Question

Starch is digested into ________ by ptyalin.
A. Maltose
B. Maltose and dextrin
C. Glucose
D. Glucose and fructose

Answer 1

Hint: Starch is a carbohydrate which is commonly found in nature. It is one of the primary sources of food energy for human beings. Starch hydrolyzing enzyme produced by human salivary glands is known as Ptyalin. It is a form of amylase which is found in the saliva of humans and some of the animals. Ptyalin enzymes are also known as alpha-amylase enzymes.

Complete answer:
Option A Maltose: Two glucose molecules bound together makes up maltose. Maltose is the key structural motif of starch which is the two-unit member of the amylose homologous series. The enzyme Ptyalin, which is secreted in the mouth, breaks down starch into both Maltose and dextrin. The reaction carried out is a hydrolysis reaction. In option A, only Maltose is given but starch is digested into both maltose and dextrin.
Hence option A is not correct.
Option B Maltose and dextrin: The group of low-molecular-weight carbohydrates produced by the hydrolysis of starch or glycogen are known as dextrin. Ptyalin is an enzyme that catalyses the conversion of starch into maltose and dextrin.
Hence option B is the correct answer.
Option C Glucose: These are a group of carbohydrates known as simple sugars and are also called as dextrose. The further hydrolysis of maltose and dextrose in the intestine forms glucose.
Hence option C is not the correct answer.
Option D Glucose and fructose: Fructose is a simple ketonic simple sugar present in many plants, where it is linked to glucose to produce sucrose, a disaccharide. Fructose is one of the three dietary monosaccharides, along with glucose and galactose which are directly absorbed into blood during the time of digestion. But the enzyme Ptyalin breaks down starch into maltose and dextrin.
Hence option D is not correct.

So, Option B. Maltose and dextrin, is the correct answer

Note:
Ptyalin can break down as much as to of ingested starches to maltose under ideal conditions during digestion in the stomach. Although ptyalin enzyme can work in a room with a high pH, it will stop working as it enters the stomach, which has a high acidity level. Ptyalin when still in the throat, can only reach a small percentage of the starch present in the diet. The majority of remaining starch will be hydrolyzed by amylase enzyme.