Formation of 6-Shogaol of Ginger Oil Under Different Drying Conditions

Abstract

Ginger (Zingiber officinalis, Roscoe) is a common ingredient in various foods and beverages. It contains potent anti-inflammatory agents and oleoresin, in which 6-gingerol and 6-shogaol are major active compounds. Studies show that 6-shogaol has stronger anti-inflammatory effects. The objectives of this study were to investigate the yield of ginger oils obtained by freeze drying at −80°C, solar drying at atmospheric conditions, and hot air drying at temperatures ranging from 40–80°C and to study the effect of temperature on the transformation of 6-gingerol into 6-shogaol. Dehydrated ginger samples obtained using the drying methods mentioned above were subjected to grinding and the powder was then subjected to supercritical fluid extraction (SFE) to extract ginger oils. The results showed that drying temperatures lower than 70°C resulted in a higher yield of ginger oil (2.4–2.6%, p < 0.05). Scanning electron microscope (SEM) images showed that high drying temperatures caused starch gelatinization during the drying process and thus reduced the yields of extracted ginger oil. However, drying temperatures lower than 70°C did not promote the transformation of 6-gingerol (113.31 mg/mL, with a peak at 12.01 min) to 6-shogaol (6.05 mg/mL, with a peak at 29.85 min). High-performance liquid chromatography (HPLC) showed that drying temperatures higher than 80°C could induce the transformation, and the amount of 6-gingerol was as high as 12.73% compared to 3.5–5.5% using other methods with temperatures lower than 80°C (p < 0.05). In addition, this study revealed that solar drying had no effect on the transformation process, probably because of the low temperatures in solar drying.

Keywords:

• 6-Gingerol
• 6-Shogaol
• Ginger (Zingiber officinalis, Roscoe)
• Supercritical fluid extraction (SFE)

ACKNOWLEDGMENTS

This work was financially supported by the National Science Council of Taiwan under Grant No. NSC98-2221-E-020-008-MY2.