Evaluation of protein-flavour binding on flavour delivery and protein thermal-gelation properties in regards to selected plant proteins
This work was undertaken to evaluate interactions between plant proteins and selected volatile flavour compounds on flavour delivery and heat-induced gelation properties for canola, pea and wheat proteins. An automated dynamic headspace GC/MS approach was adopted to monitor the change in flavour intensity in aqueous model systems. The extent of flavour binding was a function of protein source, protein isolation method and stereochemistry of the flavour compound. Using Differential Scanning Calorimetry and intrinsic fluorimetry, potential conformational changes due to partial denaturation of proteins were observed. Aldehyde flavours exhibited much higher “unfolding capacity” than ketones, which accounted for their remarkable binding affinities. Two volatile flavour by-products, 2-butyl-2-octenal and 2-pentyl-2-nonenal, were detected from the interactions between salt-extracted canola protein isolates (CPIs) with hexanal and heptanal, respectively, due to aldolisation reactions. Competitive bindings among homologous ketones and between heterologous aldehyde and ketone mixture were observed, while a synergistic effect was noted for aldehyde flavour mixtures. Environmental changes such as heating and addition of non-chaotropic salts increased binding for ketones; however, protein aggregation following continuous heating and denaturation of protein by chaotropic salt and at extreme pH values reduced ketone retention. Apart from molecular interactions, dramatic increases in flavour binding were monitored when physical adsorption of flavours on aggregated proteins was employed. By adding bonding disrupting agents, the molecular forces responsible for the interactions were probed with hydrophobic interactions, hydrogen bond and ionic interactions being prominent for benzaldehyde, 2-octanone and hexyl acetate, whereas covalent interactions were implicated for octanal and dibutyl disulfide. Selectively modifying proteins via chemical (acetylation and succinylation) and enzymatic (Alcalase) approaches significantly altered protein-flavour binding affinities and this was influenced by the type of flavours selected and associated type of binding. In general, addition of flavour compounds diminished protein heat-induced gel forming properties by disrupting protein inter- and intra-molecular hydrophobic interactions. However, gel strength was regained with increasing concentration and chain length of aldehydes possibly due to the additional unfolding effect on proteins due to aldehyde binding. This facilitated the gel formation process, consequently resulting in formation of stronger gels.
Protein, Flavour, Flavour delivery, Binding interactions, Flavour-food matrix interactions