Bioavailability digestion procedure

Experiments were conducted to determine if varying the conditions in the in vitro digestion procedure would affect post-digestion calcium solubility and in some cases, exchangeability. This was done with two purposes to test the use of the in vitro digestion procedure for studying factors which might influence calcium bioavailability and to use the results to modify the standard procedure. 

Choice of Potential Bioavailability Criterion. It is usually assumed that calcium must be soluble and probably ionized in order to be available for absorption ( ). For the in vitro procedure, as a first approximation we chose calcium solubility after centrifugation at 18,000 x g as the measure of potential bioavailability (Figure 1). We assumed that this would probably overestimate the available calcium and later work based on fractionation might define the bioavailable calcium more precisely. The data in Table IV illustrate how the choice of criterion for "solubility" could affect the in vitro estimate of potential availability, even if in vitro conditions closely resembled in vivo conditions. Since our in vitro criterion unexpectedly underestimated calcium bioavailability for two of the three foods in the direct in vivo - in vitro comparison (8), it was necessary to determine the in vitro digestion conditions which might be limiting solubility before addressing the choice of appropriate criterion. 

Experimental Procedures. Nutrient bioavailability is a complex subject when applied to protein components. In fact, it is an error to speak of the bioavailability of the protein rather one must consider the availability of the individual amino acids which make up the protein. Amino acid availability implies sufficient digestion of the protein in the intestines to allow absorption into the tissue. Then, in the case where... 

A number of operational procedures are available to determine potentially mobilizable species in solids. These involve the extraction of samples with acid, alkali, or a complexing agent. With respect to metal bioavailability, a more useful extraction is to use either cold 1 mol 1 hydrochloric acid or 0.5 mol 1 ethyl-enediaminetetraacetic acid, on the basis that this will not react with the more intractable phases. The measured values probably exceed that which might be released by at the lowest gut pH of any organisms, but it is at least an improvement on total metal measurements. Various enzyme cocktail mixtures have also been used to mimic metal mobilization in the digestive tracts of organisms. 

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