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Shelf-life of Milk Packaged in Plastic Containers With and Without Treatment to Reduce Light Transmission



The effect of prolonged light exposure on the chemical changes in milk stored at 4 degrees C in clear polyethylene terephthalate (PET) bottles was compared with milk stored in green PET bottles, containers made from PET incorporating a UV blocker, PET containers with exterior labels and high-density polyethylene (HDPE) jugs and low-density polyethylene (LDPE) pouches stored under the same conditions. Data were obtained for lipid oxidation, vitamin A degradation, protein hydrolysis, lipolysis and microbial growth. The milk stored in green PET bottles experienced less lipid oxidation and vitamin A loss than milk stored in the clear PET bottles, or the LDPE pouches and jugs. In general, the milk stored in the clear PET bottles;was not as well protected from the effects of light as milk stored in green bottles or LDPE pouches. However, during the first week of storage, only vitamin A loss showed a substantial difference between the milk stored in green PET bottles, clear PET bottles or LDPE pouches. The PET bottles with UV blockers slowed vitamin A degradation but had little effect on lipid oxidation. Blocking visible light with translucent labels helped to inhibit lipid oxidation and vitamin A degradation.
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Shelf-life of Milk Packaged in Plastic Containers
@58-6946/98iS-see front matter
With and Without Treatment to Reduce
Light Transmission
Wendy Cladmano, Steven Scheffer', Nina Goodrich'and Mansel W. Griffiths'*
" Department of Food Science, Unioersity of Guelph, Guelph, ON, Canada, NIG 2Wl
hTwinpak Inc., 910 Central Parkway 14., Mississauga, ON, Canada, LSC 2V5
(Received 12 March 1998; accepted 3 July 199E)
The eflect of prolonged light exposure on the chemical changes in milk stored at 4"C in clear polyethylene terephthalate (PET)
bottles was compared with milk stored in green PET bottles, containers made from PET incorporating a UV blocker, PET containers
with exterior labels and high-density polyethylene (HDPE) jugs and low-density polyethylene (LDPE) pouches stored under the same
conditions. Data were obtained for lipid oxidation, vitamin A degradation, protein hydrolysis, lipolysis and microbial growth. The
milk stored in green PET bottles experienced less lipid oxidation and vitamin A loss than milk stored in the clear PET bottles, or the
LDPE pouches and jugs. In general, the milk stored in the clear PET bottles was not as well protected from the effects of light as milk
stored in green bottles or LDPE pouches. However, during the first week of storage, only vitamin A loss showed a substantial
difference between the milk stored in green PET bottles, clear PET bottles or LDPE pouches. The PET bottles with UV blockers
slowed vitamin A degradation but had little effect on lipid oxidation. Blocking visibte light with translucent labels helped to inhibit
lipid oxidation and vitamin A degradation. O 1998 Elsevier Science Ltd. Al1 rights reserved
There have been many attempts to improve milk
packaging in recent years. Since milk started to be dis-
played in supermarket coolers under fluorescent lights,
there have been difficulties with maintaining a fresh,
pleasing flavour. Consumers, although concerned with
the nutritional aspects, are probably most influenced by
the flavour of the product (Thomas, 1981). Light expo-
sure, especially to wavelengthi below 500 nm causes the
destruction of light-sensitive vitamins (riboflavin, vita-
mins A and C), induces chemical reactions that affect
milk proteins and lipids, and results in the development
of unpleasant flavours in foods (Fanelli et al., 1985;Sattar
et al., 1977; Schrcider et al., !985). Changes in flavour
can be caused by the destruction of vitamin A, protein
breakdown, lipid hydrolysis, microbial spoilage or the
oxidation of unsaturated fatty acids (Thomas, 1981). Ofr-
flavours may thus be linked to a drop in the nutritional
value of the milk. Light-induced flavour development is
dependent on the availability ofoxygen (Schrirder, 1982).
This can be controlled by reducing the amount of head
space in the container. avoiding agitation ofthe product
and by using oxygen impermeable containers to prevent
further entry of oxygen. Oxidative reactions were re-
ported to be controlled after free oxygen was depleted in
glass containers, but they continued in cartons and high-
density polyethylene containers (HDPE), which were
*Corresponding author. Tel.: 5 19 824 4120 x2269; fax: 519 824
6631; e-mail:
Int. Dahy Journal E (1998) 629-636
irl 1998 Elsevier Science Ltd. All rights rescrved
Printed in GHt Britain
more psrmeable to oxygen than glass (Schrcider er al.,
Polyethylene terephthalate (PET) has been used in
r€cent years as a very effective packaging material for
carbonated beverages, edible oils and other food prod-
ucts (Feron et a1.,1994).Its use for milk packaging would
help overcome problems that have accompanied other
materials. PET is not easily breakable, is recyclable,
and the contents of PET bottles can be easily poured.
They are easy to open and close and do not require
any ancillary devices to assist opening or pouring. An
opened bottle can be easily resealed, thus minimizing
recontamination and wastage due to spills. PET bottles
may be used for individual servings or for I or 2L
In addition, the oxygen permeability of PET is 4 to
5 cc @ 15.5 sq cm- 1 24h-r compared to 100 to
200 cc for HDPE. The relative thicknesses of PET and
HDPE bottles used for beverages are 12 mil and 20 mil,
respectively, indicating that a PET bottle is 20 times less
permeable to oxygen than HDPE (data of Scheffer, Twin-
pak Inc., Mississauga, ON). To reduce the adverse effects
of light on milk quality, coloured or opaque PET bottles
can be used, This is acceptable to the consumer for
products such as cola or beer, but, when these containers
have been proposed for packaging milk, consumers have
shown a preference for clear or translucent white con-
tainers (White, 1985).
Despite the possible advantages, few studies have been
published to determine the shelfJife of milk packaged
in PET bottles. In this study, the quality of milk was
examined under storage conditions that simulated those
630 ll. Cladman et al.
expected during display in a supermarket to ascertain
how well clear PET could protect the milk from the
damaging effect of UY and visible light. A comparison
was made for milk stored in clear pET with other
packaging materials. In addition, the study inciuded
the effect of further reducing the amount of visible
light and UV radiation transmitted through pET con-
tainers on the shelfJife of milk by using (i) green pET
bottles, which largely prevent the transmission of light
wavelengths below 500 nm, (i, incorporating UV
absorbing materials into PET, and (iii) by placingllabels
on PET bottles.
Milk storage and sampling
Eight 4 L bags (each containing three 1.3 L pouches) of
each of whole and 2% freshly pasteurized milk were
obtained _fr9m a local processor. Two 2 L HDpE jugs
each of whole and 2o/o milk were purchased from a l-ocil
convenience store on the same day. All the products had
a similar expected shelf-life, as measured ty the .best-
before'date. The milk was transported to the laboratory
on ice in insulated containers. On arrival at the labora-
tory, the milk was aseptically dispensed lrom the pouches
into 20 clean, green and 20 clean, clear 600 mL pET
bottles for each of whole and 2o/o product. The milk jugs
were aseptically emptied, rinsed with sterile water, and
then refilled with the same milk as the pET bottles. The
remaining pouches were retained in the original outer
bags.. Du.ring the entire procedure, the milk was kept on
crushed ice to maintain a cold temperature.
In another experiment, sixteen 4 L bags of 2oh mllk
with 17 d until the expiry date were obiained from a
local dairy and were kept cold and in the dark until
used. The milk was aseprically dispensed into 22 bottles
e.ach of (i) clean, clear 600 mL bottles made from pET;
(ii) clean, clear 600 mL bottles made from pET combined
with UV absorbers (UV-pET); (iii) clean, clear,
labelled 600 mL bottles made from pET; (iv) clean, clear,
labelled 600 mL botrles made from UV-pET; and (vj
high-density. polyethylene (HDpE) bottles (500 mli
without Iabels.
One of the labels used was placed over the light meter
to assess the degree of translucency of the labels.
_Qne 4 L bag of 2Y, milk (from the same dairy), with
15 d until the expiry date, was used to lill four pijT and
fo.u1 HDPE bottles, which were then completely covered
with aluminum foil.
- After being dispensed, the milk was immediately trans-
ferred to an environmental chamber, 60 cm by iOS cm,
held at a constant temperature of 4 * l.C, fh! tgtrting
was provided by four 60 W cool white Sylvanii
fluorescent tubes for 13 h daily. The intensity of ilght at
the top and sides ol the bottles wa, m.aiured -using
a General Electric type DW-68 light meter and wai
found to be about one-half of the intensity of light
measured on top shelf front row bottles and tartoniin
an.average local sL.Iermarket. The light was evenly dis_
tributed over all of the bottles and fouches within the
On each test day, four clear pET, four sreen pET
bottles and 1 LDPE pouch for each milk typejwhole and
2oh) were randomly selected and a fioofia sample
(200 mL) used for analysis, Similarly, 100 mL was re-
moved from each of the 2 HDPE jugs for both milk types,
pooled and used for analysis. The milk was examined for
visual appearance (colour and the presence ofclots) and
odour. Each chemical assay was carried out in triplicate.
An ANOVA, computed using Microsoft Excel, was used
to compare treatments. Treatments were deemed to be
significantly different when P < 0.05,
Chemical testing
Pr ot ein hy dr oly si s as say
_ A,2T!Jryple of milk was deproteinized by adding
5 mL of 0.72 r{ trichloroacetic acid. The precipitate was
removed by filtration through Whatman 442 ashless
filter paper. Two mL of sodium carbonate reagent (15%
sodium_carbonate anhydrous and 1% tri-sodium phos-
phate; Fisher Scientific Ltd, Mississauga, ON, Canada)
was added to 1mL of filtrate and mixed vigorously.
Folin-Ciocalteu's phenol reagent (Sigma Chemical Co.,
St Louis, MO) was diluted 1 :3 with Aistllea warer, and
0.6 mL of the diluted reagent was added, with mixing, to
the filtrate. After standing for 5 min at room temperature,
the reaction mixture was again filtered through a O.+S pm
syringe filter (Millipore Corp.). The absorbance at
650 nm was read in a Pharmacia Novaspec II spectro-
photometer. The level of free tyrosine wajdetermined by
comparing the absorbance values with a standard curvi
of known tyrosine concentrations (Hull, 1947). The ex_
tent of proteolysis was proportional to the level of
tyrosine released during the hydrolysis of proteins.
A lipid extraction was achieved by the addition of
10 mL of extraction mix (2-propanol, petroleum ether,
4 tt HrSOa; 4O: l0: 1), 6 mL petioleum ether and 4 mL
water to 3 mL of milk, prewarmed to 30"C. The mixture
was shaken vigorously, allowed to stand for the separ-
ation of the two phases, and a 2 mL aliquot of the upper
phase removed to be titrated with 0.-02 N merhan;lic
KOH, following the addition of six drops of colour
indicltor (1% phenolphthalein). The conienrration of
free fatty acid (FFA) was determined as
p equiv. FFA mL- 1 = 1fN7f Z; x 103
where T is the net titration volume; N the normality of
KOH; P the volume titrated/volume of upper layer;
Iz the volume of milk.
A control was run without milk (Deeth et al., 1975).
Vitamin A degradation
Five mL al95V, ethanol were added to 2 mL of milk at
room temperature, mixed and allowed to stand at room
temperature for 5 min. Hexane (5 mL) was added and the
mixture vortexed for 30 s, then allowed to stand for
2min. This was repeated two more times. Three mL of
distilled water were added to the above mixture and
mixed by gentle inversion, followed by centrifugation for
l! mi1 a1 1000 g at l5'C. The ,pp.. iuyer was removed,
filtered through a-,0,!5 ru nyl,:n'filter iVfittipore Corp.j
and stored at - 20'C until HpLC analysis.'
_A Waters HPLC system was used wittra 25 cm Waters
pPorasil column and a Varian UV detector adjusted to
Shelf-hfe of milk packaged in plastic containers 631
313 nm. The mobile phase used was as follows: 49 parts
wet hexane:49 parts dry hexane:2 parts diethyl ether.
Using a flow rate of 2 mL min - 1, 100 pL of sample or of
a standard (retinol palmitate) was injected and the trans
peak eluted at 4 min. The area under the peak was
compared with known standards to calculate the concen-
tration of retinol palmitate in the milk samples (Mar-
shall, 1992).
Lipid oxidation
Lipid oxidation was determined by measuring in-
creasos in conjugated dienes according to the method of
King (1962). Milk (17.6 mL), prewarmed to 30"C, was
precipitated by the addition of 1mL of l gml-1 tri-
chloroacetic acid (TCA) and 2 mL of 95o/o ethanol. Fo1-
lowing a 5 min incubation at 30oC, the precipitate was
removed by filtration through a Whatman #42 filter
paper, and lml- of 1.4oh 2-thiobarbituric acid was
added to 4 mL of the resulting filtrate. This was then
incubated for 60 min at 60'C, cooled and the absorbance
read at 532 nm in a Pharmacia Novospec II spectro-
Psychrotrophic counts
In order to determine that the milk used in the experi-
ments was of similar microbiological quality and to ver-
ify that the type of packaging material did not affect the
microbiological shelfJife of the product, psychrotrophic
counts were determined in all milk samples. The milk
samples were spread plated on plate count agar (Difco,
Detroit, MI) using a spiral plater model D (Spiral Sys-
tems, Bethesda, MD). When necessary, ten-fold dilutions
were prepared in peptone water (Difco). Colony counts
were obtained after incubation of the plates at 22"C for
25-40h (Griffiths et a1.,1980).
Microbiological quality of the milksand light transmission
during storage
M icrobiological quality
The rate of growth of psychrotrophic bacteria in whole
milk was similar for all of the packaging types (Table l).
The bottles and jugs that were filled in the laboratory did
not appear to have higher counts than the unopened
pouches. Up to the expiry date, there were lew visible
signs olspoilage. After 18 d storage, the bacterial counts
for the 2o/o milk samplos were higher in the jugs and
pouches than in the bottles.
However, in the experiments conducted with con-
tainers treated to further reduce light transmission, the
initial psychrotrophic counts in the milk were also low
(<l0cfuml-'1, but, in this case, they remained low
throughout storage in all containers except the foil-wrap-
ped PET and HDPE bottles (Table 1). Counrs in milk
packaged in these reached counts >1x 105 cfumL-r
after 12 d, The reason for this increase is unclear.
Light tansmission
The amount of light reaching the bottles in the envi-
ronmental chamber was comparable or slightly less than
that encountered by milk stored at the front of the top
rows of chill cabinets in supermarkets. Covering the top
of the light meter with one of the labels from the milk
bottles reduced the amount of light exposure by 75%. All
of the bottles in the environmental chamber received
a similar level of light exposure throughout the test
Comparison of shelfJife of milk packaged in clear
PET bottles, green PET bottles, LDPE pouches and
HDPE jugs
Lipid oxidation
Both milk types in the green bottles and in the pouches
exhibited a similar pattern of lipid oxidation over the
18 d storage period, although minor differences could be
observed (Fig. I ). The oxidation level increased gradually
and the milk was undrinkable after 14 d. The same milk
stored in HDPE jugs showed a high level of lipid oxida-
tion after only 3 d. The clear PET bottles were not as
effective as the green bottles at inhibiting oxidation. The
oxidation levels increased at a faster rate in the clear
bottles and the milk was strongly oxidized by the 10th
day. By the 14th day, there was a significant difference
(P < 0.05) in levels of oxidation for whole milk in all
packaging types, with the lowest level of oxidation being
observed in the green PET bottles (Fig. 1). However, for
the 2o/o milk stored for 14d, there was no significant
difference between oxidation levels seen in pouches and
green PET bottles, but the levels in these two packaging
materials were significantly (P < 0.05) lower than for the
clear PET bottles and the jug (Fig. l). There was a signifi-
cant difference (P < 0.05) in levels of oxidation it the 2Yo
milk stored in green PET bottles and pouches at both 10
and 18 d, with oxidation being lower in the milk
packaged in green PET bottles.
Vitamin A ilegradation
The vitamin A concentration in all whole milk sam-
ples, except for the milk stored in the green PET bottles,
decreased by at least 47% within the first 6 d of storage.
The vitamin A content in the milk packaged in the green
PET bottles fell by 28% (Fis. 2). The milk stored in rhe
HDPE jugs had the most severe vitamin A loss (58%)
and the pouches and clear PET bottles were similar in
their respective levels of degradation.
The pattern of vitamin A degradation in 2% milk was
similar to that observed in whole milk (Fig. 2). The
vitamin A content of 2% milk in the green bottles de-
clined less than the others until 14 d when it dropped to
a level similar to the pouches(57% and 54oh, respective-
1y), The level of vitamin A in milk stored in the clear
bottles declined more rapidly than in pouch-packed milk.
In both clear and green PET bottles, the vitamin A level
decreased more in 2Y' mllk than in whole milk. This was
not observed for the other containers.
AII differences were signiflcant (P < 0.05) for the whole
milk except for the comparison between milk stored for
6 d in the clear bottles and pouches and in the clear
bottles and jugs. Similarly, for the 2Vo milk all diflerences
in vitamin A content were signilicant (P < 0.05) except
between milk stored in green bottles and pouches for
18 d.
There was little difference observed in lipid degra-
dation in milk stored in the four different packaging
632 [4. Cladman eL al.
Table 1. Psychrotrophic Counts (CFU mL- 1) During Storage at 4'C of Whole Milk and 2% Milk Packaged in Various Containers
Packaging material Count (logCFU mL- I) at storage time
Whole milk
Clear PET
Green PET
LDPE pouch
HDPE jug
2% milk
Clear PET
Green PET
LDPE pouch
HDPE jug
PET + tabel
UV-PET + label
HDPE bottle
Foil-wrapped PET bottle
Foil-wrapped HDPE bottle
< 1.0
< 1.0
< 1.0
< 1.0
< t.0
1.48 (4 d)
3.41 (4 d)
< 1.0
< 1.0
4.3 (8 dl
4.3 (8 dt
< 1.0
>5.0 (12 d)
>5.0 (12 d)
A) whole milk A) whole milk
Storage time (d)
B) 2% milk
Storage time (d)
Fig. l. Lipid oxidation in (A) whole and (B) 2% milk during
storage at 4'C in clear PET bottles (o), green PET bottles (r),
LDPE pouch (r') and HDPE jug (").
materials (Fig. 3), There was an increase in the level of
FFAs after l0 d, which continued until the end of the test.
The rate of lipolysis in the whole milk in the green PET
bottles appeared to increase less than in whole milk in the
other packaging materials.
6 10
Siorag8 time (d)
B) 2% milk
Storage tim€ (d)
Fig. 2. Vitamin A degradation in (A) whole and (B) 2o/o milk
during storage at 4'C in clear PET bottles (o), green PET
bottles (t), LDPE pouch (t) and HDPE jug (x).
For the 2% milk samples, lipolysis was the greatest in
the pouch and jug packaged milk and, by the end of the
storage trial, the level of lipolysis in the PET bottled milk
was lower than for milk in the other two packagos but the
difference was not significant (P > 0.05).
A) whole.rnilk
Shelf-lde of milk packaged in plastic containers 633
Storage time (d)
B) 2% milk
Fig. 3. Rate or riporysis,.ilHjl]:ll,r,,* mlk during
storage at 4oC in clear PET bottles (o), green PET bottles (r),
LDPE pouch (e) and HDPE jug (x).
The data obtained for protein hydrolysis were incon-
sistent, and it was difficult to establish a clear trend.
However, in all cases, there appeared to be no increase in
tyrosine values, and hence in presumed proteolysis, in
any of the samples when compared with the milk sam-
pled prior to storage (Fig. a).
Comparison of shelfJife of milk stored in PET bottles
and UV-PET bottles with and without labels
To investigate the effects of further reducing light
transmission through PET containers, milk was
packaged in PET bottles that had been treated to incor-
porate a UY-blocker and in labelled PET bottles.
Lipid oxidation
After 6 d of storage, milk in the labelled PET bottles
exhibited the lowest degree of lipid oxidation, followed
closely by milk in the labelled UV-PET bottles (Fig. 5).
At the end of the storage period, there was little dif-
ference in lipid oxidation observed in any of the milk
in the PET bottles, but lipid oxidation levels in milk in
the UV-PET bottles was slightly, but significantly
(P < 0.05), lower than those in the PET bottles. The milk
in the foil covered bottles maintained low levels of lipid
oxidation for the entire test period and there was no
significant difference (P > 0.05) between the packaging
Storage time (d)
B) 2olo milk
Storage time (d)
Fig. 4. Rate of proteolysis in (A) whole and (B) ZYo milk during
storage at 4'C in clear PET bottles (o), green PET bottles (t),
LDPE pouch (e) and HDPE jug (x).
0.1 5
00510'1520Storage time (d)
Fig. 5. Lipid oxidation in 2% milk during storage at 4'C in
PET bottles (.), PET + label bottles (r), UV-PET boules (e),
UV-PET + label bottles (x), HDPE boules (x), PET (in foil)
bottles (o), and HDPE (in foil) bottles (+).
Vitamin A analysis
The milk in PET bottles treated to block UV radiation
had the least amount of vitamin A degradation through-
out the test, with the labelled bottles permitting 20 to
30% less degradation than those that were unJabelled
(Fig. 6). The milk in the labelled, UV-PET bottles losr
30% of its vitamin A content after 6 d and 50%o after 18 d
(Fig. 6). At the end of the storage period, vitamin A levels
were the highest in milks in the labelled UV-PET bottles
\ z.s
< t.c
A) whole milk
634 ll, Cladman et al
Storage time (d)
Fig.6. Vitamin A degradation in 2% milk stored at 4'C in PET
bottles (o), PET + label bottles (r), UV-PET bottles (r), UV-
PET + label bottles (x), HDPE bottles (x), PET (in foil) bottles
(o), and HDPE (in foil) bottles (+).
(P < 0.05). Vitamin A levels in milk packaged in labelled,
untreated PET bottlos were comparable to the milk in
UV absorbing PET bottles. Except for the sampling after
3 d exposure to light, the rate of vitamin A degradation in
milk in HDPE bottles was very similar to the milk in
normal PET bottles. The milk in the foil covered bottles
showed no degradation until 12 d of storage, and then
the level of vitamin A decreased by only 20% for the milk
in HDPE bottles and 7o/o for product in the PET bottles
(Fig. 6).
The rate of lipolysis was similar in milk packaged in
all the containers, except those covered in foil (Fig. 7),
Neither the labels nor the UY blocker appeared to have
an effect on the level oflipid degradation (P > 0.05). The
milk in the foil covered Lottlei underwent greater lipo-
lysis than in the light exposed bottles.
Protein h.,-drolysis
The level of free tyrosine, which is indicative of pro-
teolysis, remained low in milk contained in all packaging
types except the containers wrapped in foil (Fig. 8). In
milk in the foil-wrapped HDPE bottles, there was a sig-
nificant increase (P < 0,05) in proteolysis. Although the
level of proteolysis remained high in milk in the foil-
wrapped PET bottles, the rate of increase was not as
great as that in milk in the foil-wrapped HDPE bottles.
Packaging did not seem to have a large effect on
lipolysis or proteolysis. This was probably due to the
similar rates of growth of bacteria. However, the milk in
the foil-covered bottles showed evidence of lipoysis and
proteolysis at the end ofthe storage period, and this was
probably due to the higher counts of psychrotrophic
bacteria in containers which resulted in the production of
extracellular proteases and lipases (Phillips and Griffiths,
PET which had been treated to absorb a minimum
of 95o/, of UV radiation appears to be eflective in
Storage time (d)
Fig, 7. Rate of lipolysis in 2Yo milk stored at 4'C in PET bottles
(.), PET + label boules (t), UY-PET bottles (^), UV-
PET + label bottles (x), HDPE bottles (x), PET (in foil) bottles
(a), and HDPE (in foil) bottles (+),
10 15 20
Storage Ume (d)
Fig. 8. Rate of proteolysis in 2% milk stored at 4"C in PET
bottles (.), PET + label bottles (r), UV-PET bottles (r), UV-
PET + label bottles (x), HDPE boules (x), PET (in foil) bottles
(o), and HDPE (in foil) bottles (-t-).
preventing vitamin A degradation and provides similar
protection against lipid oxidation as LDPE pouches. The
green PET bottles were also able to block out much of
the harmful visible and UV light. The clear PET bottles
were not as protective against harmful light effects as the
UV-PET bottles or the green PET bottles but were only
slightly less effective than the LDPE pouches. Although
the clear bottles gave less protection against the effects of
light than the pouches covered with translucent LDPE
bags, they were far less permeable to oxygen than the
LDPE pouches. This may have limited the rate of oxida-
tive reactions (Schrtider et al., 1985). The translucent
HDPE jugs were not very effective in preventing lipid
oxidation due to the higher level of permeability of high-
density HDPE to oxygen (Feron et al., 1994\; Schroder,
1982). The rates of lipid oxidation and vitamin A decline
were considerably higher for the HDPE jugs than for the
other containers. This trend was also observed when
HDPE bottles were used.
All the different containers were at the same average
distance from the light source and received a similar
Shelf-life of milk packaged in plastic containers 635
dosage of light throughout the test period. The difference
in size and in surface aroa may have made a difference in
the amount of milk exposed to light, but milk in the 2 L
HDPEjugs degraded to the greatest extent even though
the ratio of surface area to volume was lower than for the
pouches or 600 mL bottles.
In all the samples, vitamin A decreased by at least 50%
by the time the expiry date was reached. However, the
rate of decline was significantly slower in the milk
packaged in the UV-PET bottles. Vitamin A is destroyed
by light at wavelengths of less than 450 nm (Sattar
et al., 1977). The degradation of both vitamin A and
riboflavin are dependent on the amount of fat in the
milk. Levels ofdegradation have been reported higher for
skim milk than for whole milk (Senyk and Shipe, 1981),
and also higher for added vitamin A than for natural
vitamin A. This was also observed in the milk stored in
PET bottles, where the vitamin A levels in 2Yo milk
declined more than in whole milk. Since the other con-
tainers were not as impermeable to oxygen, light was
probably not the only factor influencing the degradation
of vitamin A,
The green PET bottles did help protect against chem-
ical changes in milk during storage, but they may not be
easily accepted by consumers. Incorporating light ab-
sorbers for wavelengths less than 500 nm in the clear
PET seems to offer a better alternative. Yellow pigment
has been reported to absorb light in the 40O-500 nm
wavelength range, which would protect riboflavin from
detrimental light, and removes wavelengths below
415 nm, which would prevent vitamin A from being de-
graded (Fanelli et al.,1985). However, yellow bottles may
be as unappealing to the public as green bottles for the
storage of milk. When tested, consumers preferred white,
opaque bottles and jugs to coloured containers (White,
Shielding a major portion of the main body of the
bottle with a material impermeable to the damaging
wavelengths of light has also been suggested (Hoskin,
1988). It was reported that shielding the sides of a milk
bottle from light is more effective than shielding the top,
and it was also recommended that the shield materials be
printed with a background colour that would decrease
the light transmission (Hoskin, 1988). In the present
study, the labels provided for the test covered approxi-
mately 55% of the surface of the bottle and were translu-
cent. Measured on a light meter, the labels reduced
visible light transmission by 75%. Even so, after 6 d
storage, the level of lipid oxidation in the milk in the
labelled bottles was 40-50% lower than in the unlabelled
bottles and the vitamin A content was 20-30% higher in
the labelled bottles. Since milk is rarely on the shelves of
a supermarket for such a long time, and since flavour is
a deciding factor in the purchase of milk, this result could
be considered significant.
The foil-covered control bottles clearly demonstrated
the damaging eflects of light on vitamin content. There
was little or no decrease in vitamin A and no increase in
lipid oxidation when the milk was completely protected
from light exposure. Vitamin A degradation appears to
be largely caused by UV radiation but lipid oxidation
seems to be caused by visible light.
It is recognized that the containers used in this study
were of different sizes and, hence, had different surface:
volume ratios. However, the PET bottles were the
smallest containers used, and, therefore, had the greatest
surface:volume ratio. Yet the milk packaged in these
containers generally were less affected by light and oxy-
gen than those packaged in the larger containers. It is
possible that the protective effects of PET may be Sreater
when it is used to package milk in larger volumes.
Bottles made from PET incorporating UV blocking
agents can provide an attractive and convenient form of
packaging for milk, offering protection against vitamin
degradation and lipid oxidation. The shelflife of milk of
good bacteriological quality can be further improved by
using a labelled bottle to reduce light transmission. The
use of such labels may provide an unique opportunity to
attract young consumers and, thus, increase the con-
sumption of milk.
The authors are grateful to Maple Lane Dairies in
Kitchener, Ontario for providing the milk for this test
and to Dr. Y. Kakuda for assistance with the vitamin
A analysis. MWG would like to thank Dairy Farmers of
Ontario and the Natural Sciences and Engineering Re-
search Council of Canada for research funding.
Deeth, H. C., Fitz-Gerald, C. H. and Wood, A. F. (1975)
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Sources, eds J. O. Nriagu and M. S. Simmons. Wiley, New
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Sattar, A., deMan, J. M. and Alexander, J. C. (1977) Wavelength
eflect on light-induced decomposition of vitamin A and
p-carotene in solutions and milk fat. Journal of the Canadian
Institutc of Food Science and Technology 10, 56--60.
636 W. Cladman et al.
Schrdder, M. J. A. (1982) Effect of oxygen on the keeping
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uptake in milk in relation to oxygen availability. Journal of
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Schrdder, M. J" A., Scott, K. J., Bland, K. J. and Bishop D. R.
(1985) Flavour and vitamin stability in pasteurized milk in
polyethylene-coated cartons and io polyethylene bottles.
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... The degree of proteolysis in the milk samples was unaffected by the opacity and oxygen barrier levels. Tyrosine readings following a 6-day storage period ranged from 0.011 to 0.023 mg/ml, according to Cadman., et al. [10], who also noted difficulty drawing conclusions about the specific pattern of proteolysis. The degree of lipid degradation varied very little between samples held in the four types of packaging, and the range of free fatty acid levels was between 1.24 and 4.39 equiv/ml. ...
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Objective: This research was done to examine the impact of various packaging materials on the physiochemical characteristics of pasteurized camel milk. Methods: In the current study, a variety of packaging materials were used, including (i) PET bottles, (ii) PP cups, (iii) PS cups, (iv) LDPE bottles, (v) LPET bottles, (vi) HDPE bottles, (vii) aluminum cans, (viii) emerald green glass, and (ix) cartoon bottles (250 ml size). During the summer and winter, pasteurized camel milk samples were aseptically packed in a variety of packaging materials under aseptic conditions (80°C, 16s). They were put in the refrigerator and kept there for 30 days at 5°C. The study investigated the physiochemical parameters including density, pH, acidity, protein, fat, lactose, (TS), (S-N-F), and lactose. The overall migration of the food product from the packaging was also calculated for each package. Results: The results indicated variations in almost all physicochemical properties of pasteurized camel milk packed in various packaging materials. On the other hand, the season did not affect the values of the tested physicochemical properties. Furthermore, all packaging materials showed chemical migration from the packaging to the food product in the range of 1.25 to 2.05 (mg/dm 2) according to the overall migration test of the food packaging materials. Still, the migration limit was less than the limit of 10 (mg/dm 2 of the European Union Standards and complying with the UAE regulations. Conclusion: In conclusion, we should consider the significance of packaging barrier physicochemical qualities and make our choice in accordance with the nature of the product when selecting the right packing materials for camel milk.
... Amber PETE showed the least amount of oxidation offflavor, while clear PETE with UV block showed significantly less oxidation off-flavor than glass, clear PETE or HDPE on day 7 and 18. Acetaldehyde was not detected by sensory analysis in either light-exposed or lightprotected samples. Also Cladman et al., (1998) compared the effectiveness of clear PETE, green PETE, clear PETE with UV block, HDPE jugs, and low-density polyethylene pouches for chemical changes in milk over a period of 18 days. Green PETE showed best protection of milk against lipid oxidation, with clear PETE showing the worst results. ...
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Nine types of packaging materials were tested on this study Included (I) Polyethylenetetraphthalate (PET) Bottle, (ii) Polypropylene (PP) Cup, (iii) polystyrene (PS) Cup, (iv) Low density polyethylene (LDPE) Bottle, (v) Light Proof Polyethyleneterephthalate(LPET) Bottle,(vi) High density Polyethylene(HDPE) Bottle, (vii) Aluminum Cans, (viii) Glass(Emerald Green) and (ix) Cartoon bottles (250 ml size) were dispensed in the aseptic condition with Pasteurized camel milk (80 ˚C,16s) for two seasons Summer and Winter and stored immediately inside the chiller at 5 ˚C for 30 days, The camel milk samples were examined for microbial quality, sensory evaluation, also food packaging materials were examined for overall migration test, approximate shelf life of the pasteurized camel milk at temperature 5 ˚C in all types of packaging materials in our study period 30 days, Sensory Evaluation results shown that there is significant differences within best packaging materials, so we can say best packaging materials not same in summer and winter. We see also the best packaging materials is not same in winter of all type of Sensory Evaluation with one ranking (PS, HDPE) respectively, but not difference in summer, so the best in winter is (PP - PS – PET) respectively, lastly the overall migration test analysis for the food packaging materials shown that there are no significant differences within packaging materials. So we can say responds in group equally at all packaging materials and all samples meets the specification limits as per Article 12, EU 10/2011.
... Although HDPE provides a good moisture barrier, it is rather ineffective by itself at protecting against oxygen and light. Therefore, milk packaged in HDPE jugs or bottles is susceptible to oxidation of lipids (Cladman et al., 1998) and light oxidation. To combat against light oxidation, multilayer bottles with pigmented with compounds such as titanium dioxide are typically used (Karatapanis et al., 2006). ...
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Fluid milk consumption among children has declined for decades. Adequate consumption of milk and dairy products, especially during childhood, has beneficial health outcomes for growth, development, and reduced risk of osteoporosis, hypertension, obesity, and cancer during adulthood. Satisfaction with milk flavor, perceived health benefits derived from milk, and habit are primary drivers of lifelong milk consumption. Child preferences and attitudes for milk may differ from those of adults, and as such, understanding and fulfilling the needs of children is crucial to reverse the decline in milk consumption. School meal programs make fluid milk accessible to millions of children each day; however, regulations and school lunch procurement systems in the United States sometimes make it difficult to provide novel or value-added milk products in these programs. Total consumption of all milk types in US schools declined by 14.2% from 2008 to 2017, and the percentage of children participating in the school lunch program has also declined. This decline has also been driven by declining average daily participation in the school meal program and may also reflect children's dissatisfaction with the sensory characteristics and the form of milk offered in schools. The change in form of milk offered in schools to lower fat and lower added sugar content in the United States has been driven by government-mandated school lunch calorie and fat requirements. This review describes the current milk consumption trends among children; the structure and basic requirements of the school lunch program in total and for milk; and the intrinsic, extrinsic, and environmental factors that influence child perception, preference, and consumption of fluid milk in the US school system.
Milk is a popular dairy product that provides various nutrients, but consuming too much saturated fat from milk can increase the risk of diseases and obesity. Adulterated milk containing toxic substances can be harmful to human health, and toxic substances can enter the milk at any stage of production. Thus, analytical technologies for detecting various nutrients and harmful substances inside the package are a key requisite for the assessment of dairy products on the market. In this study, we developed a Raman spectroscopic method as a quantitative tool for assessing the milk fat composition and detecting toxic chemicals in packaged milk. Using a line-illumination deep Raman system based on both conventional optics and novel optical fibers, we could quantitatively discriminate the Raman signals of milk fat from those of the packaging materials. Finally, the present system allowed the detection of melamine in adulterated milk (employed as a toxicity model) using a multiple-depth fiber probe.
A critical function of packaging is to protect the product. This often requires the inclusion of special barrier layers or coatings within a multilayer structure to manage gas and liquid permeation, provide oil and grease resistance, prevent loss or impartation of organic molecules affecting taste and aroma, and block light. This chapter examines the importance of barrier packaging, especially with respect to food packaging, describes methods for measuring barrier performance, and provides typical permeation properties of commonly used barrier materials. The science of permeation is reviewed with an emphasis on factors that control permeation in flexible packaging. The chapter concludes with a critical assessment of four emerging technologies: oxygen scavenging, layer multiplier technology, barrier nanocomposites and advanced coatings.
Development of home compostable materials based on bioavailable polymers is of high strategic interest as they ensure a significant reduction of the environmental footprint in many production sectors. In this work, the addition of thermoplastic starch to binary PLA/PBAT blends was studied. The compounds were obtained by a reactive extrusion process by means of a co-rotating twin screw extruder. Thermomechanical, physical and chemical characterization tests were carried out to highlight the effectiveness of the material design strategy. The compounds were subsequently reprocessed by cast extrusion and thermoforming in order to obtain products suitable for the storage of hot food. The extruded films and the thermoformed containers were further characterized to highlight their thermo-mechanical, physical and chemical properties. Thermo-rheological, mechanical and physical properties of the material and of the cast film were analyzed thoroughly using combined technique as capillary rheometer, MFI, DSC, VICAT/HDT, XRD, FTIR, UV-Vis, SEM, permeability and, lastly, running preliminary chemical inertness and biodegradation tests. Particular attention was also devoted to the evaluation of the thermo-mechanical resistance of the thermoformed containers, where the PLA/PBAT/TPS blends proved to be very effective, also presenting a high disintegration rate in ambient conditions.
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The recyclability of opaque PET, which contains TiO2 nanoparticles, has not been as well-studied as that of transparent PET. The objective of this work is to recycle post-consumer opaque PET through reactive extrusion with Joncryl. The effect of the reactive extrusion process on the molecular structure and on the thermal/mechanical/rheological properties of recycling post-consumer opaque PET (r-PET) has been analyzed. A 1% w/w Joncryl addition caused a moderate increase in the molecular weight. A moderate increase in chain length could not explain a decrease in the overall crystallization rate. This result is probably due to the presence of branches interrupting the crystallizable sequences in reactive extruded r-PET (REX-r-PET). A rheological investigation performed by SAOS/LAOS/elongational studies detected important structural modifications in REX-r-PET with respect to linear r-PET or a reference virgin PET. REX-r-PET is characterized by a slow relaxation process with enlarged elastic behaviors that are characteristic of a long-chain branched material. The mechanical properties of REX-r-PET increased because of the addition of the chain extender without a significant loss of elongation at the break. The reactive extrusion process is a suitable way to recycle opaque PET into a material with enhanced rheological properties (thanks to the production of a chain extension and long-chain branches) with mechanical properties that are comparable to those of a typical virgin PET sample.
Opaque PET (Polyethylene terephthalate) was recently introduced as a dairy packaging, mainly for milk bottles. Opaque PET, obtained as PET filled with mineral nanoparticles, allows for a reduction of bottles’ thickness, thus a cost reduction for industrials. For this reason, the use of opaque PET is steadily increasing. However, its recyclability is nowadays an issue: although the recycling channels are well established for transparent PET, the presence of opaque PET in the household wastes weakens the existing recycling channels. Besides, many initiatives are launched in Europe to turn wastes into resources, as one key to a more circular economy. One of the biggest challenges is an efficient sorting of the plastic solid wastes since the PET is not miscible with other plastics such as polypropylene (PP) from the bottle caps and polyethylene (PE) from the other milk bottles. In this work, the mechanical properties of uncompatibilized blends of opaque PET (rPET-O) with recycled polypropylene (rPP) have been studied; both are collected from household wastes. The tensile properties and the fatigue life of rPP, monitored by in-situ digital image correlation and in-situ infrared thermography, are increased by the incorporation of rPET-O. rPET-O/rPP blends may be substituted to rPP for similar applications, with no need to sort the caps from the bottles. Thus, as a concept, the incorporation of opaque PET into the PP recycling sector may be a new route to absorb some of the growing amounts of opaque PET.
Horse treat packaging may be composed of materials including plastic and paper which protect the product from the environment to improve shelf life. Objectives of this research were to 1) assess the impact of packaging on shelf life of horse treats, and 2) evaluate the impact of packaging on horse preferences. Three packaging treatments (control, poly, and paper) were examined at five time points over a 12-month period. Treatments were analyzed for moisture, water activity, mold, yeast, pH, and volatile organic acids. Horse preference testing evaluated first treatment sniffed, consumed, and finished as well as number of treats consumed. Significance was set at P < 0.05, and trends at P < 0.10. Moisture content and water activity increased in all treatments (P < 0.01) from month 0 to month 12, with paper packaging providing a greater fluctuation and containing visible mold at month 12 (P < 0.01). No difference was observed for first treatment sniffed, consumed, or finished during preference testing. However a trend (P = 0.09) for the period*treatment interaction was observed for number of treats consumed, with poly increasing while paper decreased. These data indicate that packaging impacts shelf life and horse preference of treats.
The influence of packaging oxygen transmission rate (OTR; 0, 3,000, 5,000, 7,000, and 20,000 [mL/m²]/day) on cooked rice quality factors, including freezing rate and time, moisture content, color parameters, texture characteristics, and morphology, were evaluated. Cooked rice was frozen at −20 and −80 °C using packaging with different OTRs for 14 days. Freezing rates in packaging with lower OTRs (0, 3,000, and 5,000 [mL/m²]/day) were higher than those in packaging with higher OTRs. The moisture content of cooked rice was the highest in OTR 5,000 packaging under all experimental conditions. Lightness (L*) and total color difference (ΔE ) values were the highest in OTR 20,000 packaging, whereas ΔE values were the lowest in OTR 5,000 packaging. Hardness and cohesiveness of frozen cooked rice gradually increased from OTR 0 to 5,000 but decreased from OTR 5,000 to 20,000. Morphology was distinct in all conditions and at all OTRs. Thus, we confirmed that the OTR of packaging influences the physical characteristics of frozen cooked rice. Therefore, packaging OTR should be considered when seeking to improve the quality of frozen cooked rice. Practical Application Packaging oxygen transmission rate (OTR) influenced quality characteristics of frozen cooked rice under various freezing conditions. Cooked rice frozen in packaging with lower OTRs (0, 3,000, and 5,000 [mL/m²]/day) showed higher freezing rates, higher moisture content, shorter freezing times, smaller ice crystal formation, homogeneous pore distribution, and lower total color differences (ΔE) than did cooked rice frozen in packaging with higher OTRs (7,000 and 20,000 [mL/m²]/day). Packaging OTR influences frozen cooked rice quality characteristics, and should therefore be carefully considered when designing rice products.
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A study was conducted to evaluate the ability of aluminum and oriented polypropylene film to protect milk in half-gallon polyethylene containers from light radiation and thereby stabilize it from light-induced off-flavor (LIOF) and riboflavin loss. Both films, applied to the major portion of the outer surface of the containers, protected milk from light radiation better than when applied only to the container top.
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The effectiveness of visible and UV light screens, compounded in polyethylene dairy resin to protect vitamins in milk from photodegradation, was investigated. Three pigments and three UV absorbers were chosen for testing on the basis of their commercial availability, FDA approval for contact with food, and advertised compatibility with polyolefins. In this study, vitamin decomposition was accelerated over what would be experienced in a commercial milk container in order to expedite the testing program and exaggerate differences in effectiveness of the various light screens. Good protection of vitamin A and riboflavin was provided by 0.3 wt % FD&C yellow #5. Protection of ascorbic acid was marginal. Two of the UV absorbers, Cyasorb 531 and Tinuvin 326, afforded protection of vitamin A, but not riboflavin or ascorbic acid. Visible and UV spectra are presented for the vitamins and light screens used in this work.
The influence of fluorescent light on vitamin A in chloroform and β-carotene in hexane at 15°C and 25°C was investigated. The protective effect of β-carotene at different levels on light-induced destruction of vitamin A in chloroform was also determined. The effect of different wavelengths of fluorescent light on vitamin A and β-carotene contents of milkfat at 25°C was studied using several sharp-cut filters transmitting exactly defined wavelength intervals over a range of 350-750 nm. A linear relation was found between the losses in vitamin A as well as β-carotene and time at both 15°C and 25°C. The rate of vitamin destruction tended to increase with increasing temperature; however, the temperature effect was not statistically significant (p ≤ 0.05). β-carotene at concentrations ≤ 1.0 μg/ml had no effect on photolysis of vitamin A; concentrations of 2.5-7.5 μg/ml significantly protected vitamin A. The loss of β-carotene in milkfat was caused by wavelengths < 465 nm; longer wavelengths (465-750 nm) had little or no effect. Vitamin A in milkfat was primarily destroyed by wavelengths ≤ 415 nm and only slightly by the wavelengths between 415 and 455 nm. It is concluded that vitamin A and β-carotene loss can be markedly reduced in foods by blocking light wavelengths below 465 nm.
Colored plastic gallon milk containers were prepared and demonstrated to consumers in three grocery stores. The four containers were colors yellow, opaque white, cream colored, and translucent plastic. A total of 393 respondents participated in the study. Several questions were asked relating to general milk consumption and preference for a particular color of milk jug. Of those respondents, 40.4% bought all their milk in plastic with 19.2% buying most of their milk in plastic. Approximately 74% indicated that they would buy milk packaged in colored plastic jugs if it were the same price as currently priced. Only 35% indicated that they would buy the plastic jug if they had to pay 3 to 5¢ more per container. The white opaque jug was the choice of consumers. Cream color was second, translucent third, and yellow fourth. Approximately 75% of the respondents indicated that it did not matter whether they could see the milk in the container.
SUMMARY The thiobarbiturie acid (TBA) reaction was used for investigating oxidized flavor in model systems containing fat globule membrane material and ascorbie acid. Triehloroaeetic acid was used to flocculate the proteins and the TBA reaction was carried out and determined in the filtrate. The method is highly satisfactm:¢ in reproducing and measuring rapid oxidation rates in the model system. When applied to milk, lactose was found to contribute considerable inter- ference in the TBA reaction. This was shown by chromatographic separation and spectrophotometric analyses of TBA pigments. A satisfactory application for milk uses trichloroacetic acid to remove fat and protein and ethanolic-TBA to increase the rate of color formation at 60 C, a temperature at which lactose degradation is minimized. Results are presented showing quantitative reeovmT of oxidized inilk from mixtures of oxidized and nonoxidized milk. Effect of ex- posing homogenized nfilk to direct sunlight for 20-rain intervals is readily detected by the method. Relation between organoleptic and TBA analyses is indicated. Detection of lipid oxidation in foods organo- leptically is considered the most sensitive and reliable method, though it does not lend itself well to quantitative measurements. The natural complexity of milk and the relatively small amounts of material or changes therein respon- sible for oxidized flavor have limited most studies to organoleptic evaluations. The use of a model system will overcome some of the in- herent problems associated with the complexity of milk, but may introduce others such as the comparison of organoleptic sensations between milk and simpler systems. Olson and Brown (4) reported that small quantities of aseorbie acid added to copper-con- taminated washed eream resulted in intense oxidized flavor. Fat globule lnembrane mate- rial obtained by churning washed cream reacts in a similar manner, even without the addition of eopper (3). The reaction proceeds very rapidly and the intense flavors are difficult to evaluate organoleptieally. The 2-thiobarbiturie acid (TBA) reaction has been widely applied
Oxidized flavour developed in whole milk only through the catalytic effect of either Cu or light. The O2 requirement for the 2 processes differed as did the characteristics of the off-flavours produced. Cu-induced oxidized flavour was described as ‘cardboardy’ and light-induced oxidized flavour was ‘painty’. Light-induced oxidized flavour increased in intensity with O2 loss, and could be prevented in stored milk by restricting access of O2. In UHT milk with a dissolved O2 content of 6·6 mg/1, and in the absence of access of further O2, light-induced oxidized flavour did not develop; similarly, O2 uptake of 7·5 mg/1 in in-bottle sterilized milk exposed to fluorescent light did not result in flavour formation. When light-induced oxidized flavour developed consistently in whole milk none developed in skim-milk, indicating the lipid source of the flavour. In contrast Cu-induced oxidized flavour development was not associated with high O2 uptake. Although nearly complete deoxygenation of whole pasteurized milk contaminated with Cu prevented the formation of the flavour, moderate deoxygenation resulted in even greater flavour intensity than non-deoxygenation. The 2 oxidized flavours also differed in relation to ascorbic acid (AA) oxidation. Light-induced oxidized flavour developed only after AA oxidation was complete, whereas Cu-induced flavour developed with AA still present. AA oxidation was greatly accelerated through the effects of both Cu and light. In milk free from Cu contamination and protected from light, after AA oxidation (plus SH group oxidation in the case of UHT milk) was complete, no further loss of O2 occurred, even during prolonged storage at 5°C, despite the presence of large O2 concentrations. However, at 20°C, a small consumption of O2 was measured, and this was associated with stale flavour.