Staff PhD

Mechanisms of selenium-mediated antioxidant effects in bovine milk and dairy products

Morten Rahr Clausen

Background

Selenium is an essential trace element for humans and animals. It is incorporated into a narrow range of critical enzymes and it plays a significant role in the immune system.

Se is specifically incorporated as selenocysteine into glutathione peroxidase (a major antioxidant enzyme of cells) and other Se-enzymes. Selenomethionine (Se-Met), in contrast, is incorporated non-specifically into proteins in place of its sulphur analogue, methionine.

Thus Se-Met may contribute distinct redox chemistry to proteins, since it is more easily oxidized compared to its sulphur analogue, and this may be important for the oxidative stability of milk.

In order to avoid selenium deficiency cows are currently supplemented with selenium in its inorganic form, as either selenite (IV) or selenate (VI). However, metabolism of inorganic selenium does not favour selenium bioavailability and transfer from diet into milk compared to organic selenium sources. Organic selenium can be provided by means of selenium yeast, where selenium primarily is present as selenomethionine.

Preliminary studies have shown that oxidation is altered in milk from cows supplemented with organic selenium, and if the increased content of seleno aminoacids in milk proteins is responsible for this, it must be due to altered catalytic properties of milk proteins, e.g. lactoperoxidase or significant changes in its substrates.

Aim

The aim of the project is to describe and characterize the antioxidant properties of selenium-supplemented milk.

Research Outline

The research will consist of descriptive and molecular mechanistic studies. The descriptive part will be focused on description of selenium concentration in milk as function of the amount of Se in the feed, formation of volatiles and oxidative stability of Se-milk.

The mechanistic studies will focus on isolation and identification of antioxidant species in Se-milk. This will be accomplished through chromatographic isolation and identification with MALDI-TOF MS analysis. Furthermore, a key-objective is to characterize lactoperoxidase through biochemical assays and identification of primary oxidation sites in this enzyme.