Encapsulation of aroma compounds in biopolymeric emulsion based edible films to control flavour release

Abstract

Flavour loss strongly affects food quality. In order to decrease flavour changes during food conservation, different strategies could be used. Aroma compound encapsulation allows the protection of food flavour from loss and degradative reactions, like oxidation. Edible films could be an encapsulation matrix: in the case of emulsified film, lipid globules incorporated can act as carriers of active molecules, such as aroma compounds. Edible films prepared from ι-carrageenans are interesting for good mechanical and gas barrier properties.

The aim of this study was to encapsulate different aroma compounds in an ι-carrageenan emulsion based edible film. Release of ten aroma compounds was compared to that obtained from a lipid matrix, Grindsted Barrier System 2000 (GBS), was also used as an edible film formulation. Flavour release was followed by HS-SPME measurements. This study allowed the influence of both matrix and aroma compounds characteristics on flavour release to be investigated. This study presents new understanding of the role of emulsion based edible films as a matrix able to encapsulate aroma compounds. Carrageenans films were possible encapsulating matrixes because they showed better performances for retention of more polar aroma compounds than the usual lipid supports. Carrageenans films were able to retain volatile compounds during film-process formation, and to release gradually with time.

Introduction

The loss of quality in food can be related to the transfer of small molecules: in particular, loss of aroma compounds causes a reduction of flavour intensity and change in the typical food flavour. Aroma compounds transfer in dense system, depends on both sorption and diffusion. The sorption mechanism consists of adsorption, absorption and/or desorption of penetrant molecules and depends on the polymer-volatile compound affinity, whereas diffusion is related to their mobility within the polymeric network of the matrix. Thus, the volatile compounds and matrix characteristics must be taken into account to explain the transfer process. In particular, physicochemical characteristics of volatile compounds influence their release: aroma compound shape and size affect its diffusivity, whereas solubility is influenced by the compound nature, polarity, and ability to condense (Reineccius, 2009). In order to decrease flavour changes during food conservation, different strategies could be used. The encapsulation of aroma compounds represents a method to increase the effectiveness of flavouring without adding high levels of aroma compounds. Encapsulation can be defined as a process where a continuous thin coating is formed around solid particles, liquid droplets, or gas cells that are fully contained within the capsule wall (King, 1995). Encapsulation with edible films allows control of flavour loss, which strongly affects food quality during the processing or storage of food (Miller and Krochta, 1997, Reineccius, 2009, Reineccius and Risch, 1988). This technique allows controlled release, defined as a strategy by which one or more active agents or ingredients are made available at a desired site and time at a specific rate (Pothakamury & Barbosa-Canovas, 1995). In this way, edible packaging does not represent only an inert barrier but it has an active role and interacts with the food or with the surrounding media. Edible films could be applied to food as active packaging, with the aim of gradually releasing aroma compounds with time and thus of maintaining the characteristic flavour of food product. Edible films or coatings have been defined as “a packaging, a film, a coating or a thin protective layer which is an integral part of the food and/or can be eaten with” (Guilbert, 1986). Two categories of ingredients have been used as film forming substances. Protein (wheat gluten, whey protein isolate, caseinate, soy protein) and polysaccharide (starch, carrageenan, alginate) are used for their mechanical, structural and oxygen barrier properties, hydrophobic substances (lipids, lacs, varnishes, resins, essential oils and emulsifiers) for their good moisture barrier properties (Kester & Fennema, 1986). Composite films make possible to combine the advantages connected to the different components. ι-Carrageenan, a water soluble polymer with a linear chain mainly composed of alternated (1,3)-d-galactose-4-sulfate and (1,4)-3,6-anhydro-d-galactose-2-sulfate units, is promising as a film-forming material. In aqueous solutions, ι-carrageenans produces thermo-reversible gels when cooling below the critical temperature. The conformation then changes from random coiled single chain to the formation of double-helices of carrageenan chain (Karbowiak et al., 2006a). This three dimensional network formed by the polysaccharide double-helices in a gel state is then dried to obtain a compact solid film. Lipids can be either dispersed in hydrocolloid aqueous solution and dried to obtain an emulsified film or cast as a layer on the hydrocolloid film used as a mechanical support, in order to obtain a bilayer film. The food industry has been focusing its research on emulsified films, which require only one step in manufacture, as opposed to the three steps required for bilayer films. With the addition of lipids to form emulsified films, they can also be used to encapsulate active molecules such as aroma compounds (Karbowiak, Debeaufort, Champion, & Voilley, 2006b).

The objective of this work was to encapsulate different aroma compounds in emulsified ι-carrageenans films. Release of ten aroma compounds from emulsified films was compared to that obtained from a lipid matrix. In the food industry, flavours are often added to lipids, because of their affinity to hydrophobic phases. Emulsified carrageenans films could represent a lipidic phase surrounded with a second layer consisted of hydrocolloids network, that is supposed to have good gases barrier properties. Headspace solid phase microextraction–gas chromatography (HS-SPME–GC) analyses were carried out. Compared to other extraction techniques, SPME technique is advantageous since it is economic, faster and concentrates the headspace, thus allowing the detection of compounds with low concentrations.