Melt-Processed Bioactive EVOH Films Incorporated with Ferulic Acid

Abstract

In this work, antimicrobial and antioxidant films based on ethylene vinyl alcohol (EVOH) copolymer containing low amounts of ferulic acid (FA) were successfully developed by melt extrusion. Optically transparent films were obtained, and the presence of FA provided some UV blocking effect. The characterization of the thermal and barrier properties of the developed films showed that the addition of FA improved the thermal stability, decreased the glass transition temperature (Tg) and increased the water vapor and oxygen transmission rates when ferulic acid was loaded above 0.5 wt.%, associated with its plasticizing effect. Mechanical characterization confirmed the plasticizing effect by an increase in the elongation at break values while no significant differences were observed in Young’s modulus and tensile strength. Significant antioxidant activity of all active films exposed to two food simulants, 10% ethanol and 95% ethanol, was also confirmed using the 2,2-diphenyl-1-pricylhydrazyl (DPPH) free radical scavenging method, indicating that FA conserved its well-known antioxidant properties after melt-processing. Finally, EVOH-FA samples presented antibacterial activity in vitro against Escherichia coli and Staphylococcus aureus, thus showing the potential of ferulic acid as bioactive compound to be used in extrusion processing for active packaging applications.

Hot-Melt-Extruded Active Films Prepared from EVOH/Trans-Cinnamaldehyde Blends Intended for Food Packaging Applications

“…The content of cinnamaldehyde remaining in both the EVOH-CIN masterbatch and in the bioactive EVOH-CIN films after the extrusion process was quantitatively determined by solid–liquid extraction followed by liquid chromatography mass spectrometry (LC/MS) analysis, as described elsewhere [ 5 ]. A calibration curve of cinnamaldehyde was created by injecting known concentrations of the agent into the LC/MS equipment.…”

“…A DSC Q-2000 analyzer from TA Instruments (New Castle, DE, USA) was used to evaluate the thermal transitions i.e., glass transition (T g ), melting (T m ), and crystallization temperatures (T c ) as well as their corresponding enthalpies of the developed films. The measurements were performed following the procedure described elsewhere [ 5 ]. T g values were determined at the midpoint of heat capacity changes.…”

“…The mechanical characteristics of the dog bone specimens were evaluated in terms of elastic modulus (E); tensile stress (TS), and strain at break (ε B %) by submitting the specimens to stress–strain tests in a universal tensile test machine Testometric M350–20CT (Rochdale, UK), using the conditions described earlier [ 5 ]. The elastic modulus (E), defined as the relationship between the stress and the strain in the elastic zone of the materials, was calculated from the elastic region of the stress–strain curve employing the following equation: where σ is the stress in Pa and ε is the strain.…”

“…Consequently, there is currently a great need to reduce and minimize food losses to make the transition to a resource efficient world. In this line, active packaging systems emerge as a promising solution to improve microbiological food safety and quality and increase the shelf-life of packaged foods [ 5 ]. In this regard, the main benefit of antimicrobial active packaging over the direct incorporation of food additives is that the antimicrobial compound is progressively released on the food surface during storage and distribution, causing an inhibitory or lethal effect against pathogen and spoilage microorganisms that affect food products [ 6 , 7 , 8 ].…”

“…However, this technique is unsuitable for scaling up in an industrial environment, being relegated to be applied for the coating of other surfaces. The main problem of using conventional technologies such as melt extrusion technology is that the process takes places at temperatures above the melting temperature of the polymer matrixes, usually above 170 °C, which may cause the degradation and losses through volatilization of the active compounds [ 5 , 25 , 26 ]. This work describes an innovative approach for the development of antimicrobial films consisting of the preparation of a polymeric masterbatch containing CIN as bioactive compound, for its further utilization in conventional melt-extrusion processing, thus, minimizing volatile losses due to direct incorporation into the extruder.…”