High Throughput Screening of Pyruvic Acid in Onions using Microplate Reader

Onions are valued for their distinctive flavor and recognized for their potential health benefits.  Pungency of onions is a major criterion for economic remuneration and it can be quantified by measuring the enzymatically produced pyruvic acid. The pyruvic acid content is significantly influenced by the variety, location, and their interaction with the environment. Approximately, 80% of the total variation is caused is due to genetic differences in the onions. This is a major problem to the cultivators in maintaining the produce quality of mild onions. Therefore, accurate measurement of pyruvic acid is critical. In the present study, a rapid colorimetric method using automated microplate reader was developed to determine pyruvic acid in onions. In brief, onion samples  were treated with 2,4-dinitrophenylhydrazine followed by potassium hydroxide (KOH) to produce a colored adduct. The absorbance of the colored complex was read at λ485 nm using a micro plate reader. KOH enhanced the stability of the colored complex up to two hours. The developed method is simple, robust, economical and reproducible for routine determination of pungency in large number of onions. The method can be applied to determine the level of pyruvic acid content in different onion cultivars. This project is based upon work supported by the USDA–NIFA # 2010-34402-20875 "Designing Foods for Health" through the Vegetable & Fruit Improvement Center, Texas.