Glossary eurofir module A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Accuracy/Accurate Closeness between the estimated value and the (unknown) true value. Synonymous term: Validity This figure illustrates the difference between accuracy and precision. Each dot represents a separate measurement. The 'true' value is represented by the bulls-eye of the target. Case-control study An epidemiological study in which a group of patients is compared with a control group with respect to food intake or another exposure. The aim is to investigate the relation between the exposure (e.g. food intake) and the disease. Back to top Chromatography Chromatography is a physical method of separation in which the components to be separated are distributed between two phases, one of which is stationary (stationary phase) while the other (the mobile phase) moves in a definite direction. Back to top Condensation Disaccharides are formed when two monosaccharides are joined together by a glycosidic bond. A hydroxyl (OH) group from one monosaccharide and a hydrogen atom (H) from the other combine to create a water molecule (H2O). The picture shows two glucose molecules joining together to form the disaccharide maltose. Back to top Crucible A heat-resistant container often made of porcelain in which materials can be heated to very high temperatures. Back to top Coefficient of variation (CV) A measure of precision. A high coefficient of variation (CV) means a low precision. The coefficient of variation is useful because the standard deviation of data must always be understood in the context of the mean of the data. Back to top CV within The coefficient of variation based on several measurement within the same laboratory. Back to top CV between The coefficient of variation based on several measurement in different laboratories. Back to top CV achievable The precision of repeated measurements expressed as coefficient of variation that is reasonable to achieve based on the concentration of the substance that is measured. This theoretically achievable CV can be calculated using the 'Horwitz equation'. Back to top Derivatization Derivatization is a technique which transforms a chemical compound into a product of similar chemical structure, called derivative. Resulting new chemical properties can be used for quantification or separation of the compound. Back to top Emulgated fat Fat particles finely dispersed in the watery part of the food matrix. Back to top Food Frequency Questionnaire (FFQ) FFQs are usually self-administered questionnaires and are designed to be easy to complete by the study subjects. FFQs usually comprise a list of foods or food groups, and a corresponding frequency response section (e.g. never, once per week, twice per week etc). FFQs often rely on assumptions regarding portion size, and are limited by the amount of detail that it is feasible to include in the questionnaire. In epidemiology, FFQs are often filled in with reference to the previous year in order to ascertain usual food consumption patterns for that period. Here you see an example of a section of a Food Frequency Questionnaire. Back to top Glycosidic bond Di-, oligo-, and polysaccharides, are formed when two or more monosaccharides are joined together by a glycosidic bonds. Many di-, oligo-, and polysaccharides consist of linked glucoses units. Glucose can appear in two isomeric forms ( α or β glucose). The designation α means that the hydroxyl group attached to C-1 is positioned trans to the -CH2OH group at C-5, while β means it is in cis position. The human body contains digestive enzymes (amylase) that are able to break down the linkages between glucose in the alpha position (like in starch) but not in the beta position (like in cellulose). Back to top Gravimetric analysis Any method of analysis in which the final stage of the analysis involves weighing. Back to top Horwitz equation The Horwitz equation describes the empirical relation between the concentration of an analyte and the precision of repeated measurements obtained by experienced analysts. This equation was developed based on a large number of collaborative studies (interlaboratory trials). This equation gives only an impression of what average precision you can reasonably expect at a certain concentration level. It does not tell you what the precision exactly has to be, because that may vary depending on the compound and method. Remember that a high coefficient of variation (CV) means a low precision. Back to top Hydrolysis In di-, oligo- and polysaccharides, monosaccharide molecules are linked together by a glycosidic bond. This bond can be cleaved by hydrolysis to yield monosaccharides. During hydrolysis, a water molecule splits to provide the hydrogen (H) atom and hydroxide (OH) group needed to complete the resulting monosaccharides. Hydrolysis reactions occur during digestion. The picture shows that the hydrolysis of lactose yields the monosaccharides galactose and glucose. Here the enzyme lactase speeds up the hydrolysis. Back to top Inductively coupled plasma Inductively coupled plasma is a type of plasma source in which the energy (=heat) is supplied by electrical currents which are produced by electromagnetic induction, that is, by time-varying magnetic fields. In physics and chemistry, plasma is a gas, in which a certain proportion of its particles are ionized. The presence of ions makes the plasma electrically conductive so that it responds strongly to electromagnetic fields. Back to top Lambert-Beer Law Lambert-Beer Law relates the absorption of light to the properties of the material through which the light is traveling. The properties of the material include: the distance that the light travels through the material (path length = b), the concentration of the absorbing compound (c), and an absorption coefficient which is specific for a given compound, also called the molar-extinction coefficient (a). Absorbance (A) = a*b*c Back to top Macronutrients, Micronutrients Back to top Mass spectrometry Mass spectrometry a principle based on ionizing chemical compounds to generate charged molecules or molecule fragments and measurement of their mass-to-charge ratios. In a typical MS procedure a sample is loaded onto the MS instrument, and undergoes vaporization. Then the components are ionized (e.g., by impacting them with an electron beam), resulting in the formation of positively charged particles (ions). The ions are then accelerated by a magnetic field. Then computation of the mass-to-charge ratio of the particles takes place (m/z ratio), based on the details of motion of the ions as they transit through electromagnetic fields. And next detection of the ions, sorted according to m/z. Back to top Minerals Minerals are inorganic compounds required in the diet in small amounts to maintain fundamental functions in the body. Minerals are compounds at the molecular level, such as cooking salt (NaCl). Sodium (Na) is the element. In inorganic analysis it is preferred to speak of elements (atomic level), since that is what is being measured. Back to top Molar extinction coefficient Molar extinction coefficient is the property of how strongly a chemical species absorbs light at a given wavelength. Back to top Organic solvent An organic solvent molecule contains carbon atoms. Examples of organic solvent are alcohol and petroleum ether. Back to top Path length In chemistry, the path length is defined as the distance that light travels through a sample. Back to top Precision/Precise Degree of correspondence between results of repeated measurements on the same material Measures: Standard deviation: SD, Coefficient of variation: CV Relative standard variation: RSD For more information see also Accuracy Back to top Resolution (related to GLC) Extent to which two components are separated. Back to top Tagnames A standardized set of identifiers (e.g. InFoods tagnames or EuroFoods component identifiers) for nutrients and other components used in the food composition tables. These identifiers provide database compilers and users with the means to avoid ambiguity and to enable comparisons and interchange of compositional data. Websites: - EuroFoods component identifiers: EUROFOODS Recommendations for Food Composition Database Management and Data Interchange. J Food Comp Anal (2000) 13, 709-744). http://dx.doi.org/10.1006/jfca.2000.0891 -InFoods tagnames www.fao.org/infoods/tagnames_en.stm Back to top Triglycerides (abbreviated TG), also called Tri-acylglycerols: Three molecules of fatty acid combined with a molecule of the alcohol glycerol. Back to top Turbidity, turbid The cloudiness or haziness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye. Back to top Validity See Accuracy Back to top Volumetric analysis Any method of quantitative chemical analysis in which the amount of a substance is determined by measuring the volume that it occupies Back to top