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Protein concentrates were prepared from defatted barley (Hordeum vulgare L.) flour using alkaline and enzymatic treatments. Milder enzymatic treatments included (i) a bi-enzymatic method involving the use of starch-hydrolyzing enzymes, and (ii) a tri-enzymatic method using the former bi-enzymatic treatment followed by digestion with glucanase. The concentrate obtained through alkaline extraction (AI-BP) was comprised mainly of low molecular weight fractions of proteins. Bi-enzymatic treatment produced a protein concentrate with the highest protein content (49.0%), while those obtained by the tri-enzymatic treatment followed by an isoelectric precipitation step (TEI-BP) gave the highest protein recovery yield (78.3%). In both of the latter concentrates, 35 kDa B-hordeins were the major protein fraction. Divergence in secondary/tertiary structure elements (AI-BP; TEI-BP) was obtained and attributed to the difference in the protein profiles. Further characterization of protein concentrates indicated that they exhibit pseudoplastic behavior. Emulsifying capacity of concentrates was comparable to that of whey protein isolate.

Interactions of vanillin with barley proteins (alkaline-based & tri-enzymatic-based barley protein concentrates, AI-BP & TEI-BP) and two control proteins (pea protein concentrate, PPC; whey protein isolate, WPI) were assessed by (a) quantifying the vanillin unbound to the protein at equilibrium, (b) characterizing the structure of protein-vanillin complexes by fluorescence spectrophotometry, and (c) conducting sensory evaluation. Effects of heat- and high-pressure-treatments of proteins on these interactions were also evaluated. The interaction between vanillin and barley proteins, estimated using Klotz plots of unbound vanillin, was found to be non-cooperative, while the quenching of the protein-vanillin complex fluorescence was related to changes in protein binding site hydrophobicity upon vanillin complexation. Using unbound vanillin, native WPI showed the lowest degree of binding, while high-pressure-treated AI-BP concentrate showed the least interaction. Fluorescence spectroscopy analysis revealed the weakest vanillin interaction with heat-treated PPC, followed by heat-treated WPI. The flavor intensity perception results obtained by the sensory evaluation of high protein cookies were well correlated with those predicted by Klotz plots of unbound vanillin., while the consumers' palettes saturation results were comparable to those estimated by the fluorescence spectroscopy. Correlating analytical data with consumers’ perception contributes to the understanding of protein/flavor interactions in foods.