Bile Salts

bilirubin, biliverdin The bile pigments, formed by catabolism of haemoglobin. Blood bilirubin is normally <17 |imol/L; when it rises above 20-30 |imol/L there is visible jaundice. biltong South African; strips of dried meat, salted, spiced and dried in air for 10-14 days. binge-purge syndrome A feature of the eating disorder bulimia nervosa, characterised by the ingestion of excessive amounts of food and the excessive use of laxatives. Bingham fluid See plastic fluids.

bio Commonly used to indicate probiotic yogurt containing live bacterial culture. See probiotics. bioactive polymers In food packaging, polymers that have enzymes or other active compounds (e.g. antimicrobial peptides) covalently bound to the surface or embedded in the polymer film, so that the active material does not migrate into the food.

bioassay Biological assay; measurement of biologically active compounds (e.g. vitamins and essential amino acids) by their ability to support growth of micro-organisms or animals. biocytin biotin bound to the e-amino group of lysine, the form in which biotin is present in enzymes. Normally hydrolysed to release free biotin by the enzyme biotinidase (EC 3.5.1.12). bioelectrical impedance (BIE) A method of measuring the proportion of fat in the body by the difference in the resistance to passage of an electric current between fat and lean tissue.

Correctly measures the impedance, since a 50 MHz alternating current (800 |A) is passed between electrodes attached to the hand and foot, and the fall in voltage is measured.

See also total body electrical conductivity. bioflavonoids See flavonoids.

biofortification The process of breeding varieties of food crops that are naturally rich in micronutrients. BiofossTM See deft.

biolistics Acceleration of heavy microparticles coated with DNA to introduce foreign DNA into plant cells as a means of creating transgenic plants. biological oxygen demand (BOD) A way of assessing bacterial contamination of water, milk, etc. by micro-organisms which take up oxygen for their metabolism. biological value (BV) A measure of protein quality. bioluminescence Emission of light by reaction of the enzyme luciferase with atp. Exploited as a rapid and sensitive way of detecting bacteria (and other cells) in milk and other foods, since all living cells contain ATP. Trade names for bioluminescence instruments include Biotrace, Bactofoss, Bio-Orbit and Hy-Lite.

biomarkers Metabolic, chemical or functional changes that can be measured in response to nutritional, drug or other interventions. Sometimes regarded as surrogate end-points, since they respond more rapidly and more sensitively than clinical disease or overt signs of toxicity. Bio-OrbitTM See bioluminescence.

biopterin Pterin coenzyme required by phenylalanine (EC 1.14.16.1), tyrosine (EC 1.14.16.2) and tryptophan (EC 1.14.16.4) hydroxylases. Not a dietary requirement, but synthe-sised from cGMP. Rare patients with a variant form of phenylketonuria cannot synthesise biopterin, and have to receive supplements. bios A name given to a factor in cell-free extract of yeast which is essential for the growth of yeast, by Wildiers in 1901. Three components were subsequently identified: inositol, P-alanine and biotin. Of these, only biotin is a vitamin and essential for human beings.

biosensor An enzyme or antibody (or intact cells), coupled to a physical or chemical reporting system to measure a specific component of a food or other product. Among other applications, used in intelligent packaging. biotin A vitamin, sometimes known as vitamin H, required as coenzyme for carboxylation reactions in synthesis of fatty acids and glucose, and in the control of cell division. Widely distributed in foods; dietary deficiency is unknown. There is no evidence on which to base reference intakes other than to state that current average intakes (between 15 and 70 |g/day) are obviously more than adequate to prevent deficiency.

The protein, avidin, in raw egg white, binds biotin strongly, preventing its absorption, and individuals who consume abnormally large amounts of uncooked egg (several dozen eggs per week) have been reported to show biotin deficiency. Avidin is denatured (see denaturation) on cooking, and does not combine with biotin; indeed cooked egg is a rich source of available biotin.

See also biocytin.

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