We previously prepared a new oyster extract (NWZ) from a mixture (WZ) of a hot water extract and a zinc-rich fraction obtained from oysters. In the present study, the availability of NWZ was investigated in comparison with WZ and zinc sulfate. Serum zinc concentration after a single oral zinc administration in rats was examined. Prior to the start of the experiment, ten-week-old male Wistar rats were given a zinc-deficient diet for 6 days. The rats were orally administered zinc-deficient diet suspension or one of three experimental diet suspensions containing two types of oyster extracts (NWZ and WZ) or zinc sulfate. A blood sample was taken from the caudal vein before and 1, 2 and 4 hours after the oral administration. Two hours after administration, rats that received the diet suspension containing zinc as NWZ or WZ showed a higher serum zinc concentration than those administered the diet suspension containing zinc as zinc sulfate. The area under the curve at 4 hours (AUC4) calculated from the serum zinc concentration after oral administration of NWZ was larger than that of those administered WZ or zinc sulfate. It is possible that zinc in NWZ is more absorbable in the gastrointestinal tract than the zinc in WZ or zinc sulfate. The effects of differences in zinc source on the absorption and tissue distribution of zinc were examined in rats fed a diet containing various concentrations of sodium phytate. Five -week-old male Wistar rats were given 0, 0.2 or 0.5 % sodium phytate-supplemented diets containing 20 ppm of zinc as NWZ or zinc sulfate for 29 days. The rats fed a diet higher in sodium phytate showed lower tissue zinc concentrations in the liver, kidney and tibia. The zinc concentrations in those tissues responded to a decrease in dietary sodium phytate. Differences in dietary zinc source (NWZ or zinc sulfate) did not significantly influence zinc concentrations in serum or various other tissues in rats receiving equal sodium phytate concentrations. The regression line between sodium phytate in the diet and tibial zinc concentration, the slope was obviously more gradual for rats receiving a diet containing zinc as NWZ than in those receiving zinc sulfate. It is possible that the zinc in NWZ is more resistant to the influence of sodium phytate. Zinc solubility was evaluated by pepsin-trypsin digestion in vitro . Zinc in NWZ diet showed higher solubility than WZ or zinc sulfate diet in pepsin-trypsin digestion. Therefore, zinc in NWZ showed higher absorbability from the gastrointestinal tract than WZ or zinc sulfate. These findings suggest that NWZ has higher zinc bioavailability than WZ or zinc sulfate.
