Incubation Time, Cultivar, and Storage Duration Affect Onion Lachrymatory Factor Quantification

Abstract

The lachrymatory factor [LF, (Z,E) propanethial S-oxide] is a direct product of 1-propenyl cysteine sulfoxide (1-PRENCSO) hydrolysis and dominates onion flavor when present in high concentrations. To evaluate LF as a potential means of assessing flavor quality, two onion cultivars were greenhouse-grown and the bulbs stored for 4 months at 3 ± 1 °C, 70% relative humidity. Onions were evaluated at monthly storage intervals for LF development in bulb macerates following a 120 seconds incubation time. When LF was compared to amounts of 1-PRENCSO hydrolysis, we found that LF was severely underestimated. The relationship of LF and 1-PRENCSO also varied between cultivars during storage. As `Granex 33' was stored for longer periods, the amount of LF measured at 120 seconds more closely reflected the amount of 1-PRENCSO hydrolyzed. LF from `Dehydrator #3', however, was consistently underestimated regardless of storage time. Therefore, a second experiment was conducted using individual bulbs of two onion cultivars in an attempt to determine the optimal incubation time for LF quantification. Maximum LF among bulbs was generally detected 5-10 seconds after tissue maceration for `Dehydrator' and after 15-30 seconds for `Sweet Vidalia'. The amount of LF quantified between 5 and 120 seconds decreased linearly for nine of ten bulbs of `Dehydrator', but this trend was less apparent for `Sweet Vidalia'. A uniform LF incubation time for individual bulbs, therefore, may not be possible for all cultivars. These data show a complex relationship among and within onion cultivars for 1-PRENCSO hydrolysis and the formation of LF in onion macerates.