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

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0036 Carboxymethylxylan has been prepared with prop-

erties similar to carboxymethylcellulose. It has poten-

tial uses in detergents, pigment dispersants, or paper

coatings. Other hemicellulose derivatives, analogous

to cellulose derivatives, include acetates, butyrates,

higher-fatty-acid esters, benzoates, and xanthates.

The acetates may be used to form films similar to

cellophane.

0037 Bread freshness can be improved up to three times

by adding hemicellulose to dough. It also improves

water-binding capacity, mixing quality, mixing

energy efficiency, and loaf volume. (See Bread: Chem-

istry of Baking.)

0038 Dietary fiber contains hemicellulose. Approxi-

mately 40–60% is digested by microbes in human

large intestines. (See Dietary Fiber: Properties and

Sources.)

Hemicellulose Isolation

0039 Holocellulose is prepared by defatting the fiber with

hot azetropic ethanol/benzene and delignifying with

hot (70–75



C) chlorous acid (HClO

). Alternatively,

it may be treated with chlorine gas and alcohol pyri-

dine, or chlorine gas and 95% alcohol containing 3%

monoethanolamine. If the sample contains a starch, it

must be heated in water to gelatinize the starch, with

subsequent hydrolysis using a-amylase. After wash-

ing, the remaining material (holocellulose) contains

cellulose and hemicellulose.

0040Hemicellulose is removed from holocellulose by

extracting with alkali (2–18% sodium hydroxide,

although 10% is common). Neutralization of the

extract precipitates ‘hemicellulose A,’ which is com-

posed of linear (or nearly linear), high DP hemicellu-

lose without acidic carboxyl groups. ‘Hemicellulose

B’ remains in solution and tends to be more branched

with lower DP and more acidic carboxyl groups.

Hemicellulose B can be fractionated by gradually

adding ethanol and collecting the various compon-

ents as they precipitate.

0041An alternate approach to fractionating hemicellu-

lose from holocellulose is to exploit differences

in alkali solubilities. For example, 24% potassium

Glucouronoxylan

Glucomannan

Galactan

Arabinan

Glucouronoxylan

Glucomannan

Galactan

Arabinan

100

Compound middle lamella

(a) (b)

S1 S2 S3

Compound middle lamella

S1 S2 S3

Hemicellulose

Content (%)

100

Content (%)

Cellulose

Lignin Lignin

Cellulose

fig0005 Figure 5 Distribution of lignin, cellulose, and hemicellulose in (a) hardwood and (b) softwood. Data sources: (1) Meier H (1964) In:

Zimmerman MH (ed.) The Formation of Wood in Forest Trees. New York: Academic Press; (2) Panshin AJ, de Zeeuw C (1970) Tex t b o o k o f

Wood Technology, 3rd edn, vol. 1. New York: McGraw-Hill. Reproduced from Hemicelluloses, Encyclopaedia of Food Science, Food Tech-

nology and Nutrition, Macrae R, Robinson RK and Sadler MJ (eds), 1993, Academic Press.

HEMICELLULOSES 3069

hydroxide extracts holocellulose xylan and galacto-

glucomannan from both hardwoods and soft-

woods, but does not extract glucomannan from the

residue. The dissolved galactoglucomannan may

be precipitated from the extract by adding barium

hydroxide. The insoluble glucomannan remaining in

the residue can be extracted using 175% sodium

hydroxide/4% borate with subsequent precipitation

by barium hydroxide addition.

0042 Acidic hemicelluloses can be precipitated and isol-

ated from neutral hemicelluloses by using quaternary

ammonium salts (e.g., cetyltrimethylammonium

bromide) under neutral or mildly alkaline conditions.

Then, the neutral hemicelluloses can be precipitated

from solution by increasing the alkalinity in the

presence of the quaternary ammonium salts.

Hemicellulose Analysis

Gravimetric Method

0043 The Cellulose article describes the Van Soest method

for preparing acid detergent fiber (ADF), which con-

tains cellulose, lignin, and insoluble ash (mainly

silica). This article describes the procedure for

making neutral detergent fiber (NDF), which con-

tains hemicellulose, cellulose, lignin, and insoluble

ash. The difference between NDF and ADF is a

measure of hemicellulose content.

0044 NDF is prepared by placing in a beaker about 1 g of

sample (ground to pass a 30-mesh screen), 100 ml of

neutral-detergent solution (30 g l

1

of sodium lauryl

sulfate 18.61 g l

1

of disodium ethylenediamine-

tetraacetatic acid (EDTA) dihydrate, 6.81 g l

1

sodium borate decahydrate, 4.56 g l

1

of anhydrous

disodium hydrogen phosphate, 10 ml l

1

of 2-ethoxy-

ethanol), 2 ml of decahydronaphthalene and 0.5 g of

sodium sulfite. The mixture is boiled for 60 min while

refluxing to keep the liquid volume constant and then

filtered on a previously tared Gooch crucible. After

being rinsed twice with boiling water and twice with

acetone, the sample is dried overnight at 100



Cand

weighed. (If the sample contains starch, it is incu-

bated with a-amylase overnight before washing with

water.)

Colorimetric Method

0045 The Technical Association of the Pulp and Paper

Institute (TAPPI) Method T 223 os-78 describes a

colorimetric method for measuring pentosans. Be-

cause pentose sugars are dominant in most hemicel-

luloses (except for softwood), this procedure

indicates hemicellulose content. The sample is boiled

in 3.85 mol l

1

hydrochloric acid, causing the pen-

toses to degrade to furfural which is collected in the

distillate. The collected furfural is reacted with or-

cinol which forms a colored compound measured

spectrophotometrically. Because of the complexity

of the apparatus, only a few samples can be run

daily. Holtzapple describes a colorimetric pentosan

assay which is performed in a sealed test tube,

which speeds up the assay. (See Spectroscopy: Visible

Spectroscopy and Colorimetry.)

Chromatographic Method

0046TAPPI Method T 249 pm-75 describes a chromato-

graphic technique for measuring mannan, arabinan,

xylan, galactan, and glucan. (In starch-free materials,

cellulose is the dominant glucan, although some glu-

can is also present in hemicellulose.) The sample is

hydrolyzed using sulfuric acid in a two-step proced-

ure. Some of the hydrolysate is neutralized and the

sugars are reduced to alditols (i.e., sugar alcohols)

using sodium borohydride. The alditols are acetylated

with acetic anhydride and sulfuric acid. The alditol

acetates are precipitated in ice water and extracted

with methylene chloride for injection into a gas chro-

matograph. Because sugars degrade under the acid

hydrolysis conditions, internal standards of the free

sugars are run under identical treatment conditions.

This method is extremely time-consuming and is used

only when complete characterization of polysacchar-

ides is required. (See Chromatography: Gas Chroma-

tography.)

See also: Bread: Chemistry of Baking; Carbohydrates:

Classification and Properties; Cellulose;

Chromatography: Gas Chromatography; Dietary Fiber:

Properties and Sources; Galactose; Gums: Properties of

Individual Gums; Legumes: Legumes in the Diet; Lignin;

Oats; Spectroscopy: Visible Spectroscopy and

Colorimetry; Sugar Alcohols

Further Reading

Aspinall GO (1970) Polysaccharides, pp. 85–115. New

York: Pergamon Press.

Aspinall GO (1982) Analysis of polysaccharides. In: Line-

bach DR and Inglett GE (eds) Food Carbohydrates, pp.

356–374. Westport: AVI.

Dintzis FR (1982) Dietary fiber analysis – concepts and

problems. In: Lineback DR and Inglett GE (eds) Food

Carbohydrates, pp. 312–332. Westport: AVI.

Holtzapple MT and Humphrey AE (1983) Determination

of soluble and insoluble pentoses in the presence of

glucose. TAPPI Journal 66: 90.

Kennedy JF (1988) Carbohydrate Chemistry, pp. 229–233.

Oxford: Clarendon Press.

Whistler RL and Shah RN (1978) Recent developments in

the industrial uses of hemicelluloses. In: Rowell RM and

Young RA (eds) Modified Cellulosics, pp. 341–356,

New York: Academic Press.

3070 HEMICELLULOSES

Whistler RL and Richards EL (1970) Hemicelluloses.

In: Pigman W and Horton D (eds) The Carbohydrates:

Chemistry and Biochemistry, pp. 447–469. New York:

Academic Press.

Whistler RL and Zysk JR (1978) Carbohydrates. In: Kirk-

Othmer Encyclopedia of Chemical Technology, 3rd edn,

vol. 4. New York: Wiley.

Herbicides See Pesticides and Herbicides: Types of Pesticide; Types, Uses, and Determination of

Herbicides; Residue Determination; Toxicology

HERBS

Contents

Herbs and Their Uses

Herbs of the Compositae

Herbs of the Labiatae

Herbs of the Umbelliferae

Herbs Used in Alcoholic Drinks

Herbs and Their Uses

K P Svoboda and T Svoboda, The Scottish

Agricultural College, Auchincruive, Ayr, UK

Background

0001 The plant kingdom produces a wide range of valuable

products. These include numerous aromatic, dye,

spice, medicinal, and other useful substances. Such

products have contributed to the quality of human

life for thousands of years. From ancient texts and

scriptures, it is known that some plants have long

served as the principal components of seasonings,

flavorings, cosmetics, dyes, and medicines.

0002 Herbs generally include plants whose leaves, stems,

flowering tops, and roots are used fresh, dried, or

frozen in the seasoning of foods, in the beverage

industry, in perfumery and cosmetic products, in the

pharmaceutical industry, and for numerous other pur-

poses, including ornamental gardening, pot-pourri,

moth and general insect deterrents and in dyeing

and fabric cleaning. There is no standard definition

of the term ‘culinary herbs,’ and the distinction

between culinary herbs and spices is imprecise. The

American Spice Association, the most important

body in the spice trade, uses the term ‘spices’ in such

a way as to include both herbs and aromatic seeds.

Scientific information on herbs, plant drugs, their

active constituents, and their therapeutic and health

uses is being published worldwide at an unpreced-

ented rate, in many different journals and in various

languages. Scientific and regulatory information is

systematically presented in various monographs.

Recommendations for new crops which can be used

as herbs are given for specialty crop growers. In

addition, there is growing interest in organically pro-

duced herbs, and such herbs have to conform to

organic certification standards. Many herbs are now

also being used as dietary supplements and ingredi-

ents in foods.

Sources of Herbs

0003Herb material is obtained from both wild and culti-

vated plants. In most cases, the demand for culinary

herbs is such that collection of material from the

wild is insufficient to satisfy market requirements.

Cultivation of herbs offers numerous advantages,

including:

HERBS/Herbs and Their Uses 3071

.0004 the development of high-yielding cultivars, which

also leads to a product with more consistent prop-

erties than would be obtained from plants growing

wild;

0005 the use of mechanization;

0006 the control of insects and diseases;

0007 planned harvesting and transport; and

0008 efficient drying and storage.

Herb production can be undertaken using either

labor-intensive techniques, as for example in north

Africa and India, or capital-intensive harvesting and

processing methods as in the USA, France, and other

Western countries.

0009 The quality of herbs is dependent on several

factors, including plant variety, growing conditions,

cultural practices, drying and processing methods,

storage, and packing. Cleanliness, color, flavor, and

aroma are the most important considerations in the

selection and utilization of herbs. National quality

standards have not yet been established for culinary

herbs, but as the market grows, the need for specific

quality standards is being recognized. The description

and chemical composition of a number of herbs

are defined in the British Pharmacopoeia, British

Pharmaceutical Codex, British Herbal Pharmaco-

poeia, New Cyclopedia of Botanical Drugs and Prep-

arations, British Herbal Compendium, ESCOP

Monographs in Herbs or Plant Drugs, WHO Herbal

Monographs, and German Commission E Mono-

graphs on Herbs.

Production and Consumption

0010 Accurate data on the area of individual herbs grown

and their production in any country are very difficult

to obtain. An unofficial estimate of total UK herb

production in 1999 was about 3000 ha. The UK

growing season is usually from April to November,

depending on the herb and the weather in any

particular year. Outside the season, fresh herbs are

imported largely from Mediterranean countries, espe-

cially Israel. A significant proportion of marketed

herbs are cultivated on smallholdings or collected

from the wild, and do not enter the trade statistics.

Most sources agree that the total national consump-

tion of herbs is increasing at around 10% per annum.

Her Majesty’s Customs and the Ministry for Agricul-

ture are the most important organizations for

reporting on the trade and production of herbs. Of

the various culinary herbs, they report separately

only on thyme and parsley, with other herbs being

generally categorised under ‘other species’ or ‘dried

vegetables’.

0011Table 1 shows the estimated annual consumption

of the major culinary herbs and volatile oils in the

UK. These statistics must be regarded as providing

orders of magnitude rather than precise measures.

Since commercial herb growing is a relatively small

part of horticulture, insufficient research has been

carried out to permit the use of more than a narrow

range of pesticides, most of them with limited off-

label use, which causes some difficulty in growing

some crops on a large scale. Traditionally, herbs are

hand-harvested, but there are now several purpose-

built harvesting machines available, and many people

have adapted conventional cereal- and grass-cutting

and harvesting equipment for use on herbs, the aim

being to cut and immediately lift the crop without

bruising. The trade estimates that about 50% of the

plants traded are used for the food industry, 25% in

cosmetics, 20% for medicinal and 5% for other uses

such as insecticides.

Herbs and Volatile Oils

0012There are 31 plant families made up of 93 species

representing the major flavor- and spice-producing

taxa. Approximately 10% of the world’s major eco-

nomic plants are sources of flavorings. These may be

classified into six main groups, according to their

principal flavor components (Table 2).

0013The volatile (essential) oils consist of a complex

mixture of chemical compounds, which combine to

give the oil distinctive characteristics. The differences

in aroma among plant types result from differences in

the volatility and quantity of chemicals in the volatile

oil. The volatile oils are products of the plant’s meta-

bolic processes and are particularly subject to sea-

sonal and climatic changes, and to the care taken in

general husbandry, harvesting, and storage. Volatile

oils, oleoresins and oleo-gum resins are produced

in various types of secretory tissues. The type of

tbl0001Table 1 Estimated UK production and imports of selected

culinary herbs

Herb Area (ha) Yield (drymatter)

(t ha

1

)

Imports (t)

Basil 5 1.7 30 – 50

Marjoram 4 1.9 40 – 75

Mint 100 3.6 80 – 175

Oregano 4 1.6 40 – 55

Parsley 500 3.0 100 – 250

Rosemary 4 2.5 20 – 75

Sage 100 1.9 100 – 500

Savory 4 1.3 10 – 12

French tarragon 40 0.8 80 – 250

Thyme 40 0.8 80 – 250

3072 HERBS/Herbs and Their Uses

secretory structure is an important character of a

plant family and includes various forms, such as oil

and oleoresin cells (ginger, pepper, vanilla), secretory

glands (bay, clove, eucalyptus), secretory ducts (tarra-

gon, anise, angelica) and glandular trichomes (mint,

sage, lavender, rosemary, chamomile) (Figures 1–4).

These structures are associated with many different

parts of the plant, such as vascular bundles in the

leaves, stems and roots, fruit wall, bark, parenchyma,

or epidermal tissue. Leafy herbs are normally used in

a well-broken state. Following drying and milling, the

finer the powder, the more readily available is the

flavor.

0014 Three major types of industrial distillation are used

to obtain the volatile oil fraction: water, water and

steam, and steam. In water distillation, the plant ma-

terial is placed in a distilling container with water and

heated until the volatile compounds have vaporized.

The gaseous mixture of oils and water is piped to a

condenser for cooling: the oil, being lighter than

water, floats to the top and can be collected. Volatile

oils used by the perfumery industry are extracted by

the use of organic solvents. Although more expensive

than distillation, it avoids elevated temperatures,

which may cause the loss of highly volatile compon-

ents and the denaturation of other chemicals in the

oil. The solvent system uses petroleum ether or ben-

zene. In a technique known as enfleurage, the plant

material is affixed to a thin layer of odorless fat

spread on a glass sheet. The volatile oils are absorbed

into the fat and can then be extracted with alcohol.

0015 A more recent development in extraction technol-

ogy, still at the research and development stage, is

the use of supercritical carbon dioxide. Liquid

carbon dioxide is used at a range of temperatures

and elevated pressure. Under these conditions, carbon

dioxide behaves like a solvent and removes different

classes of compounds from the plant material

depending on the running conditions in force. Mod-

erate pressure (< 50 bar) releases volatile oils from

plant material, while at a greater pressure (> 200

bar), waxes and resins predominate in the resultant

extracts. By careful manipulation of the operational

parameters, it is possible to sequentially remove these

different groups of compounds from the raw mater-

ial. It is also possible to deterpinate certain oils,

making them less pungent in taste.

0016Volatile oils have long been used in industry in

place of the dried herbs. Their advantages over the

fig0001Figure 1 (see color plate 89) Chamomile field in Norfolk.

tbl0002 Table 2 Flavor components of several important commercial herbs

Group Flavor component Herb

1 Cineole or eucalyptol Bay (Laurus nobilis)

Spanish sage (Salvia lavandulifolia)

Rosemary (Rosmarinus officinalis)

2 Eugenol West Indian bay (Pimenta racemosa)

3 Thymol or carvacrol Origanum (Origanum vulgare)

Wild marjoram (Origanum marjoranum)

Summer savory (Satureja hortensis)

Mexican oregano (Lippia graveolens)

Thyme (Thymus spp.)

Basil (Ocimum basilicum)

4 Linalool, methyl chavicol, or terpineol Sweet marjoram (Marjorana hortensis)

Parsley (Carum petroselinum)

English sage (Salvia officinalis)

French Tarragon (Artemisia dracunculus)

5 Thujone Dalmatian sage (Salvia officinalis)

6 Menthol, menthone, or carvone Mints (Mentha spp.)

HERBS/Herbs and Their Uses 3073

plant material include a generally uniform flavor

quality and their sterility – they are free from all

extraneous contaminants. Oils can be readily incorp-

orated into liquid concentrates and emulsions, the

flavor character and strength of which can be stand-

ardized. They can be readily mixed with fats and oils

which are commonly present in food products and are

easily dispersed throughout the mix. Being concen-

trated, these oils save both storage space and handling

costs. They are normally stable and show only a slight

deterioration over long periods provided that they are

correctly stored.

Cleanliness and Preservation

0017 Spice and herb plants tend to be heavily contaminated

with microorganisms and molds, many in spore

form. The general negligent and unhygenic way in

which they are handled from the time of harvesting

until they are eventually presented for sale results in

the presence of such contaminants such as rodent

hairs and droppings, insect parts, eggs and larvae,

hessian sacking fibers, soil, and stones. Cleanliness

is regarded as being important by the producer, pro-

cessor, and consumer, and has to be achieved without

detriment to the product itself. In the UK, following

the banning of ethylene oxide gas at the end of 1990

as the principle cleaning agent for dried herbs, firms

have devised several different methods of reducing

the microbial load. In 1991, a licence was granted

for including ionizing radiation treatment of dried

herbs and spices to a maximum load of 10 kGy. Pesti-

cide contamination and heavy metal content are be-

coming important issues on the quality market. Some

European countries permit irradiation but the laws in

the US are different.

0018 Fresh herbs are supplied prewashed, using a steril-

ized agent such as dilute sodium hypochlorite; frozen

herbs are similarly treated, chopped, and then ideally

quick-frozen using liquid nitrogen. Freeze-dried herbs

go a stage beyond frozen by being subsequently

treated at a low temperature in a vacuum, which

drives moisture from the herbs without any browning

or shrinking, a feature which may occur with conven-

tionally dried herbs. The final product may be stored

indefinitely without refrigeration, although pack-

aging requirements are stringent. The process is costly

fig0004Figure 4 (see color plate 92) Cross-section through a eucalyp-

tus leaf, showing the oil cavity.

fig0002 Figure 2 (see color plate 90) Volatile oil gland on the surface of

a Greek oregano (Origanum heracleoticum) leaf.

fig0003Figure 3 (see color plate 91) Agastache species (Korean mint)

at the Auchincruive herb garden.

3074 HERBS/Herbs and Their Uses

and is presently used in commerce to preserve highly

degradable substances, such as chopped chives, for

which other satisfactory methods of drying are in-

appropriate. Freeze-drying seems to be better for

volatile substances or vitamins but offers no apparent

advantage or preservation of certain other sub-

stances, such as alkaloids, and may promote the

oxidation of fatty acids, especially linoleic and

linolenic acid.

Food Industry

Commercially Important Herbs

0019 Commercially important herbs on the UK market

include basil, celery, chervil, chives, coriander, dill,

marjoram, mint, oregano, parsley, rosemary, sage,

savory, tarragon, and thyme. However, many other

species are used in cooking, and their range is

expanding every year. Mixed herbs usually contain

three or four herbs selected from thyme, savory, sage,

marjoram, basil, parsley, and rosemary.

Uses of Herbs

0020 Herbs are being incorporated into a variety of differ-

ent food products: butters, cheeses, biscuits, pastries,

popcorn, sausages, salami, meats and stews, fish

dishes, soups and sauces, mustards and vinegars,

chocolates, and sweets. Herbs can be used fresh,

dried, broken, or ground. Alternatively, volatile oils

or extracts are readily available on the market. A

number of companies have now introduced dehy-

drated or frozen herbs. Frozen flakes are free-flowing,

can be used without any previous defrosting, and

have a fresh aroma that is stable for 18 months.

Packaging and Storage

0021 Dried herbs are packaged for the retail trade in a wide

variety of small- to medium-sized packs, including

glass jars, drums, tubs, cellophane, polythenes, and

cartons. Freeze-dried herbs tend to be packed in poly-

ethylene terephthalate. If stored in tubs, the herbs

must be free of oxygen and water vapor in airtight,

opaque containers and, in the case of freeze-dried

material, filled with a dry inert gas. Fresh herbs are

usually packed in polystyrene trays with a clear over-

wrap or in transparent punnets with lids. The whole-

sale market also accepts polythene bags, open crates,

and cartons.

0022 Fresh herbs need to be transported and stored

chilled, between 2 and 5



C, or slightly warmer for

more sensitive herbs such as basil. Frozen herbs need

to be stored and shipped at temperatures of at least

18



C, giving a shelf-life of 12 months, which can

be extended to 2 years at 25



C. Dried and freeze-

dried herbs are stored and transported at ambient

temperature, preferably out of direct light.

Pharmaceutical Industry

0023Although synthetic and semisynthetic organic sub-

stances have achieved a substantial share in pharma-

ceutical applications, plant-derived substances still

remain a vital ingredient in modern medicine. As

estimated 25% of prescriptions contain one or more

active constituents obtained from higher plants.

The herbal ingredients are obtained from some 550

different herbs. It has been estimated that about

7000 t of herbs are extracted annually for the ingredi-

ents of UK medicines. Some particularly potent

plants, such as Areca catechu, Aconitum napellus,

Atropa belladonna, and others, have been brought

under strict pharmaceutical control. Many plant

products available to the public are capable of caus-

ing serious harm. These include products which can

cause allergenic reactions in previously sensitized in-

dividuals, preparations which induce gastroenteritis,

and products with cardiovascular involvements.

Also, many can interfere with anticoagulant treat-

ment due to the presence of substances such as

coumarins. A further problem arises from the mis-

identification of plant products and from contamin-

ation of beneficial plant material with toxic species.

If the public is to be protected from potentially

hazardous plant products available for sale, herbal

suppliers must be monitored carefully. Chemical

diversity in natural products is a rich source of new

pharmaceuticals and other economically important

chemicals. A number of new bioassays have been

designed to facilitate the isolation of natural products

from plants, rapid screening of several thousand

samples in one day, and complicated synthesis of

complex products based on a natural template. The

development of natural product chemistry and the

discovery of new natural products from indigenous

medicinal plants are becoming increasingly promin-

ent features due to their medicinal, food, and other

industrial values.

Product Development and the Future

0024The herb market has experienced significant growth

in recent years, and a considerable amount of product

development has taken place, with much input from

supermarkets. Despite the effects of economic reces-

sion in the early 1990s, this trend is set to continue

under the influence of travel abroad, TV cookery

programs, and ethnic restaurants. New methods

of production and packaging continue to evolve,

HERBS/Herbs and Their Uses 3075

offering greater quality and convenience to consumer,

caterer, and manufacturer alike. Current develop-

ments include new harvesting techniques, improved

washing chemicals, and new forms of presentation,

such as pelletized frozen herbs. These factors, com-

bined with the demand for more natural flavorings

and innovative ideas from all areas of the industry,

should ensure a steady growth in the herb market

throughout the next decade and beyond.

Research and Development

0025 Research into the biological activity of plant volatile

oils has been undertaken for several decades. How-

ever, the most interesting results had to await

the development of sophisticated analytical instru-

ments such as gas chromatography linked to mass

spectroscopy, high-performance liquid chromatog-

raphy, Fourier-transformed infrared spectroscopy,

and Fourier-transformed nuclear magnetic resonance.

With such instrumentation available, it is now

possible to identify the majority of the chemical con-

stituents in the oils and thus allocate bioactivity to

specific compounds. The possibility of synergistic

effects should not be overlooked, although the

evaluation of such phenomena becomes problematic

when many oils have over 100 different constituents.

The marked antibacterial and antifungal activities

in certain volatile oils provide the food and related

industries with a source of natural preservatives.

There is some reluctance on the part of the industry

to exploit such antimicrobials on a larger scale, owing

to the problem of balancing effective antimicrobial

activity without rendering food unacceptable because

of an overwhelming taste of plant extract. Deterpena-

tion using supercritical carbon dioxide may help to

alleviate this aspect.

0026 A number of plant secondary metabolites possess

antioxidant compounds in the volatile oil and other

fractions. There is now evidence that plant antioxi-

dants taken as diet supplements have a marked bene-

ficial effect upon the lipid metabolism in animal

model systems. The long-chained polyunsaturated

fatty acids (arachidonic and docosohexaeonic) are

well protected by such antioxidants, leading to the

reversal of the normal decline in concentration during

the ageing process. Many degenerative disease condi-

tions associated with human aging, such as senile

dementia and acute memory loss, can be described

in terms of lipid inadequacies. Hence, any natural

antioxidants capable of slowing down the disease

process are of real significance in human health and

the quality of life.

0027 Recently, it has become clear that many plant

metabolites have potential beneficial effects directly

relevant to human diet and health. Some may exert a

protective role which reflects similar protective

actions like antioxidants, some can prevent cells

from mutation (blocking and suppressing anticarci-

nogens), and certain herbs contain chemicals (isocou-

marins, flavonoids, hop acids, and terpenes) which

are structural analogs of the natural estrogens. These

compounds may interact with the estrogen receptors

in human cells. Herbs, by their nature and quality,

have the potential to influence both short-term and

long-term human health and well-being. An increased

level of certain protective factors may be desirable,

and both classical plant breeding and biotechnology

can provide the improved plant material for human

consumption.

See also: Essential Oils: Properties and Uses; Isolation

and Production; Herbs: Herbs of the Compositae; Herbs

of the Labiatae; Herbs of the Umbelliferae; Herbs Used in

Alcoholic Drinks; Spices and Flavoring (Flavouring)

Crops: Use of Spices in the Food Industry; Fruits and

Seeds; Leaf and Floral Structures; Tubers and Roots;

Properties and Analysis

Further Reading

Atta-ur-Rahman and Iqbal Choudhary M (eds) (1998) New

Trends in Natural Product Chemistry. Karachi, Paki-

stan: University of Karachi.

Bauer K, Garbe D and Surburg H (1997) Common Fra-

grance and Flavour Materials. Preparation, Properties

and Uses, 3rd edn. Weinheim, Germany: Wiley-VCH.

Bown D (1995) The Royal Horticultural Society: Encyclo-

pedia of Herbs and Their Uses. London: Dorling Kin-

dersley.

Bradley PR (ed.) (1992) British Herbal Compendium, vol. 1.

Guildford and King’s Lynn, UK: Biddles Ltd.

Deans SG and Ritchie GA (1987) Antibacterial properties

of plant essential oils. International Journal of Food

Microbiology 5: 165–180.

Deans SG, Svoboda KP and Bartlett MC (1991) Effect of

microwave oven and warm-air oven drying on the

microflora and volatile oil profile of culinary herbs.

Journal of Essential Oil Research 3: 341–347.

Dewick PM (1998) Medicinal Natural Products: A Biosyn-

thetic Approach. New York: John Wiley.

Halva S and Craker LE (1996) Manual for Northern Herb

Growers. Guildford and King’s Lynn, UK: Biddles Ltd.

Hay RKM and Waterman PG (1993) Volatile Oil Crops.

Harlow, UK: Longman.

Hodge WH (1975) Survey of flavour producing plants.

Food Flavours 22: 244–245.

Hornok L (ed.) (1992) Cultivation and Processing of

Medicinal Plants. Chichester, UK: John Wiley.

International Conference on Essential Oils and Aromas

(1998) Global Markets Present and Future. London:

International Federation of Essential Oils and Aroma

Trades.

3076 HERBS/Herbs and Their Uses

Mason L and Brown C (1999) Traditional Foods of Britain.

An Inventory. Trowbridge, UK: Prospect Books. Crom-

well Press.

Moyler DA and Heath HB (1988) Liquid carbon dioxide

extraction of essential oils. In: Lawrence BM, Mookerjee

BD and Willis BJ (eds) Flavours and Fragrances: A World

Perspective, pp. 41–63. Amsterdam: Elsevier Science.

Small E (1997) Culinary Herbs. Otawa, Ontario: NRC

Monograph Publishing Program.

Svoboda K and Deans SG (1990) A study of the variability

of rosemary and sage and their volatile oils on the

British market: their antioxidative properties. Flavour

and Fragrance Journal 7: 81–87.

Svoboda K, Gough J, Hampson J and Galambosi B (1994)

Analysis of the essential oils of some Agastache species

grown in Scotland from various seed sources. Flavour

and Fragrance Journal 10: 139–145.

Svoboda K and Hampson J (1998) Chemicals from plants.

The Horticulturist 7: 4, 26–31.

Walton NJ and Brown DE (ed.) (1999) Chemicals from

Plants. Covent Garden, London: World Scientific Pub-

lishing Co. Ltd.

Weiss EA (1997) Essential Oil Crops. Wallingford, UK:

CAB International.

Herbs of the Compositae

S G Deans and E J M Simpson, Aromatic and

Medicinal Plant Group, South Ayrshire, Scotland, UK

Introduction to the Group

0001 The Compositae represents the largest family of

flowering plants, with over 900 genera and 14 000

species comprising examples of various ecological

types and life forms, such as trees, shrubs, perennial

and annual herbs, aquatic, alpine and desert plants,

climbers, succulent, and spiny shrubs. Many species

are cultivated as vegetables (lettuce, endive, arti-

choke, salsify, sunflower) and several genera as culin-

ary and medicinal plants (Achillea, Aster, Calendula,

Helenium, Rudbeckia, Tagetes).

Special Morphological and Anatomical

Features

0002 Flowers from small florets are aggregated into heads

(capitula) simulating a single large flower and sur-

rounded by a calyx-like involucre of one or more

rows of bracts. These vary greatly in number and

arrangement. Florets can be all similar (head homog-

amous) or with central and marginal florets differing

(head heterogamous). Pollination is entomophilus,

rarely anemophilous; some genera (Taraxacum, Hier-

acium) contain apomictic species.

0003The family exhibits several specific features, such as

secretory resin canals (Achillea, Ambrosia, Anthemis,

Arnica, Artemisia, Centaurea, Cnicus, Echinacea,

Ehlinthus, Eupatorium, Inula, Matricaria, Parthe-

nium, Petasites, Pyrethrum, Senecio, Solidago, Tagetes,

Tanacetum), secretory cavities (Artemisia, Inula,

Tagetes), lactiferous canals, cells and vessels (Arctium,

Carlina, Silybum), different types of glandular

(Eupatorium, Haplopappus, Helianthus, Olearia)

and nonglandular hairs, and anomalous secondary

thickening (Artemisia, Helianthus, Taraxacum).

0004The volatile oil found in the leaves of Artemisia

dracunculus is produced partly in schizogenic volatile

oil canals and partly in characteristic glandular hairs.

Differences have been recorded between the oil found

in the canals and the oil produced by the glandular

hairs. Primary volatile oils extend from the stem into

the root system where they are located between the

endodermis and the cortex. Excretion canals are also

found in the roots, but do not extend to the stem

(Figure 1).

0005A blue volatile oil is extracted from the flowers of

German chamomile (Matricaria chamomilla L.) pro-

duced in secretory glandules and canals localized

fig0001Figure 1 (see color plate 93) Volatile oil canals in root of Arte-

misia absinthium (wormwood). Bright field 40. Reproduced

from Herbs: Herbs of the Compositae, Encyclopaedia of Food Sci-

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

Sadler MJ (eds), 1993, Academic Press.

HERBS/Herbs of the Compositae 3077

mainly in the anthodia. The content of the oil varies

considerably during the development of the plant and

the flowering of the anthodia. (See Essential Oils:

Properties and Uses.)

Harvesting and Handling Procedures

0006 Harvesting crops at the correct stage of maturity is

essential to achieve a product that will be of top

quality and meet the buyers’ standards. Harvesting

of herbs is still carried out by hand in many

cases. The development of mechanized harvesting

systems has proved to be problematical owing to

the wide variety of plant parts to be harvested

(roots, rhizomes, stems, leaves, flowers, seeds, and

pods) combined with a relatively small crop acreage.

Machinery currently in use has either been adapted

from equipment constructed to harvest other crops(u-

sually forage, grain, or vegetable products) or

specifically designed and constructed for a few

herbs or even one specific herb. The construction of

new harvesting machinery can only be considered

when the market value of the crop or related

product is high and the acreage is relatively large, or

when large commercial companies finance such

equipment development as in chamomile production

in Germany.

0007 Drying facilities are essential and may vary from an

unused room to an elaborate drying shed. Low hu-

midity is important and using a dehumidifier allows

better control over the drying process. The tempera-

ture of the drying is critical since many volatile com-

pounds can be lost at elevated temperatures (Table 1).

Use in the Food Industry

0008 Many members of the Compositae are cultivated as

edible plants, vegetables, herbs, and spices (Table 2).

The edible tubers of the Jerusalem artichoke

consist of the parenchyma of the medullary rays

and pith, together with the xylem. Fleshy parts of

the inflorescence of the globe artichoke are eaten.

The roots of scorzonera and salsify are used as

vegetable, while dried and roasted roots of dandelion

and chicory are used as coffee substitutes and in

medicine.

Research and Development

0009An increasing demand from the food, pharmaceut-

ical, and cosmetic industries calls for the development

of new varieties with high levels of active con-

stituents, consistent quality, and safe application.

The anatomy and the physiology of each plant

have to be investigated in order to elucidate the

plant’s requirements and adaptation to cultivation.

Several species are currently being investigated for

their bioactivity and a number of representative

genera will be discussed. (See Biotechnology in Food

Production.)

Chamomile

0010Roman chamomile (Chamaemelum nobile (L.) All.)

and German chamomile (Matricaria recutita L.) are

two different species of plant commonly called

chamomile. Roman chamomile, formerly classified

as Anthemis nobilis L., is a creeping, herbaceous per-

ennial native to western Europe and North Africa.

German chamomile is an erect-growing annual, native

to Europe and western Asia. The volatile oil of

Roman chamomile consists mainly of chamazulene,

angelic acid, tiglic acid and several sesquiterpene lac-

tones. German chamomile contains chamazulene,

a-bisabol, a-bisabol oxides A and B, spathulenol

and farnesene. Extracts from both plant species are

reported to have antiseptic, antibacterial, antifungal,

and antitumor activities.

0011The breeding of chamomile has been targeted to-

wards increased content of two sequiterpenes: cha-

mazulene and a- and b-bisabolol. The diploid and

tetraploid varieties have been introduced on the

market in Germany and the former Czech Republic,

with high and stable contents of these sesquiterpenes.

Other important flavanoid secondary metabolites,

namely apigenins, are now being investigated in

detail. (See Colorants (Colourants): Properties and

Determination of Natural Pigments.)

Achillea millefolium

0012Yarrow is a hardy perennial plant, native to Europe

and Asia. The chemical constituents include a volatile

oil comprised of azulene, caryophyllene, thujone,

eucalyptol, a- and b-pinene and borneol, as well

as lactones, tannins, and alkaloids. Yarrow extracts

tbl0001 Table 1 Changes in volatile oil yield (%)

with rising tem-

perature

Plant Temperature (



405060708090 100

Basil 1.0 0.7 0.7 0.7 0.3 0.3 0.1

Sweet marjoram 1.7 1.3 1.3 1.0 1.0 0.7 0.5

Rosemary 2.3 2.0 2.0 1.7 1.7 1.0 0.3

Sage 2.0 1.7 1.0 0.5 0.5 0.4 0.3

Summer savory 1.3 1.0 0.8 0.7 0.5 0.03 <0.01

French tarragon 0.5 0.3 0.3 0.2 0.2 0.2 0.1

Thyme 1.0 1.0 1.0 0.3 0.3 0.2 <0.01

Percentage of volatile oils expressed as value per gram of dry matter of

plant material.

3078 HERBS/Herbs of the Compositae