Calcium absorption: Enhancing and inhibiting food components
Abstract
The effect of the presence of food and food components, including lignin, inositol phosphates, milk proteins, and kale on calcium absorption in rats was studied by femur uptake of 45Ca. Generally, the single test meals contained 25 mg Ca as calcium ascorbate and 6 μCi 45 Ca plus either water as a control or various test substances. Lignin was isolated from kale and wheat bran by enzymatic or acidic treatment. Calcium absorption in the presence of the isolated lignins, commercial pine lignin, or original wheat bran was studied. The test meals contained 30 mg lignin or 0.5 g wheat bran. Wheat bran showed an inhibitory effect on calcium absorption. No inhibitory effect was found among the various lignin sources. Thus, lignin is unlikely to be the inhibitory constituent to calcium absorption in plant foods. Inositol phosphates (InsPs) were prepared by an enzymatic method and separated by ion-chromatography. Calcium absorption in the presence of phytic acid, inositol tetraphosphate (Ins(1,2,3,6)P4, Ins(1,2,5,6)P5), or inositol pentophosphate (Ins(1,2,3,5,6)P5) was studied. It was found that the inhibitory effect of phytate and the enhancing effect of Ins(1,2,3,6)P 4 on calcium absorption were dose-related. No difference was found in calcium absorption between Ins(1,2,5,6)P5 or Ins(1,2,3,5,6)P 5 and the control. Thus, these inositol phosphates with no-inhibitory or even an enhancing effect as a result of dephosphorylation of phytate have important implications in processed foods. Bovine casein and whey proteins were prepared by ultracentrifugation and ultrafiltration. Calcium absorption in the presence of the casein, whey, and commercial α-lactalbumin at two calcium:protein ratios were studied. Casein was not inhibitory to calcium absorption. The strong enhancing effect of concentrated whey proteins or α-lactalbumin was dose-related. Therefore, whey proteins and/or α-lactalbumin have a great potential as an enhancer for calcium absorption. Kale sap was found to have an enhancing effect on calcium absorption. Amino acids, sugars, and organic acids found in kale were not responsible for the enhancing effect of kale. The enhancing effect of kale sap was reduced significantly by cooking or dehydration. Thus, the potential calcium enhancer appears to be as a labile compound.
Degree
Ph.D.
Advisors
Weaver, Purdue University.
Subject Area
Food science
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