The Onion: Gaseous Emanation Products

Abstract

The problem of tracing normal food odors and off-odors to their source must ultimately be solved by actual identification and isolation of chemical components for individual study. To quote Turk (11): "Much of our present information on constituents of common odors is purely nominal and based on old and uncomplete research." Such is the case for the onion.Thus Semmler (9), in 1892, claimed to have obtained a sulfide of unknown constitution from the oniog, of the same molecular formula, but different boiling point than the allyl propyl disulfide which he reports in garlic oil. Kohman, (7') quoting Semmler as identifying allyl propyl disulfide as the onion flavor, measured this quantitatively by oxidizing the product of steam distillation with bromine to the sulfate state and determining sulphur gravimetrically. On the basis of the quantity of sulphur, allyl propyl disulfide was calculated. I n an earlier paper Kohman (6) attributed the lachrymating properties of the onion to a thioaldehyde (thiopropionaldehyde or thioallylaldehyde) which he determined by the expedient of distilling the onion in vacuo a t 50" C., oxidizing a weighed sample of the distillate residue with bromine and determining the sulphur present. The amount of sulphur was equivalent to that in the thioaldehyde which he hypothesized on the basis of the various observations made. Propionaldehyde was also identified by isolation and formation of its dinitrophenylhydrazone. Challenger and Greenwood ( 2 ) then detected n-propylthiol by absorption of the thiol in mercuric cyanide. They were not able to determine whether it occurs in the undamaged bulb or whether it is liberated by enzyme action after slicing.Since little positive information has been published concerning the volatile constituents of onions, it was decided to apply the methods of instrumental analysis with the intention of outlining a technique which may be applicable to most other food odor problems. The following work is a report on a mass spectrometric and infrared spectroscopic analysis of vapors trapped at various low temperatures in the absence of air. EXPERIMENTAL PROCEDUREA model 21-103B Consolidated analytical mass spectrometer and a Baird infrared spectrometer were used in the present work. Volatile constituents of onions were collected by trapping the vapors at -30", -go", and -190" C. in a system as shown in Figure 1. The contents of the traps were individually analyzed mass spectrometrically, and then condensed into the distillation tube, or examined by gas partition chromatography (GPC). The distillation technique yielded between 3 to 5 cuts from the contents of each trap. A trapping system made possible the collection of gases separated by GPC. " Presently with the Bakelite Research Center, Bloomfield, New Jersey. 657 658 W. D. NIEGTSCH A N D W. H. STAHL ii U n -19o.c. iil in -0D.C W -30.C Figure 1. High vacuum trapping system and low temperature-low pressure distillation tube for pref ractionation.Preparation of system. Approximately 100 to 140 g. of onion are frozen in l...

Flavor components of onion oil

“…All six possible compounds were positively identified in the distillate. Neither allyl propyl disulfide nor any other allyl-containing sulfide was found in significant amounts in the onion distillates by Carson and Wong, in agreement with the conclusions of Niegisch and Stahl (1956). Saghir et al (1964) determined by gas chromatography the composition of sulfides in the vapor above several species of freshly chopped Alliums.…”

“…Challenger and Greenwood (1949) identified 1-propanethiol in headspace above chopped onions. The presence of propyl disulfide in a low temperature-low pressure distillate of fresh onions was demonstrated by Niegisch and Stahl (1956).…”

Onion Flavor and Odor, Enzymatic Development of Pyruvic Acid in Onion as a Measure of Pungency

“…Thus, they react with thiamine to give rise to allithiamine analogs (14); with V-ethyl maleimide after appropriate extraction procedures (4, 20); and after heating, give rise to families of alkyl diand trisulfides which have been identified after separation by gas chromatography (3). In addition, the following volatile sulfur-containing compounds have been reported to be present in onion volatiles: rc-propanethiol (3,6,16); n-propylthioaldehyde (70); hydrogen sulfide and sulfur dioxide (4,16).…”

Composition of Volatiles in Allium as Related to Habitat, Stage of Growth, and Plant Part

“…In addition to the aliphatic disulfides reported to constitute the odor and flavor (2,3,4,6,8,10,13), Bernhard et al (1) reported the presence of allyl monosulfide and allyl alcohol among, the volatiles produced by Alliumit.…”