Impact of an Olive Leaf Polyphenol 3,4-DHPEA-EDA on Physical Properties of Food Protein Gels

Abstract

A cold-water extract of olive leaves (Olea europaea L.) is useful as a texture-improving agent for food protein gels. In this work, the compound contributing to the improvement of gel properties was investigated by using the egg white gel (EWG) as a model for food protein gels. Adding 1.0% (w/v) cold-water extract (OLEx) greatly improved the elasticity (2.1 times), viscosity (4.5 times), and breaking stress (1.4 times) of the EWG. Chemical analyses of the protein revealed that the enhancement of physical properties by OLEx was attributed to protein cross-linking activity of polyphenols. LC/MS and NMR analyses indicated that a major protein cross-linker is the dialdehydic form of demethoxycarbonylelenolic acid linked to hydroxytyrosol (3,4-DHPEA-EDA), which is an aglycone derived from oleuropein, a major polyphenol of olive leaves. These results suggest that 3,4-DHPEA-EDA generated by cold-water extraction from the leaf improves the physical properties, that is, texture, of protein gels.

The physical properties of fish gelatin gel are enhanced by the cross‐linking activity of olive leaf water extract

“…Meanwhile, OLEx contains a unique polyphenol, oleacein (peak 12), which is not a flavonoid but a form of oleuropein aglycone exclusive to the Oleaceae family. Our previous report showed that oleacein significantly enhances the breaking strength of egg white gel by acting as a covalent linker in its gel network (Akazawa et al ., 2021). A similar mechanism likely occurred in the FG gel.…”

“…FG gel (5.0% (w/v)) containing 4 m m oleacein was prepared according to the procedure mentioned above. Oleacein was purified from OLEx as previously reported (Akazawa et al ., 2021). Purified oleacein was dissolved in dimethyl sulfoxide and suspended in 10 m m sodium phosphate buffer (pH 7.0).…”

“…Oleacein possesses two formyl groups that can form covalent bonds with nucleophilic side chains of proteins. Oleacein enhances the mechanical strength of egg white gels by inserting covalent crosslinks into the protein gel network (Akazawa et al ., 2021).…”

“…Recently, we reported that olive leaf extract (OLEx) from olive leaves ( Olea europaea L.) improves the physical properties of food protein gels, sausages, and egg white gels. OLEx enhances the breaking strength, viscoelastic properties, and water‐holding capacity (Rachman et al ., 2020; Akazawa et al ., 2021). OLEx polyphenols improved the physical properties of these gels.…”

Nutraceutical potential of olive pomace: insights from cell‐based and clinical studies

“…According to Zhao et al and Akazawa et al, oleuropein-aglycone-dialdehyde (3,4-DHPEA-EDA) was the main phenolic in olive pomace, which also contains other important phenolics such as hydroxytyrosol (4.328 g.kg −1 dry basis), followed by 4-hydroxyphenylacetic acid (3.565 g.kg −1 ), hydroxytyrosol-glucoside (3.017 g.kg −1 ), and tyrosol-glucoside (2.375 g.kg −1 ). 7,8 The contribution of these compounds to human health is well documented in the literature, such as their antioxidant properties. 9,10 A quantity of residual oil still remains in olive pomace.…”