This study was designed to determine whether dietary protein is a nutritional factor influencing the bioavailability of dietary fluoride. To accomplish this, a factorial experiment was conducted with weanling rats fed a purified diet to determine the influence of dietary protein type (casein or lactalbumin) and level (12% or 36%) on fluoride bioavailability. Dietary fluoride in each case was 2 or 10 ppm supplied as sodium fluoride. After four weeks, fluoride retention was significantly reduced (P < 0.001) in rats fed high protein diets at 2 ppm fluoride, which was reflected in decreased femur and tibia fluoride concentration. A significant reduction in total femur fluoride content was observed only for rats fed diets containing 36% casein and 10 ppm fluoride. Results for molar fluoride content were less reliable than either femur or tibia in this regard. This protein-induced reduction of fluoride retention was observed despite the fact that apparent fluoride absorption was enhanced in all groups fed high protein diets (P < 0.001). Urinary excretion of fluoride was significantly increased in all rats fed high protein diets, thus accounting for the observed reduction in skeletal fluoride uptake. Significantly greater (P < 0.001) body weights were observed among rats fed high levels of protein than among rats fed normal protein diets, despite the fact that food intake for all treatment groups was adequate and similar. No consistent effect on skeletal or molar fluoride uptake due to protein type was evident under the conditions of this study. Although this study was not designed to investigate the mechanism involved in decreased fluoride retention with high protein diets, increased urinary fluoride excretion may be due to increased glomerular filtration rate coupled with decreased renal tubular fluoride reabsorption. Therefore, the results of this study demonstrate that, in the rat, a threefold increase in dietary protein level negatively influences fluoride bioavailability by promoting increased urinary fluoride excretion thus reducing fluoride available for incorporation into bones and teeth. These results suggest that excess dietary protein consumption common in the U.S. combined with marginal fluoride intake may adversely affect fluoride bioavailability in humans. This could reduce the fluoride content of teeth and bones, which may decrease resistance to dental caries and compromise skeletal integrity. / Graduation date: 1987

A study was completed to determine the extent of the protein changes occurring in ground beef stored at 2°C for 10 days. Sections of semitendinosus muscle were obtained immediately after the slaughter of three beef animals. Each section was divided into two equal portions, one of which was ground and the other remained intact (control). All samples were handled and stored under aseptic conditions. Grinding markedly accelerated glycolysis as manifested by the rapid pH decline in the ground samples during the initial 24 hours of postmortem storage. After this storage interval, however, there was little difference in pH values between the ground and intact samples. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was employed to monitor changes in myofibrillar and sarcoplasmic proteins extracted from at-death muscles and samples stored for 1, 3, 6, and 10 days at 2°C. The gels were examined visually and scanned densitometrically to detect protein changes. The principal electrophoretic changes in myofibrillar proteins of the ground samples were the gradual disappearance of nebulin and desmin components and the gradual appearance of 110,000-, 95,000-, and 30,000-dalton polypeptides. In addition, there was a progressive increase in the content of a protein around 55,000 daltons and myosin light chain-3. Intact muscles showed similar changes to those of the ground samples except that the latter had a faster initial rate in some of the changes, notably the disappearance of nebulin and the appearance of the 30,000-dalton polypeptide. It seems probable that grinding caused an early release of Ca⁺⁺ from the sarcoplasmic reticulum, which activated the Ca⁺⁺-activated proteinase (CAF). Electrophoretic changes in sarcoplasmic proteins of the ground samples closely resembled those of the intact muscles. The major alterations in both muscle treatments included the gradual appearance of a 100,000-dalton polypeptide and three proteins having molecular weights (M.W.) between 500,000 and 1,000,000 daltons, and the progressive disappearance of 300,000- and 24,000-dalton proteins. The appearance of a 100,000-dalton polypeptide and the three large M.W. proteins presumably originated from myofibrils since they appeared to be related to the changes in myofibrillar proteins. Results of microbial testing indicated very little, if any, sample contamination by psychrotrophic microorganisms. Thus, microbial proteolysis was not a factor in this study. It was concluded that grinding had no pronounced effect on the protein changes of beef muscle other than changes in pH. / Graduation date: 1985

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