Question

Glucose test Strips Benedict's test

Sucrose+ control 35-40C light blue / negative Blue/ Neg   

Sucrose + invertase 35-40C Dark blue/ 2000mg/dL Light Orange/ Pos

Sucrose + invertase 70-90C Emerald/ 100mg/dL light orange/ Pos

Sucrose + lactase 35-40C light blue / neg Blue/ neg

Sucrose + control 35-40C light blue/ neg orange/ pos

Sucrose + lactase 35-40C medium brown/ 1000mg light orange/ pos

Lactose + lactase 70-90C light blue/ neg light orange/ pos

Lactose + Invertase 35-40C Yellow green/ 100mg/dL Yellowish orange/ pos

Glucose control NA light blue/ 500mg/dL Redish orange/ pos

1. what do the results of the glucose test strips suggest about the enzyme specificity of invertase and lactase?

2. Discuss the degree of agreement between the glucose test strip results and Benedict's test results. If there were any disagreements, please explain what may have caused them.

3. Why did one of the disaccharides react with Benedict's test, even without being hydrolyzed? Explain wiht chemical terms.

Answer 1

Benedict's test:- (sodium carbonate + sodium citrate + cupper sulphate +distilled water) This is used for the detection of presence of monosaccharides and reducing disaccharide sugar.The result is positive, if the solution colour changes from green, yellow,orange,red or brick red (large) on boiling,means solution contains reducing sugar.

Reducing sugars acts as a reducing agent because it has free aldehyde and ketone group e.g. galactose, glucose and fructose.

Lactose (galactose + glucose) :- It is reducing sugar and lactase is specific to lactose only. It is positive Benedict's test.

Sucrose (glucose + fructose) :- It is non reducing sugar ,and invertase is specific to sucrose only so negative Benedict' test. Sucrose can give positive Benedict's test indirectly if heated with dil. HCl prior to the test results in hydrolysis.There is breakage of glycosidic bond due to hydrolysis and the resulting products are glucose and fructose and both are detected by Benedict's test.

1) Invertase enzyme used for thecatalysis of hydrolysis of sucrose and lactase enzyme is used for the catalysis of hydrolysis of lactose. All enzymes are specific in nature.There is hydrolysis of sucrose only in case of invertase so that the resulting solution will have glucose and fructose and glucose can be detected by glucose strip test.In case of lactose only lactase can hydrolyse it that result in the presence of glactose and glucose in solution,so only glucose can be detected by glucose strip test. Only in these two cases test will be positive.In other cases like sucrose hydrolysis with lactase and lactose hydrolysis with invertase there will be negative glucose strip test because there will be no hydrolysis so no glucose in the solution.

2) Glucose test strip is used to detect the presence of glucose in urine for diebetes. yellow colour is strip means absence of glucose,light yellow means very low concentration, dark blue means presence of large amount of glucose. As glucose is reducing sugar so it can be detected by both glucose strip test and Benedict's test. Both these test are used for the detection of glucose but Benedict's test used for detection of all reducing sugars and glucose strip test is used for the presence of glucose amount in sample only. Its mechanism is different from Benedict test mechanism. There is an agreement between these two test due to the detection of glucose and disagreement is that glucose strip test detect only glucose level in the sample but in Benedict's test detect the presence of all reducing sugars.

3) Those disacchrides which react with Benedict's test, without being hydrolysed are made up of reducing sugars and this test is specificity for benedict's test e.g lactose

RHC=O   + 2 Cu²⁺   + 5 OH^- RHCOOH + Cu₂O + 3 H₂O

aldehyde                                    carboxylic acid          Red ppt