Benders'dictionary of nutrition and food technology

372saturated fatty acid. The third hydroxyl group is esterified tophosphate and one of a number of water-soluble compounds,including serine (phosphatidylserine), ethanolamine (phosphatidylethanolamine),choline (phosphatidylcholine, alsoknown as lecithin) and inositol (phosphatidylinositol).Cell membranes are a double layer of phospholipids with thefatty acid side-chains on the inside. The water-soluble compoundesterified to the phosphate interacts with water.This is why phospholipidscan be used to emulsify oils and fats in water and arecommonly used in food manufacture as emulsifiers. From theenergy point of view they can be regarded as being equivalentto simple fats (triacylglycerols); they also provide a source ofcholine and inositol, neither of which is a dietary essential.phosphoproteins Proteins containing phosphate, other than asnucleic acids (nucleoproteins) or phospholipids (lipoproteins),e.g. casein from milk, ovovitellin from egg yolk.phosphoric acid May be one of three types, orthophosphoric acid(H 3 PO 4 ), metaphosphoric acid (HPO 3 ) or pyrophosphoric acid(H 4 P 2 O 7 ). Orthophosphoric acid and its salts are E-338–341, usedas acidity regulators and in acid-fruit-flavoured beverages suchas lemonade.phosphorus An essential element, occurring in tissues and foodsas phosphate (salts of phosphoric acid), phospholipids andphosphoproteins. In the body most (80%) is present in the skeletonand teeth as hydroxyapatite; the remainder is in the phospholipidsof cell membranes, in nucleic acids and in a varietyof metabolic intermediates, including atp.The parathyroid glands (see parathyroid hormone) controlthe concentration of phosphate in the blood, mainly by modifyingits excretion in the urine. Human dietary needs (about 1.3 gper day) are almost always met; deficiency rarely occurs in adults.The calcium :phosphate ratio of infant foods is, however,important.Phosphate deficiency is common in livestock and gives rise toosteomalacia (also known as sweeny or creeping sickness).Phosphate is also essential for plant growth, hence the use ofinorganic phosphate or bone meal as fertiliser.phosphorylase Enzyme (EC 2.4.1.1) responsible for the breakdownof glycogen and starch to glucose 1-phosphate. In vegetablesassociated with formation of sugars during ripening and onstorage. Important in potatoes during storage because it remainsactive at low temperatures whereas enzymes of glycolysis arecold labile, so that sugars accumulate rather than being utilised.photon absorptiometry Technique for determination of bonedensity, as an index of calcium and vitamin d status.