Dietary lycopene consists mostly of the (all-E) isomer. Upon absorption, (all-E) lycopene undergoes isomerisation into various (Z)-isomers. Because these isomers offer potentially better health benefits than the (all-E) isomer, the aim of the present study was to investigate if the profile of lycopene isomers in intestinal lipoproteins is affected by the profile of lycopene isomers in the meal and by the tomato preparation. Six postprandial, crossover tests were performed in healthy men. Three meals provided about 70 % of the lycopene as (Z)-isomers, either mainly as 5-(Z) or 13-(Z), or as a mixture of 9-(Z) and 13-(Z) lycopene, while three tomato preparations provided lycopene mainly as the (all-E) isomer. Consumption of the 5-(Z) lycopene-rich meal led to a high (60 %) proportion of this isomer in TAG-rich lipoproteins (TRL), indicating a good absorption and/or a low intestinal conversion of this isomer. By contrast, consumption of meals rich in 9-(Z) and 13-(Z) lycopene isomers resulted in a low level of these isomers but high amounts of the 5-(Z) and (all-E) isomers in TRL. This indicates that the 9-(Z) and 13-(Z) isomers were less absorbed or were converted into 5-(Z) and (all-E) isomers. Dietary (Z)-lycopene isomers were, therefore, differently isomerised and released in TRL during their intestinal absorption in men. Consuming the three meals rich in (all-E) lycopene resulted in similar proportions of lycopene isomers in TRL: 60 % (all-E), 20 % 5-(Z), 9 % 13-(Z), 2 % 9-(Z) and 9 % unidentified (Z)-isomers. These results show that the tomato preparation has no impact on the lycopene isomerisation occurring during absorption in humans.

Human milk trypsin was purified by adsorption chromatography on cellulose-bound 4-aminobenzamidine; its molecular weight was about 24,000 daltons. Its concentration determined by a radioimmunoassay varies between 2.9 and 5.6 micrograms/l.

Human milk samples react against anti-bovine beta-lactoglobulin rabbit antibodies, as measured by a competitive radioimmunoassay. Immunoreactivity was positive even in milk from mothers consuming a diet free of cow's milk. An increase with a diet rich in cow's milk proteins was detected by immunoelectrophoresis. The human milk fraction cross-reacting with anti-bovine beta-lactoglobulin antibodies corresponds to the 20 kDa fragment from the N-terminal end of human lactoferrin. Three regions of this fragment exhibit sequence homology with a sequence contained in cow's beta-lactoglobulin (between residues 124 and 141).

Under most physiological conditions, glucose, or carbohydrate (CHO), homeostasis is tightly regulated. In order to mechanistically appraise the origin of circulating glucose (e.g. via either gluconeogenesis, glycogenolysis or oral glucose intake), and its regulation and oxidation, the use of stable isotope tracers is now a well-accepted analytical technique. Methodologically, liquid chromatography coupled to isotope ratio mass spectrometry (LC/IRMS) can replace gas chromatography coupled to combustion-isotope ratio mass spectrometry (GC/C/IRMS) for carrying out compound-specific (13)C isotopic analysis. The LC/IRMS approach is well suited for studying glucose metabolism, since the plasma glucose concentration is relatively high and the glucose can readily undergo chromatography in an aqueous mobile phase. Herewith, we report two main methodological approaches in a single instrument: (1) the ability to measure the isotopic enrichment of plasma glucose to assess the efficacy of CHO-based treatment (cocoa-enriched) during cycling exercise with healthy subjects, and (2) the capacity to carry out bulk isotopic analysis of labeled solutions, which is generally performed with an elemental analyzer coupled to IRMS. For plasma samples measured by LC/IRMS the data show a isotopic precision SD(δ(13)C) and SD(APE) of 0.7 ‰ and 0.001, respectively, with δ(13)C and APE values of -25.48 ‰ and 0.06, respectively, being generated before and after tracer administration. For bulk isotopic measurements, the data show that the presence of organic compounds in the blank slightly affects the δ(13)C values. Despite some analytical limitations, we clearly demonstrate the usefulness of the LC/IRMS especially when (13)C-glucose is required during whole-body human nutritional studies.

Isotope labeled tracers are commonly used to quantify the turnover rates of various metabolic intermediates and yield information regarding physiological regulation. Studies often only consider either one nutritional state (fasted or fed) and/or one question (e.g., measure of lipid or protein turnover). In this article, we consider a novel application combining the global approach of metabonomics with widespread stable isotope labeling as a way of being able to map metabolism in open mammalian systems, an approach we call "isotopomics". A total of 45 15-week-old male Zucker rats were administrated different amounts (from 0.5 to 8 mmol/kg) of sodium [1,2-(13)C(2)] acetate. Plasma samples taken at 1, 4, and 24 h were analyzed with (13)C nuclear magnetic resonance (NMR) and gas chromatography/mass spectrometry (GC/MS) to measure (13)C isotopic enrichment of 39 plasma metabolites across a wide range of compound classes (amino acids, short-chain fatty acids, lactate, glucose, and free fatty acids). Isotopic enrichment from 0.1-7.1 mole percent excess (MPE) for the highest dose could be reliably measured in 16 metabolites, and the kinetics of their (13)C isotopic enrichment are reported. Clustering metabolites based on (13)C kinetic curves enabled highlighting of time dependent patterns of (13)C distribution through the key metabolic pathways. These kinetic and quantitative data were reported into a biochemical map. This type of isotopomic approach for mapping dynamic metabolism in an open system has great potential for advancing our mechanistic knowledge of how different interventions and diseases can impact the metabolic response of animals and humans.