Physical and oxidative stability of fish oil-in-water emulsions stabilized with emulsifier peptides derived from seaweed, methanotrophic bacteria and potato proteins

Abstract

This study investigated the emulsifying and antioxidant activity of 10 peptides derived from seaweed, methanotrophic bacteria, and potatoes, which were identified as emulsifiers using quantitative proteomics and predictive bioinformatics. The factors (e.g., interfacial properties, secondary structure, net charge) behind the dual-functionality of peptides were characterized and related to peptides’ ability to provide physical and oxidative stability in 5 % fish oil-in-water emulsions during 10 days of storage. The secondary structure of some of the peptides changed from highly disordered to more α-helical (GIIPATILEFLEGQLQEVDNNKDAR and GIIPGTILEFLEGQLQK) or β-strand (VGFACSGSAQTYLSFEGDNTGRGEEEVAI, ELQVSARVTLEIEL, KVKINETVEIKGKFHV, RSPQKKESDMMKATKFAVVLMAAGLTVGCA) structures when adsorbed at the oil-water interface in comparison to aqueous solution. The physical stability analyses confirmed that three seaweed peptides (IDSSFDSLPTDVVRVANSSCDAVE, VGFACSGSAQTYLSFEGDNTGRGEEEVAI, and ELQVSARVTLEIEL), one of the methanotrophic bacteria peptides (KVKINETVEIKGKFHV) and two of the potato peptides (GIIPATILEFLEGQLQEVDNNKDAR and GIKGIIPAIILEFLEGQLQEVDNNKDAR) can indeed produce physically stable emulsions. The predicted emulsifier peptide embedded in methanotrophic bacteria protein (KVKINETVEIKGKFHV) outperformed all the samples in its ability to retard lipid oxidation in emulsions. This was evident as this sample had the lowest hydroperoxides formation (peroxide value < 10 meq O2/ kg oil), tocopherols consumption, and volatile compound concentration, especially for t,t-2,4-heptadienal (14 ng/g sample) and 2-ethyl-furan (no formation). Non-enzymatic browning, which may indicate advanced stages of oxidation, occurred in all emulsions except for those stabilized with KVKINETVEIKGKFHV and sodium caseinate. Even though the positively charged peptides yielded better oxidative stability compared to negatively charged ones, there are several other factors (i.e., length, structure, charge, ability to decrease oil-water interfacial tension) affecting the physical and oxidative stability of emulsions. Therefore, it must be kept in mind that it is the collective action of these factors that ultimately define the functionality of peptides. In its entirety, KVKINETVEIKGKFHV proved to be highly effective in its technological functions as an emulsifier and antioxidant.