Colorimetric Sweet Onion Test Kit for the determination of pyruvic acid as an indicator of pungency in onions.
Sweet onions are valued for their unique flavor and praised for their health and dietary character. These varietals of onions bring a higher market price. Onion sweetness is perceived as the degree of pungency decreases. Pungency can be quantitatively determined in onions by measuring enzymatically produced pyruvic acid. The onion industry quantifies a sweet onion as one having a enzymatically produced pyruvic acid concentration of <5 μmol/g. Identification of pyruvic acid is accomplished by reacting onion extract with 2, 4-dinitrophenylhydrazine (DNPH) to produce a colored adduct that is measured spectrophotometrically (intensity of the color). Based on the laboratory method we have created a validated colorimetric chart-based field test kit that can be used on site, or in any onion packing house. The color produced when using the kit can be compared to a color chart provided (see example below) and sweetness of the onion determined.
The FSES Sweet Onion Test Kit and refill kits can be purchased by contacting peter.hoffman@oregonstate.edu. Contact us for details.
