MILK WHEY-PROTEIN ENHANCES THE BONE BREAKING FORCE IN OVARIECTOMIZED RATS

We studied the effects of whey protein (WP) and fractionated WP (HWP; heat-stable WP, LWP; low M.W. WP, EWP; ethanol-precipitated WP) on cal cium and bone metabolism in ovariectomized (OVX) rats. Six-week-old fe male Sprague-Dawley rats were ovariectomized and fed a low-calcium die t (0.03% Ca, 0.3% P) for 4 weeks. The rats were divided into five grou ps, Cent, WP, HWP, LWP and EWP group, and were fed a Cent diet (20% ca sein, 0.3% Ca) or a diet (19% casein, 0.3% Ca) containing 1% WP, HWP, LWP or EWP for 4 weeks. There were no significant differences in the c alcium balance, serum calcium and calcitonin levels among the experime ntal groups. However, serum ALP activity of the HWP and EWP groups at 14 wks. were lower than that of the Cent group. The bone breaking stre ngth and energy of femur of the HWP, LWP and EWP groups were higher th an those of the Cent group. As for the amount of calcium, phosphorus, and magnesium in the femur, there were no significant differences amon g the experimental groups; however, the amounts of total amino acids i n the femur of the HWP, LWP and EWP groups were higher than that of th e Cent group. The amounts of proline and hydroxyproline (typical amino acids of collagen) in the femur of the HWP, LWP and EWP groups were a lso higher than those of the Cent group. These data indicate that milk WP contains active components that influence bone metabolism in OVX r ats by increasing in bone protein such as collagen and enhance the bon e breaking force (strength and energy). These results suggest that the active components are existed in heat stable, low M.W. and 30-70% eth anol-precipitated fraction, respectively. (C) 1997 Elsevier Science In c.