Fig. 3: Overview of the spectroscopic analysis conducted on raw and cooked eggs.

a IR spectra of raw egg albumen (light gray) and yolk (orange) over the whole IR range (4000–650 cm⁻¹). b Cooking index derived through the FT-IR spectroscopic analysis for all cooking techniques in the case of egg albumen and yolk. The different colors of the bars evidence the different cooking methods: hard-boiling (red), soft-boiling (yellow), sous vide cooking (green) and periodic cooking (blue). c IR spectra of raw and hard-boiled albumen (light and dark gray, respectively) and (e) of raw and hard-boiled yolk (orange and red, respectively) over the whole IR range. A close up on band no. 4 and 5 (amide I region) is displayed for both albumen (d) and yolk (f) with addition of the difference spectrum magnified ×5 (purple) and the baseline used for area quantification in the Amide I region (black dashed line). The purple arrow indicates in both cases the appearance of the aggregation band.