Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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localized infection, e.g., osteomyelitis, may give rise

to resistant organisms.

The Salmonella Carrier State

0022 Although Salmonella carriage occurs more com-

monly after illness, it may also occur in individuals

who have not been ill. All patients with Salmonella

gastroenteritis usually shed up to 10

–10

organisms

per gram feces early in the course of disease and

excretion generally persists for 2–4 weeks, with 0.2–

0.6% of cases continuing to shed the organism for

1 year or more. The persistence of Salmonella does

not relate to the severity of the disease.

0023 A number of factors are involved in the pathogen-

esis of chronic carriage. Age is important: young chil-

dren tend to be prolonged convalescent carriers but

do not usually develop the chronic state. Adults in

their sixth decade or older are likely to become

carriers, with the biliary tree believed to be the site

of multiplication.

Pathogenesis of Infection

0024 There is little information concerning the number of

organisms involved in many outbreaks of naturally

acquired disease. Volunteer studies indicated that

c.10

–10

organisms were necessary to cause disease

in 50% of the healthy individuals participating. In the

case of S. typhi, none of the individuals became ill

when given 10

organisms: of those given 10

,10

and 10

organisms, 25, 50, and 95% respectively

developed disease. The clinical manifestations did

not vary with the size of the inoculum, although the

incubation periods were longer in those receiving the

smaller doses. However, volunteer studies in healthy

adults involving only a few serovars may not be

directly transferable to naturally acquired infection.

Where it has been possible to obtain the vehicle, e.g.,

chocolate, cheese, and desserts, the number of Sal-

monella have often been < 10

1

, especially in foods

with a high fat content or a good buffering capacity

which may protect the Salmonella from the gastric

acidity. It has also been demonstrated that people on

antacids, where gastric acidity has been lowered, or

on antibiotics, which may alter the gut flora, are more

susceptible to infection. The minimal infective dose

can also vary with age and the state of health. Factors

which help to determine the infective dose of Salmon-

ella are given in Table 1.

0025 Following ingestion of Salmonella, the organisms

pass through the stomach where the bactericidal

activity of the stomach produced by the low pH of

gastric juice regulates the number of organisms

entering the small intestine. The course of events

then depends on multiple factors, of which the most

important is probably the serovar of the Salmonella.

Thus, S. typhi after an initial period of multiplication

invades the intestinal mucosa, primarily it is thought

in the M cells of the Peyer’s patches of the distal

ileum, where a cellular reaction may take place in

the lamina propria. Although the infiltrate is com-

posed of mononuclear cells, in the case of S. typhi,it

contains predominantly polymorphonuclear leuko-

cytes when other noninvasive Salmonella produce

infection. It has been suggested that differences in

phagocytic effectiveness of the two types of phago-

cytes may explain the high incidence of bacteremia

with S. typhi and the relatively low occurrence with

other non-invasive Salmonella. The major factor for

intestinal penetration is encoded by genes that are

clustered in a large (40 kb) area of the chromosome,

designated Salmonella pathogenicity island 1 (PI 1).

In Salmonella there are at least five PIs, of which two

are associated with type III secretion systems, which

export proteins in response to bacterial contact with

cells. Although the onset of systemic and localized

infection is fairly similar, the symptoms produced

are not identical. Localized infection is usually mani-

fested as acute gastroenteritis, whereas only one-third

of typhoid patients develop diarrhea, usually several

days after the onset of fever. The contribution of

toxins in the etiology of diarrhea has never been

conclusively demonstrated, although several putative

toxins have been described, and it is now suggested

that the type III export system on PI 1 secretes one or

more proteins with enterotoxic activity.

0026To cause bacteremia, Salmonella must have

strategies to overcome each of the host’s deep-tissue

defenses, including resistance to phagocytic cells,

complement, specific antibodies, and cellular immun-

ity. It must be able to reach its preferred site of repli-

cation, i.e., the liver and spleen, where intracellular

multiplication occurs, which protects it from the

host’s defense mechanisms. If the bacteria are not

contained, they may then invade the blood and repli-

cate rapidly.

See also: Food Poisoning: Classification; Salmonella:

Properties and Occurrence; Detection

Further Reading

Baumler AJ, Tsolis RM and Heffron F (2000) In: Wray C

and Wray A (eds) Salmonella in Domestic Animals,

pp. 57–72. Wallingford, Oxon: CABI.

Rubin RH and Weinstein L (1977) Salmonellosis: Micro-

biologic, Pathologic and Clinical Features. New York:

Stratton International Medical Book.

Winstanley C and Hart CA (2001) Type III secretion

systems and pathogenicity islands. Journal of Medical

Microbiology 50: 116–126.

SALMONELLA

/Salmonellosis 5087

Salting See Curing; Smoked Foods: Principles; Applications of Smoking; Production; Preservation of Food

SAMNA

S A Abou-Donia and E I El-Agamy, Alexandria

University, Alexandria, Egypt

Introduction

0001 Although similar to ghee and other concentrated milk

fats, samna is of especial importance to the dairy

industry in Egypt. This article deals specifically, there-

fore, with the production and properties of samna

as traditionally manufactured in the rural areas of

Egypt.

0002 Samna is pure, clarified milk fat, produced in

Egypt. It is generally prepared from buffuloes’ milk

or cows’ milk, which constitute 63.5% and 35%

respectively of total milk output in Egypt, while

small amounts of samna are prepared from sheeps’

milk and goats’ milk, which constitute 1% and 0.5%,

respectively, of total milk output.

0003 The main object of the primitive dairy industry in

the rural districts of Egypt is to separate milk fats for

making butter, and to make the remainder into prod-

ucts which are consumed as such or, after storage,

throughout the year. In lower Egypt, farmers put

fresh milk in shallow or deep earthenware pots,

martrad or shalia, and leave it undisturbed in a

warm, dark place till the cream rises and the milk

coagulates. The cream layer is removed and beaten

into butter, which is converted into samna. The pres-

ence of earthenware pots, such as used in cream-

making, in the tomb of king Horaha of the first

dynasty (3200 bc), indicates that the art of samna-

making was known to the Ancient Egyptians.

Samna making by the Traditional Method

0004 Samna is usually made from butter produced from

ripened cream; however, nowadays, in some cases, it

can be made using cream prepared from salted or

unsalted whey. The resulting samna is called whey-

cream samna.

0005 The traditional process of samnamaking depends

primarily upon the properties of the butter with

respect to its acid degree value, taste, odor, and

weight. Weight is important to determine both the

yield of the samna and the amount of salt to be

added to the butter prior to the making process.

Liquefaction of Butter and Addition of Salt

0006Butter is placed in a stainless-steel or aluminum vat;

iron or copper pans should not be used, for if the

samna is contaminated with heavy metals, oxidation

of the fat is accelerated. The butter is then heated with

continuous stirring until liquefied (50–60



C), and the

salt is added at a rate of about 2–4% of butter weight.

0007The addition of salt leads to the following: (1) a

decrease in the water content of the resultant samna

because the salt increases the boiling point of the

water in the butter; (2) it helps in the fat separation

that arises from the difference in density between fat

and nonfat phases; (3) it increases the quantity and

shelf-life of the byproduct (morta); (4) it plays an

important role in the precipitation of the proteins in

butter during boiling. In addition, some makers of

samna believe that the addition of high levels of salt

during the making of samna is necessary in order to

store samna for a long time. This view is misguided

for the following reasons: (1) salt is not a fat-soluble

material and hence does not have a preservative

effect; (2) contamination of the salt with heavy

metals, e.g., iron or copper, accelerates fat deterior-

ation; (3) salt is a good absorber of water, and thus

the presence of salt in samna can increase the mois-

ture level and hence risk of rancidity. In general, after

the butter has been heated and salted, it is filtered

through a cloth, such as cheesecloth, to remove any

foreign matter mixed with the butter. In the case of a

good-quality butter, this step is omitted.

Butter Boiling and Ripening

0008Butter boiling and ripening are the most important

parts of the process of samnamaking with respect to

the quality of the resultant product. They are

performed as follows. The liquefied butter is heated

further to 90–96



C and, in the course of heating, a

foam is produced which is known as the boiling foam.

At this point, the level of heating should be reduced.

5088 SAMNA

After the disappearance of the foam, regular boiling

or simmering of the fat starts. After a certain time,

floating particles appear, which are principally com-

posed of proteins and phospholipids.

0009 Some makers prefer to remove the floating par-

ticles, but others do not. In general, at 103–107



most particles precipitate to the bottom of the vat. At

107–110



C the amount of nonfat particles increases.

At 110–115



C all the nonfat suspended particles are

precipitated to form morta, which has the same color

as samna, i.e., bright yellow. At 115–125



C, the color

of morta becomes dark and the characteristic cooked

odor of samna starts to appear. Moreover, a foam

suddenly appears, at which point the heating should

be stopped (this foam is called the ‘ripening foam’).

Excessive heating after this stage leads to the

following: (1) production of a darker product; (2)

the precipitated nonfat particles start to disperse and

suspend again and will be difficult to separate; (3) the

samna acquires an undesirable flavor; (4) the keeping

quality of the resultant samna is very poor, owing to

the weak body derived from the crystallization of

the fat.

0010 The quality of samna depends on the control of

the boiling and ripening processes and the expertise

of the maker. For example, continuous stirring during

boiling is very important to avoid any overcooking

defects, as is the time at which the heating and stirring

should be stopped. All these aspects must be con-

trolled by the samnamaker.

Decantation and Filtration

0011 Decantation and filtration are carried out when the

samna is slightly hot. The clear fat layer is decanted

by pouring it into another vat until just above the

level of precipitated particles (morta). The latter por-

tion of samna is passed through cheesecloth at least

twice, to retain any precipitated particles, and the

clear fat is then added to the rest.

Packaging of Samna

0012 The packing of samna is considered a vital process.

Samna should be filled into storage cans with suffi-

cient temperature to expel air bubbles inside the cans.

0013 Many different containers can be used for pack-

aging samna, e.g., jars of dark-colored glass to avoid

light-induced oxidation, tin-cans free of rust, or there

are special pots (which are known as barany and

mostly used in Egypt) made from clay with a glazed

inner surface.

0014 Too hot ambient temperatures and direct light

should be avoided for samna storage.

Factors Affecting the Keeping Quality of

Samna

1. 0015An increase in the acidity of the butter or cream

decreases the keeping quality of samna.

0016The heat treatment of the fat during the manu-

facturing process should be not less 110



Cand

not more than 125



C, since heat treatment (115–

125



C for 20 min) causes noticeable changes in

the fatty acid contents and induces changes

in unsaponifiable matter components.

0017The presence of traces of heavy metals, e.g., iron

and copper.

0018The presence of air or oxygen inside pots or cans.

0019The storage temperature.

0020The exposure of samna to light during storage.

0021A high level of moisture and/or nonfat matter in

the samna.

0022The presence or absence of natural antioxidants.

0023The source of cream prepared for buttermaking,

since samna results from whey cream has a lower

keeping quality due to higher rancid flavor and

increase in peroxide, thiobarbituric acid, and

acid values.

10.

0024Samna produced in winter has a better keeping

quality than that made in summer, spring, or

autumn. This is presumably due to the higher

phospholipids and unsaponifiable matter content

and lower levels of unsaturated fatty acids.

11.

0025The keeping quality of cows’ milk samna is better

than that of buffaloes’ milk due to the higher

contents of phospholipids and vitamin E in

cows’ milk fat. The chemical composition of

samna is shown in Table 1.

Characteristics of Good-Quality Samna

1. 0026Samna produced from cows’ milk fat has a golden-

yellow color (owing to the high content of

b-carotene), but in the case of buffalo milk fat,

the product has a white, slightly greenish color.

tbl0001Table 1 Chemical composition of samna

Constituent Cows’milk

samna

Buffaloes’ milk

samna

Water 0.3–1.0% 0.3–1.0%

Fat 98–99% 98–99%

Solid not-fat 0.2–0.3% 0.2–0.3%

Phospholipids (mg 100 g

1

) 93.2 76.6

Sterols (mg 100 g

1

) 241 316

Cholestrol (mg 100 g

1

) 33.05 42.66

Carotenoids (m g

1

) 4–15 0.2–1.0

Vitamin A (mgg

1

) 3–8 3–8

Vitamin D (mgg

1

) 7–10 7–10

Vitamin E (mgg

1

) 30–45 20–30

Vitamin K Traces Traces

SAMNA 5089

2.0027 The samna should be free of cooked, slightly sweet

flavor and it should be free of rancidity.

0028 It should have a gritty texture at 10–20



0029 The fat content should be not less than 99.5%, the

moisture not more than 0.3%; the expected chem-

ical properties of fat(s) are shown in Table 2.

0030 The main flavor compounds in samna are methyl

ketones, 2-enals, and 2,4 dienals.

Antioxidants used in Samnamaking

0031 The most common cause of deterioration in samna is

oxidative rancidity resulting from exposure to light.

To prevent this phenomenon, antioxidants are added.

These are categorized as follows:

0032 Natural antioxidants, which are present in samna,

derived from milk, e.g., phospholipids and vitamin

E (tocopherol).

0033 Antioxidants derived from nonfat matter (pro-

teins) during the heat treatment process of samna-

making, e.g., sulfhydryl groups (–SH groups).

0034 Some natural materials that may be added to cer-

tain brands of samna during packaging, e.g., soya

bean and wheat flours, dried date, fenugreek

grains, and safflower at a rate of 0.5–1%.

0035 Chemical substances, e.g., propylgallate at a rate

of 0.01–0.003%, but these materials are rarely

used.

Nutritive Value of Samna

0036 Samna is mainly composed of pure fat and thus it is

considered a good source of energy. Moreover, samna

provides significant quantities of fat-soluble vitamins,

e.g., A, D, and E. In addition, the use of samna in

cooking improves the taste of meal, and hence overall

intake may be increased.

The Byproduct (Morta) of Samnamaking

0037Morta is a byproduct of samnamaking and, if butter

rather than cream is used, the amount of morta is

usually equivalent to 6% of the weight of butter.

During boiling of butter, more than 85% and 75%

of cows’ and buffaloes’ butter cholesterols were sep-

arated with morta respectively. The composition of

morta depends primarily upon the steps in and condi-

tions of samnamaking but it is generally as follows:

0038water: 10–18%

0039fat: 40–65%

0040nonfat solids: 10–25%

0041ash and salt: 10–15%

0042cholesterol: buffaloes’ milk samna 131.6 mg

100 g

1

versus 193.6 mg 100 g

1

in cows’ milk

samna

0043The nutritive value of morta is mainly attributable

to the high content of phospholipids. Morta is con-

sumed as is, or used in making mish cheese.

See also: Buffalo: Milk; Ghee; Goat: Milk; Sheep: Milk

Further Reading

Abd El-Hady SM, Dawood AH, Montasser EA and Shinana

ME (1992) Evaluation of whey samna. In: Proceedings

of the 5th Egyptian Conference for Dairy Science and

Technology, pp. 104–113.

Abou-Donia SA (1984) Egyptian fresh fermented milk

products. New Zealand Journal of Dairy Science and

Technology 19: 7–18.

Fahmy AH (1961) Samna Manufacture, 1st edn, pp. 19–25.

Cairo: Modern Commercial Press.

Ghita El, Abd-Rabo FH, Ismail AA and Dabiza NM (1992)

Studies on cholesterol and cholesterol esterase contents

in milk and some dairy products. Egyptian Journal of

Food Science 20(2): 221–231.

Hassan MNA, Rady AH and Ibrahim MK (1989) Stability

and keeping quality of butter oil and samna. Egyptian

Journal of Dairy Science 17: 93–104.

Kankare V and Antila V (1988) Production and properties

of Indian ghee and Egyptian samna. Elintarvikey lioppi-

las 23: 28–30.

Lambert LM (1975) Modern Dairy Products, 3rd edn,

p. 307. London: Food Trade Press.

Mahran GA, Ahmed NS, Hofi AA and Asker AA (1975)

Phospholipid contents in buffaloes butter oil ‘samna’

as affected by processing. Egyptian Journal of Dairy

Science 3: 51–54.

Mahran GA, Hamzawi LF, Ahmed NS and Sayed AF (1992)

Seasonal composition variation of buffalo milk fat in

relation to keeping quality of the resulting fatty prod-

ucts. Egyptian Journal of Food Science 20(2): 263–272.

Warner JN (1976) Principles of Dairy Processing, p. 253.

New Delhi: Wiley Eastern.

tbl0002 Table 2 The fat content of samna made from cows’ milk and

buffaloes’ milk

Fat constant Cows’ milk

samna

Buffaloes’ milk

samna

Reichert–Meissl value 22 25

Polenske value 2.7 2.7

Kirschner value 19 22

Saponification value 220 222

Iodine value 29.65 37.90

Butyrorefractometer reading 40–44 40–43

Sometimes hydrogenated oils or other fats are added to samna and to

detect this kind of adulteration, milk-fat constants should be measured,

e.g., Reichert–Meissl, Polenske, Kirschner, iodine, and saponification

values.

5090 SAMNA

SANITIZATION

P N Hoffman, Public Health Laboratory Service,

London, UK

Principles

0001 Sanitization is usually defined as those disinfection

processes appropriate to use in the context of food.

Disinfection is ‘the elimination of microorganisms

such that they may remain only at levels that are not

harmful to health’, but there are, in practice, many

minor variations on this general definition. This

elimination may be by removal through cleaning, by

killing in processes such as by chemicals or heat, or a

combination of these methods. Such a definition is, in

practice, reliant on the context in which it occurs and

outlined in the following paragraph.

0002 The level of microorganisms designated as a ‘safe’

level will vary according to their location: more

bacteria could be present on a ‘safe’ floor than on a

‘safe’ chopping board. It will also depend on the type

of microorganism present: for a pathogen such as

Shigella, where very small numbers can give rise to

infection, only a total absence would be safe; for

nonpathogenic (i.e. which do not cause disease) spoil-

age organisms, low numbers present neither a threat

to health nor any immediate threat to quality. The

process of disinfection does not normally include

the killing of bacterial spores. These are highly resist-

ant dormant forms in the life cycle of members of the

genera bacillus and clostridia, such as Bacillus cereus

and Clostridium botulinum. These are normally only

eliminated by the more stringent process of ster-

ilization, that is the total elimination of all micro-

bial life, preferably in a process that has a high

quality assurance. Some chemical disinfectants are

capable of killing bacterial spores and are termed

‘sporicides.’

Mechanisms and Kinetics

0003 Chemical disinfectants kill their target microorgan-

isms by reaction with one or more components vital

to the internal integrity and function of that cell. This

reaction can be chemical, physico-chemical, or both.

A chemical reaction is one where covalent bonds

within molecules are broken or formed or where the

charge on an ion is altered. A physicochemical reac-

tion is one where non-covalent bonds, i.e., areas of

hydrophobic affinity or of noncovalent polarized

attraction are disrupted. These reactions follow

the kinetics of chemical reactions in general; thus,

the killing of microorganisms by disinfectants can be

similarly categorized. As the end effect, the death of

microbes, may be the result of a single reaction or,

more likely, of a combination of many reactions, the

kinetics of microbial death can become somewhat

more complex than the more simple chemical reac-

tions. The death of microorganisms in these circum-

stances approximates to the kinetics of a first-order

chemical reaction; the rates of microbial death

occur in a logarithmic manner. To illustrate this, if

1 000 000 bacteria are acted on by a lethal chemical

agent, they will lose a proportion, rather than a set

number, of their population with each unit of time. If

a lethal agent kills nine out of 10 of a particular

bacterium every minute (i.e., one base ten logarithmic

reduction per minute), 1 000 000 bacteria at time zero

(i.e., the start of the reaction) will be reduced to

100 000 after 1 min; to 10 000 in 2 min, and so on.

After 6 min, there will be one bacterium left. After

7 min there will be (in theory) 0.1 of a bacterium

remaining. A tenth of a bacterium does not exist,

but in statistical terms, this means one-tenth the

chance of a surviving bacterium, or one bacterium

surviving in every 10 samples processed. This con-

tinues, so that at 12 min from the start, there will be

one-millionth of a bacterium left; in effect, one bac-

terium in every million samples. Thus, the concept of

disinfection, as with the concept of safety, takes on a

statistical element.

Microbial Resistance to Chemical

Disinfectants

0004Microbial resistance to chemical disinfectants is a

less well-defined phenomenon than the better-

known analogy of microbial resistance to antibiotics.

With antibiotics, the concentration of an agent

achievable in the body will determine the so-called

‘break point.’ This provides a naturally set level of

antibiotic concentration against which to judge resist-

ance. If an organism is killed or inhibited below this

break point, it is considered sensitive; if it can grow at

or above the break point, it is resistant. Attainable

concentrations of chemical disinfectants are not simi-

larly fixed and usually can be varied within any given

use situation. Thus, ‘resistance’ to chemical disinfect-

ants has to be considered within these constraints but

can still be a useful concept.

0005There are several possible mechanisms by which

resistance to chemical disinfection exists.

SANITIZATION 5091

.0006 Innate resistance: This implies that there is either

no susceptible target within the microbial cell or

that the microbial cell is in some way impermeable

to the agent. An example of the former is the resist-

ance of viruses that comprise only nucleic acid and

protein (such as the picornaviruses, a group of

viruses that include a number of viruses that infect

by ingestion, an example of which is poliovirus) to

disinfectants such as phenolics and quaternary am-

monium compounds. An example of the latter is

the high resistance of bacterial spores to most dis-

infectants. Bacterial spores are a ‘survival’ form of

certain bacterial genera that show extreme resist-

ance to chemical and physical inactivation. Only a

few chemical disinfectants (sporicides) are capable

of inactivating bacterial spores.

0007 Acquired resistance: In this form of resistance, cer-

tain bacteria can adapt to survive or grow in the

presence of a particular disinfectant. This can be

through a process of ‘training’, whereby a bacter-

ium is exposed to a sublethal concentration of a

disinfectant and can then bring in to play a variety

of phenotypic adaptations, such as capsule produc-

tion, that can enable it to survive increasing con-

centrations of the disinfectant. Another mechanism

is by the acquisition of transmissible genetic

elements that confer resistance to lethal agents.

Although this is better known with bacterial

resistance to antibiotics, it does also exist with

disinfectants.

Reasons for Disinfection Failure

0008 It is not only genuine resistances, as above, that can

result in failures of a disinfection process. Many other

factors can affect the performance of a disinfectant

and lead to a suboptimal disinfection result:

0009 Neutralization of a chemical disinfectant can occur

by chemical or physical reaction. Disinfectants, by

their very nature, will react with molecules in a

microbial cell and thereby disrupt its vital func-

tions. They will similarly react with nonliving

organic matter, removing disinfectant molecules

from effective solution. If there is an excess of

organic matter and the disinfectant has a high af-

finity for it, this can lead to a disinfection failure

due to neutralization of the disinfectant. The disin-

fectant will have reacted with nonliving organic

matter, leaving insufficient for microbicidal pur-

poses. Although excess organic matter is the most

commonly encountered disinfectant neutralizer,

others do exist. There can be reactions between

disinfectant and neutralizing compounds, convert-

ing the disinfectant compound to a nonmicrobicidal

reaction product. These are specific chemical

reactions and tend to occur in unusual circum-

stances. The other main source of disinfectant

neutralization is from physical reaction with sur-

factants, charged, or polarized large molecules,

again removing disinfectant molecules from active

solution. Disinfectants that are especially suscep-

tible to this are those whose activity depends on

charge or polarization within their molecule. This

makes them both prone to these charge-based inter-

actions and also means that, once their charge or

polarization has been disrupted, their microbicidal

capacity is neutralized.

0010Failure to make contact with the target organism

is a common source of ineffective disinfection.

Organic matter, as well as neutralizing disinfect-

ants (see above), can form a barrier to disinfectants,

shielding microorganisms within and facilitating

their survival. In this way, microorganisms can

withstand a disinfection procedure that, to the

operator, should have been effective, i.e. the correct

concentration of disinfectant applied for the right

time to act against a microorganism innately sus-

ceptible to that disinfectant. Some disinfectants,

mainly those with innate or added surface active

capabilities, are better able to overcome shielding

barriers whilst others, especially those that coagu-

late proteins, are particularly prone to this short-

coming. However, even those disinfectants with

surfactant properties cannot be expected to pene-

trate thick layers of viscous or solid matter. A clean

surface is an essential prerequisite to routinely effi-

cient disinfection. Organisms within crevices in

surfaces are usually protected from contact with

disinfectants. This protection is enhanced by the

presence of organic matter. In situations when it

may be difficult for a disinfectant to penetrate a

crevice, it will probably be impossible for it to

penetrate that crevice when it is also filled and

protected by organic matter. So, not only an

absence of soiling, but also a crevice-free surface,

is needed. Crevices can be innate, as in the grain of

a wooden chopping board, a result of poor design,

as in machinery or pipework or a byproduct of

use, as in knife scours in a plastic chopping board.

Another situation where disinfectants do not work

due to a failure to make contact with their target is

that of poor-quality application such that the agent

does not make contact with all the surfaces intended

for disinfection. On an accessible surface, this could

be a result of human error, perhaps due to inept or

badly instructed staff, to equipment that does not

apply disinfectant to areas that are difficult to reach,

or to failure to remove extraneous objects that

5092 SANITIZATION

may shield a surface from a directly applied or sprayed

disinfectant. Inaccessible surfaces, such as those

within pipework or other enclosed vessels, present a

more substantial problem. Ideally, the application of

disinfectants should be considered at the design stage,

in the form of either a modification allowing free

access to all surfaces or ‘cleaning in place’-style dis-

pensing nozzles as permanent internal features.

0011 The concentration of a disinfectant will also deter-

mine the microbicidal efficacy. Disinfectants are

formulated to work at a specific concentration. Some-

times, different concentrations for different situations

are stated, for example, in the presence or absence of

organic soiling. If the concentration is too low,

inefficient microbicidal action will result; if the con-

centration is too high, the consequences could be

wasted resources, corrosion problems, or taint and

toxicity problems. Disinfectants should be made up

for use accurately. A ‘splash in a bucket’ approach

cannot insure accuracy. Similarly, if a disinfectant is

going to become substantially diluted during its use, it

should be formulated to be near its designated use

concentration after, rather than before, this dilution.

0012 All disinfectants need adequate time in which to

work. The exposure time of a microorganism to a

disinfectant can be determined by the method of

application; for example, it is very convenient to use

a volatile surface disinfectant, such as alcohol, in the

form of a wipe. The surface to be disinfected will be

dry and useable within seconds. The very convenience

of this form of application is also what can make it a

less effective method.

0013 Another factor that will determine the efficacy of

surface disinfection is the wetting ability of a disin-

fectant. When a disinfectant without a detergent or

other surface active agent (i.e., which has no wetting

ability) is spread on a surface, the film that it forms

will turn rapidly into discrete droplets with dry areas

in between these droplets. No substantial disinfection

will occur in these dry areas, which will comprise the

majority of the area to which liquid was initially

applied. A wetting agent, usually a detergent, will

allow the disinfectant to remain as a continuous film

on the surface and exert its full action until it is taken

out of effective solution by drying and so becoming

unavailable to microbial cells. The wetting ability

also enhances a disinfectant’s ability to penetrate or

remove layers of organic matter.

0014 As with chemical reactions in general, the tempera-

ture at which a disinfectant acts will affect the speed

of its activity. Unless otherwise specified, disinfect-

ants are formulated to work around normal ambient

temperatures. There are use situations where they

might be expected to work at low temperatures, for

instance, in a refrigerated food production unit or

out of doors in a cold climate. For a disinfectant

to work effectively in such situations, it will need a

higher concentration, a longer exposure time, or

both. From the same principles, if the temperature is

higher than normal ambient, a more rapid and effi-

cient disinfection will occur. Temperature itself starts

to become lethal to vegetative bacteria (not bacterial

spores) and other microbes around 60–65



C, at

which temperatures, the time needed for heat disin-

fection is in the range of several minutes to hours.

At 80



C, disinfection will occur far more rapidly,

needing only seconds for susceptible microbes to be

killed at this temperature.

Other Factors to be Considered in

Disinfectant Choice

0015Chemical disinfectants have a high reactivity with

biological systems, this being an integral part of

their microbicidal mechanism. As living systems

share many biochemical similarities, it is not unusual

for disinfectants to have a toxic effect on humans.

Toxicity may occur through one or more routes of

contact, such as through the skin, ingestion, inhal-

ation, or absorption into mucous membranes of the

eyes, nose, etc. There are two separate considerations

to the use of chemical disinfectants in catering and

the food industry: risk to the user and risk to the

consumer.

0016The major toxic risk is to the users of chemical

disinfectants. It is they who will handle concentrated

disinfectant solutions or solids, where any toxicity

will be many times that of the use dilution; who will

make up the use dilution, involving splash and skin

contact risks during this process; who will apply the

disinfectant with attendant risks of skin contact and

inhalation; and who will dispose of the disinfectant,

with more contact and inhalation risks. Chemical

disinfectants, especially in their undiluted form,

must always be assessed for hazard before use. Any

hazard must be eliminated by handling procedures

insuring minimal contact (especially uncontrolled

contact such as splashing), and use of effective and

appropriate personal protective equipment (gloves,

eye protection, etc.), where contact cannot be

ruled out. As a general rule, prevention of operator

contact with toxic agents by containment of the

agent is preferable to the use of personal protective

equipment.

0017Consumer toxicity, whilst much rarer, is a serious

consideration in terms of the number of people

affected as well as commercial considerations. The

dilution factors of disinfectants that find their way

from food-processing areas to consumers via a

food product will be immense. Nevertheless, the

SANITIZATION 5093

consequences of such an occurrence are equally im-

mense in terms of the potential numbers of people

affected, as well as commercial considerations. Con-

trol is achieved by segregation of significantly toxic

chemicals from food-handling areas or routes into

those areas.

0018 Taint is a problem allied in many ways to toxicity

in terms of origin and consequences. The problem

here is that certain disinfectants can impart character-

istic and undesirable taints to foods. Taint can be

caused by extremely low concentrations of these

chemicals, usually in terms of a few parts per billion

of a contaminant in food. The disinfectants most

implicated in taint problems are those with phenol-

derived molecules in them. These should be regarded

with suspicion unless an assurance of lack of taint can

be given. As with toxicity, such disinfectants are best

excluded from use in food-handling areas completely.

0019 Some disinfectants, particularly those of an oxida-

tive nature, can cause or accelerate corrosion of a

variety of metals. Whilst this is not directly connected

to microbicidal issues, it is a factor that must be

considered in the wider context of the practicalities

of disinfectant use. Particularly implicated in this are

hypochlorite disinfectants, which can start rusting

carbon steels in minutes. Corrosion is dependent on

a combination of factors, mainly: the disinfectant, its

constituents and concentration; the materials that are

in contact with the disinfectant; and the contact time

and temperature.

Characteristics of Commonly Used

Disinfectants

Hypochlorites

0020 These have a wide applicability in food-associated

use. Their advantages are a low toxicity, low

taint, wide microbicidal spectrum, and low cost.

Their disadvantages are corrosivity to some metals

(good-quality stainless steels are usually fairly

resistant to corrosion) and ready inactivation of

low-hypochlorite concentrations by organic matter.

Hypochlorites are available as sodium hypochlorite,

a liquid (‘bleach’) or sodium dichloroisocyanu-

rate (‘NaDCC’) and chloramines, both soluble

solids. Hypochlorites will decay in liquid solution,

dependent on exposure to light, elevated temperature,

and the presence of impurities. The solid hypochlor-

ites are stable on dry storage.

Iodine

0021The advantages of iodine are a low toxicity, low taint,

and a wide microbicidal spectrum. The disadvantages

include some corrosion to metals (though less than

hypochlorites), ready inactivation of low-iodine

concentrations by organic matter, and their com-

paratively high costs. Relatively insoluble in water,

iodine preparations are usually supplied as a complex

with polyvinylpyrrolidone (‘PVP’) or solubilized with

detergents. Iodine dissolved in potassium iodide

(‘Lugol’s iodine’) or alcoholic solutions (‘tincture of

iodine’) are available for medical use but have no role

in food hygiene.

Quaternary Ammonium Compounds (QACs)

0022The advantages of these are a low toxicity, low taint,

cheapness, and noncorrosivity. They all possess some

cleaning ability and are convenient to use. Their dis-

advantages are a ready inactivation by a wide range

of materials and an often incomplete microbicidal

spectrum. They are useful as general hygiene agents

but must be used with care if disinfection is a critical

step. Benzalkonium chloride is the most commonly

used QAC.

See also: Bacillus: Occurrence; Cleaning Procedures in

the Factory: Types of Detergent; Overall Approach;

Clostridium: Occurrence of Clostridium botulinum;

Microbiology: Detection of Foodborne Pathogens and

their Toxins