Green Extraction of Bioactive Compounds from Beetroot Pomace

Abstract

Beetroot (Beta vulgaris) pomace is one of the major by-products of the juice processing industry, is a rich source of betalains, phenolic compounds, and other bioactive constituents and yet it is often discarded as waste. The recovery of these compounds using environmentally friendly extraction techniques can contribute to sustainable waste utilization while providing natural ingredients for food applications. Therefore, the present study investigated green extraction methods for the recovery of bioactive compounds from dried beetroot pomace using enzymatic pretreatment, ultrasound-assisted extraction (UAE), and natural deep eutectic solvents (NADES). The study was carried out in three stages. Initially, the effects of individual cellulase and pectinase treatments on betalain extraction were evaluated. This was followed by identification of suitable ultrasonic conditions to analyze their influence on extraction efficiency; ultrasound was used as a pretreatment to NADES extraction. Subsequently, Choline chloride-based and betaine-based NADES were prepared and comparatively screened to identify a suitable food-compatible extraction solvent. The extracts obtained under different extraction conditions were evaluated for total betalain content (TBC), total phenolic content (TPC), and antioxidant activity using DPPH and FRAP assays. The results showed that enzymatic pretreatment and UAE did not significantly improve betalain recovery under the investigated conditions. In contrast, the extraction solvent had a pronounced effect on the recovery of bioactive compounds. However, some variations were observed among the NADES formulations which demonstrate the importance of solvent composition in extraction efficiency. Among the solvents evaluated, the selected betaine-based BFG NADES exhibited the highest overall extraction performance, recovering greater amounts of betalains and phenolic compounds while also producing superior antioxidant activity compared with choline chloride-based NADES and water. Under the optimized conditions, the BFG solvent achieved a total betalain content of 250.1 ± 3.8 mg/100g dry weight, total phenolic content of 574.3 ± 1.6 mg GAE/100g dry weight, DPPH radical scavenging activity of 62.59 ± 4.55 %, and a FRAP value of 70.08 ± 2.71 µmol Fe²⁺ equivalent/g dry weight. Overall, this study supports environmental sustainability in two ways. First, it demonstrates the valorization of beetroot pomace by converting agro-industrial waste into a valuable source of natural pigments and antioxidant compounds. Second, it shows that betaine-based natural deep eutectic solvents are an efficient, food-compatible, and environmentally friendly alternative to conventional solvents for the extraction of these bioactive compounds. Together, these findings provide a sustainable approach for producing natural value-added ingredients from food processing waste.