31.5?7, Cream @ 40% Fat OR 12.6% Fat 3.0% Sodium caseinate 2 1.69%, Sugar 0.3 1% Emulsifier 0.31% Emulsifier 24.6%' Spirit (69% vol. Calvados) 18.9%) Water (extra added)

On organoleptic assessment the Calvados recipe was received favourably with consistent results, although many expressed the opinion that it was 'too spirity'. The Table gives an analysis of the organoleptic assessment, where the highest points were awarded for the most pleasing product.

3.0% Sodium caseinate 2 1.69% Sugar

16.97% Alcohol 45.43% Water

Organoleptic assessment

brands, was a slightly proteolytic, thermophilic, acid-producing, Gram positive spore former. This suggested that if such an organism was present, and had an opportunity to develop, with its acid causing a pH change, then some destabilization could occur.

Organoleptic assessment showed that familiar commercial brands were more popular, although there was more variability in the reaction to them. Stability testing is time consuming. Unfortunately the quicker alternatives of centrifugation or higher incubation temperatures were unsuccessful, so the same technique of incubation at 45°C as was used by the Hannah Research Institute was relied on. I t was felt that provided a period of 50 days at 45°C was obtained, a reasonable shelf-life in similar climates could be expected, although the stability achieved by Baileys was the best of all samples tested, and similar levels would be desirable.

~

Recipe Total score Mean Standard deviation Calvados 125 3.47 I .48 Vodka I38 3.83 1.44 Deveaux I54 4.21 1.61 Baileys I51 4.36 1.81

Sample w e : 36

CONCLUSIONS The Calvados cream liqueur produced was comparable in viscosity and mouthfeel with commercial brands while possessing the characteristic aroma of its parent spirit.

In the production and analysis of the various formulations, the principles established through the literature survey were borne out, in particular the critical tolerances of pH and solids levels. The addition of the emulsifier had the characteristics of thickening the liqueur, while harmonizing its organoleptic properties.

Microbiological examination was carried out to ensure that a satisfactory product was being produced. The dominant organism in the experimental liqueur, as also in commercial

We should like to acknowledge the help of the Scottish Milk Marketing Board; Dairy Crest Creamery, Crudgington; Dairy Crest Research and Development, Crudgington; Grinsted Products Ltd; the Hereford Cider Museum Trust; and the Food and Dairy Technology Department and laboratory staff, Cheshire College of Agriculture.

BIBLIOGRAPHY Banks, W , Muir, D D & Wilson, A G (I98 I ) T h e formulation ofcream-

based liqueurs. Mi/k Industry, 83 ( 5 ) . 16. Banks, W, Muir, D D & Wilson, A G (1981) Extension o f t h e shelfl ife

of cream-based liqueurs at high ambient temperatures. Journal of Food Technology, 16, 5x7.

Banks, W , Muir, D D & Wilson, A G (1982) Formulation of cream- based liqueurs: a comparison o f sucrose and sorbitol a s the carbohydrate component . Journal of the Sociei.v oJDairy Technology. 35, 41.

Critchett, N & Flack, E A (1977) The use of emulsifying and stabilizing agents in the development o f dairy desserts. Doiry Industries International, 42 ( lo) , 21.

Mulder, H & Walstra, P (1974) The mikfaar globule. Farnham Royal: Commonwealth Agricultural Bureaux.

ORIGINAL CONTRIBUTION

Flavour and vitamin stability in pasteurized milk in polyethylene-coated cartons and in polyethylene bottles MONIKA J A SCHRODER, K J SCOTT, M A BLAND and DINAH R BISHOP National Institute for Research in Dairying, Shinfield, Reading, Berks RG2 9AT

Commercially pasteurized, non-homogenized full cream milk in 2-pt white polyethylene (PE)- coated cartons overprinted with blue, and in 4-pt PE bottles was stored fo r 4 d in the dark or under white fluorescent light of 4000 Ix, at a temperature of 7°C. Theflavour of milks kept in the dark remained good, but exposure to light resulted in early offiflavour development: cartoned milk was disliked by a flavour panel ufter about 17.5 h exposure and milk in the PE bottles after 9 h. Vitamins A and B , were stable in the milk during 4 d storage in the dark in both bottles and cartons, and in cartons exposed to light. I n the bottled milks, light-induced losses of these vitamins after 4 d were, respectively, 15% and 35%. but there was little or no loss before the development of light-induced flavour. Loss of total vitamin C by day 4 was about 50% in the dark, irrespective of container. In the cartons exposed to light, 66% of the vitamin C was lost, while virtually none remained in the exposed, bottled milk. There was also a markedly greater loss of vitamin C in the bottled milk than in the cartoned milk at the time the flavour became unacceptable. The dissolved 0, concentration dropped considerably in the bottled milk exposed to light, but only marginally in the cartons. There were small increases in dissolved 0, in the dark in both types of container.

48 Journal of the Society of Dairy Technology, Vol. 38, No. 2, April 1985

Exposure of milk to daylight or artificial light composed of wavelengths simulating those of daylight detrimentally affects its quality. It gives rise to chemical reactions affecting, in particular, milk proteins and lipids, with consequent off-flavour development. Light exposure causes destruction of vitamin B, (riboflavin), of which milk is an important dietary source, and accelerates that of vitamins A and C. Oxygen plays an important role in these processes. Pasteurized milk at filling is generally saturated with 0,, but if no additional 0, can gain access, its content falls and the rate of the adverse reactions slows or stops. However, additional 0, from a headspace or entering through a permeable container will maintain the 0, content and keep the rate of oxidative reactions high.

The occurrence and extent of these undesirable defects in practice depend chiefly on the translucency and permeability of the container and on the length and conditions of exposure. Although in the UK, as a result ofthe popularity of the doorstep system of milk delivery, clear glass bottles remain by far the most important containers for pasteurized milk, polyethylene (PE)-coated cartons have also been used for many years, especially for shop sales. Large (4-pt) PE bottles were introduced only recently, although small ones have been used for some time, in particular for in-bottle sterilization of milk. Thomas (1981) reviewed flavour surveys carried out in the USA on pasteurized milk at the retail outlet. He concluded that it was the widespread use of PE bottles that had led to light-induced flavour becoming one of the major defects. Milk packaged in cartons suffered from this problem far less often. Several studies have shown that the light-sensitive vitamins in milk are more susceptible to destruction when PE bottles are used than when cartons are used (Levey, 1982; Farrer, 1983).

We have compared the protection against light-induced loss of quality afforded to pasteurized milk processed under typical UK conditions by the 2-pt white PE-coated carton and the 4-pt white PE bottle used in the UK today. Milk was stored at 7°C in the dark or exposed to white fluorescent light of 4000 Ix, simulating the kind of exposure that might be found in a display cabinet, for a period of 4d . Samples were tasted at intervals, and the following nutrients were assayed: vitamin A (retinol), vitamin B, (riboflavin), total vitamin C and ascorbic acid. Dissolved 0, measurements and total bacterial counts were also performed.

EXPERIMENTAL Source of milk Two identical experiments were performed on separate occasions (Experiments A and B). Nine. each of 2-pt white (about 1/3 of area printed light blue), PE-coated cartons (PURE-PAKB) and 4-pt white, high density PE bottles (PLYSUB) containing pasteurized, non-homogenized full cream milk were taken from the filling lines of a commercial dairy. The lines had been fed from a common pasteurized-milk tank, and the different containers were filled at about the same time. The samples were taken to the laboratory in chilled boxes and arrived within 30 min of filling. Storage Samples were exposed to light in a cabinet where both temperature and light could be controlled (Schroder, 1979). Storage temperatures were 7fy2"C in Experiment A and S+y,'C in Experiment B. 'White 3500' fluorescent tubes (Thorn, London, UK) were used and the light intensity was about 4000 Ix at the top of the containers. Light intensity was measured with a Lightmaster photometer (Diffusion Systems Ltd, London, UK). Samples were spaced out. The non-exposed samples were stored at 7°C in both experiments. Sampling Milk from each type of container was examined on days 0,1,2,3 and 4. Bacterial count, concentrations of total vitamin C and ascorbic acid and sensory evaluation were done once on each sample. Dissolved 0, measurements were performed in duplicate, and two or three independent assays were carried out

for the measurement of vitamins A and B,. Samples were tested immediately for all characteristics except contents of vitamins A and B,. For the latter, milk was deep-frozen (-20°C), and samples were examined together after completion of each experiment. Sensory evaluation Samples were warmed to 20"C, to allow proper appraisal of flavour, and presented to the taste panel in randomly coded beakers and under redlblue light. The eight panellists were experienced in judging milk for a variety of defects. A hedonic rating scale was used with eight points of response from 1 ('dislike extremely') to 8 ('like extremely') (Fig. 1). Responses were averaged. Biochemical and microbiological evaluation Vitamin A (retinol) was measured using a fluorimetric method described by Senyk et a1 (1975). Vitamin B , (riboflavin) was assayed with Lactobacillus casei NCDO 243 using a medium based on that of Roberts & Snell (1946), samples being extracted with 0.1 M HC 1 as described by Ford et a1 (1953). Vitamin C. Total vitamin C was measured as described by Deutsch & Weeks (1965), but suitably modified for the concentrations found in pasteurized milk. Reduced vitamin C (ascorbic acid) was measured by titrating the filtrate, after metaphosphoric acid treatment of the milk, with 2:6-dichloro- phenol-indophenol. Dissolved 0,. Samples were quickly warmed to 20°C and tested in opaque 60-ml glass bottles with a Model 65 Dissolved Oxygen Meter (Simac Instrumentation Ltd, Walton-on-Thames, Surrey, UK). The samples were stirred during measurement, but the bottles were filled to capacity and the housing of the 0, electrode was a close fit on the sample bottle rim to prevent access of O2 from the atmosphere. Total viable bacterial count. Samples were serially diluted with 1/4-strength Ringer's solution and plated in Milk Agar (Oxoid). Plates were incubated for 3 d at 30"C, and colonies were counted. '

RESULTS As results obtained in Experiments A and B were very similar, only one set (B) is illustrated (Figs I to 4). However, the illumination periods before off-flavour was perceived, and the corresponding vitamin losses, are shown for both experiments in the Table.

Vitamin loss in pasteurized, non-homogenized full cream milk at 7°C and under white fluorescent light of 4000 I x at the time of light-induced off-

flavour development, as determined by interpolation

Vitamin loss (%) Time to

4.5 (h) A B, C acid Sample Expt flavour score Ascorbic

Carton A 15 0 0 13 15 B 20 0 0 5 21

Mean 17.5 0 0 9 18 Bottle A 9 0 'L3 23 39

B 9 0 'L3 17 39 Mean 9 0 'L3 20 39

Carton: 2-pt white, polyethylene-coated carton Bottle: 4-pt white polyethylene bottle Flavour rating scale:

8 Extremely 1

5 Slightly 4 Like ~ ~ ~ e ~ ~ $ Dislike

Journal of the Society of Dairy Technology, Vol. 38, No. 2, April 1985 49

Flavour Freshly produced milk in both experiments was liked 'moderately', as was the case throughout the entire storage period for samples kept in the dark, irrespective of the type of container. However, when milk was stored under fluorescent light, flavour deteriorated rapidly, as shown for Experiment B in Figure I . In Experiment A, the first flavour assessment of the stored samples was at 20 h, and by this time marked deterioration had already taken place. Milk exposed in the PE bottles had dropped by three points ('dislike moderately') and milk in cartons by one point, that is, the latter was still considered to be acceptable. O n retasting after a total of 44 h exposure, the llavour of milk from both types of container was unacceptable and did not change markedly subsequently. Milk in the PE bottles was, however, consistently rated lower than milk in the cartons ('dislike very much' as opposed to 'dislike moderately'). Because of the rapid d rop in accep.tability of the exposed milks in Experiment A, there were two tasting sessions on the first storage day of Experiment B. after 17 h and after 22 h. The acceptability of the milk in the PE bottles had decreased markedly within 17 h. That of milk in cartons had also dropped from time 0, but only by one point on the rating scale. The panel still liked this milk, albeit only 'slightly'. After 22 ho f exposure the acceptability of milk exposed in both types of package appeared similar, due to a marked decrease in that of the cartoned milk combined with a slight increase in that of the bottled milk. Perhaps panel members failed to be as discriminating in the second tasting session on that day as they had been in the first. During subsequent exposure, samples were disliked 'moderately' t o 'very much', cartoned milk again being consistently preferred slightly to milk in PE bottles.

Biochemical and microbiological results Vitamin A . The concentration of vitamin A in the fresh milk was somewhat lower in Experiment B than in Experiment A, ie, 1.0.35 pg/ml as opposed to X0.45 pg/ml. The between-assay coefficient of variation was 5.6% in both experiments. The variation in vitamin A content with storage time is shown for milk B in Figure 2. The vitamin was stable except in milk in PE bottles exposed to fluorescent light. There were losses in the latter after 2 d exposure. In both experiments by day 3, light- induced destruction of vitamin A in these samples was about 15%. and there was no further loss between 3 and 4 d exposure.

Vitamin B, . The vitamin B, content of the milk a t the beginning of storage was 1.5 pg/ml in both experiments. The between- assay coeflicient of variation was 5.9%. The variation in vitamin B2 content with storage time is shown for milk B in Figure 2. Vitamin B, was stable over 4 d except in the milk in PE bottles exposed to fluorescent light. Losses in the latter were apparent after I d exposure. After 4 d , 31%) and 37Vo had been lost in the milk in Experiments A and B.

Vitamin C and ascorbic acid. The total vitamin C contents o f the fresh milk were about 18 and 20 pg/ml, respectively, in Experiments A and B. The ascorbic acid concentrations were 15.5 pg/ml and 16.5 pg/ml, respectively. The variation during storage in the contents of total vitamin C (ascorbic acid + dehydroascorbic acid) and of ascorbic acid is shown for milk B in Figure 3. There were losses of vitamin C from all the samples. In the dark, losses amounted to 50% (Experiment A) or just under 50% (Experiment B) a t the end of 4-d storage. However, whereas in Experiment A there was a continuous decline in the total vitamin C content, in Experiment B the vitamin wasstable until day 1. Milk exposed to light for 4 d in the cartons lost just under 70% of its total vitamin C, compared with a 95% loss in the PE bottles. When sampled on day I , milk exposed to lluorescent light in the cartons had lost only marginally more of

c

_a 1 tI L

IL I I I 1 I I 1 I I

0 10 20 30 LO 50 60 70 80 90 Storage period (h )

Ratinq scale:- - 8 Extremely 1

6 Moderatelv 3 Like Very much Dislike

Fig. I .

0 LO

E ; 0.35 a

* 0.30 E

i 0.25

- -

-

E >

4

E 1.5 cn a N 1.0

m

- -

5 Slightly . L

Flavour acceptability of commercially pasteurized, non- homo wni7ed full cream milk in 4-pl polyethylene bottles ( @ , , A ) or 2-pt polyethylene-coated cartons ( 0, )s tored at 7°C in the dark ( A, ) or under 4000 Ix white fluorescent light (@, , 0 ). Means with standard deviation (Experiment B).

3 I I I I I I 1 I 1 1 0 10 20 30 LO 50 60 70 80 90

E, 0.5 Y

5 '- 0 10 20 30 LO 50 60 70 80 90

Storage period l h )

Fig. 2. Vitamin A (retinol) and vitamin B, (ribollavin) content 01' commercially pasteurized, non-homogenized full cream milk in 4-pt polyethylene bottles (A, A ) or 2-pt polyethylene- coated cartons ( 0, @ ) stored a t 7OC in the dark (A, @ ) or under 4000 Ix white fluorescent light (A, 0 ) (Experiment B).

Y Y 1 I I I 1 I I I I 1

0 10 20 30 LO 50 60 70 80 90 5 ' I

Storage period (h)

Fig. 3. Vitamin C (-)and ascorbic acid ( - - - - - - )content of commercially pasteurized, non-homogenized full cream milk in 4-pt polyethylene bottles ( A , A ) or 2-pt polyethy- lene-coated cartons (0, )s tored at 7OC in the da rk ( A ,@ ) o r under 4000 Ix white fluorescent light (A, 0 ) (Exper- iment B).

50 Journal of the Society of Dairy Technology, Vol. 38, No. 2, April 1985

its vitamin C than the same milk kept in the dark. In contrast, milk exposed in the PE bottles had lost about 50% of its total vitamin C in Experiment A, compared to just over 10% lost in the dark. The equivalent losses in Experiment B were about 35% and 3%.

Losses of ascorbic acid in the dark occurred at similar rates to those of total vitamin C. However, in milk exposed to fluorescent light the destruction of the ascorbic acid proceeded at slightly faster rates than that of total vitamin C. Again, the cartons were considerably more protective against the effects of light than the PE bottles. During 4 d exposure, cartoned milk never became completely depleted of ascorbic acid, but ascorbic acid disappeared from the bottled milk within 1 to 2 d of exposure. It appears from Fig. 4 that there. were residual amounts of ascorbic acid present in these samples, amounting to about 1 to 2 pg/ml. This is unlikely, and these apparent residual levels are probably due to the presence of reducing substances other than ascorbic acid.

9 r

- 5

': 0 10 20 30 LO 50 60 70 80 90

0

Storage period (h)

Fig. 4. Dissolved O2 level in commercially pasteurized, non- homo enized full cream milk in 4-pt polyethylene bottles c A . B , or 2-pt polyethylene-coated cartons (0, 0 )stored at 7 O in the dark (A, ) or under 4000 Ix white fluorescent light ( A , 0 ) (Experiment 9).

Dissolved 0,. The initial dissolved 0, levels in the milk in Experiments A and B were, respectively, 8.5 ppm and 8 ppm. In general, duplicate assays for dissolved 0, produced identical results, any differences amounting to 0.2 ppm at most. The variation in 0, content with storage time is shown for milk B in Figure 4. In the cartoned milks the dissolved 0, concentration increased slightly with storage (Experiment A) or remained constant (Experiment B), with levels in the illuminated cartons only marginally below those in cartons kept in the dark. There was a slight drop in the dissolved 0, concentration of milk stored in PE bottles in the dark and a very marked one in those exposed to light. The dissolved 0, in the latter after 4d was 22% and 32% of its original level in, respectively, Experiments A and B. Total viable bacterial count. The bacterial count of the freshly processed milk in both experiments was about IO'/ml and did not increase within 4 d at 7"C, so that it played no part in off- flavour development. Losses in vitamin concentration in relation to off-flavour development. Duration of light exposure of milk to bring about significant flavour deterioration was estimated by interpolation using a score of 4.5 as reference point, ie, where flavour would strictly be neither acceptable nor unacceptable. However, as this represents a two-point drop in acceptability score compared with storage in the dark (Fig. I), such milk could be expected to be rejected by a large proportion of consumers. By this criterion, milk in cartons exposed to fluorescent light was acceptable for an average of 17.5 h, milk in PE bottles for only 9 h (Table). Vitamins A and B, were stable up to these times except for

vitamin B, when milk was in PE bottles, where there was an indication of a decline (Fig. 2). Loss of vitamin C after 17.5 h exposure of cartons was about 9%, and about 20% after 9 h exposure of PE bottles. Losses increased to 66% and 95% respectively at the end of 4 d exposure. Losses of ascorbic acid were about twice as high as of total vitamin C, demonstrating greater stability of dehydroascorbic acid in the presence of light than of ascorbic acid.

DISCUSSION The detrimental effect of light on milk quality, both sensory and nutritional, is well documented. This includes development of activated and oxidized flavour caused, respectively, by protein and lipid breakdown (Shipe et al , 1978) and losses in the contents of vitamins A (de Man, 1981), B, and C(Dunkleyeta1, 1962). Vitamin B, (riboflavin) plays a central role as it is not only itself destroyed but, in addition, catalyses the development of oxidized flavour (Finley & Shipe, 1968) and ascorbic acid oxidation. Its function is that of generating excited state (singlet) 0, (Aurand et al, 1977).

Consumer acceptance of a food is largely determined by flavour rather than nutritional content, primarily because flavour can be readily judged. Although with a product such as milk its presumed nutritive value influences the buying decision (Kess, I98 l), only appropriate contents labelling on packages would enable the consumer to judge this. From the commercial point of view, flavour protection in stored milk therefore takes priority over the protection of milk vitamins. An important question generally ignored in earlier research is whether significant light-induced vitamin destruction occurs before or after off-flavour develops, and, consequently, whether development of light-induced flavour in milk provides a useful warning against the consumption of vitamin-depleted milk.

Most of the published research into light-induced flavours in milk was done in the USA, where PE bottles are widely used for pasteurized milk packaging and where this has been linked with considerable problems of off-flavours (Thomas, I98 I). In the UK, this type of container is relatively new but appears to have been well received by those consumers who purchase milk in supermarkets. The work reported here shows, in line with that of a number of US scientists (Levey, 1982), that PE-coated cartons afford greater light protection than do PE bottles. Strict comparisons should, however, not be attempted in view of the differences in processing between the two countries. Whereas our milk was full cream, non-homogenized and processed in the region of the minimum legal heat treatment of 72°C for 15 s, most pasteurized milk in the USA is homogenized and heat treatment is generally more severe. Higher pasteurization temperatures generally help to stabilize ascorbic acid in milk (Ford, 1984) and reduce oxidized flavour (Bassette et al , 1983). Homogenization promotes activated flavour and reduces oxidized flavour (Shipe e ta l , 1978). It should also be noted that very high losses of vitamin A reported in the USA (Levey, 1982) are losses of vitamin A artificially added to fat-reduced milks. Supplementary vitamin A is less stable chemically than native vitamin A, and, in addition, light penetrates further into fat- reduced milk than into full cream milk. Burgess & Herrington (1955) found that at 365 nm, a 4.5 mm layer of full cream milk transmitted 2% of incident light.

Our results show that the flavour of pasteurized milk is unchanged after storage at 7°C for up to 4 d in the dark in either PE bottles or cartons. Under fluorescent light, flavour remained satisfactory for about twice as long when cartons were used as when PE bottles were used (Table). Surprisingly, although the taste panel reacted strongly against the presence of light- induced flavours in milk, one of the eight judges consistently preferred such milk, perhaps an indication that some people can become accustomed to the defect.

As with flavour, vitamins A and B, were stable in the dark. There were losses of vitamin C and ascorbic acid, but independently of the type of container. Exposed to fluorescent

Journal of the Society of Dairy Technology. Vol. 38, No. 2, April 1985 51

light, vitamins A and B, were stable only in milk in the cartons, with losses in the PE bottles after 4 d of, respectively, 15% and 3% for A and B,. Losses of vitamin C and ascorbic acid increased in both types of container, but losses in the cartons were less than half those in the bottles. There was some loss of vitamin C and ascorbic acid before flavour became unacceptable, 10% in the cartons but 20% in the bottles. However, destruction of vitamins A and B, in the presence of light followed the development of off-flavour: the very small loss of vitamin B,, in milk in PE bottles exposed for 9 h, is negligible.

The main reason why cartons offer better protection against light-induced loss of quality in milk is almost certainly the greater translucency of white PE bottles. In addition, the relatively large surface : volume ratio of the bottles (35% greater than for the cartons) causes a larger proportion of milk to be exposed. For milk exposed to light in the cartons, dissolved 0, was not a limiting factor for the rate of the oxidative processes, but in the less permeable bottles, the 0, level dropped considerably. This partly explains why reactions slowed down particularly markedly in the bottled milks towards the end of storage. Furthermore, the limited light penetration of milk meant that reactions were confined to the outer milk layer and soon reached completion: this applies to both bottles and cartons. Agitation, which was avoided in these experiments, would allow greater loss by presentingfurther milk to the action of the light.

Because of its absorption by vitamin B,, light of wavelengths of 350-550 nm is the most damaging, the maximum being at about 450 nm (Dunkley er al, 1962). These wavelengths are contained in the emission spectra of white fluorescent tubes. Hoskin & Dimick (1979) found that milk cartons of the type used in our experiments transmit very little of light in this wavelength range, but glass and high density PE bottles let through 95% and 10-24%, respectively. They also tested a yellow pigmented plastics container which selectively excluded wavelengths of 380-480 nm: this gave considerable protection, although less than did the cartons. The small, blue printed area on our cartons would not have given any protection, as this could only have filtered out long-wavelength light. In a small number of clear glass bottles, stored alongside the principal experimental samples, the milk flavour deteriorated at a similar rate to that for cartoned milk. This may be surprising in view of the greater translucency of the glass bottle. However, light- induced flavour development depends on 0, availability (Schr6der, 1982), and 0, was limited in the glass bottles because, unlike cartons and PE bottles, they are impermeable, and 0, used up in oxidative reactions cannot easily be replenished. In fact the dissolved 0, concentration dropped much more rapidly in exposed glass bottles even than in the PE bottles and so was likely to be a limiting factor.

Although several flavour surveys of pasteurized milk at retail level have been carried out in the USA (Thomas, 1981), similar information is not available for the UK. Light-induced flavour has created problems in dairies producing sterilized milk in PE bottles, but complaints about such flavours in pasteurized milk in this type of container have not apparently been received by dairies so far. Obviously, whether light damage does occur under practical conditions depends on many things, for example, the size of the exposed surface area (this may be less than in our experiments where containers were not tightly packed), the amount of handling/agitation and the length and intensity of exposure to natural or artificial light, in the dairy, the supermarket, the home and during transport. The most critical period is likely to be in the supermarket. In the USA it was found that 71% of milk remained on supermarket shelves for at least 5 h and that 37% was still there after 24 h (Anon, 1974). It is thus hardly surprising that problems occur on a considerable scale. In the UK, supermarket sales of pasteurized

milk and in particular the use of PE bottles are still on a fairly small scale, and i t may be that the volume of the operation, together with its novelty, have so far ensured satisfactory stock rotation in the supermarkets. However, the risk of flavour problems must be recognized.

In conclusion, although milk quality is ideally protected if milk is kept in the dark and handled away from bright light, this may not be practical at all times. It is therefore important to use packaging that minimizes damage. Our comparison of white, PE-coated cartons and white PE bottles has shown that milk can be exposed to fluorescent light in the former for twice as long as in the latter before there is off-flavour development. In addition, vitamin C is much more stable. Although vitamins A and B,are better protected in cartons also, losses in these through theeffect of light d o not occur in any containers until after the flavour has deteriorated considerably. Milk is generally considered a good source of vitamins A and B,, and, from a nutritional point of view, consumer rejection of light-induced flavour is useful in that it draws attention to milk deficient in these vitamins. Vitamin C content of milk, although generally regarded as negligible in relation to that of other foods, should not be seen a s not worth protecting. After all, 1 pint of our milk after pasteurization, which contained 19 mg vitamin C/I or 1 I mg/pint, could supply over one-third of the daily intake of an adult of 30 mg recommended by the Department of Health and Social Security (DHSS, 1979). This could be especially important for the health of people who depend heavily on milk as a source of nutrients, even more so in view of the fact that 20 mg/d is sufficient to prevent overt scurvy (Bartley, Krebs & O'Brien, 1953).

This study was funded by the UK Milk Cartoning Manufacturers Association, who are thanked for their permission to publish the results. The cooperation of the dairy from which samples were obtained and that of the taste panel are also gratefully acknowledged.

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DHSS (1979) Report on Health and Social Subjects No. 15. London:

Dunkley, W L. Franklin, J D & Pangborn, R M (1962) Food Tech-

Farrer, K T H (1983) Light damage in milk. Farrer Consultants, 40 Glen

Finley, J W & Shipe. W F (196X) .lournal of Dairy Science, 51, 929. Ford, J E (1984) Private communication. Ford, J E, Gregory, M E, Porter. J W G & Thompson, S Y (1953)

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52 Journal of the Society of Dairy Technology. Vol. 38, No. 2. April 1985