Isolation of Organic Selenium Compounds from Antarctic Krill after Enzymatic Hydrolysis and Bifunctional Chromatography

Publication date
2007
Document type
PhD thesis (dissertation)
Author
Siwek, Mariana
Advisor
Niemeyer, Bernd
Referee
Kasche, Volker
Granting institution
Helmut-Schmidt-Universität / Universität der Bundeswehr Hamburg
Exam date
2007-12-07
Organisational unit
DDC Class
620 Ingenieurwissenschaften
Keyword
Antarctic Krill
Euphausia superba
Bifunctional Chromatography
Oasis MCX
Selenomethionine
Abstract
This work focuses on the extraction of organic selenium compounds (selenomethionine, Se-Met) from Antarctic Krill and on the adsorption studies with several adsorbents. Various extraction methods such as ultrasound supported digestion were employed for the separation of Se-Met from krill samples. A novel procedure for the determination of Se-Met with bifunctional chromatography is provided. --- Selenium is a trace element with recognized nutritional essentiality for human health. High bioavailability of the selenium species encountered in marine products makes the qualitative and quantitative determination and the isolation of organic selenium compounds such as Se-Met a challenging subject. Antarctic krill (Euphausia superba) is a small crustacean living in the ecosystem of the Antarctic region of the Southern Ocean and is regarded as one of the most important protein sources of the future, because of its low cholesterol level and the high levels of essential amino acids and of polyunsaturated fatty acids. --- For the isolation of organic selenium compounds from Antarctic krill, analytical methods such as aqueous extraction, enzymatic digestion and ultrasound assisted enzymatic hydrolysis were employed. Among these, the enzymatic treatment with pronase E led to quantitative selenium recovery. The enzymatic krill hydrolysate was further subjected to size exclusion chromatography and the analysis of collected chromatographic fractions demonstrated that the majority of the selenium species have a molecular weight under 600 Da. The release of low molecular weight species was also achieved by combining ultrasound and enzymatic hydrolysis. The simultaneous treatment led to a significant reduction of digestion time and an increase in sample handling easiness. --- The krill fractions collected after size exclusion chromatography were further subjected to bifunctional chromatography. For this purpose, several adsorbent materials were investigated on their ability to adsorb Se-Met. The influence of parameters such as adsorption time, pH and temperature conditions was considered. Oasis MCX, a mixed mode cation exchanger from Waters GmbH, was selected for bifunctional chromatography. A chromatographic column packed with the Oasis MCX material was employed for the adsorption studies with Se-Met standards and krill samples. Good recovery and simple determination of Se-Met were achieved. Furthermore, the employment of the Oasis MCX packed column did not show any performance diminution after multiple experiments and demonstrates the Oasis MCX potential for chromatography procedures, beyond its traditional application for sample preconcentrations in disposable columns and cartridges.
Version
Not applicable (or unknown)
Access right on openHSU
Open access