DEVELOPMENT OF A SIMPLE PUNGENCY INDICATOR TEST FOR ONIONS

Long-day yellow onions differing in pungency were used to compare methods for appraisal of pungency. Pyruvate, an established indicator of pungency for Allium species, was determined by the lactate dehydrogenase and 2,4-dinitrophenyl hydrazine methods. Thiosulfinate content, another indicator of pungency, was determined spectrophotometrically by monitoring the absorbance at 515 nm after reaction with N-ethylmaleimide. Significant correlation (R2 = 0.871) existed between thiosulfinate content and pyruvate concentration. In addition, a modified N-ethylmaleimide reaction was used to develop a simple pungency indicator test which adequately detected differences between bulbs. The color produced by this method was analyzed using a HunterLab reflectance colorimeter. The Hunter a value and saturation index (C) correlated with both thiosulfinate content and pyruvate concentration (R2 = 0.735-0.860). The procedure described provides the potential for screening of pungency of large numbers of Allium samples.