Philippine yam a good source of vitamin E

This article was first published on PCHRD website by Ciaren Hipolito

Research continues to unravel more medicinal properties of purple yam (Dioscorea alata) locally known as ube, one of the country’s most important root crops.

Scientific studies have shown that yam can lower sugar levels, improve metabolism and provide antioxidant defenses. Interests of scientists, food manufacturers, and consumers on antioxidant composition of yam heightened when the Philippine Journal of Science reported that it is a possible functional food ingredient.

To further investigate the antioxidant capacity and phenol content of yam, a study was conducted by researchers from the University of the Philippines – Diliman (UPD). The research, titled “Philippine Yam (Dioscorea spp) Tubers Phenolic Content and Antioxidant Capacity” by Djanna F. Cornago, Rowena Grace O. Rumbaoa and Inacrist M. Geronimo revealed that local ube contain significant phenolic content and antioxidant similar to alpha-tocopherol or vitamin E. In the study, five Philippine varieties of purple yam or ube – Daking Kimabajo, Rapang-rapang, Sampero, and Shiket, and two varieties of lesser yam were analyzed.

Examining the phenolic content, the study reported that production and accumulation of phenolic compounds depends on the type of yam. “Dark-colored yam variety had higher phenolic content than lighter-colored type. Highland Tugui had higher phenolic content that Lowland Tugui.” The antioxidant capacity of most plant food sources is usually associated with their phenolic contents. “Phenolic is secondary plant metabolites associated with color, nutritional and antioxidant properties of food.”

The antioxidant activity – radical scavenging, electron donation and metal chelation was compared to a commercially available antioxidant, alpha-tocopherol or vitamin E. “The results showed higher radical scavenging activity of the samples than that of the commercial antioxidant. It suggests that yam samples are more potent scavengers of free radicals. Further, the yam sample extracts also exhibited better chelating capacity. This means yam has the potential to stabilize the oxidized form of metal ions that generate free radicals,” said the researchers.

With the high antioxidant activity of locally produced ube and tugui varieties, the researchers concluded that these not fully-utilized tubers may serve as source of natural antioxidants and as a possible food supplement. The researchers said, “The substantial amount of phenolic compounds, as well as the significant antiradical activity, makes utilization of yam as a source of food antioxidant and nutraceutical commercially feasible.”