The Food & Environmental Hygiene Department has found sulphur dioxide in 29 of 179 beef samples collected in December and this month, and will prosecute the retailers involved.

Under the Preservatives in Food Regulation, sulphur dioxide - a low-toxic preservative - is allowed in preserved fruit and fruit juices, but should not be added to fresh, chilled or frozen meat. Offenders face six months' jail and a $50,000 fine.