Determination of Added Sulfites in Dried Garlic with a Modified Version of the Optimized Monier-Williams Method

Abstract

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, alliin 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.

Herbal Decoctions for the Levels of Sulfur Dioxide, Benzopyrene, and Mycotoxin from Traditional Korean Medicine Clinics: A Preliminary Study

“…Purity Test of Herbal Medicine Test Method SO 2 test method [ 17 ]. The amount of SO 2 was calculated using an automatic potentiometer for the collected solution using an SO 2 extraction device ( Figure 1 ) according to the Monier-Williams method [ 18 , 19 ]. In the Monier-Williams method [ 18 , 19 ], SO 2 is released from sulphites and some bound compounds when a sample is mixed with an acid normally hydrochloric acid, but sometimes phosphoric acid and heated.…”

“…The amount of SO 2 was calculated using an automatic potentiometer for the collected solution using an SO 2 extraction device ( Figure 1 ) according to the Monier-Williams method [ 18 , 19 ]. In the Monier-Williams method [ 18 , 19 ], SO 2 is released from sulphites and some bound compounds when a sample is mixed with an acid normally hydrochloric acid, but sometimes phosphoric acid and heated. The SO 2 is distilled using a stream of nitrogen gas which carries the gaseous SO 2 into an absorbing solution of hydrogen peroxide (H 2 O 2 ) where it is oxidised to sulphuric acid.…”