Influence of Solvent and Ultrasound-Assisted Extraction on the UV Spectral Profiles of Extracts from Agro-Waste

This study investigates the influence of extraction method and solvent on the UV spectral characteristics of extracts obtained from selected agro-industrial waste materials. Conventional maceration and ultrasound-assisted extraction (UAE) were applied using distilled water and 70% (v/v) ethanol as solvents. The analyzed materials included spent coffee grounds, orange peel, rosehip, milk thistle, eucalyptus leaves, and chili pepper. UV spectrophotometric analysis (190–400 nm) was used to compare the absorption profiles of the obtained extracts and to evaluate the effect of extraction conditions on spectral features. The results showed that both solvent type and extraction technique significantly influenced the intensity and shape of the absorption spectra. Ethanol generally resulted in higher absorbance values and more defined spectral features in the 250–350 nm region, while aqueous extracts exhibited stronger absorption in the lower UV range. Overall, UV spectroscopy proved to be a rapid and effective screening tool for evaluating extraction performance and comparing spectral characteristics of complex plant extracts, supporting the valorization of agro-industrial waste. Total phenolic content (TPC) was additionally determined to support the evaluation of extraction efficiency.