Effect of active rice straw extracts on the properties and migration of PHBV films

Abstract

Rice straw extracts (RSE) were obtained by subcritical water extractions at 160 °C (RSE160) and 180 °C (RSE180). These extracts were analysed as to the main components, phenol content and formation of 5-Hydroxymethylfurfural(5-(hydroxymethyl)furan-2-carbaldehyde (HMF). These were incorporated (6 % wt.) into PHBV films by melt blending and compression moulding. Films were characterised as to their physical properties, structural and thermal behaviour, and overall and specific migration of the phenols and HMF in different food simulants. Thermal processing of the films led to a partial degradation of the extracted sugars, producing micro-holes in the matrix and HMF formation. The RSE slightly reduced the polymer crystallinity, the film stretchability, fracture resistance, and barrier capacity to water vapour and limonene, but improved the oxygen barrier of the films and enhanced their UV light barrier due to the phenol content and antioxidant capacity. The PHBV migration did not reach the overall migration limit (10 mg/dm²) in any simulant while the specific migration of phenols and HMF depended on the food simulant and its concentrations in the films. The near total release of the phenols present in the films was achieved in less polar simulants, equivalent to 30–40 mg GAE/kg of packaged food, for RSE180 films. HMF was mainly released in acidic simulants and those containing ethanol, reaching a maximum value of 0.36 mg/kg, for RSE180 films in which more HMF was formed. This value was much lower than those HMF levels found in many commonly-consumed foods. Therefore, the materials can be considered safe for food packaging.