Abstract
Food flavonoids have a high antioxidant activity that make them bioactive to fight oxidation. However, when they are used in different formulations, these bioactive molecules are often the subject of at least one heat treatment step such as cooking, pasteurization. To establish the sensitivity of these molecules to heat treatment, the kinetics of degradation of 4 flavonoid extracts were evaluated under isothermal and non-isothermal conditions. The flavonoids tested belong to the aglycon (eriodictyol and mesquitol) and glycosylated (rutin, naringin) forms. The glycosylated flavonoids have a higher stability than the aglycons. Among the glycosylated flavonoids, rutin is more sensitive to heat than naringin because of the different degree of hydroxylation between these 2 compounds. For the aglycon form, the sensitivity to heat varies depending on the absence or presence of a carbonyl group at the 4-position and a hydroxyl at the 3-position. The addition of 10% of propylene glycol causes an effect protector delaying the thermal degradation of flavonoids. Activation energies are also affected by both the flavonoid structure and the heat treatment system. The differences observed between the isothermal and non-isothermal conditions can be attributed to the difference in heating intensity that can generate a difference in the composition of the solution. The evolution of antioxidant activity of flavonoid solutions after heat treatment is different depending on the structure of the flavonoid studied.
Highlights
Flavonoids are antioxidant molecules widespread in fruit and vegetables
The effect of the processing temperature will be observed on the degradation of flavonoids extracted from a food matrix and in a second time, kinetic and calorimetric studies will be led on flavonoid model solutions to generalize conclusions about the effect of the processing temperature on the flavonoid degradation
3.2.1 Kinetics of degradation of flavonoids under isothermal conditions The degradation kinetics of flavonoids in water and in the presence of 10 % of propylene glycol are presented in figures 3a and 3b respectively. These results indicated that naringin is the least sensitive to heat treatment compared to the 3 other studied molecules
Summary
Recent epidemiological studies have shown that a diet of fruit and vegetables rich in flavonoids leads to a general well-being of consumers. This is attributed to biological activities of flavonoids their antioxidant activity. A review on this subject, realized by Ioannou et al [2], revealed that food processing induces a severe degradation of flavonoids and a modification of their antioxidant activities. The intensity of the degradation seemed to change depending on the process and its operating conditions, the composition of the food matrix and on the structure of the flavonoids. For a given aglycon isoflavone, the sensitivity to heat treatment is variable depending on the degree of hydroxylation [7]
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