A comparison study of the nutritional, mineral and volatile compositions of three dry forms of ginger rhizomes, and antioxidant properties of their ethanolic and aqueous extracts

Objective: To compare the most accessible dry forms of ginger rhizomes (Zingiber officinale)
\nused as a spice and as a remedy in order to choose the best ginger for medicinal purpose.
\nMethods: Freshly air dried ginger, commercially dry rhizomes and ginger available in powder
\nform are investigated in terms of nutritional values (proximate and mineral compositions) and
\nvolatiles profile. Ethanolic and aqueous extracts (decoctions and infusions) were prepared for
\ntotal phenolic, flavonoid and tannin contents determination. Also, three standard tests were
\nestablished in order to estimate the best extract with the better antioxidant potential.
\nResults: The results showed unlike proximate composition revealing different nutritional
\nvalues. In fact, freshly dried ginger contained much ash, while already dry samples contained
\nmuch protein. In addition, mineral contents of studied samples indicated their dissimilar
\nrichness especially in Ca, Mg, Na, K, Cu, Fe, and Mn. Solid phase micro-extraction gave
\nvolatile profiles with many interesting compounds, only 26 from the 51 identified components
\nwere common to studied samples with bioactive compounds predominance in freshly dried
\nsample. Also, the antioxidant potential established by three different tests was higher in
\nalready dry samples and was positively correlated with their higher contents in the determined
\nphytochemicals. The ethanolic extracts showed higher antioxidant activities than aqueous
\nextracts. Decoctions and infusions were almost similar proving that long cooking time did not
\naffect ginger antioxidant potential.
\nConclusions: This work highlighted the benefits of traditional preparations of ginger as sources
\nof bioactive compounds, namely antioxidants, and proved that the available commercial
\nsamples are not identical and encouraged analyzing samples before uses depending on needs.