Valorization of ginger and turmeric peels

The Zingiberaceae family includes ginger (Zingiber officinale) and turmeric (Curcuma longa) zhizomes which are primarily used in the dried spices or essential oil production and are widely recognized for their health benefits due to their strong anti-inflammatory and antioxidant activities. This work is aimed to investigate the antioxidant potential of ginger and turmeric peels which are usually discarded during post-harvest operations.The total phenolic contents and the antioxidant activities of the extracts obtained from the powdered peels of ginger and turmeric rhizomes resulted in statistically relevant differences (P≤0.0001) depending on the Zingiberaceae species and extraction method. In details, the ethanol extraction compared with infusion and sonication techniques was more effective in increasing their antioxidant activities based on DPPH (4.16, 2.17, 2.17 mg TE/g, respectively) and FRAP (65.07, 18.81, 15.49 mg TE/g, respectively) assays because of higher yields of phenolic substances (78.73, 36.84, 33.08 mg GAE/g, respectively) such as 6-gingerol (12.78, 0.41, 0.58 mg/g, respectively) and curcumin (48.62, 5.42, 1.38 mg/g, respectively) detected by HPLC analysis in ginger and turmeric extracts, respectively. Moreover the ethanolic extracts of turmeric peels showed the better performances than those of ginger peels with higher amounts of phenolic substances (104.88, 52.57 mg GAE/g, respectively) and consequently greater antioxidant activities based on DPPH (4.45, 3.87 mg TE/g, respectively) and FRAP (72.38, 57.77 mg TE/g, respectively) assays. In conclusions, the discarded peels of ginger and turmeric rhizomes can be recovered as a source of natural antioxidants not only in food additives but also cosmetic and medicinal products