According to findings published in the Journal of Food Science, researchers from the University Autónoma de Querétaro in Mexico found that soy-based films were demonstrated to have good antioxidant properties but that this effect is greatly improved when oregano extracts were added.
However, they noted that the addition of the extracts did not enhance the barrier properties of the film but instead resulted in an increase of water vapour permeability (WVP).
The team concluded that “future research could be conducted to evaluate the addition of pure antioxidant compounds from the oregano to the films and to evaluate their potential for food wrapping or edible coatings.”
Packagers and researchers are exploring the use of edible coatings - transparent films that cover food items and act as a barrier to humidity and oxygen.
Research has shown that such films can be used as a host for additives in the conservation of the properties of the product or simply in order to improve its appearance.
Edible films could also help packagers meet the demand from food companies for new packaging that can help prolong the shelf life of products, while being recyclable or biodegradable.
Aim of study
The researchers said that they were motivated to carry out the study into the incorporation of oregano in SPI films as research on the antioxidant properties of edible films using extracts rich in polar substances such as flavonoids is limited.
The aims of their research were to incorporate aqueous soluble extracts from Mexican oregano (Lippia graveolens) into SPI films and evaluate the effect on mechanical, water and vapour permeability, colour properties as well as the films antioxidant capacity.
Soy protein-based films have been shown in previous investigations to be good oxygen and lipid barriers but have poor water barrier properties, according to the study.
Powdered oregano was extracted with hexane and acetone to remove the essential oil components that can add odour and strong flavour to the film but also to determine the effect of antioxidant water-soluble extracts on the film properties.
Methanolic, butanolic and aqueous extracts from Mexican oregano were incorporate into SPI films plasticized with sorbitol, glycerol, as well as glycerol-sorbitol 1:1.
Antioxidant activity was measured using the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging capacity and reducing power.
The team said that all the oregano SPI films exhibited antioxidants properties.
“The extracts were capable of scavenging DPPH radicals in a concentration-dependent fashion,” said the researchers.
Since the oregano extracts contain polar compounds such as phenolic acids and flavonoids, the hydrophilic properties of the films improve and therefore increases the WVP values but this effect was less prominent in the case of the sorbitol oregano SPI film, explained the researchers.
“The sorbitol plasticized SPI film showed the lowest WVP due to the larger molecular weight (MW) and less hydrophilic nature of sorbitol compared to glycerol, which allowed less moisture absorption,” said the researchers.
Changes in tensile strength for the glycerol SPI films only were observed and the addition of the extracts resulted in a dark red appearance for all the films, according to the findings.
Source: Journal of Food Science, Vol 73, Nr. 6, 2008Published online ahead of print“Water Vapour Permeability, Mechanical Properties and Antioxidant Effect of Mexican Oregano-Soy Based Edible Films.”Authors: E. Pruneda, J.M. Peralta-Hernández, K. Esquivel, S.Y. Lee, L.A. Godínez, S. Mendoza