Evaluation of dissolved organic carbon (DOC) as a measure of cell wall degradation during enzymatic treatment of microalgae

The feasibility of using Dissolved Organic Carbon (DOC) measurements as a means to assess the efficacy of an enzyme-assisted pretreatment on the recovery of lipids from microalgae was investigated. Attention was focused on Nannochloropsis sp., a marine microalga of great biotechnological interest for its ability to accumulate large amounts of lipids and other valuable compounds. The enzymatic pretreatment was carried out using two commercial enzyme preparations, one (CEL) rich in cellulase and the other (GMA) rich in galactomannase. Experiments were performed according to a fractional two-level factorial design. The factors studied were temperature (15–75 °C), pH (2–8), pretreatment time (30–270 min), CEL dosage (0–20mg/g) and GMA dosage (0–2 mg/g). DOC was determined by a TOC analyzer and used as the response variable. Under the experimental design conditions, temperature, pH, pretreatment time and CEL dosage were found to be statistically significant (p < 0.05), with the former factor being the most influential. No significant interactions were observed between the main factors, indicating that each of them exerted its effect independently of the others. A good correlation was also found between the measured DOC values and the yields of lipid extraction from the enzymatically treated biomass, demonstrating that DOC measurements can be used to quantify the enzyme-induced degradation of algal cell walls.