Abstract
The aim of this study was to investigate the influence of the food microstructure on the release, absorption and partitioning of the volatile antimicrobials from antimicrobial packaging film. Carvacrol loaded polylactic acid (PLA) film was prepared and tested on a food gel model simulating products like jellies, jams and dressings. Whey protein isolate/carrageenan gels with different microstructures were prepared by varying the NaCl concentration (50–250 mM): the higher the salt concentration the lower the gel consistency. Results showed carvacrol partitioning in the gel increase at higher concentration of NaCl. A 41% increase of carvacrol absorption after 7 days was found in gels prepared with 250 mM of NaCl, compared with the gels at 50 mM NaCl. The results can be explained by the differences in gel microstructures: gels with higher NaCl concentrations showed the small WPI-containing aggregates and large pores from confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) images, in turn facilitating carvacrol absorption by proteins in the gels. The physical properties of gels revealed that gels with higher NaCl concentrations showed lower strength and water holding capacity, pointing to a more loose structure of the gel. The results demonstrate that the microstructure of gels have a clear effect on carvacrol absorption and this factor should be taken into account for designing antimicrobial packaging for the preservation of the gel-like foods.
Highlights
Antimicrobial packaging (AP) is developing as a response to con sumer demands or industrial production trends towards foods with prolonged shelf-life and controlled quality (Dainelli, Gontard, Spyr opoulos, Zondervan-van den Beuken, & Tobback, 2008)
Considering the fact that the location and interaction of the carrageenan with the protein phase could not be visualised by confocal laser scanning microscopy (CLSM) due to the low resolution of CLSM and lack of the specific dye that is capable of binding to carrageenan, we proposed that the observed clusters from CLSM images were whey protein isolate (WPI)-containing aggregates
The microstructure of the WPI-carrageenan gel is a result of the competition between gelation of the protein aggregates or carrageenan and the phase separation between protein aggregates and polysaccharide molecules (De Jong, Klok, & Van de Velde, 2009; Zhang & Vardhanabhuti, 2014)
Summary
Antimicrobial packaging (AP) is developing as a response to con sumer demands or industrial production trends towards foods with prolonged shelf-life and controlled quality (Dainelli, Gontard, Spyr opoulos, Zondervan-van den Beuken, & Tobback, 2008). An aromatic and volatile compound, is the major component (50–86%) of oregano and thyme essential oils (Guarda, Rubilar, Miltz, & Galotto, 2011) It has been broadly studied as a food preservative to extend the shelf life of foods as carvacrol is able to effectively inhibit the growth of a wide range of microbes (Avila-Sosa et al, 2012; Fernandez-Saiz, Lagaron, Hernandez-Mun~oz, & Ocio, 2008; Garrido Assis & de Britto, 2011). Among different food products with gel structure, products like jellies, jams and salad dressings have a weak gel structure having structural features in between solutions and strong gels They are formed due to non-covalent interaction between proteins and polysaccharides, like hydrogen bonds, electro static and hydrophobic interactions, which are weak and reversible (Dickinson, 2008; Schmitt, Sanchez, Desobry-Banon, & Hardy, 1998). Adapting the concentration of NaCl is a straightforward way to influences the microstructure of WPI-carrageenan gels
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