Influence of pH, Temperature, and Water Activity on Covalent Adduct Formation between Selected Flavor Compounds and Model Protein β‑Lactoglobulin

This study investigates the influence of pH, temperature, and water activity on the occurrence of covalent adduct formation between select flavor compounds and a model food protein (β-lactoglobulin). These reactions potentially result in the loss of flavor during processing and storage, reducing consumer acceptability. Foods present a diverse reaction environment encompassing a wide range of a_w, pH, and storage temperature, which potentially influence protein: flavor reaction rates. Liquid chromatography/mass spectrometry (LC/MS) data showed that covalent adducts were formed more slowly at low pHs (3) than basic pHs (8) (for citral, allyl isothiocyanate, and dimethyl trisulfide). No reactivity was observed for benzaldehyde at pH 3, but substantial reactivity was found at pHs 7 and 8. The amount of adducts formed increased with an increase in storage temperature. Higher temperatures (45 °C) led to the formation of products that were not observed at lower temperatures (4 and 20 °C). An increase in water activity (0.11–0.75) led to an increase in formation of adducts for allyl isothiocyanate. There were no observable differences in adduct formation as a function of a_w for benzaldehyde, citral, and dimethyl disulfide. However, this lack of observed effect may be due to the rate of reaction being too slow to be detected in the timeframe of this study.