Use of carvacrol as antimicrobial in edible matrices based on starch and HPMC

Abstract

Oregano (Origanum vulgare L.) is an herbaceous plant native to the Mediterranean regions that has been used for medicinal purposes, owing to its antimicrobial, antioxidant and antifungal properties. In particular, the essential oil (EO) of this plant is extracted with the aim of being used mainly in pharmaceutical, cosmetic and food industry. Many of these EOs are safe compounds classified as GRAS (generally recognized as safe). The primary components of the oregano EO are:carvacrol and thymol. These main components are phenolic substances, responsible for the antimicrobial properties. The objective of this work was to evaluate the effect of the carvacrol addition (0.10% or 0.5% w/w) on the antimicrobial, mechanical and physical properties of self-supporting edible films based on native cassava starch (2.67% w/w) and hydroxypropyl methylcellulose (HPMC, 0.67% w/w), plasticized with glycerol (1.70% w/w) and additionally added with potassium sorbate (0.30% w/w). Moreover, the effect of different emulsification speeds (6500 rpm or 21500 rpm) on the film properties was analyzed. It was observed that the films were structurally amorphous and prone to yellow color. A high shear rate generated a higher solubility and tensile strength than the film obtained at a lower speed, while the deformation showed no significant differences between studied films. To evaluate the antimicrobial action, films were formulated with 0.50% w/w of carvacrol and the agar diffusion assay was carried out. The spoilage microorganisms of foods such as Z. bailii, L. plantarum, and P. fluorescens were tested, observing a complete inhibition of the microbial growth in the contact zone of the film with the agar. For this formulation, the physical properties were evaluated and compared with films containing only sorbate. It was evidenced that Elastic Modulus, rupture stress and deformation decreased with respect to those films that did not contain the component of the oregano EO. On the other hand, films did not show differences in color, water solubility and water vapor permeability. The results obtained provide essential information on the carvacrol performance as edible films component to increase the shelf life of food products and improve their quality, helping to optimize their production and behavior and to satisfy consumer demand for more natural and safe products, benign with the environment.