Microwave hydrodiffusion and gravity versus conventional distillation for Acacia dealbata flowers. Recovery of bioactive extracts for cosmetic purposes

Abstract

Natural extracts recovered from underutilized wild Acacia dealbata flowers using microwave hydrodiffusion and gravity (MHG) were compared with those obtained from conventional steam distillation. Several irradiation powers (50–125 W) were studied. MHG solid phases were treated by solid-liquid extraction (SLE) with ethanol solvent. Their total phenolic content, antioxidant capacity, total carotenoid content, color characteristics, pH value and solar protection factor (SPF) were tested. Selected extracts were incorporated to an oil-in-water emulsion cosmetic model made with three thermal spring waters and preliminary sensory analysis was made. These creams were chemically and rheologically analyzed jointly with their bioactive capacity by an acceleration oxidation test. The optimum MHG extract was collected at 75 W for 180 min, since this flower liquor exhibited the highest total phenolic content (around 0.15 mg GAE/g flower dry weight) and antioxidant capacities (about 0.39 mg Trolox eq/g flower dry weight and 0.36 μg β-carotene/g flower dry weight) of microwave extracts. Distillation extracts presented higher concentrations (about 0.20 mg GAE/g flower dry weight and around 0.58 mg Trolox eq/g flower dry weight), but with larger (two times) estimated specific energy requirements. Selected extracts provided sunscreen creams with similar chemical (i.e., pH and SPF values) and bioactive properties (i.e., thiobarbituric acid reactive substance outcomes) that cosmetics prepared with BHT or (±)-α-tocopherol commercial antioxidants. The viscosity features of the different cosmetic samples were similar, except for those sun creams elaborated with one thermal spring water. This sample presented lower apparent viscosity profiles, which could be an important advantage from the skin application point of view.