Sinalbin is a glucosinolate

Glucosinolate

The glucosinolates are a class of organic compounds that contain sulfur and nitrogen and are derived from glucose and an amino acid. They occur as secondary metabolites of almost all plants of the order Brassicales , but also in the genus Drypetes .-Chemistry:Glucosinolates are water-soluble...

 found in the seeds of white mustard, Sinapis alba, and in many wild plant species. In contrast to mustard from black mustard (Brassica nigra) seeds which contain sinigrin

Sinigrin

Sinigrin is a glucosinolate that belongs to the family of glucosides found in some plants of the Brassicaceae family such as Brussels sprouts, broccoli, and the seeds of black mustard to name but a few...

, mustard from white mustard seeds has only a weakly pungent taste.

The less sharp taste is because the mustard oil from this specific glucosinolate, 4-hydroxybenzyl isothiocyanate, is unstable. With a half-life of one or a few hours, the pungent mustard oil degrades to 4-hydroxybenzyl alcohol and thiocyanate ion, which are not pungent. Glucobrassicin

Glucobrassicin

Glucobrassicin is a type of glucosinolate that can be found in almost all cruciferous plants, such as cabbages , mustards, cress, and woad. As for other glucosinolates, degradation by the enzyme myrosinase is expected to produce an isothiocyanate, indol-3-ylmethylisothiocyanate...

is a structurally related glucosinolate that likewise yields a non-pungent isothiocyanate due to reaction with water.