Development and characterization of hybrid corn starch-microalgae films: Effect of ultrasound pre-treatment on structural, barrier and mechanical performance

This work is aimed at evaluating the ability of the microalgae to partially substitute biodegradable materials with improved physicochemical properties. To this end, starch films containing the microalga Nannochloropsis gaditana sp. (N. gaditana) have been developed and characterized. Initially, different ultrasound treatments were evaluated for microalgae cell wall disruption. Although surfactant-aided sonication was the most efficient disruption method, the presence of the surfactant hampered continuous film formation. Subsequently, the ability of intact and ultrasound-treated N. gaditana cells to improve barrier properties of starch films was evaluated. Combined small and wide angle X-ray scattering experiments (SAXS/WAXS, respectively) evidenced slight nanostructural and crystallinity changes induced by the presence of N. gaditana cells. Incorporation of intact or ultrasound-treated microalgae into starch led to more hydrophobic films, with enhanced barrier properties for most of the formulations. However, the films containing the microalgae treated with the greatest ultrasound intensity, did not show any barrier improvement due to the plasticization promoted by the cell components (probably lipids) released during the ultrasound treatment, as suggested by SAXS/WAXS and the mechanical properties.Synchrotron experiments were performed at NCD beamline at ALBA Synchrotron with the collaboration of ALBA staff (2016021658 project). M.J. Fabra, Marta Martinez-Sanz and L.G. Gómez-Mascaraque are recipients of a Ramon y Cajal (RYC-2014-158), Juan de la Cierva (IJCI-2015-23389) and predoctoral (call 2013) contracts from the Spanish Ministry of Economy, Industry and Competitiveness, respectively. Authors would also like to thank the Central Support Service for Experimental Research (SCSIE) of the University of Valencia for the electronic microscopy service.Peer reviewe