Influence of pre-heating of food contact polypropylene cups on its physical structure and on the migration of additives

Abstract

Laboratories unexpectedly carried out pre-heating of polypropylene beverage cups prior to performing a migration test in a proficiency test. Principal component analysis of the data collected showed that the preheating temperature of the cups contributed to an increased variance of the data and distinguishing pre-heating and non-pre-heating groups. This triggered to study the effect of applying such pre-heating on the physical structure of the material and on the migration of additives to food simulant D1 (ethanol 50% v/v). Several cups were pre-heated at selected temperatures and either analyzed with differential scanning calorimetry to establish the degree of crystallinity or used for the migration test. Six target additives from Regulation (EU) No 10/2011 were quantified in the food simulant using HPLC-FLD and LC-MS. Results show that pre-heating of the beverage cups led to a significant change in the degree of crystallinity, resulting in a change of analyte migration in comparison to the migration results from non-pre-heated cups.

Keywords: Degree of crystallinity; Differential scanning calorimetry; Food contact materials; Migration of additives; Pre-heating.

Graphical abstract

Fig. 1

DSC thermograms of PP sample cups: (a) melting curves and (b) crystallization curves.

Fig. 2

GA thermograms of PP cups: overlay of the thermal decomposition curves.

Fig. 3

Degree of crystallinity vs. the duration of the heat treatment at different temperatures.

Fig. 4

Optical microscopy images (500×) of the surface of PP cups after heat treatment: (a) no heating; (b) at 40 °C for 1 day; (c) at 75 ° C for 1 day.

Fig. 5

Typical total ion chromatogram of food simulant D1 after the migration experiment with the PP cups.

Fig. 6

Specific migration (SM) of 1-palmitoyl glycerol (a, in mg/kg), FCM No. 500 (b, in μg/kg) and FCM No. 808 (c, in mg/kg) after pre-heating the PP cups, at different temperatures, followed by migration at 70 °C for 2 h with food simulant D1 as a function of the pre-heating contact time (presented as log-time scale).

Fig. 7

Degree of crystallinity and specific migrations for pre-heated cups at 75 °C as a function of the pre-heating contact time (presented as log-time scale) for (a) 1-palmitoyl glycerol, (b) FCM N° 500 and (c) FCM N° 808 and remaining glycerols.

Fig. 8

PCA score plot (a) and loading plot (b), for the five studied parameters. Data points in the blue dashed circle are the non-pre-heated data and data points in the red dashed circle are the pre-heated data. The colored dots represent: green, FCM No. 808; blue, 2-palmitoyl glycerol; brown, 2-stearoyl glycerol; light blue, 1-stearoyl glycerol; red, 1-palmitoyl glycerol; purple, FCM No. 500. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).