Purple yam is a species of yam, a tuberous root vegetable that contains anthocyanins (water-soluble vacuolar pigments) similar to potatoes. Anthocyanin is a natural source of antioxidants, acts as a free radical scavenger and plays a role in aging, cancer and degenerative illness prevention. It also protects the liver, reduces coronary artery disease symptoms and enhances retinal function1.
Anthocyanin is a natural pigment found in vegetables, fruits, leaves and tubers. Anthocyanins may appear red, blue or purple, depending on pH and are water-soluble. Anthocyanin is one of the subclasses of phenolic phytochemicals. The types of anthocyanin in yam are cyanidin and peonidin which are acylated with sinapic acid2. Purple yams contain a variety of acylated anthocyanins that exhibit higher levels of antioxidant activity than nonacylated compounds3.
Anthocyanins can be extracted from tubers and used as natural colorants that play a role as a natural antioxidant. Anthocyanin is a polar compound, so it requires polar solvent for its extraction process. The polar solvents commonly used for the anthocyanin extraction include methanol, ethanol and water4.
Isolation of anthocyanin pigments from plants is typically done using a solvent extraction process5. Several extraction methods have been proposed in order to obtain extracts rich in anthocyanins, these methods are usually based on solvents such as methanol, ethanol, acetone, water or mixtures. The addition of a small amount of HCL or formic acid is recommended to prevent the degradation of the acylated compounds6.
The above mentioned context led the researchers to perform a new study to determine the effects of solvent type (methanol or ethanol) and acid type (HCl, citric or tartaric acid) on anthocyanin extraction with high antioxidant activity from purple yam flour and to assess the relationship between antioxidant activities and anthocyanin concentrations in addition to phenolic compounds7.
For this purpose Anthocyanins were extracted using methanol and ethanol-based solvents that were acidified with hydrochloric acid (HCl), citric acid or tartaric acid. The resulting extracts were assayed for anthocyanin and total phenolic contents, antioxidant activity and ferric reducing antioxidant power (FRAP).
The study results showed that purple yam flour contains anthocyanin and phenolic compounds were potent as natural antioxidants. This study discovered the type of solvent and acid for anthocyanin extraction from purple yam flour that could be beneficial for obtaining anthocyanin extracts with high antioxidant activity. It provides scientific information on the type of solvent(s) and acid(s) that are useful for extracting the anthocyanin purple yam flour with high antioxidant activity.
- Bridgers, E.N., M.S. Chinn and V.D. Truong, 2010. Extraction of anthocyanins from industrial purple-fleshed sweet potatoes and enzymatic hydrolysis of residues for ferment able sugars. Crops Prod., 32: 613-620.
- Shoyama, Y,. I. Nishioka, W. Herath, S. Uemoto, K. Fujieda and H. Okubo, 1990. Two acylated anthocyanins from Dioscorea alata. Phytochemistry, 29: 2999-3001.
- Moriya, C., T. Hosoya, S. Agawa, Y. Sugiyama and I. Kozone et al., 2015. New acylated anthocyanins from purple yam and their antioxidant activity. Biotechnol. Biochem., 79: 1484-1492.
- Lapornik, B., M. Prosek and A.G. Wondra, 2005. Comparison of extracts prepared from plant by-products using different solvents and extraction time. Food Eng., 71: 214-222.
- Kong, J.M., L.S. Chia, N.K. Goh, T.F. Chia and R. Brouillard, 2003. Analysis and biological activities of anthocyanins. Photochemistry, 64: 923-933.
- Fan, G., Y. Han, Z. Gu and D. Chen, 2008. Optimizing conditions for anthocyanins extraction from purple sweet potato using Response Surface Methodology (RSM). LWT-Food Sci. Technol., 41: 155-160.
- Tamaroh, S., Raharjo, S., Murdiati, A. and Anggrahini, S., 2018. Total Phenolic Content and Antioxidant Activity of Anthocyanin Extract from Purple Yam (Dioscorea alata) Flour Using Different Solvents. Pak. J. Nutri., 17: 260-267.