Investigation of functional properties of sugar beet (beta vulgaris) leaf extract

Food proteins constitute the main source of amino acids needed by the body and are obtained from both plant and animal sources. While the increasing world population is increasing the need for new sustainable protein sources, plant sources stand out with their low cost, accessibility, and nutritional value. Sugar beet (Beta vulgaris L. ssp. vulgaris) is a raw material whose root is utilized in sugar production, while the leaves are mostly left as feed or waste. Considering that protein constitutes the second largest fraction in dry matter, this study aimed to investigate protein extraction from sugar beet leaves using different methods and their biofunctional properties. Three precipitation methods (heat, isoelectric point, ammonium sulfate) and eight ultrasound-assisted enzymatic protocols (Conditions 1–8) were applied for protein extraction. Ultrasound treatments were conducted at 60% amplitude in batch mode for 20 min; in some protocols, Viscozyme®, pectinase, and cellulysin enzymes were used. Total/soluble protein, total phenolic substance, antioxidant capacities (DPPH, ABTS) and enzyme inhibition activities (ACE, α-amylase, lipase) were determined in the obtained extracts. Among the precipitation methods, PF2 (isoelectric precipitation) gave the highest total protein content, while PF1 (heat precipitation–supernatant) showed the highest soluble protein, phenolic content and antioxidant capacity; lipase inhibition was also found to be the highest in PF1. ACE and α-amylase inhibition could not be detected. Ultrasound-assisted enzymatic protocols provided higher yields compared to precipitation. Application of ultrasound before the enzyme (pre-ultrasound) significantly increased the extraction yield (p<0.05). Indeed, the highest values were reached with 16.47% protein content and 67.23% yield in Condition 3; 12.63% and 51.54% in Condition 5; In Condition 7, 15.90% and 63.71% were obtained. Furthermore, performing enzyme inactivation after centrifugation (e.g., Condition 5) increased the total yield while preserving protein solubility. The results demonstrate that sugar beet leaves are a suitable raw material for functional proteins, and the ultrasound-enzyme combination, in particular, offers an efficient and sustainable extraction approach applicable on an industrial scale.