Enhancement of enzymatic digestion of Antarctic krill and successive extraction of selenium organic compounds by ultrasound treatment

In a previous work we described the isolation of selenium organic species from Antarctic krill after enzymatic hydrolysis. In this paper we present the results of the influence of ultrasonication on the enzymatic treatment and the successive isolation of selenomethionine. We showed that ultrasound-assisted enzymatic digestion leads to quantitative release of selenium in the soluble fraction and recovery of selenomethionine from the krill protein within a time 2 orders of magnitude shorter. The solubilised sample was analysed by size-exclusion chromatography and the selenomethionine content was quantified by high-performance liquid chromatography-inductively coupled plasma mass spectrometry. In total, 99% of the selenomethionine in the krill hydrolysate was recovered from the chromatographic fractions. It corresponds to 35% of the total selenium content in Antarctic krill. Monitoring by microscopy of the changes in the structure of the krill samples during ultrasonication suggested that the enhancement of the ultrasound-assisted enzymatic reaction was mainly due to decrease of mass transfer limitations. A reference experiment for ultrasound-assisted enzymatic digestion of cell-free protein in a homogeneous system does not exclude direct influence of the ultrasound energy on the enzyme-substrate interaction.