Download 1) The PT closure for Baby Food

Annex 4 to FCP/328/04E
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ESBO in Metal Twist Food Closures
1) Twist Closure design and sealing gasket composition
The metal Twist closure is characterized by having metal lugs that engage on the
threaded glass neck of the jar – this distinguishes it from the PT (Push-on Twist-off)
closure which has no metal lugs but has threads formed in the gasket material in the
sidewall of the closure. The PT closure is predominantly used for Baby Food, and is the
subject of a separate document.
Jar rim embedded in
gasket material
Cutaway of typical wide mouth Twist Closure
Twist closures are used for a very wide range of predominantly wet foods ranging from
cold fill no process applications through to fully heat sterilised products, and come in
diameters from 27mm to in excess of 110mm. The key elements to the Twist closure
are:
 a metal shell to give “perfect” barrier properties as well as structural integrity,
 a re-sealable sealing gasket to protect the foodstuff from the environment and to
eliminate and microbiological contamination of the food from external sources. This
sealing gasket has to withstand abuse during transit and storage without any
leakage whilst being openable without tools and to allow continued opening and
closing during extended usage for e.g. Pickles, Preserves and Condiments.
 optionally, the closure can include a pop up safety button to show the consumer that
the jar has not been opened and remains microbiologically sound.
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The sealing gasket is key to the overall performance of the Twist closure, and it is the
formulation of the gasket material that gives the combination of compliance and
toughness necessary for optimum sealing performance, abuse resistance and vacuum
retention over extended shelf life and microbiological safety.
Although the detailed capping process will vary between different food product types
and different applications, in most cases, the closure is pre-heated with steam, and the
jar/bottle filled with cold or preheated product. The headspace in the jar may be filled
with steam to exclude air before the closure is applied, pulling a vacuum on cooling.
After application of the closure, and depending on the nature of the foodstuff, the filled
product undergoes the thermal process appropriate to this application varying up to a
full high temperature sterilisation (125 °C). The physical nature of the gasket ensures
that the hermetic seal withstands the abuse that occurs during transit, storage and
handling of the jars. The final demand placed on the gasket material is that it should be
readily openable without tools throughout the shelf-life of the product
This gasket is made from a PVC Plastisol consisting of PVC, plasticiser (ESBO or other
authorized material), stabilisers, fillers, pigments, blowing agent (in some cases) and
lubricants. The ingredients are physically blended together forming a paste which
consists of swollen PVC particles together with the additives in a plasticiser matrix. The
blending process, the PVC particle size/shape, the properties of the plasticiser, and the
relative levels of PVC and plasticisers are all critical in ensuring the correct viscosity
and mobility of the mix.
The paste is then applied to the seal area of the drawn metal caps and gelled in a
continuous oven where the closures are heated at ca. 200C for typically 90-120
seconds. In the case of foamed gaskets, the blowing process occurs in the compound
gelling oven.
The combination of the performance and safety demands placed on the gasket material
and the complex interaction of the components and the manufacturing process is the
main reason why the fundamental technology of the Twist Off closure has remained
relatively unchanged over many years.
2) ESBO Migration
Factors Affecting ESBO Migration
In view of the experience gained from the work on PT compound, much of this work can
be applied to Twist closures
More work is currently underway specifically on the Twist closure, but will take some
time to conclude. The factors identified for the PT closure were:
Area of gasket exposed to food
- The closure manufacturing process inevitably leads to some residual gasket
material inside the glass closure seal line – this ensures that incomplete gasket
formation due to insufficient gasket material does not occur. However, the
greater the amount of gasket material inside the glass/closure seal, the greater
the level of ESBO migration.

Extent to which fat in the food is accessible for contact with the gasket
- A very wide range of foods is packed using Twist closures, with big differences
in fat/oil level and the extent to which that fat/oil is accessible to the gasket
during processing. As well as the more obvious difference between foods where
there is visible free fat/oil, and foods that appear emulsified and homogeneous,
there are also differences within the homogeneous category. It appears that in
some cases of homogeneous foods the fat has more protection (perhaps from
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protein or starch components of the food), minimizing the opportunity for
migration of oleophilic substances such as ESBO.

Contact between food and gasket, particularly during the heat sterilisation process
- There are a number of different heat process preservation methods with differing
degrees of heating, and agitation of the product. This can vary from cold fill for
ambient stable products though hot fill, and pasteurization, up to full high
temperature sterilisation depending on the nature of the foodstuff. During
processing, the packages can be upright static through to continuous end over
end rotated during the process. The greater the temperature, time and degree of
agitation, the higher levels of ESBO migration generally found although the
extent of the difference will also be related to the composition and structure of
the food itself. “Dynamic” processing gives improved product quality both due to
reduced overall thermal treatment and to product mixing during cooking –
indeed some heterogeneous recipes would be impossible to prepare without
“dynamic” retorting.
Potential Routes to Reduce ESBO Migration from Twist Closures
Modifications to Closures
Industry has already identified a number of potential ways to reduce ESBO migration
from Twist closures although it is not yet clear how feasible some of these may be in
practice. This is particularly an issue when considered together with the vital need to
retain the current excellent food protection properties of this style of packaging, and the
need to urgently eliminate the use of Azodicarbonamide in that proportion of Twist
closures which use a foamed gasket. The timescale for elimination of
Azodicarbonamide is dictated by the timings in EU Directive 2004/1/EC.
Potential ways to reduce ESBO migration are:
Changes to the closure design to reduce gasket exposure
- There could be scope for some reduction of the area of exposed gasket, but this
is limited by the need to retain a margin of safety ensuring that the glass neck of
the container properly beds into the gasket. A more radical change could be to
add a barrier between the foodstuff and the closure gasket. However, such a
barrier would need to form a seal onto the glass neck and so would potentially
introduce further potential migrateables to the food from the bonding layer of the
“barrier”. In addition, such an approach would inhibit the use of the ”pop-up
button” for tamper evidence, and add further significant practical difficulties.

Retaining the existing closure design but investigating alternatives to ESBO
in the gasket material formulation, either in part or totally
- The Closure manufacturing industry together with its suppliers are currently
investigating a range of potential alternatives to ESBO, both singly and in
combination with the aim of at least matching the performance of the existing
finished ESBO plasticised closure. This includes satisfying the requirement that
any change should not prejudice the current high degree of safety intrinsic to the
existing closure or lead to migration of substances which have less toxicological
information. Plasticisers such as phthalates, adipates, and citrates have some
issues associated with them. However, certain polymeric plasticisers and other
more recent plasticisers such as Acetylated Glycerides are more promising, and
in the latter case are authorized both for use as direct food additives and as
constituents of plastics materials and articles for use in contact with food without
restriction. Some of these alternatives have been used successfully in some PT
applications but global migration can be higher than for ESBO and performance
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is not quite as high as ESBO at this stage. There are a number of further “new”
materials now coming onto the market which have undergone assessment by
EFSA . These will be assessed for their performance in this application as soon
as their status is clarified.

Changes in closure design to allow the use of fundamentally different gasket
materials
- Closure manufacturers are following individual routes towards the use of nonPVC sealing Gaskets for Twist closures that will fulfill all the positive safety and
quality attributes of the existing closure without the need either for plasticisers
or blowing agents. These developments are still at an early stage, and
considering the wide range of Twist closures and applications, this will not be a
rapid solution.
Modifications to Food Composition and Sterilisation Process
It is recognized that the presence of free fat/oil and the way in which fat/oil is protected
by components of the food is critical to ESBO migration and there is potentially scope
for change to the food composition without compromising the nutritional value, stability,
or consumer acceptability of the product. In addition, although the general relationship
between the food process and ESBO migration is only partly understood, there is
potentially scope for change in the food process without compromising food
quality/acceptability.
Current ESBO Migration Levels
In general, the main applications for Twist closures are for use with aqueous and not
fatty foods and for these foods, ESBO migration is not an issue. Higher levels of ESBO
migration will be seen with fatty foods, particularly so with small volume jars of speciality
foods. Although in these cases, migration will be higher, the quantity of foodstuff
consumed is generally much lower and so the exposure will not be significant. The wide
range of different variants of the Twist closure and the variety of different foodstuffs
packed using these closures makes an estimate of actual exposure more difficult but a
realistic assessment should be within the scope of modern exposure techniques.
Issues Involved in Change
Industry continues to work on changes to reduce ESBO, but it is essential that any
changes retain the existing high degree of safety and security of the closure and that
any alternative plasticiser has as much or more data on its toxicological properties and
migration characteristics. There has been some progress in these areas, but so far
these changes have generally led to a reduction in closure performance.
3) Exposure Assessment – Consumption of Jarred/Bottled Food
In order to undertake a detailed risk assessment for ESBO, it is necessary to have
realistic consumer exposure data. This is a complex requirement for a packaging article
with such a wide variety of styles and applications as the Twist closure. Distinction
needs to be made between predominantly aqueous packs (juices, syrups, fruit,
vegetables, jams, pickles, ketchups, and some sauces) where ESBO migration is low
and the high fat/oil products where ESBO migration levels become significant. In
addition, there needs to be inclusion in the assessment of typical daily intakes of
different food types from different packaging. This is of particular importance where the
instances of high ESBO migration are often in products which are consumed in very
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small quantities. Exposure models such as that being developed in an industry funded
project at CSL York (UK) are now becoming capable of handling such complex patterns
of exposure.
4) Derivation of the Tolerable Daily Intake (TDI) for ESBO
The key toxicology study1 used by the SCF to derive a TDI involved a control and 3
dose levels of nominally 0, 0.025, 0.25 and 2.5 % ESBO in the diet. The animals in this
study were bought in as weanlings and testing started after 14 days so the study
includes the juvenile phase increasing the relevance to the issue of ESBO in baby food
as well as for adult food.
Taking into account feed intake and bodyweight (bw) the average dose levels during
the study were:Male rats 0, 10, 100, 1000 mg/kg bw per day
Female rats 0, 14, 140, 1400 mg/kg bw per day
In order to address concerns that the high triglyceride intake at the higher dose levels
could have an effect due to nutritional imbalance, an additional variable of Soya Bean
Oil (SBO) at the 2.5% diet level was also included (1000/1400 mg/kg bw per day).
The only significant effect seen in the study was for the highest dose level for female
rats which had a statistically significantly higher level of endometrial changes. The SBO
dose at 1000/1400 mg/kg bw per day also showed some of these effects but at a lower
level and there was no statistically significant difference either between the SBO and
ESBO dose or between the SBO and control (0) dose. The study authors commented
that these changes are not unusual in older animals, and considering the presence of
the endometrial changes in the SBO group as well as the ESBO group (no significant
difference between groups), they concluded that the NOAEL for males and females
was the nominal 1000mg/kg bw level giving a TDI of 10mg/kg bw/day.
The SCF however took the precautionary approach and chose the nominal 0.25% diet
level which they took to equate to 100mg/kg bw and applied a 100 x safety factor giving
a TDI of 1mg/kgbw. However, in fact, even if the endometrial changes are considered to
be a dose related effect, the NOAEL for the females is 140mg/kg bw/day and for males
it is 1000 mg/kg bw/day. Therefore the overall NOAEL would be 140mg/kg bw/day
which on applying the conventional 100x safety factor should give a TDI of 1.4mg/kg
bw. It is this figure which industry believes represents the most relevant value for the
TDI, recognising that modern toxicological prudence would not accept the original study
conclusion that the NOAEL was 1000mg/kg bw /day (equating to a TDI of 10mg/kg bw)
Further detail on the derivation of a TDI for ESBO is given in the attached letter to
industry from an independent toxicological advisor – Appendix 1
4) Conclusions
The Twist closure is an important element in the provision of a safe, wholesome,
nutritious and varied food supply that is valued by consumers in terms of quality,
convenience and choice. The key to the Twist closure performance is its sealing
properties giving a long safe shelf-life and eliminating environmental contamination of
the foodstuff. This sealing performance relies extensively on the physical properties of
the sealing gasket which in turn is a function of its composition. Migration of plasticiser
(in this case ESBO) will always tend to be a side effect of the use of soft sealable
1
Long Term Study of Epoxidised Soya Bean Oil in the Diet of Rats – BIBRA Oct 1986
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materials with fatty foods under elevated temperatures, but it is the plasticiser that plays
a significant role in ensuring the seal performance. Whilst the majority of Twist closed
food packages have low ESBO migration, there are some product categories where
levels are higher and industry recognises the need to reduce these levels whilst
retaining the high level of safety over extended shelflife offered by the current closures.
When exposure is taken into consideration it is most unlikely that the Tolerable Daily
Intake (TDI) of ESBO would be exceeded on anything but an occasional basis for a
small number of consumers and so it does not present a hazard to consumer health.
The industry chain is currently working on the ESBO issue together with the
SEM/Azodicarbonamide and 2-Ethyl Hexanoic Acid (2EHA) issues with the aim to
resolve all three issues in a way which does not lead to disruption of the existing
extensive programme on Azodicarbonamide replacement. Because of the wide range
of Twist closure variants and the variety of foodstuffs packed using Twist closures, it is
most improbable that one solution to the ESBO issue will be appropriate across the
board and a single joint industry “solution” will not be appropriate or practicable.
However the Metal Vacuum Closures Industry Group2 will work together on
understanding the scale of the issue, the key factors affecting migration and generic
routes to migration reduction.
2
Metal Vacuum Closures Industry Group - MVC-IG involving European metal vacuum closures
manufacturers together with their materials suppliers and the users of these closures together
with trade associations SEFEL and CIAA
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Appendix 1: Derivation of a TDI for ESBO – independent opinion (3pages)
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