The study, which has been accepted for publication in Food Chemistry, looked at whether a multi-layer pea protein isolate-pectin complex was more effective than a pea protein isolate coating alone at protecting oil droplets from flavour loss.
One of the most common techniques for producing flavours is to create an oil-in-water emulsion to encapsulate the flavour molecules, then spray dry the emulsion to produce an easy-to-work-with powder.
“The incorporation of hydrophobic volatile food flavour molecules into dry powders is of great interest to the food industry, since microencapsulation improves the chemical stability of food flavours and provides controlled release,” wrote the researchers.
However, the high temperatures used for spray drying can lead to the loss of volatile molecules. The retention of volatile flavouring esters during spray drying has been shown to be largely dependent on the stability of emulsion droplets and the ability of the droplet walls or ‘membrane’ to protect the encapsulated ingredient and control its release.
In recent years, several scientific studies have investigated the use of multi-layer emulsions for stabilising oil-in-water emulsions. Multi-layer emulsions are composed of small oil droplets dispersed in an aqueous medium, and each oil droplet is surrounded by a multi-layered membrane generally composed of an emulsifier and a charged biopolymer.
The aim of this study was to determine whether multi-layer coatings can be used to improve the flavour protective properties of pea protein coated oil droplets.
Pea proteins and pectins are electrically charged biopolymers. The same group of researchers had previously used them to produce stable mono and multi-layer emulsions, and had found them to improve the stability of oil droplets to ageing, pH changes and spray drying versus those droplets coated by a protein single-layer membrane.
In the current study, oil-in-water emulsions were created using three flavour compounds: ethyl acetate (EA), ethyl butyrate (EB), and ethyl hexanoate, one with and one without pectin. Two samples of the oil-in-water emulsions, one with and one without pectin, were then dried in a spray-drier.
The results showed that when pectin was used as an additional oil droplet coating, flavour retention increased significantly, and that the beta-sheet structure was protected by the presence of pectin.
“This protective pectin effect against heat-induced loss of the beta-sheet structure could be used to partly explain the high retention during spray-drying of flavour compounds in oil droplets coated by two-layered interfacial membranes of pea protein and pectin,” wrote the authors.
In summary, pectin was able to improve the physical integrity of emulsion oil droplets during spray drying - improving both droplet stability and flavour retention.
“Engineering the interface of oil in water emulsion droplets with biopolymers that modify its permeability could provide a novel technique to improve flavour retention in dry powders,” concluded the researchers.
Source: Food Chemistry
Published online ahead of print, doi: 10.1016/j.foodchem.2011.03.028
“Properties of spray-dried food flavours microencapsulated with two-layered membranes: roles of interfacial interactions and water”
Authors: Gharsallaoui, A., Roudaut, G., Beney, L., Chambin, O., Voilley, A., Saurel, R.