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

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0015 Hypertension Elevated levels of both systolic and

diastolic blood pressure (blood pressure 140/

90 mmHg) are associated with increased risk of

developing atherosclerosis. The relationship appears

to be linear. Recent evidence has confirmed that

sodium restriction is an efficacious dietary approach

to reducing blood pressure. In addition, compared to

more conventional dietary patterns of developed

countries, diets high in fruits, vegetables, and low-

fat dairy products have also recently been demon-

strated to result in lower blood pressures in both

normotensive and hypertensive subjects.

0016 Low HDL Cholesterol Levels HDL cholesterol

levels are inversely correlated with the risk of de-

veloping atherosclerosis. HDL particles are involved

in the process of reverse cholesterol transport, the

only means by which cholesterol in peripheral tissues

can be transported to the liver for metabolism and

excretion from the body. Low HDL cholesterol levels

(< 1.03 mmol l

1

) are a risk factor for the develop-

ment of atherosclerosis. High HDL cholesterol levels

(> 1.6 mmol l

1

) have been designated a negative

risk factor (to be subtracted from the total number

of risk factors when ascertaining an individual’s risk

profile) (Table 2). It is more difficult to raise HDL

cholesterol levels than lower LDL cholesterol levels

with nonpharmacological intervention. Common

approaches are increased exercise, cessation of

smoking, weight loss, and moderate alcohol intake.

The magnitude of each intervention varies between

individuals.

0017 Diabetes mellitus Atherosclerosis is the most

common cause of death in diabetic patients. Individ-

uals with diabetes frequently have what is commonly

referred to as an atherogenic lipoprotein profile: low

HDL cholesterol levels and elevated triglyceride

levels. In addition, insulin resistance, hyperinsulin-

emia, and glucose intolerance have been found to

be atherogenic. Some evidence suggests that the

increased risk of developing atherosclerosis observed

in diabetic patients is contributed to by both the

adverse lipoprotein profile and hyperinsulinemia

itself. Adult-onset diabetic patients (type II) fre-

quently present with a combination of obesity,

adverse lipoprotein profile, and elevated blood

pressure. This combination is frequently termed the

‘insulin resistance syndrome’ and is strongly associ-

ated with increased risk of developing atherosclerosis.

Weight loss, in addition to the other dietary and

lifestyle approaches to decreasing atherosclerosis

risk, is among the most efficacious modalities of

treating these patients.

Secondary Risk Factors

0018Certain risk factors are informally referred to as sec-

ondary risk factors, either because they are thought to

be a consequence of a primary risk factor or due to

insufficient evidence to classify them as a primary risk

factor at the current time. The following gives details

of some of these. As new data are accumulated, some

may in the future shift from one category to another.

Obesity

0019Increased body weight for height is associated with

various primary risk factors for atherosclerosis. These

include hypertension, elevated LDL cholesterol levels,

and low HDL cholesterol levels. Additionally, central

or abdominal obesity is more strongly related to in-

creased risk of developing atherosclerosis than over-

weight alone. When treating overweight patients

cessation of weight gain should be the first goal and

then a slow gradual approach to weight loss that

combines energy restriction with increased energy

output should be the second goal. Emphasis should

be on permanent lifelong changes rather than drastic

approaches.

Physical Inactivity

0020Physical inactivity has been associated with increas-

ed risk of developing atherosclerosis. It is difficult

to determine whether physical fitness itself is the

determining factor or whether individuals who habit-

ually have low levels of physical activity also have

a greater number of risk factors for atherosclerosis

(i.e., obesity, hypertension, insulin resistance) that

contribute to the clinical outcome. Regardless of the

relationship, increased levels of physical activity

should be encouraged. Currently, a number of health

organizations are emphasizing the importance of

maintaining a physically active lifestyle throughout

the life cycle as a means of decreasing the risk of

developing atherosclerosis and other degenerative

diseases.

Elevated Homocysteine Levels

0021Homocysteine is a metabolite of methionine, an

essential amino acid. Elevated homocysteine levels

have been associated with an increased incidence of

atherosclerosis. High levels of homocysteine can

result from deficiencies in folic acid and vitamins B

and B

. Since 1998 the USA has mandated that folic

acid be added to all grain products. As a result there

has been a secular decrease in homocysteine levels.

There are ongoing studies to determine whether the

decline in homocysteine levels due to folic acid sup-

plementation or fortification will result in decreased

rates of vascular disease.

344 ATHEROSCLEROSIS

Lp(a)

0022 Lp(a) is a lipoprotein particle formed by the addition

of a carbohydrate-rich protein (apolipoprotein;

apo(a)) via a disulfide bond to apo B-100 on an

LDL particle. High levels of Lp(a) are associated

with an increased risk of developing atherosclerosis.

There is a high degree of homology between Lp(a)

and plasminogen. Plasminogen is converted to plas-

min in plasma. Plasmin functions by dissolving blood

clots. It has been hypothesized that high levels of

Lp(a) compete with plasminogen, counteracting the

fibrinolytic system, and increasing the risk of throm-

bosis. Whether Lp(a) levels are an independent risk

factor for atherosclerosis have yet to be determined.

Lp(a) levels are, for the most part, determined by

genetics. Although dietary modification, hormone re-

placement therapy, and some lipids-lowering medica-

tions have been reported to alter Lp(a) levels, the

changes tend to be small and, although statistically

significant, may not be of a great enough magnitude

to have a physiologically significant effect. More

work in this area is likely to emerge in the near future.

Inflammation

0023 Recent interest has centered on markers of inflamma-

tory response, such as C-reactive protein and the risk

of developing atherosclerosis. Epidemiological

studies have noted an association between C-reactive

protein and risk of an atherosclerotic event in appar-

ently healthy males and those with a history of a prior

event. Again, at this point it is premature to designate

C-reactive protein as a primary risk factor for athero-

sclerosis. However, the results of future work will

likely cause the issue to be revisited.

Dietary Modification to Decrease Risk of

Developing Atherosclerosis

Diet

0024Current recommendations (individuals over the age

of 2 years) to decrease the risk of developing athero-

sclerosis are to limit fat intake to 25–35 of energy,

saturated fat to < 7% of energy, and cholesterol to less

than 200 mg day

1

. This diet is termed a therapeutic

lifestyle change (TLC) diet. Additional lifestyle rec-

ommendations include maintenance of body weight

and regular physical activity. Table 6 includes the

commonly occurring fatty acids, in both the body

and food.

0025Saturated fatty acids Early evidence has clearly

demonstrated that the consumption of foods rela-

tively high in saturated fatty acids increases serum

total cholesterol levels and that not all saturated

fatty acids behave in the same way. Relatively short-

chain fatty acids (C6:0 to C10:0) and stearic acid

(C18:0) produce little or no change in serum choles-

terol levels. Saturated fatty acids with chain lengths of

C14:0, C16:0, and possibly C12:0 appear to be the

most potent in increasing serum lipid levels. It has

been postulated that stearic acid (18:0) is rapidly

converted to oleic acid (18:1) and for this reason has

a relatively neutral effect on plasma lipid levels. Sub-

sequent work has further refined what is known

about the hypercholesterolemia effect of saturated

fatty acids. Dietary saturated fatty acids result in an

increase in both LDL cholesterol and HDL choles-

terol levels with little or no effect on triglyceride

levels.

tbl0007 Table 6 Common fatty acids

Code Common name Formula

Saturated

12:0 Lauric acid CH

(CH

)

COOH

14:0 Myristic acid CH

(CH

)

COOH

16:0 Palmitic acid CH

(CH

)

COOH

18:0 Stearic acid CH

(CH

)

COOH

Monounsaturated

16:1n-7 cis Palmitoleic acid CH

(CH

)

—

(c)CH(CH

)

COOH

18:1n-9 cis Oleic acid CH

(CH

)

—

(c)CH(CH

)

COOH

18:1n-9 trans Elaidic acid CH

(CH

)

—

(t)CH(CH

)

COOH

Polyunsaturated

18:2n-6,9 all cis Linoleic acid CH

(CH

)

—

(c)CHCH

—

(c)CH(CH

)

COOH

18:3n-3,6,9 all cis a-linolenic acid CH

—

(c)CHCH

—

(c)CHCH

—

(c)CH(CH

)

COOH

18:3n-6,9,12 all cis g-linolenic acid CH

(CH

)

—

(c)CHCH

—

(c)CHCH

—

(c)CH(CH

)

COOH

20:4n-6,9,12,15 all cis Arachidonic acid CH

(CH

)

—

(c)CHCH

—

(c)CHCH

—

(c)CHCH

—

(c)CH(CH

)

COOH

20:5n-3,6,9,12,15 all cis Eicosapentaenoic acid CH

(CH

—

(c)CH)

(CH

)

COOH

22:6n-3,6,9,12,15,18 all cis Docosahexaenoic acid CH

(CH

—

(c)CH)

(CH

)

COOH

c, cis;t,trans.

ATHEROSCLEROSIS 345

0026 Foods relatively high in saturated fatty acids in-

clude meat and full-fat dairy products. Saturated

fatty acids tend to be solid at room temperature.

The notable exceptions are the tropical oils; palm,

palm kernel, and coconut. Efforts to reduce saturated

fatty acid intake should include use of lean meat,

trimming of excess fat or the skin of poultry, and the

substitution of fat-free or low-fat dairy products for

their full-fat counterparts. Judicious use of ingredient

listings and nutrient labels on processed foods will

help individuals achieve the goal of reducing the

saturated fatty acid content of their diet.

0027 Omega-3 (n-3) polyunsaturated fatty acids Reports

of low rates of atherosclerosis in Greenland Eskimos

and the inverse relationship between fish consump-

tion and mortality from atherosclerosis raised interest

in oils derived from fish and marine mammals. These

oils, high in polyunsaturated fatty acids, are distin-

guished from other oils high in polyunsaturated fatty

acids, such as vegetable oils, by the presence of n-3

fatty acids. As a class, n-3 fatty acids are defined as

having a double bond at the third carbon from the

methyl end of the acyl chain. In contrast, the more

common n-6 fatty acids are defined as having a

double bond at the sixth carbon from the methyl

end of the acyl chain. Potential mechanisms of n-3

fatty acids in decreasing risk of developing athero-

sclerosis include decreased postprandial triglyceride

levels, reduced risk of arrhythmic events, decreased

blood pressure, altered endothelial function, and re-

lease of cytokines and other inflammatory mediators.

The relative importance of each of these factors to the

epidemiological observation of an inverse relation-

ship of atherosclerosis incidence and fish or n-3

fatty acid intake has yet to be determined. The

major dietary n-3 fatty acids from plant sources is

alpha-linolenic acid (18:3n-3) and from marine

sources are eicosapentaenoic acid (20:5n-3), and doc-

osahexaenoic acid (22:6n-3) (Table 6). The different

physiological effects of each is under active investi-

gation at this time.

0028 Trans fatty acids Trans fatty acids are fatty acids

that contain at least one double bond in the trans

configuration. Dietary trans fatty acids occur natur-

ally in meat and dairy products as a result of anaer-

obic bacterial fermentation in ruminant animals.

Trans fatty acids are also created when liquid vege-

table or fish oil is hydrogenated; this is frequently

done to increase their plasticity and chemical stability

for subsequent food processing. Trans fatty acids

raise LDL cholesterol levels, similarly to saturated

fatty acids. However, trans fatty acids do not raise

HDL cholesterol levels, as do saturated fatty acids.

For this reason there is concern that dietary trans fatty

acids are worse than saturated fatty acids. Addition-

ally, some literature suggests that trans fatty acids

may increase Lp(a) levels. Over the past decade it

appears that as a result of changes made by industry

the intake of trans fatty acids is decreasing. Due to the

considerably higher intake of saturated than trans

fatty acids it still seems prudent to maintain emphasis

on reducing saturated fat intake.

0029Dietary cholesterol In humans there is a positive

correlation between dietary cholesterol intake, and

both serum cholesterol levels and risk of developing

atherosclerosis. Interpretation of the dietary choles-

terol literature is complicated by the large degree of

variation among studies and the tendency for respon-

siveness to vary over a wider range than other dietary

variables. Nonetheless, the majority of evidence sup-

ports the premise that increased dietary cholesterol

intake results in increased LDL cholesterol levels. The

major sources of dietary cholesterol are eggs, meat,

and dairy products. Since dietary cholesterol is fre-

quently found in foods which are also relatively high

in saturated fatty acids, reducing the saturated fatty

acid intake should also result in a reduction in the

cholesterol content of the diet.

0030Soluble fiber Dietary soluble fiber has been reported

to have a modest hypocholesterolemic effect. A major

contributor to this outcome is the b-glucan fraction of

the soluble fiber. A variety of mechanisms have been

proposed for the cholesterol-lowering effect, most

likely relating to decreased absorption of cholesterol.

There is no evidence that insoluble fiber has an effect

on plasma lipid levels.

0031Dietary pattern It can be difficult for individuals,

however well intended, to modify their diet to meet

certain dietary goals, for example, to consume < 7%

of energy as saturated fat. However, with the excep-

tion of high-risk individuals who need more indi-

vidualized instruction provided by a qualified

professional, the general recommendation to con-

sume a diet high in fruits, vegetables, and whole

grain which also includes nonfat or low-fat dairy

products, fish, poultry, and lean meat is consistent

with the more technical recommendations and should

be consistently encouraged on a population-wide

basis. Additionally, it is important to couple such

dietary recommendations with a prescription that

further encourages a pattern of regular activity,

through the life cycle, that matches levels of physical

activity to energy intake with the expressed intent of

avoiding overweight or obesity.

346 ATHEROSCLEROSIS

Summary

0032 Atherosclerosis is a disorder of blood vessels charac-

terized by a thickening of the arterial wall. This pro-

cess frequently leads to partial or total occlusion of

the vessel to blood flow. The location of the impeded

or blocked blood flow determines the clinical conse-

quence of the disorder. A major contributing factor to

the development of atherosclerotic lesions is elevated

LDL cholesterol levels, followed by other risk factors.

The primary risk factors include advanced age, family

history of premature atherosclerosis, current cigarette

smoking, hypertension, lower HDL cholesterol levels

(high HDL cholesterol levels are classified as a nega-

tive risk factor), and diabetes mellitus. Sometimes

referred to as secondary risk factors, either because

they are thought to be a consequence of a primary risk

factor or due to lack of sufficient evidence to classify

them as a primary risk factor at the time, are obesity,

physical inactivity, elevated homocysteine levels,

elevated Lp(a) levels, and elevated inflammation

markers. With the intent of lowering LDL cholesterol

levels, the major dietary interventions are decreased

saturated fat, cholesterol, and trans fatty acid intakes,

and increased n-3 fatty acid intakes and soluble fiber.

These changes from the current diet of developed

countries can best be achieved by encouraging the

consumption of a diet high in fruits, vegetables, and

whole grain which also includes nonfat or low-fat

dairy products, fish, poultry, and lean meat. Add-

itionally, these recommendations should be coupled

with a pattern of regular activity that is matched to

energy intake to avoid overweight or obesity.

Seealso: Amino Acids:PropertiesandOccurrence;

Cholesterol:RoleofCholesterolinHeartDisease;

Coronary Heart Disease:EtiologyandRiskFactor;

Diabetes Mellitus:Etiology; Exercise:Metabolic

Requirements; Hypertension:HypertensionandDiet;

Obesity:EtiologyandDiagnosis; Smoking, Diet, and

Health; Fatty Acids:Trans-fattyAcids:HealthEffects

Further Reading

American Heart Association website. http://www.ameri-

canheart.org.

Benowitz NL (1997) The role of nicotine in smoking-

related cardiovascular disease. Preventive Medicine

26(4): 412–417.

Brown L, Rosner B, Willett WW and Sacks FM (1999)

Cholesterol-lowering effects of dietary fiber: a meta-

analysis. American Journal of Clinical Nutrition 69(1):

30–42.

de Valk B and Marx JJ (1999) Iron, atherosclerosis, and

ischemic heart disease. Archives of Internal Medicine

159(14): 1542–1548.

Hankey GJ and Eikelboom JW (1999) Homocysteine and

vascular disease. Lancet 354(9176): 407–413.

Hobbs HH and White AL (1999) Lipoprotein(a): intrigues

and insights. Current Opinion in Lipidology 10(3):

225–236.

Journal of the American Medical Association (2001) Ex-

ecutive Summary of the Third Report of the National

Cholesterol Education Program (NCEP) Expert Panel on

Detection, Evaluation, and Treatment of High Blood

Cholesterol in Adults (Adult Treatment Panel III). Jour-

nal of the American Medical Association 285(19): 2486–

2497.

Krauss RM, Eckel RH, Howard B et al. (2000) AHA Diet-

ary guidelines. Revision 2000: a statement for healthcare

professionals from the Nutrition Committee of the

American Heart Association. Circulation 102: 2296–

2311.

Kritchevsky D (1999) Diet and atherosclerosis. American

Heart Journal 138(5): S426–S430.

Ordovas JM and Schaefer EJ (1999) Genes, variation of

cholesterol and fat intake and serum lipids. Current

Opinion in Lipidology 10(1): 15–22.

Sacks FM, Svetkey LP, Vollmer WM et al. Effects on blood

pressure of reduced dietary sodium and the dietary

approaches to stop hypertension (DASH) diet. New

England Journal of Medicine 344: 3–10.

World Health Organization website. http://www.who.int.

Authenticity See Adulteration of Foods: History and Occurrence; Detection

ATHEROSCLEROSIS 347

AVOCADOS

A K Cowan, Stockholm, Sweden

B N Wolstenholme, University of Natal, Scottsville,

South Africa

Background

0001 The fruit of the avocado is regarded as one of the

most nutrient-dense fruits available. Although its

high oil content has been mistakenly thought of as a

disadvantage, closer scrutiny of the nutritional facts

reveals that avocado eaten in moderation does not

contribute to weight gain, contains large quantities

of the desirable unsaturated and monounsaturated

fatty acids, and is rich in fiber, protein, vitamins,

antioxidants, and minerals. This nutrient-rich fruit

is therefore without rival and, in many respects, a

veritable fruit of paradise.

0002 In this chapter, brief descriptions of avocado pro-

duction, emphasizing the ‘subtropical’ ecotype, and

processing are provided. These are followed by an

account of the nutritional status of avocado as a

food source. Data on nutrient, fat, vitamin, anti-

oxidant, mineral, and sugar content and composition

are supplied and are synthesized based on minimum

and maximum values published in the literature. The

nutritional benefit of a diet containing avocado is also

discussed. Reference is also made to the major aller-

gen in avocado that is relevant in the ‘latex-fruit

syndrome’ that affects latex-allergic individuals.

Avocado Fruit Production

History, Cultivation, and Fruit Growth

0003 Avocado originated in central America, and the fruit

has been consumed as part of the diet by the indigen-

ous peoples of that region for more than 5000 years.

The word ‘avocado’ derives from a corruption of

the Spanish words ‘ahuacate’ or ‘aguacate,’ which

are adaptations of the Aztec ‘ahuacatl.’ The fruit of

the first vegetatively propogated cultivar ‘Fuerte’ is

pear-shaped, and this characteristic probably resulted

in the inappropriate colloquialism, ‘avocado pear.’

However, the horticulturally and agriculturally cor-

rect term for the fruit is simply avocado.

0004 The botanical name for avocado is Persea

americana Mill., and three ecological races (today

regarded as botanical varieties or subspecies) are rec-

ognized; Persea americana var. drymifolia (Mexican

ecotype), Persea americana var. guatemalensis

(Guatemalan ecotype), and Persea americana var.

americana (West Indian ecotype). Fruits of the West

Indian ecotype are usually large with a thick peel and

have a low oil content (< 8%) and higher water and

sugar content. Trees of the Mexican ecotype yield

fruit with a high oil content (up to 30%). Those of

the Guatemalan ecotype are recognized as having the

most horticulturally desirable traits, have an inter-

mediate oil content, and are characterized by a

‘nutty’ flavor. Amongst the most important commer-

cial cultivars of the ‘subtropical’ avocado are ‘Hass,’

‘Fuerte,’‘Ettinger,’ and ‘Pinkerton,’ which, are all

chance seedlings with superior fruit quality. Several

countries have extensive selection and breeding pro-

grams which are starting to produce fruit of improved

quality. ‘Hass’ is the most sought after subtropical

cultivar, having almost eclipsed ‘Fuerte’ in California,

and forms the basis of the subtropical avocado export

industry to Europe.

0005The Mexican and Guatemalanm ecotypes, whose

progeny today form the basis of the technologically

advanced ‘subtropical’ avocado industries, are indi-

genous to subtropical and tropical highland climates.

So-called ‘West Indian’ avocados are lowland tropical

in origin. Mexico (by far the largest producer), Cali-

fornia, Israel, Spain, Chile, South Africa, and Austra-

lasia all have industries based on Guatemalan and

Guatemalan Mexican hybrid cultivars. However,

virtually all subtropical countries grow avocados to

some extent. Large crops of ‘West Indian’ and ‘West

Indian’ Guatemalan hybrid avocados are also pro-

duced in tropical countries, from less technologically

advanced industries. Tropical avocado industries,

with the conspicuous exception of Florida, USA, are

usually based on seedling (not grafted) trees. The

fruits, although making a substantial contribution to

the diets of mostly poor, tropical lowland peoples,

are horticulturally and nutritionally inferior to the

selected subtropical cultivars.

0006The avocado tree is evergreen and flowers in early

spring, and fruitlets are usually visible by late spring/

early summer. Typically, careful and correct orchard

management practise is required to ensure production

of quality fruit. Amongst the most important eco-

physiological factors that affect fruit production are

irradiance, temperature, water stress, and salinity.

Botanically, the fruit of the avocado is described as a

berry. Fruit growth continues for anything from 20 to

60 weeks, depending on the cultivar, environment,

and cultural practice, and the fruit is harvested

when horticulturally mature as it does not ripen on

the tree. Harvested fruit are washed, graded, often

348 AVOCADOS

waxed, and packed in cartons typically holding

4–6 kg of uniform fruit. European markets prefer

the individual fruit weight to be in the range of

200–350 g, for which higher prices are paid. It is

now known that the final fruit size of avocado is the

result of the number of cell divisions during flower set

and fruit growth and that cell division is dependent

on isoprenoid biosynthesis, carbohydrate metabol-

ism, and maintenance of plant hormone homeostasis.

Zinc, boron, magnesium, and calcium are considered

important elements in the production of quality fruit.

Nitrogen is a ‘manipulator element’ used to control

tree vigor, and must be appropriately managed as

excessive tree vigor is counterproductive to good

fruit quality.

Maturity

0007 Oil content and/or dry matter of the fleshy mesocarp,

which surrounds the single large seed, is used by most

producers to determine harvestable maturity and

consumer acceptability. For the cultivar ‘Fuerte,’ a

minimum oil content of 8% (dry mass) was applied

in California for many years, but today, this has been

replaced by a minimum dry matter standard of

c. 21%, depending on the cultivar and region. This

is based on the percentage moisture (determined

using a microwave oven), which is an indirect

measure of oil content based on the cultivar-specific

constant of the sum of percentage moisture and per-

centage oil. By 1983, percentage dry matter (or its

reciprocal, percentage moisture) had become stand-

ard for the determination of avocado fruit maturity

and is now used worldwide.

Ripening

0008 Avocado fruit are classified as climacteric (i.e., fruit

that can be harvested unripe and then undergo

normal ripening). Although detachment of the fruit

is not a prerequisite for ripening of most climacteric

fruit, avocado fruit do not ripen while attached to the

tree. Postharvest, the fruit ripen within 5–10 days at

temperatures between 15 and 24



C. Both ripening

and fruit softening are delayed by precooling the

fruit immediately after harvest to 5–6



C, and this

strategy is used by most producers to maintain fruit

quality during transport/export of fruit. A return to

ambient temperature after a period of cold storage

sees the acceleration of the ripening process. Ripening

in avocado can also be stimulated by exposure to the

plant hormone, ethylene.

0009 During ripening, the fruit undergoes marked

changes in a variety of biochemical processes. These

include an increase in respiration (i.e., consumption

of oxygen and release of carbon dioxide), increased

ethylene production, changes in texture (i.e., fruit

softening), and the production of volatiles such as

b-caryophyllene (28% of total volatiles), a-copaene

(11%), a/b-cubebene (8%), a-farnesene (6%), deca-

nal (6%), and heptanal (3%), which impart flavor.

The substrate for respiration in avocado appears to

be carbohydrate and not oil. However, some degrad-

ation of oils does take place. An increase in ethylene

biosynthesis is typical of climacteric fruits such as

avocado, and the maximum ethylene production usu-

ally coincides with the maximum respiration rate

(amount of carbon dioxide released). Cold storage

reduces this climacteric rise in respiration.

0010Fruit softening is a consequence of changes in cell-

wall metabolism resulting from alterations in cellu-

lase (EC 3.2.1.4), polygalacturonase (EC 3.2.1.15)

and pectinesterase (EC 3.1.1.11) activities. In some

varieties (e.g., ‘Hass’), the color of the peel changes

from green to purple/black owing to the accumula-

tion of anthocyanin pigments. Other changes include

a slight increase in the concentration of glucose and

fructose in the fruit flesh.

Processing of Avocado

0011Avocado is usually consumed fresh in salads, as a

savory dish, as a sandwich filling, as guacamole, or

sweetened as a dessert. It was the extraction of oils

from avocado and the production of guacamole that

really started avocado processing. Apparently, the

production of guacamole on a commercial scale was

started as long ago as 1964 in California, and

by 1981, 6000 tonnes of fresh avocado was being

processed annually.

0012For processing, the preferred cultivar is ‘Hass’ be-

cause of its superior flavor, mesocarp color, ‘keeping’

quality, and year-round availability. Fruit with a 25%

dry matter content (or 13% oil) are considered ideal

for processing. Avocado flesh is also marketed frozen,

processed into a sauce, dehydrated to a powder, and

extracted for its oil.

Guacamole, Avocado Sauce, and Oil

0013Before processing can take place, fruit are uniformly

ripened at 22



C in the presence of ethylene gas for

2–5 days. When the fruit are soft, they are cooled to



C and surface-sterilized in 200 mg of hypochlorite

per liter. After removal of the stems (pedicels) and

seed, the pulp (mesocarp) is mechanically separated

from the peel. The pulp is then mixed with the ingre-

dients (usually includes lime or lemon juice, salt, and

salsa or Picante) to yield a uniform textured guaca-

mole. The guacamole is then placed in containers and

stored frozen.

AVOCADOS 349

0014 The process for the production of avocado sauce is

similar to that used for the preparation of guacamole

up to pulp extraction. For sauce, the pulp is sheared in

a high-speed blender with water, emulsifiers, and

spices. Sauces are usually packaged in polyethylene

containers and then stored frozen.

0015 Dehydration of avocado is either by spray- or

drum-drying in much the same way as for the prepar-

ation of milk powder, but the product is less attractive

than that of sugar-storing fruits.

0016 Oil is extracted from avocado with organic solv-

ents, hydraulically (pressing), or by centrifugation.

The last method is more desirable as the product is

free from solvent residue. Nevertheless, solvent ex-

traction enables the extraction of various fractions,

some of which are used in the pharmaceutical indus-

try. For example, avocado unsaponifiables (including

hydrocarbons, tocopherols, triterpenes, sterols, and

other unidentified compounds), which seem to be

beneficial in the treatment of periodontal and

osteoarticular diseases, function by stimulating

deposition of repair material in affected areas by

enhancing transforming growth factor b (TGF b)

in articular cartilage. Avocado oil is also used in

cosmetic preparations such as skin moisturizers and

body lotions.

Nutritional Status

0017 Avocado is considered a nutritious fruit and contains

higher quantities of soluble and insoluble fiber and

protein than many other fleshy fruits. Avocado is also

a rich source of potassium and the vitamins E and C,

and b-carotene (provitamin A). Although low, a vita-

min A value of 150 mg RE (retinol equivalents) per

kilogram has been reported. Furthermore, the mono-

unsaturated fatty acids in avocado effectively reduce

blood levels of the undesirable low-density lipo-

protein (LDL, cholesterol) while increasing levels of

the beneficial, high-density lipoprotein (HDL). (See

Cholesterol: Factors Determining Blood Cholesterol

Levels; Vitamins: Overview.)

Nutrient Composition/density

0018 Unlike foods that are described as providing ‘empty

calories,’ the avocado is a nutrition-rich ‘protective’

fruit. The energy content per 100-g serving has been

estimated at 800 kJ, depending on the cultivar and

growing conditions. A detailed analysis of the com-

position of avocado mesocarp (the edible portion of

the fruit) of a typical subtropical cultivar has revealed

a nutritional status, which is summarized in Figure 1.

0019 Avocado contains approximately 2.3% protein on

a fresh-weight basis, which is between two and 10

times that of most other fleshy fruits and vegetables

analyzed. Although avocado contains all of the essen-

tial amino acids (i.e., it is ‘complete’), it is not gener-

ally regarded as nutrient-dense for protien, certainly

not in comparison to meat or eggs, for example. A

mixture of soluble and insoluble fiber is ideal in the

diet, and avocado contains appreciable quantities of

both (2.1 and 2.7%, respectively).

0020In avocado, the sum of percentage water plus per-

centage oil is constant in the range 88–91%, and for

each gram of water lost, there is a 1 g increase in oil,

in fruit containing between 8 and 22% oil. Changes

in oil content are also associated with changes in fiber

and protein. Therefore, the energy value of avocado is

almost entirely due to its oil content, and any vari-

ation is due solely to changes in the percentage oil. It

is probably this observation that led to the mistaken

idea that consuming avocado increases body mass.

On the contrary, addition of avocado to the diet has

been shown to cause a small but significant average

weight loss. One possible explanation is that avocado

speeds up the basal metabolic rate in humans.

Another hypothesis relates to the type of oil, and

avocado is rich in the beneficial monounsaturated

fatty acids.

Fibre: 2.42%

Water: 72.60%

Protein: 2.30%

Fat: 16.48%

Carbohydrate: 4.90%

Minerals: 1.30%

Figure 1 Nutrient content and composition of subtropical fruit

flesh. Data are the average between the minimum and maximum

values reported by Ahmed EM and Barmore CD (1980) Avocado.

In: Nagy S and Shaw PE (eds) Tropical and Subtropical Fruits: Com-

position, Properties and Uses, pp. 121–156. Westport, CT: AVI;

Seymour GB and Tucker GA (1993) Avocado. In: Seymour GB,

Taylor JE and Tucker GA (eds), Biochemistry of Fruit Ripening,

pp.53–81. London: Chapman & Hall; Slater GG, Shankman S,

Shepherd JS and Alfin-Slater RB (1975) Seasonal variation in

the composition of Californian avocado. Journal of Agricultural

and Food Chemistry 23: 468–474, and references cited therein.

350 AVOCADOS

0021 The fatty acid content and composition of avocado

have been iterated in most texts on the physiology

and biochemistry of fruit growth and ripening.

Avocado lipids can be divided into the following frac-

tions: (1) neutral lipids (tri-, di-, and monoacylglycer-

ols), (2) phospholipids, (3) glycolipids, and (4) free

fatty acids. The neutral lipid fraction constitutes 96%

of the total lipid content of avocado, and the majority

are triglycerols. The major triglycerols identified in

avocado are dioleyl palmitin, triolein, dioleypalmito-

lein, linoleyl oleyl palmitin, and linoleyl diolein.

Within each of these triglycerols, 18:1, 18:2, 16:0,

and 16:1 are the major fatty acids present, and the

relative concentration (percentage of total lipid) of

each is in the range 59–81% (18:1), 7–14% (18:2),

7–22% (16:0), and 3–11% (16:1). These values are

comparable with those for olive oil, making avocado

which is easily digested, an ideal substitute for olive

oil in cooking, and in the preparation of salad dress-

ings, although it is currently more expensive.

0022 Unsaturated fats are either mono- or polyunsatur-

ated, and the ratio of polyunsaturated fatty acids to

saturated fatty acids (P/S), which is used as an indica-

tor of nutritional value by nutritionists, is about 0.74

for avocado. A diet high in polyunsaturated fatty

acids reduces the level of the undesirable LDL,

whereas a high dietary level of monounsaturated

fatty acids also maintains levels of the desirable

HDL. Thus, it should not be surprising that results

from trials in which the monounsaturate-rich avo-

cado was used as a dietary component revealed a

significant decline in total cholesterol with preserva-

tion of the HDL level. Likewise, substituting avocado

for butter, margarine, and cheese significantly re-

duced blood cholesterol levels, and increased HDL

up to 16%. Accordingly, avocados have gained

acceptance by the Heart Foundations of several coun-

tries, and can even be prescribed for convalescent

heart patients.

Fat- and Water-soluble Vitamins, and Antioxidants

0023 The vitamin content and composition of avocado are

shown in Table 1. Although vitamin D has been

identified in avocado, no values have been published.

It has been reported, however, that the vitamin D

content of avocado is higher than that of butter

and eggs. Vitamins C and E and provitamin A (b-

carotene) are believed to function as antioxidants

and protect against damage from oxygen ‘free rad-

icals.’ Although oxygen is essential to life processes, it

is also damaging if converted to reactive oxygen

species (e.g., the superoxide anion or the hydroxyl

radical), which can cause cell mutation and contrib-

ute to aging, cancers, arthritis, and heart disease. The

three antioxidant vitamins are effective at disarming

these reactive oxygen species, and it has been stated

that for each of the three, and for any given daily kJ

proportion, the avocado provides about twice the

proportion of this nutrient.

0024In addition to the antioxidant vitamins, 2(R)-(12Z,

15Z)-2-hydroxy-4-oxoheneicosa-12,15-dien-1-yl ac-

etate and persenone A and persenone B have been

isolated from avocado mesocarp as inhibitors of

superoxide and nitric oxide generation. These com-

pounds do not scavenge reactive oxygen species (like

the vitamins) but rather suppress free-radical gener-

ation and may therefore be effective chemopreventive

agents in inflammation associated carcinogenesis.

Thus, the consumption of avocado may be one way

of ingesting more of the antioxidants that help to

protect against cancers, heart disease, and aging.

Mineral Composition

0025The mineral content and composition of avocado are

presented in Table 2. As shown, avocado is a rich

source of potassium, which is purported to protect

against the risk of strokes in humans and reduces the

incidence of strokes by up to 40%. One of the con-

founding factors in the cause of strokes is increased

blood pressure, which has been associated with a high

intake of sodium. The avocado is as low in sodium as

it is high in potassium. (See Minerals – Dietary Im-

portance.)

0026Phosphorus, calcium, and magnesium are abun-

dant minerals in avocado. Most other minerals,

including iron, occur in amounts of less than 1 mg

per gram fresh weight of edible fruit.

tbl0001Table 1 Vitamin content and composition of avocado fruit flesh

Component (per 100 g fresh weight) Concentrationrange

b-Carotene (provitamin A) (IU) 370–750

a-Tocopherol (vitamin E) (IU) 1.6–2.4

Ascorbic acid (vitamin C) (mg) 1.6–30.0

Biotin (mg) 3.2–10.0

Choline (mg) 17–22

Folacin (mg) 30–62

Niacin (mg) 1.4–3.5

Pantothenic acid (mg) 0.25–1.14

Pyridoxine (vitamin B

) (mg) 0.22–0.62

Riboflavin (vitamin B

)(mg) 95–230

Thiamine–HCl (vitamin B

)(mg) 60–240

Phytyl menaquinone (vitamin K) (mg) 0–8

Calciferols (vitamin D) Unknown

Concentration is dependent on the cultivar and stage of ripening. Values

were derived from data published by Ahmed EM and Barmore CD (1980)

Avocado. In: Nagy S and Shaw PE (eds) Tropical and Subtropical Fruits:

Composition, Properties and Uses, pp. 121–156. Westport, CT: AVI; Seymour

GB and Tucker GA (1993) Avocado. In: Seymour GB, Taylor JE and Tucker

GA (eds), Biochemistry of Fruit Ripening, pp. 53–81. London: Chapman &

Hall; Slater GG, Shankman S, Shepherd JS and Alfin-Slater RB (1975)

Seasonal variation in the composition of Californian avocado. Journal of

Agricultural and Food Chemistry 23: 468–474, and references cited therein.

AVOCADOS 351

Carbohydrates

0027 During avocado fruit ripening, there is an increase in

the concentration of glucose and fructose. In addition

to these monosaccharides, avocado also contains sev-

eral unusual sugars including the seven-carbon sugar

alcohol, perseitol, and its reduced form, d-manno-

heptulose. The sugar content and composition of

avocado are given in Table 3.(See Carbohydrates:

Classification and Properties.)

0028 Studies in the 1940s indicated that ingestion of

avocado could lead to the presence of sugar in urine.

It was later discovered that manno-heptulose, the

major reducing sugar in avocado, could induce hyper-

glycemia when administered to humans and other

animals orally. Even so, this author knows of no

unequivocal information linking the consumption of

avocado with diabetic symptomology. In fact, the

manno-heptulose content of the edible portion of

avocado declines by up to 80% as the fruit ripens.

Thus, any amounts of manno-heptulose ingested are

likely to be very low, and some cultivars appear to

have none in harvested fruit.

0029Interestingly, manno-heptulose is regarded as an

inhibitor of hexokinase activity in plants. This

enzyme phosphorylates glucose during glucose me-

tabolism to give glucose-6-phosphate, which is then

metabolized in the glycolytic pathway to provide

energy and organic substrates. Whether this biochem-

ical pathway is affected by a diet rich in avocado

(and therefore some manno-heptulose) in humans is

unknown.

Nutritional Benefits and Costs

Nutrient Density

0030The extraordinary nutrient density, at least of the

fruits of subtropical avocado cultivars which form

the basis of world trade and of consumption in

the affluent first world, has been noted, and the

subtropical avocado has been described as very nutri-

tious of all fleshy fruits. Thus, comparatively small

amounts of avocado are extremely helpful in upgrad-

ing the quality of the diet in an increasingly health-

conscious world. Furthermore, the relatively small

amounts consumed per serving (80–100 g) are no

cause for concern where affluence has contributed to

overweight or even obesity. The problem in poor,

mostly tropical third world countries is very different,

and here the energy and nutrient density of the fruit,

even of less nutritious cultivars, can make a substan-

tial contribution to guarding against malnutrition.

Protection from Coronary Heart Disease

0031Coronary artery disease results from the build-up of

cholesterol and other lipids in coronary arteries.

Cholesterol is carried by lipoproteins, and LDL

causes the most damage. HDL, however, protects

vessel walls from atherosclerosis. Monounsaturated

fatty acids increase the blood level of HDL. Avocado

is high in monounsaturated fats and contains no chol-

esterol. A diet rich in avocado therefore has a favor-

able effect on blood fats, decreases cholesterol, and

preserves HDL. Trials have revealed that a diet rich in

avocado causes a decline in total serum cholesterol of

16% in healthy individuals. In hypercholesterolemic

subjects, a decrease in serum cholesterol of 17%,

LDL-cholesterol of 22%, and triglycerols of 22%

was observed, while HDL-cholesterol increased by

11%. There has, therefore, been a welcome change

in attitude towards avocado consumption in people at

risk of coronary heart disease. (See Coronary Heart

Disease: Prevention.)

Hypersensitivity

0032Hypersensitivity occurs in latex-allergic individuals

who react to avocado (and other fruits including

tbl0002 Table 2 Mineral content and composition of avocado fruit flesh

Mineral (mg per 100 g fresh weight) Concentration range

Potassium 340–723

Magnesium 40–60

Phosphorus 20–80

Calcium 10–15

Sodium 5–15

Iron 0.5–2

Boron 1–3

Concentration is dependent on the soil type, cultivar, and cultural

practice. Values were derived from data published by Ahmed EM and

Barmore CD (1980) Avocado. In: Nagy S and Shaw PE (eds) Tr o p i c a l a n d

Subtropical Fruits: Composition, Properties and Uses, pp. 121–156. Westport,

CT: AVI; Slater GG, Shankman S, Shepherd JS and Alfin-Slater RB (1975)

Seasonal variation in the composition of Californian avocado. Journal of

Agricultural and Food Chemistry 23: 468–474, and references cited therein.

tbl0003 Table 3 Sugar content and composition of ripe avocado fruit

flesh

Sugar (mg per 100 g fresh weight) Concentrationrange

Glucose 0.14–1.28

Fructose 0.08–0.65

D-Manno-heptulose 0–3.82

Perseitol 0–2.06

Concentration is dependent on the cultivar and stage of ripening. Values

were derived from data published by Liu X, Robinson PW, Madore MA,

Witney GA and Arpaia ML (1999) ‘Hass’ avocado carbohydrate

fluctuations. II. Fruit growth and ripening. Journal of the American Society of

Horticultural Science 124: 676–681; Seymour GB and Tucker GA (1993)

Avocado. In: Seymour GB, Taylor JE and Tucker GA (eds), Biochemistry of

Fruit Ripening, pp. 53–81. London: Chapman & Hall, and references cited

therein.

352 AVOCADOS

banana and kiwifruit) within 60 min of ingestion and

typically display one or more of the following symp-

toms: mouth irritation, angiodema, urticaria, asthma,

nausea, vomiting, diarrhea, rhinitis, or anaphylaxis.

Allergy to avocado is increasing, especially in the USA

and Mexico, and has been estimated at around 1% of

the general population. Avocado allergy is of particu-

lar importance in the ‘latex-fruit syndrome’ observed

in at least 40% of latex-allergic individuals. As men-

tioned above, the allergens elicit diverse immuno-

globulin E-mediated reactions in sensitized

individuals. Many of the known plant food allergens

are in fact proteins produced in plants either

following pathogen attack or after induction of

the plant stress syndrome. These are called pathogen-

esis-related proteins (PR), and 14 families are now

recognized. The major allergen in avocado has been

identified: a 32-kDa protein known as ‘Prs a 1,’

which has endochitinase activity and is recognized

by 15 out of 20 avocado and/or latex-allergic individ-

uals. This allergen belongs to the PR-3 family of

pathogenesis-related proteins and is induced in plants

by ethylene treatment, but allergic activity is lost in

heating. This probably explains why plant foods con-

taining this allergen that are consumed after cooking

(e.g., green beans) are not usually associated with the

latex-fruit syndrome.

See also: Allergens; Atherosclerosis; Coronary Heart

Disease: Etiology and Risk Factor; Prevention; Diabetes

Mellitus: Etiology; Fatty Acids: Dietary Importance;

Food Intolerance: Food Allergies; Minerals – Dietary

Importance; Salad Crops: Dietary Importance;

Slimming: Slimming Diets; Vegetable Oils: Oil

Production and Processing; Vitamins: Overview