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Comparison on the total phenol contents and the color of fresh and infrared dried olive leaves

Boudhrioua, Nourhène, Bahloul, Neila, Ben Slimen, Imen, Kechaou, Nabil
Industrial crops and products 2009 v.29 no.2-3 pp. 412-419
water content, Olea europaea, olives, leaves, color, drying, phenolic compounds, chemical constituents of plants, protein content, lipid content, carbohydrate content, ash content, plant byproducts
The color (L*, a*, b* parameters), the total phenols content and the global chemical composition (moisture, protein, fat, carbohydrates and ash) of four fresh varieties of olive leaves (Chemlali, Chemchali, Zarrazi and Chetoui) were determined. Fresh olive leaves are characterized by a green color (greenness parameter, a*, varying from -5.01±0.26 to -9.14±1.21), an intermediate moisture content (0.85 to 1.00g/gdry matter, i.e. 46 to 50g/100g fresh matter) and a variable amount of total phenols according to the olive leaf variety (from [almost equal to]2.32 to [almost equal to]1.40gcaffeic acid/100gdry matter). Fresh leaves were submitted to blanching and/or infrared drying at 40, 50, 60 and 70°C in order to be stabilized by reducing their moisture contents. The impact of IR drying temperature on some quality attributes (color, total phenols and moisture rate removal) was evaluated. Nevertheless, the effect of prior blanching treatment on the quality attributes of dried leaves is less significant and it depends on the olive leaf variety. The infrared drying induces a considerable moisture removal from the fresh leaves (more than 85%) and short drying durations (varying from [almost equal to]162 at 40°C to 15min at 70°C). IR drying temperature showed a significant effect of on total phenols content and the color of the leaves whatever the leaf variety. In fact, total phenols content of dried olive leaves increased if compared to fresh ones. For example, total phenols of Chemlali leaves increased from 1.38±0.02 (fresh leaves) to 2.13±0.29 (dried at 40°C) and to 5.14±0.60gcaffeic acid/100gdry matter (dried at 70°C). IR drying allows preserving the greenness color of fresh leaves and enhancing their luminosity. It could be suggested for preserving olives leaves before their use in food or cosmetic applications.