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Do Plastic Chemicals Leach into Food From Sous Vide (SV) Cooking?


RAPID RESPONSE QUESTION:

Can plastic chemicals used in a sous vide (SV) wrap product migrate into food during cooking? Are there any associated toxicity concerns?

Request by: a culinary school

Background

There are many uses of plastics in cooking, including using plastics in the microwave, baking turkeys and hams in plastic bags, using plastic liners in crock pots, and pre-prepared foods in boil-in bags intended for one-time use (e.g., rice and other items). One company, Lekeu, even offers a reusable silicone “boil-in” bag.

Sous-vide (SV) is a lesser known method of cooking wherein a product is vacuum-sealed in a food wrap bag or pouch. In French, Sous-vide means “under vacuum.” Compared to typical cooking methods like boiling or baking, the vacuum-sealed food is cooked in lower temperature water baths and for longer periods of time. Little data exists indicating whether any of the resins or additives used in these SV plastics, or their degradation products, migrate from the plastic into the food during cooking.

All end-use plastics include base polymer(s) along with different types of additives used to enhance the product and/or performance. Additives serve as antioxidants, stabilizers, plasticizers, lubricants, antimicrobials, anti-static and anti-blocking agents, “slips,” or heat resistance agents. While unconfirmed by SV packaging manufacturers, it is highly probable that SV packaging contains additives to allow it to withstand heated water and food contact, for extended time periods.

Two plastic additives in recent media coverage are bisphenol-A (BPA) and phthalates. BPA is used in rigid plastic such as polycarbonate. While many plastic manufacturers have gone “BPA free”, there is always a question of how safe the replacement additive for BPA truly is. For more information on BPA and possible alternatives, see PPRC’s Rapid Response report on BPA in Receipt Papers or the EPA’s Design for the Environment report on BPA Alternatives in Thermal Paper. Phthalates are often used as plasticizers to make polyvinyl chloride (PVC) more pliable. Like BPA, some of the substitutes for phthalates may not significantly reduce the toxicity threat over the original phthalate(s).

Plastics and Food Contact Regulation

The FDA does not “approve products” containing any of the regulated polymers; it only regulates use of individual polymers and additives in food contact materials per the Inventory (above) and/or appropriate CFRs. The two resins likely to be used in SV packaging are low density polyethylene (LDPE) and nylon, with corresponding CFR references below.

To be used in food contact articles or products in commerce in the U.S., any polymer and each individual additive must be authorized by the U.S. Food and Drug Administration (FDA), with limitations or specifications for its intended use. These stipulations often include concentration of the additive in the final product, end uses, and which FDA-defined “conditions of use” (e.g., temperatures during use) are acceptable, per Title 21 of the Code of Federal Regulations (CFR), Section 176.170(c), Table 2. Indirect Food Additives: Adjuvants, Production Aids, And Sanitizers (21 CFR Part 178) includes regulatory information about certain plastic additives.

While it may seem comforting to know that FDA regulates what can be added in plastic food-contact products, the actual Inventory of Effective Food Contact Substances (FCS) Notifications currently lists 963 different chemicals that can be used in food contact packaging. This inventory includes questionable compounds such as BPA, certain phthalates, and urea-melamine-formaldehyde resins. (The latter is only acceptable in small concentration for use in food washing pallets).

The FDA’s Guidance for Industry: Preparation of Premarket Submissions for Food Contact Substances: Chemistry Recommendations [6], Section 10, provides migration testing methods for individual food contact material per various use conditions (Uses A through G). This protocol also refers to “boil-in bags” but does not specifically refer to materials used in SV cooking. Within this non-mandatory protocol, and the FDA regulations, it appears that “Use D” (defined below, including the testing method) may be most applicable to SV cooking, although “Use C” could also be applicable when SV bath temperatures are above 150 dF. The definitions for the Conditions of Use are below. Recommended testing protocols for these conditions are found in the guidance.

Use C.  Hot filled or pasteurized above 66°C (150°F).   

Use D.  Hot filled or pasteurized below 66°C (150°F).     

 

What plastics and additives are used in SV pouches and wraps?

SV packaging suppliers have not been transparent about the additives found in their products. Also, no specifications or MSDS’ have been provided by manufacturers, or found online. Two manufacturers did disclose that their base resin materials are LDPE or LDPE/nylon layers.

One supplier, when asked, defensively stated, “Our material is FDA-approved, BPA and phthalate free.” First,  BPA should not be found in film products, as the compound is used in rigid (#7) plastics. Second, calling a product “FDA-approved,”is a misnomer because, as explained above, the FDA does not approve products. Finally, listing a chemical on the FCS inventory does not guarantee its safety, and many of the FCS Notifications are chemicals of concern from a toxicity standpoint. It is unknown whether the limitations on use, as stipulated in each FCS, are tight enough to protect consumers from these chemicals of concern.

Another supplier claimed that their material is “100% LDPE.” However, LDPE requires additives to provide necessary functional attributes.

Do chemicals migrate from the plastic during SV cooking?  

This answer to this question is unable to be confirmed due to lack of data and studies on migration of chemicals from plastics in simulated SV cooking conditions (e.g., 120 to 180 dF for an hour or more).

It has not been confirmed by the literature, but acidic or oily foods would conceivably increase the amount or concentration of any migration.

With suppliers unable to provide any information on these additives, and no existing studies on migration of contaminants specifically from SV packaging, uncertainty remains about any health impacts. Impacts of these chemicals depend on the amount of chemical migration from the plastic into the food during SV cooking, as well as their toxicity, and the susceptibility of anyone consuming the food cooked via SV.

A few studies may provide insight into the potential for migration from plastic during various cooking methods, and some of the health impacts. These are briefly described in Table 1 below.

Table 1

Study identified

Findings

Relevance to SV

Most Plastic Products Release Estrogenic Chemicals:

A Potential Health Problem That Can Be Solved.  Yang, et al 2011.

 

In nine different types of food wrap (unspecified composition), the test found 78% of the samples leaching estrogenically active compounds via saline extraction, and 100% of samples using EtOh extraction.

This shows that food wraps contain estrogenic active compounds, but does not help determine if those compounds can migrate out during SV conditions, because the materials were extracted via chemicals.  (Note that saline extraction is used to simulate food contact in experiments, but that does not appear to be the intent for this test).

Also, the food wrap samples tested were “unstressed”, meaning unlikely exposed to heat or other conditions similar to SV.

It is highly probable that “food wrap” type products will have EA based on the high number of samples testing positive in the Yang study.  Other health impacts are unknown until more chemical information is found.

Analysis of migrants from nylon 6 packaging films into boiling water.

Barkby et al, 1993

Nylon food packaging in boiling water caused oligimers and caprolactum to migrate.

Need exact oligimer formulas to look at their toxicity.   Caprolactum, however, does have toxicity information and data.  One cited study here states that, “Although caprolactam is not especially toxic on oral administration, it may cause minor protracted effect on thermo-regulation  and disagreeable bitter taste in foods” [Begley et al].    Despite the comment on low oral toxicity,, toxicity data sources indicate that caprolactum has human health concerns and has these risk and safety phrases in the European Union hazard system:

-    Harmful by inhalation and if swallowed.

-    Irritating to eyes, respiratory system and skin.

-    Keep out of the reach of children.

Determination of potential migrants present in Nylon ‘microwave and roasting bags’ and migration into olive oil.

Soto-Valdez et al. 1997.

Volatile and non-volatile compounds  were found to migrate into olive oil at ~400 dF and ~350 dF for 1 h, respectively.   The test found these non-volatiles:  Nylon 6,6 cyclic monomer and cyclic oligomers up to the tetramer and Nylon 6 monomer and cyclic oligomers.

They did find migration of volatiles using methanol and water extraction:   cyclopentanone, octadecane, heptadecane and 2-cyclopentyl cyclopentanone. 

The test temperature for the non-volatile compounds was much higher than SV, but the chemical names provided are not adequate to identify the exact compound to look at toxicity data.

The extraction of volatiles tells us these constituents are in the plastic, but not whether they would leach out in SV conditions.

Antimicrobial food packaging in meat industry.

Quintavalla et al 2002

During longer-term storage (as opposed to immediate SV use), antimicrobials diffused from packaging to food.

Possibly no relevance to SV used in culinary programs where the food is prepared and wrapped/sealed just before cooking.  Also, it appears that antimicrobials may be added to purposefully migrate and be in contact with the food.

Conclusions

-          It is difficult to find the true composition of SV products. Manufacturers have mentioned two resins (nylon and polyethylene) that are used in their SV plastics, but have been unwilling to disclose the full formulations and additives.

-          No studies were found in the literature evaluating migration of chemical additives from plastics in simulated SV conditions.

-          For heated plastics in contact with food, several studies have shown migrated contaminants or additives that would be present in or on the contacted food. The amount or potency is unknown and dependent on many variables.

-          Testing (Yang et al, Barkby et al, Soto-Valdez et al) has shown migration of plastic additives from various ‘’food wrap” plastics, including additives that have estrogenic or hormonal affects.

-          Available study results provide information on the chemicals that migrate from the plastic, but have not provided any toxicity or health impacts.

References

[1] Begley , Gay , Hollifield.  1995. Determination of migrants in and migration from nylon food packaging.

[2] Crompton, 2007. Additive Migration from Plastics Into Foods: A Guide for Analytical Chemists

[3]  National Academies Press, 1999. Hormonally Active Agents in the Environment. (Reproduced from a naturopathic approach to health).

[4] Sheftel. 2000. Indirect Food Additives and Polymers: Migration and Toxicology.

[5] Yang, et al 2011. Most Plastic Products Release Estrogenic Chemicals: A Potential Health Problem That Can Be Solved.

[6] FDA’s Guidance for Industry: Preparation of Premarket Submissions for Food Contact Substances: Chemistry Recommendations

Additional Information: 

[a] Canada Domestic Substance List (DSL)

Toxicity Findings for nylon 6, polyethylene, and caprolactum (a chemical known to migrates from nylon).

CAS Number      Material                               Findings in DSL

25038-54-4          Nylon 6                                 Persistent in environment

9002-88-4          Polyethylene                 Persistent in environment

105-60-2               Caprolactam                       Categorized for human and environment health toxi

[b] U.S.  FDA Packaging & Food Contact Substances (FCS)   Webpage

[c]  From:  Schellers, 1993, FLAIR (FOOD-LINKED AGRO-INDUSTRIAL RESEARCH)

** Excerpt  from:  SOUS VIDE” COOKING

Testing of PVC film (“cling film”) plasticized with di-(2-ethylhexyl)a dipate (DEHA) was carried out in the UK (Startin et al., 1987) for a variety of foods which were either cooked or reheated in microwave ovens. They found that migration of the compound did occur, that it increased with the length of contact time and temperature of exposure, and that levels of migration were highest where there was direct contact between the film and foods with a high fat content at the surface. Highest levels of migration were observed for cheese, cooked meats, cakes and for microwave-cooked foods. An assessment of the DEHA migration from these films in such situations led to the recommendation that this type of film should not in future be used under any circumstances in conventional ovens, nor should it be used for lining of dishes or wrapping of foods in a microwave oven (Ministry of Agriculture, Fisheries and Food, 1987).

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