Microbiological and ageing performance of polyhydroxyalkanoate-based multilayer structures of interest in food packaging

Polyhydroxyalkanoates undergo crystallization during film processing and storage. In this paper, the physico-chemical ageing properties of multilayer structures based on a commercial polyhydroxybutyrate (PHB) and a polyhydroxybutyrate-co-valerate copolymer with 3% valerate content (PHBV3), containing a nanostructured zein interlayer, were analysed. The microbiological safety of the films was also evaluated by monitoring the growth of an inoculum of Listeria monocytogenes over time. Polyethyleneglycol (PEG) was added to PHBV3 films to facilitate handling as the PHBV3 mutlilayer systems (without plasticizer) cracked during film-formation. Crystallinity, thermal, mechanical, barrier and optical properties were studied over a period of three months. From the results, it was found that the storage time did not alter the degree of crystallinity of PHB multilayer structures. However, a slight increase was observed in multilayer films prepared with PHBV3-PEG. Storage time did not significantly modify optical and barrier properties of PHBV3-PEG or PHB multilayer films (p < 0.05) although stored multilayer films were stiffer and less deformable. Concerning the microbial safety of the films, only storing at 100% RH, allowed Listeria survival, which was not influenced by the presence of the internal zein interlayer. (C) 2014 Elsevier Ltd. All rights reserved.