaged in 1.9-L containers under similar conditions. They attributed this finding in part to less light transmission by the 1.9-L containers. Hedrick and Glass (14) pointed out that both size and shape of container influence light-induced vitamin losses in milk. Season of production affects light-induced changes in milk. Herreid et al. (15) and Dillman et al. (7) reported a greater incidence of light activated flavor in milk during the winter months, possibly due to seasonal differences in feeding conditions. However, Herreid et al. (15)also found greater photodegradation of riboflavin in milk during summer. Light-induced changes in milk are dependent on the intensity and wavelength of the light to which the milk is exposed. Sattar et al. (22) reported that the spectral wavelength range of 350 to 510 nm was generally damaging to riboflavin in solution and that the wavelengths of 415 to 455 nm were responsible for its destruction. This finding was
1362
LIGHT-INDUCED OFF-FLAVORS IN MILK of interest since most retail dairy cases are equipped with white fluorescent lamps, which have maximum emission at 450 to 500 nm (9, 11). Use of yellow fluorescent lamps or fluorescent lamps with yellow shields was effective to reduce off-flavor development in milk since these lighting systems show minimum energy emitted at wavelengths below 540 nm (5, 13). Most studies dealing with light-induced changes in milk were conducted under simulated store conditions and very few were under actual display conditions (7, 12, 18). Because studies in which milk was sampled from the market place were not comprehensively designed and did not fully clarify the effects of milk exposed to display lights in the dairy case, the National Dairy Council (16) called for further studies on the vitamin content and flavor quality of market milks to establish the significance of light exposure. This research was done to comprehensively investigate the effects of type and size of container, fat content, season of production, and store conditions on the flavor quality and riboflavin content of retail milk in the local market place. MATERIALS A N D METHODS Samples
Batches of whole milk and skim milk commercially packaged in 3.8-L plastic containers 1.9-L, .95-L, and .48-L fiberboard containers were followed from production in two local dairy plants to purchasing by consumer in four local retail stores (stores 1 and 2 for the first plant and stores 3 and 4 for the second plant. Stores 1 and 3 were large volume stores 34,200 L of milk/wk), whereas stores 2 and 4 were small volume stores (950 L of milk/wk). In atl stores, milk in various containers was displayed in the dairy case under white fluorescent light 24 h/d. In each dairy plant, samples were obtained of the raw milk from storage tanks, after pasteurization and homogenization, and immediately after packaging in different containers (control samples). Milk containers were then followed, by code date and brand, to the particular supermarkets, and samples of all containers were randomly taken daily from the same batch until the milk was sold out. The light intensity in the dairy case of each store
1363
was measured daily at center and sides of display shelves using a triple range light meter type 214 (General Electric, Cleveland, OH). The temperature inside the dairy case was also measured daily at different locations with a thermometer. Two samples were taken of each treatment. All samples were transported in ice immediately to the laboratory and were kept in a dark refrigerator at 4°C until further analysis. To study the effect of season of production, sampling was in September (summer run) and January (winter run). Sensory EvaLuation
Refrigerated milk samples were analyzed for flavor, odor, and appearance on the day of sampling. Twenty-five untrained panelists evaluated the milk samples for preference using a nine-point hedonic scoring system (from 1, dislike extremely, to 9, like extremely). Each panelist was given, on the average, eight samples to evaluate at a time, and enough water to rinse mouth after each evaluation. Riboflavin Analysis
Milk samples were analyzed for riboflavin content following the HPLC method of Ashoor et al. (2). The newly developed method was simple, rapid, and compared favorably with the AOAC official method (2). Statistical Analysis
Means obtained from flavor scores and riboflavin determinations were subjected to analysis of variance according to the Statistical Analysis System (SAS) (19). RESULTS AND DISCUSSION
The four stores chosen for this study were representative of local grocery stores. Display conditions of the dairy cases of these stores are given in Table 1. Light intensities in the dairy cases of the stores were generally lower than reported intensities in other dairy cases. In a 1974 nationwide survey, the average illumination in the dairy cases of 105 supermarkets was 2001 lx (8). In another survey, Sattar and deMan (20) indicated that the intensity of fluorescent lighting in milk display cases ranged from 269 to 5380 lx with values of 1076 to 2152 Ix being most common. Three of the four Journal of Dairy Science Vol. 70, No. 7, 1987
1364
OLSEN AND ASHOOR
stores chosen for this study had a light intensity in their dairy cases much lower than the national average, and although one of the stores (store 3) had higher light intensity, it had the fastest milk turnover and the shortest display time (Table 1). The milk display time in the dairy case of each store was monitored closely, because milk photodegradation is a function of light intensity and exposure time. The actual display time, time o f milk exposure to fluorescent light in the dairy case, was very difficult to determine. Therefore, the milk shelf-life (time after milk left the dairy plant until sold out in each store) was easier to record and was considered the "display time". Of course, this milk display time included the storage time in the dark cooler before milk was displayed in the dairy case under fluorescent light. The best estimate of the time an average milk container was exposed to fluorescent light in any of the dairy cases was 5 to 10% o f the display time. The temperature o f each dairy case at the time milk samples were picked up for evaluation was also reported (Table 1). In every store, the temperature range of the dairy case was always higher in the summer than in winter. Data obtained from evaluation of summer whole and skim milk in all containers available in our area (during this study, the only plastic containers available in the market place were the 3.8-L containers) are presented in Tables 2 and 3. This part of the study was planned for July and August; however, it could not be carried out until September. In our location, the average daytime temperature during September was 38.3°C, which is hotter than the
summer months of many other locations. Statistical analysis of the flavor scores in Table 2 indicated that all b u t two scores 3.8-L and .48-L after a display time of 1 d were not significantly different (P<.05). The riboflavin content (Table 2) varied slightly among whole milk samples, but the variation did not follow a pattern. F o r example, the riboflavin content of whole milk packaged in .95-L and .48-L fiberboard containers did not change after display times of 4 and 7 d (Table 2). Riboflavin content of the same milk in 1.9-L fiberboard containers decreased by 12.0% after display time of 4 d, whereas whole milk packaged in 3.8-L plastic containers lost only 7.9% of its riboflavin during the same display time. Similar conclusions can be derived from the data in Table 3 resulting from evaluating summer skim milk. In general, flavor scores for skim milk were lower than for whole milk, whereas skim milk had higher riboflavin content. Data in Table 3 did not include skim milk in 3.8-L plastic containers because they were not available for the same milk from the same dairy plant. Tables 2 and 3 indicate that flavor quality and riboflavin content o f marketplace milks were not significantly affected by type of container (plastic vs. fiberboard), size of container (3.8, 1.9, .95, and .48 L), or fat content (whole milk vs. skim milk). In order to study the effect o f season and to confirm the data obtained in the summer, a winter evaluation of market place milks in January (the average daytime temperature was 18.3°C) was performed under similar conditions. Data obtained from winter samples are presented in Tables 4 and 5. These results
TABLE 1. Display conditions of the dairy cases at local grocery stores.
Store
Light intensity
1
(Ix) 215-1076
2
215-1076
3 4
915--4304 129-1076
Temperature range Summer Winter (°C) 4-13 5-15 6-I0 4-12
(-1)--3 4-8 3-9 3-6
Display time I (d) 5 4--5 3--4 3-7
1Includes storage time in dark cooler prior to display. An average container was exposed to light for approximately 5 to 10% of display time. Journal of Dairy Science Vol. 70, No. 7, 1987
T A B L E 2. F l a v o r s c o r e a n d r i b o f l a v i n c o n t e n t o f s u m m e r w h o l e m i l k . ~
Flavor score 3
Display time 2
3.8L s
Riboflavin content 4
.95 L 6
1.9 L 6
.48 L 6
3.8 L s
1.9 L 6
.95 L 6
.48 L 6
(~g/ml) (d)
R
SD
0 1 2 3 4 5 6 7
7.0 4.9 6.8 6.8 6.6 , . .7 . . . . . .
1.2 a 2.5 b 1.3 a 1.8 a 1.8 a
6.9 6.0 7.3 7.1 7.2
SD
X
SD
1.0 a 1.8 a 1.1 a 1.5 a 1.2 a
5.7 4.2 4.8 5.2 5.0
2.0 a 2.2 a 2.7 a 2.3 a 2.2 a
6.1 4.9 5.4 6.1 5.1 5.7 6.2 5.5
SD
X
SD
2.1 a 2.0 b 1.8 a 1.7 a 1.9 a 2.2 a 1.9 a 1.9 a
1.40 1.34 1.23 1.22 1.29 ... . .. . . .
.03 a .02 b .01 c .02 c .02 c
1.34 1.18 1.15 1.21 1.18
SD
X
SD
.02 a .03 b .03 b .03 b .03 b
1.28 1.29 1.22 1.25 1.29
.05 a .05 a .03 a .02 a .03 a
SD 1.25 1.20 1.21 1.15 1.21 1.27 1.33 1.25
.07 a .04 a .07 a .04 b .03 a .04 a .01 a .04 a
Z t~
t~ O
-h t"
> < 0
a'b'CMeans within columns with unlike superscripts differ (P<.05). ~a
1 P l a n t 2, s t o r e 4.
o
2 I n c l u d e s s t o r a g e t i m e in d a r k c o o l e r .
N
3 M e a n o f 25 s c o r e s . 4 Mean of 6 determinations. t~
s High d e n s i t y p o l y e t h y l e n e (plastic) container. 6 Fiberboard container.
< o .,a 9 Z 9
M
7 Sold o u t .
ox Ln
1366
OLSEN AND ASHOOR
TABLE 3. Flavor score and riboflavin content of skim milk in summer) Flavor score 3
Display time 2
Riboflavin content 4
1.9 L s
1.9 L s
.95 L s
(d)
.95 L s (/~g/ml)
SD
X,
SD
2.1 a 1.9 a
4.5 2.7
2.1 a 1.5 b 2.2 a 2.3 a
0 1
4.9 4.1
2 3
4.6
1.9 a
3.9
5.3 . . .~
2.1 a
4.3 4.4
4
SD 1,59 1.51 1.48 1.33
2.1 a
.07 a .05 a .08 a .02 b
SD 1.42 1.65 1.32 1.33 1.26
.07 a .05 b .02 c .01 c .01 c
a b,c .
'
. . . . Means wlmm columns with unlike superscripts differ (P<.05).
1Plant 2, store 3. 2 Includes storage time in dark cooler. aMean of 25 scores. a Mean of 6 determinations. s Fiberboard container. 6 Sold out.
confirm the s u m m e r data and indicate that season of p r o d u c t i o n does n o t have a significant effect on the flavor quality or riboflavin stabilit y of retail milk. Flavor scores o f winter whole milk and skim milk presented in Tables 4 and 5 were n o t significantly different (P<.05), indicating no significant effect o f type, size o f container, o r fat c o n t e n t on flavor quality o f milk. Loss in riboflavin c o n t e n t in winter whole m i l k (Table 4) was 8.1% in 3.8 13.6% in and (1.9-L) c o n t a i n e r milks during 4 d of display. In w i n t e r skim m i l k (Table 5), the only loss in riboflavin was in 3.8-L milk (9.7%). However, t h e riboflavin c o n t e n t o f b o t h whole milk and skim milk was generally lower in winter than in summer. Tables 6 and 7 were c o n s t r u c t e d for easier c o m p a r i s o n of flavor scores and riboflavin c o n t e n t o f w i n t e r w h o l e milk o b t a i n e d f r o m t w o dairy plants in 3.8-L plastic containers and 1.9-L fiberboard containers and stored and displayed in three stores u n d e r different lighting and handling conditions. O n c e again the flavor scores were n o t significantly different (P<.05), and t h e variation in riboflavin c o n t e n t was within the e x p e r i m e n t a l variation o f the analytical m e t h o d with no definite pattern. Similar results were o b t a i n e d for s u m m e r milks. U n d e r typical p r o d u c t i o n and display c o n d i t i o n s in local dairy plants and grocery Journal of Dairy Science Vol. 70, No. 7, 1987
stores, neither flavor quality nor riboflavin c o n t e n t o f retail milk was significantly damaged by the t y p e or size of containers, fat content, season of p r o d u c t i o n , handling, or s t o r a g e conditions. The data therefore disagree with previous reports, especially t h o s e concluding t h a t plastic containers are m o r e detrimental to retail milk t h a n fiberboard containers (6, 8, 13, 18, 19). The data also contradict studies showing that retail skim milk is m o r e susceptible to p h o t o d e g r a d a t i o n t h a n whole milk (1, 23). One reason for the disagreement is because m o s t previous studies were done u n d e r controlled l a b o r a t o r y conditions. A n o t h e r reason may be t h e lower light intensities used in t h e dairy cases of the local stores. Reif et el. (18) studied the quality o f retail milk in California and f o u n d no difference in the riboflavin c o n t e n t of milks purchased in paper or plastic containers; however, t h e y r e p o r t e d that milk samples in plastic containers were criticized for light-induced flavor over 10 times as freq u e n t l y as those packaged in paper containers. T h e light intensity and display t i m e o f the dairy cases and the previous history o f the milk samples used in the study of R e i f et al. (18) were n o t given. Optimal m i l k quality is essential for cons u m e r acceptance, and the milk industry has always encouraged studies on p r o b l e m s related
T A B L E 4. F l a v o r score a n d r i b o f l a v i n c o n t e n t o f s u m m e r w h o l e m i l k . I ,,,,
,
Display time 2
Riboflavin content 4
F l a v o r scor e S _ . ~ 3.8 L s
1.9 L 5
3.8 L s
.48 L 6
.95 L 5
.95 L 6
1.9 L 6
.48 L*
(~g/ml)
(d) SD 0 1 2 3 4
5.9 6.7 6.8 6.7 6.5
1.7 a 1.3 b 1.3 a 1.6 a 1.9 a
.~ 5.7 6.8 6.3 6.8 6.7
SD 1.8 a 1.5 a 2.0 a 1.4 a 1.3 a
X 4-.2 4.8 5.1 5.0 ...7
SD
R
SD
"X
SD
2.0 a 2.4 a 2.2 a 2.1 a
4.2 5.0 5.9 5.4 5.7
2.0 a 2.0 a 2.0 a 1.9a 1.7 a
1.24 1.15 1.17 1.17 1.14
.01 a .02 b .01 b
a'bMeans w i t h i n c o l u m n s w i t h u n l i k e s u p e r s c r i p t s d i f f e r ( P < . 0 5 ) .
.01b .01 b
SD 1.25 1.12 1.16 1.14 1.08
.01 a .01 b .01 b .olb .03 b
1.13 1.12 1.12 1.13
SD
.~
SD
.01 a .01 a .02 a .01 a
1.16 1.13 1.14 1.13 1.12
.O2 a .01 a .01 a .01 a .01 a
C
O *lq
O
1 P l a n t 2, s t o r e 4. C
I n c l u d e s storage t i m e in d a r k cooler.
ga
3 Mean of 25 scores.
t"
4 Mean of 4 d e t e r m i n a t i o n s .
,9
s High d e n s i t y p o l y e t h y l e n e (plastic) c o n t a i n e r . 6 Fiberboard container. Sold o u t .
< O .,...
o X .0 O~
1368
OLSEN AND ASHOOR
T A B L E 5. F l a v o r s c o r e a n d r i b o f l a v i n c o n t e n t o f w i n t e r s k i m m i l k )
Flavor s c o r e 3
Display time 2
Riboflavin content 4
3.8 L ~
3.8 L s
1.9 L 6
1.9 L 6
(d)
(/~g/ml)
0 1 2 3 4
4.8 4.9 4.9 4.3 5.4
SD
X
SD
2.0 a 2.2 a 2.2 a 2.0 a 1.8 a
5.1 5.6 4.8 4.9 ...
2.0 a 1.9 a 1.7 a 1.7 a
so 1.24 1.24 1.16 1.14 1.I2
SD
.01 a .01 a .01 b .03 b .02 b
1.25 1.25 1.21 1.24
.01 a .01 a .02 a .01 a
a'bMeans within columns with unlike superscripts differ (P<.05). i P l a n t 2, s t o r e 3. 2 I n c l u d e s s t o r a g e t i m e in d a r k c o o l e r . ZMean of 25 scores. 4Mean of 4 determinations. s High density polyethylene (plastic) container. 6Fiberboard container. 7 Sold out.
T A B L E 6. F l a v o r s c o r e a n d r i b o f l a v i n c o n t e n t o f w i n t e r w h o l e m i l k in 3 . 8 - L p l a s t i c c o n t a i n e r s f r o m d i f f e r e n t grocery stores) Flavor score 3
Display time 2
Store 1
Riboflavin content 4
Store 2
Store 4
Store 1
Store 2
(d)
0 1 2 3 4 5
Store 4
(/zg/ml) .X
SD
X
SD
.~
SD
X
SD
X
SD
X
SD
6.9 6.9 6.5 5.3 6.6 6.1
1.1 a 1.4 a 2.1 a 2.1 a 1.4 a 1.7 a
6.9 6.3 5.2 6.1 6.6 . . .s
1.1 a 1.7 a 2.0 a 1.9 a 1.5 a
5.9 6.7 6.8 6.7 6.5 . . .
1.7 a 1.3 a 1.3 a 1.6 a 1.9 a
1.09 1.08 1.14 1.11 1.11 1.08
.01 a .01 a .01 a .01 a .02 a .01 a
1.09 1.09 1.14 1.07 1.12 . . .
.01 a .02 a .01 a .01 a .01 a . .
1.24 1.15 1.17 1.17 1.14
.01 a .02 b .01 b .01 b .01 b
.
a'bMeans within columns with unlike superscripts differ (P<.05). W h o l e m i l k in g a l l o n p l a s t i c c o n t a i n e r s f r o m t h i s b a t c h w a s n o t a v a i l a b l e in s t o r e 3. V o l u m e w a s a p p r o x i m a t e l y 3 4 , 2 0 0 L / w k f o r s t o r e I a n d 9 5 0 L / w k f o r s t o r e s 2 a n d 4. 2 I n c l u d e s s t o r a g e t i m e in d a r k c o o l e r . 3Mean of 25 scores. 4 Mean of 4 determinations. s Sold out.
J o u r n a l o f D a i r y S c i e n c e Vol. 70, N o . 7, 1 9 8 7
1369
LIGHT-INDUCED O F F - F L A V O R S IN MILK
T A B L E 7. Flavor score and riboflavin c o n t e n t of winter whole milk in 1.95-L fiberboard containers from different grocery stores.a Flavor score 3
Display time 2
Store 1
Riboflavin c o n t e n t 4
Store 2
Store 4
Store 1
Store 2
(d) 0 1 2 3 4 5
Store 4
(/~g/ml) R
SD
R
SD
X
SD
R
SD
.X
SD
X"
SD
6.4 6.6 5.8 6.0 6.0 6.4
1.5 a 1.4 a 2.2 a 1.5 a 2.1 a 1.47 a
6.4 6.1 5.4 5.9 6.5
1.5 a 1.8 a 2.2 a 1.9 a 1.8 a
5.7 6.8 6.3 6.8 6.7 ...s
1.8 a 1.5 a 2.0 a 1.4 a 1.3 a
1.12 1.12 1.13 1.12 1.07 ...
.01 a .02 a .02 a .04 a .04 a
1.12 1.10 1.13 1.09 1.13 1.09
.01 a .01 a .02 a .02 a .02 a .01 a
1.25 1.12 1.16 1.14 1.08 ...
.01 a .01 b .01 b .01 b .03 b
a'bMeans within c o l u m n s with unlike superscripts differ (P<.05). 1Whole milk in 1.9-L fiberboard containers f r o m this batch was n o t available in store 3. V o l u m e was approximately 34,200 L of milk per wk for store 1 and 950 L of milk/wk for stores 2 and 4. 2 Includes storage time in dark cooler. 3Mean of 25 scores. 4 Mean of 4 determinations. s Sold out. t o m i l k q u a l i t y . It is h o p e d t h a t t h i s s t u d y h a s shed some light on the quality of market milks in o u r a r e a a n d t h a t s i m i l a r s t u d i e s in o t h e r areas with different production and display c o n d i t i o n s will t a k e p l a c e s o o n .
ACKNOWLEDGMENTS The authors thank the Arizona Society of Dairy Technologists, local dairy plants, and l o c a l s t o r e s f o r t h e i r c o o p e r a t i o n in c a r r y i n g out this study. REFERENCES 1 Allen, C., and O. W. Parks. 1979. Photodegradation of riboflavin in milks exposed to fluorescent light. J. Dairy Sci. 6 2 : 1 3 7 7 . 2 Ashoor, S. H., M. J. Knox, J. R. Olsen, and D. A. Deger. 1985. Improved liquid chromatographic determination of riboflavin in milk and dairy products. J. Assoc. Offic. Anal. Chem. 68:693. 3 Aurand, L. W., J. A. Singleton, and B. W. Noble. 1966. P h o t o o x i d a t i o n reactions in milk. J. Dairy Sci. 50:138. 4 Bradfield, A., and A. H. Duthie. 1965. Protecting milk f r o m fluorescent light. A m . Dairy Rev. 27:110. 5 Bradley, R. L., Jr. 1980. Effect of light on alteration o f nutritional value and flavor o f milk: review. J. Food Prot. 43:314. 6 Coleman, W. W., G. H. Watrous, Jr., and P. S. Dimick. 1976. Organoleptic evaluation o f milk in various containers exposed to fluorescent light. J.
Milk Food Technol. 39:551. 7 Dillman, W. F., E. O. Anderson, and L. Hankin. 1971. An assessment o f the flavor quality of whole milk available at commercial outlets. J. Milk Food Technol. 34:244. 8 Dimick, P. S. 1973. Effect of fluorescent light on t h e flavor and selected nutrients of h o m o g e n i z e d milk held in conventional containers. J. Milk Food Technol. 36: 383. 9 Dimick, P. S. 1978. Photochemical effects o n constituents of milk. Page 32 in Proc. 32nd A n n u . Prod. Conf. Pennsylvania Manuf. Conf. Assoc., Lancaster, PA. 10 Dunkley, W. L., J. D. Franklin, and R. M. Pangborn. 1962. Effects o f fluorescent light on flavor, ascorbic acid and riboflavin in milk. Food Technol. 16:112. 11 Gregory, M. E., A. P. Hansen, and L. W. Aurand. 1972. Controlling light-activated flavor in milk. A m . Dairy Rev. 34:10. 12 Hankin, L., and W. F. Dillman. 1972. Further studies on the flavor quality of retail milk in Connecticut. J. Milk Food Technol. 35:710. 13 Hansen, A. P., L. G. Turner, and L. W. Aurand. 1975. Fluorescent light-activated flavor in milk. J. Milk F o o d Technol. 38:388. 14 Hedrick, T. I., and L. Glass. 1975. Chemical changes in milk during exposure to fluorescent light. J. Milk Food Technol. 38:129. 15 Herreid, E. O., B. Ruskin, G. L. Clark, and T. B. Parks. 1952. Ascorbic acid and riboflavin destruction and flavor development in milk exposed to t h e s u n in amber, clear paper and r u b y bottles. J. Dairy Sci. 35:772. 16 National Dairy Council's Statement. 1984. Effect of light on milk's n u t r i e n t c o n t e n t and flavor. Natl. Journal of Dairy Science Vol. 70, No. 7, 1987
1370
OLSEN AND ASHOOR
Dairy Counc., Rosemont, IL. 17 Nelson, K. H., and W, M. Cathcart. 1984. Transmission o f light through pigmented polyethylene milk bottles. J. Food Prot. 47:346. 18 Reif, G. D., A. A. Franke, and J. C. Bruhn. 1983. Retail dairy foods quality - an assessment o f the incidence o f off-flavors in California milk. Dairy Food Sanit. 3:44. 19 Statistical Analysis System. 1982. SAS User's guide: statistics. SAS Insti., Inc., Cary, NC. 20 Sat-tar, A., and J. M. deMan. 1973. Effect of packaging material on light induced quality deterioration of milk. J. Inst. Can. Sci. Technol. 6:170. 21 Sattar, A., and J. M. deMan. 1975. Photooxidation
Journal o f Dairy Science Vol. 70, No. 7, 1987
22
23 24
25 26
of milk and milk productS: a review. CRC Crit. Rev. Food Sci. Nutr. 7:13. Sattar, A., J. M. deMan, and J. C. Alexander. 1977. Light-induced degradation of vitamins I. Kinetic studies on riboflavin decomposition in solution. Can. Inst. F o o d Sci. Technol. J. 10:61. Senyk, G. F., and W. F. Shipe. 1981. Protecting your milk from nutrient losses. Dairy Field. 64:81. Stull, J. W. 1983. The effect of light on activated flavor development and on the constituents of milk and its products: a review. J. Dairy Sci. 36:1153. White, C. H. 1985. Consumer reaction to colored plastic milk jugs. J. Dairy Sci. 68:261. Wishner, L. A. 1964. Light induced oxidations in milk. J. Dairy Sci. 47:216.