Taiwan's health authorities will conduct stringent checks of potato suppliers after reports that French fries served at fast food restaurants were found with green patches.

Food and Drug Administration (FDA) official Cheng Wei-chih (鄭維智) said that potatoes can turn green due to exposure to enough light. However, consuming a large amount of green potato can cause nausea, vomiting, and diarrhea as it often contains a toxic chemical called solanine. No regulations regarding the maximum level of solanine are imposed yet, Cheng added.

To ease public concerns about food safety, fast food restaurants in Taipei and Tainan were checked for their potato wedges and no safety concerns were found, Cheng said. Moreover, Cheng urged that green potatoes shall not be sold from the upstream suppliers.

According to Cheng, food vendors which were found to either sell or use potatoes containing solanine can be fined around NT$30,000 (US$993.5) to NT$3 million based on the Act Governing Food Safety and Sanitation.

The scoop of green-tinted potatoes was first posted online by a user of PTT, the largest terminal-based bulletin board system (BBS) in Taiwan. He wrote that his tongue felt weird when he was eating potato wedges at McDonald's and he found there was a green tint in the food.

McDonald’s later responded that the company has adopted strict control measures requiring suppliers and workers to remove green potatoes. However, both McDonald's and KFC argued that the green color found in potatoes exposed to enough sunlight is chlorophyll and not poisonous.

PotatoPro, a news website covering the potato sector wrote that the statement by the companies was a bit misleading.

"The statement by McDonald's and KFC that the green color found in potatoes exposed to enough sunlight is chlorophyll and not poisonous is rather disappointing."

"Although the statement is true, it is misleading: the green colour is a clear indicator the potato has been exposed to light, an important indicator for the potential presence of increased levels of solanine."

"Fastfood chains should make sure their french fries do not contain excessive amounts of green potato. The bottom line is though, avoid eating eating lots of green potatoes and do not eat potatoes or potato products that taste bitter or cause a burning sensation in your mouth," PotatoPro wrote.