Subcritical water extraction of bioactive compounds from waste cotton (Gossypium hirsutum L.) flowers

Abstract The diversified utilization of cotton waste or by-product will bring great practical benefit for the development of agriculture. In this work, withered cotton flowers were indicated to contain an abundance of bioactive compounds including various flavonols and anthocyanins, as is demonstrated by a targeted metabolomics approach. Subcritical water extraction (SWE), an environmentally friendly technique, was then applied to collect bioactive compounds from the red discarded flowers. Response surface methodology (RSM) was employed to determine the optimal parameters to extract these bioactive components with hot water and ethanol. When the extraction temperature was 180 °C, the ethanol concentration was 65 % and the solid-liquid ratio was 65 mL/g, the total content of phenolics and flavonoids, as well as their antioxidant activity, was the best. In addition, the flavonoid compositions of SWE extracts were identified and quantified. The most abundant flavonoid was isoquercetrin, with its content of 110.54 mg/g. This study enables comprehensive utilization of the waste resources in the cotton planting process and provides a theoretical basis for a waste-to-profit solution.