Determination of added sulfites in dried garlic with a modified version of the optimized Monier-Williams method.
The optimized Monier-Williams method is slightly modified so that it could be applied for determining sulfite content in dried garlic. Dried garlic sample is directly acidified in a reactor at a pH below 3. At this pH level, the alliinase enzyme activity is irreversibly blocked, and the sulfur-containing amino acids such as alliin (the most abundant) present in dried garlic cannot be transformed into corresponding thiosulfinates such as allicin, which is absent in dried garlic. This prevents allicin from reacting with added sulfites and being probably converted to S-allyl thiosulfate, which is not volatile and has no taste. It is found that at a pH below 2.4 and at boiling water temperature, allicin produces sulfur dioxide in adequate quantity to explain the false-positive results when utilizing the optimized Monier-Williams method with allicin suppression for unsulfited dried garlic samples. Finally, when garlic samples are stabilized in a phosphoric acid buffer at a final pH around 2.4, no sulfite is produced during the Monier-Williams distillation, which is further proof there are no naturally occurring sulfites in unsulfited dried garlic under these mild conditions.
Lafeuille
Jean-Louis
JL
McCormick France, Central Analysis Laboratory, 999 Avenue des Marchés, 84200 Carpentras, France. jlafeuille@fr.mccormick.com
Lefevre
Stephane
S
Achouri
Djamila
D
D002021:Buffers; D013437:Carbon-Sulfur Lyases / Q000737:chemistry; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D004220:Disulfides; D005189:False Positive Reactions; D005504:Food Analysis / Q000379:methods*; D005737:Garlic / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D015203:Reproducibility of Results; D013441:Sulfinic Acids / Q000737:chemistry; D013447:Sulfites / Q000032:analysis* / Q000737:chemistry; D013458:Sulfur Dioxide / Q000032:analysis / Q000737:chemistry; D013696:Temperature; D013885:Thiosulfates / Q000737:chemistry; D014867:Water / Q000737:chemistry
D002021:Buffers; D004220:Disulfides; D013441:Sulfinic Acids; D013447:Sulfites; D013885:Thiosulfates; D014867:Water; D013458:Sulfur Dioxide; C006452:allicin; D013437:Carbon-Sulfur Lyases; C019243:alliin lyase