Hybrid extraction and spray drying for the co-encapsulation of sulforaphane and curcumin: Process optimization and functional application

Abstract In this study, sulforaphane (SF) from cabbage seeds and curcumin from turmeric powder were extracted using a hybrid green extraction approach combining ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE). Extractions were performed at 100 W microwave power and 40% ultrasonic amplitude at 30 °C. Solvent systems were selected according to the target compounds: 65% ethyl acetate and 35% water for cabbage seeds, and 70% ethanol and 30% water for turmeric. The optimal solid-to-solvent ratios were 1:25 (w/v) for sulforaphane and 1:10 (w/v) for curcumin. Extracts were analyzed for sulforaphane and curcumin content, total phenolic content (TPC), and antioxidant activity. To enhance stability, mask undesirable sensory attributes, and improve applicability in food systems, the extracts were microencapsulated by spray drying using maltodextrin (MD) and gum arabic (GA) as wall materials. Prior to encapsulation, the extracts were combined in a 1:1 (w/w) ratio. Spray drying was conducted at a feed temperature of 25 °C, an airflow rate of 473 L/h, and an aspiration rate of 60%. Process optimization was performed using a Central Composite Face-Centered Design (CCFD), with extract concentration (1–5%), MD: GA ratio (1:3–3:1, v/v), and inlet air temperature (170–190 °C) as independent variables. The resulting microcapsules were evaluated for physicochemical and functional properties, including TPC, antioxidant activity, sulforaphane and curcumin content, moisture content, water activity (aw), color parameters, bulk and tapped density, solubility, wettability, and microencapsulation efficiency. Sulforaphane and curcumin encapsulation efficiency and water activity were selected as key response variables for optimization, targeting maximal encapsulation efficiency and minimal water activity. Numerical optimization using Design-Expert software identified the optimal conditions as 3.69% extract concentration, an MD: GA ratio of 3:1, and an inlet air temperature of 170.08 °C. Under these conditions, encapsulation efficiencies were 88.35–97.86% for curcumin and 52.34–80.23% for sulforaphane, while water activity ranged from 0.055 to 0.320. To assess functional applicability, both microencapsulated sample and crude extract were incorporated into orange juice and kefir at concentrations of 0.01%, 0.03%, and 0.05%. Sensory evaluation indicated that 0.03% addition provided the highest acceptability in kefir, while 0.01% was optimal for orange juice. Overall, the results demonstrate that microencapsulation significantly improves the stability and sensory acceptability of sulforaphane and curcumin in functional beverages, supporting their potential as antioxidant-rich functional food ingredients.