New chemical marker-model food systems with d-ribose and NaOH precursors as color indicators and gellan gels as chemical marker carrier were explored for the assessment of the heating pattern of in packaged foods processed in microwave-assisted pasteurization system (MAPS). In determining appropriate precursor concentrations, a solution of 2% (w/w) d-ribose and 60 mM NaOH was heated at 60–90 °C for 0–20 min. The solution absorbance at 420 nm increased linearly, while the color parameters L* decreased linearly with heating time at all processing temperatures. In storage, the produced brown color was stable at 4 and 22 °C within 7 days. The new chemical marker-model foods were prepared by mixing 2% (w/w) d-ribose and 60 mM NaOH with 1% (w/v) low-acyl gellan gum and 20 mM CaCl2·2H2O solution. The dielectric constant of the model food samples decreased with the addition of sucrose, and the loss factors increased with the addition of salt. After processing in the pilot MAPS, the heating pattern and cold and hot spots in the new chemical marker-model food system could be clearly recognized and precisely located through a computer vision method. This is the first time that the caramelization reaction was used as a time-temperature indicator in gellan gel model food. This study shows the possibility of using the new chemical marker-model food system for heating pattern determination of the MAPS.