Assessment of the flavour of fresh uncooked onions by taste‐panels and analysis of flavour precursors, pyruvate and sugars

Abstract

Flavour in fresh onions is dominated by volatile sulphenic and thiosulphenic acids that are liberated once alk(en)yl cysteine sulphoxide (ACSO) flavour precursors are cleaved by the enzyme alliinase after tissue disruption. The levels of pyruvate and ACSOs in over 100 samples of onions marketed in the UK were measured, and compared with assessment by taste-panels. There was a linear relationship between the content of ACSOs and pyruvate. Measurements of pyruvate indicated that the marketing classification of some types of onion did not correspond to their pyruvate levels. A significant linear relationship was found between a sensory measure of strength and pyruvate over the range 1.2-9.3 µmol pyruvate g −1 fresh weight. In most cases, when a flavour classification of sweet, mild or strong was applied to a sample of onions based on pyruvate content, the taste-panels agreed with the categorization. The taste-panels were unable to identify a sweet flavour in onions, except at low levels of pyruvate. Taste-panels were able to define a likeability character (attractiveness of flavour) for onions, which correlated with the level of pyruvate. However, for some varieties, the flavour classification or likeability did not correspond to predictions based on pyruvate levels alone. Pyruvate measurements were seen as a suitable method for routine quality control once the characteristics of a variety of onion had been established, but initial evaluations should include well-designed taste-panel assessments.

Molecular and biochemical identification of alien chromosome additions in shallot (Allium cepa L. Aggregatum group) carrying extra chromosome(s) of bunching onion (A. fistulosum L.)

“…Since 1 mol of pyruvic acid is produced for each mole of ACSO hydrolyzed by alliinase, enzymatically produced pyruvic acid has long been used as a proxy for measuring pungency (Schwimmer and Weston, 1961). Crowther et al (2005) showed a linear relationship between the content of ACSOs and pyruvic acid. In addition, they showed a negative correlation between the sweetness and pyruvic acid content.…”

Development of Novel Glucose and Pyruvate Biosensors at Poly(Neutral Red) Modified Carbon Film Electrodes. Application to Natural Samples

“…Flavor in fresh onions is dominated by volatile sulfenic and thiosulfenic acids that are liberated when alk(en)yl cysteine sulfoxide (ACSO) flavor precursors are cleaved by the enzyme after tissue disruption. It was proved that there is a linear relationship between the content of ACSOs and pyruvate [28].…”

“…The amount of pyruvate produced by hydrolysis of the ACSOs was obtained by subtracting a measurement of the endogenous pyruvate, obtained from tissue where aliinase has been inactivated, from the total pyruvate generated after disruption of the tissue [28].…”

Implications of spatial and temporal changes in concentration of pyruvate and glucose in onion (Allium cepa L.) bulbs during controlled atmosphere storage

“…1 Pyruvate concentration has been correlated with the degree of pungency experienced using taste panel evaluation, 1 -3 but has occasionally been confused with overall onion flavour. 3 Onion flavour and taste preference are complex and related to many compounds, including sugars. 3,4 Carbohydrates in onion constitute the bulk of dry matter.…”