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On the Effectiveness of Malt Amylase on the Gastric Digestion of Starches

Department of Physiology and Pharmacology, Northwestern University Medical School, Chicago

1. When cooked starch containing malt extract was placed in the stomach of dogs with a pouch of the entire stomach and retained there and histamine injected to stimulate the secretion of the pouch, 20 % (corrected) of the starch was digested in 1 hour before the acidity rose to a point at which malt amylase is inactivated. Ninety-five per cent of the digestion occurred in the first 30 minutes.

2. A. In dogs with a complete duodenal fistula with the bile and pancreatic juice excluded, the addition of malt extract to a meal of cereal (‘farina’) appreciably facilitated gastric emptying because of the liquefying action of amylase. The addition of malt amylase increased the digestion of the starch from a control value of from 5 to 12 % to a value of from 30 to 65 % (average increase 370 %). About 87 % of the amylase passed into the duodenum in active form in these experiments. Variations in the per cent of starch digestion were directly correlated with the rate of evacuation and the rise in acidity of the gastric contents.

B. When a known quantity of malt amylase in water was drunk after the ingestion of a cereal meal, 75 % of the enzyme passed into the duodenum within 10 minutes the remainder becoming mixed with the gastric contents to promote the gastric digestion of starch (16 to 20 % increase). Thus, if it is desired to introduce malt amylase rapidly into the intestine in active form, this is best accomplished by taking the enzyme in water after a meal (vide infra).

3. A. The results obtained on dogs with an incomplete duodenal fistula and with pancreatic juice and bile excluded compared favorably with those on the complete duodenal fistula dogs, except that the percentage gastric digestion of starch was somewhat less on the average, varying from 30 to 40 %. This was due to the more rapid rise in gastric acidity in incomplete duodenal fistula dogs.

B. When a diastatically equivalent amount of human saliva was substituted for malt amylase, considerably more starch digestion resulted with malt amylase. This is due to the fact that ptyalin, which is inactivated at pH 4.5 does not act as long in the stomach as malt amylase which is inactivated at pH 2.5.

C. When the experiment cited under 2 B above was repeated on these dogs, which more closely simulate the normal, both milk and water being used as a solvent of the malt extract, it was found that with water from 69 to 71 % of the enzyme is obtained from the duodenum in 30 minutes, whereas with milk 34 to 54 % of the enzyme is obtained, because the milk does not leave the stomach as rapidly as water. The milk buffers acid and the acidity rises somewhat more slowly. However, with the administration of an excess of malt amylase little difference, if any, in the amount of gastric digestion of starch would obtain.

4. A. In experiments on human subjects performed so as to simulate a salivary deficiency, the addition of malt extract to a cereal meal definitely augmented the gastric digestion of starch in seven out of eight subjects. The variations observed depended upon the rate at which the acidity of the gastric contents rose.

B. In experiments designed to ascertain the amount of active malt amylase given with a cereal meal that passes into the intestine before the acidity rises to the lethal point of the enzyme, the minimum figure of 42 and a maximum of approximately 100 % was obtained, the average being 51 %.

C. In experiments in which salivary amylase was permitted to play its normal role and a mixed meal (mashed potatoes, milk, liver sausage and butter), containing a moderate amount of acid buffering substances was ingested after which milk with and without malt extract added was drunk, it was found that the addition of malt amylase increased the gastric digestion of starch in four of ten subjects. In six the gastric digestion of starch was completed by ptyalin and the addition of malt amylase was superfluous. Thus, in the larger percentage of normal human subjects who partake of a mixed meal containing a moderate amount of substances which buffer acid, the gastric starch digestion resulting from salivary amylase is practically complete.

5. Neither salivary nor malt amylase after being inactivated in the stomach are reactivated in the intestine. This confirms Bergeim.