Optimization of Phenolic Extracts of Sugar Beet Leaves with Minimal Chlorophyll Content using Response Surface Methodology (RSM) to Enhance the Oxidative Stability of Different Oils

Background: Sugar beet leaves (SBLs), as unexploited food by-products, are a potential source for polyphenol recovery. However, the presence of chlorophylls in the phenolic extracts of SBLs hinders utilizing them in food products, as they may act as prooxidants when exposed to light. This project aims to use phenolic extracts with minimal chlorophyll content, optimized through response surface methodology (RSM), to enhance the oxidative stability of different vegetable oils. Methods: The extracts were obtained from freeze-dried SBLs (Beta Vulgaris L., var. SMART DJERBA-KWS) using an ultrasound device (HD 2200.2, Bandelin, Berlin, Germany). A central composite design, using Design Expert software, was employed to set the extraction parameters, including solid-to-liquid ratio (SLR) (1-5% w/v), EtOH concentration (0-100%), amplitude (20-40%), and extraction time (2-10 min). In optimization through RSM, total phenolic content (TPC), total flavonoid content (TFC), and ferric-reducing antioxidant power (FRAP) were maximized, and chlorophylls yield was minimized. The phenolic profile and metal chelating activity of the optimized extract (OE) were analysed using HPLC, and spectrophotometric methods, respectively. OE was added to different vegetable oils, and their oxidative stability was monitored using the Rancimat method. Results: Optimized extraction parameters were EtOH 25%, 8 min time, 25% amplitude, and 4% w/v SLR, resulting in 11.49 ± 0.66 mmol GAE/L TPC, 2.09 ± 0.06 mmol QE/L TFC, 3.16 ± 0.25 mmol TE/L FRAP, and 0.05 ± 0.01 mg/g chlorophylls yield. Trans-ferulic acid had the highest quantity among other phenolic compounds. Cupric and ferrous chelation activity of 300 µM TPC of OE were 48.95 ± 1.06% and 66.18 ± 1.31%, respectively. OE significantly increased the oxidative stability of all the oils. Conclusions: This research proposes a green approach to utilize the by-products of sugar beet to obtain optimized natural extracts for increasing the shelf-life of lipid-containing food products. Keywords: Ultrasonic-assisted extraction, Polyphenols, Lipid oxidation.