On 18 January 2017 the FSSAI issued an advisory on the code of practice for the reduction of contamination of food with Polycyclic Aromatic Hydrocarbons (PAH) from smoking and direct drying.
The smoking process is used in the preparation of food for browning, flavouring cooking or preserving. Food is exposed to smoke from burning or smouldering material like wood. It is seen that a number of chemical contaminants like polycyclic aromatic hydrocarbons (PAH), dioxins, formaldehyde, nitrogen and sulphur oxides (relevant for formation of e.g. nitrosamines etc.) are formed during combustion of fuel both in smoking or direct drying process. Combustion gases also contain heavy metals. The type of contaminants found depends on the amount of fuel used, temperature and other parameters. Further PAH may also be present in the raw materials because of environmental contamination deposited through air on crops, contaminated soil or through water on fresh foods.
Commercial and domestic food preparations such as smoking, drying, roasting, baking, barbecuing or frying are recognized as important sources of food contamination. Presence of PAH in vegetable oils can also originate from smoking and drying processes used to dry oil seeds prior to oil extraction.
The major contributors to intake of PAH are foods like
- cereals and cereal products because they are consumed in large quantities
- vegetable fats and oils as they are made from foods that could contain them
- smoked fish, meat and barbecued products if these foods make up a large part of the diet
OBJECTIVES
The FSSAI has adopted the Code of practice for reducing and preventing contamination with PAH from smoking and direct drying process as per the Codex guidelines.
- This Code of Practice is intended to provide guidance to regulatory bodies and manufacturers so they can prevent and reduce contamination of foods with PAH in commercial smoking and direct drying process.
- Code of practice can also be used as an information base for consumers
- This Code of Practice offers guidance only for the reduction and prevention of PAH. However, reduction of PAH in the final product should not lead to increase in other contaminants or reduced microbiological safety and cause risk to human health.
The Code of Practice does not cover PAH contamination in food originating from
- Use of herbs and spices in the smoking process
- Indirect drying
- Other food processes, including barbecuing and other types of cooking in private homes or catering sector
- Environmental contamination of raw materials
The advisory defines terms used in the Code of Practice like HACCP, plant materials, PAH, smoke, smoke condensates, smoking, smoking direct and smoking indirect, etc.
General principles of reducing PAH contamination in food contain steps and important points where the first step is to analyse and identify
- Possible sources of PAH from the environment and the process
- Possible effect on consumer health
- Controllability and possible measure to reduce PAH contamination.
Manufacturers must know the
- microbiological status and possible risks from other contaminants
- organoleptic properties and quality of the final product so there is no adverse effect on the appearance, flavour, taste or nutritional properties of the product.
- feasibility and effectiveness of controls
PAH formation is dependent on the following variables
- Fuel, other plant material, diesel, gases, liquid/solid waste and other fuels
- Direct or indirect drying method
- Smoke generation process in relation to temperature pyrolysis and to airflow in the case of a smoke generator
- Distance between and position of food and heat source
- Fat content of food
- Duration and temperature of smoking and direct drying
- Cleanliness and maintenance of equipment
- Design of the smoking chamber and equipment used for smoke or air mixture
- Application of HACCP system
SMOKING
Smoking techniques have been used for centuries as a method for preserving fish and meat products. Smoking impregnates the high-protein food with aromatic components, which lend flavour and colour to the food, and also play a bacteriostatic and antioxidant role.
Fuel used in smoking
Normally wood is used for smoking but bagasse (sugarcane material), corn cob, coconut husk and shell are also used. PAH contamination is higher when using coconut husk as compared to the shell. It is therefore important to evaluate individual materials used in the smoking process.
- It is advisable not to use resinous wood.
- Other fuels like diesel oil, rubber (e.g. tyres) or waste oil also must not be used even as a partial component, as they may lead to significantly increased PAH levels.
- Neither should wood treated with chemicals for preserving, waterproofing or fireproofing be used for smoking.
- As PAH are particle bound, a greater distance from the smoke source to the smoked product might reduce content of PAH
- Fat dripping from the food into the source of the smoke might increase the content of PAH in the smoke. In order to avoid increase in PAH content through fat dripping perforated metal sheets can be used between the food to be smoked and the heat source.
Four types of smoking processes are generally recognized: smouldering, thermostat plates, friction processes, and smoking with smoke condensates.
Smoking processes are often divided into three groups depending on the temperatures used in the smoke chamber during processes:
- Cold smoking requires temperatures of 18–25 °C and is used for some fish species and meat sausages.
- Semi-warm smoking requires temperatures of approximately 30–40 °C and is used for some fish species, bacon and pork loin.
- Warm (or hot) smoking is smoking combined with heating requires temperatures of 70–90 °C and is used for some fish species, hams and sausages
Reduction of PAH from smoking
- To produce smoke for smoking food, flames should be prevented from forming by adjusting airflow as that increases PAH
- Identifying the parameters critical for PAH formation in a specific process can help to reduce PAH.
- Replacing direct smoking with indirect smoking can significantly reduce contamination of smoked foods.
- In modern industrial kilns, an external smoke generator is operated automatically under controlled conditions, to wash the smoke from particles before coming in contact with the food and to regulate its flow as it is brought into contact with the food. For more traditional or smaller scale operations, this may not, however, be an option.
- An assessment of possible reduction will help determine the type of generator to be used and washing of the smoke after the generator and before the smoke chamber reduces PAH. Installing good baffles after the smoke generator equipped with a device for decantation of tar also helps.
- As PAH are particulate bound, a filter may be used to remove particulate material from the smoke.
- Oxygen needs to be balanced as both too much and too little oxygen produces PAH.
- Generally, PAH formation increases with increasing temperature therefore temperature must be minimised. However, in hot smoking care should be taken to ensure food is cooked thoroughly.
- Products made with condensed smoke generally have lower PAH levels than products made with freshly generated smoke.
Post smoking treatment
- During the process smoke may be washed before it enters the smoking chamber. This can be achieved by washing or scrubbing, using a tar condenser, cooling or filtering all of which can remove particle-bound PAH from the smoke
- Cleaning the smoked product by rinsing the product or immersing it into water may remove soot and particles containing PAH on the surface of the food. This type of cleaning would not be possible to use for all types of products especial fish.
- Shaving the surface of the smoked product is another method used to reduce PAH
Direct drying process using sun, wind or other fuels
- While sun or wind drying has advantages of free energy but the fact is that PAH can enter foods through the environment like soil and dust from construction and traffic as well as adverse weather conditions.
- Other fuel used for direct drying is natural gas, peat and mineral oils.
- Using combustion gases, increases contamination 3 to 10 fold.
- Use of coke causes less contamination than the use of oil
Direct drying process
- Dehydrators are useful for larger drying yards and growers. It offers a steady production cycle, reduces labour costs and more favourable for unfavourable weather unlike sun drying.
- During direct drying, hot air is blown directly into the foodstuffs and combustion products can therefore directly enter the food.
- Continuous flow drying, where cereals pass the drying area continuously, is a widespread grain drying method for cereals. Direct drying is done in temperatures up to 120°C and indirect drying in temperatures between 60 and 80°C and time used is between half to one hour, depending on initial moisture content of the grain.
- A high temperature that causes visible burning of the product causes PAH so overheating must be prevented. Fuel must be completely combusted in the burner as incomplete combustion cause higher PAH
- The drying time should be as short as possible to decrease the exposure of the food to the potentially contaminating gases as much as possible. Active carbon is required during refining of the oil as a way to reduce PAH content after direct drying.
Important points for direct drying
- Temperature of the air should be optimal
- Minimize the time that food is in contact with combustion gasses
- Use active carbon while refining oil
- Avoid fire drying of oil seeds
- Avoid direct contact of oil seeds or cereals with combustion products
Keep equipment clean and well maintained like driers.
Dr Sudhir Kamar says
Is PAH is the same thing as we call otherwise as trans Fat
Dr Sudhir Kumar Rao
Designated Officer North Central Railway,
Indian Railways (D O code 905 }
Dr. Saurabh Arora says
Hi Dr. Sudhir, PAH (Polyaromatic hydrocarbons) and trans fat are different chemical compounds.