Lihua Shen

Interlaboratory trial on the determination of the In Vitro iron dialysability from food

An in vitro method for the estimation of iron bioavailability was subjected to an interlaboratory trial. The method involved a simulated gastrointestinal digestion using pepsin for the gastric stage followed by pancreatin and bile salts for the intestinal stage. The proportion of iron diffused through a semipermeable membrane (molecular mass cut-off 10 kDa) was used to measure the iron dialysability. An interlaboratory trial between nine laboratories was conducted to evaluate the repeatability and reproducibility of the agreed method. The reproducibility of the method among the participating laboratories was 20-30% and depended on the content of dialysable iron. Several factors contributing to the variation in the in vitro dialysability among laboratories are discussed. The pH adjustment in the intestinal digestion was identified as one of the critical parameters. The present in vitro method was used to evaluate the iron dialysability from three meals. The dialysability data were in reasonable agreement with human absorption data. The usefulness of the in vitro dialysability method is discussed.

Modification of an in-vitro method for estimating the bioavailability of zinc and calcium from foods

ZusammenfassungEine continuous-flow-Methode zur in-vitro-Bestimmung der Bioverfügbarkeit von Mineralien und Spurenelementen wurde verbessert. Die Proben werden mit Pepsin in einer Dialysezelle verdaut, der pH-Wert dabei graduell verändert und bei der nachfolgenden Verdauung mit Pankreas-Galle-Extrakt die freigesetzten Mineralstoffe kontinuierlich durch Dialyse abgezogen. Der dialysierbare Anteil gilt als Maß für die Bioverfügbarkeit. Ein Vergleich der so erhaltenen Daten für Zink und Calcium aus Milch- und Soja-Formulanahrung zeigt gute Übereinstimmung mit in-vivo-Messungen. Die Methode dürfte sich zur Vorhersage der Bioverfügbarkeit für Mineralstoffe eignen.AbstractA continuous flow in-vitro method for estimating the bioavailability of minerals and trace elements was modified. This modified method includes a simulated gastric digestion with pepsin, gradual pH change during the first 30 min of dialysis in an Amicon stirred cell, and a further 2 h of continuous dialysis accompanied by intestinal digestion with pancreatin-bile extract. The percentage of continuously dialysed minerals or trace elements (dialysability) is used to express the bioavailability. Comparison of different in-vitro methods by using the dialysability of zinc and calcium from milk- and soy-based formula samples revealed that with the modified method the results are closer to the in-vivo situation and could be used as a relative index for predicting the bioavailability of some minerals and trace elements.

Estimation of the bioavailability of zinc and calcium from human, cow's, goat, and sheep milk by an in vitro method.

The availability of zinc and calcium from human, cows, goat, and sheep milk is evaluated by an in vitro method that involves a simulated human gastrointestinal digestion followed by measurement of dialyzability of zinc and calcium. Zinc availability of milk showed the highest value for human milk (15.0%) and the lowest for sheep milk (1.0%), in both whole and skim milk. Calcium availability of the different types of milk did not differ significantly and ranged between 18 and 23%. No significant differences in availability between whole and skim milk were found for both elements, except for zinc in cows milk.

Selenium content of goat milk and its distribution in protein fractions

ZusammenfassungDie vorliegenden Studien wurden unternommen, um die Selen-Verteilung in Kuhmilch zu charakterisieren. Magermilch enthält 93% des gesamten Selens der Milch. Ungeachtet der Trennungstechnik ist das Selen der Magermilch in der Hauptsache in der Casein-Fraktion (>55%). Ungefähr 10% bzw. 25% bzw. 10% des Selens wurden aus Magermilch bzw. Molke bzw. Casein durch Dialyse entfernt (molekulare Ausschaltung 10 kDa). Isolierung des Caseins und der Molkenproteine durch Ionenaustauschchromatographie bzw. Gelfiltration ließ die hauptsächliche Proteinbindung des Selens erkennen.κ-Casein wurde als das selenreichste Protein erkannt (550 ng/g). Der Selengehalt der anderen Caseine lag bei 153 bis 355 ng/g. Von allen Milchproteinen trug dasβ-Casein am stärksten zum gesamten Magermilch-Selen bei (33% des Gesamtselens). 17% des Selens der Magermilch war an den Molkenproteinen gebunden, und ihre Selen-Konzentration lag bei 130–270 ng/g.SummaryThe present studies were undertaken to characterize selenium distribution in cows milk. Skim milk was found to contain 93% of the total milk selenium. Irrespective of the separation technique used, skim milk selenium was mainly found to be associated with the casein fraction (>55%). Approximately 10%, 25% and 10% of selenium was removed from skim milk, whey and casein, respectively by dialysis (molecular cut-off of 10 kDa). Isolation of individual casein and whey proteins by ion-exchange chromatography and gel filtration revealed that selenium was mainly protein bound. κ-Casein was determined to be the protein richest in selenium (550 ng/g). The selenium content of the other caseins ranged from 153 ng/g to 355 ng/g. Of all the milk proteins,β-casein contributed most to the total skim milk selenium (33% of total Se). Seventeen percent of the total skim milk selenium was associated with whey proteins and their mean selenium concentration ranged from 130 to 270 ng/g.

Estimation of selenium bioavailability from human, cow's, goat and sheep milk by an in vitro method

The trace element selenium (Se) has been recognized to be essential for human health. The dependence of infants on milk as their principal food source, generally low in Se content, makes them more vulnerable to inadequate Se intake. The present study compared the Se availability as estimated by a simulated gastrointestinal digestion procedure, of human milk and some common ruminant milks, namely cow, goat and sheep milk. The Se availability of human milk (11.1%) was significantly higher compared to that of cow (6.8%), goat (6.2%) and sheep milk ( < 2%). Further study suggested that the Se availability may be related to the gastric digestibility of protein. The high Se availability of human milk might be attributed to the high gastric digestibility of human milk protein. It was found that removal of the milk fat fraction increases the Se availability.

Diffusibility of selenate, selenite, seleno-methionine, and seleno-cystine during simulated gastrointestinal digestion.

The present study was undertaken to evaluate the in vitro availability of chemically varying forms of selenium (Se), supplemented in cows milk. Two inorganic (selenite and selenate) and two organic (seleno-methionine [Se-Met] and seleno-cystine [Se-Cys]) Se sources were evaluated. The in vitro availability was estimated by the diffusibility of Se during simulated gastrointestinal digestion. First, the diffusibility was compared after adding a constant amount of Se as either selenate, selenite, seleno-methionine, or Se-Cys in milk samples. Se-Met and selenate were found to be significantly more diffusible than selenocystine and selenite under the simulated gastrointestinal conditions. The tendency for superior in vitro availability of selenate and Se-Met compared to selenite and Se-Cys was confirmed for a supplementation range of 5–40 ng/g of Se. This study suggests that the high diffusibility of selenate and Se-Met in a simulated gastrointestinal environment may contribute to their high absorption in vivo.

Evaluation of an in vitro method for the estimation of the selenium availability from cow's milk

ZusammenfassungDiese Studie bewertet die Anwendung eines In vitro Digestionsverfahrens für die Bestimmung der biologischen Verfügbarkeit von Selen in Kuhmilch. Danach ist nur eine kleine Portion (<10%) des Milchselens verfügbar. Die verfügbare Fraktion von Vollmilch (4,7%) war erheblich niedriger als die der Magermilch (7,3%). Die Untersuchung der Methode legt dar, daß der Anteil des totalen potentiellen verfügbaren Selens, bestimmt als das totale dialysierbare Selen, gleichzeitig zunimmt mit der Proteindigestierbarkeit während des Digestionsverfahrens. Hieraus kann geschlossen werden, daß die Protein-digestierbarkeit einen Einfluß auf die Verfügbarkeit des Selens in Milch haben kann.AbstractThe present study evaluates the application of an in vitro digestion procedure for estimating the selenium (Se) availability from cows milk. The results obtained by this in vitro method indicate that only a small portion (<10%) of milk Se can be estimated as available. The available fraction of whole milk (4.7%) was significantly lower compared to the Se availability of skim milk (7.3%). Investigations on the methodology of the in vitro method indicate that the portion of total potentially available Se, determined as total dialysable Se, increases simultaneously with protein digestibility along with the digestion process. Therefore it is concluded that protein digestibility might largely influence the Se availability from milk.

Selenium distribution in egg white proteins

ZusammenfassungDie vorliegenden Studien wurden vorgenommen, um die Selen-Verteilung in Eiweiß zu charakterisieren. Ionenaustauschchromatographie und Atomabsorptionspektrometrie wurden gebraucht, um Eiweißproteine zu trennen und den Selengehalt verschiedener Fraktionen zu bestimmen. Nach Isolation wurden neun verschiedene Proteine mit SDS-PAGE identifiziert und 56% des totalen Seleninhalts ist an Ovalbumin-1 und −2 (zirka 500 ng/g) gebunden, was dem höchsten Proteinwert in Eiweiß entspricht. Flavoprotein war das an Selen reichhaltigste Protein (1800 ng/g). Der Seleninhalt der anderen Proteine Lysozym, Conalbumin, Glo bulin und Ovomucoid lag zwischen 359 und 1094 ng/g.AbstractThe present studies were undertaken to characterize selenium distribution in egg white. Ion-exchange chromatography fast protein liquid chromatography (FPLC) and flow injection atomic (absorption) spectrometry (FIAS) were used to separate egg white proteins and to determine the selenium content of different fractions. After purification, nine different proteins were identified with sodium dodecyl sulphate-polyacrylamide gel electrophoresis and 56% of the total selenium content was found to be associated with ovalbumin −1 and −2 (±500 ng/g), which is the main protein in egg white. Flavoprotein was determined to be the richest seleniumcontaining protein (1800 ng/g). The selenium content of the other proteins (lysozyme, conalbumin, globulins and ovomucoid) ranged from 359 to 1094 ng/g.