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 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, according to Taiwannews.com.

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.

After a complaint regarding the potato wedges in one of their restaurant, McDonald’s 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.