Investigation into the acidic protein fraction of bovine whey and its effect on bone cells : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Chemistry at Massey University, New Zealand
Milk is provided to new borns as their first food source and it contains essential
nutrients, vitamins and other beneficial components, such as enzymes and antibodies
that are required for rapid growth and development of the new born and for sustained
growth over time.
Milk contains two main types of proteins; casein proteins and whey proteins. Although
casein proteins account for up to 80% of the proteins found in bovine milk, it is the
whey protein that has become of high interest because of its bioactive content.
Whey, a very watery mixture of lactose, proteins, minerals and trace amounts of fat, is
formed from milk when the milk is coagulated and/or the casein proteins are removed
from the milk.
Bovine whey protein, including both the acidic and basic fractions (low and high
isoelectric point, respectively), has previously been studied in vitro (cell based) and in
vivo (using rats) for its impact on bone to determine if it can help improve bone mineral
density and help reduce the risk of developing bone diseases, such as osteoporosis.
Bone is constantly undergoing a remodelling process of being dissolved and reformed
and the two main cell types responsible for this bone remodelling process are mature
osteoclasts, which dissolve (resorb) bone, and osteoblasts, which reform the bone.
Prior work has shown that acidic protein fractions derived from different sources of
whey protein concentrate (WPC) have both in vivo and in vitro activity on bone,
particularly anti-resorptive properties. However, the component(s) which confer
activity have not yet been identified. In this thesis, work was undertaken to better
understand the analytical composition of three types of WPC (cheese, mineral acid and
lactic acid) and their associated acidic protein fractions and relate this to bone activity
in the hope of identifying where the activity lies. Bone activity was assessed using in
vitro screening with osteoblast cells (MC3T3-E1) and osteoclast cells (RAW 264.7).
Comparison of the cell-based bone activity of the parent WPCs and corresponding
acidic fractions indicated that the acidic fractions derived from both mineral acid and
lactic WPC were superior in their ability to inhibit osteoclast development. Although
compositional data was complex and definitive correlations with both bone
bioactivities could not be made, it appeared that elements common to both the acidic
fractions were a higher proportion of GLYCAM-1 and bone sialoprotein-1
(osteopontin). Further studies to more closely investigate the bone bioactivity of the
acidic fractions are warranted.