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Exercise
Practical 9 - Estimation of sugars (non-reducing and total sugars) |
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Aim: Estimation of non -reducing and total sugars in fresh fruits and processed products using Lane and Eynon method
Theory: Glucose and fructose in the fruits represent reducing sugars while sucrose or cane sugar added to the fruit products represents the non-reducing sugar. They are estimated by using Lane and Eynon method which measures sugar as reducing sugar and total sugar as invert sugar. Non-reducing sugar is determined by subtracting the total reducing sugar from reducing sugar and multiplying the remainder with 0.95 factor. Principle: Invert sugar reduces the copper in Fehling’s solution to red, insoluble cuprous oxide. The sugar content in a food sample is estimated by determining the volume of the unknown sugar solution required to completely reduce a known volume of Fehling’s solution. Glucose and other sugars are capable of reducing oxidizing agents and are called reducing sugars and this property is used for the estimation of sugars. The cupric ion in Fehling’s solution is reduced to cuprous state which precipitates as red cuprous oxide (Cu2O). Only reducing sugars reduce the copper solution. CuSO4 + 2NaOH → Cu (OH)2 + Na2SO4 Cu (OH)2 → CuO (Cupric oxide) 2CuO + CHO → Cu2O (Cuprous oxide) + COOH Apparatus, reagents and glassware required
Standardization of Fehling’s solution: Mix 5ml Fehling A + 5ml Fehling B solution in 250ml conical flask. Add 25-50ml water and heat the flask. Add standard invert sugar solution from the burette dropwise till the solution turns brick red. Add few drops of Methylene blue indicator and add drop-wise invert solution, when the blue color disappears, note the titre value of invert solution, repeat the titration and calculate factor for Fehling’s solution as under:- Titre x 2.5 Factor for Fehling solution (g of invert sugar)= ------------------× 1001000 Procedure for estimation of Total Sugar
Calculations mg of invert sugar x dilution x dilution x 100 Total sugar as invert sugars (%) = --------------------------------------------------------------------------------------- x 100 titre x weight of sample taken x Volume of aliquot taken for hydrolysis ×1000 Sucrose or non-reducing sugar (%) = (% total sugar as invert sugar ¬¬ % reducing sugar) x 0.95 Total sugar (%) = % Reducing sugars + % sucrose Non-reducing sugars (%) = Total sugars - reducing sugar Results: Fruit contain more reducing sugar while fruit product prepared by using cane sugar contains more non-reducing sugars. Problem: 25gm of mango juice was neutralized with 1N NaOH and made to 250 ml and filtered. 50ml of filtrate was deleaded and made to 100ml followed by filtration. The solution was utilized for estimation of reducing sugar whose titre was 15ml. Out of this deleaded filtrate 50ml was acidified for inversion and neutralized with NaOH and made to 100ml. The sample was utilized for estimation of total sugar, the titre value of which was found to be 18ml. Calculate total and non-reducing sugars of the given mango squash. Factor for Fehling’s solution is 0.05. Solution: Given
For total sugar Volume of deleaded sample taken for total sugar 50 ml Factor for Fehling=0.05 0.05 × 250 × 100 × 100 % reducing sugar = ----------------------------------------× 100 15 × 25 × 50 Total sugar as reducing sugars (%) = 6.67% % 0.05 × 250 × 100 × 100 × 100 18 × 25 ×50 × 50 Total sugar as invert sugar = 11.11% % Sucrose (Non-reducing sugar)= (Total sugar as invert sugar - reducing sugar) × 0.95 = (11.11 – 6.67) × 0.95 = 4.44 × 0.95 = 4.22% Total sugar= % reducing sugar + % non-reducing sugars
= 6. 67 + 4.22 = 10.89% Inference: Thus, the sample of mango juice contained 6.67% reducing sugars, 4.22% non-reducing sugars and 10.89% total sugars. |
Last modified: Wednesday, 7 March 2012, 10:33 AM