Development of activate-at-home-type edible antimicrobial films: An example pH-triggering mechanism formed for smoked salmon slices using lysozyme in whey protein films
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The aim of the present study was to develop the first generation of a novel natural antimicrobial packaging system which could be activated by consumers at home. For this purpose, antimicrobial films having a pH-triggering mechanism which could be activated by acidification were developed by exploiting isoelectric properties and pH induced charge-charge interactions between whey proteins (WP) and lysozyme (LYS). The release tests of films in buffers and on coated smoked salmon slices at 4 °C showed the immobilization of positively charged LYS by the negatively charged WP films at pHs ≥ 5.5. The LYS release initiated when pH was reduced below 5.5 where WP started to gain positive charges. The amount of LYS released and LYS release rate increased as pH reduced gradually from 5.5 to 3.0. The preparation of composite films of WP with beeswax (BW) and oleic acid (OLE) increased the total released LYS from films. WP, WP-OLE and WP-BW films showed antimicrobial activity against Listeria innocua in laboratory media. The smoked salmon slices coated by activated LYS containing WP-OLE films showed significantly lower (almost 0.6 decimal) L. innocua counts than controls after 1 week at 4 °C. This study clearly showed that the antimicrobial films could be activated by consumers to improve safety of opened packed food stored in home type refrigerators.