Green optimization of microwave and ultrasound-assisted extraction of zeaxanthin from dehydrated goji berries using corn oil as a solvent

This research aimed to investigate and compare the extraction of zeaxanthin from lyophilised goji berries using ultrasonic-assisted extraction (UAE) and microwave-assisted extraction (MAE), employing food-grade corn oil as a green solvent. Optimisation of both processes was carried out using Response Surface Methodology (RSM). The selected combinations of variables studied were the ultrasonic amplitude and treatment time for UAE and microwave power and treatment time for MAE. The zeaxanthin-enriched corn oils and the commercial corn oil were characterised for carotenoids content, colour and oxidative stability. The highest extraction yields were obtained for UAE (68 %; 151.8 mg zeaxanthin/kg oil), while for MAE (54.5 %; 116.88 ± 1.77 mg zeaxanthin/kg oil). Both extraction methods result in enriched oils with darker, deeper, and more vivid orange colours than the original corn oil, with oxidation stability like that of the no enriched corn oil. In terms of environmental impact, MAE had lower energy consumption and CO₂ emissions than UAE, but the latter achieved the highest oil enrichment.

Compared to conventional organic solvent-based methods, the proposed solvent-free approach using edible oil minimizes toxicity, eliminates the need for post-extraction solvent removal, and allows direct application of the enriched product in food systems. Although the extraction condition providing maximum yield was not the greenest, MAE represented a more sustainable alternative. These findings highlight the need to balance extraction efficiency and environmental impact when designing green extraction processes. The resulting zeaxanthin-enriched corn oil could be used as a functional ingredient and natural colourant for the food industry.