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Food Safety Focus (175th Issue, February 2021) – Incident in Focus

A Closer Look at Sulphur Dioxide in Foods

Reported by Ms. Sosanna WONG, Scientific Officer,
Risk Assessment Section, Centre for Food Safety

Recently, food surveillance conducted by the Centre for Food Safety (CFS) identified two prepackaged date samples that contained sulphur dioxide at a level exceeding the legal limit and had not declared its usage on the food label, respectively. The CFS then issued food alerts and prompted the distributors to initiate recalls. This article discusses the use of sulphur dioxide in food production.

Why is Sulphur Dioxide Added to Foods?

Sulphur dioxide may not sound new to you due to its long history of use in food production for its versatile properties, but do you know how it works?

Sulphur dioxide can act as a preservative in a variety of foods and beverages such as dried fruits and vegetables, pickled vegetables, fruit juices and grape wines. It inhibits growth of microbes such as yeasts, bacteria and moulds by crossing the cell walls of microbes and disrupting the normal functioning of microbes. Sulphur dioxide can inhibit spoilage caused by microbes and extend the shelf life of food products.

Other than its antimicrobial properties, sulphur dioxide is also an antioxidant that prevents browning associated with oxidation in foods, particularly dried fruits and vegetables. This helps maintain the appearance and colour of the products. Without sulphur dioxide, light-coloured fruits such as dried apricots can darken quickly upon exposure to air.

Sulphur dioxide is also commonly used in wine making that prevents spoilage and oxidation in wines to preserve the quality and freshness.

Figure 1: Sulphur dioxide is used in a variety of foods and beverages.

Is Sulphur Dioxide Safe for Use as a Food Additive?

Same as other food additives, sulphur dioxide has gone through rigorous safety assessments before it is ascertained as safe for food use. The Joint Food and Agriculture Organization / World Health Organization Expert Committee on Food Additives (JECFA), an international food safety authority, has evaluated the safety of sulphur dioxide. When sulphur dioxide is used in foods in accordance with the Good Manufacturing Practice (GMP) in which only the minimum amount is added to achieve the desired technological effect, it should be safe upon normal consumption.

However, susceptible individuals who are hypersensitive to sulphur dioxide may experience allergic symptoms including breathing difficulties, headaches and nausea after consumption.

How is Sulphur Dioxide Regulated in Hong Kong?

In Hong Kong, the use of sulphur dioxide as preservative and antioxidant is regulated under the Preservatives in Food Regulation (Cap. 132BD) that stipulates its use in specified foods within specified levels.

According to the requirements under the Food and Drugs (Composition and Labelling) Regulations (Cap. 132W), if sulphur dioxide is used in a prepackaged food, its functional class (i.e. preservative) together with its specific name (i.e. sulphur dioxide, sulphites and sulphite derivatives) or identification number under the International Numbering System (INS) (i.e. 220-228 and 539) must declared in the ingredient list.

In addition, since sulphur dioxide is a potential allergen for susceptible individuals, the Food and Drugs (Composition and Labelling) Regulations also stipulate that for all prepackaged foods containing sulphite in a concentration of 10 parts per million or more, the functional class and name of the sulphite should be specified in the ingredient list as well.

In some cases, foods in bulk packages are re-packaged into smaller packages for retail sale. The presence of sulphur dioxide, if any, should be declared on the label for both bulk and smaller packages. When in doubt, check with your suppliers for the ingredient details.

Key Points to Note:

  1. Sulphur dioxide is used as preservative and antioxidant in a variety of foods, such as dried fruits, to extend the shelf life and prevent browning of foods.
  2. In Hong Kong, the use of sulphur dioxide is regulated under the Preservatives in Food Regulation.
  3. Proper labelling of sulphur dioxide is required according to the Food and Drugs (Composition and Labelling) Regulations.

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