Phytic acid and phytase in cereals / by Sir Edward Mellanby.

  • Mellanby, Edward, Sir, 1884-1955.
Date:
[1944?]
Catalogue details

Licence: In copyright

Credit: Phytic acid and phytase in cereals / by Sir Edward Mellanby. Source: Wellcome Collection.

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    now FcCance and WIddowson have emphasized the importance of the hydrolysis of phytic acid that accompanies the change from flour to bread as the result of the action of the abundant phytase in the flour. They point out that oats and oatmeal, on the other hand, contain but little phytase to break down the phytic acid. They suggest that the difference in phytase content of wheat and oats explains the results described many years ago of the smaller rachitogenic action of bread as compared with oatmeal (2)* That this explanation is true is undoubted, but it is only part of the truth. Oats and wheat are both rich in phytic acid. In my experience oats are the richer source, but the variation in different samples of both grains is large and for the purpose of the argument we wall assume that the amount Is the same In each cereal and of .the order of 200 mgms. ohytic acid phosphorus in 100 gm. of the grain. Now; the husk which is removed in the preparation of the oatmeal forms about 30 per cent, by weight of the grain, and since this husk contains no phytic acid (it does contain a little phytase) the percentage of phytic acid In the dehusked grain rises correspondingly, namely, up to 270 mgm. or more of phytic acid phosphorus per 100 gm. oatmeal. On the other hand, in processing wheat to flour, assuming that the wheat-meal flour • is of 85 per cent, extraction, the 15 per cent, removed in the milling is largely made up of the coarser bran, .which is very rich both in phytic acid and phytase. Thus 85 per cent, extraction wheat-meal flour would contain about 120 mgm. or even less phytic acid phosphorus per 100 gm. flour. Starting, therefore, with-oats and wheat grain both containing 200 mgm. phytic acid phosphorus uer 100 gm. of grain, by the time each preparation reaches, the cook, there is a great difference between their contents: 270-300 mgm* phytic acid phosphorus in oatmeal and 120 mgm. in national wheat-meal flour; and this Is not the end of the story. . In preparing these products for the consumer, the cook again alters their relative phytic acid, content. The oatmeal is boiled as porridge, its small phytase content Is destroyed and the phytic acid remains at the same high figure. In, the case of wheaten flour, the matter is different* The high phytase content gets a chance of destroying phytic acid in the flour during the period when the dough is standing. In this process, however, the flour phytase Is not the only phytase present. The added ye.ast is also rich In this enzyme and it may, under some conditions, assist the hydrolytic breakdown of phytic acid. Whether It does so assist, seems to depend on .'.he method of bread-making adopted. If the amount of yeast added