The influence of temperature on the stability of hydroxytyrosol

Temperature is a key factor affecting the stability of hydroxytyrosol, with its mechanism primarily acting through accelerating molecular oxidation, triggering structural degradation, and altering the reaction environment. Specifically, elevated temperatures exert a significant negative impact on hydroxytyrosol stability, and this effect intensifies with increasing temperature and prolonged exposure time.

Hydroxytyrosol is a phenolic antioxidant containing multiple phenolic hydroxyl groups in its molecule. While these active groups endow it with antioxidant capacity, they also make it susceptible to temperature-induced chemical changes. In low-temperature environments (e.g., 0-4°C), the molecular motion of hydroxytyrosol is slow, and oxidation reactions of phenolic hydroxyl groups (such as combining with oxygen to form quinone derivatives) and structural rearrangements are difficult to proceed. At this point, its chemical properties are relatively stable, retaining activity for an extended period in solutions or food matrices, with a degradation rate typically below 5%.

When the temperature rises to room temperature (20-25°C), molecular thermal motion intensifies, increasing the collision frequency between hydroxytyrosol and oxidants such as oxygen and free radicals in the environment. This accelerates the oxidation reaction, leading to slow degradation. For example, in liquid beverages, the retention rate of hydroxytyrosol may decrease by 10%-15% after 1 month of storage at room temperature, and degradation products may cause slight darkening of the solution or a mild off-odor.

Moderate to high temperatures (50-100°C) have a more significant impact on hydroxytyrosol stability. In addition to oxidation reactions, thermal decomposition may occur: phenolic hydroxyl groups easily lose hydrogen atoms at high temperatures, forming unstable free radical intermediates, which then trigger intramolecular rearrangement or cleavage, generating small-molecule compounds (such as benzoic acid derivatives and aldehydes). For instance, during pasteurization (60-80°C) in food processing, the loss rate of hydroxytyrosol can reach 20%-30%; under high-temperature sterilization (121°C), its retention rate may drop below 50%, with the degradation rate increasing exponentially with treatment time.

Extreme high temperatures (exceeding 100°C) cause rapid inactivation of hydroxytyrosol. In processing scenarios such as frying and baking, when temperatures exceed 150°C, its phenolic ring structure may be destroyed, completely losing antioxidant activity. Meanwhile, it may undergo cross-linking reactions with other components in food (such as fats and proteins), further reducing its stability.

Furthermore, the impact of temperature on hydroxytyrosol stability is related to the matrix environment: in acidic solutions, protonation under high temperatures can delay the oxidation of phenolic hydroxyl groups to a certain extent, making its stability slightly higher than in neutral or alkaline environments; in systems with high oil content, high temperatures may accelerate the reaction between hydroxytyrosol and lipid free radicals, indirectly promoting its consumption.

In summary, elevated temperatures significantly reduce the stability of hydroxytyrosol by accelerating oxidation, thermal decomposition, and reactions with other components. Therefore, controlling temperature (e.g., low-temperature storage, adopting mild processing techniques) during its production, storage, and application is a key measure to maintain its activity and efficacy. This has also driven research and development in the food and pharmaceutical industries toward low-temperature processing technologies and antioxidant synergistic formulations to mitigate the adverse effects of temperature on hydroxytyrosol.