FOOD SCIENCE
A2 or not A2? A cautionary tale in dairy (goat) science Words by Dr Martin Palmer, Dr Xu Li, Garrick Spencer, Dr Lydia Ong and Dr Sally Gras
O
ver the last 20 years, following the formation of the a2 Milk Company in New Zealand, the publication of “Devil in the Milk” and some very successful marketing campaigns, foods with compositional and/or nutritional claims relating to “A2 protein” or “A2 beta-casein protein”, now account for a significant share of the global market for bovine milk and dairy products (including infant formulae).1,2 Although there has been some controversy around the validity of some biochemical and nutritional studies that purport to indicate beneficial health effects of such products and/or undesirable effects of milk containing A1 beta-casein (A1 β-casein), there remains strong consumer interest in this category. More recently, the dairy goat industry has taken an interest in the β-casein content of caprine milk and
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milk products to better understand some apparently beneficial nutritional characteristics of goat’s milk and potentially to provide a stronger basis for health claims. Although there is some inconsistency in the scientific literature, it is generally accepted that the main protein in most commercial types of caprine milk is caprine β-casein, which has often been characterised as “A2” or “A2-like”, with reference to bovine β-casein.6 This, together with the reported absence of A1 β-casein in goat’s milk, has led many to equate caprine milk directly with A2 bovine milk biochemically and in relation to some nutritional and health claims. A Google search on “goat milk A2” reveals numerous examples of commercial, research and consumer advisory sites that make these assumptions. Our interest in this topic started
with some analytical work on locally sourced goat’s milk. This gave results on protein composition that were inconsistent with some scientific and commercial publications, in that the major proteins corresponded to caprine β-casein A and C, which differ in amino acid sequence to both bovine β-casein A1 and bovine β-casein A2.6,7 This led us to undertake a thorough review of recent advances in the science of both bovine and caprine β-caseins, to try and understand reasons for inconsistency in the scientific literature and possible implications for physiological functionality and health claims.6 The following is a summary of the main findings - please refer to the original review for a detailed analysis and discussion of this issue.6 The complexity of these protein families is shown in Figure 1, based on a compilation of data from both
