Hello everyone.The protein content of food is mostly determined on the basis of total nitrogen content. Kjeldhal method is almost universally applied to determine nitrogen content but the calculation of total nitrogen content multiplied by 6.25 is unsuitable for plant sample due to presence of high NPN.So for seaweed what should be the standard formula for protein estimation?Please suggest.
Generally, protein may be generalized by nitrogen percent multiplied by 6.25
Take 0.2 g of dried plant sample powder after passing through a 1 mm diameter sieve and then digest the sample by adding 4% H2O4 + HClO4 mixture with heating until a solution is obtained according to Pearson and Cresser (1979) method. Transfer the output of digestion in bottles size and full size to 50 cm 3 is estimated Nitrogen and according to the following: The protein percentage is then calculated on the basis of the following equation: Percentage of protein =% of nitrogen × Factor depends on plant type
Hi Sushri, in our lab we calculate the total protein content in seaweed samples
based on the nitrogen content (N) according to the Dumas combustion method described in the German Food Act (2005) using a nitrogen analyser FP
528 (Leco Corporation, St. Joseph, MI, USA) with a conversion factor of 6.25.
Nitrogen may be analysed by Kjaldahal method and percent of protein analysed may be
multiple by conversation factor of protein 6.25.
Take 0.2 g of dried plant sample powder after passing through a 1 mm diameter sieve and then digest the sample by adding 4% H2O4 + HClO4 mixture with heating until a solution is obtained according to Pearson and Cresser (1979) method. Transfer the output of digestion in bottles size and full size to 50 cm 3 were estimated elements and according to the following: Total nitrogen is estimated by distillation after the addition of 10 NaOH by a micro-Kieldahl device as indicated (Haynes, 1980). Protein% = Nitrogen percentage × 6.25
Suitable amount weight (.5 to 1 gm ) of oven dry plant sample at 60 to 70 degree centigrade taken in a microjalda flaxk and digestion mixture of sodium thiosulfate and copper sulphate (0.5 to 1 gm )and concentrate sulphuric acid 5 ml digested on a heater so about 350 to 400 degree centigrade and digestion mixture indicate blue colour as completion of digestion. Digestion mixture may be transferred to distillation apparatus for distillation with about 40 % NaOH and liberated ammonia absorb in 20 % boric acid with mix indicator of methyl red and bromocresol indicator and titrated against standard 0.02 N sulphuric acid with end point of titration with faint red colour . Nitrogen percent ×6.25 = % of protein.
Thank you.But due to presence of high Non protein nitrogen content in plant sample 6.25( nitrogen conversion factor) is not suitable.So what is the suitable conversion factor for plant sample?
Dear Sushri S.Behera
The conversion factor is calculated on the basis of the amount of nitrogen present in 100 gm in the specific plant protein
One correction may be made for method of estimation of total nitrogen in plant .In case of sodium thiosulphate potsssium sulphate should be use .Plant body generally contain about 5 % total protein. On that basis correlation factor has been evaluated. So,you please observed types of plant sample and develop corretion factor for your sample.In this case you may substruct nonprotein nitrogen compound and evaluate actual value of protein.
Standard method of estimation may be done by aminoacid estimation of plant protein by HPLC method.
Approximate protein may be
developed throug multiplcation of nitorogen percent by 6.25.
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