Tự điển Food Science, Technology And Nutrition - Vần G

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  1. 205 fungi Subdivision of Thallophyta, plants without differentiation into root, stem and leaf; cannot photosynthesise, all are parasites or saprophytes. Microfungi are moulds, as opposed to larger fungi, which are mushrooms and toadstools. yeasts are some- times classed with fungi. Mycorrhizal fungi form symbiotic asso- ciations with tree roots. Species of moulds such as Penicillium, Aspergillus, etc. are important causes of food spoilage in the presence of oxygen and relatively high humidity. Those that produce toxins (mycotoxins) are especially problematical. On the other hand, species of Penicillium such as P. cambertii and P. rocquefortii are desirable and essential in the ripening of some types of cheese. A number of larger fungi (mushrooms) are cultivated, and other wild species are harvested for their delicate flavour. The mycelium of smaller fungi (including Graphium, Fusarium and Rhizopus spp.) are grown commercially on waste carbohydrate as a rich source of protein (mycoprotein) for food manufacture. furans Derivatives of five-membered heterocyclic compounds (C4H4O), associated with caramel-like, sweet, fruity, nutty and meaty flavours in foods; formed in foods by the maillard reac- tion and thermal degradation of carbohydrates. furcellaran Danish agar; an anionic, sulphated polysaccharide extracted from the red alga, Furcellaria fastigiata, structurally similar to carrageenan; used as a gelling agent. fusel oil Alcoholic fermentation produces about 95% alcohol and 5% fusel oil, a mixture of organic acids, higher alcohols (propyl, butyl and amyl), aldehydes and esters, known collectively as con- geners. Present in low concentration in wines and beer, and high concentration in pot-still spirit. On maturation of the liquor fusel oil changes and imparts the special flavour to the spirit. Many of the symptoms of hangover can be attributed to fusel oil in alcoholic beverages. fussol Monofluoroacetamide, a systemic insecticide for treating fruit. F value The time required to destroy a given percentage of micro- organisms at a specified reference temperature and Z value. G gaffelbitar Semi-preserved herring in which microbial growth is checked by the addition of 10–12% salt and sometimes benzoic acid. galactans polysaccharides composed of galactose derivatives; a major constituent of carageenan.
  2. 206 galacticol See dulcitol. GalactominTM A preparation free from lactose and galactose, for people suffering from lactose intolerance. galacto-oligosaccharides Small oligosaccharides consisting of glucosyl-(galactose)2–5, formed from lactose by galactosyl transfer catalysed by lactase (EC 3.2.1.23). Considered to be a prebiotic. galactorrhoea Abnormal secretion of milk, due to excessive secretion of prolactin. galactosaemia Congenital lack of UDP-glucose galactosyltrans- ferase (EC 2.7.7.12), or more rarely galactokinase (EC 2.7.1.6) leading to elevated blood concentration of galactose, and hence non-enzymic glycation of proteins, and the development of cataract and neurological damage; subjects suffer mental retar- dation, growth failure, vomiting and jaundice, with enlargement of liver and spleen. Treatment is by severe restriction of lactose intake, since this is the only significant source of galactose. galactose A six-carbon monosaccharide (hexose), differing from glucose in orientation of the hydroxyl group on carbon-4. About one-third as sweet as sucrose. The main dietary source is the disaccharide lactose in milk, important in formation of the galactolipids (cerebrosides) of nerve tissue. See also carbohydrates; galactosaemia. b-galactosidase Enzyme (EC 3.2.1.23) that hydrolyses β-galactans in non-starch polysaccharides; responsible for loss of firmness during ripening and storage of fruits. galangal Root spices (Alpinia galanga, A. officinarum) related to ginger, but with a faint flavour of camphor. GalanolTM borage seed oil, a rich source of γ-linolenic acid, as a dietary supplement. galenicals Crude drugs; infusions, decoctions and tinctures pre- pared from medicinal plants. gallates Salts and esters of gallic acid, found in many plants. Used in making dyes and inks, and medicinally as an astringent. Propyl, octyl and dodecyl gallates are legally permitted antioxidants in foods (E-310–312). gall bladder The gland in the liver that stores the bile before secretion into the small intestine. See also gallstones; gastrointestinal tract. gallon A unit of volume. The Imperial gallon is 4.546 litres, and the US (or Queen Anne) gallon is 3.7853 litres; therefore 1 Imperial gallon = 1.2 US gallons. gallstones (cholelithiasis) Crystals of cholesterol, bile salts and calcium salts, formed in the bile duct of the gall bladder when the bile becomes supersaturated.
  3. 207 game Non-domesticated (i.e. wild) animals and birds shot for sport and eaten. rabbit and pigeon may be shot at any time, but other game species, such as grouse, hare, partridge, pheasant, quail, deer (venison) and wild duck, may not be shot during the closed season, to protect breeding stocks. Game birds are gen- erally raised on farms to provide sport, rather than being hunted in the wild, and increasingly game species are farmed and killed in conventional ways to provide food. Traditionally, game is hung for several days to soften the meat, when it develops a strong flavour. gammelost Norwegian dark brown cheese with mould growth on the rind that is pressed into the paste while it is ripening. gammon See bacon. gangliosides Glycolipids, structurally similar to cerebrosides, but with a charged polar oligosaccharide head region. garam masala A mixture of aromatic spices widely used in Indian cooking; contains powdered black pepper, cumin, cinnamon, cloves, mace, cardamom seeds and sometimes also coriander and/or bay leaf. garbanzo See chickpea. garbellers 15th century; people appointed by the Grocers’ Company of London to inspect spices and other groceries, and destroy adulterated products. gari Fermented cassava meal. Cassava is grated, soaked in water and left to undergo bacterial fermentation for 2–5 days in per- meable sacks so that liquid drains out; the resulting solid mass is sieved and lightly toasted or fried (garified). garlic The bulb of Allium sativum with a pungent odour when crushed, widely used to flavour foods. There is some evidence that garlic has a beneficial effect in lowering blood cholesterol. Composition/100 g: (edible portion 87%) water 58.6 g, 624 kJ (149 kcal), protein 6.4 g, fat 0.5 g, carbohydrate 33.1 g (1 g sugars), fibre 2.1 g, ash 1.5 g, Ca 181 mg, Fe 1.7 mg, Mg 25 mg, P 153 mg, K 401 mg, Na 17 mg, Zn 1.2 mg, Cu 0.3 mg, Mn 1.7 mg, Se 14.2 µg, 26 µg carotenoids, vitamin K 1.4 mg, B1 0.2 mg, B2 0.11 mg, niacin 0.7 mg, B6 1.24 mg, folate 3 µg, pantothenate 0.6 mg, C 31 mg. garlic mustard A common wild plant of hedgerows and woodland (Alliaria petiolata); the leaves have a garlic-like flavour and can be used in salads or cooked as a vegetable. gas storage, controlled (modified) See packaging, modified atmosphere. gastrectomy Surgical removal of part or all of the stomach. gastric inhibitory peptide Peptide hormone secreted by the mucosa of the duodenum and jejunum in response to absorbed fat and carbohydrate; stimulates the pancreas to
  4. 208 secrete insulin.Also known as glucose-dependent insulinotropic polypeptide. gastric secretion Gastric juice contains the enzymes chymosin (EC 3.4.23.4), lipase (EC 3.1.1.3), pepsinogen (the inactive pre- cursor of pepsin, EC 3.4.23.1), intrinsic factor, mucin and hydrochloric acid. The acid is secreted by the parietal (oxyntic) cells at a strength of 0.16 mol/L (0.5–0.6% acid); the same cells also secrete intrin- sic factor, and failure of acid secretion (achlorhydria) is asso- ciated with pernicious anaemia due to failure of vitamin b12 absorption. Pepsinogen is secreted by the chief cells of the gastric mucosa, and is activated to pepsin by either gastric acid or the action of existing pepsin; it is a proteolytic enzyme (see proteolysis). See also anaemia, pernicious; proton pump. gastric ulcer See ulcer. gastrin Peptide hormone secreted by G-cells of the antrum of the stomach; stimulates parietal cells to secrete acid. gastroenteritis Inflammation of the mucosal lining of the stomach (gastritis) and/or small or large intestine, normally resulting from infection, or, in the case of gastritis, from excessive alcohol consumption. gastroenterology The study and treatment of diseases of the gas- trointestinal tract. gastrointestinal tract (see p. 209) A term for the whole of the digestive tract, from the mouth to the anus. Average length 4.5 m (15 feet). gastrolith Stone in the stomach, usually builds up around a bezoar. gastroplasty Surgical alteration of the shape of the stomach without removing any part. Has been used to reduce the physi- cal capacity of the stomach as a treatment for severe obesity. gastrostomy feeding Feeding a liquid diet directly into the stomach through a tube that has been surgically introduced through the abdominal wall. See also enteral nutrition; nasogastric tube. GatoradeTM A sports drink containing mineral salts in approxi- mately the proportions they are lost in sweat. gavage The process of feeding liquids by stomach tube. Also feeding an excessive amount (hyperalimentation). GC-MS Gas chromatography linked to a mass spectrometer as the detection system. gean Scottish name for the fruit of Prunus avium; also known as wild cherry, sweet cherry and mazzard. gefillte fish (gefilte, gefültte) German for stuffed fish; of Russian or Polish origin, where it is commonly referred to as Jewish fish.
  5. 209 GASTROINTESTINAL TRACT The whole fish is served and the filleted portion chopped and stuffed back between the skin and the backbone. More fre- quently today, the fish is simply chopped and made into balls, which are either fried or boiled. In the UK has been referred to legally as ‘fish cutlets in fish sauce’ instead of a fish cake. gel Colloidal suspension (see colloid) consisting of a continuous phase (commonly water) and a dispersed phase (the gelling agent); the water molecules are held in a three-dimensional network of the gelling agent. Examples include plant gums, gela- tine, pectin.
  6. 210 gelatine A soluble protein prepared from collagen or bones by boiling. Type A is prepared by acid treatment of collagen and has an isoionic point of 7–9. Type B is prepared by alkaline treatment and has an isoionic point of 4.8–5.2 because of loss of the amide groups of glutamine and asparagine. Used for sugar confec- tionery, in canned meats, for table jellies and in pharmaceutical capsules. Gelatine from fish (especially the swim bladder) is isinglass. Gelatine has an unusual amino acid composition: 14% hydroxyproline, 16% proline and 26% glycine; of poor nutritional value, since it lacks tryptophan. Chinese gelatine is agar. gelatine sugar Obsolete name for glycine. gelatinisation Formation of a water-retentive gel by expansion of starch granules when heated in moist conditions. See also staling. gelation The formation of the pectin gel that gives fruit preserves and jams their texture; dependent on the pectin, sugar, acid and water content of the fruit. gellan gum A polysaccharide produced by fermentation of the bacterium Sphingomonas elodea (Pseudomonas elodea), used in some foods. gelograph Instrument for measuring the viscosity or gel strength of a protein (or other) solution using an oscillating needle. gelometer See bloom gelometer. gemfibrizol See fibric acids. generic descriptor The name used to cover the different chemi- cal forms of a vitamin that have the same biological activity. genetic diseases Also known as inborn errors of metabolism. Dis- eases due to a single defective gene, with a characteristic pattern of inheritance in families. Many affect the ability to metabolise individual amino acids or carbohydrates and can be treated by dietary restriction. See also amino acid disorders; disaccharide intolerance. genetic modification A change in the genes of a living organism, as occurs in nature, and which has been used for many years in selective breeding, or, more quickly and specifically, in the labo- ratory, when genes from another organism may be introduced (sometimes known as genetic engineering). See also gm foods; substantial equivalence. genome The complete genetic sequence of an organism, hence the science of genomics. genomics, nutritional General term to include both nutrigenet- ics and nutrigenomics. gentiobiose A disaccharide consisting of two molecules of glucose joined β-1,6.
  7. 211 TM Gentleman’s relish A paste of anchovies, butter, cereal, salt and spices developed in the UK in the 19th century; also called patum peperium. geophagia Eating of dirt or soil. See also pica. geosmin Dimethyl-bicyclodecanol; microbial metabolite that can cause earthy or musty off-flavour in fish and drinking water. GEP Gas exchange preservation, see packaging, modified atmosphere. Gerber test For fat (cream) in milk. The milk is mixed with sul- phuric acid (or detergent) and amyl alcohol; the protein and car- bohydrate are dissolved, and the fat separates out. The reaction is carried out in a Gerber bottle with a thin graduated neck, in which the fat collects for measurement after centrifugation. germ, wheat The embryo or sprouting portion of the wheat berry, comprising about 2.5% of the seed. Contains 64% of the vitamin B1, 26% of the vitamin B2, 21% of the vitamin B6 and most of the fat of the grain. It is discarded, with the bran, when the grain is milled to white flour. Wheat germ oil is 20% saturated, 16% mono-unsaturated, 65% polyunsaturated, contains 149 mg vitamin E, 25 mg vitamin K/100 g. See also flour, extraction rate. geuse (gueuze) See beer. GFP See green fluorescent protein. ghatti gum Or Indian gum, polysaccharide exudate of the tree Anogeissus latifolia. The gum is formed as a protective sealant when the bark. Used in the same way as gum arabic. ghee (or ghrt) Clarified butter fat; may also be made from veg- etable oils. Composition/100 g: water 0.2 g, 3667 kJ (876 kcal), protein 0.3 g, fat 99.5 g (of which 66% saturated, 30% mono-unsaturated, 4% polyunsaturated), cholesterol 256 mg, carbohydrate 0 g, Ca 4 mg, P 3 mg, K 5 mg, Na 2 mg, vitamin A 840 µg RE (824 µg retinol, 193 µg carotenoids), E 2.8 mg, K 8.6 mg. gherkin Young green cucumber of a small variety (Cucumis anguira), used mainly for pickling. ghrelin A peptide hormone secreted by cells in the gastrointesti- nal tract that both stimulates the secretion of growth hormone and regulates feeding behaviour and energy balance by acting on the hypothalamus. Secretion is increased in the fasting state and under conditions of negative energy balance, and decreased under conditions of positive energy balance. Secretion is increased in anorexia and is low in the fasting state in obese people.
  8. 212 ghrt See ghee. giardiasis Intestinal inflammation and diarrhoea caused by infection with the protozoan parasite Giardia lamblia. gibberellins Plant growth substances derived from gibberellic acid, originally found in the fungus Gibberella fujikori growing on rice. About 30 gibberellins are known; they cause stem exten- sion and allow mutant dwarf forms of plants to revert to normal size, induce flower formation and break bud dormancy. Used in horticulture to control flowering and fruit maturation, also to induce α-amylase in malting (see malt) of barley. giblets The edible part of the entrails of a bird; gizzard, liver, heart and neck. gigot French; leg of lamb or mutton. In Ireland gigot chops are neck chops used for stewing. gill Obsolete British measure of liquid, 5 or 10 fl oz (1/4 or 1/2 pint), varying regionally. gin Alcoholic drink made by distilling fermented starch or other carbohydrate, flavoured mainly with juniper berries together with coriander seeds, angelica, cinnamon, orange and lemon peel. Distillate is diluted to 40% alcohol by volume, 925 kJ (220 kcal)/ 100 mL. Name derived from French genièvre (juniper); originally known as geneva, schiedam or hollands, since it is Dutch in origin. There are two types of English gin: Plymouth gin with a fuller flavour, and London gin. Plymouth gin has a protected designa- tion and legally may only be distilled in Plymouth; it is made by adding the botanicals to the still, while for London gin they are added to the distilled liquor. Dutch and German gins are more strongly flavoured than English or American; steinhäger and schinkenhäger are distilled from a mash of wheat, barley and juniper berries; wacholder is made from neutral spirit flavoured with juniper. Dutch gin may be jonge (young) or oude (aged, matured). gingelly (gingili) See sesame. ginger The rhizome of Zingiber officinale, used as a spice. Pre- served ginger is made from young fleshy rhizomes boiled with sugar and either packed in syrup or crystallised. Fresh ginger, composition/100 g: (edible portion 93%) water 78.9 g, 335 kJ (80 kcal), protein 1.8 g, fat 0.8 g, carbohydrate 17.8 g (1.7 g sugars), fibre 2 g, ash 0.8 g, Ca 16 mg, Fe 0.6 mg, Mg 43 mg, P 34 mg, K 415 mg, Na 13 mg, Zn 0.3 mg, Cu 0.2 mg, Mn 0.2 mg, Se 0.7 µg, E 0.3 mg, K 0.1 mg, B1 0.03 mg, B2 0.03 mg, niacin 0.8 mg, B6 0.16 mg, folate 11 µg, pantothenate 0.2 mg, C 5 mg. ginger beer Alcoholic beverage made by fermenting a sugar solu- tion flavoured with ginger.
  9. 213 ginger paralysis See jamaica ginger paralysis. gingivitis Inflammation, swelling and bleeding of the gums; may be due to scurvy, but most commonly the result of poor oral hygiene. gingko The maidenhair tree, Gingko biloba. The seeds are edible when roasted but may be toxic when raw. Extracts from the leaves are used as a herbal remedy; they contain potentially active flavonoids and terpenes, but there is limited evidence of efficacy. gin-nan Food poisoning associated with excessive consumption of gingko seeds, especially if uncooked. ginseng Herbal products from the roots of three species; Korean or Chinese ginseng is Panax ginseng, Siberian is Eleutherococcus senticosus; American is P. quinquefolius. Reported to have an immunostimulant action and act as a tonic, with limited evidence of efficacy. GIP Glucose-dependent insulinotropic peptide, originally thought to act as inhibitor of gastric acid secretion based and named Gastric Inhibitory Peptide. Like glp-1, it stimulates insulin secretion (hence the higher insulin response to oral than to intravenous glucose). See also incretins. gipping (of fish) Partial evisceration to remove intestines but not pyloric caeca, which contain the enzymes responsible for the characteristic flavour of herring when it is subsequently salted. gjetost Norwegian sweet, semi-caramelised hard cheese made from whey. Normally goat milk; mysost is similar, made from cow milk. Composition/100 g: water 13.4 g, 1951 kJ (466 kcal), protein 9.6 g, fat 29.5 g (of which 69% saturated, 28% mono-unsaturated, 3% polyunsaturated), cholesterol 94 mg, carbohydrate 42.7 g, ash 4.8 g, Ca 400 mg, Fe 0.5 mg, Mg 70 mg, P 444 mg, K 1409 mg, Na 600 mg, Zn 1.1 mg, Cu 0.1 mg, Se 14.5 µg, vitamin A 334 µg retinol, B1 0.31 mg, B2 1.38 mg, niacin 0.8 mg, B6 0.27 mg, folate 5 µg, B12 2.4 µg, pantothenate 3.4 mg. A 40 g serving is a source of vitamin A, a good source of Ca, P, pantothenate, a rich source of vitamin B2, B12. Glamorgan sausage Welsh; dish based on Caerphilly cheese, breadcrumbs and egg, fried in sausage shape. GlanolinTM blackcurrant seed oil, a rich source of γ-linolenic acid, as a dietary supplement. Glasgow magistrate See red herring. glass transition temperature In sugar confectionery, the temper- ature at which a rubbery gel becomes a clear glass, a change that does not involve latent heat.
  10. 214 gliadin A prolamin, one of the proteins that make up wheat gluten. Allergy to, or intolerance of, gliadin is coeliac disease. globins proteins that are rich in the amino acid histidine (and hence basic), relatively deficient in isoleucine. Often found as the protein part of conjugated proteins such as haemoglobin. globulins Class of proteins that are heat-coagulatable and soluble in dilute solutions of salts; they differ from albumins in being relatively insoluble in water. They occur in blood (serum globulins), milk (lactoglobulins) and some plants, e.g. edestin from hemp seed and amandin from almonds. glossitis Inflammation of the tongue; may be one of the signs of riboflavin deficiency. GLP-1 Glucagon-like peptide-1, a peptide hormone secreted by cells of the distal ileum in response to food intake; formed by post-synthetic modification of proglucagon. Like gip it stimu- lates insulin secretion (hence the higher insulin response to oral than to intravenous glucose). See also incretins. glucagon Peptide hormone secreted by the α-islet cells of the pancreas. Elevates blood glucose by increasing the breakdown of liver glycogen and stimulating gluconeogenesis. glucagon-like peptide Peptide hormone secreted by the terminal ileum; increases secretion of insulin and decreases that of glucagon. glucans Soluble undigested polysaccharides of glucose; found particularly in oats, barley and rye. See also fibre, soluble; non-starch polysaccharides. glucaric acid Or saccharic acid, the dicarboxylic acid derived from glucose. glucide (gluside) Name occasionally used for saccharin. glucitol Obsolete name for sorbitol. glucoamylase See amylase; debranching enzyme. glucocorticoids The steroid hormones secreted by the adrenal cortex (see adrenal glands), which regulate carbohydrate metabolism. See also corticosteroids. glucokinase An isoenzyme of hexokinase (EC 2.7.1.1), with a high Km, found only in liver and β-islet cells of the pancreas. One type of a rare form of diabetes mellitus (mody, maturity onset diabetes of the young) is due to a genetic defect in glucokinase. glucomannan A polysaccharide consisting of glucose and mannose. gluconeogenesis The synthesis of glucose from non-carbohydrate precursors, such as lactate, pyruvate, glycerol and glucogenic amino acids.
  11. 215 gluconic acid The acid formed by oxidation of the hydroxyl group on carbon-1 of glucose to a carboxylic acid group. Also termed dextronic acid, maltonic acid and glycogenic acid. glucono-d-lactone gluconic acid lactone; liberates acid slowly, and used in chemically leavened (aerated) bread to form carbon dioxide from bicarbonate. glucosaccharic acid See saccharic acid. glucosamine The amino derivative of glucose, a constituent of a variety of complex polysaccharides. glucosan A general term for polysaccharides of glucose, such as starch, cellulose and glycogen. glucose A six-carbon monosaccharide sugar (hexose), with the chemical formula C6H12O6, occurring free in plant and animal tissues and formed by the hydrolysis of starch and glycogen. Also known as dextrose, grape sugar and blood sugar. The carbohydrate in blood is glucose; normal concentration is between 4.5 and 5.5 mmol/L (80–100 mg/100 mL). In the fed state, glucose is used for the synthesis of glycogen in liver and muscle, as well as for synthesis of fats; in the fasting state, glyco- gen is hydrolysed as a source of glucose to maintain the blood concentration. Used in the manufacture of sugar confectionery when it is sometimes known as dextrose. The mixture with fructose prevents sucrose from crystallising. It is 74% as sweet as sucrose. glucose, confectioners’ Glucose syrups are known as glucose in confectionery making (glucose is referred to as dextrose). glucose isomerase Bacterial enzyme (EC 5.3.1.5) that catalyses isomerisation of glucose to fructose. Used in the production of fructose syrups. Main commercial source is Streptomyces spp. glucose metabolism Series of reactions in which glucose is oxidised to carbon dioxide and water as a metabolic fuel (i.e. to provide energy). The overall reaction is: C6H12O6 + 6O2 → 6CO2 + 6H2O, yielding 16.4 kJ (3.9 kcal)/g, or 2.88 MJ (686 kcal)/mol. The first sequence of reactions does not require oxygen and is referred to as (anaerobic) glycolysis or glucose fermentation, yielding two molecules of the three-carbon compound pyruvate. Under anaerobic conditions this can be reduced to lactic acid. Pyruvate is normally oxidised to acetyl CoA, which is then oxi- dised to carbon dioxide and water via the citric acid or Krebs cycle. Both glycolysis and the citric acid cycle are linked to the formation of atp from adp and phosphate, as a metabolically usable energy source.
  12. 216 An alternative to part of glycolysis, the pentose phosphate pathway or hexose monophosphate shunt, is important in the formation of reduced NADPH for fatty acid synthesis. glucose oxidase Enzyme (EC 1.1.3.4) that oxidises glucose to glu- conic acid, with the formation of hydrogen peroxide. Used for specific quantitative determination of glucose, including urine and blood glucose, and to remove traces of glucose from food- stuffs (e.g. from dried egg to prevent the maillard reaction during storage). Also used to remove traces of oxygen from products such as beer, wine, fruit juices and mayonnaise to prevent oxidative rancidity. Originally isolated from Penicillium notatum and called notatin; main commercial source is Aspergillus niger. glucose6-phosphate dehydrogenase deficiency See favism. glucose syrups See syrup; dextrose equivalent value. glucose tolerance The ability of the body to deal with a relatively large dose of glucose is used as a test for diabetes mellitus. The fasting subject ingests 50 or 75 g of glucose (sometimes calculated as 1 g/kg body weight) and the concentration of blood glucose is measured at intervals. In normal subjects the fasting glucose con- centration is between 4.5 and 5.5 mmol/L, and rises to about 7.5 mmol/L, returning to the starting level within 1–11/2 h. In dia- betes, it rises considerably higher and takes longer to return to the baseline value. The graph of the results forms a glucose tolerance curve. glucose tolerance factor (GTF) Organic chelate of chromium, Mr around 1500, variously reported to contain nicotinic acid (see niacin), glutathione and other amino acid derivatives. Potenti- ates the action of insulin, but has no activity in the absence of insulin. Acts by increasing the protein kinase activity of the insulin receptor when insulin is bound. glucosides See glycosides. glucosinolates Substances occurring widely in Brassica spp. (e.g. Brussels sprouts, cabbage, watercress, radishes); broken down by the enzyme myrosinase (thioglucosidase, EC 3.2.3.1) to yield, among other products, the mustard oils which are respon- sible for the pungent flavour (especially in mustard and horseradish). Several of the glucosinolates that are thioesters interfere with the metabolism of iodine by the thyroid gland (see thyroid hor- mones), and hence are goitrogens. There is evidence that the various glucosinolates in vegetables may have useful anticancer activity, since they increase the rate at which a variety of poten- tially toxic and carcinogenic compounds are conjugated and excreted (phase ii metabolism).
  13. 217 glucostatic mechanism A theory that appetite depends on the dif- ference between arterial and venous concentrations of glucose; when the difference falls, the hunger centres in the hypothala- mus are stimulated. glucosuria (also glycosuria) Appearance of glucose in the urine, as in diabetes and after the administration of drugs that lower the renal threshold. glucuronic acid The acid derived from glucose by the oxidation of the hydroxyl group on carbon-6. Many substances, including hormones and potentially toxic ingested substances, are excreted as conjugates with glucuronic acid, known as glucuronides. It is present in various complex polysaccharides. glucuronides A variety of compounds are metabolised by conju- gation with glucuronic acid to yield water-soluble derivatives for excretion from the body (see phase ii metabolism). glutamic acid A non-essential amino acid; abbr Glu (E), Mr 147.1, pKa 2.10, 4.07, 9.47, codons GAPu. Acidic since it has two car- boxylic acid groups; the amide is glutamine. See also monosodium glutamate. glutamine A non-essential amino acid, abbr Gln (Q), Mr 146.1, pKa 2.17, 9.13, codons CAPu. The amide of glutamic acid. glutathione A tripeptide, γ-glutamyl-cysteinyl-glycine (GSH). Important in protection against oxidative damage, since it can be oxidised to the disulphide compound (GSSG), which can then be reduced back to active glutathione. Also important in phase ii metabolism of foreign compounds, yielding mercapturic acids as a result of S-conjugation, and in the transport of amino acids into cells. glutathione peroxidase selenium-containing enzyme (EC 1.11.1.9) that protects tissues from oxidative damage by removing per- oxides resulting from free radical action, linked to oxidation of glutathione; part of the body’s antioxidant protection. Low activity in red blood cells indicates selenium deficiency, but not useful as an index of marginal status. glutathione reductase Enzyme (EC 1.6.4.2) that catalyses the reduction of oxidised glutathione (GSSG) to glutathione (GSH), and hence an important antioxidant system. Activation of this enzyme in vitro by added cofactor (flavin adenine dinu- cleotide, derived from vitamin B2) provides a means of assessing vitamin B2 nutritional status, sometimes known as the erythro- cyte glutathione reductase activation coefficient (EGRAC) test. An activation coefficient above 1.7 indicates deficiency. See also enzyme activation assays. glutelins Proteins insoluble in water and neutral salt solutions but soluble in dilute acids and alkalis, e.g. wheat glutenin.
  14. 218 gluten The protein complex in wheat, and to a lesser extent rye, which gives dough the viscid property that holds gas when it rises. None in oats, barley, maize. It is a mixture of two proteins, gliadin and glutelin. Allergy to, or intolerance of, the gliadin frac- tion of gluten is coeliac disease (gluten-sensitive enteropathy). In the undamaged state with extensible properties it is termed vital gluten; when overheated, these properties are lost and the product is termed devitalised gluten, used for protein enrichment of foods. gluten-free foods Formulated without any wheat or rye protein (although the starch may be used) for people suffering from coeliac disease. gluten-sensitive enteropathy See coeliac disease. glutose A six-carbon sugar (hexose) with a keto group on carbon- 3; not metabolised and non-fermentable. glycaemic index The increase in blood glucose after a test dose of a carbohydrate, relative to that in response to an equivalent amount of glucose. A measure of the rate and extent of small intestinal digestion of the carbohydrate. See also starch, resistant. glycation Non-enzymic reaction between glucose (or other car- bohydrates) and amino groups in proteins, resulting in formation of a glycoprotein. Glycation of collagen, crystallin and other pro- teins is the basis of many of the adverse effects of poor glycaemic control in diabetes. See also glycosylation; haemoglobin, glycated; maillard reaction. glycerides Esters of glycerol with fatty acids. See triacylglyc- erol; fat, superglycerinated. glycerine (glycerin) See glycerol. glycerol (glycerine) 1,2,3-Propane triol (CH2OH—CHOH— CH2OH), a trihydric alcohol. Simple or neutral fats are esters of glycerol with three molecules of fatty acid, i.e. triacylglycerols, sometimes known as triglycerides. Glycerol is a clear, colourless, odourless, viscous liquid, sweet to taste; it is made from fats by alkaline hydrolysis (saponification). Used as a solvent for flavours, as a humectant to keep foods moist, and in cake batters to improve texture and slow staling. glycerose Glyceraldehyde, a three-carbon sugar (CHO— CHOH—CH2OH) derived from glycerol. glyceryl lactostearate Or lactostearin. Formed by glycerolysis of hydrogenated soya bean oil followed by esterification with lactic acid, resulting in a mixture of mono- and diacylglycerols and their lactic mono-esters. Used as an emulsifier in shortenings (E-472b).
  15. 219 glyceryl monostearate See fat, superglycerinated. glycine A non-essential amino acid, abbr Gly (G), Mr 75.1, pKa 2.35, 9.78, codons CGNu. It has a sweet taste (70% of the sweet- ness of sucrose) and is sometimes used mixed with saccharin as a sweetener. Known at one time as collagen sugar. glycinin A globulin in soya bean. glycitols See sugar alcohols. Glycitol was used at one time as an alternative name for sorbitol. glycochenodeoxycholic acid The glycine conjugate of chen- odeoxycholic acid, one of the bile acids. glycocholic acid The glycine conjugate of cholic acid, one of the bile acids. glycogen The storage carbohydrate in the liver and muscles, a branched polymer of glucose units, with the same structure as amylopectin, and sometimes referred to as animal starch. In an adult there are about 250 g of glycogen in the muscles and 100 g in the liver in the fed state. Since glycogen is rapidly broken down to glucose after an animal is killed, meat and animal liver do not contain glycogen; the only dietary sources are oysters and other shellfish that are eaten virtually alive and contain about 5% glycogen. glycogenesis The synthesis of glycogen from glucose in liver and muscle after a meal, stimulated by the hormone insulin. glycogenic acid See gluconic acid. glycogenolysis The breakdown of glycogen to glucose for use as a metabolic fuel and to maintain the concentration of blood glucose in the fasting state. Stimulated by the hormones adren- aline and glucagon. glycogen storage diseases A group of rare genetic diseases caused by a defect of one or another of the various enzymes involved in glycogen synthesis and mobilisation, characterised by excessive accumulation of glycogen in liver and/or muscle and, in some forms, profound fasting hypoglycaemia. Treatment is by feeding small frequent meals, rich in carbohydrate. glycolysis The first sequence of reactions in glucose metabolism, leading to the formation of two molecules of pyruvate from each glucose molecule. glycoproteins Also known as proteoglycans; polysaccharides covalently bound to a protein, commonly via N- or O- acylglucosamine linkage to the hydroxyl group of serine or threonine. See also mucopolysaccharides; mucoproteins. glycosides Compounds of a sugar attached to another molecule; called glucosides when glucose is the sugar. glycosuria See glucosuria.
  16. 220 glycosylation Chemical reaction leading to the substitution of one or more glycosyl groups into a compound; glycation is a general term for any reaction leading to incorporation of glucose into a protein. glycyrrhizin Triterpenoid glycoside extracted from liquorice root Glycyrrhiza glabra; 50–100 times as sweet as sucrose but with liquorice flavour. Used to flavour tobacco and pharmaceu- tical preparations, and as a foaming agent in some non-alcoholic beverages. glyoxylate (sometimes also glyoxalate) The keto-acid of glycine. See also hyperoxaluria; oxalic acid. GM foods Produced by genetic modification of the plant or animal. EU legislation requires that all foods containing geneti- cally modified protein or DNA, including those sold in catering outlets, must be so labelled, unless there is less than 0.9% GM material in the food (this limit is subject to negotiation at the time of publication). Products made from GM crops, but highly purified, so that no GM protein or DNA is present (substantial equivalence), were exempt from labelling, but new legislation will require that they be labelled. Foods manufactured using products of GM organisms (e.g. cheese made using GM chy- mosin) and meat, milk and eggs from animals fed on GM crops need not be labelled as containing GM material. GMP See good manufacturing practice. GMS Glyceryl monostearate, see fat, superglycerinated. goat Ruminant, Capra spp. Young is kid. Composition/100 g: water 76 g, 456 kJ (109 kcal), protein 20.6 g, fat 2.3 g (of which 37% saturated, 53% mono-unsaturated, 11% polyunsaturated), cholesterol 57 mg, carbohydrate 0 g, ash 1.1 g, Ca 13 mg, Fe 2.8 mg, P 180 mg, K 385 mg, Na 82 mg, Zn 4 mg, Cu 0.3 mg, Se 8.8 µg, B1 0.11 mg, B2 0.49 mg, niacin 3.8 mg, folate 5 µg, B12 1.1 µg, A 100 g serving is a source of Se, a good source of Cu, Fe, P, Zn, niacin, a rich source of vitamin B2, B12. goblet cell Secretory cell in the intestinal mucosa which secretes the major constituents of mucus. gobo See burdock. goitre Enlargement of the thyroid gland, seen as a swelling in the neck, commonly due to deficiency of iodine in the diet or to the presence of goitrogens in foods. In such cases there is commonly underproduction of the thyroid hormones, i.e. hypothyroid goitre. Euthyroid goitre is a condition in which the enlargement of the thyroid gland is sufficient to compensate for a deficiency of iodine and permit normal production of thyroid hormones. In infancy, iodine deficiency can also lead to severe mental retar- dation, goitrous cretinism, with deafness. Supplementation with
  17. 221 iodide often prevents the condition, hence the use of iodised salt. Hyperthyroid goitre (thyrotoxicosis) is due to excessive stim- ulation of the thyroid gland, with overproduction of the thyroid hormones. goitrogens Compounds in foods (especially Brassica spp., groundnuts, cassava and soya bean) that inhibit either synthesis of thyroid hormones (glucosinolates) or uptake of iodide into the thyroid gland (thiocyanates), and hence can cause goitre, especially when the dietary intake of iodine is marginal. golden berry See cape gooseberry. golden syrup Light coloured syrup made by evaporation of cane sugar juice. See also treacle; sugar. Gomez classification One of the earliest systems for classifying protein–energy malnutrition in children, based on percentage of expected weight for age: over 90% is normal, 76–90% is mild (first degree), 61–75% is moderate (second degree) and less than 60% is severe (third degree) malnutrition. good manufacturing practice (GMP) Part of a food and drink control operation aimed at ensuring that products are consis- tently manufactured to a quality appropriate to their intended use (detailed in Food and Drink Good Manufacturing Practice, IFST 1998). goose Domesticated water-fowl, Anser anser. Composition/100 g: (edible portion 47%) water 68 g, 674 kJ (161 kcal), protein 22.8 g, fat 7.1 g (of which 50% saturated, 34% mono-unsaturated, 16% polyunsaturated), cholesterol 84 mg, carbohydrate 0 g, ash 1.1 g, Ca 13 mg, Fe 2.6 mg, Mg 24 mg, P 312 mg, K 420 mg, Na 87 mg, Zn 2.3 mg, Cu 0.3 mg, Se 16.8 µg, vitamin A 12 µg retinol, B1 0.13 mg, B2 0.38 mg, niacin 4.3 mg, B6 0.64 mg, folate 31 µg, B12 0.5 µg, pantothenate 2 mg, C 7 mg. A 100 g serving is a source of Fe, Zn, vitamin folate, C, a good source of Cu, Se, vitamin B2, niacin, a rich source of P, vitamin B6, B12, pantothenate. gooseberry Berry of the shrub Ribes grossularia. The British National Fruit Collection contains 155 varieties. Composition/100 g: water 88 g, 184 kJ (44 kcal), protein 0.9 g, fat 0.6 g, carbohydrate 10.2 g, fibre 4.3 g, ash 0.5 g, Ca 25 mg, Fe 0.3 mg, Mg 10 mg, P 27 mg, K 198 mg, Na 1 mg, Zn 0.1 mg, Cu 0.1 mg, Mn 0.1 mg, Se 0.6 µg, I 2 µg, vitamin A 15 µg RE, E 0.4 mg, B1 0.04 mg, B2 0.03 mg, niacin 0.3 mg, B6 0.08 mg, folate 6 µg, pantothen- ate 0.3 mg, C 28 mg. A 110 g serving a rich source of vitamin C. gooseberry, Indian See emblic. goosefoot See epazote.
  18. 222 gossypol Yellow toxic pigment found in some varieties of cot- tonseed. When included in chicken feed, it causes discoloration of the yolk, but has not been found to be toxic to human beings, and has been investigated as a possible male contraceptive agent. Chemically a dialdehyde, it reacts with the ε-amino group of lysine, thus reducing available lysine and protein quality. gossypose See raffinose. goujon Small deep fried pieces of fish. The name is derived from gudgeon, a small freshwater fish. Now also used for small pieces of chicken breast. gourds Vegetables of the family Cucurbitaceae, including cal- abash or bottle gourd (Lagenaria vulgaris), ash gourd (Benincasa hispida), snake gourd (Trichosanthes anguina), cucumber (Cucumis sativus), vegetable marrow (Cucurbita pepo), pumpkin (Cucurbita moschata), squash (Cucurbita maxima), coocha or chayote (Sechium edule), cantaloupe melon (Cucumis melo), watermelon (Citrullus vulgaris). The hedged gourd is kiwano. Calabash gourd, composition/100 g: (edible portion 70%) water 95.5 g, 59 kJ (14 kcal), protein 0.6 g, fat 0 g, carbohydrate 3.4 g, ash 0.4 g, Ca 26 mg, Fe 0.2 mg, Mg 11 mg, P 13 mg, K 150 mg, Na 2 mg, Zn 0.7 mg, Mn 0.1 mg, Se 0.2 µg, vitamin A 1 µg RE, B1 0.03 mg, B2 0.02 mg, niacin 0.3 mg, B6 0.04 mg, folate 6 µg, pantothenate 0.2 mg, C 10 mg. Chayote, composition/100 g: (edible portion 99%) water 95 g, 71 kJ (17 kcal), protein 0.8 g, fat 0.1 g, carbohydrate 3.9 g (1.9 g sugars), fibre 1.7 g, ash 0.3 g, Ca 17 mg, Fe 0.3 mg, Mg 12 mg, P 18 mg, K 125 mg, Na 2 mg, Zn 0.7 mg, Cu 0.1 mg, Mn 0.2 mg, Se 0.2 µg, vitamin E 0.1 mg, K 4.6 mg, B1 0.03 mg, B2 0.03 mg, niacin 0.5 mg, B6 0.08 mg, folate 93 µg, pantothenate 0.2 mg, C 8 mg. A 100 g serving (half fruit) is a source of vitamin C, a rich source of folate. Wax gourd, composition/100 g: (edible portion 71%) water 96.1 g, 54 kJ (13 kcal), protein 0.4 g, fat 0.2 g, carbohydrate 3 g, fibre 2.9 g, ash 0.3 g, Ca 19 mg, Fe 0.4 mg, Mg 10 mg, P 19 mg, K 6 mg, Na 111 mg, Zn 0.6 mg, Mn 0.1 mg, Se 0.2 µg, vitamin B1 0.04 mg, B2 0.11 mg, niacin 0.4 mg, B6 0.04 mg, folate 5 µg, pantothenate 0.1 mg, C 13 mg. gout Painful disease caused by accumulation of crystals of uric acid in the synovial fluid of joints; may be due to excessive syn- thesis and metabolism of purines, which are metabolised to uric acid, or to impaired excretion of uric acid. Traditionally associ- ated with a rich diet; both alcohol and fructose increase purine synthesis. G proteins Guanine nucleotide binding proteins. Part of a trans- membrane signalling mechanism in response to hormones, etc.,
  19. 223 that bind to cell surface receptors, leading to activation of enzymes that form intracellular second messengers. Gracilaria Genus of red algae, widely cultivated as a source of agar, now also cultivated to feed farmed abalone. graddan Hebrides, historical; cereal grains dehusked by holding ears of corn over flames until the husk is burnt, but before the grain is charred. grading Assessment of the overall quality of a food by a number of criteria (e.g. size, colour, flavour, texture, laboratory analysis). Graham bread Wholewheat bread in which the bran is very finely ground. Graham cakes are made from wholemeal flour and milk. The name is that of a miller of wholemeal flour who advocated its use in the USA (Treatise on Bread and Bread Making, 1837). See also allinson bread. graining Crystallisation of refined sugar when boiled. Prevented by adding glucose or cream of tartar as sugar doctors. grains of paradise See pepper, melegueta. Gram-negative, Gram-positive A method of classifying bacteria depending on whether or not they retain crystal-violet dye (Gram stain). Named after the Danish botanist H. C. J. Gram (1858–1938). grams, Indian Various small dried peas (legumes), e.g. green gram (Phaseolus aureus), black gram (Phaseolus mungo), red gram (Cajanus indicus), Bengal gram or chickpea (Cicer aretinum). grana Hard dry grating cheeses such as parmesan. granadilla See passion fruit. grape Fruit of a large number of varieties of Vitis vinifera. One of the oldest cultivated plants; three main groups: dessert grapes, wine grapes and varieties that are used for drying to produce raisins, currants and sultanas. Of the many varieties of grape that are grown for wine making, nine are considered classic varieties: Cabernet Sauvignon, Chardonnay, Chenin Blanc, Merlot, Pinot Noir, Riesling, Sauvignon Blanc, Sémillon, Syrah. Composition/100 g: (edible portion 96%) water 81 g, 289 kJ (69 kcal), protein 0.7 g, fat 0.2 g, carbohydrate 18.1 g (15.5 g sugars), fibre 0.9 g, ash 0.5 g, Ca 10 mg, Fe 0.4 mg, Mg 7 mg, P 20 mg, K 191 mg, Na 2 mg, Zn 0.1 mg, Cu 0.1 mg, Mn 0.1 mg, Se 0.1 µg, I 1 µg, vitamin A 3 µg RE (112 µg carotenoids), E 0.2 mg, K 14.6 mg, B1 0.07 mg, B2 0.07 mg, niacin 0.2 mg, B6 0.09 mg, folate 2 µg, pantothenate 0.1 mg, C 11 mg. Grapeseed oil is 10% saturated, 17% mono-unsaturated, 73% polyunsaturated, contains 28.8 mg vitamin E/100 g. grapefruit Fruit of Citrus paradisi; thought to have arisen as sport of the pomelo or shaddock (Citrus grandis), a coarser citrus
  20. 224 fruit, or as a hybrid between pomelo and sweet orange. The pith contains naringin, which is very bitter. Name said to have arisen because the fruit is borne on the tree in clusters (like grapes). Ruby grapefruit, with red flesh, was discovered as a sport in Texas in 1929. Composition/100 g: (edible portion 50%) water 90.9 g, 134 kJ (32 kcal), protein 0.6 g, fat 0.1 g, carbohydrate 8.1 g (7 g sugars), fibre 1.1 g, ash 0.3 g, Ca 12 mg, Fe 0.1 mg, Mg 8 mg, P 8 mg, K 139 mg, Zn 0.1 mg, Se 0.3 µg, vitamin A 46 µg RE (1703 µg carotenoids), E 0.1 mg, B1 0.04 mg, B2 0.02 mg, niacin 0.3 mg, B6 0.04 mg, folate 10 µg, pantothenate 0.3 mg, C 34 mg. A 170 g serving (half fruit) is a rich source of vitamin C. grape sugar See glucose. grappa See marc. GRAS (generally regarded as safe) Designation given to food additives when further evidence is required before the substance can be classified more precisely (US usage). grass tetany magnesium deficiency in cattle. gratin (1) A fireproof dish. (2) Also gratiné, French term for the thin brown crust formed on top of foods that have been covered with butter and bread- crumbs, then heated under the grill or in the oven. Au gratin when cheese is also used. grattons (gratterons) French; crispy remains of melted fat tissue of poultry or pork. German equivalent is gribbens. Grau-Hamm press For determination of the water binding or water holding capacity of meat (see meat, water binding capac- ity; meat, water holding capacity). gravadlax (gravlaks, gravlax) Originally Scandinavian; pickled or marinated raw salmon. Graves’ disease See thyrotoxicosis. gravity, original The concentration of solids in the wort from which beer is made. gray (Gy) The SI unit for ionising radiation (= 100 rad). 1 Gy = 1 J/kg. great millet See sorghum. green butter See vegetable butters. green fluorescent protein (GFP) A protein from the jellyfish Aequorea victoria that emits green fluorescence when excited by UV light. The GFP gene is widely used as a reporter gene in genetic engineering. greengage Green variety of plum introduced into England in the early 18th century by Sir William Gage. green S Food colour, also known as Wool green S and Brilliant acid green BS, E-142.
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