Writing in the Journal of Agricultural and Food Chemistry, the Finnish researchers report that modifying the isoelectric point of the protein could extend the range of products the ingredient could be used in, particularly for acidic foods.
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.
By modifying the isoelectric point using ethylene diamine (EDA) or succinic anhydride, the VTT researchers could extend the range of products in which sodium caseinate could be used as an emulsifier.
“So far, there has been no work published on using EDA-modified caseinate as an emulsifier,” explained the researchers, led by Harry Boer. “Ethylenediamine used for this type of modification might not be an ideal chemical for food emulsion applications, but it can be used as a model to validate the impact of an increased pI on emulsion stability.”
Boer and his co-workers reported that the reaction between succinic anhydride and the caseinate was almost immediately, and easier than the EDA type of modification.
Oil-in-water emulsions were subsequently prepared and the modified caseinates tested as emulsifiers.
“The pH stability behavior of the emulsions was monitored, and interestingly, the stability of the emulsion could be modulated through steering the pI of caseinate,” wrote the researchers.
“Using different modified caseinates, it was possible to create emulsions that were stable in the acid, neutral, and alkaline regions of the pH spectrum,” they added.
Tests of the stability of the emulsions showed similar storage ability to unmodified caseinate emulsions, they added.
“For proteins, such as sodium caseinate, whose isoelectric point is slightly acidic, the EDA modification is very interesting since it gives the opportunity to study caseinates as emulsifiers in a different pH range,” wrote the researchers.
“The modified protein had good solubility and emulsifying properties throughout acidic and neutral regions up till pH 7, showing that introducing additional positive charges in caseinate is an efficient way to improve its functionality in this pH range where most of the food applications of emulsion are applied.”
Boer and his co-workers noted that, while EDA is not the most ideal compound of use for producing ingredients for food applications, the results of this study highlighted the potential of this approach, and that food grade analogues should be investigated to achieve similar results.
“Most interesting would be a protein modification procedure using a biocatalytic approach to reach this goal,” they added. “Transglutaminase catalyzes the deamination and amine fixation of proteins and has been widely used in the food industry.”
Source: Journal of Agricultural and Food Chemistry
Published online ahead of print, ASAP Article, doi: 10.1021/jf803104s
"Sodium Caseinates with an Altered Isoelectric Point As Emulsifiers in Oil/Water Systems"
Authors: H. Ma, P. Forssell, R. Partanen, R. Seppnen, J. Buchert, H. Boer