Q. Determine the fructose to glucose ratio in honey?
This activity will help you to:
• check the given samples of honey for any adulteration with commercial sugars, and
• check the conformance or non-conformance of the samples to the standards for fructose to glucose ratio
Principle
The major sugars present in honey are fructose, glucose, followed by lower concentration of sucrose and maltose. The actual proportion of glucose to fructose in any particular honey depends largely on the source of the nectar. The average ratio of fructose to glucose is 1.1:1. Other sugars found in small amounts in honey are isomaltose, nigerose, kojibiose, turanose, gentibiose and laminaribose. Although, analysis of honey for physical, chemical and microbiological parameters give a good picture about the quality of honey, but, it is possible that the adulteration with the low cost sugar syrups such as invert syrups or high fructose corn syrup (HFCS) may go undetected. Thus, now-a-days carbon isotope ratio methods are recommended by Association of Official Analytical Chemists (AOAC) to detect the adulteration of expensive honey with cheap HFCS and invert cane sugar. According to this method, the carbon isotope ratio of the honey and that of the protein isolated for that honey should be similar, as nearly all the protein in honey originates from the bee in the form of enzymes that ripen the nectar. The addition of corn syrup to honey will change the carbon isotope ratio of the honey but not of the protein. If the honey has been adulterated with invert sugar or HFCS, the honey will have ratio of the carbon isotope significantly different from that of honey protein.
But, here in this exercise we will be carrying out the simple experiment on detection of fructose to glucose ratio titration.
Reagents Required
Iodine (I2) solution (0.05 N)
NaOH - 0.1 N
Standard sodium thio sulphate solution = 0.05 N = 12.4 g/l
Starch solution (freshly prepared)
Materials Required
Sample of honey
Iodination flask
Beaker
Burette
Procedure
Carry out the activity following the steps enumerated herewith.
1) Place accurately 1 gm of honey solution in 250 ml of volumetric flask.
2) Dilute with about 150 ml of water.
3) Mix thoroughly contents of glass and make the volume to 250 ml.
4) Pipette 50 ml of honey solution in a 250 ml stoppered iodination flask.
5) Add 40 ml of Iodine solution.
6) Add 25 ml of NaOH solution.
7) Stopper the flask and keep in dark place for 20 minutes.
8) Acidify the solution with 5 ml of H2SO4 and titrate quickly the excess of I2 against standard Sodium thiosulphate solution.
9) After adding some sodium thiosulphate add few drops of starch solution and see the change of colour from voilet to colourless.
10) Now repeat steps 5 to 9 once again. Start by taking 50 ml water (distilled) instead of honey solution.