Effects of Ultrasonic Processing and Oil Type on Maillard Reaction of D-Glucose and L-Alanine in Oil-in-Water Systems

This study investigated the effects of high-intensity ultrasonic processing on a Maillard reaction (MR) model system of D-glucose and L-alanine and its corresponding oil-in-water systems with canola, olive, palm, and coconut oil, respectively. The MR in the water phase was significantly promoted in the olive and canola oil-MR systems with the higher depletion of reactants and the higher generation of final MR products compared with those in the oil-free-MR model system; however, the MR was suppressed in the systems of palm and coconut oils. The concentration of pyrazines with shorter side chain, e.g., 2,5-dimethylpyrazine and 2,6-dimethylpyrazine, was significantly increased in the presence of oils with a lower degree of unsaturation; meanwhile, the oils with higher degree of unsaturation suppressed the generation of the shorter side chain-pyrazines, but promoted the generation of pyrazines with a longer side chain, e.g., 2,3-diethyl-5-methylpyrazine and 3,5-diethyl-2methylpyrazine. Due to the oils undergoing ultrasonic processing at 80 degrees C, the oxidation of oils was significantly promoted, as reflected by a relatively low iodine value and high peroxide and p-anisidine values in the processed oils compared with those in the raw oils. On one hand, various carbonyl compounds were generated due to the lipid oxidation; meanwhile, these carbonyl compounds participated in the MR as part of intermediate MR products and subsequently generated various desired flavors. On the other hand, off-flavors coming from the oxidation of oils were also detected, which may affect the overall flavor profile of the oil-in-water MR systems.