Speeding up enzymatic hydrolysis procedures for the multi-element determination in edible seaweed Original Research Article

A novel accelerated enzymatic hydrolysis by mean of ultrasonication has been developed and applied as sample pre-treatment for edible seaweed in order to determine total levels of As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn. Three enzymes, α-amylase, pepsin and trypsin, have been evaluated and the released metals from seaweed have been measured by inductively coupled plasma–optical emission spectrometry (ICP–OES). Variables such as pH, sonication temperature, ultrasound frequency, ionic strength, hydrolysis time, extracting volume and enzyme mass were simultaneously studied by a Plackett–Burman design (PBD). Results have showed that there had not been any significant variable (confidence interval of 95%) affecting the conventional or the ultrasound-assisted enzymatic hydrolysis processes. This fact is attributed to the high salt content in seaweed, which generates a solution with a high ionic strength. The ultrasound-assisted enzymatic hydrolysis can be completed in 30 min when using an ultrasound frequency at 35 kHz. Quantitative recoveries were only reached when using pepsin, while recoveries close to 80% were obtained for the use of α-amylase and trypsin. The methods were validated by analyzing IAEA-140/TM, Fucus – Sea Plant Homogenate – and NIES-09, Sargasso, certified reference materials.