In response to the recent public concern over “blackening sweet potato”, Taiwan Agricultural Research Institute has issued a statement to clarify that the sweet potato industry does not use any storage roots infected with soft rot or black rot as the raw materials for processing, and any black spots on the surface of storage roots are of no health concern.

    Sweet potatoes are susceptible to soft rot and black rot caused by fungi during the postharvest storage period and during shipping. When first infected, circular black spots or lesions appear on the surface. Two to three days later, the affected and adjacent tissues start to turn watery rot and produce characteristic foul odor. The odor evidently will deter consumers from consuming the rotten storage roots, thus there should be no health concern.

    The black spots that appear on the surface of storage roots can be caused by bruises or wounds. Bruises would cause secretion of latex rich in polyphenols, which turn the bruises into black spots when exposed to the air, and wounds would cause formation of wound tissues that turn black during the healing process. In either case, the black spots pose no risks to human health.

    Furthermore, after the storage roots are dug, the processors usually cure them to heal the cut wounds and improve storability. The newly dug out storage roots are usually cured by storing in a warm, humid room for four to ten days. A temperature of 29-30°C and a relative humidity of 90-95% in the storage room are ideal for wound tissue formation to prevent disease infection and excessive water loss. In this case, the black spots formed by the cured wounds are harmless for human consumption either.

    Besides starches, sweet potatoes are rich in dietary fiber and beta-carotene, while having moderate contents of other micronutrients. And sweet potatoes are considered a health promoting alkaline food. In recent years, the Council of Agriculture (COA) is actively implementing the certification program of Taiwan’s agricultural products. In this connection, the production and marketing groups of sweet potato in the country are proactive in the adoption of the guidelines of good agricultural practices and traceability outlined by COA. This not only protects the health of consumers, but also reduces financial risks involved in production and marketing.