Effect of Drying Techniques on the Moroccan Pelargonium graveolens L’Hér. Leaves Essential Oil: Yield, Composition, Total Polyphenol Content, Antioxidant Activity, and Hygroscopic Parameters

Abstract

The hygroscopic behavior and the effect of different drying methods (shade, oven and forced convective drying at 40°C, 50°C, and 60°C, natural convective, and greenhouse drying) on Pelargonium graveolens leave essential oils' quantity and quality parameters were studied. The optimal water activity for storage was estimated at awap = 0.363±0.005 and the net isosteric heat of sorption was 61.20±1.01 kJ.mol−1. The GAB model was the best fitting model for the experimental data. The essential oil yields were between 0.3±0.08% (w/w) and 1.27±0.21% (w/w) calculated on a dry weight basis. The highest yield was obtained by natural convective drying while greenhouse caused the most important loss of essential oils. β-Citronellol was the main compound, the ratios were from 25.8% to 12.1%. Natural convective drying had the highest content for total polyphenol content (6.71±0.38 mg GAE/g DM). The same for the antioxidant activity, the highest antioxidant activity was found for shade (384.78±15.59 µg/ml), followed by natural convective drying (424.19±17.86 µg/ml). While the lowest antioxidant activity was revealed by forced convective drying at 60°C (724.54±15.82 µg/ml). Greenhouse gives the lowest values. The color evaluation revealed that forced convective drying at 40°C preserves the appearance of Pelargonium leaves. The biochemical parameters were significantly affected by the drying technique, temperature, and air velocity. Convective drying was more suitable for drying the Moroccan rose geranium leaves. It will contribute to the development of a working methodology for food industries to solve problems related to the deterioration of the quality of the dried Moroccan rose geranium leaves.