¹⁴C-Isotope Use to Quantify Covalent Reactions between Flavor Compounds and β-Lactoglobulin

Area of Science:

• Food Chemistry
• Protein Chemistry
• Chemical Kinetics

Background:

• Understanding flavor-protein interactions is crucial for food product development.
• Covalent bond formation can alter flavor perception and protein functionality.
• Beta-lactoglobulin is a common food protein susceptible to chemical modifications.

Purpose of the Study:

• To quantify the rate and extent of covalent reactions between beta-lactoglobulin and model flavor compounds.
• To compare the reactivity of different functional groups (ketone, aldehyde, isothiocyanate) with the protein.
• To assess the influence of temperature on these reaction kinetics.

Main Methods:

• Utilized a 14C-labeling method to track flavor compound incorporation into beta-lactoglobulin.
• Incubated protein solutions with labeled flavor compounds (UDO, DAL, PEITC) at 25, 45, and 65 °C for 28 days.
• Monitored reaction progress at multiple time points (1, 3, 7, 14, 21, 28 days).

Main Results:

• 2-phenylethyl isothiocyanate (PEITC) exhibited the highest reactivity (up to 71.8% reacted), followed by decanal (DAL, up to 16.4%), and 2-undecanone (UDO, up to 0.9%).
• Reaction rates for all compounds were rapid initially, slowing significantly after approximately 7 days.
• High temperatures, particularly 65 °C, accelerated the reaction rates and extent of binding for PEITC.

Conclusions:

• The reactivity of flavor compounds with beta-lactoglobulin varies significantly based on their chemical structure.
• Isothiocyanates are highly reactive towards beta-lactoglobulin, suggesting potential for significant covalent modification in food systems.
• Temperature plays a critical role in the kinetics and extent of flavor-protein covalent interactions, with PEITC potentially saturating reactive sites at elevated temperatures.