Effect of pre-washing on mercury content of fish

September 15, 2009

A study published in Food Additives & Contaminants shows that the reduction in mercury content of the fish flesh significantly depended on the pH of the solution used. Research by a team based at Universiti Putra Malaysia investigated the effect of pH (citric acid and sodium hydroxide), salt (sodium chloride, NaCl), and exposure time on the removal of mercury from short-bodied mackerel (Rastrelliger brachsoma).

Response surface methodology (RSM) was used to evaluate the effect of the three variables: pH (1–6.5), NaCl (0–1% w/v), and exposure time (0–30 min). The short-bodied mackerel was chosen because it is one of the most commonly consumed marine fish in Malaysia, and previous tests had shown that this type of mackerel contained a mercury level higher than the limits recommended by the World Health Organization/Food & Agriculture Organization. The fish fillets were completely submerged in the solutions, with the ratio of solution to fish being 2:1. The solution was subsequently decanted and the fish rinsed with water.

The researchers found that more than 80% of the mercury was removed by a pH of 2.79, NaCl of 0.5%, and an exposure time of 13.5 mins. This treatment did not result in an appreciable loss of protein due to denaturation, and it is suggested that it is unlikely that it would affect the organoleptic quality of the fish or its nutritional properties.