A Novel Method for Decolorization of Phenolic Extracts using UV-A LEDs: A Case Study on the Extracts of Sugar Beet Leaves

Green plants contain valuable bioactive compounds that offer health benefits to consumers. However, when these compounds are extracted, the green colour of the extracts may interfere with the analytical measurements and complicate the application of extracts in food systems. Since UV-A could break the chlorophylls into smaller compounds, this research was aimed at evaluating the effect of UV-A LEDs on the colour and bioactive compounds of the phenolic extracts of sugar beet leaves. After obtaining the extracts using an ultrasound-assisted extraction method, they were subjected to a UV-A exposure post-treatment using a prototypic UV-A illuminator with different voltages (10-20 V), durations (10-60 min) and LED numbers (9 and 30) at a 0.5-cm distance. Then, the colour, chlorophyll and carotenoid contents, antioxidant activity, soluble sugar concentration, and phenolic profile of the extracts were analysed before and after UV-A exposure. The yield of chlorophyll a in the extract exposed to 30 UV-A LEDs for 60-minute at 20 V decreased significantly from 256.46 ± 049 to 29.23 ± 2.12 μg/g, and the greenness parameter (-a* value) reduced from 27.33±0.32 to 8.64±0.16. UV-A increased the concentration of most phenolic compounds, glucose, and fructose simultaneously. Both treated and untreated extracts improved the oxidative stability of corn oil significantly. The antioxidant activity index of the obtained extracts was as high as butylated hydroxytoluene (BHT), which was used as a benchmark synthetic antioxidant. This research underscores the potential of UV-A post-treatment for facilitating the integration of phenolic extracts into colour-sensitive food applications, while preserving their bioactive integrity.