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

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quality of groundnut oil, mills for crushing were soon

found in other European countries and then through-

out the world. In recent years, the world production

of groundnut oil has accounted for about 7–10% of

the world vegetable oil total. More than 50% of the

groundnuts produced are crushed for oil. In India,

75–80% of the groundnuts produced are crushed

for oil, whereas in the USA, groundnuts used for

crushing are only approximately 12% of recent pro-

duction. This low percentage is indicative of the eco-

nomic importance of groundnuts as a food crop in the

USA. Owing to their high content of digestible pro-

tein and unsaturated oil, and their exceptional

roasted nutty flavor, groundnuts have substantial

value and desirability as a food commodity. On a

world-wide basis, more than one-third of the ground-

nuts produced are used as food. In the USA, a high

percentage of the limited number of groundnuts used

for oil extraction have been separated from edible

stocks because of the potential for aflatoxin. The

pressed cake, low in oil and high in protein, may be

used for animal food if aflatoxin is found to be below

acceptable levels. Unacceptable pressed cake is rele-

gated to fertilizer usage. Depending on the extraction

methods (hydraulic press, expeller, and/or solvent ex-

tractor), residue may contain 1–7% oil, and with

inefficient equipment, the percentage may be much

higher. Pressed cake from edible-grade groundnuts

with low oil content may be ground into flour for

human consumption. In many parts of the world,

extraction efficiency and lack of hygienic conditions

relegate residues unfit for human consumption. In

these situations, the residue is utilized either for

animal feed or as fertilizer. (See Peanuts; Vegetable

Oils: Oil Production and Processing.)

Uses

0002 Peanut oil uses include cooking and frying oil, prep-

aration of shortenings, margarines, and mayonnaise.

Some salad oil use is found, and use in pourable

dressings is good because of the length of time solids

are held in suspension in the oil. However, peanut oil

does not meet the strict terminology for salad oil

because it solidifies at 0–3



C. As a cooking oil, espe-

cially in deep-fat frying, groundnut oil is excellent

since it has a smoke point of 229.4



C. Refined

groundnut oil is odorless, whereas crude oil usually

has a nut-like aroma. Groundnut oil develops few off-

flavors or odors in use as a frying oil, but degradation

of glycerides during frying results in the increase of

free fatty acids (FFA) and a decrease in smoke point.

Oil Characteristics

Composition

0003The seed of the groundnut fruit commonly contain

40–50% total oil, but data indicating a range of 36–

56% may be found. Oil content is considered to

average about 50% and is generally independent of

market type or growth habit. However, some reports

suggest that the small-seeded Spanish types tend to

have a higher oil content than the large-seeded Vir-

ginia types. The composition of the oil changes some-

what among varieties, but the triacylglycerol content

is generally in the region of 95%. As peanuts mature,

the total oil, triacylglycerol, and oleic acid/linoleic

acid (O/L) ratio increase, whereas free fatty acids,

polar lipids, monoacylglycerols, and diacylglycerols

decrease (Table 1). The relative weight percentage of

free fatty acid has been shown to decrease from 4.5 in

very immature seed to 0.7 in mature peanut seed. In a

study of oil characteristics of peanuts, we reported

that free fatty acids decreased (0.8 to 0.05% as oleic

acid), the O/L ratio increased, and the oil oven stabil-

ity increased with maturity. The consistent relation-

ship of these components to shelf-life leaves little

doubt as to the relationship of maturity and shelf-

life. Diacylglycerol and polar lipid fractions generally

account for an additional 2% of the oil weight. Some

reports suggest that the total oil percentage decreases

tbl0001 Table 1 Influence of maturity on quantity and composition of selected oil components of Florunner peanuts

Maturity stage

Oil (percentagedry weight) Triacylglycerol

Free fattyacid

Diacylglycerol

Polar lipid

5 25.3 85.3 4.5 4.7 2.0

6 30.8 89.3 3.1 3.5 1.4

7 34.4 88.3 2.5 3.6 1.9

8 42.8 90.8 1.8 3.0 1.6

9 45.6 92.6 1.3 2.2 1.3

10 46.7 94.3 0.9 2.0 1.0

11 48.4 94.8 0.7 1.9 0.7

12 48.2 95.8 0.7 1.7 0.6

Relative maturity ranking based on internal shell color. Stage 5 seed are soft and watery. Stage 12 is fully mature.

Relative weight percent.

2968 GROUND NUT OIL

after full maturation, as lipids are utilized for respir-

ation. Factors such as maturity, environment, cultural

practices, variety, and soil temperature affect oil

content and composition.

Fatty Acids

0004 As previously indicated, groundnut oil is composed of

mixed glycerides and contains a high proportion of

unsaturated fatty acids, in particular, oleic (18:1) and

linoleic (18:2). Additional fatty acids are palmitic

(16:0), stearic (18:0), arachidic (20:0), 11-eicosenoic

(20:1), behenic (22:0), and lignoceric (24:0). With

maturation, the percentage of oleic acid increases,

whereas the percentage of linoleic acid decreases

slightly. The stability of groundnut oil is highly cor-

related with the ratio of oleic acid to linoleic acid.

This ratio generally increases with seed maturity, and

oil stability increases simultaneously. Fatty acid

composition values have been reported to vary

widely, as indicated in Table 2. The fatty acid com-

positions of the lipid classes of groundnut are some-

what variable. The fatty acid composition of three

groundnut varieties and composition of lipid classes

from those varieties are shown in Table 3. The tria-

cylglycerol composition approximates that of whole

oil since the fraction comprises about 95% of the

total. Oleic acid, linoleic acid, and palmitic acid com-

prise about 90% of the total fatty acids. Free fatty

acid fractions consistently contained higher percent-

ages of palmitic acid than did the triacylglycerol

fractions. Long-chain fatty acids (C20–C24) were

generally more predominant in the sn-1,3-diacylgly-

cerol than in other fractions, and only traces of

long-chain fatty acids were found in the sn-1,2 (2,3)

diacylglycerol fraction. The phospholipid fractions

contained the highest concentrations of palmitic

acid. (See Fatty Acids: Properties.)

0005Production location has a significant effect on the

fatty acid composition of peanut oil, with cooler cli-

mates resulting in a greater degree of unsaturation, a

lower O/L ratio, and thus, according to published cor-

relations, a shorter shelf-life. These effects have been

variously ascribed to temperature, irrigation, and ma-

turity. The relationship between mean temperature at

critical growth periods appeared to have a definite

effect on oil composition. The relationships examined

may provide at least partial explanation for observed

problems with oxidative stability in peanuts grown in

tbl0002 Table 2 Reported percentages of major fatty acids in

groundnut oil

Fatty acid Percentage

Palmitic 7.4–12.5

Stearic 2.7–4.9

Oleic 41.3–67.4

Linoleic 13.9–35.4

Arachidic 1.2–1.9

Behenic 2.1–3.6

Lignoceric 0.9–1.7

tbl0003 Table 3 Fatty acid composition of various lipid classes in petroleum ether-extracted Starr, Florunner, and Florigiant peanut oil

Variety Lipid class 16:0 18:0 18:1 18:2 20:0 20:1 22:0 24:0

Mole %

Starr TG 14.1 3.3 44.6 32.1 1.5 0.8 2.7 0.9

FFA 21.0 4.2 40.4 29.9 1.2 0.4 2.2 0.8

sn-1,3-DG 17.7 3.8 48.2 22.9 1.5 1.2 3.4 1.3

sn-1,2(2,3)DG 15.5 2.5 48.9 33.1

MG 17.9 2.4 46.5 27.8 0.8 0.8 2.4 1.4

PL 22.3 3.6 44.8 24.6 0.8 1.0 1.6 1.2

WO 14.0 2.6 43.9 34.2 1.3 0.8 2.5 0.8

Florunner TG 11.4 2.3 51.9 28.5 1.2 1.2 2.4 1.2

FFA 16.9 3.0 45.0 30.1 1.1 1.2 1.9 0.8

sn-1,3-DG 13.8 2.6 51.5 25.1 1.2 1.6 2.4 1.4

sn-1,2(2,3)DG 13.6 1.5 48.6 36.3

MG 16.1 3.3 47.9 27.4 0.7 0.6 3.2 0.8

PL 21.3 3.4 45.1 28.9 0.7 0.7

WO 11.0 1.8 51.7 29.9 1.0 1.1 2.4 1.1

Florigiant TG 11.2 3.5 52.7 26.6 1.5 0.9 2.3 1.2

FFA 16.1 3.9 46.6 28.2 1.6 1.0 1.9 0.7

sn-1,3-DG 13.2 3.9 52.1 22.2 2.4 1.7 3.4 1.2

sn-1,2(2,3)DG 12.6 2.2 48.9 35.8 0.3 0.3

MG 16.7 4.4 48.4 26.8 0.8 2.3 0.6

PL 22.1 3.8 42.8 29.0 0.4 1.0 0.9

WO 11.0 2.8 54.3 27.2 1.3 0.9 2.0 0.8

All values are the means of three replicate analyses. TG, triacylglycerol; FFA, free fatty acid; DG, diacylglycerol; MG, monoacylglycerol; PL, polar lipid;

WO, whole oil.

GROUND NUT OIL 2969

cooler climates or with cooler temperatures during the

later weeks of the growing season.

0006 This research has demonstrated several highly sig-

nificant variations in oil production from year to year

for all three major peanut types, highly significant

differences among the same varieties grown in differ-

ent commercial production area, and highly signifi-

cant interactions between location and year of

production. The study has also demonstrated highly

significant correlations between mean temperatures

during apparently critical growth periods and the

levels of major fatty acids produced.

Triacylglycerol

0007 Studies defining over 20 and up to 36 triacylglycerol

species in peanut oil have been conducted. Triacyl-

glycerol species OOL, OOO, OLL, POL, and POO

(O ¼oleic, L ¼linoleic, P ¼palmitic) comprised the

greatest proportions of the triacylglycerol fraction.

This should be expected since oleic acid, linoleic

acid, and palmitic acid comprise the greatest percent-

ages of fatty acids in peanut oil. The US Customs

Service has utilized triacylglycerol species distribution

as one method of identification of some international

origins of peanuts. After examination of 18 Argentine

and 13 Chinese samples, observations for distinguish-

ing between the two production locations were:

(1) the ratio of OOO/OOP was less than 1.0 for

Chinese peanuts; it was approximately 1.5–1.7 for

the Argentine peanuts; (2) PSL (S ¼stearic) was not

measurable in Chinese peanuts and was present at

about 0.2% in Argentine samples; (3) in Chinese

samples, OOB (B ¼behenic) accounted for about

0.4% of the total triacylglycerols, whereas in the

Argentine samples, it accounted for about 1.1%; (4)

the percentage of OOO was about 10% in Chinese

samples versus about 14% in Argentine samples.

Triacylglycerol species percentage ranges for Argen-

tine and US samples often overlapped; however,

origin identification was possible through trace elem-

ent analysis. (See Fats: Classification.)

0008Data presented in several studies have clearly dem-

onstrated the fact that the environment affects not

only the fatty acid composition of peanut oil, but

also, although apparently indirectly, the spatial ar-

rangement of those acids on the triacylglycerol mol-

ecule. Triacylglycerol composition and structure are

important in the areas of nutrition, oil stability, and

possible physiological effects. Table 4 provides data

demonstrating the differences in triacylglycerol struc-

ture that are reasonably expected among different

varieties of peanuts. The data shown in Table 4 indi-

cate a nonrandom distribution of fatty acids among

the sn-1, -2, and -3 positions of the triacylglycerols.

tbl0004 Table 4 Stereospecific analyses of triacylglycerols from six peanut varieties

Variety Compoundor position Fattyaciddistribution (mole %)

16:0 18:0 18:1 18:2 20:0 20:1 22:0 24:0

Florigiant TG 10.8 2.9 53.1 27.3 1.8 1.0 1.9 1.1

1 20.1 4.9 50.7 22.6 0.5 0.7 0.4 0.3

2 2.2 0.7 51.5 45.3 0.1 0.3 0.1

3 10.3 3.2 57.2 14.0 4.8 2.0 5.3 3.0

Early Bunch TG 13.3 2.6 42.0 36.3 1.5 0.9 2.4 1.1

1 24.7 4.4 38.3 31.2 0.3 0.4 0.5 0.2

2 3.5 1.5 37.2 57.4 0.1 0.2

3 11.8 1.9 50.6 20.3 4.0 1.9 6.5 2.9

Florunner TG 11.4 2.1 50.9 29.1 1.6 1.1 2.4 1.3

1 20.7 3.5 49.5 24.4 0.3 0.7 0.5 0.5

2 2.1 0.6 47.8 48.8 0.1 0.4 0.1 0.1

3 11.4 2.3 55.5 14.1 4.4 2.3 6.5 3.4

Tifrun TG 12.6 2.4 42.4 36.8 1.5 0.9 2.6 0.8

1 22.7 4.2 38.8 32.7 0.3 0.4 0.6 0.2

2 3.2 1.2 36.1 58.8 0.2 0.2 0.1

3 11.9 1.7 52.2 18.9 4.0 2.0 7.2 2.2

Starr TG 14.2 3.3 43.3 33.0 1.8 1.1 2.7 0.7

1 24.2 4.9 40.4 28.4 0.4 0.6 0.7 0.3

2 2.4 0.8 39.5 56.9 0.1 0.2 0.1

3 16.0 4.2 50.0 13.8 4.8 2.4 7.3 1.8

Spancross TG 13.5 2.9 44.1 33.4 1.9 1.1 2.2 0.9

1 24.2 5.2 40.3 28.4 0.3 0.5 0.6 0.4

2 2.6 0.9 40.2 56.2 0.1

3 13.5 2.8 51.8 15.6 5.2 2.5 6.5 2.3

Each value is the mean of three replications.

2970 GROUND NUT OIL

The percentages of palmitic and stearic acids were

generally very low for the sn-2 position, higher for

sn-3, and highest for sn-1. The long-chain (C20–C24)

fatty acids were located almost exclusively at the sn-3

position. The sn-2 position of triacylglycerols from all

the varieties was high in unsaturated fatty acids. The

general patterns of fatty acids found at the sn-1 and

sn-3 positions were similar for all varieties, although

the mole percentages of each acid at the two positions

frequently differed widely. Mole percentages of palm-

itic, stearic, and linoleic acids were always higher for

the sn-1 than for the sn-3 position, whereas those of

oleic acid were consistently higher for the sn-3 pos-

ition. The patterns of fatty acid distribution at sn-2

differed not only from those at sn-1 and -3, but also

with variety. On the sn-2 position, the percentage of

oleic acid was higher than that of linoleic acid in

Florigiant, but the percentages were about the same

in Florunner. In the other four varieties, there was

more linoleic acid esterified at the sn-2 position than

oleic acid. Florigiant and Florunner triacylglycerols

contained more oleic acid and less linoleic acid than

the other varieties examined, and the concentration

effect probably was reflected by the fatty acid place-

ment in the molecule.

0009 Using the data in Table 4, linear regression equa-

tions and correlation coefficients were calculated for

the plots of the percentage of a fatty acid in the total

triacylglycerol vs. the percentage of that fatty acid at

one of the positions of the triacylglycerol (Table 5).

Significant correlations indicate that the total fatty

acid present influenced placement of that fatty acid

on the triacylglycerol. It has been reported that major

saturated, monoene, and diene fatty acids of corn

triacylglycerols exhibited a concentration effect in

all cases except for saturated acids in the sn-2 pos-

ition. Peanut triacylglycerols exhibited this same pat-

tern, and the low concentrations of the long-chain

fatty acids in the triacylglycerol were significantly

correlated with percentages found at the sn-3 position

only. This may be due to the general restriction of the

saturated acids (16:0 and 18:0) from the sn-2 position

and the long-chain acids from the sn-1 and sn-2 pos-

itions. Any substantial deviation from the regression

line has been attributed to a change in the mechanism

of fatty acid distribution and suggests genetic control

of the deviation. No substantial deviation of any fatty

acid from the regression lines was detected in the six

peanut varieties examined. Although the concentra-

tion effects were similar for the varieties, the variation

in percentage of a fatty acid at any position is suffi-

cient to indicate possible concentration differences in

the various triacylglycerol species found in the total

triacylglycerol fraction.

Phospholipids

0010Phospholipids of peanut oil have been examined, and

it has been determined that oven stability of peanut

oil was related to the solvent used for extraction and

that removal of phosphatides from the oil by precipi-

tation reduced oven stability. Thus, differences in the

relative amounts of polar lipids extracted by different

solvents might explain some variation in oven stabil-

ity. Stability and resistance to oxidation due to sterols

and phospholipids are not well documented and

warrant further investigation. The concentration of

phospholipids in peanut oil is only about 1%. Phos-

pholipids or membrane lipids have been recognized

for some time in the form of lecithin materials (pri-

marily phosphatidylcholine (PC)) as a byproduct of

oil and fat processing. Phospholipids, especially PC,

were found to be important in the treatment of neuro-

logical diseases, respiratory distress, liver diseases,

and many others. This class of compounds has been

shown to be synergistic with tocopherols in delaying

onset of lipid oxidation. The major phospholipids of

peanut oil are phosphatidic acid (PA), phosphatidyl-

glycerol (PG), phosphatidylethanolamine (PE), phos-

phatidylinositol (PI), and PC. Phospholipid content

and concentrations have been shown to be affected by

maturity and postharvest treatment, as shown in

Table 6. The higher concentrations of PA and PC in

immature peanuts might be explained on the basis

that these phospholipids are precursors to other phos-

pholipids. Excessive heat and freezing both affect

membrane stability with the result of significant

tbl0005 Table 5 Linear regression analyses and correlation

coefficients for the relationship of fatty acids in total

triacylU

glycerols and fatty acids at each position

Fatty acid Position Slope y intercept r

16:0 1 1.43 4.68 0.95

2 0.43

3 1.32 4.23 0.86

18:0 1 1.28 1.03 0.88

2 0.09

3 1.82 2.23 0.83

18:1 1 1.16 10.33 0.99

2 1.28 16.87 0.99

3 0.56 26.84 0.95

18:2 1 1.01 5.07 0.99

2 1.38 8.83 0.95

3 0.60 3.75 0.82

20:0 3 2.78 0.15 0.99

20:1 3 2.31 0.16 0.91

22:0 3 2.39 0.88 0.96

24:0 3 2.65 0.01 0.99

r ¼ correlation coefficient.

Significant at 1% level.

Not significant.

Significant at 5% level.

GROUND NUT OIL 2971

differences in the phospholipid content and distribu-

tion. The large increase in PA and great decrease in

PC with freezing of nondried peanuts may be related

to the fact that freezing induces phospholipase-D ac-

tivity, with PC being the most susceptible to action of

the enzyme. (See Phospholipids: Properties and Oc-

currence.)

Sterols

0011 Peanut oil contains several sterols, which are second-

ary alcohols with 27–29 carbon atoms, and unlike

short-chain alcohols, they are crystalline solids at

room temperature. Peanuts contain b-sitosterol, cam-

pesterol, stigmasterol, D5 avenasterol, D7 stigmas-

terol, D7 avenasterol, and brassicasterol (Table 7).

b-Sitosterol (SIT), the major component in peanut

sterols, has been shown to inhibit cancer growth. SIT

may offer protection from colon, prostate, and breast

cancer. Unrefined peanut oil contains approximately

200 mg of SIT per 100 g of oil, and this value is

comparable with soybean oil, which contains ap-

proximately 183 mg of SIT per 100 g.

Antioxidants

0012 Few studies on the relative quantity of antioxidants in

peanuts have been published, and studies on the rela-

tionship of antioxidant content to shelf-life potential

are even less abundant. Data on tocopherol content

and individual fatty acids from 31 cultivars for 4

years used in a multiple regression equation for the

prediction of stability of cold pressed oil revealed that

87% of the stability could be correlated with total

tocopherol/percent linoleic acid. A 3-year study of oil

composition factors of peanuts from several origins

indicated that tocopherol content was consistently

different in peanuts from various origins. Peanuts

produced in the USA had a consistently higher toco-

pherol content than peanuts produced in China or

Argentina. The highest levels reported in US peanuts

were almost 250 p.p.m. in whole seed, whereas the

lowest levels were about 100 p.p.m. The tocopherol

content of peanut oil has been demonstrated to be as

high as 650 p.p.m., depending on the variety of peanut

and growing conditions. Vitamin E intake has been

shown in numerous studies to be inversely related to

the risk of heart disease. The 3-year study on peanuts

from the USA, China, and Argentina reported on

levels of copper and iron. The copper content was

always significantly lower in US peanuts, and the

iron content was generally lower. These factors were

related to higher O/L ratios, and oil oven stability

studies indicated the overall longer shelf-life potential

of peanuts produced in the USA. These data, without

consideration of the areas of production, demon-

strated the consistent close relationship of oil quality

factors such as FFA, O/L ratio, peroxide value, total

carbonyls, tocopherols, copper, and iron to most

measures of shelf-life stability. The data may be

extrapolated to the end that any factor that generates

inappropriate levels of these compounds will then

contribute to a shorter shelf-life of resulting products.

(See Antioxidants: Natural Antioxidants; Synthetic

Antioxidants.)

Properties of Peanut Oil

General

0013The general properties of peanut oil have been com-

piled from several references and are provided in

Table 8. Crude peanut oil has a bland, but slightly

beany, nut-like flavor that is removed during refining.

Oxidized oil may have a wet cardboard or painty

(oxidized linseed oil) flavor.

Acetyl Value

0014The acetyl value is the number of milligrams of KOH

required to neutralize the acetic acid produced by the

hydrolysis of 1 g of acetylated fat and is a measure of

the free hydroxyl groups present in the oil. The acetyl

number of peanut oil (8.5–9.5) is lower than other

vegetable oils but higher than coconut oil, palm oil,

and the animal fats and oils.

tbl0006 Table 6 Effect of postharvest treatment on total phospholipid

Treatment Phospholipid (% area) Totalphospholipid

(mgper100 gDWT)

PA PG PE PI PC

Control 2.2 2.5 13.3 15.7 66.4 500

Immature 4.5 2.3 14.0 7.6 71.7 700

Heat cured 9.5 1.1 16.0 15.4 58.1 900

Freeze-damaged 28.3 14.1 15.2 33.5 8.8 250

PA, phosphatidic acid; PG, phosphatidylglycerol; PE,

phosphatidylU

ethanolamine; PI, phosphatidylinositol; PC,

phosphatidylcholine; DWT, dry weight.

tbl0007 Table 7 Sterol content of unsaponifiables of peanut oil and

whole peanuts

Peanut oil

(mgper100 g)

Whole peanuts

(mgper100 g)

Total sterol 337 220

b-Sitosterol 217 142

Campesterol 49 24

Stigmasterol 36 23

D5-Avenasterol 26 nr

D7-Stigmasterol 6 nr

D7-Avenasterol 2 nr

Brassicasterol Trace nr

Other 31

nr, not reported.

2972 GROUND NUT OIL

Percent Free Fatty Acid (FFA)

0015 Peanut oil generally has low levels of FFA. The

highest natural percentages are found in very imma-

ture seed (0.8), and the percentage decreases to c. 0.05

in fully mature seed. Improper handling, moisture,

fungal invasion and other factors contribute to hy-

drolysis of triacylglycerols and cause significant in-

creases in FFA. Saponification in the refining process

removes FFA, but crude oil used in many parts of the

world may contain high levels of FFA with resulting

rapid deterioration in quality, flavor, and stability.

Iodine Value (IV)

0016 The iodine value is a measure of the relative degree of

unsaturation in oil components, as determined by the

uptake of halogen. Because the melting point and

oxidative stability are related to the degree of unsat-

uration, IV provides an estimation of these quality

factors. The greater the iodine value, the more unsat-

uration and the higher the susceptibility to oxidation.

Peanut oil (IV 82–107) is more saturated than corn

(IV 103–128), cottonseed (IV 99–113), or linseed (IV

155–205) oils; however, it is considerably less satur-

ated than coconut (IV 7.7–10.5), palm (IV 44–54) or

butter (IV 25–42) oils.

Color

0017 The light yellow color of peanut oil is due to b-

carotene and lutelin, and becomes lighter as peanuts

mature. Although oil color may be used to assess

maturity, other methods are preferred because many

factors such as curing temperature and duration influ-

ence oil color. Color measurement is frequently done

by visual comparison under a CIE standard light

source. The Gardner color is determined using a

Gardner-delta color comparator, which has a scale

between 1 and 18.

Heat of Fusion

0018The heat of fusion, or latent heat, is the quantity of

heat required to change 1 g of solid to a liquid with no

temperature change. This latent heat increases with

increasing molecular weight. The heat of fusion of

peanut oil is 21.7 cal g

1

Melting Point

0019At refrigeration temperatures (0–3



C), peanut oil

sets to a gel. In contrast to safflower, soybean, corn,

and olive oils, peanut oil is not filterable during

winterization.

Peroxide Value

0020Elevated peroxide values indicate that lipid oxidation

has taken place and is measured as reactive oxygen

content in terms of milliequivalents per 1000 g of fat.

In raw peanuts, once the cell structure is disrupted by

pressing, lipoxygenase reacts with linoleic, linolenic,

or arachidonic acid to form hydroperoxides. These

oxidation products are correlated with reduced flavor

scores and cardboard or painty flavor defects. The

peroxide value is often used as an indicator of peanut

quality related to oil oxidation.

Unsaponifiable Lipids

0021The unsaponifiable matter in peanut oil is largely

sterols (mainly b-sitosterol and campesterol).

Health Issues

0022Early work with animals suggested a high atherogenic

potential when peanut oil was fed in relatively high

doses. Because chemical treatment to randomize

peanut oil resulted in a decrease in atherogenicity,

the triacylglyceride structure was believed to be in-

volved. However, recent numerous human epidemi-

ological studies have indicated an amazingly high

30–50% reduction in cardiovascular disease in

people who ate nuts, including peanuts, four to five

times a week. In a recent 4.2-year study, researchers

found that compared with those who rarely or never

consumed them, study participants who consumed

two or more servings of peanuts and nuts per week,

decreased their risk of heart disease by 25%. These

significant data align with the numerous research

studies that have shown that diets high in mono-

and polyunsaturated fats and low in saturated fat

can be heart-healthy. Recent studies have been con-

ducted in which healthy subjects consumed one of

five diets: a low fat diet; one including olive oil; one

including peanuts and peanut butter; one including

peanut oil, and a typical American diet. Results show

that the diet including peanuts and peanut butter, the

tbl0008 Table 8 Chemical and physical characteristics of peanut oil

Characteristic Value

Flavor and odor Bland

Acetyl value 8.5–9.5

Color (visual) Light yellow

Color (Gardner, maximum) 4

Free fatty acid (as oleic acid,

maximum)

0.05%

Heat of fusion (unhydrogenated) 21.7 cal g

1

Melting point 0–3



Peroxide value (maximum) 10 meq of peroxides oxygen

per kilogram of oil

Refractive index (n



C) 1.46–1.465

Smoke point (minimum) 229.4



Specific gravity (21



C) 0.915

Unsaponifiable lipids 0.40%

GROUND NUT OIL 2973

diet including peanut oil, and the diet including olive

oil (all low in saturated fat and cholesterol, and high

in monounsaturated fat) lowered total cholesterol

and low-density lipoprotein cholesterol. Further,

each of these three diets lowered triacylglycerol

levels, but did not lower the beneficial high-density

lipoprotein cholesterol.

New Developments – High-oleic Peanut

Oil

0023 Peanut lines with a high-oleic acid trait have been

identified, and this trait has been incorporated into

commercial peanuts. The original two lines identified

had approximately 80% oleic and 2% linoleic acid.

The lines developed with the high oleic acid trait have

O/L ratios of approximately 30, and the lines do

not show any meaningful differences in oil content,

flavor, color, or texture. Oxidative stability compari-

sons made on extracted, neutralized, and bleached oil

from high oleic (76.3% oleic/4.7% linoleic) and con-

ventional (56.6% oleic/24.2% linoleic) lines differing

only in fatty acid composition resulted in up to 15

times more stability in the high oleic oil. The use of

high oleic oil in roasting of peanuts resulted in slight

increases in shelf-life, as measured by the oxidative

stability and peroxide value, and the degree of im-

proved shelf-life was related to the O/L ratio of the

peanut roasted. Swine fed a diet incorporating high

oleic acid peanuts had increased monounsaturates

and lower polyunsaturates in backfat relative to use

of a feed incorporating standard peanuts or canola

oil. Further, the use of high oleic acid peanuts as the

fat source in a low-fat and high-monounsaturate diet

produced significant and positive changes in blood

lipids in postmenopausal women including a reduc-

tion in total cholesterol from 264 to 238 mg dl

1

See also: Antioxidants: Natural Antioxidants; Synthetic

Antioxidants; Synthetic Antioxidants, Characterization

and Analysis; Role of Antioxidant Nutrients in Defense

Systems; Fatty Acids: Properties; Metabolism; Gamma-

linolenic Acid; Dietary Importance; Peanuts;

Phospholipids: Properties and Occurrence;

Determination; Physiology; Tocopherols: Properties and

Determination; Physiology

Further Reading

Ahmed EM and Young CT (1982) Composition, quality

and flavor of peanuts. In: Pattee HE and Young CT

(eds) Peanut Science and Technology. Yoakum, TX:

American Peanut Research and Education Society.

Cobb WY and Johnson BR (1973) Physicochemical proper-

ties of peanuts. In: Peanuts – Cultures and Uses. Still-

water, OK: American Peanut Research and Education

Association.

Holaday CE and Pearson JL (1974) Effects of genotype and

production area on the fatty acid composition, total oil

and total protein in peanuts. Journal of Food Science 39:

1206–1209.

Salunke DK and Desai BB (1986) Groundnut. In: Post-

harvest Biotechnology of Oilseeds. Boca Raton, FL:

CRC Press.

Sanders TH (1979) Varietal differences in peanut triacyl-

glycerol structure. Lipids 14: 630–633.

Sanders TH (1980) Effects of variety and maturity on lipid

class composition of peanut oil. Journal of the American

Oil Chemists Society 57: 8–11.

Woodroof JG (1983) Peanut oil. In: Peanuts – Production,

Processing, Products. Westport, CT: AVI Publishing.

Young CT (1996) Peanut oil. In: Bailey’s Industrial Oil and

Fat Products Edible Oil and Fat Products: Oils and Oil

Seeds, vol. 2, pp. 377–392. New York: John Wiley.

GROWTH AND DEVELOPMENT

R Tojo and R Leis, Santiago de Compostda University,

Hospital Clı

nico Universitario de Santiago de

Compostela, Spain

Introduction

0001 Human growth is a product of continous interaction

between inheritance and a large number of environ-

mental variables, which act both in fetal period and in

the two first decades of the life. Hormones, growth

factors, and nutrition play an important role in

growth velocity and the attainment of adult size.

0002Growth is an excellent indicator of health status or

illness. Periodic growth assessment must be an obliga-

tory exploration in the supervision of children and

adolescents.

Growth and Development

0003Growth is a complex process. It is the product of

continuous interaction between inheritance and

environment from conception to adulthood. Each

individual has a genetic basis with a well-defined

growth potential, modulated by a wide range of

extragenic factors. Therefore, body composition and

2974 GROWTH AND DEVELOPMENT

predetermined final adult size will only be reached if

all factors act harmoniously.

0004 Growth and development refer to the trans-

forming process of a fertilized ovum into an adult

individual. Growth basically implies an enlargement

of body dimension originated by an increase in

cell number and size, that is, a process of cell hyper-

plasia and hypertrophy. Development is a physio-

logical process which makes possible – from a

pluripotential and undifferentiated cell – the differen-

tiation, maturation, and function of all the tissues,

organs, and apparatus which make up the human

organism.

Cell-Growth Stages

0005 Each tissue, organ, or apparatus growth process, in

spite of having a development program of its own, is

conditioned by cell division and size. This process of

tissue growth generally is in three stages:

0006 Cell hyperplasia: the initial stages of growth,

mainly during organogeny and the fetal period,

are characterized by cell division and prolifer-

ation, by hyperplasia.

0007 Hyperplasia-hypertrophy: as the organ or tissue

approaches its predetermined cell total, cell div-

ision and increase in cell number are less, whilst

cell size rises.

0008 Hypertrophy: when total adult cells are reached,

cell division stops and cell growth exclusively

depends on the increase in existing cell size.

Types of Tissue According to their Growth

and Maturation: Tissular Specialization

0009 There are three types of tissue, according to their life

span and cellular cycle.

Permanent or Static Tissues

0010 These tissues, once they have reached the adult cell

number – which happens precociously – remain

theoretically invariable. Their subsequent renovation

does not occur, or is only minimal. That is, dead cells

cannot be replaced, and cell size and structures can

only change or renew their subcellular constituents.

Nerve cell, cardiac muscle, and retina cells are the

paradigms for this behavior.

Renewing Tissues

0011 These are characterized by a high rate of continu-

ous cell proliferation throughout life. They have a

very active turnover of cell populations, which are

continously eliminated and renewed, but keep a stable

mass. Epidermis, intestinal mucus, seminiferous

tubules and hematopoietic tissue are renewing tissues.

Expanding Tissues

0012Once they have attained adult growth and develop-

ment level, expanding tissues do not vary unless dam-

aged, in which case a regenerative compensatory

phenomenon of cell hyperplasia and hypertrophy

takes place. Liver and kidney are typical expanding

tissues.

Patterns for Organic and Tissular Growth

General Pattern for Human Growth, or Scammon’s

General Curve

0013Scammon’s general curve is the curve followed by the

whole organism. A good example is size, which, ex-

pressed in adult-size percentages, follows a sigmoid

curve with two periods of rapid increment (first, pre-

natal and immediately postnatal ones, and second,

pubertal growth) and, between both, a curve of slow

and stable growth corresponding to preschool and

school age. Many other corporeal components follow

roughly this growth pattern (respiratory and digestive

systems, kidney, spleen, muscles and osteal system)

(Figure 1).

100

120

140

160

180

200

B 2 4 6 8 101214161820

Size attained as a percentage of total postnatal growth

Lymphoid

Brain and head

General

Reproductive

Age (years)

fig0001Figure 1 Growth curves of different parts and tisu

es of the

body. All the curves are of the size attained and plotted as a

percentage of total gain from birth to 20 years. Reproduced with

permission from Tanner JM (1962) Growth at adolescence, 2nd

edn. Oxford: Blackwell.

GROWTH AND DEVELOPMENT 2975

Neural, Cerebral, or Cranial Growth Pattern

0014 The growth of the central nervous system is extremely

quick during the prenatal period and in the first years

of life, reaching 90% of adult weight at the age of 5.

Lymphoid Growth Pattern

0015 The growth processes of some lymphoid structures,

such as thymus, lymphatic nodes, and adenoid glands

or tonsils, undergo great development in early life.

Thus, at the age of 5, they will have already reached

100% of their adult size, following their enlargement

up to 180%, which is achieved at 12–13 years of age.

From that time onwards, size nearly halves so that,

roughly at 20, it reverts to the 5-year-old size.

Growth Pattern of the Reproductive System

0016 Gonad and external genital growth takes place in two

stages: embryonic–fetal stage, permitting sexual dif-

ference, followed by a long period when growth is

very slow, without significant changes from birth to

the end of prepuberty. At the beginning of puberty,

and within a 3-year period, the second stage of

growth, takes place when gonad and external sexual

character growth is completed and reproductive

capacity is achieved.

Growth Pattern of Adipose Tissue

0017 This is characterized by rapid growth during the first

year of life. Then it decreases, and from 10 years

onwards there is a new increase, which is more evi-

dent in women’s case, which continues in puberty. In

contrast, in men it decreases, so that at the end of the

growth process women’s rate of body fat is almost

twice that of men.

Growth and Variation of Body Proportions

0018 After 2 months of fetal life, craniofacial section rep-

resents 50% of total body length. This decreases to

25% in the newborn, whilst in adulthood it is only

one-eighth of total size. Leg proportion undergoes an

opposite evolution to that of the cranium. Trunk

proportional changes are much more limited. They

affect the superior/inferior body segment ratio, which

ranges from 1.7 at birth to 1.0 at 10 years.

Critical or Sensitive Periods of Cell

Growth

0019 Teratogens, infections, and nutrient deficiency have

different effects on the growth and function of

organs, depending on growth speed. That is, during

the growth process there are critical or sensitive

periods which are characterized by an increase of

vulnerability to a specific stimulus. This phenomenon

occurs along periods of maximum cell proliferation

(cell hyperplasia), mainly in the fetal period and the

first year of life, and in puberty, to a lesser extent.

0020In line with this is the ‘programming phenomenon.’

Poor nutrition and other adverse biological and envir-

onmental influences in the critical periods of fetal

development and the first year of life may cause per-

manent changes in gene expression, cell replication,

organic function and structure, hormone action and

secretion, and growth factors. These factors, apart

from affecting growth and body composition, will

also favor the development of degenerative diseases

such as cardiovascular disorders, high blood pressure,

diabetes or hyperlipidemia (X-syndrome) during

adulthood, and these diseases are nowadays the

main cause of morbid mortality. Fetal growth is a

significant predicting factor for postnatal growth

and adult size (Figure 2).

Human Growth Pattern: The Infancy–

Childhood–Puberty Model

0021Currently, the most accurate model for the relation-

ship between growth and the biological factors re-

sponsible for growth at different stages of life is

Kalberg’s ICP (infancy–childhood–puberty) model.

Based on experimental data, this model shows a

general growth curve representing the additive and

partially overlapping effect of its biological basis,

from the fetal period to the end of puberty (Figure 3).

Normal

growth

Catch-up

growth

No catch-up

growth

Gestation Birth

Insult

Fewer cells

Cell proliferation

Cell growth

Smaller

cells

Fetal weight

fig0002Figure 2 This diagram illustrates how fetal growth is predom-

inantly by cell proliferation in early pregnancy and later by cell

growth. For this reason, an early insult may result in a permanent

reduction in cell number, whereas one later in pregnancy may

reduce cell size and be reversible after birth. Reproduced with

permission from Holmes R and Soothill PW (1998) Normal fetal

growth. In: Kelmer ChJH, Savage MO, Stirling HF and Saenger P

(eds) Growth disorders, pp. 143–157. Cambridge: Chapman & Hall.

2976 GROWTH AND DEVELOPMENT

Infancy Component (I)

0022 Infancy is from the second half of gestation to the

second to third year of life. It is represented by an

exponential function (y ¼a þb(1exp(ct)). There-

fore, it covers an accelerated period of fetal growth

and one of high-speed postnatal deceleration. Growth

during the fetal period and the first stage of life

depends on the mother to a great extent, since her

size, health, nutrition state, placental structure and

function, and nutrient contribution to her child exert

a great influence. In this sense, growth is mainly

‘nutrition-dependent’ as growth hormone (GH)-

receptor scarcity and tissular insensitivity to their

action show their secondary role in fetal growth and

during the first period of life.

Childhood Component (C)

0023 Up to the second to third year, the infancy component

continues to influence growth. But, from the sixth

month onwards, the childhood component starts to

exert a progressive influence too, acting in both an

additive and complementary way. After the second

to third year, the childhood component keeps on

exerting this influence until puberty begins. It is

characterized by slow and stable growth. The math-

ematical model for the childhood component is a

second-grade polynomial function: y ¼a þbt þct

0024In normal conditions, the childhood component

starts between sixth and 12th month of life, becoming

manifest by means of an increase in growth velocity.

Its appearance represents the beginning of a progres-

sive and significant GH effect on linear growth. At

this stage, the highest percentage of body growth

takes place at the inferior limbs and is related to a

greater sensitivity of long bones to GH action in

comparison to short ones and vertebrae. The fact

that it starts after the 12th month may have a crucial

influence on final adult size, as proved by the fact that

the biggest difference in adult size between develop-

ing and developed countries is established during the

very first period of the childhood component. More-

over, socioeconomic, health, and nutritional situation

are also involved. Whilst the infancy component is

‘nutrition-dependent,’ GH action is essential for the

childhood component, although nutrition continues

to play an important role.

Pubertal Component (P)

0025The pubertal component is described as a logistic

function: y ¼a/(1þexp[b[ttv]], and is the result

of the synergy of two hormonal systems promoting

growth, one of them depending on GH and the other

one on sexual steroids (estrogens, testosterone).

Growth accelerates, ending with a high-speed peak,

and then decelerates to adult size.

Growth Velocity According to the

following ICP Model

Fetal Growth

0026The fetal period is the most intensive period of life as

regards growth and development. One characteristic

is the elevated rate of cell division – there is maximum

cell hyperplasia. It is a chronologically short although

biologically active time. Let’s say that 42 consecutive

cell divisions take place in the fetus whilst from post-

natal period to the end of growth only five more

divisions take place. Thus, from the fertilized cell,

the newborn gains 3500 g weight, whereas from new-

born to adulthood its weight is only multiplied 20

times (3.5 kg to 70 kg). As regards length, the fertil-

ized cell reaches 50 cm at birth. Subsequently, this

length is multiplied 3.5 times (50 cm to 175 cm).

Age (years)

Puberty (3)

Combined

growth

Infancy (1)

Childhood (2)

(1+2+3)

(1+2)

Centimeters

100

120

140

160

180

−1

1357911131517

Attained

supine length/height

boys

fig0003 Figure 3 The infancy–childhood–puberty (ICP) model of

growth: the infancy component is initially rapid but decelerates

as the influence of growth hormone appears by the end of the first

year. The effect of growth hormone is sustained through child-

hood but, in the absence of adequate sex steroid secretion, the

pubertal growth spurt is blunted or absent. The combined input of

the three components results in the normal pattern of growth until

final height is achieved. Reproduced with permission from Karl-

berg J (1989) A biologically oriented mathematical model (ICP)

for human growth. Acta Paediatrica 350 (suppl.): 70–78.

GROWTH AND DEVELOPMENT 2977