Date Published: June 10, 2019
Publisher: Public Library of Science
Author(s): Hui Teng, Kemueli T. Seuseu, Won-Young Lee, Lei Chen, Patrizia Restani.
The active component obtained from ginger is a high value-added product, but continued research is required for improved extraction techniques that will lead to better quality extracts and greater yields. In this study, major functional compounds of 6-gingerol and 6-shogaol in ginger rhizomes (Zingiber officinale Rosc) were extracted using microwave assisted extraction (MAE). Possible ranges for optimal MAE conditions were predicted by merging of the contour plots of each response to observe the overlapping area of all responses. Optimal conditions predicted were ethanol concentration of 70%, extraction time of 10 min, and microwave power of 180 W. Verification tests carried out at a set of random condition within the above mentioned optimal ranges, which got experimental values for total soluble solid yield, antioxidant activity, 6-gingerol and 6-shogaol of 30.0±0.8%, 87.8±0.8%, 2.8±0.6 mg/g and 1.3±0.5 mg/g, respectively. Analysis results showed that steamed ginger sample contained lower 6-gingerol content, soluble solid as well as reduced antioxidant activity, but higher in 6-shogaol as compared with fresh sample.
Among the spices of the world, ginger assumes considerable importance, along with turmeric (Curcuma longa L.), as one of the most important and sought-after medicinal spices. Ginger, botanically known as Zingiber officinale Rosc, belongs to the family Zingiberaceae and in natural order Scitamineae . Gingerhas been used as a spice for over 2000 years. Owing to its universal appeal, its spread has been rapid to both tropical and subtropical countries, from the China–India region, where ginger has been cultivated from time immemorial. It also was most valued for its medicinal properties, in ancient times, and also played a very important role in primary health care in India and China, and was widely used in European medicines as a carminative as well .
There are a number of factors that should be considered when using microwave assisted extraction method such as the choice of solvent, microwave application time, microwave power, effect of contact sample surface area, and effect of temperature (Table 2). This is vital as it give us a fair idea of what sort of results to expect when running the main CCD experiment.
The optimal microwave assisted extraction conditions for TSSY, 6-gingerol and 6-shogaol are the following conditions: ethanol concentration of 70%, extraction time of 10 min and microwave power of 180 W. The predicted values of the above conditions for TSSY, 6-gingerol, 6-shogaol and AA were 28%, 3.0 mg/g, 1.0 mg/g, and 84.1%, respectively. Results obtained from the verified experiment that was conducted using the above optimal conditions were as follows: 30.0±0.8% TSSY, 2.8±0.6 mg/g 6-gingerol, 1.3±0.5 mg/g 6-shogaol and 87.8±0.8% AA. Verification experimental data obtained under optimal MAE matched well with the predicted values.