Volatile constituents of the solvent extracts of Welsh onions (Allium fistulosum L. variety maichuon) and scallions (A. fistulosum L. variety caespitosum) (original) (raw)
1992, Journal of Agricultural and Food Chemistry
Volatile components were isolated from Welsh onions and scallions by solvent extraction at ambient temperatures and analyzed by GC and GC-MS. There were 67 volatile components identified, including 12 novel polysulfides. Methyl methanethiosulfinate and 10 dialk(en)yl thiosulfonates were among those volatiles in Welsh onion and scallion extracts. These thiosulfinates and thiosulfonates were not previously identified in their distilled oils, probably due to their instability to heat. INTRODUCTION Green onions, Allium fistulosum L. var. Maichuon (Welsh onions) and A. fistulosum L. var. Caespitosum (scallions), are used as vegetables or spices in many countries. They are important ingredients and are commonly used in Chinese cuisine. Recently, we reported the volatile constituents of the distilled oils of Welsh onions and scallions (Kuo and Ho, 1992). In addition to the sulfur compounds commonly reported in the genus Allium 41 novel volatile sulfurcontaining compounds were found in the distilled oils of Welsh onions and scallions. The novel compounds can be grouped as (1) l-[alk(en)ylthio]alkyl alk(en)yl disulfides, (2) alkyl tetra-or pentathiaalkanes or-alkenes, and (3) thiaheterocycles. The purpose of this study was to investigate the volatile components of Welsh onions and scallions obtained by solvent extraction at ambient temperatures. It will be interesting to see whether those novel sulfur-containing volatiles identified in distilled oils can also be found in the solvent extracts. EXPERIMENTAL PROCEDURES Materials. Welsh onions and scallions were purchased fresh from the local market. A standard of n-paraffins (CS-CB) was purchased from Alltech Associates, Inc. (Deerfield, IL). cis-and trans-methyl l-propenyl disulfides, syn-and anti-2-mercapb 3,4-dimethyl-2,3-dihydrothiophenes, cis-and trans-propyl l-propenyl disulfides, dipropyl disulfide, syn-and anti-3,5-diethyl-1,2,4-trithiolanes, 6-ethyl-4,5,7-trithia-2,8-decadiene, methyl methanethiosulfonate, cis-and trans-l-propenyl methanethiosulfonates, methyl l-propenethiosulfonate, propyl propanethiosulfonate, propyl l-propenethiosulfonate, and 1-propenyl propanethiosulfonate were kindly provided by Dr. Eric Block of the Chemistry Department of the State University of New York at Albany. 2-Undecanone and 2-tridecanone were gifts from Givaudan Corp. (Clifton, NJ). Propanethiol and dimethyl disulfide were obtained from Pfaltz and Bauer, Inc. (Waterbury, CT). Preparation of Solvent Extracts from Welsh Onions and Scallions. The solvent extracts of Welsh onions and scallions were obtained by glass-redistilled methylene chloride extraction of a freshly prepared slurry. The slurry was prepared by blending 500 g of samples with 500 mL of distilled water; lo00 mL of solvent was added to the slurry. The mixture was then stirred at room temperature for 12 h. The filtered methylene chloride extracts were dehydrated with NaZSO, and then passed through a silica gel column (60-200 mesh, 20 cm X 2 cm, Mallinckrodt, Inc., Paris, KY) to remove most of the chlorophyll. The solvent was then removed by nitrogen at ambient temperature to a final