Effect of Enzymatic Deamidation of Soy Protein by Protein–Glutaminase on the Flavor-Binding Properties of the Protein under Aqueous Conditions

Abstract

The effect of the enzymatic deamidation by protein-glutaminase (PG) on flavor-binding properties of soy protein isolate (SPI) under aqueous conditions was evaluated by a modified equilibrium dialysis (ultrafiltration) technique. Binding parameters, such as number of binding sites (n) and binding constants (K), were derived from Klotz plots. The partial deamidation of SPI by PG (43.7% degree of deamidation) decreased overall flavor-binding affinity (nK) at 25 °C for both vanillin and maltol by approximately 9- and 4-fold, respectively. The thermodynamic parameters of binding indicated that the flavor-protein interactions were spontaneous (negative ΔG°) and that the driving force of the interactions shifted from entropy to enthalpy driven as a result of deamidation. Deamidation of soy protein caused a change in the mechanism of binding from hydrophobic interactions or covalent bonding (Schiff base formation) to weaker van der Waals forces or hydrogen bonding.

Effect of Enzymatic Protein Deamidation on Protein Solubility and Flavor Binding Properties of Soymilk

“…The lower overall binding of vanillin in DSM was expected because deamidation by PG reduces the number of available amide groups by converting most of glutamine residues in soy protein to glutamic acids. Therefore, the potential to form covalent bonds (Schiff bases) with the carbonyl group of vanillin was decreased (Suppavorasatit and Cadwallader 2012). …”

“…This is in agreement with the results for odor detection thresholds. This could be explained in terms of flavor‐protein interactions in these 2 soymilks in that the deamidation by PG decreased the interactions between proteins in soymilk and carbonyl groups of the flavor compounds (Lozano 2009; Suppavorasatit and Cadwallader 2012). …”

“…Flavor‐protein binding interactions can be altered by changing the conformation of proteins by physical, chemical, and enzymatic modification (O’Keefe and others 1991; Mikheeva and others 1998; Liu and others 2005; Kühn and others 2008; Suppavorasatit and Cadwallader 2012). Deamidation has been used to improve solubility and functional properties of proteins, by converting amide groups into acid residues (carboxyl groups) with a release of ammonia.…”

“…In addition to improvements in solubility and functional properties, deamidation has excellent potential for altering the flavor binding properties of a protein (Lozano 2009; Suppavorasatit and Cadwallader 2012). Previously, our research group reported that the partial deamidation of soy protein isolate (SPI) by PG improved protein solubility and decreased overall flavor binding affinity to selected carbonyl containing flavor compounds (vanillin and maltol; common flavor compounds used in industry; with vanilla and cotton candy notes, respectively) in an aqueous model system (Suppavorasatit and others 2011; Suppavorasatit and Cadwallader 2012). However, the impact of PG deamidation on protein solubility and flavor binding potential in an actual aqueous soy food system (for example, soymilk) has not been studied.…”

Flavour binding mechanism between a typical meat flavour compound (nonanal) and porcine myofibrillar proteins with consideration of conformational changes

“…Reversible binding forms contain hydrogen bond and hydrophobic interaction, which play a primary role during the flavour substances absorbing process (Liu et al ., ; Zhou et al ., ). For example, studies have found that small aldehydes could bind to proteins by the irreversible covalent bond or hydrophobic interaction (Gianelli et al ., ; Suppavorasatit & Cadwallader, ). Herrera‐Jimenez et al .…”