The study by Hong Kong's food watchdog came after there were rumors about the rapid increase of nitrite contents in cooked vegetables that have been stored overnight in the refrigerator.

According to the Centre, they have collected from retail outlets samples of five vegetables, including amaranth, pak choi, flowering white cabbage, Chinese lettuce, and zucchini, that are commonly consumed, and measured their nitrite content before and after cooking.

“The study results showed that the nitrite contents did not increase after the cooked vegetables had been stored in the refrigerator overnight, and the nitrite contents still remained low when the cooked vegetables had been stored in the refrigerator for three days,” a statement of the Centre wrote.

“Storage temperature is the main factor affecting the increase of nitrite contents in cooked vegetables. Refrigerated temperature inactivates bacteria and delays nitrite formation,” it read.

The spokesman of the food watchdog noted that nitrite can lower the ability of blood to carry oxygen and may also produce nitrosamines, chemicals that cause cancer in animals, in the body.

However, currently available scientific evidence does not support the conclusion that nitrate and nitrite intake from the diet is associated with cancer risk in humans, the spokesman added.

Meanwhile, the spokesman also reminded the public that spoilage bacteria can still grow at refrigerated temperature even though most harmful bacteria cannot, calling on people to prepare food in suitable amounts to reduce the amount of leftovers.