Scientists from the University of Burgundy report that using a combination of pectin and pea protein as emulsifiers increased the stability of the powder when the emulsion was dried.
Dry emulsions are powders from which an oil-in-water emulsion can be obtained when exposed to aqueous liquid, an example being milk replacers. Such emulsions may also be used to encapsulate, and therefore protect, sensitive food ingredients such as health ingredients or flavours.
By dehydrating an emulsion, it is also possible to enhance the shelf-life of a product, as well as reduce transport and storage costs. However, according to the University of Burgundy researchers, dehydrating poses its own problems, and may lead to a destabilisation of the layers surrounding the oil droplets.
“For many applications, it is therefore important that emulsions have good resistance to dehydration so that they can be converted into powders,” wrote the researchers, before adding: “At present there is a lack of natural emulsifiers that can be used to stabilise emulsified food products to protect them against dehydration stress.”
In order to address these limitations, the Dijon-based researchers prepared emulsions using pea protein (Roquette) as an emulsifier at pH2.4, and then pectin was added to produce droplets coated with protein-polysaccharide membranes.
“Pectin was selected as a second stabiliser of pea protein stabilised emulsions because it is an anionic polysaccharide that is already widely used as a functional ingredient by the food industry,” explained the researchers, led by Remi Saurel.
The emulsion was subsequently spray-dried and the researchers noted that the new pectin-protein system was more stable to dehydrating than spray-dried oil droplets coated by pea protein alone.
In an attempt to explain the results, Saurel and his co-workers noted that the addition of pectin improved the stability of the spray-dried droplets by producing a thicker membrane, which would reduce the effects of steric repulsions.
The researchers confirmed that study was ongoing in this area, noting that the “effect of layer pectin adsorption to pea protein interfacial membrane on both protective and controlled release properties of these microcapsules will be further examined in our future studies”.
Emulsifiers work by stabilizing oil suspended in water, and this is achieved electrostatically. Part of the emulsifier is attracted to water, while another part is attracted to the oil. The isoelectric point (pI) is the pH at which the emulsifier has no electrical charge, and therefore in a food with a pH close to the pI the emulsifier can no longer stabilize the emulsion effectively.
Source: Food Chemistry
Volume 122, Pages 447–454
"Utilisation of pectin coating to enhance spray-dry stability of pea protein-stabilised oil-in-water emulsions"
Authors: A. Gharsallaoui, R. Saurel, O. Chambin, E. Cases, A. Voilley, P. Cayot