Transparency is a very important technical parameter to evaluate and validate certain food packaging materials. In the recent scientific literature, several methods (i.e. transmittance, opacity, haze, and absorbance) have been used and such variety hinders a direct comparison of results from different authors. In this Review, we describe and discuss the most widely employed methods to measure transparency, with special emphasis on two main parameters: transmittance and opacity. Moreover, a comparison of the different techniques is addressed and the typical values of transmittance and opacity of common transparent food packaging materials are provided. Our current opinion is that transparency should be expressed as transmittance in the visible range due to both the quickness and easiness of the measurement and the standardization of data. This information should be accompanied by the thickness value and a graphical image of the analysed samples for a useful and complete characterization.

Free-standing, robust, and transparent bioplastics were obtained by blending cellulose and naringin at different proportions. Optical, thermal, mechanical, antioxidant, and antimicrobial properties were systematically investigated. In general, the incorporation of naringin produced important UV blocking and plasticizer effects and good antioxidant and antibacterial properties. Moreover, the barrier properties were characterized by determination of their water and oxygen transmission rates, finding that both parameters decreased by increasing the naringin content and reaching values similar to other petroleum-based plastics and cellulose derivatives used for food packaging applications. Finally, the biodegradability of these films was determined by measurement of the biological oxygen demand (BOD) in seawater, demonstrating an excellent decomposition in such conditions.

The valorization of vegetable waste can create opportunities to produce new valuable bioplastics. In this study, a one-step process to fully convert a variety of vegetable waste materials into bioplastic films is reported. The process is carried out in a diluted aqueous HCl solution at room temperature, it is easily scalable, and with no environmental concerns associated with the use of organic or dangerous chemicals. The generated bioplastics are completely biodegradable and environmentally friendly. Freestanding, flexible bioplastic films were obtained from vegetable waste like carrot, parsley, radicchio and cauliflower. They have similar mechanical properties with other bioplastics, like thermoplastic starch, and showed to have little migration in a food simulant. The color and the functional properties (i.e. antioxidant capability) of the starting vegetables are preserved in the bioplastics, thanks to the mild conditions of the fabrication process. The new conversion process allows the blending of the bioplastics with other natural or synthetic polymers, in order to improve their mechanical and gas barrier properties, like the oxygen permability (OP), thus expanding their field of applications. Poly vinyl alcohol (PVA)/carrot bioplastic film showed an OP of 31.2 cm³ μm m⁻² day⁻¹ kPa⁻¹, which is lower than the OP for other synthetic films, like high density polyethylene films (HDPE), and similar to edible materials like chitosan.