Canned Food Storage: Detecting PVC Lining Migrants by UHPLC-HRMS

Pile of tin cans without labels Vaclavikova et al. (2016) explored a targeted and non-targeted mass spectrometric approach to examine migration of lining materials into foods stored in metal cans. Using a simulated aqueous food scenario, the team developed a workflow for detecting and quantifying polyvinyl chloride (PVC) lining additives in canned foods.

Canning is a traditional method for preserving a variety of foodstuffs. Since its inception, manufacturers have constantly worked towards improving packaging to provide safe and aesthetic food storage for consumers. The food industry has found metal cans safe, economical and practical for long-term food storage. However, since the foodstuff will be often in contact with the internal surface of a metal can for prolonged periods, there is a lot of research into suitable lining materials in addition to developing regulations that govern their safe use. To be effective and safe, a lining material should provide a stable, relatively inert surface that does not interact with the food matrix or deteriorate over the expected storage life of the can.

PVC linings for metal cans are a popular choice for food use, since they provide an effective packaging interface. However, reaction with the food could lead to migration of PVC additives and constituents with time. Consumer concerns require that manufacturers conduct migration studies, using a standard protocol like the USFDA safety test run over 10 days at 40°C following an initial heating period of 120°C for two hours to monitor appearance of contaminants within the food itself. Vaclavikova et al. optimized ultra high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) as a rapid and reliable method to detect and quantify PVC additives migrating from can linings.

First, the researchers conducted FTIR (Fourier Transform Infrared Spectroscopy) analysis of the can lining to establish that the material was indeed PVC. They used prepared samples from the cans under investigation and analyzed them using a Thermo Scientific Nicolet 6700 equipped with a Smart Performer ATR accessory (both Thermo Scientific). They then developed the UHPLC-HRMS workflow on an Accela UHPLC coupled with a Q Exactive quadrupole-orbitrap ion trap mass spectrometer (both Thermo Scientific). Using analytical standards obtained from commercial sources to determine optimal instrument operation for the analytes under investigation, the researchers found that ESI (electrospray ionization) was sufficient for ionization of the majority with APCI (Atmospheric pressure chemical ionization) required only for ESBO (epoxidized soybean oil) and ELSO (epoxidized linseed oil). They also added in an additional column stage to prevent contamination from internal instrument plastic tubing. Vaclavikova et al. achieved good linearity and repeatability for standard dilution calibrations, calculating limits of detection and quantitation (LOD, LOQ) for each.

In addition to optimizing and validating the UHPLC-HRMS workflow, the researchers also prepared PVC can lining extracts in acetonitrile, which they analyzed using the workflow. From these data, they identified PVC additives that could potentially migrate from can linings into foods.

Following the initial validation steps, the researchers then turned to UHPLC-HRMS analysis of can contents under simulated food scenarios. They chose water and 3% acetic acid (white vinegar) as representative contents since the majority of foods stored in metal cans are aqueous in nature. The team used a commercial manufacturer to process the experimental cans and add the aqueous contents. They then subjected some cans to an extra heat treatment before storing at 40°C for periods ranging from 24 hours to 1.5 years. At each time point, the research team opened the can and withdrew aliquots into laboratory glassware, avoiding plastic consumables to avoid cross contamination with external PVC additives. They analyzed the samples directly using the established UHPLC-HRMS workflow.

Vaclavikova et al. examined the can content simulations for presence of 18 plasticizers, 2 slip agents and a cross-linking agent (benzoguanamine, BGA) shown to be present in the PVC lining material. Of these, they found only BGA present in the simulated food scenario samples, with increased migration found following initial heat treatments and into 3% acetic acid. The researchers also noted that the PVC lining deteriorated visibly in contact with 3% acetic acid, showing cracks and becoming detached from the underlying metal. BGA migration increased over time although the researchers achieved results similar to the FDA 10-day guidelines.

In conclusion, Vaclavikova et al. advise that standard long-term migration tests for food packaging should be extended beyond the 10-day guideline, and that higher temperature treatments be included in the protocol. Although they advise further testing in a wider variety of food matrices including fats, the researchers are confident that UHPLC-HRMS is a rapid and reliable method for detecting and quantitating migrants from PVC can linings in food.

Enjoyed this article? You might also find our recent article on canned products and the microbial environment of interest.

Reference

1. Vaclavikova, M. et al. (2016) “Target and non-target analysis of migrants from PVC-coated cans using UHPLC-Q-Orbitrap MS: evaluation of longterm migration testing“, Food Additives & Contaminants: Part A, 33:2, 352-363, DOI: 10.1080/19440049.2015.1128564