A LACK OF STANDARD METHODS FOR BIOACTIVE MILK PROTEINS

R S Roberts, P A Marshall and A W Scammell, NorthField Laboratories Pty Ltd, Adelaide, South Australia

IMMUNOGLOBULIN G IN BOVINE COLOSTRUM 

As the most dominant among the greatly increased bioactive milk proteins that distinguish bovine colostrum milk from commercial milk, Immunoglobulin G (IgG) has become the accepted marker to quantify the "quality level" of natural colostrum, its powder and its products.

Claims for the IgG content of Bovine Colostrum Powders now reaching the market vary from 8% to 45% by weight. Some claims are reasonable, but many are misleading - being over-estimated. This creates an unfair trading situation for those companies which are disadvantaged competitively by taking the trouble to ensure that their science is soundly based.

The level of whey protein in colostrum and in its products can be determined readily and accurately by the established nitrogen determinations that have been standardised and accepted for decades. IgG normally constitutes 65% - 75% of that whey protein. This was confirmed by an extensive survey of the literature on the major proteins found in colostrum, as determined by several methods.

Any claim that natural bovine colostrum or its powder contains IgG well in excess of this range clearly must be questioned.

In many results from several countries, the traditional radial immunodiffusion (R.I.D.) method used for immunoglobulins was found to over-estimate the IgG content of liquid and powdered colostrum.

The level of IgG generally equalled or exceeded the level of whey protein. No room was left for the other whey protein components!

At NorthField Laboratories, a much more accurate and precise method using immunoaffinity chromatography has replaced R.I.D.

The chromatography medium is based on a bioactive binding receptor, and denatured IgG is not measured.

After development and cross-checking in use with colleagues in Finland, and confirmation by capillary gel electrophoresis in the Netherlands, the method has proven itself to be convenient and reliable. A close variation of it is also being used in New Zealand.

The affinity chromatography method should undergo further inter-laboratory examination and be considered for industry-wide acceptance as the standard determination for IgG label claims within the rapidly growing international trade in bovine colostrum and its products.

The main need is an appropriate and accepted reference standard.