Evaluation of color photostability and structure of thylakoids in isolation and after undergoing food processing treatments

Improving the photostability of natural chlorophyll remains a substantial challenge for its application in the food industry. Thylakoids in chloroplasts are pouch-like compartments contain over 90 % of total chlorophyll. In this study, the color photostability of thylakoids were evaluated. Accelerated photodegradation experiments were conducted at 5 °C under an intense illumination model (15,000 lm). Thylakoids exhibited a green retention rate of 79.2 % after five days of illumination, comparable to sodium copper chlorophyllin (78.1 %), a commonly used synthetic chlorophyll derivative. The light-harvesting complex (LHC) proteins, situated in the thylakoid membranes, are regions abundant in chlorophyll. Results of electrophoresis and TEM analysis indicate that both the LHC proteins and the overall structure of thylakoids may contribute to the color photostability of thylakoids. We further evaluated if common food processing treatments changed the subsequent photostability of thylakoids and their structure. The results showed that heating, acidification, and freezing led to a loss of photostability, which appeared to positively associate with the damage to the thylakoid structure, as shown in TEM images. In contrast, storage at 25 °C for 30 days and high-pressure processing (HPP) up to 1400 MPa showed minimal effects on the thylakoid structure and their photostability. Our study highlights the potential of thylakoids as a photostable green colorant in neutral foods that have undergone cold sterilization treatments.