Microencapsulation of red onion (Allium cepa L.) extracts by spray and freeze drying: Chemical characterization and release behavior during in vitro digestion

Red onions ( Allium cepa L.) are rich in polyphenols, particularly quercetin. This study focused on the extraction, drying, and microencapsulation of red onion polyphenols via spray- and freeze-drying using maltodextrin (MD) and gum arabic (GA) as encapsulating agents. The extraction process was optimized using response surface methodology, with optimal conditions being 20°C, 15 min, and 60% ethanol, yielding 1716.43 ± 57.44 mg/kg total phenolics, 349.5 ± 21.06 mg/kg flavonoids, and 29.16 ± 1.11 mg/kg anthocyanins. The obtained extracts were spray-dried, achieving the highest bioactive content with a 1:1 MD:GA ratio at 170°C. Powdered extracts were microencapsulated using MD or MD:GA through both spray- and freeze-drying, and the resulting microcapsules were characterized to assess their physicochemical properties. Microencapsulated extracts retained over 90% of their bioactive content compared to the free extract and exhibited improved in vitro bioaccessibility of flavonoids, with notable resistance to degradation under simulated gastric conditions. Thermal stability tests confirmed that encapsulation significantly improved resistance to heat degradation, maintaining over 92% of polyphenols at 80°C for 1 hour. In vitro digestion studies further revealed a controlled release of flavonoids, with minimal degradation in the gastric phase and enhanced bioaccessibility in the intestinal phase. Spray-drying with an MD:GA ratio of 1:1 at 170°C was identified as the most effective and economical encapsulation method, suggesting its suitability for developing functional food formulations enriched with bioactive onion compounds.