COSMO-RS screening and synthesis of deep eutectic solvents for the extraction of delphinidin-3-sambubioside from Hibiscus sabdariffa

The underutilization of Hibiscus sabdariffa (roselle), despite being rich in valuable anthocyanins such as Delphinidin-3-sambubioside (Dp3-sam), presents a missed opportunity for developing functional ingredients. Conventional extraction relies on hazardous organic solvents and long maceration periods (up to 48 h), which contradict green chemistry principles and limit industrial scalability. Although deep eutectic solvents (DESs) have emerged as greener alternatives, most reported studies employ DESs as primary solvents. Limited work has evaluated DESs as additives to water for improving selectivity towards standardised Dp3-sam while simultaneously integrating process optimization and kinetic understanding. In this study, DESs as additive in water were investigated as greener extraction media combined with irradiation-assisted extraction. A COSMO-RS screening approach was first applied to evaluate solute-solvent compatibility based on capacity, selectivity and performance index. Choline chloride(ChCl)-based DESs with betaine (Be), triethylene glycol (TEG), levulinic acid (LevA) and oxalic acid (OA) were identified as promising candidates. The selected DESs were synthesised, characterized, and subsequently incorporated as additive in water for microwave-assisted extraction and ultrasonic-assisted extraction (UAE). Response surface methodology was used to determine optimal extraction conditions, and kinetic modelling was conducted to describe mass transfer behaviour. Experimentally, ChCl:TEG (1:1) produced the highest total anthocyanin content (TAC) of 73.54 mg CGE/L at a solid-to-solvent ratio of 1:15. Under UAE conditions, 5% DESs with a particle size of 750 µm yielded 96.83 mg CGE/L. Optimization identified 5% DESs, 60% amplitude, and 19.87 min as the best operating conditions, resulting in 100.48 CGE/L TAC with an AARD of 3.82%. Kinetic evaluation showed that the Modified Fick’s Law provided the best fit (AARD 3.03%), with the kw coefficient ranged from 0.0554 to 0.2600 min-1 while the kd coefficient ranged from 0.0002 to 0.1938 min-1, indicating washing dominance at 5% DESs with 60% amplitude and enhanced diffusion at 20% DESs and 40% amplitude. This work demonstrates that using DESs as additives rather than the main solvents, together with optimized UAE, can enhance selectivity towards standardized Dp3-sam while reducing hazardous solvents dependence and extraction time. The findings contribute a greener extraction strategy that is scientifically justified, technically scalable, and relevant for the development of stable, standardized roselle-based extracts that support safer food, nutraceutical, and colorant applications.