Effect of Enzyme-Assisted Extraction on Protein Yield and Purity of Duckweed Proteins

Abstract

Duckweed is an aquatic plant rich in proteins and other valuable nutrients, making it a promising sustainable alternative protein source. Its rapid growth, low environmental footprint, and minimal re source requirements have attracted increasing interest for protein recovery and valorization. However, alkaline extraction of duckweed proteins is often limited by low extraction efficiency and insufficient protein isolate purity. Therefore, the aim of this study was to evaluate the effect of ultrasound-assisted enzymatic pretreatment on the yield and purity of protein isolates obtained from duckweed biomass. Dried duckweed biomass, which had been pretreated with ethanol (70%) to reduce phenolic com pounds, was used for protein extraction. The control sample was subjected to the same processing conditions as the enzyme-assisted treatments, including ultrasound pretreatment and incubation at pH 4.5 and 35 °C for 2 h, but without enzyme addition. In the enzyme-assisted treatments, ultrasound pretreatment was combined with Viscozyme® and pectinase from Aspergillus aculeatus at enzyme concentrations of 3% and 5% v/w, calculated based on dry biomass weight. After pretreatment, alkaline extraction was performed at pH 11 for 2 h, followed by protein precipitation at pH 4.5. The control sample showed the highest precipitation yield of 9.3%, but the lowest protein purity of 25%. The addition of 3% enzyme mixture reduced the precipitation yield to 6.4%, while increasing protein purity to 43.3%. Treatment with 5% enzyme mixture resulted in a slightly higher yield of 7.58%, with a protein purity of 40.6%. Although enzyme-assisted extraction did not increase the overall precipitation yield compared with the control, it markedly improved the protein purity of the isolates. These findings indicate that enzymatic pretreatment with Viscozyme® and pectinase from Aspergillus aculeatus can improve the quality of duckweed protein isolates by increasing protein purity, despite a moderate reduction in yield. Among the tested treatments, the 3% enzyme concentration provided the highest protein purity, whereas the 5% treatment offered a slightly better balance between yield and purity.