Sustainable biorefinery strategies for coffee processing residues: multi-stream valorization, cross-domain applications, and system-level assessment

Apple pomace, the leftover from juice and cider making, is 25–30% of the fruit's mass—and it's packed with polyphenols worth saving. But the way we dry it could make or break those precious compounds.

Every glass of apple juice leaves behind a mountain of pomace—25–30% of the fruit's fresh weight, loaded with fiber, vitamins, and polyphenols. The challenge? Keeping those bioactive compounds intact while drying the by-product for storage. This study put two drying methods head-to-head: hot-air convection (CA) and infrared (IR). Both changed the color and polyphenol content, with higher temperatures showing a notable effect, likely due to partial inactivation of browning enzymes. But IR had a clear edge: shorter drying time and lower energy use. The next step was choosing the right solvent for ultrasound-assisted extraction (UAE). Here, a natural deep eutectic solvent (NaDES) made of choline chloride and glycerol (1:1) outperformed conventional solvents and other NaDESs, recovering more phenolic compounds with high antioxidant activity. Optimizing the UAE conditions with this polyol-based NaDES yielded an extract rich in flavan-3-ols (catechin, epigallocatechin) and phenolic acids like chlorogenic acid. The takeaway: apple pomace is a treasure trove of bioactives, and polyol-based NaDESs offer a green, efficient route to unlock them.

Key Points

• Apple pomace is 25–30% of fruit mass, rich in polyphenols.
• Infrared drying beats hot-air: faster, lower energy.
• Choline chloride-glycerol NaDES boosts phenolic recovery.