Effects of different drying conditions on bioactive potential of Brazilian olive leaf

Efeitos de diferentes condições de secagem no potencial bioativo da folha de oliveira de origem brasileira

Abstract

Olive leaf is a residue in olive oil and fruits production, which is considered with bioactive potential due to the high antioxidant activity attributed mainly to the phenolic compounds. The research aimed to investigate the Brazilian olive leaf drying, and also study its influence on the bioactive potential of the leaf. The desorption isotherms of olive leaves were determined and experimental curves were fitted to GAB, BET and Peleg models. Convective drying in a fixed bed dryer was used in different conditions of air temperature (50 ºC and 70 ºC) and air speed (0.9 m s^-1 and 1.5 m s^-1). Drying curves were obtained for each experimental test. The bioactive potential was reflected in the determination of total phenolic content, antioxidant activity and color parameters. Among the moisture equilibrium predictions between the GAB, BET and Peleg models, the first showed a better predictable capability. The results showed that in the drying operation, the increase in air temperature and speed influenced the increase in the drying rate and the reduction of time. The values of the effective diffusivity of the olive leaves varied between 2.61 x 10^{- 9} m² s^-1 and 10.12 x 10^-9 m² s^-1. The samples dried until 10% of moisture (wet-basis) showed a good antioxidant activity, higher than 85%, and maintenance of the phenolic compounds regarding the fresh leaves around 70%. Bleaching and yellowing of leaves after drying were observed for all studied conditions and a decrease in green color at 70 ºC and 1.5 m s^-1, in this condition the L*a*b* color parameters were 35.39, -5.00 and 42.66, respectively. This study demonstrated that the proper drying condition was at 70 ºC and 1.5 m s^-1 for olive leaf drying and these conditions were important to maintain the original characteristics of the leaves and to spend less time in operation. Thus, this paper describe a viable drying process to take advantage of the olive leaf for the benefit of the environment and human health.

Keywords:
Olea europaea L.; Convective drying; Fixed bed dryer; Total phenolic content; Antioxidant activity; Desorption isotherms; Dehydration; Equilibrium moisture content

HIGHLIGHTS

Olive leaf is a residue of the production of olive oil and fruits;

This residue is important due to its high antioxidant activity attributed mainly to its content of phenolic compounds, taking advantage of this product by a variety of industries such as food, pharmaceutical and cosmetics;

To be used by the industry, the leaves need to be dried after collection for their best preservation;

The present work provides valuable results for the industry that intends to use this raw material, showing the influence of the conditions of the convective drying process on the variation of bioactive compounds.