Estimation of tryptophan
Cereals like maize and sorghum are deficient in tryptophan in addition to lysine. Methods to determine these essential amino acids are useful to identify nutritionally superior types.
The indole ring of tryptophan gives an orange-red color with ferric chloride under strongly acidic condition. The color intensity is measured at 545nm.
» Papain Solution: Dissolve 400mg technical grade papain in 100mL 0.1N sodium acetate buffer pH 7.0. prepare the solution fresh every day.
» Reagent A: Dissolve 135mg FeCl3.6H2O in 0.25mL water and dilute to 500mL with glacial acetic acid containing 2% acetic anhydride.
» Reagent B: 30N H2SO4.
» Reagent C: Mix equal volumes of reagent A and B about one hour before use.
» Standard Tryptophan: Dissolve 5mg Tryptophan in 100mL water (50mg/mL)
Draw a standard curve. Subtract the absorbance value of the blank from that of the sample and calculate tryptophan content from the graph.
1. Mertz, E T, Jambunathan, R and Misra, P S (1975) In: Protein Quality Agricultural Research Stn. Bull No. 7 Purdue Univ USA p. 9.
2. Theymoli Balasubramanian and Sadasivam, S (1987) Plant Foods Hum Nutr 37 41.
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