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

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Further Reading

Atherton JG and Rudich J (eds) (1986) The Tomato Crop.

London: Chapman and Hall.

Davies JN and Hobson GE (1981) The constituents of

tomato fruit, the influence of environment, nutrition,

and genotype. CRC Critical Reviews in Food Science

and Nutrition 15(3): 205–280.

FAO www.fao.org Statistical data bases. Food and Agricul-

ture Organization of the United Nations. Rome: Food

and Agriculture Organization.

Fulton TM (ed.) (1998) Report of the Tomato Genetics

Cooperative, vol. 48. Ithaca, NY: Department of Plant

Breeding, Cornell University.

Giovannucci E (1999) Tomatoes, tomato-based products,

lycopene and cancer: review of the epidemiologic litera-

ture. Journal of the National Cancer Institute 91(4):

317–331.

Gould WA (1983) Tomato Production, Processing and

Quality Evaluation, 2nd edn. Westport, Connecticut:

AVI.

Hobson G and Grierson D (1993) Tomato. In: Seymour GB,

Taylor JE and Tucker GA (eds) Biochemistry of Fruit

Ripening, pp. 405–442. London: Chapman and Hall.

Nevins DJ and Jones RA (eds) (1987) Tomato Biotechnol-

ogy. Plant Biology. New York: Alan R Liss.

Seymour GB, Colquhoun IJ, DuPont MS, Parsley KR and

Selvendrant RR (1990) Composition and structural fea-

tures of cell wall polysaccharides from tomato fruits.

Phytochemistry 29: 725–731.

Tigchelaar EC (1986) Tomato breeding. In: Bassett MJ (ed.)

Breeding Vegetable Crops, pp. 135–171. Westport, Con-

necticut: AVI.

Wills RBH (1987) Composition of Australian fresh fruit

and vegetables. Food Technology in Australia 39:

523–526.

Tongue See Offal:TypesofOffal

Tooth Decay See Dental Disease:StructureofTeeth;EtiologyofDentalCaries;RoleofDiet;Fluorideinthe

PreventionofDentalDecay

TORTILLAS

S O Serna Saldivar,InstitutoTecnologicoyde

EstudiosSuperioresdeMonterrey,MonterreyN.L.,

Mexico

L W Rooney,TexasA&MUniversity,TX,USA

Introduction

000 1 A tortilla can be defined as a flat, round, unfermented

bread produced from wheat (Triticum aestivum L.)

flour or lime Ca(OH)

cooked maize (Zea mays L).

Processes and characteristics of wheat flour and

maize tortilla differ considerably. Both types of tor-

tillas originated in Mexico, where they are considered

the national bread and are generally consumed with

others foods such as beans, meat, and vegetables.

Tortillas are increasing in popularity throughout the

world. Global sales were estimated at 6 billion dollars

in 1998. Processing plants have been started in the

UK, Spain, France, Australia, Brazil, India, China,

Korea, and other countries around the world.

0002For wheat tortilla production, refined or whole-

meal flour is mixed with shortening or lard, salt,

baking powder, and other ingredients. The tortilla

blend is mixed and kneaded with water to yield a

gluten-developed dough that is divided into balls

and hand-rolled or hot-pressed into a flat disk. The

disk is baked on a hot griddle to yield the tortilla

(Figure 1). Like bread dough, wheat flour tortilla

dough is gluten-structured.

0003For maize tortillas, mature grain is cooked in water

containing lime to produce nixtamal, which is ground

5808 TORTILLAS

into a moist dough called masa. Masa is the base for

the production of a wide array of indigenous foods,

ranging from table tortillas and chips (Figure 1)tothe

popular tamales and breakfast gruels. Maize-based,

lime-cooked snack foods are competing strongly with

potato chips and other salty snack foods in North

America.

0004 Maize, lime, and water are three basic ingredients

needed for the production of masa. Lime softens the

pericarp and endosperm and protein hydration and a

small amount of starch is gelatinized. Due to its high

pH, the starch chains are charged, which helps to

retard retrogradation and staling. Other ingredients,

such as preservatives, acidulants, emulsifiers, and

gums, are used to improve the shelf-life of table tor-

tillas. Frying oil is the second major ingredient in fried

snacks. Snacks are usually salted and flavored.

Wheat Tortillas

0005 Historically, tortillas were homemade, prepared on a

daily basis, and consumed fresh. The fastest-growing

tortilla area in the USA is wheat flour tortillas.

Flour tortillas represents about two-thirds of the ap-

proximately 3 billion dollars of tortillas sold in the

USA in 1998. Most wheat tortillas are industrially

manufactured by hot-press, die-cut, or hand-stretch

procedures. Each operation requires different flour

specifications, dough preparation, and baking condi-

tions, which result in various tortilla characteristics.

0006 Hot-press tortillas are slightly off-round, elastic,

resistant to tearing, have a smooth surface texture,

and resist moisture absorption from fillings. Hot-

press tortillas are consumed as gourmet table tor-

tillas, fajitas, and soft tacos. Die-cut tortillas have

a lower moisture content, are circular, less resistant

to cracking, and often have dusting flour on the

surface. Die-cut tortillas are mainly used in burritos,

frozen Mexican foods, and fried products, i.e.,

taco salad bowls, taco shells, chimichangas, and

bun

uelos. Hand-stretch tortillas are irregular in

shape, elastic, moderately resistant to tearing, and

have dusting flour on the surface. Hand-stretch tor-

tillas are consumed as table tortillas, burritos, and

some fried products.

0007All wheat tortillas contain flour, water, fat, and

salt. However, in the USA, tortillas may contain

several other ingredients to improve flavor, softness,

rollability, and shelf-life (1–4 weeks). These ingredi-

ents include chemical leavening agents, emulsifiers,

antimicrobial agents, acidulants, gums or hydro-

colloids, reducing agents, sugar, and yeast.

0008Wheat flour, the most important ingredient, is

usually enriched, bleached, hard wheat flour with a

protein content ranging from 9.5 to 14%. Equipment

limitations and processing conditions determine the

functionality of the flour. Flours for hot-press and

hand stretch tortillas generally require less protein

and gluten strength than flours for die-cut tortillas.

Dough mixing time and dough properties are modi-

fied by reducing agents (sulfite, cystine), emulsifiers

(lecithin, mono- and diglycerides, sodium stearoyl-2-

lactylate), salt, gums, fat, water content, and dough

temperature. (See Emulsifiers: Organic Emulsifiers;

Gums: Properties of Individual Gums.)

0009Water (45–55% of flour weight) is needed to form

the gluten complex. Solid or liquid fats (5–15% of

flour weight) are added to improve dough properties,

retard staling, and produce a softer and more flexible

tortilla. Salt (1–2%) is added for taste and to

strengthen the gluten complex. Baking powder (1.0–

2.5%) gives a whiter, less dense, spongy product.

Various natural and modified cellulose gums are

added at 0.1–0.5% levels to improve dough ma-

chinability and decrease the stickiness of baked tor-

tillas. Antimicrobial agents (propionates, sorbates)

and acidulants (citric, fumaric, and phosphoric

acids) limit fungal growth and extend shelf-life.

Optimum pH for propionate activity is 5.5, and for

sorbate activity is 6.0 when used at 0.2% of flour

weight; however, dough mixing is more difficult

below pH 5.8.

0010Wheat tortilla dough is mixed to incorporate the

dry ingredients, fat and water, and to form a pliable,

viscous dough. Tortilla dough is optimally mixed to

slightly overmixed and varies in temperature from

26 to 38



C, depending upon subsequent operations.

fig0001 Figure 1 Wheat tortillas and lime-cooked maize products.

Clockwise, from center top: corn on the cob; wheat tortillas;

corn chips; a wheat burrito and corn taco; fried taco shells filled

with meat and vegetables; tortilla chips; a stack of maize table

tortillas. Courtesy of Electra Food Machinery Inc, El Monte, Cali-

fornia, USA. Reproduced from Tortillas, Encyclopaedia of Food

Science, Food Technology and Nutrition, Macrae R, Robinson RK

and Sadler MJ (eds), 1993, Academic Press.

TORTILLAS 5809

The dough is divided and rounded into dough balls

in the hot-press and hand-stretch procedures. The

dough balls are rested in a warm, moist environment

for 5–20 min to relax the gluten complex. Rested

dough balls machine easier and form better tortillas.

In die-cut operations, the dough is pumped and

shaped into a sheet that is further thinned by a series

of cross-rollers on a moving belt. The thin sheet

of dough (about 0.5 mm) is cut by a circular die

which forms the shape. The scrap dough is returned

to the dough pump and processed. Regardless of

the process, the formed tortilla are baked (190–

260



C for 30–50 s) in gas-fired ovens that generally

have three tiers. Oven conditions vary depending

upon tortilla thickness, type of conveyor (slat or

wire), and forming operation. Puffing of tortilla

occurs near the end of baking and is more common

in hot-press and hand-stretch tortillas. Tortillas are

cooled to < 32



C on cooling conveyors before placing

into plastic bags for distribution. Improper cooling

causes the tortilla to stick together and increases

microbiological problems. Wheat flour tortilla pro-

ducers have recently developed low-fat and fat-free

products. The USA market for fat-free tortillas is

between 35 and 40 million dollars. Kosher tortillas

are another market under development.

Lime-Cooked Maize Products

0011Three basic types of product are industrially pro-

duced from lime-cooked maize: table or soft tortillas,

corn chips, and tortilla chips (Figure 2). Corn and

tortilla chips are primarily produced and consumed

in developed countries, where they have an important

share within the salted snack-food market. In 1998,

sales of US-made corn and tortilla chips totaled 3.57

and 0.74 billion dollars, respectively. In contrast with

sales in 1989, the market of these salted snacks

increased 70% and 15.6%, respectively.

Table Tortillas

0012The technology for maize tortilla production was

developed by early Mesoamerican civilizations. Tor-

tillas and masa products constitute the staple food for

large groups of people in Mexico and Central Amer-

ica. In Mexico, annual per capita intake in some

Sifting and blending

Additives (preservatives,

gums, emulsifiers) and

enrichment mix

(vitamins and minerals)

Baking

(gas-fired oven)

Lime

Ca(OH)

Corn

Water

Lime cooking; steeping and washing

Nixtamal

(lime-cooked grain)

Grinding

Drying

(countercurrent air flow)

Dough or masa

(lime-cooked dough)

Dry masa

flours

(10% moisture)

Deep-fat frying

(160−180 ⬚C/50−70 s)

Corn chips

Soft tortillas

Tortilla chips

fig0002 Figure 2 General scheme for the production of table tortillas, corn chips, tortilla chips, and dry masa flour.

5810 TORTILLAS

groups of people is higher than 120 kg. In the USA,

sales of table tortillas was estimated at 1 billion

dollars in 1998. Tortillas are produced using trad-

itional and industrial processes. In the traditional

process maize is lime-cooked in clay pots over a fire,

followed by steeping for 8–16 h (generally overnight).

The cooking liquor, called nejayote, is discarded and

then the nixtamal is hand-washed. Nixtamal is ground

into a fine masa with a stone grinder called metate, or

with hand-operated grinders. Masa is hand-molded

or pressed into disks which are baked on a hot griddle

or comal. Traditional tortillas are generally produced

on a daily basis and are usually thicker and heavier

than their industrially produced counterparts. Tor-

tillas are the main source of energy, protein, calcium,

and other important nutrients in Mexico and Central

America. Lime-cooking considerably increases cal-

cium and the bioavailability of niacin, and signifi-

cantly decreases the amount of aflatoxins in

contaminated maize. (See Aflatoxins; Niacin: Proper-

ties and Determination; Pellagra.)

0013 The industrial production of maize tortillas is

labor-intensive and requires considerable equipment.

Quality of end products depends on the nature of raw

material and manufacturing practices. The ideal grain

should be sound, free of fissures, uniform, brightly

colored, and with intermediate-to-hard endosperm.

In addition, the kernels should have a rounded crown

and a shallow, unwrinkled dent, and the pericarp

should be easily removed after lime-cooking. Yellow

and white maize, or mixtures therefrom, are commer-

cially manufactured into alkaline products.

0014 The industrial tortilla process starts when the

maize is lime-cooked in agitated open baths, vertical

cookers, or steam kettles. The grain is generally mixed

with three parts water and 1% lime, based on grain

weight, and cooked for 15–45 min at temperatures

ranging from 85 to 100



C. The nixtamal is then

steeped for 8–16 h in the hot lime solution. After

steeping, the maize is pumped with the steep liquor

or dropped by gravity to washers. The cooking liquor

is drained and the nixtamal washed with pressurized

water. Most of the pericarp and excess lime is removed

during this step. The cleaned nixtamal is discharged

into a stone grinder, where masa is produced. The

grinder consists of two volcanic or synthetic (alumi-

num oxide) stones carved radially, one stationary and

the other rotating at 500–700 rpm. Masa particle size

is directly related to the gap or pressure between the

stones and the size and depth of the grooves. During

grinding, the nixtamal is disrupted into a plastic and

cohesive masa. Masa is then kneaded by mixers or

extruders that feed the forming machine or sheeter

rolls. During forming, the masa is rolled into a sheet

which is cut by a rotating cutter positioned underneath

the rolls. The formed pieces of masa are fed into a

three-tier, gas-fired oven for baking. Tortillas are

baked at temperatures ranging from 280 to 302



for 30–45 s, then cooled through a series of open tiers

and packaged. Tortillas are generally treated with

acidulants and antimold agents such as sorbates and

propionates to improve their shelf-life. These additives

are incorporated during grinding or masa kneading.

Dry Masa Flour

0015The use of dry masa flour is growing rapidly because of

its convenience. More than 2 million metric tons of dry

masa flour for table tortilla production are annually

produced in Mexico. These flours are transformed

into approximately 3.4 million tons of table tortillas.

The dry masa flour industry supplies about 40% of the

tortillas consumed in Mexico. Dry masa flour is pro-

duced by drying and grinding lime-cooked, coarsely

ground masa (Figure 2). The masa is dried in large

tunnels, or drying towers, in which warm air flows

countercurrently to the masa. Awide array of products

can be manufactured by selecting and blending

streams with different particle size and color. In most

cases, resulting flours are enriched with vitamins thia-

min, riboflavin, niacin, and folic acid and minerals

iron and zinc. Coarser flours with lighter colors are

required for snacks. The flour with less than 10%

moisture is shelf-stable and only requires water to

form masa. Many manufacturers use dry masa flour

because it does not require much labor, equipment, or

space, and processors do not have to worry about

effluent disposal and control of scheduling and manu-

facturing practices. Dry masa flours are generally

mixed with 1.1 to 1.2 parts water for about 3–5min

to produce a suitable dough for further processing.

Fried/Snack Products

0016Frying has expanded the market for masa-based

foods because the final product has excellent organo-

leptic properties and a long shelf-life. The two most

popular snacks, tortilla and corn chips, are usually

made from coarsely ground fresh masa or masa

flours. Corn chips are produced directly from masa

(Figure 2) and contain more oil than tortilla chips

(Table 1). Tortilla chips are baked similarly to tor-

tillas before frying. Tortilla chips absorb less oil, and

have a firmer texture and a stronger corn flavor than

corn chips. Nixtamal for these snack foods is gener-

ally cooked less than nixtamal for table tortillas, and

it is ground into coarse masa which allows steam to

escape through the many small pores during baking

and frying. This prevents the formation of serious

quality defects, such as oily appearance and pillowing

or blistering. Masa for corn chips is extruded through

a die, and cut by rotating knives before frying. Masa

TORTILLAS 5811

for tortilla chips is formed into triangles, strips, or

circles before baking, equilibrating, and frying. Masa

from yellow maize requires a lower frying tempera-

ture and longer residence time than masa from white

maize. Frying temperatures and times range from 165

to 195



C and 50 to 90 s.

0017 Corn and tortilla chips are often salted and flavored

immediately after frying. The hot chips are conveyed

into an inclined rotating cylinder on to the product.

Most popular flavorings include nacho cheese, hot/

spicy, barbecue, lemon salt, and jalapen

o. Corn and

tortilla chips are packaged in moisture-proof or alu-

minized bags filled with an inert gas to protect the

product physically and to prevent rancidity. Blue

maize tortilla chips are often served in specialty res-

taurants and are available as organic and regular

products. Blue maize has a pigmented aleurone that

imparts an intense blue color. It has high levels of

flavanoids and other phenolics that may have nutra-

ceutical properties. The low-fat market of these prod-

ucts is increasing in the USA and other developed

countries. Special processes to produce baked low-

fat tortilla chips that combine air impingement, infra-

red, and microwaves have been developed. Olestra is

currently being utilized to produce reduced-calorie

chips. (See Organically Farmed Food.)

Nutritional Value

0018The nutrient composition of some lime-cooked maize

foods is compared with white pan bread and wheat

tortillas in Table 1. Tortillas, especially wheat flour

tortillas, are commonly used as a substitute for pan

bread by many people. Wheat flour tortillas have

nutritional attributes similar to bread. Flour tortillas

are higher in gross and digestible energy because their

formula contains more shortening (5–15% based on

flour weight). Wholemeal flour tortillas have higher

amounts of fiber, protein, and ash than do white flour

tortillas.

0019Lime-cooked maize products are an important

source of energy, protein, dietary fiber, and calcium

for people who depend on these items as their staple

foods. Lime-cooking significantly improves the bio-

availability of niacin. The caloric density of corn

chips and tortilla chips is significantly higher than

table tortillas. This is due to oil absorption during

frying and their low moisture content. Tortillas and

snacks produced from enriched dry masa flour

contain higher levels of B vitamins and Fe and Zn

than counterparts produced from fresh masa. In

Mexico, dry masa flours are industrially enriched by

a federal regulation and some of these flours are

tbl0001 Table 1 Nutritional profile (per 100 g serving) of flour tortillas, lime-cooked corn products, and table bread

Nutrient Wheat flour tortilla Lime-cooked products Table bread

Table tortilla Corn chips

Tortilla chips

Water (g) 29.3 41.9 0.9 1.6 35.8

Energy (kcal) 351.3 238.3 573.1 514.3 274.0

Energy (kJ) 1471 998 2399 2153 1147

Digestible energy (kcal) 331.2 223.5 544.4 487.0

Digestible energy (kJ) 1387 9360 2280 2039

Protein (g) 7.2 6.5 6.3 7.6 8.7

Digestible protein (g) 6.4 5.38 6.2 7.7

Fat (g) 9.8 2.53 36.6 23.9 3.9

Ash (g) 2.2 0.90 1.9 1.1 1.9

Total dietary fiber (g) 7.4 12.4 2.7

Dietary insoluble fiber (g) 6.3 9.0

Dietary soluble fiber (g) 1.1 3.1

Starch (g) 44.9 59.9

Calcium (mg) 42.2 92.8 105.0 124.0 126.0

Phosphorus (mg) 77.0 162.6 177.5 208.6 87.0

Magnesium (mg) 84.8 69.7 76.1 89.4 21.7

Sodium (mg) 573.0 13.3 1091.1 494.8

Potassium (mg) 99.0 205.3 211.2 103.0

Iron (mg) 1.5 2.5 2.9 3.5 2.6

Zinc (mg) 0.6 2.5 2.5 3.0 0.6

Copper (mg) 0.8 0.07 0.09 0.11 0.14

Data from Betschart AA (1988) Nutritional quality of wheat and wheat products. In: Pomeranz Y (ed.) Wheat Chemistry and Technology. St Paul, Minnesota:

American Association of Cereal Chemists, Bressani R (1990) Chemistry, technology, and nutritive value of maize tortillas. Foods Reviews International

62(2):225–264, Gonzalez Agramon MM and Serna Saldivar SO (1988) Effect of defatted soybean meal and soybean isolate on the nutritional, physical,

chemical and organoleptic properties of wheat flour tortillas. Journal of Food Science 53: 793–797. Serna Saldivar SO, Knabe DA, Rooney LW, Tanksley TD

and Sproule A (1988a) Nutritional value of sorghum and maize tortillas. Journal of Cereal Science 7:83–94, and Sproule AM, Serna Saldivar SO, Bockholt A,

Rooney LW and Knabe DA (1988) Nutritional evaluation of tortillas and tortilla chips from quality protein maize. Cereal Foods World 33: 233–236.

Salted corn chips.

Unsalted tortilla chips. Salted tortilla chips contain approximately 774 mg of sodium per 100 g.

5812 TORTILLAS

optionally fortified with soybean protein. Human

nutritional studies have demonstrated that fortified

and enriched flours upgrade the nutritional status of

low-income and marginal people, especially children.

(See Dietary Fiber: Properties and Sources; Niacin:

Properties and Determination.)

See also: Aflatoxins; Dietary Fiber: Properties and

Sources; Emulsifiers: Organic Emulsifiers; Gums:

Properties of Individual Gums; Maize; Niacin: Properties

and Determination; Organically Farmed Food; Pellagra

Further Reading

Almeida Dominguez HD, Cepeda M and Rooney LW

(1996) Properties of commercial nixtamalized corn

flours. Cereal Foods World 41: 624–630.

Anonymous (1999) Snack Food Association state of the

industry report. Snack World June.

Betschart AA (1988) Nutritional quality of wheat and

wheat products. In: Pomeranz Y (ed.) Wheat Chemistry

and Technology. St Paul, Minnesota: American Associ-

ation of Cereal Chemists.

Bressani R (1990) Chemistry, technology, and nutritive

value of maize tortillas. Foods Reviews International

62(2): 225–264.

Dally V and Navarro L (1999) Flour tortillas: a growing

sector in the US food industry. Cereal Foods World 44:

457–459.

Gonzalez Agramon MM and Serna Saldivar SO (1988)

Effect of defatted soybean meal and soybean isolate on

the nutritional, physical, chemical and organoleptic

properties of wheat flour tortillas. Journal of Food

Science 53: 793–797.

Rooney LW and Serna Saldivar SO (1987) Food uses of corn

and dry milled fractions. In: Waston SA and Ramstad PE

(eds) Corn Chemistry and Technology. St Paul, MN:

American Association of Cereal Chemists.

Rooney LW and Suhendro EL (1999) Perspectives on nixta-

malization (alkaline cooking) of maize for tortillas and

snacks. Cereal Foods World 44: 466–470.

Saldana G and Brown HE (1984) Nutritional composition

of corn and flour tortillas. Journal of Food Science 49:

1202–1203.

Serna Saldivar SO (1996) Quı

mica, Almacenamiento e

Industrializacio

n de los Cereales. Mexico, DF: AGT.

Serna Saldivar SO, Knabe DA, Rooney LW, Tanksley TD

and Sproule A (1988a) Nutritional value of sorghum and

maize tortillas. Journal of Cereal Science 7: 83–94.

Serna Saldivar SO, Rooney LW and Waniska RD (1988b)

Wheat flour tortilla production. Cereal Foods World 23:

855–864.

Serna Saldivar SO, Gomez MH and Rooney LW (1990) The

chemistry, technology and nutritional value of alkaline

cooked corn products. In: Pomeranz Y (ed.) Advances of

Cereal Science and Technology, vol. X. St. Paul, MN:

American Association of Cereal Chemists.

Serna Saldivar SO and Rooney LW (1994) Quality protein

maize processing and perspectives for industrial utiliza-

tion. In: Larkins B, Mertz ET (eds) Proceedings of the

International Symposium on Quality Protein Maize,

pp. 89–120. Sete Lagoas, MG, Brazil: EMBRAPA/

CNPMS.

Sproule AM, Serna Saldivar SO, Bockholt A, Rooney LW

and Knabe DA (1988) Nutritional evaluation of tortillas

and tortilla chips from quality protein maize. Cereal

Foods World 33: 233–236.

Waniska RD (1999) Prespectives on flour tortillas. Cereal

Foods World 44: 471–473.

Yau JC, Waniska RD and Rooney LW (1994) Effects of

food additives on storage stability of corn tortillas.

Cereal Foods World 39: 396–402.

Toxicology See Toxins in Food – Naturally Occurring; Mycotoxins: Classifications; Occurrence and

Determination; Toxicology

TOXINS IN FOODS – NATURALLY OCCURRING

S L Taylor, University of Nebraska, Lincoln, NE, USA

Background

0001 The central axiom of toxicology is that all chemicals

are toxic at some dose. Thus, all chemicals in foods,

both synthetic and naturally occurring, are toxic.

Though theoreticazlly correct, it is impractical

to view all food constituents as toxicants. For the

purposes of this review, naturally occurring toxicants

are those chemicals of natural origin in foods that

may present a hazard to consumers when eaten

under some reasonable circumstances of exposure.

Although toxicity is an intrinsic property of all chem-

icals, hazard is the capacity of a substance to produce

TOXINS IN FOODS – NATURALLY OCCURRING 5813

injury under the circumstances of exposure, taking

into account the dose and frequency of exposure as

well as the toxicity of the particular chemical. Ill-

nesses caused by exposure to hazardous levels of

chemical toxicants are called intoxications.

Definition of Natural

0002 No legal definition exists for the word ’natural’ in US

food laws or the food laws of most other countries.

Thus, there are no legal limitations on the use of the

term. Webster’s dictionary defines natural as ‘‘planted

or growing by itself: not cultivated or introduced

artificially (e.g., grass); existing in or produced by

nature: consisting of objects so existing or produced:

not artificial.’’ Most consumers would likely define

natural as being anything that is not artificial. Of

course, artificial is another term that defies definition.

Foods derived from animal or plant materials,

whether processed or raw, are considered to be nat-

ural. The addition of additives to foods or the synthe-

sis of a food from chemical sources would create a

food that is perceived as not natural. To the food

industry, additive-free or preservative-free foods are

often described as natural. Naturally occurring chem-

icals from foods would be those chemicals that exist

in foods in the raw, unprocessed state, although many

of those chemicals would not be altered by processing

or preparation practices.

Sources of Naturally Occurring Toxicants in Foods

0003 Naturally occurring toxicants in foods can be either

naturally occurring constituents of foods or contam-

inants that are produced in foods by various natural

processes. Whereas naturally occurring constituents

can be considered to be normal and unavoidable, nat-

urally occurring contaminants are not always present

and can be avoided, if contamination is prevented.

0004 Naturally occurring toxicants are present in foods

of animal, plant, or fungal origin. The majority of

foods of animal origin, including meat, milk, cheese,

eggs, fish, mollusks, and crustacea, are not hazard-

ous. The most hazardous chemicals occurring in this

category are found in poisonous seafoods. Foods of

plant origin include vegetables, fruits, grains, seeds,

nuts, and spices. Most plant-derived chemicals are

also not especially hazardous, although some have

the potential to be hazardous under some conditions

of exposure. The major food of fungal origin is mush-

rooms, and many mushroom species are considered

as poisonous and inedible.

0005 Naturally occurring contaminants can be formed

in foods as the result of contamination by bacteria,

molds, algae, and insects. The chemicals produced

from these biological sources can remain in the food

even after the living organism has been removed or

destroyed. Such contaminants represent the most im-

portant and potentially hazardous chemicals of nat-

ural origin existing in foods.

Additives Versus Natural

0006Consumers are often concerned about the chemicals

added to their foods. These concerns likely arise from

government regulatory actions against certain food

additives or incidental contaminants such as pesti-

cides. In contrast, natural products are widely viewed

as beneficial to health.

0007Food laws are often predicated on the assumption

that natural foods are safe, whereas most additives,

especially all newly developed additives, must be

proven to be safe. Although foods naturally contain

many toxicants, including many chemicals that have

been shown to be carcinogens in animal studies, gov-

ernment regulatory agencies have rarely taken any

action to limit the availability of natural foods as a

result of the presence of such toxicants. Meanwhile,

the government has banned several food additives

(cyclamate, FD&C Red No. 2 in the USA) and pesti-

cides (DDT, ethylene dibromide in the USA) because

of concerns about their safety, especially with respect

to their possible carcinogenicity. Given this contrast,

it is not surprising that consumers have developed a

suspicious attitude regarding chemicals added to

foods while remaining naı

ve about the potential

hazards presented by naturally occurring chemicals

in foods. (See Food Additives: Safety.)

0008Although unrecognized by many consumers, natur-

ally occurring chemicals in foods present the greatest

risk of any of the chemicals in foods. Thankfully,

most of the potentially hazardous naturally occurring

toxicants are ingested at doses that are unlikely to

cause widespread illness, although the margin of

safety is often lower for naturally occurring toxicants

than it is for food additives. For example, the major-

ity of the carcinogens in our diets are of natural

origin. However, our diets also contain many natur-

ally occurring compounds that have been shown

to have anticarcinogenic activity in experimental

animals and may also demonstrate similar activity in

humans.

Hazards from Naturally Occurring

Toxicants

0009Many naturally occurring, potentially hazardous

chemicals exist in foods. These naturally occurring

toxicants include acute toxicants (those capable of

eliciting symptoms within a few minutes to hours

after ingestion) and chronic toxicants (those that may

5814 TOXINS IN FOODS – NATURALLY OCCURRING

cause symptoms after life-long exposure or many

years after exposure). Their ingestion does not invari-

ably cause illness, because the dose and other circum-

stances of exposure are key factors. Chronic illnesses,

such as cancer, are particularly difficult to correlate

with foods or specific foodborne toxicants, since

many confounding variables exist that affect the

onset and course of such chronic diseases. Many nat-

urally occurring carcinogens are known to exist in

foods, but their relationship to cancer in humans

remains unclear. A few of these carcinogens will be

discussed. With acute toxicants, the relationship be-

tween ingestion of the toxicant and the development

of symptoms is much stronger. Thus, many of the best

examples of naturally occurring toxicants in foods

involve acute illnesses.

0010 The US Centers for Disease Control keep records

on the incidence of foodborne disease. These statistics

focus on acute illnesses, because the role of foods in

chronic illnesses is uncertain. The most common

foodborne illnesses are bacterial infections such as

salmonellosis. Toxins produced by bacteria such

as Staphylococcus enterotoxins and the botulinal

toxins are important in the pathogenesis of some

foodborne bacteriological illnesses. Illnesses of chem-

ical etiology, other than bacterial toxins, account for

20–30% of all foodborne disease outbreaks in the

USA. Fish and shellfish toxins account for the major-

ity of these outbreaks, although other natural toxi-

cants such as poisonous plants and mushrooms are

also involved. The total number of foodborne disease

outbreaks, including those of chemical etiology, is

unknown because the reporting of such illnesses is

very incomplete.

0011 As noted earlier, the circumstances of exposure

affect the likelihood of intoxication resulting from

naturally occurring chemicals in foods. Table 1 de-

scribes some of the circumstances in which naturally

occurring chemicals in foods can cause foodborne

intoxications.

Naturally Occurring Contaminants

0012 As noted in Table 1, the sources of naturally occur-

ring contaminants in foods can include algae, molds,

bacteria, and insects.

0013 Algal toxins in seafoods Seafoods, both fish and

shellfish, can be occasionally contaminated with

toxic substances that cause acute illnesses, and

even death, within minutes after ingestion. These

toxins are acquired by fish and shellfish through

the food chain after being produced by certain

species of microscopic, dinoflagellate algae. The fish

and shellfish are hazardous only when feeding on

toxin-producing algae. Seafood poisonings were

once considered a public health problem only in

coastal areas, but modern practices involving the

shipment of fresh and frozen seafoods over long dis-

tances have made these a cosmopolitan concern.

0014Ciguatera poisoning is probably the most common

cause of foodborne disease of chemical etiology on a

world-wide basis. Ciguatera poisoning is common

throughout the Caribbean and much of the Pacific.

Fish that inhabit reef and shore areas in temperate

regions, such as barracudas, groupers, sea basses, red

snappers, and eels, are most commonly implicated in

ciguatera poisoning. The identity of all the species

of dinoflagellate algae associated with ciguatera

poisoning remains unknown, although Gambierdis-

cus toxicus is one of them. Small reef fishes feed on

the toxic dinoflagellate algae and are, in turn, con-

sumed by the larger reef fishes. The toxins accumulate

in the liver and viscera, but enough can enter the

muscle tissues to result in ciguatera poisoning among

humans ingesting these fish. Ciguatera poisoning is a

neurologic illness initially characterized by tingling of

the lips, tongue, and throat followed by numbness.

Nausea, vomiting, a metallic taste, dryness of the

mouth, abdominal pain, diarrhea, headache, and gen-

eral muscular pain will ensue in many cases. Weak-

ness may progress until the person is unable to walk.

No antidotes are known, but many affected individ-

uals recover within a few weeks, although deaths

from cardiovascular collapse have occurred in a few

instances.

0015Paralytic shellfish poisoning occurs in many coastal

areas world-wide, including the Pacific and North

Atlantic coasts of North America, Japan, and south-

ern Chile. Many species of shellfish, such as clams

and mussels, become poisonous through the con-

sumption of toxic dinoflagellate algae. Two of the

tbl0001Table 1 Intoxications from consumption of naturally occurring

foodborne toxicants

1. Abnormal though natural contaminants that adversely affect normal

consumers eating normal amounts of the food

Algal toxins in seafood

Staphylococcal enterotoxins in various foods

Mycotoxins in various foods

2. Unusual ‘foods’ that adversely affect normal consumers eating

normal amounts of this ‘food’

Poisonous mushrooms

Poisonous plants

Poisonous fish such as pufferfish

3. Normal constituents of food that can cause illness if ingested by

normal consumers in abnormally large amounts

Cyanogenic glycosides in lima beans, cassava, and fruit pits

Glycoalkaloids in potatoes and tomatoes

Estrogens in soybeans

TOXINS IN FOODS – NATURALLY OCCURRING 5815

most common algal species incriminated in paralytic

shellfish poisoning are Gonyaulax catenella and

G. tamarensis. The blooms of the toxic dinoflagel-

lates are quite sporadic, so shellfish are hazardous

only at certain times. Most shellfish clear the toxins

from their system within a few weeks after the end of

a dinoflagellate bloom, but some shellfish species,

especially the Alaskan butter clam, appear to retain

the toxins for long periods. The toxins involved in

paralytic shellfish poisoning are known as saxitoxins.

These are neurotoxins that act by blocking the pas-

sage of sodium ions into the nerve cells, an essential

process in nerve transmission. The symptoms of para-

lytic shellfish poisoning include a tingling sensation

and numbness of the lips, tongue, and fingertips,

followed by numbness in the legs, arms, and neck

with general muscular incoordination. Respiratory

distress and muscular paralysis often occur. Death

from respiratory failure can occur within 2–12 h

depending on the dose. If the victim survives 24 h,

the prognosis for a full recovery is good. No antidote

exists for paralytic shellfish poisoning.

0016 Pufferfish poisoning occurs more rarely because

pufferfish are not frequently consumed except in

Japan and China. About 30 species are found world-

wide, but most are not poisonous. The most poison-

ous species occur along the coasts of Japan and

China. The most choice, edible species belonging to

the genus Fugu are the most poisonous and the most

commonly consumed. The toxin in pufferfish accu-

mulates in the ovaries, liver, intestine, skin, and roe

(egg sac), so a carefully cleaned and eviscerated puf-

ferfish may be safe to eat. Pufferfish likely become

toxic through the ingestion of toxic dinoflagellate

algae, although the food-chain relationships have

not been completely elucidated. The toxin involved

in pufferfish poisoning is a potent neurotoxin called

tetrodotoxin, which also acts by blocking the sodium

channel in nerve cells. The symptoms resemble those

of paralytic shellfish poisoning. Death can result if a

sufficient dose of tetrodotoxin is ingested.

0017 Mycotoxins Mycotoxins are produced by a wide

variety of molds that can grow on a wide variety of

foods. The toxicity of many of the mycotoxins has

been recognized by observing domestic animals fed

moldy animal feeds. Their effects on humans are not

so clearly established, although they are potentially

hazardous to humans as well. (See Mycotoxins: Toxi-

cology.)

0018 Historically, ergotism was the first mycotoxin-as-

sociated illness recognized in humans. Claviceps

purpurea is the responsible mold, which infects the

heads of rye and sometimes wheat, barley, and oats.

The shriveled, purplish grain kernel contains the

mycotoxin. Ergotism is caused by a group of toxins

known collectively as the ergot alkaloids and can be

manifested in two forms: gangrenous ergotism and

convulsive ergotism. In the former, also known as

St. Anthony’s fire, a burning sensation in the feet

and hands is followed by a progressive restriction of

blood flow to the hands and feet. This results in

gangrene, which can lead to the loss of limbs. Con-

vulsive ergotism involves hallucinations leading to

convulsive seizures and sometimes death. No out-

breaks of ergotism have been recorded since the

early 1950s.

0019Aspergillus molds are known to produce several

types of mycotoxins, most notably the aflatoxins

and ochratoxin. The aflatoxins are produced primar-

ily by Aspergillus flavus and A. parasiticus and often

contaminate moldy peanuts and corn. Feeding of

aflatoxin-contaminated grains or oilseeds to dairy

cows can result in aflatoxin contamination of milk.

The aflatoxins are potent carcinogens, especially

affecting the liver. The role of aflatoxins in human

carcinogenesis remains uncertain, but they are among

the most potent animal carcinogens known. (See

Aflatoxins.) Ochratoxin is produced primarily by A.

ochraceus, which can contaminate cereals, peanuts,

and tree nuts. Ochratoxin affects both the livers and

kidneys of domestic animals, with the effects on the

kidney being particularly damaging. The toxicity of

ochratoxin to humans is unknown.

0020Fusarium molds produce a number of different

mycotoxins, including the trichothecenes, fumoni-

sins, and zearalenone. The trichothecenes are known

to cause human illness and can be found as contam-

inants of grains primarily. Alimentary toxic aleukia

(ATA) was observed in the former Soviet Union,

owing to consumption of grains containing trichothe-

cenes. ATA has four stages. In the first stage, a person

experiences a burning sensation in the mouth and

throat, which proceeds down the esophagus to the

stomach. This is followed by diarrhea, nausea, and

vomiting, occurring 1–3 days later and ceasing after

about 9 days. The second stage occurs from about 2

weeks to 2 months and involves bone-marrow de-

struction, leukemia, agranulocytosis, anemia, and

loss of platelets. At the end of this stage, small hem-

orrhages may occur on the skin. The third stage of

ATA lasts from 5 to 20 days and involves total loss of

bone marrow with necrotic angina, sepsis, total

agranulocytosis, and moderate fever. The hemor-

rhages become larger, and necrotic lesions appear on

the skin. Bronchial pneumonia appears, along with

abscesses and hemorrhages in the lungs. The fourth

stage is death, with the mortality rate approaching

80% and dependent on the dose and frequency of

exposure to the trichothecenes.

5816 TOXINS IN FOODS – NATURALLY OCCURRING

0021 Fumonisins are produced primarily by Fusarium

moniliforme, which contaminates various grains and

soybeans. The fumonisins have been implicated in

equine leukoencephalomalacia, a fatal neurotoxic

syndrome in horses characterized by extensive necro-

sis of the white matter in the brain. The fumonisins

may also be carcinogenic, although this remains an

active area of scientific scrutiny. Their effects on

humans remain unknown, although low-level con-

tamination of grains with fumonisins seems to be

fairly common. Zearalenone is an estrogenic sub-

stance produced in grains by F. graminearum.It

causes spontaneous abortions in pigs, but its effects

on humans are unknown.

0022 Penicillium molds produce a wide variety of myco-

toxins, including rubratoxin, patulin, and citrinin.

These mycotoxins cause various effects in domestic

animals, but their effects, if any, on humans are quite

uncertain. Many other mycotoxins have been identi-

fied, though most of these others have received little

scientific study.

0023 Bacterial toxins Most pathogenic bacteria exert

their effects by the infectious route. They invade

cells and tissues, multiply, and cause a variety of

symptoms. A few bacteria produce exogenous toxins

in foods before they are eaten. The ingestion of the

toxins initiates the disease process even if the bacteria

are destroyed in processing or preparation. The best

examples of bacterial intoxications are the staphylo-

coccal enterotoxins and botulinal toxins.

0024 The staphylococcal enterotoxins can be produced

in foods by certain strains of Staphylococcus aureus.

When ingested, these protein enterotoxins cause

nausea and vomiting within 1–6 h. Staphylococcal

food poisoning is one of the most common forms

of foodborne disease. (See Staphylococcus: Food

Poisoning.)

0025 The botulinal toxins can be produced in foods

under anaerobic conditions by Clostridium botuli-

num. Toxin formation often occurs in canned foods

subjected to improper thermal processing. The com-

mercial canning process is predicated on the destruc-

tion of this organism and its spores so that the spores

will not germinate, grow, and produce toxin on stor-

age of the canned product. Botulinal toxins are

among the most potent toxins known to humans

and frequently result in respiratory paralysis and

death. (See Clostridium: Botulism.)

0026 Insect-produced toxins Insects can also produce and

secrete toxic chemicals into foods, yet insect infest-

ation of foods is often considered only in esthetic

terms. Natural toxicants produced by insects in

foods have received very little study. Flour beetles

are known to secrete benzoquinones into flour,

which are mutagenic and carcinogenic. The hazards

posed by insect-produced toxicants in foods to

humans remain unknown.

Naturally Occurring Constituents Eaten in Normal

Amounts

0027Some plants and animals that should not be eaten

are consumed intentionally or accidentally on occa-

sion, resulting in foodborne chemical intoxications.

Many plants and some animals contain levels of

naturally occurring toxicants that are probably not

hazardous to humans ingesting typical amounts of

these foods.

0028Animals Very few animal species are poisonous.

Several species of poisonous fish exist, the best

example being the pufferfish, although recent evi-

dence suggests that the toxin in pufferfish arises

from an algal contaminant.

0029Plants Many plant species are decidedly poisonous.

Plants such as hemlock and nightshade were used in

ancient times to poison enemies. Consumers can

easily avoid poisonous plants by purchasing foods

from commercial sources. Intoxication from the in-

gestion of poisonous plants occurs primarily from

misidentification of plants by individuals harvesting

their own foods in the wild. The most frequent

examples occur when harvesting herbs for herbal

tea. For example, an elderly couple succumbed after

mistaking foxglove for comfrey while harvesting

herbs for tea.

0030Very rarely, intoxications from poisonous plants

occur with products purchased from retail outlets.

An example was the contamination of an herbal tea

by Senecio, a well-known poisonous plant. The tea

was fed to infants as an herbal remedy for viral infec-

tions. The infants suffered acute symptoms, involving

impaired liver function, from the presence of pyrroli-

zidine alkaloids in the Senecio leaves. Several infants

died in this unfortunate incident. (See Alkaloids:

Toxicology.)

0031Occasionally, intoxications from poisonous plants

occur from the intentional addition of such materials

to foods. The most frequently encountered example

would be the preparation of brownies laced with

marijuana, a potent hallucinogenic plant.

0032In times of severe food shortages, humans may

resort to eating large quantities of plants that contain

hazardous components. Lathyrism is an unusual dis-

ease that has occurred on such occasions in India and

Italy when seeds of Lathyrus sativus or chickling

vetch are ingested as a principal part of the diet.

TOXINS IN FOODS – NATURALLY OCCURRING 5817