Monitoring of Maillard reaction products in soy-based milk alternatives during storage

During the thermal processing of milk and soy-based milk alternatives (SBMAs), ultra-high temperature (UHT) leads to Maillard reaction and glycation, forming α-dicarbonyl compounds, fructosyl-lysine, N-ε-carboxymethyllysine (CML), and N-ε-carboxyethyllysine (CEL). In this study, different SBMAs and one cow’s milk sample bought from a local market in Türkiye were investigated for the formation of glycation markers during six months of storage at 22 °C. Furosine, an early-stage glycation marker, was found at substantially higher levels in UHT cow’s milk (3.07 ± 0.14–4.37 ± 0.90 g/kg protein) compared to SBMAs (0.34 ± 0.01–1.78 ± 0.16 g/kg protein). Over six months of storage, furosine content significantly decreased in all samples. As an advanced glycation marker, CML concentration increased significantly after six months of storage, showing a rise from 60.75 ± 5.18 to 143.91 ± 11.52 mg/kg protein for SBMAs and from 70.67 ± 2.96 to 178.57 ± 15.85 mg/kg protein for UHT milk. Meanwhile, CEL concentrations in SBMAs approximately doubled within two months. The CEL content in cow’s milk (11.43 ± 1.3–15.7 ± 1.14 mg/kg protein) was found to be lower than SBMAs (27.09 ± 7.18–94.97 ± 6.05 mg/kg protein). The decreasing content of 3-deoxyglucosone in all samples, glyoxal in SBMAs, and methylglyoxal in SBMA-1 and − 2 are related to the increasing formation of advanced glycation end products. Besides, total lysine showed no significant change over six months of storage. These results indicate that thermal processing of SBMAs causes the Maillard reaction, and during the six months of storage, glycation reactions continue, resulting in a decrease in early-stage markers, furosine and α-dicarbonyl compounds, and an increase in advanced glycation end products, i.e., CML and CEL.