Pungency evaluation of onion cultivars from the Venezuelan West-Center region by flow injection analysis–UV–visible spectroscopy pyruvate determination

Abstract

A flow injection analysis (FIA) method was developed for the determination of pyruvate in onion cultivars ( Allium cepa L.) from the West-Center region of Venezuela. The reference Schwimmer and Weston (1961) (J. Agric. Food Chem. 9 (1961) 301) Batch method was modified and adapted to FIA conditions. The formation kinetic of the 2,4-dinitrophenylhydrazine (DNPH)–pyruvate complex was evaluated at room temperature and at 37 °C. It was demonstrated the suitability of the chromopher formation at room temperature. The optimal values for the FIA parameters were: sample injection volume 3 mL, flow rate 6 mL min −1, reactor length 1.5 m, sodium hydroxide concentration 1.0 mol L −1 and hydrochloric acid concentration 0.5 mol L −1. The working calibration range was extended from 80 mg L −1 (Batch method) to 700 mg L −1 with the FIA set up. The sample dilution step is thus avoided, simplifying the whole analysis process. The pungency in representative samples of the cultivars Yellow granex 438, Ultra Hybrid and Red onion “Sangre de Toro” was evaluated by the flow injection analysis (FIA)–pyruvate method and the results were compared to the reference Batch pyruvate method and to the taste panel test. Non-significant differences were found at the 95% of confidence level between the FIA method and the Batch reference method. Correlation coefficient when comparing the FIA results to the taste panel test was r 2 = 0.8353. Significant differences ( P < 0.05) were found in the pungency of the cultivars, the Ultra Hybrid having the highest pungency. The pungency order from minor to major was: Red onion, Texas Grano 438 and Ultra Hybrid.