Convective drying kinetics of strawberry (Fragaria ananassa): Effects on antioxidant activity, anthocyanins and total phenolic content

- Degradation of antioxidant compounds depend on the duration of drying.
- Phenolics and antioxidant activity kinetics followed two first-order reaction phases.
- During drying two-stage of degradation of antioxidant compounds are exhibited.

The thermal drying effects on strawberries were investigated in terms of the kinetics of antioxidant activity (AA), anthocyanins (A) and total phenolic compound content (TPC), as well as the final colour. The evaluated drying temperatures were 50 and 60 °C with an air rate of 1.5 m/s. The 2,2-diphenyl-2-picryl-hydrazyl, pH differential and Folin-Ciocalteu methods were used to assess the antioxidant properties. The kinetics of TPC and AA showed an initial and final period of degradation attributed to inhibition of enzymes. A plateau between these two periods suggests that under certain conditions of temperature and water content, no degradation reactions occurred. Final losses of up to 74, 45 and 78% were found for AA, A and TPC, respectively. The total colour change (ΔE) was lesser degree at 60 than 50 °C. Thermal degradation of the antioxidant compounds followed a first-order reaction kinetics and the degradation rate constants (k) were calculated.