Annales de la nutrition et de l'alimentation最新文献

An investigation carried out by French Ministration of Agriculture (S.R.A.E.L.) has worked out an inventory and defined the nitrate amount evolution in waters, specially originated with underground formations, stared out by collectivities. The investigation spreading has brought about some ascertainment in Lorraine country. Particularly, the "Laboratoire d'hygiène et de recherche en santé publique" has so identified in a commune near Nancy, where nitrate amounts in water are particularly high, gastrointestinal troubles probably caused by minor methemoglobinemias which water supply origin have not been locally suspected. This note so shows that medical and paramedical corps cooperation with administrative authorities charged with water resource can attempt some interventions: better diagnosis, population and mayors information, search of technical and administrative settlements according to local environment.

We have observed some important changes in the distribution of fatty acid classes in cultured nerve cells according to the normal or tumoral origin of the cells: normal cells exhibit higher levels of polyunsaturated fatty acids and lower levels of monounsaturated fatty acids than tumoral cells do. When the culture medium of neuroblastoma cells is supplemented with polyunsaturated fatty acids, these fatty acids are incorporated into membrane phospholipids and some specific alterations of membrane functions occur: modification of the kinetic parameters of ecto-enzyme activities, modification of amino-acid transport characteristics. A brief review of the literature shows that polyunsaturated fatty acids are not essential for cell life in vitro, provided that monounsaturated fatty acids can be present in the cells. Polyunsaturated fatty acids seem therefore play only a regulatory role of some membrane functions.

In fish, essential acids belong to the n-3 series. In trout, carp and salmon a dietary supply of 0.7 to 1% linolenate allows to prevent any symptoms of deficiency and ensures a normal growth. This is not the case for see fish such as daurade and turbot, where a supply of a similar proportion of n-3 high polyunsaturated fatty acids (HPUFA) appears to be necessary. However, recent experiments show that this requirement for HPUFA is not specific, since they can be replaced by linolenate in the turbot provided that the linolenate dietary amount is substantially higher than in the trout. The 6-desaturase activity seems to be lower in see fish than in freshwater fish and there is a good agreement between the nutritional tests of growth rate of fish and the biological tests of bioconversion rate of linolenate into HPUFA. Fish seem to be a highly valuable tool for determining the role and mechanism of action of essential fatty acids. In our opinion it is very interesting to use differences between fish and mammals to apprehend all the specific biological processes related to the presence of essential fatty acids in the organism.

The turn-over of polyunsaturated fatty acids in membrane is carried out through three differet ways: 1) de novo synthesis of lipids, 2) fatty acyl chains and/or polar head replacement (transacylation processes), 3) exchange with plasma-lipoproteins. De novo synthesis takes place in microsomes. Then phospholipids are exported towards other subcellular structures, carried by exchange proteins or spreadontby lateral diffusion. Polar head groups are modified by transmethylation (PE leads to PC), by decarboxylation (PS leads to PE) or by base-exchange reaction (ethanolamine/serine/inositol) in various subcellular loci. Transacylation process implies three enzymatic steps: A1/A2 phospholipases, acyl CoA synthetase, acyl CoA-lysoderivatives transacylated. It is localized on the cytoplasmic side of the membrane (plasma membranes and microsomes) and in mitochondrial membranes. Lipid exchange occurs primarily with the outer halve of the cytoplasmic membrane and penetrates through the so-called "flip-flop" mechanism or in especially organized (non-bilayer) parts of the membrane. This fatty acids turn-over could play a role in various membrane functions: 1) release of fatty acids acting as precursors of PG or TXA, 2) adaptation of physical parameters of the membrane (fluidity, phases segregation), 3) steady state for membrane composition asymmetry. Their disturbances could account or diseases seen in plasma fatty acids abnormalities.

In a review of the subject, the authors show that nitrite play an important role upon stability and safety of cured meat products. In non heated cured meat, they have a synergistic effect together with pH, NaCl concentration and storage temperature, in such a way that 150 ppm seem to be necessary. Usefullness of nitrite is also advocated in heated systems, though it seems difficult to establish quantitative requirements. In any way, there is a general agreement on the fact that curing without nitrite would enhance food poisoning risks, especially where botulism is concerned.

When dealing with the environmental impacts of nitrate nitrogen, one must, first, underline the main place of nitrogen in the dietary needs of man. This element is simultaneously one of the main factors of crop yields, and the first step in the elaboration of proteins. The accumulation of nitrates in crops is defined, its draw-backs are briefly reminded. Nitrate content differs between the organs: stems, petioles, young roots are richer than limbs of leaves; fruits are very poor. The factors of nitrate accumulation are reminded: the nitrogen availability in soil, the light, the other nutrients, and the plant characteristics (e.g., age, cultivar). Ways to obtain a better control of nitrate content in edible parts of spinach, carrot and tomato are discussed. Then, the nitrogen cycle in the soil is briefly described. The influence of various agricultural systems (pastures, annual cropping, wheat, corn, soja) on the nitrate content of groundwater is shown.

In order to compare results obtained from various analytical techniques, nitrate determinations in soils and vegetables were made by four usual methods. These are a selective electrode, an autoanalyser with dialyser that determines nitrites following a nitrate reduction step by hydrazine sulfate, another autoanalyser that reduces nitrates with cadmium metal, and the usual DEVARDA method. Interferences and limitations of these techniques are discussed.

122 foods and 46 beers from the north-east of France and other areas are analysed. The solid frozen samples are finely ground, homogenized and suspended in mineral oil. The volatile nitrosamines are vacuum distilled and extracted with dichloromethane from the acidified distillate. The sample is concentrated and analysed with a gas chromatograph coupled to a TEA detector. The liquid samples are directly extracted with dichloromethane. The non grilled cured meat products are lightly polluted. The nitrosodimethylamine and nitrosopiperidine concentrations usually do not exceed 1 ppb. Only two samples out of about thirty are very polluted by the nitrosopiperidine (28,6 and 26 ppb), and also by the nitrosopyrrolidine (3 and 11 ppb). In the other samples this last nitrosamine is seldom and occurs only in trace amounts. The precooked canned meals and the cheese products are rarely and only lightly polluted. However beers are polluted most of the time. The nitrosodimethylamine is found in all the pale beers, with a concentration ranging from 0.1 to 21.3 ppb (m: 3.1). In dark beers the nitrosodimethylamine concentration ranges from 7.2 to 16.8 ppb (m: 10.1) and the nitrosopyrrolidine concentration has a mean value of 0.2 ppb.