Pertanika 10(3), 305 - 309 (1987)
Food Energy from Palm Oil and its Fractionation Products,
Palm Olein and Palm Stearin*
T.K.W. NG, Y.H. CHONG'andH.T. KHOR2
Division of Human Nutrition,
Institute for Medical Research,
50588 Kuala Lumpur
Key words: Palm oil; palm olein; palm stearin; food energy; calorific value; energy availability
rat assay.
ABSTRAK
Tenaga tersedia minyak sawit, olein dan stearin sawit telah diukur dart kaedah kadar tumbesaran tikus muda di bawah keadaan berkurangan bekalan tenaga. Berasaskan atas nilai tenaga tersedia minyak biji kapas sebanyak 8.93 kilokalori setiap satu gram (kcal/g), minyak sawit, olein sawit
dan stearin sawit yang bertapis jernih telah didapati mengandungi 8.92, 9.06 dan 8.55kcal/g. Ini
menunjukkan bahawa bagi tujuan amali, 9.0kcal/g yang telah biasa digunakan untuk kiraan tenaga
tersedia lemak-lemak yang dimakan adalah sesuai untuk pengiraan tenaga tersedia minyak sawit dan
olein sawit.
ABSTRACT
The energy availability of palm oil, palm olein and palm stearin was determined by growth
responses of young rats under conditions of energy restriction. The energy values are found to be 8.92
kilocalories per gram (kcal/g) for refined, bleached and deodorised (RBD) palm oil, 9,06kcal/gfor
RBD palm olein and 8.55kcal/gfor RBD palm stearin, based on the energy availability of 8.93kcal/g
established for cottonseed oil. These findings indicate that for practical purposes, the traditional use
of 9.0kcal/g as the energy availability of edible fats is appropriate for RBD palm oil and RBD palm
olein.
INTRODUCTION
The major nutritional sources of energy for the
human body are fat, carbohydrate and protein.
As an energy source, fat is more than twice as
efficient as either carbohydrate or protein; it has
an energy availability of 9.0kcal/g as compared
with 4.0kcal/g for either carbohydrate or
protein (FAO, 1977; WHO, 1985). Thus, fat is
the most concentrated form of food energy and
the fat content of a diet generally determines its
energy density.
Food energy is traditionally measured by
the complete combustion of food in a bomb calo-
rimeter. However, the gross energy value so
obtained includes energy that is not available
for metabolism, i.e. energy that would be lost in
the faeces due to incomplete digestion or absorption of food and in the urine due to incomplete
oxidation of absorbed food, particularly that of
protein (Merrill and Watt, 1955; WHO, 1985).
Thus, gross energy gives the energy content of
food but does not reflect the digestibility nor the
utilization of the food concerned. However, it is
the energy availability or to be more precise, the
metabolizable energy which is of practical
interest when considering whether food will meet
*The information reported in this paper is contained in the Ph.D. thesis of T.K.W. Ng, University of Malaya, 1987.
Senior Research Fellow, Palm Oil Research Institute of Malaysia, Bandar Baru Bangi, 43000 Kajang.
Associate Professor, Department of Biochemistry, University of Malaya, 59200 Kuala Lumpur.
T.K.W. NG, Y.H. CHONG AND H.T. KHOR
energy requirements. To measure the metabolizable energy of fats and other foods, Rice and
associates (1957) introduced a convenient assay
based on the growth of young rats under conditions of energy restriction. This technique has
been widely accepted and has been used by
several investigators to determine the metabolically available energy of edible fats before
and after heat treatment or commercial frying
(Keane, Jacobsen and Krieger, 1959; Poling,
Warner, Mone and Rice, 1960; Rice, Poling,
Mone and Warner, 1960).
In Malaysia, RBD palm oil and its fractionation products, RBD palm olein and RBD
palm stearin are now used in a wide range of
edible products such as cooking oils, margarines,
shortenings, confectionery fats, cocoa butter
substitute, ice-cream, 'Tilled" milk and vanaspati (Berger, 1981; PORAM 1984/85). However, progress in the area of palm oil product
development is well ahead of the knowledge on
the nutritive value and dietary role of palm oil.
Currently, information on basic nutritional
criteria such as energy availability, digestibility,
absorbability and utilization are lacking for
RBD palm olein and RBD palm stearin. Hence,
this study was conducted to determine the energy
availability of RBD palm oil, RBD palm olein
and RBD palm stearin, and to compare the
energy values obtained with that of another
common edible oil — soybean oil. The information obtained should be of interest to both producers and consumers of Malaysian processed
palm oil.
Bomb Calorimetry
The heat of combustion of the fat/oil samples
was determined by a Gallenk;;mp bomb calorimeter. Three separate analyses were performed
for each sample and the mean calorific values of
the samples were calculated.
Rat Assay
The rat assay used in this study is based on the
technique introduced by Rice and associates
(1957) but cottonseed oil was used as the reference fat instead of "prime steam lard" because
the energy availability of the former oil has been
established by the authors (Ng, 1987).
Twenty-one day old Albino-Swiss strain
male rats were weaned, housed individually and
fed 5.0g of a basal diet (see Table 1) daily for 7
days. At the end of this period, the rats were
weighed and those with body weights differing
by 5g or less were selected and then divided into
9 uniform groups. Each group of animals was
randomly assigned to one of the levels of the
reference fat (cottonseed oil) or to one of the test
fats. The animals were again placed in individual cages which were arranged so that the
animal groups were equally represented on each
shelf of the cage rack used. Water was provided
ad libitum to the animals throughout the study.
Two separate 7-day rat assays were performed. In each assay, the experimental animals were
TABLE 1
Composition of the basal diet used in the rat assay1
Component
MATERIALS AND METHODS
Fat Samples
RBD palm oil, RBD palm olein and RBD palm
stearin were obtained from Lam Soon Oils and
Soap Manufacturing in Petaling Jaya. Refined
soybean oil ("soyalite"), included in the study
for the purpose of comparison, was purchased
from a nearby supermarket. The identity and
nature of these fat samples were confirmed by
fatty acid analysis.
Reagent grade cottonseed oil was purchased
from United States Biochemical Corporation,
Cleveland, U.S.A. and was used as the reference
fat in the rat assay.
306
g/lOOg diet
Casein
40.0
Cornstarch
34.0
Sucrose
10.0
Cottonseed oil
4.0
Celufil (alpha-cellulose)
5.0
AIN 2 mineral mixture 76
5.0
AIN vitamin mixture 76A
1.5
DL-methionine
0.3
Choline bitartrate
0.2
1
Provides 380kcal/100g-or 19kcal/5g
* American Institute of Nutrition
PERTANIKA VOL. 10 NO. 3, 1987
FOOD ENERGY FROM PALM OIL AND ITS FRACTIONATION PRODUCTS
each given a fixed amount of basal diet, either
5.0g or 4.0g, plus 1.5g of either RBD palm oil,
RBD palm olein, RBD palm stearin or soybean
oil per day. This daily regimen was mixed well
before being served in the morning at 0900
hours. Spilled food was put back into the respective food cups at 1600 hours later in the day.
Care was taken to ensure that all the food served
daily was consumed completely by the experimental animals.
In each rat assay, the animals were weighed
at the end of 3 days and again at the end of 7
days of feeding. The experimental room was
well-ventilated and provided with 12 hours of
light and dark cycles. Room temperatures
during the study ranged from 26° to 29°C.
The reference curve was established from
the rat growth response obtained on the same
amount of basal diet plus the following amounts
of cottonseed oil daily: O.Og, 0.5g, l.Og, 1.5g
and 2.0g. The cottonseed oil was assigned an
energy availability of 8.93kcal/g based on a coefficient of digestibility and gross energy value of
97.0% and 9.30kcal/g respectively (Ng, 1987).
The mean 7-day weight gain per rat in the
experimental groups fed the various levels of
cottonseed oil (0.0 —2.Og) were plotted against
the corresponding quantity of available energy
in these amounts of the reference fat which were
added to the daily basal diet. The energy availability of each test fat can then be calculated by
interpolating the mean 7-day weight gain per
animal of the dietary group concerned on the
reference curve and reading off the energy provided by 1,5g of the test fat.
Statistical Analysis
The coefficient of variation in the 7-day weight
gain in each animal group was calculated using
the formula: (standard deviation/mean) 100%.
Differences in energy values among the fats
studied were computed using the one-way
analysis of variance (Welkowitz et al, 1976).
RESULTS AND DISCUSSION
The reference curves obtained in the two
separate rat assays are shown in Figure 1 while
the growth responses in the animals fed the
energy-restricted diets are indicated in Table 2.
Table 2 shows that the mean energy avail-
I TO U1AL »l*T (flCAL)
Fig. 1: Growth response obtained by feeding various
amounts of cottonseed oil to 4.0g and 5.0g
of basal diet
ability obtained for RBD palm oil, RBD palm
olein, RBD palm stearin and soybean oil are
8.92, 9.06, 8.55 and 8.92kcal/g respectively.
While no significant difference was observed
among these energy values for the various test
fats in the first rat assay, the energy availability
of RBD palm stearin was found to be significantly ( ch - 0.05) lower than that for RBD palm
olein and soybean oil in the second assay using
4.0g of basal diet. Thus, the use of this lower
amount of basal diet per animal appeared to
make the rat assay more sensitive.
The amount of basal diet used per rat was
reduced to 4.0g in the second assay after the
following observations which suggested that the
daily energy intakes of the experimental animals
were higher than required when 5.0g of basal
diet was used viz: (a) the weight gains of the
animals fed the various amounts of cottonseed
oil ranged from 15,7g to 42.Og for the 7-day
feeding period, which were much higher than
the gains reported by Keane et al. (1959) for rats
allocated similar amounts of basal diet and
cottonseed oil even though a different strain of
animal was used, and (b) the animals on a daily
allowance of 5.0g basal diet plus 2.0g of the
reference fat had difficulty finishing their daily
food allocations.
The energy availability values for the
various fats illustrated in Table 2 are generally
PERTANIKA VOL. 10 NO. 3, 1987
307
T.K.W. NG, Y.H. CHONG AND H.T. KHOR
TABLE 2
Growth responses of male rats fed energy-restricted diets
4.0g basal diet
5.0g basal diet
Wtgain 4
in 7 days
(g)
Coeff. of
variation 2
(%)
10.2
4.73
6.58
19.4
4.70
2.26
26.6
3.45
1.12
31.8
1.16
42.0
2,05
37.7
1.46
36.7
3.10
9.12
31.9
1.07
9.00a
9.06
31.4
2.05
8.80
b
8.92
30.8
2.19
8.53C
8.55
0.70
a
8.92
Wt gain l
in 7 days
(g)
Coeff. of
variation2
(%)
O.Og
15.7
4.09
0.5g
23.0
l.Og
30.5
1.5g
36.2
2.0g
Supplement to
basal diet
Energy
avail. s
(kcal/g)
Energy
avail.:)
(kcal/g)
Mean
Energy
availability
(kcal/g)
Cottonseed oil
Palm olein, 1.5g
Palm oil,
1.5g
36.5
3.78
9.03
P. stearin,
1.5g
35.5
2.99
8.57
Soybean oil, 1.5g
36.2
2.87
8.90
31.7
8.93
Mean of 5 animals per group
Calculated from the individual growth in each group
3
No significant difference among the means
Mean of 4 animals per group
a is significantly higher than c using one-way ANOVA ( <?> P 0.05); b is not significantly different from the other means
lower than the corresponding gross energy
content of these fats shown in Table 3. This is
expected as not all the gross energy of a fat is
available for metabolism; some of the "ingested"
energy is lost in the faeces and urine (Merrill and
Watt, 1955; WHO, 1985).
TABLE 3
Calorific values of fats by bomb calorimetry
Fat/oil
Calorific value'
(kcal/g)
RBD palm oil
RBD palm olein
9.09
RBD palm stearin
Soybean oil
9.10
9.20
Cottonseed oil
9.30
9.14
•Values represent the mean of 3 determinations.
No significant difference among the population means
308
It is recognised that the reliability of the
energy values obtained for the fats studied
depends on the accuracy of the energy availability value established for the reference fat,
cottonseed oil. However, when different fats are
compared as sources of "metabolizable food
energy", the reference fat can be assigned an
arbitrary value such as "100%" since absolute
energy values need not be known.
It must be emphasized that it is generally
acknowledged that the results obtained with
Rice's 7-day rat assay technique are uniform and
highly reproducible, thus permitting the use of
small groups of animals as described in this study
and obviating the need to extend the period of
feeding.
CONCLUSION
RBD palm oil and RBD palm olein have energy
availability values comparable to that of soybean
PERTANIKA VOL. 10 NO. 3, 1987
FOOD ENERGY FROM PALM OIL AND ITS FRACTIONATION PRODUCTS
oil. However, the energy availability of RBD
palm stearin is slightly lower than that of the
other fats studied which suggests that the digestibility and absorbability of RBD palm stearin
are probably lower than that of the other two
palm oil fractions mentioned.
ACKNOWLEDGEMENT
The authors are indebted to Dr. Mohd Ismail
Noor for arrangements made regarding the
bomb calorimetric determinations of the gross
energy values of the fats studied at the Department of Food Science and Nutrition, Universiti
Kebangsaan Malaysia.
This study was supported by a grant provided by the Palm Oil Research Institute of
Malaysia (PORIM).
KEANE, K.W.,
G.A.
JACOBSEN and
C.H.
KRIEGER.
(1959): Biological and chemical studies on commercial frying oils. /, Nutr. 68: 57 - 74.
MERRILL, A.L,. and B.K. WATT. (1955): Energy value
of foods — basis and derivation. U.S. Dept. Agri.
Handbook No. 74.
NG, T.K.W. (1987): Nutritional and biochemical
studies of palm oil as a dietary fat in the rat.
Ph.D. thesis, University of Malaya.
POLING, C.E.,
W.D.
WARNER, P.E. MONE and
E.E.
RICE. (I960): The nutritional value of fats after
use in commercial deep fat frying. / Nutr. 72:
109-120.
PORAM. (1984/85): Technical Brochure: Malaysian
Palm Oil Refining Industry.
RICE, E.E.,
C.E.
POLING, P.E.
MONE and
W.D.
WARNER. (1960): A nutritive evaluation of overheated fats./ Am. Oil Chem. Soc. 37: 607 - 613.
RICE, E.E.,
W.D.
WARNER, P.E.
MONE and
C.E.
POLING. (1957): Comparison of the metabolic
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253-266.
REFERENCES
BERGER. K.G. (1981): Food uses of palm oil. PORIM
Occasional Paper No. 2.
WHO. (1985): Energy and protein requirements.
Technical Report Series 724.
FAO. (1977): Dietary Fats and Oils in Human Nutrition. Food and Nutrition Paper No. 3.
(Received 10July, 1987)
PERTANIKAVOL. 10 NO. 3, 1987
309