Influence of PET as single-use contact material on gloss and surface properties of chocolate

Polyethylene terephthalate (PET) is a commonly used polymer in many industry sectors including confectionery industry. In the latter, PET is utilized for single-use moulds for chocolate manufacturing. Despite the broad application of PET in these areas, information regarding its influence on chocolate gloss and surface properties is not available. Meanwhile, it is already well established that fat crystal modification influence these properties (including gloss) distinctly. To bridge this disparity, this study examined how amorphous and glycol-copolymerized PET sheets influence non-pre-crystallised and pre-crystallised dark chocolate properties throughout a 28-day storage period. Polymorphic properties of cocoa butter were analysed via DSC. Non-pre-crystallised and pre-crystallised chocolate surfaces were characterised regarding colour, gloss, polarity, adhesion, roughness, and topography. While pre-crystallised chocolate shows consistent results, non-pre-crystallised chocolate experiences considerable changes in surface properties due to fat crystal transitions during storage. The findings show that the polymorphic state had a major impact on chocolate surface properties. Furthermore, results demonstrated that the type of PET had a significant impact on chocolate surface properties as well. Pre-crystallised chocolate gloss was significantly impacted by the choice of PET contact material. As a result, pre-crystallised chocolates exhibited a larger tendency to gloss inhomogeneities following amorphous PET monolayer sheet contact.