Submitted to: Journal of Dairy Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/7/2007
Publication Date: 8/22/2007
Citation: Mora-Guitierrez, A., Farrell Jr, H.M., Attaie, R., Mcwhinney, V.J., Wang, C. 2007. Influence of bovine and caprine casein phosphopeptides differing in alpha s1-casein content in determining the absorption of calcium from bovine and caprine calcium-fortified milks in rats. Journal of Dairy Research. 74(3):356-366. Interpretive Summary: Milk and dairy products represent the chief source of calcium in the typical western diet. The major proteins of milk, called caseins, carry calcium in small packages called micelles. However, an interesting question arises with regard to calcium fortification of milks. Experiments on the comparison of goat’s and cow’s milk caseins showed that one genetic type of goat’s milk casein, regardless of breed, is much better at carrying calcium than that of other goat’s or cow’s milk. Milks with two types of calcium additives: calcium alone (+Ca) and calcium with a casein ‘booster peptide’ made from each milk (CaCP) were made from the high calcium carrying goat milk, a normal goat’s milk and normal cow’s milk. Feeding studies in rats showed that in all cases added calcium could be absorbed, but in the case of the CaCP the calcium was more readily taken up. Moreover the high calcium carrying goat milk with CaCP resulted in better calcium deposition in the bones of growing rats while +Ca normal goat and cow milks were about equal. So these genetically different goats produce caseins that can carry extra calcium and then this milk has the potential to produce stronger bones in the rats. This shows that manipulation of the casein types in milk can lead to stronger bones in animals. Extension of this information to human studies will aid cheese manufactures who are attempting to enhance the nutritional quality of their products. These studies could also lead to the improved nutritional value for milk proteins in all dairy products and possibly as ingredients in other foods.
Technical Abstract: Bovine and caprine milks have a similar overall gross composition, but vary considerably in the ratios of their casein components. These differences cause significant changes in the casein’s ability to bind and stabilize calcium (Ca). It might be expected that these in vitro variations, which are thought to be due to differences in casein phosphopeptides (CPP) content, could lead to in vivo differences in the digestion and absorption of Ca. To test this hypothesis three milks with different casein ratios [bovine, caprine high in alpha s1-casein (H) and caprine casein low in alpha s1-casein (L)] were compared with regard to Ca absorption and deposition in growing male rats. For comparison, each milk was Ca-fortified (bovine Ca-milk, caprine Ca-milk H, and caprine Ca-milk L) and CPP, prepared by enzymatic hydrolysis from the respective caseins (extrinsic CPP), were added. The effects of added CPP (extrinsic) could then be compared with intrinsic CPP released from the gastrointestinal digestion of caseins. Total gastric Ca was sampled at 15, 30 and 60 minutes after ingestion. No differences were found among the bovine, caprine H, and caprine L native milks with or without CPP, but the Ca from all Ca-milks (regardless of casein type) appeared to clear the stomach more rapidly and this was enhanced by the extrinsic CPP. The total intestinal Ca was not different among the native milks ± CPP; it rose more rapidly with Ca fortification, and was higher at 30 minutes for all CPP-Ca-milks. At 60 minutes the total intestinal Ca level fell for the CPP-Ca-milks while all others continued to rise. These observations suggest that the CPP in Ca-milks enhance gastric clearance and uptake from the intestine. Ca availability from bovine Ca-milk, caprine Ca-milk H, and caprine Ca-milk L with and without CPP was estimated by femur uptake of 45Ca. Ca availability was enhanced in each case by added CPP. The increase in Ca availability caused by caprine CPP (L) was significantly (P <0.05) higher than that of either caprine CPP (H) or bovine CPP (extrinsic CPP). Based on the results of this study we can conclude that the addition of CPP will have beneficial effects on the absorption of Ca in growing rats from CaCO3 added to bovine, caprine H, and caprine L milks.