Joop Luten

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.

Bioavailability of selenium from fish, yeast and selenate:a comparative study in humans using stable isotopes

Objective: To measure the bioavailability of selenium from cooked and raw fish in humans by estimating and comparing apparent absorption and retention of selenium in biosynthetically labelled fish with labelled selenate and biosynthetically labelled selenium in brewers yeast.Design: The intervention study was a parallel, randomised, reference substance controlled design carried out at two different centres in Europe.Setting: The human study was carried out at the Institute of Food Research, Norwich, UK and at TNO Nutrition and Food Research, Zeist, The Netherlands.Subjects: In all, 35 male volunteers aged 18–50 y were recruited; 17 subjects were studied in Norwich (UK) and 18 in Zeist (Netherlands). All of the recruited subjects completed the study.Interventions: Biosynthetically labelled trout fish (processed by two different methods), biosynthetically labelled brewers yeast and isotopically labelled selenate were used to estimate selenium apparent absorption and retention by quantitative analysis of stable isotope labels recovered in faeces and urine. Subjects consumed the labelled foods in four meals over two consecutive days and absorption was measured by the luminal disappearance method over 10 days. Urinary clearance of isotopic labels was measured over 7 days to enable retention to be calculated.Results: Apparent absorption of selenium from fish was similar to selenate and there was no difference between the two processing methods used. However, retention of fish selenium was significantly higher than selenate (P<0.001). Apparent absorption and retention of yeast selenium was significantly different (P<0.001) from both fish selenium and selenate.Conclusions: Fish selenium is a highly bioavailable source of dietary selenium. Cooking did not affect selenium apparent absorption or retention from fish. Selenium from yeast is less bioavailable.

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 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.

Mass spectrometric methods for studying nutrient mineral and trace element absorption and metabolism in humans using stable isotopes : a review

Mass spectrometric methods for determining stable isotopes of nutrient minerals and trace elements in human metabolic studies are described and discussed. The advantages and disadvantages of the techniques of electron ionization, fast atom bombardment, thermal ionization, and inductively coupled plasma and gas chromatography mass spectrometry are evaluated with reference to their accuracy, precision, sensitivity, and convenience, and the demands of human nutrition research. Examples of specific applications are described and the significance of current developments in mass spectrometry are discussed with reference to present and probable future research needs.

Translating barriers into potential improvements: the case of new healthy seafood product development

Purpose – The aim of this study is to explore potential barriers to seafood consumption by young adults and the parents of young children. Knowledge of these barriers will be used to assist the development of new seafood product concepts that fulfil the needs of consumers.Design/methodology/approach – To gather this information, 28 infrequent consumers of seafood participated in three semi‐structured two‐hour focus group discussions in Denmark, Norway, and Iceland. The results were then linked to the Stage‐Gate model for consumer‐based new product development (NPD).Findings – The participants thought of seafood as either healthy or convenient, although there were concerns about the amount of effort required to prepare it. These concerns resulted in an expression of their need for products that are attractive, healthy, palatable, and convenient. In particular, the newly developed products should be accompanied by clear advice on preparation methods and materials. An increase in seafood availability coupled...

Frozen herring as raw material for spice-salting

One batch of herring (Clupea harengus) was spice-salted fresh and as thawed after 32 days of frozen storage at -24 °C. After salting, samples of both groups were sent to participating laboratories in Iceland, Denmark, Norway, Germany and England. The herring was kept at 5 ± 1 °C and sampled three times during a 26 week storage period. The development of taste and texture characteristics (determined by sensory evaluation and instrumental texture measurements), formation of low-molecular-weight nitrogen compounds and changes in proteolytic activity were followed in both groups. The sensory evaluation results showed that thawed salted herring ripened in a similar manner to herring salted fresh, but at a faster rate. Instrumental texture analysis showed a faster rate of tenderising in thawed salted herring. Proteolytic activity measured as general activity and with specific synthetic substrates was higher in the thawed salted herring. The formation of trichloroacetic acid-soluble nitrogen and free amino acids was faster in the previously frozen herring. The results show an accelerated but similar rate of ripening in thawed spice-salted herring in comparison with fresh salted herring

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.

Determination of total volatile bases in fish: a collaborative study by the West European Fish Technologists' Association (WEFTA)

ZusammenfassungEs wurden zwei Serien von Ringversuchen durchgeführt. An der ersten nahmen neun, an der zweiten sechs WEFTA-Laboratorien teil. Alle Laboratorien wendeten eine gebräuchliche Methode an, die die Präcipitation des Fischproteins durch Trichloressigsäure mit nachfolgender Destillation des Extraktes nach Zugabe von Natriumhydroxid einschließt („Codex method”). Außerdem führten die Teilnehmer die TVB-N-Bestimmungen (gesamte flüchtige Basen) mit ihren hauseigenen Methoden durch („home methods”). Verwendet wurden Makrelen-und Kabeljauproben. Die Ergebnisse beider Ringversuche zeigen einen bedeutenden systematischen Fehler zwischen den teilnehmenden Laboratorien sowohl mit der „Codex method” als auch mit der „home method”. Wurden reine Lösungen von Ammoniak, Di- und Trimethylamin (die Hauptbestandteile von TVB) mit den gleichen Methoden untersucht, wurde eine bessere Vergleichbarkeit erzielt. Andererseits führte die Addition von Trimethylamin zu mittleren Wiederfindungsraten von nur 75% mit einer signifikanten Variabilität zwischen den Teilnehmern. Die analytischen Methoden sollten weiterhin genau untersucht werden und die Einflüsse von kleineren, möglicherweise aber wichtigen Abänderungen sollten erforscht werden, bevor eine einzelne TVB-N-Bestimmungsmethode als Referenzmethode vorgeschlagen wird.SummaryTwo series of collaborative tests were performed. Nine WEFTA laboratories participated in the first exercise, six in the second one. All laboratories applied a common method involving the precipitation of fish proteins by trichloroacetic acid followed by distillation of the extract after addition of sodium hydroxide (“Codex method”). They also carried out the TVB (total volatile bases) analyses by their own methods (“home methods”). Mackerel and cod were used. The results of both collaborative exercises showed important systematic errors between participating laboratories both with the codex and with the home methods. Better comparability was obtained when pure solutions of ammonia, di- and trimethyl-amine (the main components of TVB) were subjected to the same methods. On the other hand, the addition of TMA showed average recoveries of only 75% with significant variability among collaborators. The analytical methods should be further scrutinized and the effects of minor but possibly important variations should be investigated before proposing a reference TVB method.

Determination of phenol, guaiacol and 4-methylguaiacol in wood smoke and smoked fish-products by gas-liquid chromatography.

ZusammenfassungDie Bestimmung von Phenol, Guajacol und 4-Methylguajacol im Holzrauch und in geräucherten Fischerzeugnissen wird beschrieben. Ein alkalischer, homogenisierter Fischbrei wird mit Äther extrahiert, um die Fette zu entfernen. Nach der Eiweißfällung mit Trichloressigsäure werden die Phenole mittels Chloroform isoliert. Der Chloroform-extrakt wird gaschromatographisch analysiert. Geringe Verluste der Phenolen während der Isolierung wurden festgestellt. Die entwickelte Methode eignet sich zur Analysierung der Räucherrauchs und von Fischproben aus einer modernen Kaltrauchanlage.SummaryThe determination of phenol, guaiacol and 4-methylguaiacol in smoke and smoked fish products is described. An alkaline fish homogenate is extracted with ethyl ether in order to remove the lipids. After protein precipitation, the phenols are isolated by extraction with chloroform. The chloroform extract is analysed by gas chromatography using a packed column and a flame ionisation detector. Some losses of the phenols during the isolation procedure have been observed. The analytical method developed has been applied to smoke and smoked fish samples from a cold-smoking experiment with a modern smoking kiln.