Enzyme-grafted nylon membranes for sequential filtration of Tetraselmis chui extract with enhanced protein recovery

Microalgae are considered a promising and sustainable source for valuable biomolecules such as proteins. Extraction of proteins from microalgae suspensions by membrane technology is still limited by fouling and inefficient recovery due to the complex mixture of biomolecules. In this work an enzyme-modified nylon microfiltration membrane was prepared to efficiently recover proteins from an extract of the microalgae Tetraselmis chui using a simple sequential filtration setup. A mixture of hydrolytic enzymes, trypsin and a lipase, was successfully grafted onto flat-sheet membranes using an electron beam-based approach. It was shown that for generating high lipase activity, co-immobilization with trypsin or another protein is beneficial. A design of experiments approach was used to determine the effect size of selected parameters for the sequential filtration process. Derived empirical models were used for optimization and confirmed by experiments resulting in protein recovery within the filtrate of up to 1.4 g/L marking a significant increase compared to 0.8 g/L with the commercial reference membrane. Furthermore, up to 40 % of the total protein content from the microalgae dry matter could be recovered, compared to 24 % with the reference membrane. The sequential filtration was found to be advantageous compared to direct filtration allowing a combination of both enzymatic incubation and filtration. Various characterization methods were performed showing that the enzyme grafting layer reduces fouling.