Evaluation of physicochemical changes in hard-boiled eggs stored at different temperatures

Eggs that have been hard-boiled are frequently used as ready-to-eat food. Refrigerated and frozen storage of hard-boiled eggs causes issues, such as customer rejection owing to textural changes. The objective of this research is to ascertain how storage temperature affects hard-boiled eggs' alteration in texture over time. Medium-sized brown shell eggs were acquired from a local market, boiled at 100°C for 15 min, and then stored at room temperature (27°C), refrigeration (4°C), and freezing (-18°C) conditions for 0, 12, 24, and 48 h. Fourier transform infrared spectroscopy (FTIR), texture profile, visual observation using a gemological microscope, free amino acid content, and color were measured. Freezing had a substantial impact on the eggs' hardness, gumminess, chewiness, and cohesiveness (p < 0.05). The FTIR spectrums confirmed the textural changes in bonds of amide A (3271 cm^-1), amide I (1626.2 cm^-1), amide II (1539.0 cm^-1), C=O stretch of COO^- (1397 cm^-1), asymmetric PO₂^- stretch (1240 cm^-1). Gemological microscopic images confirmed structural changes in eggs stored at -18 °C. The free amino acid content was lower in fresh and frozen eggs than in the rest (p < 0.05). However, there was no discernible variation in the egg white's color when eggs were kept at 4°C (p > 0.05). Salmonella spp. was found exclusively in eggs kept at room temperature. In conclusion, hard-boiled eggs did not exhibit structural or chemical changes when stored at 4°C for up to 48 h compared to freezing and room temperature conditions.