Design and Characterization of Bioactive Bilayer Films: Release Kinetics of Isopropyl Palmitate

Abstract

Active packaging incorporating antioxidants and antimicrobials is creating a niche in the market and becoming increasingly important. The main goal of this work was the design of bioactive bilayer films (zein/pullulan) incorporating licorice essential oil. The bilayer films were fully characterized in terms of their chemical, physical, barrier, antioxidant, and antimicrobial properties. Furthermore, the release kinetics of isopropyl palmitate, the major compound of the licorice essential oil, was evaluated by HPLC-DAD (high-performance liquid chromatography coupled to diode-array detector). Scanning Electron Microscopy (SEM) micrographs of cross-sections of the bilayer films clearly show the two layers of the films. Besides presenting the capacity to scavenge free radicals and to inhibit the lipid peroxidation, the developed bilayer films were also able to inhibit the growth of known foodborne pathogens (Enterococcus faecalis and Listeria monocytogenes). The release kinetics profile of isopropyl palmitate from bilayer films incorporating licorice essential oil demonstrated that in 50% ethanol at room temperature, the release was more effective, suggesting that the bilayer films will be more efficient if applied to package semi-fatty food.

Pullulan–Apple Fiber Biocomposite Films: Optical, Mechanical, Barrier, Antioxidant and Antibacterial Properties

“…Pullulan films not including apple fiber were also produced, to be used as a control. Finally, the dried films were detached from the Petri dishes and kept under controlled relative humidity (RH) (50 ± 5%) and temperature (23 ± 2 °C) [ 1 , 2 , 4 , 12 , 13 ].…”

“…The biocomposite films’ grammage was determined by the quotient between their mass and area (g/m 2 ), according to the ISO 536:1995. An Adamel Lhomargy Model MI 20 micrometer (TMI, Veenendaal, Netherlands) was used to measure the thickness (µm) of the films, considering different random assessments, following the ISO 534:2011 [ 12 , 13 ].…”

“…The mechanical properties of the biocomposite films (Peak Elongation (%), Tensile Index (N m/g), Tensile Strength (N/m), and Elastic Modulus (MPa)) were determined using a Thwing-Albert Instrument Co. (West Berlin, NJ, USA) tensile tester, adjusting the crosshead at 10 mm/min, and the initial grip at 50 mm, following the ISO 1924/1 [ 12 , 13 ].…”

“…The determinations were achieved considering several arbitrary positions of the films using the illuminant D65 (daylight with a UV component) and an observation angle of 10°. Color coordinates L*, a*, and b* (lightness; redness/±red-green; yellowness/±yellow-blue) were obtained [ 12 , 13 ].…”

“…The values of the contact angles of the biocomposite films were measured by the sessile drop method using an OCAH 200 model from DataPhysics Instruments (Filderstadt, Germany), which allowed for image acquisition and data analysis at the same time [ 12 , 13 ]. The surface free energy (total, dispersive, and polar components) of the biocomposite films was calculated by determining the contact angles using three reference liquids (distilled water, diiodomethane, and ethylene glycol) [ 16 ].…”