Characterization and antimicrobial efficacy of active biocomposite containing polylactic acid, oregano essential oil and nisin for pork storage

Abstract

Traditional packaging made from non-renewable compounds such as petroleum has a negative impact on the environment, which has led to a growing body of research on biodegradable packaging. This paper details the characterization of a biocomposite which was made from cassava bran, coffee husk, and water (BCCW). After this, a layer of polylactic acid (PLA) was added, mixed with nisaplin 1000UI, and 8, 10, 12% concentrations of oregano (Origanum vulgare L) essential oil (OVEO) in order to create an active biocomposite (AB) which could be used as an antimicrobial material in the packaging of pork. In vitro inhibitory effects were evaluated against Listeria monocytogenes, Escherichia coli and Salmonella typhimurium. After obtaining the active biocomposite, the characterization was performed by means of Infrared Spectroscopy (FT-IR), Water Vapor Permeability (WVP), a Mechanical Property analysis, Differential Scanning Calorimetry (DSC), and Scanning Electron Microscopy (SEM). Using the concentration with the highest inhibition against pathogenic bacteria, antimicrobial tests were carried out after the application of the AB in pork meat for 0, 1, 3, 5, and 10 days. Inhibition tests against pathogenic bacteria showed that nisin had a greater effect on Gram positive bacteria, while OVEO had an effect on both Gram positive and Gram negative bacteria. FT-IR analysis allowed for the characterization of the molecular interactions of OVEO and nisin in the matrix compounds of the different biocomposites by identifying and interpreting their respective vibration bands. According to the statistical analysis, the different concentrations of the biocomposites affect WVP (p <0.05). BCCW showed the highest permeability to water vapor, whereas the other treatments did not show significant differences. The mechanical properties test of the AB showed that the different treatments had a significant effect (p <0.05) on the maximum flexural strength and flexural modulus. These values decreased with the application of the PLA layer, the concentrations of the biocomposites did not have a significant maximum deformation effect (p> 0.05). The DSC test on the ABs showed two melting peaks and an increase in the glass transition temperature (Tg) of the PLA, a finding that indicates greater thermal stability in the ABs. SEM images revealed that the nisaplin and OVEO particles were uniformly distributed in the PLA polymer matrix on the surface of the ABs. The ABs showed a significant reduction in Listeria monocytogenes in pork as of day 3 and in the other pathogens as of the 10th day. The biocomposite containing OVEO and nisaplin, showed good potential to be used to food packaging.

Keywords:
active packaging; antimicrobial; alimentary pathogens; renewable materials; nisin