Smoking Preservative of Fish

Dipanjan Kashyap¹, Sonmoina Bhuyan¹, Rajita Devi² and Pran Jyoti Sharma²

¹FEES Division, Central Institute of Fisheries Education, Versova, Mumbai-400061

²College of Fisheries, AAU, Raha, Nagaon, Assam-782103

Email of corresponding author: dipankashyap@gmail.com

Introduction

Smoking is one of the oldest methods of fish preservation developed in prehistoric period. In recent times smoking is used as a method of preservation with the incorporation of smoke flavour and development of colour. In under developed countries this method is used as a means of preservation only, while in developed countries this method is used to impart smoke flavour to the product since in these countries there are other sophisticated means of preservation of fish. Smoking is a method of preservation effected by the combination of drying, deposition of naturally produced chemicals resulting from thermal breakdown of wood and salting. All these three factors help in preservation of fish. Smoked fish is ready to eat and has great demand in western sophisticated markets. Smoking is also used as an intermediatory step in the preservation of canned smoked fish. Here before canning, fish is smoked to impart smoky flavour. Smoke is a good preservative since it contains bacteriocidal and antioxidant properties. Around 2% of the total world catch is used for preparing smoked fish all over the world. In India, "masmine" is prepared in Lakshadweep group of islands.

Different types of smoking

1. Hot smoking: In this type, the temperature should be maintained above 30^oc and the normal range is 70-80^oc. In hot smoking fish is completely cooked and consumer can take it without further cooking.

2. Cold smoking: In cold smoking temperature should be maintained below 30^oc. Here meat will not be cooked and it is used to impart flavour in the meat. So it has to be cooked before consumption. This method is followed in temperate countries as temperature in these countries is very low.

3. Combined method of hot and cold smoking: Here fish is first smoked below 30^oc for few hours and finally it is hot smoked.

4. Liquid smoking: Liquid smoking extract is prepared by dry distillation of wood and then it is concentrated to a particular degree and later it is used in proper dilution. Dilute smoke is concentrated, fishes are dipped into it for required time and then it is dried.

5. Electrostatic smoking: Here smoked particles are charged into an electrical field (usually positively charged) and at the same time fishes are negatively charged. The positively charged smoke particles are attached by the fish. It is a rapid process.

Types of wood used for smoking

Smoke is prepared by "smouldering fibre" ie. burning without flame. The source of producing smoke is the wood. All types of wood are not suitable for smoking purpose. Depending on types of wood odour and taste differs. For smoking hard wood is suitable and we should not use soft wood. Types of wood used for smoking are mentioned below.

• Coconut shell and husk

• Sag wood dust

• Sag wood ships (leaves)

• Mango wood

• Paddy husk etc.

Wood consists of two parts: combustible and non combustible. The main combustible substances are divided into three parts- polyoses, lignins and to some extent resins. Polyoses contain cellulose and hemicelluloses. Polyoses and lignins are the main components of hard wood, but in soft wood resins are more common eg. turpentine. In hard wood, polyoses comprise 2/3 rd and lignin comprise 1/3 rd of the wood. Freshly cut wood contains 40-60% moisture which is not suitable for smoking. A good wood containing <25% moisture is preferred for smoking. If the moisture is more than 25% then it is considered as damp wood. When wood is burnt it gives compound mixture of chemicals in addition to main gas like CO₂ and traces of H₂O and CO. When wood is burnt polyose part gives out aliphatic chemicals and when temperature reaches 280^oc, the released chemicals are alcohol, aldehyde, ketone and acids. Lignin part is resistant to heat and when temperature reaches 350^oc, they will burn and give out phenolic compounds.

Bacteriocidal properties of smoke

It is due to combined effect of heating, drying, salting and also deposition of chemical constituents of fish. Chemical constituents like formaldehyde and acetic acid are found to show bacteriocidal effect, can prevent fungal growth and can inhibit viral activities. Deposition of smoke is more on the surface and hence smoke is more effective against bacteria on the surface than on the inner portion of fish.

Antioxidant properties of smoke

Smoke also has antioxidant properties and it is mainly due to the presence of three important chemicals namely 2,6-dimethoxyphenol, 2,6-dimethoxy-4-methylphenol and 2,6-dimethoxy-4-ethylphenol.

Carcinogenic compound

Smoke has carcinogenic property due to the presence of 3,4-benzopyrene. It is a polynuclear aromatic hydrocarbon and its formula is C₂₀H₁₀. Depending on the method of smoking the amount of carcinogenic compound in smoke varies. To prevent the carcinogenic compound, electrostatic precipitation is used through which smoke is allowed to pass. The electrostatic precipitation can absorb the carcinogenic compound and we can get pure smoke.

Importance of relative humidity in smoking

Smoked vapours are usually absorbed quickly by moist surface than dry surface. Moist surface can absorb 20 times more than the dry surface. So before smoking we should see that there is a relative humidity of 60% and it is optimum for absorption of smoke.

Colour formation in smoked fish

The colour of the smoked fish is due to the deposition and subsequent oxidation of phenol. In recent times fish curers use dyers for colouring of smoked fish in a uniform way. Colours are not permitted in some countries like UK, whereas in countries like USA it is permitted. From vegetable source colours may also be used in smoked fish to enhance the appearance of the product.

Conclusion

Today there are two main methods of smoking fish: the traditional method and the mechanical method. The traditional method involves the fish being suspended in smokehouses over slowly smouldering wood shavings. The fish are left overnight to be naturally infused with smoke. In the mechanical method smoke is generated through the use of smoke condensates, which are created by the industrial process of turning smoke into a solid or liquid form. The flow of smoke in the mechanical kiln is computer controlled and the fish generally spend less time being smoked than in a traditional kiln.

Smoking fish is one of the best ways to preserve fish. Smoked salmon and smoked mackerel are two of the top purchased smoked fish items in the world. Salmon, mackerel and herring are universally available both as hot-smoked and cold-smoked, while other fishes are traditionally preserved by anyone of the smoking methods.

References

• Burt, J.R., 1988. Fish smoking and drying, Elsevier Applied Science, ISBN 9781851662470.

• Hui, Y. H. et al. (2001). Meat Science and Applications. New York: Marcel Dekker. ISBN 9780824705480.

• McGee, Harold (2004). "Wood Smoke and Charred Wood". On Food and Cooking (Revised ed.). Scribner. pp. 448–450. ISBN 0-684-80001-2.

• en.wikipedia.org

• http://www.articlesnatch.com