Introduction

Recently, there have been media reports regarding the use of industrial grade hydrogen peroxide as a bleaching agent in the processing of shark fins and pistachio nuts.

Properties of Hydrogen Peroxide

1. Hydrogen peroxide (H2O2) is a strong oxidising agent that is commonly used in industry and in the medical field.
2. The anhydrous form of the chemical is a colourless, bitter-tasting liquid with an ozone-like odour.
3. It is unstable and decomposed upon standing, agitation, and exposure to light or heating, producing water and oxygen.

Use of Hydrogen Peroxide in Food Processing

1. Because of its strong oxidising property, hydrogen peroxide is used as a bleaching agent in some foods such as wheat flour, edible oil, egg white etc. in countries like the US, Canada, Australia and New Zealand.
2. It is also allowed to be used as an antimicrobial agent in food, e.g. milk, and as a sterilizing agent for food packaging materials.
3. In processing food, the dosage of hydrogen peroxide should be limited to the amount sufficient for the purpose.
4. In the Mainland, hydrogen peroxide is included in the list of food processing aid. In general, processing aids used in food should be removed from the final products.

Safety of Hydrogen Peroxide

1. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) had evaluated the safety of hydrogen peroxide in 1965, 1973 and 1980 respectively. JECFA considered that ingestion of small amount of hydrogen peroxide would produce no toxicological effects due to rapid decomposition of the chemical by the enzyme catalase of the intestinal cells.
2. Oral ingestion of 3% hydrogen peroxide solutions (household strength) generally does not result in severe toxicity but may result in vomiting, mild irritation to mucosa and burns in the mouth, throat, oesophagus and stomach. Ingestion of higher concentration, e.g. >10%, can result in more dangerous sequelae such as burns to mucus membranes and gut mucosa.
3. Regarding the carcinogenicity of hydrogen peroxide, the International Agency for Research on Cancer (IARC) considered that there was inadequate evidence for carcinogenicity in human.
4. Hydrogen peroxide is unstable and would decompose in contact with food and after cooking.

Situation in Hong Kong

1. In Hong Kong, hydrogen peroxide can be used in food as a bleaching agent provided that the residue should be removed in the finished products. Furthermore, only food grade hydrogen peroxide should be used in processing food and the dosage used should be limited to the amount sufficient for the purpose.
2. We have stepped up our local surveillance on shark fins and pistachio nuts. 25 samples of shark fin and 21 samples of pistachio were collected from the local market, including those imported from the Mainland, and were sent to the Government Laboratory for testing of hydrogen peroxide. Tests on preservatives and possible contaminants like heavy metals were also performed.
3. 14 out of 25 shark fin samples were found to have residual hydrogen peroxide ranging from 0.0002% to 1.5%. This indicated that the processing of some shark fins had not followed good manufacturing practice. As hydrogen peroxide is unstable, the levels found in the dry shark fin samples would not have adverse health effects as the usual steps of preparation and cooking of shark fin would effectively remove the residual hydrogen peroxide, if any, in shark fins. Nevertheless, the traders have been warned to adhere to good manufacturing and processing procedures.
4. Hydrogen peroxide or preservatives were not detected in any of the pistachio nuts samples. Test results for heavy metals were found to be within permitted levels for both the shark fins and pistachio nuts samples.

Advice to the Trade

1. If hydrogen peroxide is used in processing food, only food grade hydrogen peroxide should be used in processing food.
2. The amount of hydrogen peroxide to be used in food processing should be limited to the amount sufficient for the purpose.
3. Appropriate measures should be taken to remove residual hydrogen peroxide from the finished products.

Advice to the Public

1. Purchase shark fins from reputable retailers.
2. Wash thoroughly and soak shark fins well (e.g. soak overnight) before cooking. The water should be changed during soaking and discarded after use.

Risk Assessment Section
December 2003