Mineral oils in recycled paperboard
Packaging is an important part of the food industry, designed to transport foods safely to the consumer while protecting against external contamination. But sometimes the packaging itself is the source of the problem. It was reported in 2010 that recycled board used for food packaging contained levels of mineral oils that far exceeded safety levels set by the joint FAO/WHO Expert Committee on Food Additives.
The oils originate from printing inks which are not removed during the recycling process. Average concentrations of the mineral oil hydrocarbons up to C28 were estimated at 28 mg/kg food, comprising both saturated and aromatic hydrocarbons. The deployment of internal bags made from paper or polyethylene terephthalate did not prevent migration.
A joint Swiss-Japanese research team has now undertaken a detailed examination of the mineral oil contents of various types of paper or board that are used to produce recycled board for food packaging. They also wished to identify the main sources of the oils and to see if some types fall within acceptable limits.
Koni Grob and Maurus Biedermann from the Official Food Control Authority of the Canton of Zurich and Yoko Uematsu from the Tokyo Metropolitan Institute of Public Health published their findings in Packaging Science and Technology.
Paper sources probed by HPLC-GC
Newspapers, magazines, books, leaflets, reports, office paper from different sources and countries were collected, along with paperboard and corrugated board. All of the samples were shredded and homogenised for extraction and subsequent analysis of the mineral oil saturated hydrocarbons (MOSH) and aromatic hydrocarbons (MOAH) up to C24.
They were determined by HPLC-GC-FID and also by 2D GC-FID following HPLC separation of the fractions. Both MOAH and MOSH were separated initially by normal-phase HPLC on a silica gel column, using a gradient of dichloromethane in hexane.
MOSH eluted first in the retention window covering 2.0-3.5 minutes, followed by MOAH over 4.0-5.5 minutes. The eluting fractions were transferred to the GC column via a retention gap for further separation on a dimethylpolysiloxane column.
The analysis was carried out with the inclusion of internal standards used for quantitation but also to confirm that adequate cuts of the HPLC fractions were transferred to the GC column and that there were no losses of volatile compounds.
Newspapers are bad, corrugated board is better
The worst offenders by far were newspapers and leaflets, with mean total mineral oil contents (24) of 3240 and 2300 mg/kg, respectively, about 82% originating from the MOSH.
Paperboard from recycled fibres contained 845 mg/kg total mineral oils, which was more than three-fold higher than the levels from paperboard produced from virgin fibres. Office paper, books and corrugated board contained the lowest levels of mineral oils at 40, 94 and 156 mg/kg, respectively.
The researchers homed in on corrugated board due to its relatively low mineral oil content and its wide availability. This material was also of interest because its content was independent of the country of origin for samples from 16 countries, a surprising finding given that most corrugated board is produced locally and could well be produced from different starting materials.
Even though mineral oil levels were low, the team calculated that migration into food from corrugated board-based packaging would still exceed the acceptable daily intake by up to 20-fold. Nevertheless, it is still one of the best prospects of those tested, provided that a further reduction of mineral oil content could somehow be achieved.
Taking a closer look at the results for newspapers, there were marked differences between European, Japanese and Italian newspapers. This was attributed to differences in the inks used for the printing process.
The mineral oils levels in Italian newspapers were about 10-fold lower than European ones, due to the use of water-based inks. Japanese newspapers also contained less mineral oil than those from Europe because the inks contain a higher proportion of vegetable oil and less MOAH, as required by the national authorities. However, they were still not suitable for food packaging.
The results illustrate the problems associated with the use of recycled paper-based fibres for food packaging applications. Only when new practices are introduced to deplete the mineral oils in the paper sources will the paperboard be suitable. In the meantime, the insertion of an impermeable sheath between the packaging and food would prevent migration and maintain food safety.
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.
|
