Reliable and inexpensive colorimetric method for determining protein-bound tryptophan in maize kernels

Area of Science:

• Agricultural Science
• Biochemistry
• Nutritional Science

Background:

• Biofortification programs have developed Quality Protein Maize (QPM) with enhanced lysine and tryptophan.
• Monitoring these essential amino acids is vital for genetic gain in QPM breeding.
• Maize is a staple food for protein-deficient populations, making QPM improvement critical.

Purpose of the Study:

• To develop an accurate, reliable, and inexpensive method for tryptophan analysis in whole-grain maize flour.
• To support global Quality Protein Maize (QPM) research and breeding efforts.
• To facilitate monitoring of tryptophan content for maximizing genetic gains.

Main Methods:

• A colorimetric method utilizing the reaction of tryptophan with glyoxylic acid, sulfuric acid, and ferric chloride.
• Optimization of reagent concentrations, hydrolysis time, and colorimetric reaction duration.
• Adaptation of the method for high-throughput analysis using a microplate platform.

Main Results:

• An optimized protocol was established using 0.1 M glyoxylic acid in 7 N sulfuric acid and 1.8 mM ferric chloride with a 30-minute reaction time.
• The method yielded stable and reproducible tryptophan concentration results in whole-grain maize flour.
• Validation demonstrated strong correlation with existing methods: r(2) = 0.80 with acetic acid colorimetry and r(2) = 0.71 with HPLC.

Conclusions:

• A cost-effective and robust colorimetric method for tryptophan analysis in maize flour has been successfully developed.
• The method's reliability and adaptability for high-throughput screening will significantly aid QPM breeding programs.
• This analytical tool will contribute to enhancing the nutritional value of maize for vulnerable populations worldwide.