Question

Would the glucose test be suitable for analyzing the following samples? Which of the three unknown enzyme treatments would give positive results? Explain your answers.

• the amount of glucose present in a fruit
• the amount of carbohydrates in a beverage sweetened with high fructose corn syrup
• the number of monosaccharides present in a bacterial sample

Answer 1

By glucose test,

glucoe test help to identify the presence of monosaccharides not the amount of monosaccharide is determined so the amount of glucose in fruit and amount of carbohydrate in sweetened beverage with fructose cannot be determined. Only the presence can be identified.But the number of monosaccharides present in the bacterial sample can be determined.

• this is by benedict's and fehling's reaction positive result shows the presence of monosaccharides
• reducing sugars such as glucose, fructose, .. give positive result
• in case of benedict's test reducing sugars reduce cupric ions to cuprous forms which form red ppt
• in case of fehling's test here Rochelle's salt is used and positive result is with red colour solution
• barfoed's reaction is used to distinguish between monosaccharide and disaccharide.aldose and ketose reduce cupric ions even in the acidic medium .This reaction is faster in case of monosaccharide if we prolong heating disaccharide give positive result so restriction of time of heating is important
• phenylhydrazine test is used to find the type of monosaccharide and disaccharide based on their osazone formation needle shape osazone formd by glucose/ fructose/ mannose, sunflower shape osazone by maltose,cotton ball shaped osazone by lactose and sucrose is negative for this test
• presence of fructose is confirmed by seliwanoff's test , cherry red coloured complex formation is the positive result