Digestion procedure

In the in vitro digestion method, the compound of interest is transferred from the food matrix to a bile salt micelle suspension that simulates the in vivo digestion process. This in vitro digestion procedure was first developed to estimate iron availability from meals and since then has been modified and applied to studying carotenoid bioaccessibility from various food matrices. This approach assesses the bioaccessibility of the compound from a certain meal before it is presented to and taken up by intestinal cells. 

One recent report involving the use of the in vitro digestion procedure noted that the micellarization of zeaxanthin from digested foods was dependent on its degree of esterification with transfer efficiency levels of 80, 44, and 11%, respectively, for the free form, monoesters, and diesters of zeaxanthin." In vivo studies" " ... 

Fig. 5.2 Chromatogram of the enzymatic digests of different types of insulin employed to demonstrate the suitability of the digestion procedure and the chromatographic system.

The analyst s requirements to digestion procedures are given in Table 8.3. 

Nagoumey and Madan [20] have considered both AAS and ICP-AES as reliable measurement techniques for the determination of metal components in mixed-metal/phosphite stabiliser systems in PVC. For reasons given elsewhere (Section 8.3.2.4), in this case ICP-AES was considered the technique of choice for most metal stabiliser determinations, while AAS remains a useful method to corroborate the ICP-AES results. For the determination of tin in rigid PVC by means of HG-AAS, the main effort has been to develop a sample digestion procedure [118]. Tin and Ti from a PVC potable... 

Table 8.22 shows some rubber analyses by FAAS after dry ashing. The concentration of Rh in polymers was measured by FAAS [128], The accuracy of 10-20% was in agreement with a dissolution procedure the precision obtained for direct solid analysis was between 10 and 20 %. Due to the relatively high analyte content of lead in paint, the determination is mostly performed by FAAS. Typical digestion procedures include dry ashing, wet and microwave digestion. 

For the proteolytic digestion procedure, dissolve pronase in water at a concentration of 1 percent (w/v). 

Selenium (IV) adsorbed as selenotrisulfate was then eluted from the column with either 0.1 M penicillamine or 0.1M cysteine. The eluate was then subjected to an acid digestion procedure to reduce selenium to the tetravalent state with diaminonaphthalene for fluorometric determination. Approximate agreement with the tellurium coprecipitation method was obtained. The application of both methods to the analysis of estuarine waters permitted the separate determination of both selenium (IV) and selenium (VI), since the tellurium coprecipitation methods did not differentiate between the two species. 

Thallium has been determined in 10 ml of ashed serum or in urine by extracting with sodium diethyldithiocarbamate into MIBK n°). More recently, Savory and co-workers 1131 described a wet digestion procedure for 50 ml of urine or 5 ml of serum in which the thallium is separated by extracting the bromide into ether, evaporating the ether and then taking up in dilute acid for aspiration. As little as 0.1 ppm is determined in urine. Curry et al.114) determined less than 1 ng of thallium in 200 /d of urine by using the tantalum sample boat technique. The sample in the boat is dried by holding the boat 1 cm from the flame and then it is inserted into the flame where it is vaporized. A similar procedure is used for >3 ng of thallium in 50-100/al of blood, except that the blood is preashed with 3 drops of nitric acid. Since the tantalum boat method is susceptible to interelement interferences, the method of standard additions is used for calibration. 

Methods for FLAA/ICP-AES and GFAA/ICP-MS require slightly different digestion procedures which must be followed [13],... 

Tamba, M. G., del M., Falciani, R., Lopez, T. D., and Coedo, A. G. (1994). One-step microwave digestion procedures for the determination of aluminium in steels and iron ores by inductively coupled plasma atomic emission spectrometry. Analyst 119 2081-2085. 

Evaluation and Potential Uses of an In Vitro Digestion Procedure... 

We have developed an in vitro digestion procedure, not as a substitute for in vivo studies, but as a useful adjunct. Our initial objective was to develop an in vitro procedure for measuring exchangeability, the fraction of the food mineral which exchanges with an extrinsic isotope tracer added to the food. This was expected to facilitate the measurement of food mineral absorption in humans by the extrinsic tag method. Secondary objectives were to determine if in vitro mineral solubility could be used to estimate potential... 

Figure 1. In vitro digestion procedure. (Reproduced with permission from Ref. 7. Copyright 1982 J. Nutr., American Institute of Nutrition.)...

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. 

The term "standard" is not meant to denote a digestion procedure which should be routinely used to determine potentially available calcium. Since the number of foods tested so far is limited, it will be more useful to think of the "standard" procedure as a set of conditions to be used to see how well we understand food chemistry and calcium solubility in the gastrointestinal environment. It should be used for measuring the relative solubility of calcium from foods and meals, but mostly in the context of comparisons with in vivo results to define factors which require further study. 

Fractionation of Digest Calcium. The in vitro digestion procedure provides a means of producing the starting material for a more detailed study of the calcium complexes in intestinal digests. This may be desirable in a number of situations ... 

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