Total Soluble Proteins

Potato is a very good source of high quality protein. Average protein content of potato is 2% on fresh weight basis and about 10% on dry weight basis. The total nitrogen of potato tubers can be divided into soluble protein, insoluble protein and soluble non-protein nitrogen. The insoluble protein fraction is mainly present in the peel. Soluble potato protein contains substantial levels of the essential amino acids. Free amino acids present in potatoes are totally available for absorption. Potato protein has an adequate ratio of total essential amino acids to total amino acids and a balance among individual essential amino acid concentrations to meet the needs of infants and small children. Potato protein has a very high biological value since all the essential amino acids are present in it in a good proportion. With its high lysine content, potato can supplement diets which are limiting in lysine. Potato is a superb food which has correct balance between net protein calories and total calories adequate for all age groups.

Reagents :

1. 0.1N sodium hydroxide

2. 15% trichloroacetic acid

3. Solution A: 2% sodium carbonate in 0.1N sodium hydroxide

4. Solution B: 0.5% CuSO₄.5H₂O in 1% sodium potassium tartarate

5. Solution C: Prepared by mixing 50mL of solution A with 1mL of solution B. This reagent is freshly prepared at the time of use.

6. Solution D: Folin-Ciocalteu phenol reagent and distilled water are added in equal quantity at time of use

7. Standard: 20mg Bovine serum albumin/100mL DW

Extraction Procedure

• Take 1g dry sample and add 5mL of 0.1N sodium hydroxide.

• Vortex and centrifuge (10,000rpm, 10 min).

• Collect supernatant and raise the volume to 5mL with 0.1N sodium hydroxide.

• Add 1mL of 15% trichloroacetic acid.

• Incubate the samples at 4°C for 24h.

• Centrifuge the samples at 5000rpm for 20 min.

• Discard supernatant.

• Dissolve the residue in 5mL of 0.1N sodium hydroxide.

Analysis procedure :

• Take 0.5mL of aliquot and add 5mL of solution C to it.

• Shake the samples and keep it for 5 min.

• Add 0.5mL of solution D. Incubate the samples at room temperature for 60 min.

• Measure the absorbance at 570nm.

Reference: Lowry OH, Rosenbrough RJ, Fern AL, Randall RJ (1951) Protein measurements with Folin-phenol reagent. Journal of Biological Chemistry193: 263-75.