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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 FSESLab@oregonstate.edu. Contact us for details.

The kit includes the following supplies; enough for 30 tests:

  • 30 Marked square Cuvettes with caps
  • Handheld Press
  • Sample Cups
  • Pipet
  • 30 Pipet tips
  • Color chart
  • 30mL Distilled water
  • 30mL DNPH solution (2,4-Dinitrophenylhydrazine)
  • 30mL NaOH solution (Sodium hydroxide)
  • Safety Data Sheets for DNPH and NaOH
  • Instructional sheet

Not included: knife and cutting surface
 
The refill kit includes the following supplies; enough for 30 tests:

  • 30 Marked square Cuvettes with caps
  • Sample Cups
  • 30 Pipet tips
  • 30mL Distilled water
  • 30mL DNPH solution (2,4-Dinitrophenylhydrazine)
  • 30mL NaOH solution (Sodium hydroxide)
  • Safety Data Sheets for DNPH and NaOH

Please direct all pre-sales inquires to FSESLab@oregonstate.edu. For post-sales inquires, call 541-737-1781 for immediate assistance.