Gingerol, shogaol and paradol: The chemistry of pungent ginger constituents

Ginger (Zingiber officinale Roscoe) rhizomes are well-known for their aromatic properties, being used to impart a characteristic pungent flavour to a variety of food and beverage products. The major pungent compounds are the gingerols and their derivatives, while numerous volatile compounds contribute additional aromatic flavour overtones. Ginger forms a niche crop in Australia, with a current farmgate value of $32 million; hence there is limited information available on the chemical profiles of Australian-grown ginger. We chemically profiled 100 samples of dried Queensland ginger, finding that 6-gingerol levels vary significantly depending on the growing conditions (3720-5351 mg kg-1). In contrast, 6-shogaol levels were largely consistent between different samples (approximately 1400 mg kg-1), suggesting that the drying process is the primary controller of the 6-shogaol content in the final product. The proportions of 6-gingerol and 6-shogoal in the dried ginger translate to those in the subsequent wort and ginger beer products, with younger ginger samples containing a higher 6-gingerol:6-shogaol ratio. Given that several other microorganisms have been observed to convert 6-shogoal to 6-paradol, it is believed that this process would also be mediated by the ginger beer bug (actually a combination of Saccharomyces pyriformis and Brevibacterium vermiforme). However, paradol has not been identified in ginger beer to date, hence further work is required to determine the role this compound and its precursors play in determining the final organoleptic properties of ginger beer.