Four out of 300 Hong Kong-style dessert samples have been found to contain the illicit preservative boric acid, the Centre for Food Safety says.

They were a mung bean sweet soup with root starch jelly, a bean curd sheet sweet soup with root starch jelly and its follow-up sample, and another follow-up sample of root starch jelly collected from the supplier.

Based on the levels of boric acid detected in the unsatisfactory samples, normal consumption should not pose an adverse health effect on consumers.

The samples were collected from two food premises and a grocery. The centre has issued warning letters to the operators concerned. Prosecution is being considered.