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BY PRODUCTS
Potential of coconut
dietary fiber
K.S.M.S. Raghavarao, S.N. Raghavendra and N.K. Rastogi
Department of Food Engineering, Central Food Technological Research Institute,
Mysore - 570 020, INDIA
Abstract (cellulose, hemicellulose, pectin and
he present work is aimed at the lignin) as well as intracellular
Tproduction of dietary fiber from polysaccharides such as gums and
underutilized coconut residue left mucilage that are not digested by
after extraction of milk, by human digestive enzymes [1]. The
subjecting it to physical treatments main components of dietary fiber are
such as water wash, hot water wash, cellulose, hemicellulose, starch,
boiling water wash and pressure pectin substance (polygalacturonic
cooking as well as solvent acid components) and lignin [2].
extraction. The fat content was Amongst these, only cellulose and a
Coconut fiber has maximum reduced from 62 per cent to 45 per portion of retrograded starch (called
capacity to swell when cent and to 41 per cent by treating resistance starch) are insoluble in
compared to other fibers, with boiling water and pressure- water, while the other are soluble.
which is the most desirable cooking, respectively. Water The non-starch polysaccharides act
parameter for physical holding, water retention and as bulking agent or roughage in the
functioning of dietary fiber. swelling capacity increased with food. Dietary fiber is considered as
decreasing fat content. A marked a physiologically inert material
Coconut fiber showed highest increase was observed in hydration although the bulking and laxative
water holding, water retention properties when the fat content properties of many fiber sources
and swelling capacity when decreased from 10 to 2 per cent. The have long been appreciated [3]. It
compared to other dietary hydration properties were maximum has been shown to play an important
fibers. for 550 µm particle size coconut role in the prevention of the risk of
fiber. For higher particle size (1127 carcinogenesis, atherosclerosis and
µm), the oil got trapped inside the in the control and proper
fiber matrix, resulting in decreased management of diabetes mellitus [4].
hydration properties, whereas for Adequate amount of dietary fiber in
lower particle size (390 µm) the food is good for the proper bowel
rupture of fiber matrix was moments. Consumption of cereal-
responsible for low hydration based dietary fiber has been
properties. An attempt was made to promoted for its prophylactic value
compare the hydration properties of in regulating colonic function [5].
coconut dietary fiber with other Incorporation of dietary fiber in
commercially available dietary our food also serves nutritional,
fibers. technological as well as
Introduction physiological purposes. Insoluble
fibers in biscuits, cooked meat
Dietary fiber refers to the plant products, confectionery, drinks,
substances including plant cell wall sauces, desserts and yogurt act as
October 2008 2 l
BY PRODUCTS
bulking agent and reduce the calorie Materials and methods temperature (treatment 1); with hot
0
content [6]. Fibers are added to Preparation of sample water at 90 C (treatment 2); with
cooked meat products to increase the boiling water (treatment 3); and
cooking yield owing to their water The coconut endosperm after pressure-cooked for 10 min
and fat retention properties. In fried removal of shell and paring was (treatment 4).
food products, addition of fiber passed through Krauss-Maffei Solvent extraction
reduces lipid retention and increases (Rotary wedge type) cutter having a
moisture content. A wide range of sieve plate (3 mm hole) through Coconut fiber (100 g) was mixed
dietary fibers is available in the which shredded coconut meat was with hexane (1L). The samples were
market. Dietary fibers from different forced out. The resulting coconut withdrawn after 1, 2, 3, 4, 5 and 9 h,
0
sources differ in chemical gratings were expressed in a screw and kept in a hot air oven at 45 C
composition and physico-chemical press to extract coconut milk. for 3 h to remove hexane, and
properties and they have been Material balance of the process for weighed.
extensively studied for their ability 100 kg of coconut has been provided Determination of hydration
to regulate transit time due to in Fig. 1. The coconut fiber was properties
increased stool bulk and other given the following physical
beneficial properties such as treatments as well as solvent The clear definition and
hydration properties like swelling extraction to reduce the fat content. standards for measurement of
capacity, water holding and water Size separation properties were major
retention capacities [7]. Hydration considerations for hydration
properties of dietary fibers One hundred gram of sample was property [7]. Water absorption
determine their optimal usage levels taken in a set of standard sieves (BSS property of dietary fiber is an
in food because a desirable texture mesh number 12, 18, 25, 30, 36 and important determinant of stool
must be retained [8]. 44) and the following fractions were bulking effect, which is due to the
Practically no reports are available separated: 12/18 (1127 µm), 18/25 manner in which water is held, rather
in literature regarding the utilization (725 µm), 25/30 (550 µm), 30/36 than the absolute amount held.
of spent coconut fiber as dietary fiber, (462 µm) and 36/44 (390 µm). Strongly bound water has been
except the one by Trinidad et al [4], Physical treatments found to have no effect on stool
in which only the physico-chemical weight, where as loosely associated
and nutritional properties of coconut Coconut fiber was washed with water readily increases stool weight
fiber are emphasized. running tap water at ambient [9]. The maximum amount of water
The present work deals with the Dehusked coconuts 500 kg (1000 nuts)
technological aspects of the Shelling
production of dietary fiber from Shelled coconut
underutilized coconut residue (after Coconut water (60 kg) (280 kg) Shells
separation of milk) by physical (160 kg)
treatment (such as cold water, hot Paring
water and boiling water treatments) Pared coconuts
as well as solvent extraction. The (240 kg) Parings
effect of residual fat and particle size (40 kg)
on the hydration properties of Disintegration
coconut fiber has also been Coconut gratings
investigated. Attempts have been Screw pressing
made in comparing the hydration
properties of coconut dietary fiber Coconut fiber Coconut milk
with commercially available dietary (72 kg) (156 kg)
fiber. Fig. 1: Flow chart for the production of coconut fiber
l 3 Indian Coconut Journal
BY PRODUCTS
that the fiber can hold is a function centrifugation). Accurately weighed Determination of fat content
of the fiber source and its chemical, dry sample (1 g) was taken in a The fat content of the sample was
physical and structural graduated centrifuged tube, around determined by using Soxhlet
characteristics. 30 ml of water was added and extraction with petroleum ether (40
Water holding capacity hydrated for 18 h, centrifuged (3000 - 60o C) [10].
x g; 20 min) and the supernatant Determination of soluble and
Water holding capacity is defined solution was removed by passing insoluble dietary fiber
by the quantity of water that is bound through sintered glass crucible (G4)
to the fibers without the application under applied vacuum. The hydrated Total soluble and insoluble
of any external force (except for residue weight was recorded and dietary fiber content in coconut was
gravity and atmospheric pressure). then sample was dried at 105°C for determined by Enzyme-Gravimetric
Accurately weighed dry sample (1g) 2h to obtain its dry weight [7]. method. Dry sample was suspended
was taken in a graduated test tube, Water retention capacity (g/g) in phosphate buffer (pH 6.0) and
around 30 ml of water was added and treated with different enzymes such
hydrated for 18 h. The supernatant =(Residue hydrated weight after as termamyl (pH 1.5), pepsin (pH
was removed by passing through centrifugation - Residue dry weight)/ 6.8) and pancreatin (pH 4.5) for one
sintered glass crucible (G4) under Residue dry weight hour at specific pH as provided in
vacuum. The hydrated residue Swelling capacity the brackets. In order to find out
weight was recorded and it was dried insoluble dietary fiber, the fiber was
at 105°C for 2 h to obtain residual Swelling property is defined as separated after enzymatic digestion,
dry weight [7]. ratio of volume occupied when the washed with ethanol and acetone,
Water holding capacity (g/g) sample is immersed in excess of finally incinerated and weighed.
water after equilibration to the actual Soluble dietary fiber was estimated
=(Residue hydrated weight - weight. Accurately weighed dry by precipitating the filtrate by
Residue dry weight) / Residue dry sample (0.2 g) was taken in a ethanol. The precipitate was washed
weight graduated test tube, around 10 ml of with ethanol and acetone, dried,
Water retention capacity water was added and hydrated for incinerated and finally weighed [11].
18 h. After 18 h, the final volume Results and discussion
Water retention capacity was attained by fiber was measured [7].
defined as the quantity of water that Swelling capacity (ml/g) Effect of processing treatments on
remains bound to the hydrated fiber hydration properties of dietary fiber
following the application of an = Volume occupied by sample / Coconut fiber after extraction of
external force (pressure or Original sample dry weight milk contains about 62% of fat on
Fig. 2. Effect of (a) different physical treatments (1 Control; 2 Water wash; 3 Hot water wash; 4 Boiling water wash; 5 Pressure cooking) and (b) solvent extraction
on fat content of coconut fiber
October 2008 4 l
BY PRODUCTS
dry basis. The fiber was given
different physical treatments as well
as solvent extraction to reduce fat
content.
Effect of physical methods
The coconut fiber was given
treatments such as water wash, hot
water wash, boiling water wash and
pressure-cooking to remove the fat.
Fig. 2(a), shows that at ambient
temperature, water wash as well as
hot water wash were not effective for
fat reduction. The fat content of the
sample (62 per cent) was reduced to
45 and 41 per cent by boiling water
wash and pressure-cooking,
respectively.
Effect of solvent extraction
The fat present in coconut fiber
was removed by treating with hexane.
The experiments were conducted for
different immersion time intervals (1,
2, 3, 4, 5 and 9 h of solvent extraction)
and the fat content was determined
(Fig. 2 (b). It can be seen that increase
in the immersion time resulted in
decrease in fat content from 48.1 per
cent to 2 per cent.
Effect of fat content on hydration
properties
Fat content of the dietary fiber
plays an important role in
determining the hydration properties
such as water holding, water
retention and swelling capacities.
Fig. 3 (a, b and c) shows the variation
of these properties when the fat
content is reduced from the original
fat content of 62 per cent (fresh
residue without any treatment) to 2
per cent (solvent extracted for 9 h),
for three typical particle sizes (390,
550 and 1127 µm). Water holding,
water retention and swelling Fig. 3. Effect of fat content on hydration properties (a) water holding (b) water retention and (c) swelling
capacity increased with decreasing capacities of coconut dietary fiber of different particle sizes (= 1127 µm, z= 390 µm, = 550 µm).
l 5 Indian Coconut Journal
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