Traditional Preservatives – Wood Smoke

LJ Ogbadu, National Biotechnology Development Agency, Abuja, Nigeria

Ó 2014 Elsevier Ltd. All rights reserved.

Introduction Range of Smoked Foods

Smoking as a method of food preservation is an age-old Quite a wide range of foods are subjected to smoking depending
process that probably dates back to the start of human civi- on the food culture of the population. Certain foods are
lization. It is likely that the practice of smoking meat and fish commonly smoked across all food cultures where smoking is
outdates the art of cooking in containers, as open-fire contact a culinary tradition. Animal flesh, which encompasses both meat
(roasting) with food must have been the earliest form of and fish, forms the major category of foods that are processed by
cooking even before earthenware pots were made. The exposure to wood smoke. While meat covers mammalian flesh,
importance of wood as fuel, with wood smoke as an integral other specific types are poultry and game. Fish includes both
part of that, and perhaps later its utilization in food processing marine and nonmarine water fish, all of which are commonly
is tied to the same aspect of civilization. Since wood smoke is smoked. Other smaller marine animal life, like lobsters, shrimps,
generated by burning wood, both smoke and heat of wood and crustaceans, are equally processed by smoking. The list of the
combustion likely were discovered to be useful for food pro- specific types of each of these categories of animal flesh is as
cessing about the same period. The traditional practice of numerous as the number that exists in nature that is edible. And
exposing food to wood smoke goes hand in hand with drying a variety of recipes exists for smoked products that are obtainable
and is a food-preservative effort that involves a combination from each flesh type, again depending on the food traditions of
of several preservation processes and substances. This art must the people. Some of the well-known animal flesh that commonly
have assumed more importance and became adopted out of is smoke processed both by traditional uncontrolled methods
the relish for the products of the process, which contain and by modern industrial techniques is listed in Table 1. Foods of
desirable attributes of added flavor, odor, and color by the animal flesh are highly perishable and require immediate
wood smoke. preservative processing to halt microbial deterioration as soon as
The preservative role of food smoking is still of primary the animal is caught or slaughtered.
significance in developing countries because alternative or Foods other than those of animal flesh that are smoke pro-
complementary methods for effective preservation require cessed vary across the continents and are known by local names
equipment that depends on electricity or kerosene, which are in different parts of the world. In many parts of Africa, as in Asia,
costly and out of reach of the majority of the populace. different types of alcoholic and nonalcoholic beverages are
Smoking, for instance, is the major form of preservation prac- smoke produced by preparing the drink in smoked pots. A
ticed by the artisanal fishing populace, which constitutes about number of alcoholic beverages are smoke processed in Ethiopia.
70% of the fishing entrepreneurs in Sub-Saharan Africa, with The fermentation vessels for these beverages are densely smoked
the other being large fishing vessel companies. The bulk of all by inverting them over smoldering wood before being used to
fish caught and all game hunted for food, accounting for about ferment ground barley or wheat malt, as in the case for talla beer
80% of the total, are smoke or heat preserved. More than 500 production or diluted honey fermentation, in the case of tej
metric tons of smoked fish is exported from West Africa to the wine. These alcoholic beverages have a special smoky aroma and
United Kingdom alone, annually. This quantity is valued at flavor. Nonalcoholic drinks are prepared in parts of Asia by
between 9.3 and 14.9 million United States dollars. On the collecting and preparing different plant saps in smoked pots.
other hand, smoking is no longer primarily a preservative effort Jaggeri is a Sri Lankan drink prepared from coconut sap in this
in the modern food industry in different parts of the industrial way. Copra meals are prepared by exposing coconut kernels to
world, as its importance lies more in the desirable flavors and heat and smoke. Additionally, the oil obtained from smoked
odors that it imparts to food. Efforts at simulating this form of copra has a desirable smoky flavor. Smoked foods in other parts
food processing have been actualized in condensing wood of the world include smoked plant products like nuts and seeds.
smoke derived through a process of destructive distillation into
water in the form of liquid smoke. The smoke solution is
further modified to develop a wide range of smoke flavors. African Smoked Fish
Food is brought into contact with liquid smoke, which
contains essentially the chemical constituents of wood smoke. The predominant traditional mode of meat, fish, and game
While food legislation in European Union countries defines preservation in Sub-Saharan Africa especially the West African
food preservatives as excluding, among others, wood smoke or subregion is by smoking. Documentary estimates put the
liquid solutions of smoke, legislation in Canada, countries of proportion of smoked fish at between 70 and 90% of total
Asia, and countries of Africa allow wood smoke to be used as catch. West African smoked fish has assumed a level of
a natural preservative along with other chemical preservatives. importance on international trade, particularly to the United
The legislative directive on food smoking generally allows only Kingdom and North America. This is a result of demands by
the smoke or liquid solution of smoke obtained from wood or consuming migrants arising from their preference for smoky
woody plants in their natural state and disallows those woods flavor and the formation of food habits. While the smoking of
that have been impregnated, colored, glued, painted, or treated foods is now practiced in combination with other comple-
with any form of chemical. mentary hurdle technology in other cultures of the industrial

Encyclopedia of Food Microbiology, Volume 3 http://dx.doi.org/10.1016/B978-0-12-384730-0.00261-5 141

142 PRESERVATIVES j Traditional Preservatives – Wood Smoke

Table 1 Animal flesh types commonly smoked and accessory preservative treatment

Type of smoking/accessory treatments

Animal flesh/source Controlled Traditional uncontrolled
Category Specific type Method Accessory Method Accessory

Meat Beef H/s Curing/refrign H/s Dry-salting/drying/refrign

Mutton H/s Curing/refrign H/s Dry-salting/drying/refrign
Pork H/s Curing/refrign
Ham – –
Bacon H/s Curing/refrign – –
Frankfurter – –
Bush (undomesticated) – – H/s Drying/refrign
Poultry Chicken – – H/s Curing/refrign
Duck – – H/s Curing/refrign
Turkey H/s Curing/refrign – –
Game Partridge – –
Pigeon – – H/s Drying
Guinea fowl – –
Fish: marine Salmon
Herring
Mackerel C/s Brining/refrign H/s Drying
Sardine
Cod
Haddock – –
Trout H/s Brining/refrign – –
Fish: nonmarine Catfish – –
Mudfish – –
Cichlid – – H/s Drying
Mullet – –
Miscellaneous Prawn H/s Brining/drying
Shrimp C/s Brining/refrign – –
Mussel – –
Molluse H/s Brining/refrign H/s Dry salting

H/s, Hot smoking; Refrign, chilling and freezing; C/s, cold smoking; –, uncommon method.

world, it is essentially the sole method of preserving animal gradient that exists between the outer combusting wood surface
flesh in Africa. The moisture level is reduced to a minimum as it is being oxidized and the dehydrating inner core of the
level through repeated smoking as the fish is subjected to high wood. The temperature rises from about 100
C to between 300
temperatures, especially in the first few hours of smoking. The and 400
C as the internal moisture content of the wood
resulting heat sterilizes the fish and halts the activity of approaches zero. It is this temperature gradient that favors wood
enzymes in the tissues and intestines. It also frees part of the degradation, giving rise to smoke generation. Wood smoke can
moisture, thus allowing quick drying of the fish. Within be generated from any type of wood obtained from hewn dried
3–5 days of smoking, the fish becomes dry and brittle and may green plants, but dicotyledonous plants give harder, more
remain wholesome up to this point. The moisture loss is so compact woody stems than monocots and are more suitable for
rapid that the following pattern is observable: about 3% of steady smoke generation. Plants that have fibrous stems are not
weight loss between catch and after preparation for smoking as good as hard woods that burn longer and that have good-
which further rises to about 55% weight loss within 24 h of quality smoke. In addition, fibrous soft woods hold significant
smoking, then to about 65% weight loss after 48 h and further levels of resins that upon combustion give harsh-tasting soot.
rises to about 80% loss within 72 h of smoking. All fish types Different types of hard woody plants serve as sources for smoke
found in coastal waters (Table 2(a)) as well as those found in generation and certain types are preferred over others. The major
the fresh water bodies in the hinterland (Table 2(b)) are components of hard wood are cellulose and hemicelluloses,
smokable. Smoked fish of all edible species and smoked game which form the basic structural materials while lignin serves as
commonly are found on display in the open markets and along the bonding glue for them. Because these structural materials are
major highways close to intersections with rivers. basically sugar compounds, they caramelize to give carbonyl
compounds with sweet flowery and fruity aromas. Lignin, on the
other hand, is a complex aggregate of phenolic molecules that
Active Antimicrobial Constituents of Wood Smoke gives smoky, spicy, and pungent compounds, such as guaiacol,
phenol, and syringol, in addition to sweeting vanillin and iso-
Thermal combustion of wood generates both smoke and heat eugenol. Wood is used in the form of logs, chips, peats, or
simultaneously. Smoke generation results from the temperature sawdust for smoke generation. Hard woods commonly valued
 PRESERVATIVES j Traditional Preservatives – Wood Smoke 143

Table 2(a) Major West African estuarine fish and shrimps of commercial value in smoked fish trade

Aquatic environment Family Species Common name

Marine, continental shelf, Sciaenidae Pseudotolithus elongatus Croakers

estuarine, brackish, P. senegalensis
creeks, coastal and P. typhus
delta waters Clupeidae Ethmalosa frimbriata Bonga
Ilisha Africana Shad
Polynemidae Galeoides decadactylus Threadfin
Polynemus quadrifilis
Pentanemus quinquarius
Sphyraenidae Sardinella spp. Sardine
Barracuda
Cyanoglossidae Cyanoglossus spp. Soles
Carangidae Caranx spp. Jack
Ariidae Arius spp. Marine catfish
Bagridae Chrisichthys nigrodigitatus Brackish water catfish
Pomadasyidae Pomadasys jubelini Grunters
Penaeidae Penaeus notialis Southern pink shrimp
Parapenaeopsis atlantica Guinea shrimp
Palaemonidae Palaemon spp. White shrimp

in the tropics for smoking are obtained from the plants of hardwood is scare. The smoking industries make use of hard-
Anthonata mycrophylla, Rhizophora racemosa, Dialium guinensis, wood logs, chips, or sawdust from hickory and oak. For a kiln of
Lophira alata, Entadrophragma cylindricum, and Naudea diderrichii, about 375 kg capacity, about 13 kg of wood is combusted
among others. Many other woody stems available in the vast per hour.
tropical regions serve equally well and sometimes fibrous stems Smoke is made up of vaporized chemical compounds,
such as from the coconut plant and coconut shell are used where most of which have been identified. They are mainly acidic

Table 2(b) Major West African inland fresh water fish of commercial value in smoked fish trade

Aquatic environment Family Species Common name

Inland fresh waters: Rivers, Gymnarchidae Gymnarchus niloticus Aba Asa

tributaries, dams, CichlidaeF Oreochromis niloticus Nile tilapia
lakes, and ponds Oreochromis aureus Blue tilapia
Astatotilapia bloyeti Bloyet’s haplo
Hemichromis fasciatus Banded jewelfish
Tilapia zillii Redbelly tilapia
Sarotherodongatilaeus gatilaeus Mango tilapia
ClariidaeF Heterobranchus bidorsalis African catfish
Heterobranchus longifilis Vandu
Clarias angiullaris Mudfish
Clarias gariepinus North African catfish
Latidae Lates niloticus Nile perch
Citharinidae Citharinus citharus Moon fish
Distichodus rostiratus Grass eater
Schilbeidae Schilbe mystus African Butter catfish
Bagridae Bagrus bayad Bayad
Carcharhinidae Carcharhinus leucas Mudfish
Clariidae Clarias lazerra Mudfish
Cyprinidae Ctenopharyngodon idella Grass carp
Cyprinus carpio carpio Common carp
Labeo coubie African carp
Clupeidae Ethmalosa fimbriata Bonga shad
Mormyridae Mormyrus rume rume Mormyrids
Channidae Parachanna obscura Snake-head
Protopteridae Protoperus annectens anneteus West African lung fish
Polypteridae Polypterus angsorgii Guinean bichir
Arapaimidae Heterotis niloticus Heterotis
Mochokidae Synodontis euptera Featherfin squeaker

F, Family of fish species that are farmed.

144 PRESERVATIVES j Traditional Preservatives – Wood Smoke

compounds, terpenes, carbonyl compounds, phenolic to have antimicrobial properties (as used by Lister), it is not
compounds, and hydrocarbons, all of which vary in their roles directly applied to foods as a preservative because of its toxicity
(Table 3) and number about 200 different chemical even at low concentrations. About 60% of the phenolic fraction
compounds. Carbonyl compounds are brownish and in wood smoke is made up of guaiacol (2-methoxyphenol),
responsible for most of the color imparted on smoked foods syringol (2,6-dimethoxyphenol), and their 4-substituted
by wood smoke. Formaldehyde, which is one of the carbonyl derivatives, namely, eugenol (4-allylguaiacol), isoeugenol
compounds, is notable for its antimicrobial activity. It has (4-propenylguaiacol), syringaldehyde (4-formylsyringol), and
a broad spectrum of activity and is the most active among the acetosyringone (4-methylketone guaiacol). Guaiacol is
antimicrobial constituents of wood smoke. It is directly used responsible for the smoky taste and syringol is responsible for
as a bacteriostat in cheese milk to prevent Clostridium sp. from the smoky aroma. Phenols are therefore said to be responsible
forming gas holes during the manufacture of Provolone for the main desirable flavors and odors characteristic of smoked
cheese. It is equally used as a sterilizant in food-wrapping foods.
materials. Hexamethylene tetramine is a chemical compound The rate and extent of smoke deposition on the food
commonly used to wash fruit; this compound eventually exposed during the process of smoking depend on a number
breaks down to formaldehyde to give protection against of factors that are difficult to control with traditional kilns.
microorganisms. Higher aldehydes are among the other These difficulties led to development of the modern tech-
carbonyl constituents and are produced in quantities five niques that place the important parameters under control
times greater than formaldehyde. The acidic constituents of within ranges that are best for safe and good-quality products.
wood smoke include acetic, formic, pyroligneous, and higher Such factors include smoke density and velocity, the
acids, all of which are antimicrobial in activity. Organic acids concentration of certain smoke constituents in the air
generally have antimicrobial properties. They lower the (particularly vapor), the location and distance of the food
internal pH of microbial cells through easy passage across the within the kiln and from the smoke source, the proportion of
membrane, as a result of their lipophilic property. They air and air velocity, and the relative humidity and food surface
inhibit growth by interacting with the microbial cell moisture, among other factors. The rate of smoke absorption
membrane, thus neutralizing its electrochemical potential. by smoking food under standard conditions of operation is
Other antimicrobial constituents of note are the organic proportional to the optical smoke density. Smoke density is
alcohols and the ketones. measurable using a smoke density meter, which is incorpo-
The main preservative function of phenolic compounds in rated in the kiln or smoke house. The cumulative smoke
wood smoke is their antioxidant activity. They prevent oxidative treatment applied to the food also can be measured. For
rancidity in smoked foods, thereby contributing to the preser- normal commercial practice, the smoke density value for fish
vation effect of smoking. Although phenol has long been known is about 0.9 m1. The extent of smoke deposition on food can

Table 3 Major constituents of wood smoke of significance in food smoking function and importance

Group of compounds Chemical compounds Specified compoundsa Group

Carbonyl compounds Formaldehydea Antimicrobial Antimicrobial

Other Aldehyde Surface pellicle formation coloring
Alcohols
Phenolic compounds Phenola Antioxidant
Guaiacol Antimicrobial Antioxidant
Syringcol Surface pellicle formation
Eugenol Aroma enhancing
Isoeugenol Flavor enhancing
Taste enhancing
Acetosyringone Coloring
Syringaldehyde
Vanillin
Acetovanillone
Cathecol
Acid compounds Formic acida Antibacterial Antibacterial
Acetic acida Antibacterial
Hydrocarbons Benzo(a)pyrena Carcinogenic Coloring
Tars Surface pellicle formation
Benzo(a)anthracene
Benzo(b)flouranthene
Dibenz(ah)anthracene
Indeno(1,2,3-cd)pyrene
Terpenes Hemiterpenes Aroma enhancing
Sesquiterpenes Surface pellicle formation
Triterpenes
a
Specific compound capable of exerting the specified function.
 PRESERVATIVES j Traditional Preservatives – Wood Smoke 145

be directly estimated by measuring the phenol concentration disruptive to the cells of contaminating microorganisms. The
as the phenol value. microflora associated with brined flesh foods are largely halo-
philic and osmotolerant microorganisms. These include both
spoilage flora and pathogenic bacteria. The spoilage flora
Effect of Deposition on Microbial Cells and Microflora include Lactobacillus, Micrococcus, Halobacterium, Halococcus,
Pseudomonas sp., and other members of Enterobacteriaceae,
Achievement of smoke deposition on products is visible giving while the pathogenic bacteria are Staphylococcus aureus, Vibrio
a characteristic dark-brown creosote coating appearance. parahaemolyticus, and Clostridium botulinum. At the salt concen-
Creosote normally is applied to wood for protection against tration attained during brining or salting, inhibition of growth
deterioration; however, in spite of the known specific activity of of most of these microorganisms is achieved without making
some smoke constituents, the levels at which they are deposited the product unpleasantly salty to taste. Brining reduces the
seem to be more enhancing of esthetic appeal than having microbial load by as much as 85–90% and it provides a surface
a direct effect on the microorganisms. Smoking deposits its gloss after smoking, in addition to serving as a condiment, thus
constituents on the outer surface of the food and does not improving the desirability of the product. Brining and curing
penetrate deep into the food especially with hot-smoked foods. also withdraw moisture that otherwise would be available for
Cold-smoked foods allow more smoke penetration as there is microbial growth. Brine strength is regularly checked using
little hardening of the outer surface. Barring the effects of all a brineometer and old brines are discarded at intervals; other-
accessory preservative efforts, such as brining and drying, the wise the microbiological quality of the product may be
microflora of the food does multiply even in the presence of the affected. As brines continue to be used, bacterial contamination
smoke deposits. The concentration of the smoke constituents – builds up in them; this may increase the load on good-quality
particularly the antimicrobial constituents, formaldehyde, and raw food entering the brine. In addition, reduction in brine
acidic compounds – seems not to be at levels that are inhibitory strength results from either drip water from the subsequent
to the microflora. Smoked foods that have not undergone some flesh dips or absorption of salt. All these act on the effectiveness
other hurdle treatments readily go moldy when moisture levels of the preservation process and must be prevented. After
are high enough to permit growth but aflatoxin production, for brining, the flesh food is drained and allowed to dry. Drying is
instance, is delayed. Smoke deposits exert an indirect effect; the done in chill rooms in industrial setups and can go on for
glossy pellicle formed on the food surface by the phenol- several hours; with traditional processors in developing trop-
coagulated surface protein presents the microbial cells with an ical countries, drying fish is achieved within 1–2 h in a sunny,
unsuitable environment for optimal multiplication. windy atmosphere. This step dries the surface water of the
fish, leaving a firm skin barrier against entry of microorganisms,
which is also suitable for smoke deposition. On the other hand,
Likely Preservative Effect of Smoking it exposes the fish to microbial contaminants. Fish sizes above
1.5–2 kg are usually sliced vertically across their lengths into
Given that the initial efforts at smoking foods was for preser- cuts before smoking. This gives more surface areas for brining,
vative purposes, the achievement of that purpose can be drying, and smoke deposition and offers better preserved
attributed to a combination of accessory processes that are portions of large fish that ordinarily would take longer to
preparatory to smoking as well as to smoke deposition on the process and smoke effectively. The process of smoking requires
food surface. These accessory processes include reduction of arranging the food on racks or trolleys with separate smoking
available moisture from the food tissues through brining or compartments from the fire chamber. Arrangement of the food
salting and evaporation due to heat generated by the thermal is done in a manner to ensure that all surfaces are exposed but
combustion of the wood. The effectiveness of any food pres- not piled on top of each other so as to hasten drying from the
ervation method has to do with the quality of the raw material heat of combustion and for smoke deposition. The wood is
or its sanitary state. Most foods that go for smoking have high allowed to burn, producing smoke, but not allowed to burst
levels of moisture, thus making them liable to the fast devel- into flame. This ensures a moderately low but steady heat that
opment of microorganisms. The raw material stands to give is allowed to rise within the first hour. The heat generated
a better quality smoked product when its initial microbial causes the food temperature to rise up to 55–80
C with the
count is low. Should there be any delay in processing, the food traditional uncontrolled system and sometimes up to 120
C
must be held at suitably low temperature until the process for meat. For the more advanced techniques of smoking using
begins. the Torry kilns where smoke-influential parameters are
The process starts by cleaning the raw materials for smoking controlled, cold smoking is done at about 30
C for about 2 h
to rid the surface of dirt and slime (fish). For scaly fish, the while hot smoking is done at temperatures of 70–80
C for
scales are removed before washing after which they are drained 2–3 h after initial holding at 50
C for 30 min. At these
of water. This also helps to reduce the surface microflora, temperatures most saprophytic, non-spore-forming microor-
particularly putrefying bacteria. Flesh foods like fish and meat ganisms are killed. The food is thus pasteurized. Moreover,
are cured by direct application of salt to the surface or are enzymatic activities are usually halted at about 60
C, pre-
dipped in brine (70–80% saturated salt solution) for about venting activity of the endogenous enzymes of the food.
5 min for small fillets and cuts for large fillets. This leaves Furthermore, the smoke generated in the process deposits its
a desirable tissue salt concentration of about 2–4% or up to 8% constituents on food surfaces as efforts are made to trap the
in direct salt applications. The result is a preservative effect as it smoke in the kiln to prevent its escape. The formaldehyde and
plasmolyzes the microbial cells and is thus microbistatic or phenols convert the brine-solubilized protein on the food
146 PRESERVATIVES j Traditional Preservatives – Wood Smoke

surface into a coagulated, smooth, resinous pellicle on which found is Dermestes species, while for bacteria the most common
other smoke constituents such as tars, aldehydes, alcohols, are S. aureus, Pseudomonas aeruginosa, Klebsiella, Bacillus, and
ketones, acidic compounds, and phenols are deposited. These Proteus species. Commonly encountered mold contaminants
together serve as reinforcement of the food surface against include Aspergillus flavus, Aspergillus fumimigatus, Aspergillus
development of microorganisms, thus helping to preserve the tereus, Aspergillus niger, and Rhizopus, Absidia, Mucor, Cladospo-
food. The phenols in their capacity as antioxidants also prevent rium, and Penicillium species. About 17.5% of airfreighted
oxidative rancidity, which is a common spoilage feature of fatty consignments of smoked fish to the United Kingdom from
foods. West Africa are rejected by the Port Health Authority for reasons
Established synergies between other preservative processes of improper packaging, labeling, and contamination. A lack of
and smoking allow for desirable results of food smoking emphasis on other synergistic packaging practices in the African
through various combinations (Figure 1). The options in use smoking procedure is responsible for some of the losses
by food-smoking practitioners all ensure unfavorable envi- incurred in smoked fish trade. Vacuum packaging of smoked
ronments for microbial growth. In the uncontrolled system of meat or fish products is an equally effective complementary
smoking, even in tropical countries, intermediate-moisture method in use with smoking. It removes much of the air that
foods are smoke dried until their water activity (aw) falls within supports growth of spoilage microorganisms or causes oxida-
the range (aw 0.6–8.5) as they are shelf-stable without refrig- tive rancidity, while preserving the distinct taste and aroma of
eration. In such a form, they are almost brittle and are retailed the smoked food. These factors together illustrate the efficacy of
in the market for as long as 2 weeks. When moisture levels rise a combination of preservative treatments, termed the hurdle
as a result of absorption from the atmosphere, they are effect (Figure 1) or synergism. Smoked foods therefore can
returned for further smoking to check the development of rightly be classified as hurdle-technology foods. By definition,
microorganisms. Nonetheless, sanitary assessment of such these are products whose shelf life and microbiological safety
retailed fish often shows evidence of insect infestation as well as are extended by several factors, none of which on its own
bacterial and mold contamination. The most common insect would be sufficient to inactivate undesirable microorganisms.

STEPS IN FACTORS PREDISPOSING HURDLES

SMOKING TO SPOILAGE

Food

High moisture level

Microbial load
Endogenous enzymes
Presmoking Intrinsic factors Curing
treatment Brining
Dry-salting
High aw
osmotolerant flora
Endogenous
enzymes Antimicrobial chemical
Intrinsic factors deposition
Smoking Antioxidant chemical
deposition
Moisture evaporation
Pasteurization

aw > alarm level (0.7) Packaging

Osmo- and xerotolerant Freezing
thermophiles Chilling
Postsmoking Intrinsic factors
handling Vacuuming
Packaging

Drying
Packaging

Preservation incomplete Preservation complete

Figure 1 Wood smoking and complementary hurdle technology in food preservation. aw, water activity.
 PRESERVATIVES j Traditional Preservatives – Wood Smoke 147

Possible Risks to the Consumer contents of B(a)P in fish smoked in traditional kilns are
higher than in fish smoked in smoke houses under
The agelong practices of wood preservation with chemicals, controlled parameters. Whether it is cold smoking (at
many of which are hazardous to health, constitute a problem 30
C) or hot smoking (at 80
C), temperatures are well
that requires scrutiny of the type of wood allowed for food below those established as favoring PAH generation.
smoking. Other possible hazards associated with smoking of 3. Certain condensates of liquid smoke have been queried
foods began to attract attention in the 1950s when it was over their safety. The safety of some liquid smoke flavorings
discovered that the polycyclic aromatic hydrocarbon (PAH) like Primary Product FF-B is under investigation by the
constituent of wood smoke could be carcinogenic. Equally European Food Safety Authority as it is regarded as weakly
hazardous are other chemicals generated as a result of reactions genotoxic. Primary Product AM 1 is another flavoring in
during the exposure of food to smoke and heat. The following liquid smoke described as potentially toxic to human.
risks may be encountered by consumers of smoked products.
Heat-Based Risks
Wood-Based Risks 1. Other hazardous chemicals closely associated with smoked
animal proteins result from the effect of heat on the food
Logs of wood specially hewn for cooking or smoking are
components during the smoking process. A group of these
desirable for good-quality smoking of foods. The problem of
are water-soluble, heat-stable polar substances with muta-
deforestation leading to scarcity of such wood and the rising
genic activity. Mutagens such as amino-carbolines are
level of urbanization makes lumber acquired from demolition
formed when the surface temperature of meat rises to about
sites easy alternatives that are available for smoking especially
200
C or even 115
C for fish in the presence of high
in developing countries.
moisture content. The mutagens are formed as a result of
1. The possibility of using discarded construction wood or pyrolysis of amino acids and proteins in heated meat and
lumber from a mill may constitute a health hazard as such fish; heat is an integral part of smoking.
pieces of wood usually are treated with chemicals to prevent 2. Maillard browning of food, which is observed when food is
fungal or insect infestation to resist rot. Ingestion or inha- exposed to heat, is a reaction between sugars and amino
lation of chemicals used in wood treatment can be highly compounds of foods. Heating and dehydration give rise to
dangerous and hence the use of wood treated with chem- brown polymeric compounds – melanoidins – which are
icals is prohibited in food smoking. A lot of lumber is sugar–amino acid Amadori compounds. Maillard reactions
treated with powdered subcarbonates of soda, mercury, and occur readily in smoked products processed even under
pentachlorophenol (a blend of mercury with chlor- controlled conditions. Prolonged consumption of Maillard
ophenates) to prevent sapstains. Other antisapstains browned diets causes physiological disorders of the liver
include borate mixtures, 3-iodo-2-propylyl-butylcarbonate, and kidneys. Purified Maillard reaction products such as
propiconazole all of which are biocidal and therefore pyrazines, reductones, dicarbonyls, and furan derivatives
hazardous to living fauna, including humans and aquatic have shown mutagenic activities.
forms. Some of these wood preservatives can introduce 3. Heating of proteinaceous foods also leads to the formation
carcinogens, such as sodium o-phenylphenate, to the food if of amino acid complexes that may be hazardous to health.
such chemically preserved wood is used in food smoking. Lysinoalanine is formed when stock fish (dried cod) is
2. The hydrocarbon fraction of wood smoke consists of about exposed to a temperature of 90
C at a pH above 13. This
30 different PAHs as well as 40 other compounds. Among complex has been implicated in renal damage. Although
the PAHs, benzo(a)pyrene (b(a)P) is carcinogenic and has there is a dearth of information regarding formation of
been detected in smoked foods in varying amounts. Levels lysinoalanine in foods, since conditions for smoked fish
ranging from 5.3 ng g1 to 14.8 mg g1 of foods have been products are suitable for the formation of lysinoalanine, its
detected in various species of fish as well as smoked ready- importance cannot be overlooked.
to-eat meats. Improved knowledge about food smoking 4. Gizzerosine (2-amino-9-(4-imidazolyl)-7-azanonanoic) is
allows for the control of smoking parameters to limit another chemical substance associated with heat-exposed
hydrocarbon generation in smoke. Important influential fish. This substance is a derivative of histamine or histidine.
factors are temperature and air velocity. At temperatures Gizzerosine causes stomach or gizzard erosion and black
above 400
C for wood decomposition and 200
C for vomit in chicks.
oxidation, hydrocarbon generation from lignin and cellu- 5. While it is common for smoked foods to be viewed as ready-
lose is highly favored. Poplar wood is known to produce the to-eat foods that do not need further cooking, certain risks
greatest amount of PAH among other wood types. are associated with this habit. Curing and smoking are not
Concentration of PAH is lowest when temperature for substitutes for cooking, particularly for flesh foods, given
production of liquid smoke was 530–559
C. Below these some of the temperatures attained during the process. Flesh
values, high concentrations of the desirable constituents foods that are known to harbor parasites require further
(phenols, carbonyl compounds, and acidic compounds) of cooking to remove any cysts. Pork (ham) retained in smoke
wood smoke are produced with little or no carcinogenic houses until it reaches an internal temperature of 61
C will
aromatic hydrocarbons. Specific conditions at which not be safe if it contains Trichinella. Ham labeled as ready to
formation of PAH is effectively suppressed while favoring eat is held at a temperature that raises the internal temper-
production of desirable compounds are operated. The ature to 68
C, at which point it is considered safe.
148 PRESERVATIVES j Traditional Preservatives – Wood Smoke

Ikeme, A.I., 1990. Meat Science and Technology. A Comprehensive Approach.

See also: Chilled Storage of Foods. Dried Foods; Heat
Africana Fep, Onitsha, Nigeria.
Treatment of Foods: Synergy Between Treatments; Hurdle Kordylas, J.M., 1990. Processing and Preservation of Tropical and Subtropical Foods.
Technology; Intermediate Moisture Foods; Packaging of Foods. Macmillan Education Ltd, London.
Neyboom, B., 1975. Fish Handling and Processing in the Kainji Lake Basin and
Suggestions for Improvements and Future Research. Food and Agriculture Orga-
nization of the United Nations, Rome.
Further Reading Russel, N.J., Gould, G.W., 1991. Food Preservatives. Van Nostrand Reinhold,
New York.
Burt, J.R., 1998. Fish Smoking and Drying: The Effect of and Drying on the Nutritional Ward, A., 2003. A Study of the Trade in Smoked-dried Fish from West Africa to the
Properties of Fish. Elsevier Science Publishers, Essex, UK. United Kingdom. Fisheries Circular No. 981. Food and Agriculture Organization of
Connell, J.J., 1979. Advances in Fish Science and Technology. Torry Research Station the United Nations, Rome.
Document. Fishing New Book, Aberdeen, Scotland.