GINGEROL: a Marker Compound in Ginger

by Godras Jati Manuhara
from Department of Food Science and Technology, Sebelas Maret University, Indonesia


Name and structure
The IUPAC name for the gingerol is (S) -5-Hydroxy-1- (4-hydroxy-3-methoxyphenyl) -3-decanone. This compound is available in the form of 6-gingerol, 8-gingerol, and 10-gingerol (Wang et.al. 2012). Gingerols are unstable substances towards heating (drying, distillation, steaming, etc.). The structure of gingerols enable dehydration reaction to shogaol, for example 6-gingerol is dehydrated into 6-shogaol (Zhang et al. 1994).

Botanical source and concentration of gingerol
Gingerol can be found specifically in some parts of the Zingiber genus, especially fresh rhizomes. There are many varieties of ginger plants that have been examined for gingerol, including Z. officinale and Z. cornubracteatum (Kantayos & Paisooksantivatana, 2012).
Ginger plants are cultivated in various regions with different soil and climate conditions. Differences in cultivation factors affect the size, shape, amount of fiber, juiciness, and flavor (Attokaran, 2017). According to the Food and Agricultural Organization of the United Nations, Statistics Division (FAOSTATD), the main ginger producing countries, respectively, are India, Nigeria, China, Indonesia, Nepal and Thailand, with total production in 2016 reaching 3,270,762 tonnes. India contributed the most production (33.9%) of the total production.
Young et al. (2002) reported that parts of the ginger plant such as leaves, rhizomes (as a whole), rhizome skin, and buds of ginger contained 6-gingerol with different levels. Ginger rhizome skin contains 6-gingerol more than ginger buds. Rhizome and ginger rhizome skin have 6-gingerol 1.67 times more than ginger buds and 39.0 times more than ginger leaves. The level of 6-gingerol in ginger skin is 0.823 mg / g fresh weight and in ginger rhizome is 0.806 mg / g fresh weight. Therefore, removing ginger skin may reduce the yield and quality of essential oils.
Varieties affect the content of gingerol in the ginger rhizome. Z. officinale rhizome extract showed 6-gingerol content was 255.35 to 291.78 mg/kg while Z. cornubracteatum was 63,032 to 68,418 mg/kg. Interesting results showed that of several species of the genus Zingiber (Z. montanum, Z. ottensii, Z. rubens, Z. zerumbet, Zingiber 'Phlai-chompoo', Z. bisectum, Z. spectabile, and Z. barbatum) were not detected level of 6-gingerol. The level of gingerol that is too low is thought to be the cause (Kantayos & Paisooksantivatana, 2012). Baranowski (1985) reported 6-, 8-, and 10-gingerol in Queensland ginger, sequentially present in a ratio of 4: 1: 2, while gingerol in Hawaiian ginger, respectively, is in the ratio 7: 1: 2 to 6-, 8-, and 10-gingerol. Thus, the relative content of 6-gingerol in Hawaiian ginger is higher than in Queensland ginger, but the relative content of 8- and 10-gingerol is the same as that of Queensland ginger.
Long storage and use of heat in processing such as blanching, steaming, drying, distillation, and paste processing are reported to reduce the concentration of gingerol in products of ginger. Gingerol will dehydrate to shogaol, depending on the initial structure. For example, 6-gingerol will dehydrate to 6-shogaol. (Baranowski, 1985; Baladdin et al. 1996, Baladdin et al., 1997; Zhang et al., 1994).

Biosynthesis
Research on gingerol biosynthesis was been carried out a long time ago. Denniff et al. (1980) have examined the biosynthesis of 6-gingerol in Zingiber officinale plants and parts of their rhizomes. They concluded from that phenylalanine is elaborated to ferullic acid which is then condensed through the Claisen reaction, with hexanoate and malonate to produce 6-dehydrogingerdione. This last compound (6-dehidrogingerdione) is reduced into 6-gingerol through two stages. The 6-gingerol biosynthesis can be seen in Figure 3.

Importance and use in food
In fresh ginger, the pungency is mainly caused by 6-gingerol. The pungent flavor combined with the distinctive aroma of ginger makes ginger one of the most recognized spices in the world, both in the West and East. However, during processing withheat and storage, shogaol is formed as a gingerol dehydrated product. Decreasing the concentration of gingerol in the product of ginger might cause a decrease in panelist acceptance of the product. This is presumably because based on the sensory analysis towards pure compounds and crude extract, that showed shogaol to have a higher pungent taste than the original gingerol (Baranowski, 1985). Therefore, gingerol has also been recommended as a chemical marker for quality control of fresh ginger, because higher levels of gingerol indicate freshness of ginger. Testing of 6-gingerol content can also be accepted as an indicator for the level of pungency of fresh ginger (Mishra et al., 2004; Jolad, et al., 2005). Gingerol also plays an important role in inhibiting the growth of E. coli and B. subtilis bacteria, while the antioxidant ability comes from the content of gingerol and shogaol (Uhl, 2000). Gingerol was also reported to demonstrate antiemetic, antipyretic, analgesic, antiarthritic, and anti inflammatory activities (Mishra et al. 2012).

References
Attokaran, M. (2017). Natural food flavors and colorants (2nd edition.). Hoboken: Wiley-Blackwell.
Balladin, D.A., Yen, I.A., McGaw, D.R., and Headly, O. (1996) . Solar drying of West Indian ginger (Zingiber officinalle Roscoe) rhizome using a wire basket dryer. Renewable Energy 7: 409 – 418
Balladin, D.A., dan Headley, O. (1997). Extraction and evaluation of the main pungent principles of solaar dried West Indian ginger (Zingiber officinale Roscoe) rhizome. Renewable Energy 12: 125 – 130.
Baranowski, J.D. (1985). Storage stability of a processed ginger paste. Journal of Food Science 50: 932 – 933
Denniff, P., Macleod, I., & Whiting, D. (1980). Studies in the biosynthesis of [6]-gingerol, pungent principle of ginger (Zingiber officinale). Journal of the Chemical Society, Perkin Transactions 1: 2637–2644.
Jolad, S.D., Lantz, R.C., Chen, G.J., Bates, R.B., Timmermann, B.N. (2005). Commercially processed dry ginger (Zingiber officinale). Phytochemistry 66: 1614 – 1635.
Kantayos, V., & Paisooksantivatana, Y. (2012). Antioxidant Activity and Selected Chemical Components of 10 Zingiber spp. in Thailand. Journal of Developments in Sustainable Agriculture, 7: 89–96.
Mishra, B., Gautam, S., & Sharma, A. (2004). Shelf-life extension of fresh ginger (Zingiber officinale) by gamma irradiation. Journal of Food Science, 69(9): M274-M279.
Mishra, R.K., Kumar, A., & Kumar, A. (2012). Pharmacological activity of Zingiber officinale. International Journal of Pharmaceutical and Chemical Sciences 1: 1422 – 1427.
Uhl, S.R. (2000). Spices, Seasonings, dan Flavorings. Technomic Publ. Co. Inc., Lancaster – Basel. Young, H.Y., Chiang, C.T., Huang, Y.L., Pan, F.P., Chen, G.L. (2002). Analyical and stability studies of ginger preparations. J.Food and Drug Analysis 10: 149 – 153.
Zhang, X. Iwaoka, W. T., Huang, A. S., Nakamoto, S. T., R. Wong. (1994). Gingerol decreases after processing and storage of ginger. Journal of Food Science 6: 1338 – 1340.

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