Kinetics of available lysine in stored commercial skim milk powder at moderate temperatures

Kinetics of lysine blockage, as an early step of the Maillard reaction, was investigated in commercial skim milk powder to understand the extent of the reaction, specifically after packages are opened and during the subsequent storage. Samples were stored at six conditions including three temperatures (30, 32.5 and 35 °C) and two relative humidities (43% and 52%) for 30 days, the period in which the product is recommended to be consumed after opening. The reaction rate was determined using a dye-binding method. Based on our findings, decrease in available lysine follows first-order reaction kinetics model. Small changes in temperature (2.5 °C) caused significant increase in the reaction rate constants. Relative humidity affected temperature dependency of the reaction, and activation energies were estimated to be 142.5-170.8 kJ mol^-1. This study aims to increase the awareness of the significance of storage quality in relation to the nutritional status of the products.