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

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account for the remainder. Of importance to the food

industry has been the past use of lead for water pipes,

as a lining for containers, and in solder used in the

manufacture and sealing of steel cans. Most inorganic

lead compounds, with the exception of lead acetate

and lead chloride, are not readily soluble in water.

Solubility of lead compounds is enhanced in acidic

solutions.

Absorption and Distribution

0002 Human studies indicate that, in adults, approxi-

mately 10% of ingested lead in the diet is absorbed

from the gastrointestinal tract. The fraction absorbed

is greater if a solution of lead salts is ingested in a

fasting state, compared to the same amount of lead

ingested with food. In children, evidence suggests that

the fraction absorbed may be as high as 40–50%.

Absorption appears to be increased if the diet is

deficient in protein, calcium, or iron. In addition

to gastrointestinal absorption, significant lead ab-

sorption can occur through the respiratory system

from inhalation of lead particles.

0003 Absorbed lead is transported by blood, predomin-

antly in red blood cells. It is initially rapidly distrib-

uted throughout the various soft tissues and organs. It

is then slowly redistributed into two pools, a rapidly

exchangeable pool in blood and soft tissue, and a less

mobile pool in bone. In humans, about 90% of the

total body burden is in bone. Placental transfer of

lead occurs and there is a relatively good correlation

between blood lead concentrations of mothers and

newborn infants; the levels in infants are 5–10%

lower than those in the mothers.

0004 Excretion of absorbed lead is primarily through the

kidneys; about 75% of the loss is through this route.

The mechanism of urinary excretion appears to be

essentially a filtration process. Gastrointestinal losses

account for about 16% of the loss. The remainder of

the loss is through hair, skin, and sweat.

0005 The body half-life of lead is approximately 10–30

years. The half-life in the blood and soft-tissue com-

partment is about 20 days. The bone pool has a much

longer half-life, 10–30 years, and accounts for the

long total body half-life.

0006 Lead in blood is generally accepted as the best

indicator of exposure and body burden for soft tissues

and organ systems. Average blood lead levels in the

general population of industrial countries are

typically found to be between 5 and 15 mgdl

1

Toxic Effects

0007 Lead has toxic effects on several organ systems. The

blood cell-forming system is the first to be affected by

lead exposure. Frank anemia begins to occur in adults

with blood lead above 60 mgdl

1

. Children are more

sensitive to lead effects and begin to show anemia

with blood levels above 30 mgdl

1

. At levels as low

as 10 m gdl

1

, reversible biochemical changes in the

hemoglobin synthetic pathway occur that are with-

out clear adverse effects. This early change consists

of progressive inhibition of d-aminolevulinic acid

dehydrase activity. Abdominal pain or ‘lead colic’

occurs at somewhat higher levels of 80–100 mgdl

1

in adults.

0008Acute central nervous system toxicity can occur

when blood levels are above 100 mgdl

1

in adults,

and are above 80–90 mgdl

1

in children. This syn-

drome is an acute encephalopathy, characterized by

coma, convulsions, and death or irreversible loss of

function. Lead encephalopathy is much more

common in children than adults. There is evidence

that a chronic intellectual impairment may occur at

lower blood levels, with children again being signifi-

cantly more sensitive to these effects. The extent of

intellectual impairments and the blood lead levels at

which they occur are still a matter of controversy. In

the USA blood lead levels above 10 mgdl

1

in children

are felt to be potentially harmful by public health

authorities. Concern over this potential effect has

been the prime motivator behind environmental regu-

latory efforts to reduce lead exposure for the general

population.

0009Lead can also produce a peripheral neuropathy,

resulting in significant weakness in some individuals.

This effect is usually seen at relatively high blood

levels. Electrophysiological changes in peripheral

nerve function in the absence of any clinical symp-

toms have been reported at blood lead levels below

70 mgdl

1

in some studies of lead-exposed workers.

The significance of these findings is controversial in

terms of indicating a clear toxic effect. Lead encephal-

opathy and neuropathy may be reversible if adequate

treatment is instituted early in the evolution of these

symptoms.

0010A prolonged high-level exposure is associated with

kidney disease in some individuals. This takes the

form of an interstitial fibrosis and a loss of renal

function, which appears to be irreversible. Reversible

change in renal function is more common and is

characterized by mild elevation of blood urea nitro-

gen or creatinine, blood tests that indicate altered

kidney function. There have been reports that serum

concentration of 1,25-dihydroxy vitamin D, the

active form of vitamin D, is depressed in children

with moderate blood lead levels. This metabolite is

formed in the kidneys. Recent studies suggest that the

effect may only be seen against a background of

nutritional deficiency, or low vitamin D intake.

LEAD/Toxicology 3483

0011 In a given individual the manifestations of these

toxic syndromes are variable at any given level of

lead in the body. The factors responsible for the vari-

ability are poorly understood. Children, in general,

are more sensitive to the toxic effects of lead.

0012 Other possible toxic effects of lead in humans are

less well defined and remain unsubstantiated. Al-

though long-term high-level lead exposure in rodents

can produce kidney tumors, there is no conclusive

evidence that lead is carcinogenic in humans. In

some studies an association between increasing

blood lead levels and small increases in blood pres-

sure were noted. Other investigators believe that con-

founding factors may account for the blood pressure

changes. Although there are experiments indicating

that high doses of lead are toxic to the reproductive

functions of both male and female laboratory

animals, data in humans are limited and inconsistent.

There is no clear association of lead with the fre-

quency of congenital anomalies in humans. There

has been concern that in utero lead exposure may

have harmful effects on brain development, in view

of the toxic syndrome seen in children.

0013 Lead toxicity is treated by identification and elim-

ination of the source of exposure if symptoms are

mild. In more severe toxicity, treatment with a chelat-

ing agent such as calcium ethylenediaminetetraacetic

acid, d-penicillamine, or succimer is used to increase

lead excretion.

Lead in the Food Chain

0014 Lead is ubiquitous throughout the food chain. Table 1

is a compilation from a World Health Organization

(WHO) document illustrating the typical lead content

of various foods. Plants subject to the effects of air

pollution potentially have the highest lead concentra-

tion, followed by root and tuberous plants. The

lowest lead concentrations are found in plants in

which the edible portion is above ground and shielded

from airborne lead deposits. In animal food sources,

muscle tissue has the lowest concentration of lead;

the concentration in visceral organs, such as liver or

kidney, is considerably higher. Concentrations of lead

in all raw foodstuffs will vary, depending on the

environment in which they were produced. Tetraethyl

lead, where it is still in use as a gasoline additive, can

be a significant source of airborne lead.

0015 Food processing and preparation can contribute

significantly to the lead content of foodstuffs. As

noted in Table 1, lead concentrations in canned

foods are noticeably higher in this study, primarily

as a result of the lead contamination from solder used

in steel cans. Alternative packaging can eliminate this.

Significant reduction in dietary lead intake in the USA

is attributed to increased consumption of fresh and

frozen foods and elimination of lead-soldered cans

for foods. Lead contamination of food may occur,

beyond lead migration from soldered cans, from

other sources during food processing. Water with a

high lead content that is used in processing would be

one such source of contamination. Contact with lead

or lead-containing substances would be another

potential source of contamination. The likelihood of

this type of contamination is increased if the food in

contact with the lead source is acidic. A common

source for this form of lead contamination has been

the use of pottery dishes or containers with improp-

erly fired glazes that contain lead. Acidic food can

leach large amounts of lead from such glazes, and

tbl0001Table 1 Lead content in foods (mgg

1

fresh weight)

Uncanned Canned

Dairy products and eggs

Milk 0.02 0.10–0.13

Butter 0.07

Icecream 0.01

Cheese 0.05

Eggs 0.17

Meat and poultry

Beef, pork, lamb, veal 0.06 0.24

Hamburger 0.25

Beef liver 0.09

Poultry 0.12 0.24

Fish and shellfish

Salmon 0.39 0.72

Mackerel 0.40 0.99

Tuna 0.45

Cod 0.06

Flounder 0.10

Oysters 0.17

Clams 0.21

Cereal, nut, and sugar products

Flour (white) 0.05

Bread (white) 0.08

Cereals (breakfast) 0.11

Peanut butter 0.06

Sugar (refined) 0.03

Vegetables

Potatoes 0.05 0.12

Cabbage 0.1–0.04 0.08

Lettuce 0.12–0.15 0.39

Beans 0.01–0.04 0.16–0.32

Peas 0.03 0.27

Carrots 0.14 0.13

Onions 0.18 0.32

Tomatoes 0.05–0.08 0.30–0.37

Cucumbers 0.02

Fruit

Citrus (oranges, lemons) 0.01 0.39

Apples 0.02 0.22

Cherries 0.02 0.39

Pears 0.02 0.18–0.19

Compiled in IMO/FAO/UNESCO/WHO/IAEA/UN/UNEP Joint Group of

Experts on the Scientific Aspects of Marine Pollution Report (GESAMP)

and Studies no. 22 (1985). Geneva: World Health Organization.

3484 LEAD/Toxicology

cases of clinical lead poisoning continue to be

reported from this source of contamination. Despite

awareness of this potential problem improperly fired

pottery with lead-containing glazes continue to be

produced, predominantly in developing countries.

0016 Total food-related lead intake can be highly vari-

able, depending on the dietary pattern. Estimates of

average daily lead ingestion from food in western

cultures where studies have been performed have

typically ranged from 25 to 200 mg day

1

, although

intakes as high as 400 mg day

1

have been reported

for some populations. The current US recommended

daily intake from all sources is 75 mg day

1

or less for

adults and 6 mg day

1

or less for children under 6

years of age. These amounts are one-tenth the daily

intake estimate to produce blood lead levels of

30 mgdl

1

in an adult and 10 mgdl

1

in a child.

0017 Dietary lead intake accounts for approximately

70% of the total daily lead absorption from all

sources in most studies. More recent studies, from

the US Food and Drug Administration, have found

significant reductions from these figures that are

attributed to almost complete elimination of lead-

soldered food cans and reduced airborne lead con-

tamination from leaded petrol. In these studies,

dietary lead was found to be less than half of the

daily lead intake.

Monitoring and Surveillance

0018 Monitoring of the lead content of foods is not rou-

tinely performed. Avoidance of lead contamination in

food preparation and food processing should be

sought as a part of an integrated public health pro-

gram to minimize lead exposure of the population.

While lead exposure from the diet is normally far

below that associated with toxic symptoms, it should

be remembered that dietary lead is a major source of

an individual’s total lead intake. Although it is not

clear at what level harmful effects first occur in

humans, it is clear that lead is not an essential dietary

component and it is prudent to avoid the addition of

lead to food during its processing or preparation. This

begins with the obvious exclusion of food contact

with any lead-containing alloy in food processing

and preparation. It also means attention to more

subtle details, such as the exclusion of lead-based

solder from the repair of food-handling equipment

and being aware of the potential risk of lead contam-

ination from improperly glazed pottery containers.

See also: Contamination of Food; Renal Function and

Disorders: Kidney: Structure and Function

Further Reading

Carrington CD and Bolger PM (1992) An assessment of the

hazards of lead in food. Regulatory Toxicology and

Pharmacology 16: 265–272.

Ehle AL and McKee DC (1990) Neuropsychological effects

of lead in occupationally exposed workers: a critical

review. Critical Reviews in Toxicology 20: 237–255.

Mahaffey KR (ed.) (1985) Dietary and Environment Lead:

Human Health Effects. Amsterdam: Elsevier Science.

Smith MD, Grant LD and Sors AI (eds) (1989) Lead Expos-

ure and Child Development: An International Assess-

ment. Dordrecht: Kluwer.

Tsuchiya K (1986) Lead. In: Friberg L, Nordberg GF and

Vouk VB (eds) Handbook of the Toxicology of Metals,

vol. II. Amsterdam: Elsevier Science.

US EPA (1986) Air Quality Criteria for Lead. Research

Triangle Park, North Carolina: US Environment Protec-

tion Agency.

LEAVENING AGENTS

J L Vetter, Technical Assistance Services, Leawood,

KS, USA

History of Chemical Leavening

0001 Bakery foods that depend on chemical leavening

systems for their appearance, texture, and taste

are relatively recent developments. Whereas yeast-

leavened products have nourished humans for over

4000 years, chemically leavened products have been

available for less than 200 years. We have come to

enjoy a wide variety of chemically leavened products

as part of our daily menu. Some are sweet, e.g., cakes,

doughnuts, and biscuits, whereas others are more

bland, e.g., baking powder biscuits and many types

of crackers (see Figures 1 and 2).

Leavening with Yeast

0002The word ‘leaven’ comes from the Latin word ‘levare’

or ‘levo,’ which means ‘to raise’ or ‘to make light by

aeration.’ Leavened or aerated baked foods can be

LEAVENING AGENTS 3485

traced as far back as 2000 bc, when Egyptians used

yeast to leaven bread. (See Bread: Breadmaking Pro-

cesses; Yeasts.)

Chemical Leavening

0003 Yeast was the primary source of leavening gas to raise

baked foods until late in the eighteenth century, when

it was discovered that sour milk or buttermilk would

release carbon dioxide gas from sodium bicarbonate

(baking soda) during baking of a dough or batter

to which these ingredients had been added. Carbon

dioxide from baking soda is the same gas as that

released by yeast during fermentation of a dough.

0004 Sour milk and buttermilk were replaced in many

recipes with cream of tartar after about 1835. Cream

of tartar (potassium bitartrate) was obtained as a

byproduct from wine-making. There were early

attempts to combine the baking soda and cream of

tartar into a more convenient blended product, and

this led to the development of baking powders. A US

chemist by the name of Hoagland, living in Fort

Wayne, Indiana, originated the cream of tartar baking

powder in 1850 and founded the Royal Baking

Powder Company.

0005Sour milk, buttermilk, and cream of tartar all had

one thing in common: they released the carbon

dioxide from baking soda very rapidly, and much of

the leavening gas was actually lost during the mixing

of a dough or batter, resulting in a baked product with

less volume than desired. There was a need for a

material that would not react so quickly and allow

sufficient time for mixing and forming products

before the leavening gas was released. This led to

the development in the mid-1800s of monocalcium

phosphate (MCP; also known as acid calcium phos-

phate, ACP) as an alternative to cream of tartar.

Although MCP is considered a ‘fast-acting’ leavening

acid, it is a little slower than cream of tartar. A patent

was issued in 1864 for such an acidic phosphate

leavening agent. However, better agents for control-

ling or delaying leavening activity were still required,

and this need led to the development of a number of

alternatives to cream of tartar and MCP for use with

baking soda. Sodium aluminum sulfate (SAS) was

developed in the early 1890s, sodium acid pyropho-

sphates (SAPPs) in the early 1900s, and sodium alu-

minum phosphates (SALPs) around 1960.

Design of Leavening Systems

0006There are three primary factors to consider in

designing a chemical leavening system for a specific

product. These are:

0007How much leavening gas is needed to produce the

desired finished product?

0008What leavening acid is needed to achieve the

desired product characteristics?

0009What other effects might the leavening acid have

on the dough, batter, or finished product?

This article will discuss these three factors and

describe the characteristics of commercially available

chemical leavening agents and their application in

specific bakery foods.

Mechanisms of Chemical Leavening

Air and Water as Leaveners

0010Although air and water are ‘chemicals’ in the truest

sense of the word, they are generally not considered

‘chemical leavening agents.’ Nevertheless, air and

water do provide leavening activity in a number

of bakery products. Air, which is incorporated

into a dough or batter as small gas cells during

mixing, will expand during baking and cause some

leavening of the product. In fact, air is the primary

leavening agent in a fat-free sponge cake. During

baking, water contained in the dough or batter will

fig0001 Figure 1 Leavening agents: machine-cut doughnut production.

(Courtesy of Rhone-Poulenc, New Jersey.)

fig0002 Figure 2 Examples of chemically leavened baked goods.

3486 LEAVENING AGENTS

be vaporized by the heat of the oven and cause a

leavening – or raising – of the product. Water is the

primary leavening agent for saltine crackers, contrib-

uting to the tender, flaky texture of the product. The

contributions of air and water to the leavening and

characteristics of baked products should not be over-

looked in designing a leavening system based on more

traditional ‘chemical’ leavening agents.

Leavening by Decomposition

0011 There are two primary chemical leavening agents that

can release carbon dioxide gas by decomposition

during baking. These are sodium bicarbonate (baking

soda) and ammonium bicarbonate. Heat is required

for these materials to decompose, and the tempera-

ture of baking is generally adequate for this purpose.

Sodium bicarbonate decomposes when dissolved and

heated to release carbon dioxide according to eqn (1).

(1)

2NaHCO

O + CO

+ Na

Heat

Ammonium bicarbonate decomposes when dissolved

and heated according to eqn (2).

(2)

HCO

+ H

O + CO

Heat

Both ammonia and carbon dioxide are gases and

contribute to the leavening of the baked product.

Leavening by Chemical Reaction

0012 The vast majority of chemical leavening systems are

based on the reaction of an acid with sodium bicar-

bonate to release chemically the carbon dioxide from

the soda, and it is with these systems that the majority

of this article is concerned. A general equation for the

reaction is shown in eqn (3).

(3)HX + NaHCO

NaX + H

O + CO

(Neutral sodium salt)

Moisture

Heat

In addition to the carbon dioxide leavening gas, water

is released, and a sodium salt of the leavening acid

is formed. The nature of the neutral sodium salt

depends on the leavening acid being used.

001 3 There are a number of leavening acids from which

to choose in formulating a chemical leavening system.

They differ in the amount required to release com-

pletely all of the carbon dioxide in the soda, the speed

with which they release this leavening gas, and their

effects on doughs, batters, and finished product

characteristics.

0014 Neutralizing value The neutralizing value (NV) is a

term used to describe the amount of leavening acid

needed to react completely with the amount of baking

soda used in formulating a bakery product. If all of

the soda reacts with the leavening acid, the finished

product should be close to neutral in pH, which is

desired in most products. Higher (alkaline) or lower

(acidic) pHs can be achieved, if desired, by adjusting

the amount of leavening acid and/or soda from the

amounts needed for complete reaction.

0015The NV is defined as the weight of soda neutralized

by 100 parts of leavening acid. Since most formulae

for bakery products begin with a given weight of soda

(the weight needed to give the desired amount of

leavening gas), the NV is most commonly used to

determine the amount of leavening acid required for

the amount of soda used according to the following

equation:

%Leavening acid ¼

%Soda  100

:ð4Þ

The NVs for commonly used leavening acids are listed

in Table 1. It should be noted that larger amounts of

leavening acids with low NVs are required for a given

amount of soda than for those leavening acids with

higher NVs. This could be a factor in the economics of

developing a leavening system.

0016Rate of reaction The speed with which a leavening

acid reacts with baking soda to release carbon dioxide

leavening gas is very important in controlling the

characteristics of the finished baked product. If

the acid reacts too rapidly with the soda, all of the

leavening gas could be released during mixing and,

therefore, would not be available to raise the product

during baking. In this case, the finished product

would be low in volume and dense in texture. How-

ever, if the acid reacts with the soda too late in the

baking process, the structure of the product will be

‘set’ by the heat of baking, and the leavening gas

cannot raise the product without causing cracks or

splits.

0017The release of some leavening gas, or incorporation

of some air, during mixing is desirable for the forma-

tion of small air or gas cells in the dough or batter.

This process, called ‘nucleation,’ is responsible for the

development of a fine and uniform grain in the final

tbl0001Table 1 NVs of commonly used leavening acids

Leavening acid NV

Monocalcium phosphate monohydrate 80

Anhydrous monocalcium phosphate 83

Sodium acid pyrophosphate 74

Sodium aluminum phosphate 100

Dicalcium phosphate dihydrate 33

Dimagnesium phosphate 40

Sodium aluminum sulfate 104

Cream of tartar 45

Glucono-d-lactone 45

LEAVENING AGENTS 3487

product. However, most of the leavening gas should

be reserved for release at the proper time during

baking in order to achieve the total volume desired.

0018 A number of factors affect the proper time for

release of gas during baking. Product size is certainly

important. A small product will heat, and the struc-

ture will set, faster than a larger product. Oven

temperature obviously affects the rate at which a

product’s temperature rises to the point of setting

the structure. Other ingredients in the formula can

affect the temperature at which a product sets. The

amount of time to mix fully a dough or batter and the

time required to form or deposit the product to be

baked will influence the time at which the leavening

acid should react with the baking soda.

0019 The manufacturers of leavening acids have at-

tempted to meet all the diverse needs of the house-

hold, institutional and large-scale wholesale baker by

developing and marketing products with a wide range

of ‘reaction rates.’

0020 Some materials have essentially no delay in their

reaction with baking soda. They react as soon as they

dissolve in the water present in the formula; the soda

has probably already dissolved. These materials

include the lactic acid in sour milk or buttermilk,

cream of tartar, and MCP monohydrate.

0021 Anhydrous monocalcium phosphate (AMCP) has a

time delay, which, although relatively short, does

allow time for preparing doughs and batters for

baking. A major use for AMCP has been self-raising

flour, which is often used to prepare baking powder-

type biscuits. The time delay of AMCP allows suffi-

cient time for mixing, rolling, and cutting the dough

prior to baking.

0022 Manufacturers of SAPPs have been able to vary the

amount of time delay of these leavening acids from a

few minutes to as much as an hour or more. This is

done by controlling the conditions under which the

SAPP is manufactured.

0023 SAS, SALP, and dicalcium phosphate dihydrate

(DCP) are basically heat-triggered leavening acids.

They have essentially no reaction with soda until the

temperature of the product is raised by the heat of

baking. In some baked products, this delay may be

too long, and SAS, SALP, and DCP perform better

when used in combination with a faster-acting

leavening agent such as MCP or AMCP. Of course,

all leavening agents are essentially ‘heat triggered,’

since they dissolve and react with soda faster as the

temperature of the dough or batter increases. Never-

theless, the term ‘heat triggered’ is usually reserved

for those materials that have an almost indefinite time

delay until the temperature rises to a certain point, in

contrast to those leavening agents that are both time

and temperature triggered.

0024Glucono-d-lactone (GDL) does not fit any of the

above categories of no delay, time delay, and tempera-

ture triggered. GDL reacts continuously, but slowly,

with baking soda. The speed of reaction, of course,

increases with temperature and becomes quite rapid

during baking. The steady release of carbon dioxide

in a dough containing GDL is very similar to the

release of carbon dioxide by yeast in a fermenting

dough. Therefore, GDL has been popular in the

development of chemically leavened bread.

0025The rates of reaction of commonly used leavening

acids are listed in Table 2.

0026Ionic effects of leaveners Although the primary

function of chemical leavening systems is to leaven,

or raise, a product, leavening agents can also affect

characteristics of doughs, batters, and the finished

baked product. These effects are due to reactions

between the leavening agents and components (par-

ticularly starch and protein) of the dough or batter.

These are called ‘ionic’ effects, since the leavening

agents dissolve in the water of the dough or batter

and dissociate into positive cations and negative

anions. In some cases, it is the cation (such as calcium

ions) that is responsible for the observed effect. In

other cases, it is the anion (such as pyrophosphate)

that causes a change in the dough, batter, or finished

product.

0027The calcium and aluminum cations in phosphate-

based leavening acids provide more resiliency to cake

products than the sodium cation in other phosphate-

based leavening agents. Therefore, if resiliency is a

property desired in a cake product, the formulator

may choose a leavening system containing calcium

and/or aluminum ions. Calcium ions tend to stiffen

doughs and thicken batters; they also tend to dry out

moist or slightly sticky doughs. These properties of

doughs and batters are important considerations in

handling and processing, particularly in high-speed,

automated commercial bakeries. (See Bread: Dough

Mixing and Testing Operations.)

tbl0002Table 2 Rates of reaction with baking soda for commonly used

leavening acids

Leaveningacid Rate ofreaction

Cream of tartar Rapid

Monocalcium phosphate monohydrate Intermediate

Anhydrous monocalcium phosphate Intermediate (slower)

Sodium acid pyrophosphates Slow

Sodium aluminum phosphate Very slow

Sodium aluminum sulphate Very slow

Dicalcium phosphate dihydrate Very slow

Dimagnesium phosphate Slow

Glucono-d-lactone Slow

3488 LEAVENING AGENTS

0028 The pyrophosphate anion in SAPP leavener inter-

acts with proteins from other ingredients in the for-

mula. This tends to result in a moister texture, which

is usually desirable. Unfortunately, the pyrophos-

phate ion also imparts a slightly bitter aftertaste

when used at higher levels. Therefore, the product

formulator must try to balance such desirable and

undesirable effects in developing a leavening system

for a specific product.

0029 Final product pH can affect the color of a baked

product, and the pH can be controlled by the

leavening system. In white products such as white

layer cakes, a pH that is slightly below neutral accen-

tuates whiteness. This lower pH can be achieved by

adjusting the balance between leavening acid and

baking soda (more acid, less soda) or by selection of

leavening acid. Pyrophosphate leavening acids tend to

buffer pH in the range 7.3–7.5 and it is somewhat

difficult to lower the pH by adjusting the pyro-

phosphate and soda balance. Calcium phosphates,

however, do not have the pH buffering capacity of

the pyrophosphates, and pH can be manipulated

more easily by adjusting the acid/soda balance. The

color and flavor of chocolate products are enhanced

by higher pH. Again, this can be achieved by selection

of leavening acid and/or adjustment of the acid/soda

balance (less acid, more soda).

0030 The development of a suitable leavening system is a

highly complex activity. The formulator has a number

of objectives to meet, and fortunately, there is

available a number of leavening agents with varying

properties to help meet these objectives.

Characteristics of Leavening Agents

Sodium Bicarbonate (Baking Soda)

0031 As mentioned previously, the heat of baking can cause

baking soda to decompose, giving off carbon dioxide

leavening gas without reacting with a leavening acid.

The sodium carbonate formed by the decomposition

of baking soda is very alkaline and will tend to give

the baked product a high pH. This is desirable in

some applications, because the high pH enhances

certain flavors, such as chocolate. Many recipes for

chocolate chip cookies call for leavening only with

baking soda.

Ammonium Bicarbonate

0032 Ammonium bicarbonate will also decompose during

baking and release ammonia and carbon dioxide

leavening gases without reacting with a leavening

acid. Unlike sodium bicarbonate, which leaves a resi-

due of alkaline sodium carbonate, ammonium bicar-

bonate leaves no residue when it decomposes by heat.

It, therefore, has no effect on the pH of the baked

product. If there is more than about 5% moisture in

the baked product, however, the ammonia gas will

dissolve in this water and impart an ammoniacal

flavor to the product. For this reason, ammonium

bicarbonate is used only in low-moisture products

such as crackers.

Cream of Tartar

0033Cream of tartar (potassium acid tartrate) reacts very

rapidly with soda in a dough or batter, releasing

70–80% of the leavening gas within 2 min of comple-

tion of mixing. For this reason, it has little application

in commercial production of bakery foods, since

there is insufficient time to process the dough prior

to baking.

Sodium Aluminum Sulfate

0034SAS is a very slow-reacting leavening agent and does

not release leavening gas until the product is in the

oven, and its temperature rises. SAS is most often

used in combination with a faster-acting leavening

acid such as MCP. This combination (SAS and

MCP) is the most popular composition of household

baking powders. SAS is not used extensively in com-

mercial baking.

Monocalcium Phosphates

0035Monocalcium phosphate leavening acids are avail-

able in two forms: the monohydrate (MCP) and the

anhydrous product (AMCP). The monohydrate is

fast-acting, although slightly slower than cream of

tartar. It is usually used in combination with slower-

acting leavening agents. MCP will release leavening

gas from baking soda during mixing, which is desir-

able in achieving a fine, uniform grain in the baked

product as long as a slower-acting leavener is present

to provide leavening gas during baking. AMCP is

coated with a slowly dissolving phosphate material

that delays its reaction with baking soda. This delay is

relatively short, but sufficient for some products that

are baked in the home. These products include

biscuits, pancakes, and waffles.

Sodium Acid Pyrophosphates

0036SAPPs are available with a range of reaction rates

from slow to very slow. SAPPs are used almost exclu-

sively in some applications such as cake doughnuts

and canned, refrigerated biscuit doughs. They are

one of several options available to the formulator of

cakes, biscuits, pancakes, etc. The aftertaste, to which

many people are sensitive, somewhat limits the use of

LEAVENING AGENTS 3489

SAPPs, particularly since the development of SALP

leavening agents.

Sodium Aluminum Phosphates

0037 SALPs are the most recently developed chemical

leavening agents. They are very slow-reacting with

baking soda and are often marketed as blends with a

faster-acting leavener such as MCP or AMCP. SALPs

have become quite popular with product formulators,

because of their high NV, relatively low cost, lack of

undesirable flavors, and ability to be blended with

other leaveners to achieve optimized properties for

specific applications.

Dicalcium Phosphate Dihydrate

0038 DCP is not technically a leavening ‘acid,’ because it is

an alkaline phosphate salt. However, when incorpor-

ated into a dough or batter and subjected to the heat

of baking, DCP decomposes to MCP and tricalcium

phosphate (TCP). The TCP is insoluble, precipitates

out of the system, and leaves MCP – a fast-acting

leavening agent – to react with baking soda. The

temperature at which DCP decomposes is relatively

high (55–60



C), so that decomposition occurs rather

late in the baking process. For this reason, DCP is

classified as a very slow-acting leavening agent and is

commonly used in combination with a fast-acting

leavener.

Dimagnesium phosphate

0039 Magnesium phosphate is a new leavening acid that is

slow-acting and is activated by heat (40



C). It has a

clean flavor profile, provides a uniform cell structure,

and imparts moistness to baked product crumbs. It is

particularly useful in frozen and fresh baked cakes,

muffins, biscuits, and pizza crusts.

Glucono-d-lactone

0040GDL is an organic compound that forms gluconic acid

when dissolved in water. It reacts slowly, but steadily

with baking soda. The rate of reaction, of course, in-

creases as the temperature of the dough or batter in-

creases during baking. GDL has a low NVof about 45,

requiring about two parts of GDL for every one part of

soda. It is, therefore, relatively expensive to use and

finds limited application in specialized products.

Summary

0041The technology of chemical leavening is quite com-

plex, because of the varying requirements of different

products and processes. It is made even more complex

by the availability of a variety of chemical leavening

agents, each with its own set of properties, advan-

tages and disadvantages.

0042An understanding of the technology of chemical

leavening should lead to the production of even better,

cost-effective, and consumer-satisfying bakery foods.

See also: Bread: Dough Mixing and Testing Operations;

Breadmaking Processes; Yeasts

Further Reading

Dubios DK (1981) Chemical leavening. Technical Bulletin,

vol. 3, No. 9. Manhattan: American Institute of Baking.

Kichline TP and Conn JF (1970) Some fundamental aspects

of leavening agents. The Bakers Digest August: 36–40.

LaBaw GD (1982) Chemical leavening agents and their use

in bakery products. The Bakers Digest February: 16–21.

Reiman HM (1977) Chemical leavening systems. The

Bakers Digest August: 33–36, 42.

Lecithin See Phospholipids: Properties and Occurrence; Determination; Physiology

Leeks See Onions and Related Crops

3490 LEAVENING AGENTS

LEGISLATION

Contents

History

International Standards

Additives

Contaminants and Adulterants

Codex

History

P Berry Ottaway, Berry Ottaway & Associates Ltd,

Hereford, UK

Background

0001 The history of food legislation can be traced back

over millennia. Laws have been introduced into all

civilized society for one or more of four main reasons.

The first is food safety and protection of the popula-

tion; the second is fiscal, for the collection of taxes;

the third covers various aspects of the adulteration of

food; and the fourth is concerned with weights and

measures.

Food Safety

0002 Although food safety now predominates in the legis-

lation of our modern society, it was not until the

nineteenth century that food laws protecting public

health became important in western Europe and

North America. However, laws based on early experi-

ence of food safety problems go back many thousands

of years. The detailed Jewish dietary laws (kashrut)

can now be rationalized with our knowledge of food

safety, microbiology, and parasitology. The dietary

laws are mainly written down in Deuteronomy and

Leviticus in the Old Testament in the Bible.

0003 In these works, the Israelites were given the rules

on permitted and forbidden foods. The only animal

(mammal) meat allowed was from those species that

chewed the cud, parted the hoof, and were cloven-

footed. This meant that sheep and deer were allowed

as food but the pig was strictly forbidden. It had

already been deduced that the meat from grazing

herbivores was likely to be safer than that from a

scavenging omnivore.

0004 Similar explanations can now be applied to the rest

of the detail of the early Jewish food law. All birds of

prey, such as vultures, eagles, seagulls, and owls, had to

be excluded from the diet. Of the lower orders of

animals, none which were creeping and go on all-

fours, or winged, swarming animals were allowed,

except if the legs of the swarming beasts were jointed

so that they could jump. Within the insects these defin-

itions separated the disease-carrying flies and cock-

roaches from the grasshoppers and locusts; locusts are

still a common food in many parts of the world.

0005Among the aquatic animals only those fish that

possess both scales and fins were permitted. Crust-

aceans such as prawns, lobsters, and crabs, and all

shellfish may not be eaten. Again, the scavengers with

their higher risk of disease are excluded.

0006Even with the permitted animal foods there are

further rules. No animal that has died naturally or

from the result of an attack from another animal must

be eaten and complex laws were developed on the

separation of meat and dairy products and the use of

utensils. These strict dietary laws originated thou-

sands of years ago and many are still strictly observed

today by followers of both Judaism and Islam.

0007It was not until the second half of the nineteenth

century that legislation relating to the public health

and safety aspects of food began to be generally

established in Europe.

0008In the UK the 1860 Adulteration of Food and

Drink Act prohibited the sale of impure food

and food to which materials or ingredients injurious

to health had been added. This was strengthened in

1872 by the Adulteration of Food and Drugs Act

which required the appointment of public analysts

and empowered local enforcement officers to take

samples and bring prosecutions.

0009The Sale of Food and Drugs Act, passed in 1875,

increased the scope of the previous legislation by

making it an offence to sell, to the prejudice of the

customer, food which was not of the nature, quality,

or substance demanded by the consumer. In the same

year, the Public Health Act 1875 permitted the local

enforcement authorities to take preemptive action by

inspecting food. That which was considered to be

‘diseased or unsound, or unwholesome or unfit for

LEGISLATION/History 3491

the food of man’ could be officially seized and taken

before a justice of the peace.

0010 It was over 50 years later, in 1928, that significant

changes were made to the 1875 Acts, and in 1938 a

consolidation took place and the appropriate sections

of the Sale of Food and Drugs Act and the Public

Health Act were brought together in the Foods Act

1938. The 1938 Act introduced the offence of apply-

ing false or misleading labels to food and also con-

tained the powers to make regulations to govern the

preparation, storage, and sale of food. This Act

brought most of the British food safety legislation

into place. The 1938 Act was further consolidated

in 1955 (Food and Drugs Act), by the Food Act

1984, and the Food Safety Act 1990.

0011 During the second half of the nineteenth century

and first half of the twentieth century, the develop-

ments in food safety legislation in the UK had a very

significant influence on the introduction of similar

legislation into the British dominions and colonies at

the time.

Fiscal Laws

0012 The idea of levying taxes on foods goes back more

than two millennia in Europe. Import and export

duties (portoria) on goods, including food commod-

ities, formed an important part of the well-organized

taxation system of the Roman Empire.

0013 In the UK the earliest written reference to customs

dues being levied is to be found in a charter dated

743. In a document from 979 there is evidence of duty

to be paid on cheese, butter, and eggs coming into

England through the port of Billingsgate. Until the

beginning of the thirteenth century, there were spe-

cific grants giving permission to individual ports to

charge duties on imported foods. Introduction of a

nationally organized English customs service started

in the reign of King John (1166–1216). In 1203 a duty

of one-fifteenth of the value was placed on all imports

and exports, including food. This was called the quin-

decima. It was decreed that the duty raised be paid

direct to the treasury and removed the permission for

it to be retained by the ports. This established a basic

centralized system of customs control at the ports,

which has survived in the UK with very little change

to the present day.

0014 For a number of centuries, most of the food-related

laws in what is now the UK were based on the need to

raise taxes and at one time or another a wide variety of

food and drink has been subject to tax. It is interesting

to reflect that a tax imposed on tea by the English in

1773 initiated the American War of Independence and

the American colonies breaking away from the control

of Europe, eventually to become the USA.

The Adulteration of Food

0015Sadly, history shows that where food is traded there

is the temptation to adulterate or misdescribe the

food to make illicit profits. It would appear that

in all ages and societies the temptation has been

irresistible. An Indian law dated to about 300 bc

prohibited the adulteration of grain, scents, and

medicines.

0016Documents in the UK show that food adulteration

has been a problem for nearly a thousand years. For

centuries the methods of adulteration, and methods

of detection, were very crude and adulterated foods

often caused illness and even death.

0017In England during the Middle Ages, the trade

guilds took the first positive actions against adulter-

ation of the foods for which their members were

responsible. This was voluntary regulation by the

tradesmen in the guilds to insure their reputation

and also to insure a trading advantage. As time went

on, the voluntary controls began to be replaced or

supplemented by statutes.

0018In each age to the present day it has been the case

that the more expensive items of food and drink are at

risk of adulteration and manipulation. Thus, sugar,

spices, tea, coffee, wine, beer, and spirits have all been

the targets of malpractice. Milk was commonly

diluted with water and a proportion of butterfat

removed from the top of the milk. Bread was also

commonly adulterated and records show that in a

number of towns in medieval England bakers were

pilloried. In the more serious cases, where widespread

illness or death resulted from the malpractice, the

tradesmen were sent to the gallows.

0019During the eighteenth century, legislation was

introduced (in 1718) to prevent the adulteration of

coffee. This was followed by a similar law on tea in

1730 and one on bread in 1758. The weakness of

these laws at the time was due to the lack of effective

analytical methods. Most methods that had been

developed for the detection of adulteration were

based on taste, smell, or texture.

0020It was not until 1860 that the Adulteration of Food

and Drink Act was passed in England. This was more

broad-based than the previous commodity-related

legislation and it created an offence of knowingly

selling food containing injurious material. Between

1860 and 1870, similar laws were passed in Germany

and Sweden.

0021In the USA, Professor GW Wigner won a Board of

Trade prize in 1880 for a paper recommending legis-

lation to combat food adulteration. The US Congress

failed to pass the first act drafted on the basis of the

paper, but between 1880 and 1890 several states

passed laws based on Wigner’s work.

3492 LEGISLATION/History