Protein content in foods, animal feeds, milk, etc. is commonly determined by com

Question

Protein content in foods, animal feeds, milk, etc. is commonly determined by
combustion analysis for nitrogen content in CnHmOpNq. The average N-content of pure
proteins is about 16% by weight. In comparison, carbohydrates typically contain no (or little)
nitrogen, with C:H:O ratios close to 1:2:1. In recent years, many products including dairy
products and pet food manufactured in China were found to be tainted with a synthetic
chemical known as Melamine, C3H6N6. Industrial applications of Melamine include
polymers and adhesives. The best known scandal related to Melamine contamination in
China is that Melamine was found in milk powder for infants, which led to the deaths of six
babies and made some 300,000 ill. Six people were linked to the scandal and two of the
convicts were sentenced to death and executed in 2009.
(a) Calculate the N-content by weight in Melamine.
(b) If a diary product is analyzed to have an N-content of 10%, what are the proportions of
protein and carbohydrate in this product?
(c) If 100 kg of the same product as in (b) is tainted with 5 kg Melamine, what is the apparent
N-content of this product?

Explanation / Answer

(a) Calculate the N-content by weight in ( Melamine) C3H6N6

Weight of 1 mol of (Melamine)C3H6N6 =12*3+6*1+6*14.01 = 126.06

Weight of N = 6*14.01 = 84.06

N-content by weight % = 84.06/126.06*100 = 66.7%

(b) If a diary product is analyzed to have an N-content of 10%, what are the proportions of protein and carbohydrate in this product?

Let protein is x%.

100gm diary contains

N = 10gm

Protein = x gm

Carbohydrate = (100 - x) gm

The average N-content of pure

proteins is about 16% by weight.

100gm of protein contains 16 gm N

X gm protein contains 0.16*x gm N

So 0.16*x = 10

X = 62.5gm

Proportion of proteins = 62.5/100 = 0.625

Proportion of carbohydrate = 1-.625 = 0.375

(c) If 100 kg of the same product as in (b) is tainted with 5 kg Melamine, what is the apparent N-content of this product?

Final product contains

protein 62.5kg

Carbohydrate 37.5kg

N-content in diary product is 10% of 100kg = 10kg

Melamine 5 kg

N-content in Melanine is 66.7% of 5kg = 0.667*5 = 3.335kg

Total N-content = 10+3.335 = 13.335kg

Total weight = 200+5 = 105kg

% N-content = 13.335/105*100 = 12.7%

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