The objective of this study was to determine whether in heat-treated milk-resembling models or milk there is a lag phase, before lactulosyllysine (LL) is converted into advanced Maillard products (AMP), and if there is a step during the heat treatment where LL is actively degraded into AMP. For that purpose, a low temperature (60-85 degrees C) and a long heat treatment (15-90 h) were chosen. We observe that the heat treatment first induces a parallel increase in furosine and AMP fluorescence, confirming that AMP are produced very early during the heat treatment. At this step, both indicators are correlated with each other and precisely reflect the lysine damage. After a time, however, furosine reaches a steady-state concentration, whereas AMP fluorescence still increases, remaining correlated with the lysine blockage. Nevertheless, heat treatment applied to milk does not reach this step so that AMP fluorescence appears as a rapid alternative to furosine quantification.