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

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mostly rabbits and hares, is in the millions. Australia

exports kangaroo meat, although the quantity has de-

clined over recent years. Of the total game meat

marketed internationally, it has been estimated that

less than one-half the tonnage is from ungulate species.

Game Farming

0006 Game farming has existed for centuries: reindeer

husbandary in Fennoscandinavia and deer farming

in China are ancient practices. Herds of bison have

been maintained on farms and ranches in North

America for most of this century and game ranching

in southern Africa involves enclosure of wild species

to control numbers and facilitate harvesting. In the

thirty years intensive game-farming systems have de-

veloped which involve careful reproductive and nu-

tritional management, and rather strict containment

of a group of animals. Intensive farming systems exist

throughout the world to raise, manage, and process

game animals, primarily for meat production or

velvet antlers, or both (Table 3).

0007 The greatest number of farmed game animals,

mainly red and fallow deer, exists in New Zealand.

The farmed deer population is approaching 1 million

animals with about 10% slaughtered for meat

annually. China, the former Soviet Union, Australia,

Korea, and Ireland also have large populations of

farmed deer, although in Asia, deer production is

mainly for velvet antler used for medicinal purposes,

rather than meat. Whenever cervids are intensively

farmed, however, velvet antler production is an import-

ant byproduct. A large bison population exists in North

America with over 70 000 animals in the USA and 5000

in Canada on farms and ranches. Approximately

11 000 bison were slaughtered in 1985 for meat.

0008 The intensive New Zealand deer-farming system

evolved in barely two decades from the successful

commerical hunting, processing, and export pra-

ctices of prior years. Capture and containment of

free-ranging red deer allowed selection and reproduct-

ive management, development of a breeding herd and

controlled, but rapid, expansion of the farmed-deer

population. The processing and export of deer meat

have been facilitated in New Zealand by construction

of specially designed deer slaughter and processing

plants. Ante- and postmortem inspection of animals

and carcasses, and fabrication and packaging of meat

are accomplished in a manner similar to that used for

domestic livestock. In many other areas where game

animals are bred or managed for meat production,

notably Africa, animals are often still harvested by

shooting with processing of the carcasses carried out

by mobile processing units. Absence of suitable hand-

ling and processing facilities for bison is a major factor

constraining wider development of the bison-meat

industry in North America. (See Meat: Slaughter.)

Processing Considerations

0009Game is generally subject to handling and treatment

different from that of domestic livestock because of

the conditions under which carcasses are obtained.

Carcass weight and the composition of meat from

some common large game and domestic species are

shown in Table 4.

Carcass and Meat Characteristics

0010Most game animals (Cervidae and Bovoidea families)

produce carcasses significantly lighter than beef

cattle; exceptions are moose, bison, and eland. The

most obvious differences between game and domestic

species are the lower fat and metabolizable energy

levels in cuts of meat from the game species. Differ-

ences in leanness between game and domestic species

are even larger when whole carcass composition is

determined. Carcass fat content of market lambs, for

example, may exceed 30% but the carcass fat content

of game animals is usually below 10% and often

substantially lower. There can be wide seasonal,

tbl0003 Table 3 Major game-farming systems

Location Species Approximate numbersmanaged Main products/byproducts

New Zealand

Red, fallow deer, and wapiti >900 000 Meat and velvet antler

China Sika and malu deer 300 000 Velvet antler

Former Soviet Republic Sika and maral deer 90 000 Velvet antler

North America Bison 88 000 Meat

Wapiti 6000 Meat and velvet antler

Australia Fallow, red, and rusa deer 40 000 Meat and velvet antler

Korea Sika deer 52 000 Velvet antler

Red deer 2000

Wapiti 3000

UK Red deer 10 000 Meat

Drew K, personal communication. Other data from Hudson RJ, Drew KR and Baskin LM (eds) (1989) Wildlife Production Systems. Cambridge: Cambridge

University Press.

2858 GAME/Mammals

age-, and gender-related variations in the leanness of

game animals. Males postrut are generally much lea-

ner than prerut and older animals often contain more

fat than younger.

0011 Game meat is often much darker red in color than the

meat from domestic species. The darker color may be

due to increased muscle myoglobin concentration de-

creased intramuscular fat content (marbling), elevated

muscle pH, or a combination of all these factors. Myo-

globin concentration is a function of animal age and

muscle fiber type and muscle from game animals gener-

ally possesses a higher proportion of fibers of the red,

aerobic type geared to oxidative metabolism than does

muscle from domestic species. Red, aerobic fibers con-

tain more myoglobin and are smaller in diameter than

less oxidative fiber types. In all species, myoglobin

content in muscles increases with age.

0012 Hunter-harvested game animals are particularly

subject to excitement and stress which may result in

depletion of muscle glycogen levels prior to death.

Postmortem lactic acid production in the muscle is

decreased, resulting in a higher than normal ultimate

muscle pH (5.4–5.7) and a dark appearance. Muscle

pH of hunter-harvested pronghorn, mule deer, and

white-tail deer when determined ranged from some-

what elevated (5.8–6.0) to normal (5.4–5.6). Both

hunter-harvested elk (wapiti) and farmed red deer

showed normal ultimate meat pH (< 5.7). (See Exer-

cise: Muscle.)

0013 Texture and tenderness of meat are primary quality

characteristics and are related to muscle connective

tissue content and maturity, muscle fiber diameter,

and degree of postmortem muscle proteolysis. There

can be wide variations in the tenderness of game

meat, due primarily to the wide range of ages at

which individuals are harvested and to seasonal

fluctuations in growth rate. Increasing age results in

muscle connective tissue maturation, increased colla-

gen cross-linking, and decreased meat tenderness.

Variable growth rate alters collagen synthesis rate

and may similarly affect muscle collagen quality and

meat tenderness, especially in males during and after

the rut. Variable carcass chilling rates and aging tem-

peratures also contribute to differences in tenderness.

(See Meat: Preservation.)

0014The smaller ungulate game species, particularly

fallow deer, produce a fine-textured meat that is

highly valued. The fine texture of meat from the

smaller game species is due in part to decreased

muscle fiber diameter. Both pronghorn and deer can

develop an objectionable, mushy texture with in-

creased postmortem hanging time. A comparison of

endogenous muscle protease activity and postmortem

myofibrillar protein degradation, however, revealed

no differences between pronghorn and beef muscle.

Aging

0015The major differences between processing of conven-

tionally slaughtered domestic livestock and game are

the recommendations for reduced length of postmor-

tem refrigerated storage time (aging) for game prior to

freezing or consumption. Aging of carcasses with little

or no fat results in excessive carcass dehydration,

weight loss, and discoloration of the lean meat. The

vast majority of game carcasses and meat are not

subject to the rigid inspection and slaughter standards

applied to conventionally slaughtered animals. With

game, high levels of microbial contamination, slow

carcass chilling, and elevated muscle pH often result

in rapid microbial proliferation. Higher bacterial

counts in ground meat from deer and pronghorn

than from elk carcasses occur because of the increased

carcass surface area relative to total meat in the smaller

animals. Intensive game-farming systems and the

slaughter and processing of game in specially designed

facilities reduce or eliminate many of the difficulties

associated with processing and handling hunter-har-

vested animals. Bacterial counts and refrigerated shelf-

life of meat from farmed New Zealand red deer are

comparable to values obtained for conventionally pro-

cessed domestic livestock. Meat from game carcasses

often requires addition of fat to enhance palatability.

tbl0004 Table 4 Composition of meat from selected game and domestic ruminants

Pronghorn

b,e

Mule deer

c,e

Elk (wapiti)

d,e

Red deer

Lamb

Beef

Carcass weight (kg) 28 43 165 69.4 13.6 275

Protein (g 100 g

1

) 22.4 22.6 22.4 24.7 17.4 21.7

Fat (g 100 g

1

) 2.5 2.7 2.0 3.3 18.2 5.0

Water (g 100 g

1

) 70.0 66.7 73.4 70.8 63.6

Ash (g 100 g

1

) 1.2 1.0 0.9 1.4 0.9

Metabolizable energy (kJ 100 g

1

) 489 497 468 545 969 568

Data for male game species reported.

Field RA, Smith FC and Hepworth WG (1972) The pronghorn antelope carcass. University of Wyoming Agriculture Experiment Station Bulletin 575.

Field RA, Smith FC and Hepworth WG (1973) The mule deer carcass. University of Wyoming Agriculture Experiment Station Bulletin 589.

Field RA, Smith FC and Hepworth WG (1973) The elk carcass. University of Wyoming Agriculture Experiment Station Bulletin 594.

Miller GJ, Field RA, Riley ML and Williams JC (1986) Lipids in wild ruminant animals and steers. Journal of Food Quality 9: 331–343.

Drew KR and Seman DC (1987) The nutrient content of vension. Proceedings of the Nutrition Society of New Zealand 12: 49–55.

GAME/Mammals 2859

Species Identification

0016 Substitution of less valuable meat for game or illegal

trade in game species meat poses worldwide concern.

Methods for the identification of raw (uncooked) game

meat based on protein differences detected by electro-

phoresis are well established for most species. Heating

or cooking denatures and inactivates meat proteins and

enzymes, greatly reducing solubility and extractability.

Specialized techniques for the identification of game

species in processed and cooked meat products based

on protein or immunological variations have, there-

fore, been developed in recent years.

Dietary Significance

0017 Medical and nutritional dietary recommendations

currently emphasize decreased overall dietary fat

intake and lower saturated fat consumption. There

is generally significantly less total lipid associated

with meat from game animals than from domestic

livestock (Table 4). Substitution of game for meat

from domestic livestock in the diet often provides

consumers with a means of decreasing dietary energy

supplied by fat. At the same time, nutrient intake

associated with red meat consumption, including B-

vitamins, minerals, and high-quality protein, is main-

tained. Refer to individual nutrients.

0018 The fatty acid composition and cholesterol content

from game animal and beef lean muscle are shown in

Table 5. Species differences exist in amounts and

proportions of saturated, monounsaturated, and

polyunsaturated fatty acids in meat. Decreased diet-

ary intake of saturated fatty acids, particularly

myristic and palmitic acids, are associated with

lower blood serum cholesterol and, therefore, dimin-

ished risk of cardiovascular disease development.

Consumption of o-6 and o-3 polyunsaturated fatty

acids may lower blood serum cholesterol and protect

against coronary heart disease development. Game

meat is lower in saturated and higher in polyunsatur-

ated fatty acids than grain-fed beef. There are no wide

species-related difference in muscle cholesterol con-

tent because cholesterol is present in both fat and lean

tissues as a component of cellular membranes. Meat

from small species is somewhat higher in cholesterol

partly because the decreased muscle fiber (cell) diam-

eter in these species favors increased cell membrane

mass relative to total muscle mass. (See Fatty Acids:

Properties.)

See also: Electrophoresis; Fatty Acids: Properties

Further Reading

Chapman JA and Feldhammer GA (eds) (1982) Wild

Mammals of North America: Biology, Management and

Economics. Baltimore: Johns Hopkins University Press.

Fennessy PF and Drew KR (eds) (1985) Biology of Deer

Production. Wellington: Royal Society of New Zealand.

Hudson RJ, Drew KR and Baskin LM (eds) (1989) Wildlife

Production Systems. Cambridge: Cambridge University

Press.

McCormick RJ, Moore TD, Field RA and Hepworth WG

(1988) Identification of deer meat cooked products.

Wildlife Society Bulletin 16: 433–436.

Patterson RLS (ed.) (1985) Biochemical Identification of

Meat Species. London: Elsevier.

tbl0005 Table 5 Lipid composition and cholesterol content of meat from selected game species and beef

a,b

Pronghornantelope Mule deer Elk Bison Grain-fedbeef Grass-fedbeef

Fatty acid (mg per 100 g)

Saturated

875 972 664 421 2028 933

Stearic 441 401 172 197 651 327

Myristic, palmitic 434 571 492 224 1377 606

Monounsaturated

582 732 508 444 2144 754

Polyunsaturated

530 463 399 182 291 191

o-6

442 359 343 156 275 139

o-3

88 104 56 26 16 52

Cholesterol (mg 100 g

1

)52 54 4845 48 49

Uncooked, lean only.

Miller GJ, Field RA, Riley ML and Williams JC (1986) Lipids in wild ruminant animals and steers. Journal of Food Quality 9: 331–343.

Myristic, palmitic and stearic acids.

Palmitoleic and oleic acids.

Linoleic, arachidonic and linolenic acids.

Linoleic and arachidonic acids.

Linolenic acid.

2860 GAME/Mammals

GARLIC

H Amagase and B L Petesch, Wakunaga of America

Co Ltd, Mission Viejo, CA, USA

Introduction

0001 Garlic is a very well-researched herb with centuries of

culinary and medicinal uses. This powerful herb

appears in the historical writings of numerous cul-

tures. This article touches on the cultivation, history,

chemistry, pharmacology, and safety of garlic.

Cultivation

0002 Garlic, or Allium sativum, is a member of the lily

family. It is a perennial, which is usually grown as

an annual. A typical plant consists of one large bulb

made up of numerous small cloves. The word ‘clove’

came from the word ‘cleave’ which means both to

cling together and to divide along natural lines. Garlic

is typically planted in autumn and harvested about 8

months later in the summer. Various cultivars can

grow under an array of climates, temperatures, rain-

fall, and soil types.

Historical Effects

0003 Garlic has been utilized as a medicinal for centuries.

References to this herb have been recorded in the Old

Testament of the Bible, the Codex Ebers, an ancient

Egyptian medical volume, Shin ching, the Chinese

Book of Songs, and in medical texts of Sumeria,

considered to be the world’s oldest pharmacopeia.

From pharaohs to pharmacies, it is known as the

king of the herbs and with more than 2000 scientific

publications in the last century alone, it has rightly

earned and maintained such a title. A plethora of

recent research has confirmed many of the empirical

usages of garlic for medicinal purposes. Some of the

historical usages of garlic have included remedies for

heart problems, headaches, coughs and colds, snake

and insect bites, asthma, arthritis, hair growth,

worms, respiratory ailments, digestive disturbances,

toothaches, and tumors.

0004 Garlic has been used as a poultice to treat respira-

tory conditions. Since many of its sulfur compounds

are modified in the intestinal tract, this was a

means of introducing salubrious compounds into the

blood stream, as confirmed by garlic breath noted

after topical administration. However, careless

administration without an adequate vehicle (thick

layer of Vaseline) added to the feet prior to adminis-

tration has led to severe secondary chemical burns.

0005Tales of garlic as a cure for the great plagues

were passed along and written about for several cen-

turies. It was recommended more for protection

rather than for actual treatment of the disease. Garlic

was coined as ‘Russian penicillin’ due to its potent

antibiotic effects. During both world wars it was used

to prevent wounds from growing gangrenous. How-

ever, since it can also induce chemical burns, and

more practical and effective antibiotics have since

been developed, this usage has mostly been aban-

doned.

0006Historical interest in garlic has led to extensive

research to test its pharmacological effects, resulting

in more than 1000 publications over the past decade

alone.

Garlic Chemistry

0007Garlic is quite a complex herb. It is well known with

its characteristic odor. Garlic has many intrinsic spe-

cific enzymes and chemical constituents that cause a

specific odor by crushing the garlic cloves. This odor

comes from allicin and decomposes to other com-

pounds instantly. Allicin thus appears to be a transi-

ent compound to many of the other sulfur compounds

in garlic. It has shown potent antimicrobial effects

against even pathogenic and resistant microorgan-

isms in testtubes. However, it is extremely unstable

and not bioavailable, absorbed from the intestinal

tract, so its testtube effects may not be demonstrated

in the body upon consumption. Further, its toxicity is

rather high (LD

in mg kg

1

body weight in mice is

309 in males and 363 in females). It is converted

mainly into diallyl disulfide and allylmercaptan in

the body. Diallyl disulfide, an oil-soluble compound,

has shown remarkable anticancer potential in an

array of studies; however, its toxicity is even higher

(LD

in mg kg

1

body weight in mice is 145 in males

and 130 in females) than allicin. Chemically garlic is

best known for its characteristic sulfur compounds,

possessing more than 200 kinds, many of which have

scientifically documented pharmacological effects.

The water-soluble sulfur compounds derived from g-

glutamyl cysteine, such as S-allyl cysteine (SAC), have

shown diversified pharmacological activities with

little or no toxicity (LD

of SAC in mg kg

1

body

weight in mice is 8890 in males and 9390 in females).

Further, they are much more stable and have demon-

strated bioavailability in both preclinical and clinical

GARLIC 2861

studies. Garlic also contains nonsulfur compounds

with pharmacological effects. A protein fraction,

identified in aged garlic extract, has been shown to

enhance immune function, nerve growth, to combat

cancer, and enhance the growth of friendly bacteria.

Steroidal glycosides or saponins in garlic have dem-

onstrated cardioprotective and antifungal activities.

And various minerals, such as selenium, germaninum,

calcium, copper, iron, and vitamins such as A, B

,and

C, are found in this herb. In fact, garlic is one of the

richest sources of selenium. Though garlic is not a

rich source of protein, it does contain an array of

amino acids.

Pharmacology

Cardiovascular Effects

0008 Extensive research has suggested that garlic intake

may reduce various cardiovascular disease risk

factors. Randomized, placebo-controlled, double-

blind clinical studies have shown modest reductions

in elevated blood lipids or fats, such as serum choles-

terol, low-density lipoprotein (LDL) cholesterol and

triglycerides, and elevated blood pressure. Though

the effects are not as pronounced as those of medica-

tions designed specifically for such ailments, the side-

effects are also nominal or nonexistent, unlike their

drug counterparts. Further, garlic is more versatile in

its effects on the heart than drugs designed merely to

lower blood pressure or lower blood lipids. Garlic has

been shown not only to reduce elevated blood lipids,

but some studies have even shown an improvement

in high-density lipoprotein (HDL)-cholesterol. How-

ever, some recent studies utilizing garlic powders and

oil have shown no effect on cholesterol, so that stand-

ardization of garlic products for effective active ingre-

dients appears to be relevant. Of greater concern than

elevated lipids may be their oxidation. Recent work

has shown that extracted garlic may prevent the oxi-

dation of blood fats, reducing their ability to adhere

to and damage the veins. Garlic has also been shown

to reduce the build-up of plaque in the arteries in-

duced by a high-cholesterol diet, as shown in athero-

genic models.

0009 Garlic has shown blood-thinning effects, such as

inhibiting platelet aggregation and adhesion. These

effects have been demonstrated in testtubes and in

humans. Thermography has confirmed the ability of

garlic to enhance peripheral circulation in humans

within 90 min of its intake.

0010 Garlic has also recently been reported to suppress

the elevated level of homocysteine, a strong indicator

of atherosclerosis, further heart attack, stroke or any

kind of stenosis. Thus, garlic has many beneficial

effects on the cardiovascular system to reduce mul-

tiple risk factors of this disease.

Immune-Enhancing Effects

0011Garlic has been shown to mitigate infectious

diseases through enhancement of the immune

system. It has been found to enhance various immune

factors such as the phagocyte (cell-killing) activity

of macrophages, T-lymphocyte activity, natural

killer cell activity, and antibody generation. It has

also demonstrated antiviral and antifungal activities.

Further, it has been shown to modify, both directly

and indirectly, the function of immune cells which

play a leading role in allergic cascade reactions,

including inflammation. Garlic has also been shown

to improve age-related deterioration of the immune

response.

0012Clinical studies have shown that both raw garlic

and especially aged garlic extract significantly en-

hance natural killer cell activity in normal subjects.

In a clinical study done on acquired immunodefi-

ciency syndrome (AIDS) patients, who have poor

immune function, aged garlic extract was shown to

bring natural killer cell activity to normal within only

6 weeks of oral intake. Subjects also experienced

improvement in subjective symptoms such as candi-

diasis and pansinusitus.

Antimicrobial Effects

0013In testtubes, garlic and some of its constituents have

shown potent antimicrobial effects against even

pathogenic and resistant microorganisms. Fresh raw

garlic and its constituents have been shown to kill

Escherichia coli, Salmonella enteritidis, S. typhimur-

ium, Staphylococcus aureus and S. vulgaris, Shigella

dysenteriae, S. flexneri, S. sonnei, Mycobacterium

tuberculosis, Giardia lamblia, Helicobacter pylori,

Entamoeba histolytica, and other organisms. How-

ever, few clinical studies have been done in regards to

such antiinfectious effects and some of the effective

compounds may not be absorbed from the intestinal

tract. Quality research still needs to be done in this

area to confirm an effect in humans.

0014Garlic has demonstrated antifungal effects against

Candida albicans, Aspergillus niger, Cryptococcus

neoformans, Coccidiodes immitis, Epidermophyton,

Trichophyton, and other fungi. Candida albicans is

responsible for secondary yeast infections that often

occur after intake of antibiotics. Aged garlic extract

was shown to reduce candidiasis, or systemic Can-

dida albicans infections, in AIDS patients.

0015Antiviral effects have also been noted against

herpes simplex and influenza. Orally and topically,

aged garlic extract has been utilized for genital

herpes.

2862 GARLIC

Anticancer Effects

0016 A great deal of epidemiological, chemopreventive, and

other research has been done in the area of cancer.

Various epidemiological studies conducted in China,

Italy, and the USA have shown an inverse relationship

between garlic intake and stomach and colon cancer.

Various cell culture studies have suggested that com-

pounds in garlic may inhibit the growth of human breast

cancer cells, several human melanoma cells, and neuro-

blastoma cells. Aged garlic extract has been shown to

inhibit the growth of breast cancer, bladder cancer, skin

cancer, colon cancer, the development of esophageal

tumors, and stomach and lung tumors in animal models.

The anticarcinogenic effects of garlic are believed to be

due to its ability to reduce the rate of activation of

chemical carcinogens, that is, preventing the conversion

of inactive cancer-causing agents into active ones; its

ability to enhance the rate of chemical carcinogen excre-

tion, to protect DNA from carcinogen-DNA adduct

formation, to enhance enzymes that detoxify carcino-

gens, and to suppress tumor cell growth through stimu-

lation of immunoresponder cells. Garlic compounds,

injected into cancerous tumors, have resulted in immune

cells more aggressively attacking the tumor. Oral intake

of garlic has been shown to enhance the activity of

various immune cells.

0017 Studies have also suggested that garlic may be a

promising adjuvant to cancer therapy. Aged garlic

extract was shown to reduce side-effects such as fa-

tigue and anorexia in head-and-neck tumor patients

on radio- and chemotherapy and to reduce the cardi-

otoxicity of the potent anticancer drug doxorubicin/

Adriamycin. Aged garlic extract has also been shown

to reduce the intestinal damage caused by the anti-

cancer drugs 5-fluorouracil and methotrexate, sug-

gesting that garlic should be included in an overall

strategy to reduce/prevent cancer.

Liver Protection

0018 Aged garlic extract and some of its water-soluble

compounds, including S-allyl cysteine and S-allyl

mercaptocysteine, have shown significant liver-

protective effects against an array of liver toxins,

including carbon tetrachloride, aflatoxin B

, acet-

aminophen (paracetamol), and others. The protective

effects appear to be due to the enhancement of de-

toxifying phase II enzymes, such as the glutathione-

related enzymes. Enhancement of glutathione level by

aged garlic extract has been demonstrated in both

testtubes and humans.

Other Potential Effects

0019 Recent research has demonstrated antiaging and neu-

rovascular support from garlic and its constituents.

Compounds in garlic have been shown to enhance

memory in genetically age-accelerated rodents with

learning deficits (used for Alzheimer models). Garlic

has also been shown to prolong their life span. En-

hanced nerve growth and branching have been dem-

onstrated in culture. Garlic, specifically aged garlic

extract, has been shown to protect nerve cells from

oxidative damage caused by the accumulated neuro-

toxin beta-amyloid (Aß), which is a hallmark for

Alzheimer’s disease. One of the water-soluble sulfur

compounds, S-allyl cysteine, is found in the brain

after the consumption of garlic. This may suggest

that bioavailable compounds such as S-allyl cysteine

may work at the target sites of the body and can pass

the blood–brain barrier. Moderate but significant

ergogenic or energy-enhancing and antistress

effects have been noted in athletes following intake

of garlic. Garlic has also been shown to reduce stress-

induced suppression of immune function and adrenal

hypertrophy.

Dosages

0020Various forms of garlic have shown health-enhancing

effects – from fresh garlic, cooked garlic, garlic oils,

garlic powders, to aged garlic extract. More than 250

studies have been conducted on aged garlic extract.

Some clinical studies have been done on garlic

powders that have shown both positive and no

effects. Thus, the efficacy of garlic powders, espe-

cially in regard to cholesterol reduction, is controver-

sial. The following are dosages used in various

studies:

Raw garlic 1–2 cloves (3000–6000 mg)

Garlic oil 2–5mg

Garlic powder 600–900 mg

Aged garlic extract 4 ml

1000–7200 mg (as dried form)

Safety

0021For the most part, garlic is quite a safe herb when

taken in reasonable amounts by appropriate means.

However, taking garlic as a preventive involves long-

term supplementation, which leads to the necessity of

consideration of the issue of toxicity. One of the

greater concerns associated with long-term garlic sup-

plementation is the general attitude of the public that

if a little of something is good for the body, a larger

quantity must be even better.

0022Although garlic has been safely used in cooking as a

popular condiment/flavoring and used traditionally

for medicinal purposes, it is commonly known that

excessive consumption of garlic can cause burning

GARLIC 2863

sensations and diarrhea. Excess intake of raw garlic

or garlic powders can cause the following adverse

effects/toxicity: stomach disorders and diarrhea;

decrease in serum protein and calcium; anemia;

bronchial asthma (via inhalation, seen from factory

workers); contact dermatitis (skin burns); and inhib-

ition of spermatogenesis. It appears that allicin and

some of its degraded compounds may be responsible

for some of the harmful effects of garlic, such as

anemia and skin burns. The oil-soluble sulfur com-

pounds in garlic have been shown to be much more

toxic than water-soluble compounds.

0023 Cooking can reduce the toxicity of garlic but also

eliminates its antimicrobial effects. Aging garlic by

long-term extraction, by reducing oil-soluble com-

pounds and increasing water-soluble compounds,

greatly reduces the toxicity of garlic so that even

large amounts can be and have been consumed safely.

Further, aging garlic improves its pharmacological

activity.

0024 Since garlic has shown potent antiplatelet or blood-

thinning activity, it is typically contraindicated with

Coumadin (sodium warfarin) or other anticoagulant

medications. However, a clinical study has shown

that aged garlic extract does not worsen the side-

effects of Coumadin in patients. Thus, unlike fresh

garlic or other forms of garlic, such as dehydrated

garlic powder, aged garlic extract does not have a

contraindication with medication.

0025 It may not be suitable for pregnant and nursing

women to consume a large amount of garlic products,

except aged garlic extract that is approved for those

women in Japan as a medication for nourishment

pregnant and nursing women.

Conclusions

0026 Garlic is a unique herb loved the world over for

centuries. The odorous compounds were formerly

believed to be responsible for its beneficial effects.

However, recently numerous nonodorous compounds

in garlic have been discovered which have potent

pharmacological activity. Recent clinical studies sup-

port many of the historical usages of garlic, suggest-

ing that its long-term intake may reduce many risk

factors for various diseases.

See also: Aflatoxins; Cancer: Carcinogens in the Food

Chain; Diet in Cancer Prevention; Cholesterol: Factors

Determining Blood Cholesterol Levels; Role of

Cholesterol in Heart Disease; Coronary Heart Disease:

Antioxidant Status; Liver: Nutritional Management of

Liver and Biliary Disorders

Further Reading

Bradley PR (ed.) (1992) British Herbal Compendium. A

Handbook of Scientific Information on Widely Used

Plant Drugs, vol. 1, pp. 105–108. Bournemouth, UK:

British Herbal Medicine Association, Scientific Com-

mittee.

Ho C-T and Zheng QY (eds) (2001) Quality Management

of Nutraceuticals. ACS Symposium Series 803. Washing-

ton, DC: American Chemical Society.

Ho CT, Osawa T, Huang MT and Rosen RT (eds) (1994)

Food Phytochemicals for Cancer Prevention II. Teas,

Spices, and Herbs. ACS Symposium Series 547. Wash-

ington, DC: American Chemical Society.

Huang MT, Osawa T, Ho CT and Rosen RT (eds) Food

Phytochemicals for Cancer Prevention I. Fruits and

Vegetables. ACS Symposium Series 546. Washington,

DC: American Chemical Society.

Lachance PA (1997) Nutraceuticals: Designer Foods III–

Garlic, Soy and Licorice. Trumball, Connecticut: Food

and Nutrition Press.

Lau B (1997) Garlic and You: The Modern Medicine. Van-

couver, Canada: Apple.

Mathew B (1996) A Review of Allium Section Allium. Kew,

UK: Royal Botanic Gardens.

Moyers S (1996) Garlic in Health, History, and World

Cuisine. St. Petersburg, Florida: Suncoast Press.

Saito H (2000) Garlic Science. Tokyo, Japan: Asakura

Shoten.

Shahidi F and Ho CT (2000) Phytochemicals and Phyto-

pharmaceuticals. Champaign, Illinois: AOCS Press.

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Gas Chromatography See Chromatography: Principles; Thin-layer Chromatography; High-

performance Liquid Chromatography; Gas Chromatography; Supercritical Fluid Chromatography; Combined

Chromatography and Mass Spectrometry

Geese See Poultry: Chicken; Ducks and Geese; Turkey

2864 GARLIC

GELATIN

P Harris, V Normand and I T Norton, Unilever

Research Laboratory, Sharnbrook, Bedford, UK

Introduction

0001 Gelatin is a nutritious protein containing essential

amino acids and is derived from collagen present in

the skin and bones of animals. The main food use

for gelatin is as a gelling agent for ready-to-eat prod-

ucts residing in the refrigerator (e.g., mousse, trifles,

etc.). Other uses are as a dry ingredient (crystal table

jellies) or in a highly concentrated gel form (fruit

pastilles, marshmallow). More gelatin is sold to the

food industry than any other gelling agent; it is rela-

tively cheap to produce in quantity, and there is a

ready supply of suitable raw material. This article

will review the source, manufacture, and properties

of gelatin.

Collagen

Occurrence

0002 Collagen is an important component of skin and

bones, and constitutes as much as 30% of total

human protein, with similar proportions being found

in many other animals. It is widespread in both

vertebrates and invertebrates, differing somewhat in

amino acid composition, but providing the same

function-strength and support for the tissues and

organs of the animal concerned.

Structure

0003 The collagen molecule exists as a triple helix compris-

ing three discrete a-chains stabilized by hydrogen

bonding. It is characterized by high percentages of

glycine (33%), and the imino acids proline and

hydroxyproline (22%).

0004 At least 10 collagen types have been identified and

another four tentatively recorded on the basis of dif-

ferences in the three a-chains; the best known are

types I and III, from which all commercial gelatins

are produced.

0005 The molecular weight of collagen is around

285 kDa, and that of the a-chains 95 kDa.

0006 In most tissues, collagen is arranged in bundles of

four or five molecules to form structures known as

fibrils. These are further associated with other fibrils

nearby to form further bundles of larger diameter.

These fibrils are stabilized by the formation of

intermolecular cross-links formed from lysine or

hydroxylysine residues; the degree of this cross-

linking increases with maturity of the animal.

Gelatin

Manufacture

0007Three types of gelatin are available commercially –

ossein (from bones), bovine hide, and pigskin. Gelatin

is extracted from collagen by a controlled acid or

alkali hydrolysis. The source, age, and type of colla-

gen each influence the properties of the gelatins

derived from them. The following steps make up

the manufacturing process:

0008Washing Initial washing of the starting raw material

removes impurities; this step also includes degreasing

and demineralization of bones to produce ossein.

0009Pretreatment The pretreatment process is designed

to convert collagen into a form suitable for extrac-

tion. To achieve this, a sufficient number of covalent

cross-links in the collagen must be broken in order to

enable the release of free a-chains. The process is also

designed to remove other naturally occurring organic

substances such as proteoglycan, blood, mucins,

and sugars. Pretreatments are optimized by each

manufacturer to give the required physical and chem-

ical properties to the gelatins that are produced. The

degree of collagen cross-linking governs the pretreat-

ment process required for gelatin manufacture. In

young fetal tissues, the concentration of cross-links

is at a minimum, and much of the collagen is soluble

in mild acid or salt buffer. As collagen matures, the

proportion of soluble fraction (procollagen) reduces

markedly as cross-linking progresses. To convert in-

soluble collagen into soluble gelatine three processes

are in current use:

0010Acid pretreatments leading to acid process type A

gelatins.

0011Alkaline or basic pretreatments leading to alkaline

process or type B gelatins.

0012Acid pretreatment processes, which are less

aggressive than those using alkali, are applied

to pigskin and fresh ossein from young animals.

Alkaline pretreatment processes are normally

applied to bovine hide and ossein.

GELATIN 2865

0013 Extraction The extraction process is designed to

obtain the maximum yield by optimizing the balance

between pH, temperature, and the extraction time. In

practice, gelatin is obtained from the raw material in

three or four separate extractions, each at an increasing

temperature. Typical values are 55



C for the first ex-

traction, 60



Cforthesecond,70



C for the third, and

80–90



C for the final extraction, each giving gelatins

of decreasing gel strength, viscosity, and increasing

color. The simplest result of the denaturation is solubil-

ization of the a-chain, however, the denaturation pro-

cess also leads to secondary products due to random

cleavage of single collagen molecules (small units). The

other important point to remember is that hydrolysis is

sometimes incomplete, leaving covalent bonds between

molecules. When two or three a-chains are linked to-

gether they are commonly called b-andg-chains, and

when more then three chains are covalently linked, the

macromolecules form what are known as microgels.

The molecular distribution produced from any extrac-

tion can be divided into three broad molecular weight

classes: small units, a þ b þ g, and microgels. As the

extraction number increases, the fraction of a þ b þ g

chains decreases, the fraction of small units increases,

and the fraction of microgels decreases.

0014 Purification Following extraction, the gelatins are

filtered to remove suspended insolubles such as fat

or unextracted collagen fibers. The gelatin is further

purified by deionization which both removes inor-

ganic salts left from pretreatment and also adjusts

the pH to that suitable for sale. Most commercial

gelatins are sold in the pH range 5.0–5.8.

0015 Concentration The final stage is evaporation, steril-

ization, and drying. These are performed as quickly as

possible to minimize loss of properties; after this the

gelatins are subjected to laboratory testing for their

physical and bacteriological characteristics.

Structure

0016 The primary structure of gelatin closely resembles the

parent collagen. Small differences are due to raw

material sources together with pretreatment and

extraction procedures.

0017 These can be summarized as: (1) Partial removal of

amide groups of asparagine and glutamine resulting in

an increase in the aspartic and glutamic acid content;

and (2) conversion of arginine to ornithine during pro-

longed alkali pretreatment processes. Typical amino

acid composition data of gelatins are shown in Table 1.

Properties

0018 Commercial gelatins consist of gelatin protein in a

high state of purity; the nonproteinaceous matter

present is mainly mineral ash and residual moisture.

The only additive sometimes incorporated during

manufacture is sulfur dioxide, used as a color inhibi-

tor during extraction and evaporation and not as a

preservative. There is also a small proportion of

carbohydrate (1–1.5%) in the form of glucose and

galactose bound to gelatine at hydroxylysine residues.

0019The main gelatin properties of interest to food

users are:

0020Bloom value, which is a function of the gel

strength.

0021Viscosity, which gives a measure of the solution

properties.

0022Surface activity or polyelectrolyte properties.

These main properties will be discussed in more detail

later.

0023Other properties which are important are as

follows.

0024Particle size and solubility Gelatin, although insol-

uble in cold water and other liquids such as milk,

sugar solution, dilute food acids, etc., will swell and

absorb up to 10 times its weight in water, the rate of

which is dependent on particle size. Swelling charac-

teristics in cold water are determined by temperature

and salt or sugar content of the liquid, all of which

can affect the rate of water uptake.

0025Isoelectric and isoionic points The isoelectric point

is defined as the pH at which no net migration takes

place in an electric field, while the isoionic point is

defined as the pH at which there is no net charge on

tbl0001Table 1 Average amino acid distribution for the three a-chains

found in the collagen precursors of gelatin

Residue Residues per 1000 residues

3-Hydroxyproline 1

4-Hydroxyproline 108

Proline 115

Lysine 25

Hydroxylysine 9

Glycine 340

Cysteine 0

Serine 34

Alanine 104

Histidine 7

Valine 23

Methionine 7

Isoleucine 11

Leucine 24

Arginine 49

Phenylalanine 11

Aspartic acid 42

Threonine 16

Glutamic acid 71

Tyrosine 3

2866 GELATIN

the molecule. In a deionized solution, the isoelectric

and isoionic points are for most purposes identical.

0026 The isoelectric point of gelatine is dependent on the

type of pretreatment applied during manufacture.

Type A or acid-processed gelatins have isoelectric

points that can vary from 6.5 to 9.0. Acid ossein

gelatins are at the lower end of the range with isoelec-

tric point values of 6.5–7.5, while acid pigskin is more

likely to have values from 7.5 to 9.0.

0027 Many physical properties of gelatine have either a

minimum or a maximum at the isoelectric point. This

means that acid- and alkali-derived gelatines can

sometimes perform quite differently in the same

system.

Solution Properties

0028 Typical commercial gelatins tend not to find use as

thickening agents due to their relatively low specific

viscosity (Z

< 60 m.ps., @ 6.66) as there are more

efficient polysaccharides available for this purpose.

Instead, gelatins in the liquid phase can be used for

their surface-active properties, either as a stabilizer

and emulsifier or as a polyelectrolyte.

0029 Higher-viscosity gelatins will give higher melting

temperatures and somewhat quicker setting times,

while those of lower viscosity can be prepared in a

much higher concentration without causing problems

due to tailing when depositing in molds.

0030 A solution of gelatin in water will possess a viscos-

ity or thickening power proportional to its concen-

tration, pH, ionic strength, and the specific viscosity

of the gelatin itself. The relationship of viscosity with

concentration is not directly proportional but is

approximately logarithmic. There is a straight-line

dependence for log viscosity with the reciprocal of

absolute temperature. The viscosity is always at a

minimum at the isoelectric point, and increases as

the overall charge on the molecule is increased.

Gel Properties

0031 Preparation of a gel The gelatin is first dispersed in

cold water (never the reverse) and allowed to swell.

The dispersion is then heated to 50–60



C and the

resultant solution allowed to cool without agitation.

A gel is formed at temperatures below about 25



depending on the type of gelatin used and its concen-

tration. The critical concentration for a gelatin gel to

form is approximately 1% w/w.

0032 Mechanism of gel formation When a solution of

gelatin is hot (> 65



C), it exists as near to random

coil chains. As the solution is cooled, the chains lose

some of their mobility and start to order locally as

segments: on further cooling, these ordered segments

associate into triple helices. The site where this

association takes place is referred to as cross-link or

junction zone. The structure of these junction zones is

similar to that of the native collagen. When sufficient

junction zones are formed, a three-dimensional net-

work or gel is produced. The gelation kinetics can be

divided into two phases:

0033During the first hour, the gel strength increases

rapidly. The reinforcement of the network is be-

lieved to be mainly due to formation of new cross-

links.

0034From 1 h to several hundred hours, the gel strength

increase slows down and is linear with the loga-

rithm of time. The reinforcement of the network is

believed to be due to the extension of existing

cross-links rather than the formation of new ones.

0035The exact nature of the junction zones is still under

investigation, although it has been shown that (GLY-

PRO-HYP) triplets are involved. Hydrogen bonding

takes place between the amino acids and nearby C–H

groups, e.g., on glycine found on adjacent chains. (It

is well known that hydrogen bond breakers, such as

thiocyanate or urea, can prevent gelation.)

0036The equilibrium of junction zone formation and

breakage moves to create a dynamic gel structure as

the temperature of the solution approaches the setting

point. At this stage, the larger branched molecules

(microgels) begin to grow via junction zone forma-

tion with other smaller a- þ b- þ g-chains. The con-

densation reaction corresponds to a second-order

reaction, even if triple helices are formed. This has

been visualized microscopically, which suggests that

an a-chain loops back on to itself and then reacts with

a second a-chain to form a triple helix involving just

two chains and the junction zone has four free ends.

The current thinking is that the elasticity of gelatin

gels comes from the relatively free rotation of the

segments before these junction zones.

Measurement of Gel Strength

0037The gel strength of gelatin is nearly always quoted

commercially as the Bloom strength. The Bloom

value of gelatin is defined as the weight required to

push a cylindrical plunger of 12.7 mm diameter 4 mm

into a previously prepared gel of 6.66 w/w concen-

tration matured at 10



C for 16–18 h. Gel strength

determinations not performed under these strict con-

ditions cannot be quoted as Bloom strength.

0038To determine the gel strength, one of the following

three instruments can be used:

0039The lead shot gelometer, also known as the Bloom

gelometer.

0040The Boucher gelometer.

0041The Stevens-LFRA texture analyzer.

GELATIN 2867