Benders'dictionary of nutrition and food technology

307methotrexate 4-Amino-10-methyl folic acid, a folic acid antagonistused in cancer chemotherapy; inhibits dihydrofolate reductase(EC 1.5.1.3).methylated spirits See alcohol, denatured.methyl cellulose See cellulose.methylene blue dye-reduction test When the dye methylene blueis added to milk, any bacteria present take up oxygen anddecolourise the dye. A similar test uses resazurin, which changesfrom blue-purple to pink. The speed of the change indicates thebacterial content. Pasteurised milk (see pasteurisation) must notreduce the dye in 30 min.methylene tetrahydrofolate reductase Enzyme (EC 1.7.99.5)involved in folic acid metabolism.A thermolabile variant occursin 10–20% of the population leading to high blood levels ofhomocysteine, associated with atherosclerosis, thrombosis andpossibly neural tube defect.methyl folate trap Hypothesis to explain the occurrence of megaloblasticanaemia and functional folic acid deficiency in vitaminb 12 deficiency. Folic acid is transported between tissues as methylfolate, which can only be utilised by the vitamin B 12 -dependentenzyme methionine synthetase (EC 2.1.1.13), so in vitamin B 12deficiency there is accumulation of folate as methyl folate, whichcannot be utilised.3-methylhistidine Derivative of the amino acid histidine, foundalmost exclusively in the contractile proteins of muscle (myosinand actin). Useful as an index of lean meat content of foods,because it is not present in collagen or other added materials.Formed in protein after synthesis, and not reutilised whenprotein is catabolised. Urinary excretion has been proposed asan index of muscle protein turnover, but smaller pools of methylhistidine in non-muscle tissues turn over faster than muscle, andconfound the interpretation of results.methylisoborneol (MIB) Microbial metabolite that can causeearthy or musty off-flavour in freshwater fish.methylmalonic acid Methylmalonyl CoA is an intermediate inthe metabolism of valine, isoleucine and the side-chain of cholesterol,as well as (rare) odd-carbon fatty acids. It is normallymetabolised by a vitamin b 12 -dependent enzyme, methylmalonylCoA mutase (EC 5.4.99.2); in deficiency, the activity of thisenzyme is impaired and methylmalonic acid is excreted in theurine, especially after a test dose of valine or isoleucine. Methylmalonicaciduria also occurs as a genetic disease due to deficiencyof methylmalonyl CoA mutase.N 1 -methyl nicotinamide Major urinary metabolite of niacin, andmeasured as an index of niacin status. Some methyl nicotinamide