Download Copra Meal Hydrolysis: A Review

Copra Meal Hydrolysis: A Review
C.L.L. Banta1
INTRODUCTION
opra meal is the residual cake left after extracting oil from copra, the dried meat of a mature coconut
(Fernandez 1984). Copra yields 32%-35% copra meal (PCA). Copra meal is usually employed as
an ingredient in animal feed, mainly because it contains 23% protein (Momongan et al. 1964).
However, it can only be used in limited quantities because of its low digestibility (Creswell and Brooks
1971). The presence of fiber lowers the biological value of copra meal protein (Lachance and Molina
1974). Although the protein may have high nutritive value (Krisnamurthy et al. 1958), humans do not have
the enzymes to degrade the fiber and make the protein available for use (Balasubramaniam 1976). Copra
meal has 11% crude fiber (Van Socest and Mc Queen 1973) although its total carbohydrate is 43%-45%
(Rhee and Lusas 1979). Different researchers have presented different findings on the specific
polysaccharide that predominates, whether galactomannan (Balasubramaniam 1976) or mannan
(Saitagaroon et al. 1983; Takahashi et al. 1983). What is established, nevertheless, is that upon hydrolysis
of the polysaccharides in the meal, the hydrolyzate is composed of a higher percentage of mannose than
galactose. According to Takahashi and co-workers (1983), copra meal contains 70.5% mannose, 21.9%
glucose, 5.1% galactose, and 2.5% arabinose. When they delignified the copra meal, they found that the
percentage of mannose increased to 82% while glucose decreased to 10.7%. Copra meal also contains
10%-11% oil (Rhee and Lusas 1979).
C
The polysaccharides, oil and protein in copra meal are presumed to be in complex with one another,
limiting each other’s availability. The digestibility of the polysaccharide itself is limited. To increase the
availability of the protein (Bondad and del Rosario 1979) and oil that copra meal contains, the
polysaccharide have to be hydrolyzed. Teves et al. (1989) and Rosario (1988) found that when copra meal
was predigested, copra meal became more utilizable and nutritious. Copra meal hydrolysis will not only
increase protein and oil extractability but will also yield higher value products. Copra meal is only sold at
less than PhP per kilo (UCAP 1998).
The main chain of the major polysaccharide in copra meal is made up of (1→4) – linked β-Dmannosyl residues. An alpha-D-galactose residue is attached to the O-6 position of some of the mannose
building blocks. There is no pattern in the occurrence of these galactose branches. The structure of copra
meal polysaccharide is similar to that from other sources, e.g. locust bean gum, guar gum, and soybean hull
(Dea and Morrison 1975; Harada and Misaki 1974). However, the ratio of the mannose and galactose
residues in the different polysaccharides varies widely (11:1 to 90:1) (Kusakabe et al. 1986). Hydrolyzing
copra meal polysaccharides yields manooligosaccharides. Manooligosaccharides favor the growth of
intestinal microorganisms, especially Bifidobacteria. The intestinal mucosal cells and the intestinal
microflora that increase fecal mass are also benefited (Hill 1983; Kobayashi et al. 1987). Furthermore,
manooligosaccharides are one of the best growth factors for Lactobacillus sp. (Horikoshi 1991). Both
bacterial genera are now in cultured milk products. The products are supposed to inhibit harmful bacteria
that can affect the digestive system.
If copra meal polysaccharides are hydrolyzed completely, mannose is produced. The mannose, along
with other sugars with other sugars in copra meal, can be hydrogenated to produce sugar alcohols.
Saitagaroon et al. (1985) produced the sugar alcohol, mannitol, from mannose in copra meal hydrolyzate.
Mannitol has been used as a nutrient (at 5% level) and a dietary supplement. Because of its low
hygroscopicity, it has been used in food as a dusting agent. It can modify flavor and improve mouthfeel
(Emodi 1982). It can be used in preventing and treating experimental and clinical acute renal failure.
Because it can scavenge hydroxyl radicals, it inhibits peroxide formation caused by soybean liposygenase
(Morrison et al. 1982). Mannitol has been produced by hydrogenating invert sugar in the presence of a
catalyst.
1
Technical Supervisor, Philippine Coconut Research & Development Foundation, Inc. (PCRDF), 3F PCRDF Bldg., Pearl Drive, Ortigas Center,
Pasig City 1600, PHILIPPINES.
METHODOLOGY
Efforts to hydrolyze the polysaccharides in copra meal have been made. Bondad and del Rosario
(1979) used sulfuric acid (9.2%) at elevated temperature (126 0 C) and pressure (20 psi). The hydrolysis
was conducted for 1 hr. Twenty-six to twenty-eight percent of the cry weight of the copra meal was
converted to reducing sugars. This means that about sixty percent of the polysaccharide component was
hydrolyzed. The hydrolyzate was also made up to 24% protein. They suggested that this could be used as
animal feed component. These proteins, though, were of lower molecular weight than the original proteins
in copra meal because the former was also hydrolyzed under said conditions (Flavier et al. 1980). Animal
feeding trials would have to be done. The proteins were also extracted from the hydrolyzate at 84%
efficiency (Bondad and del Rosario 1979).
Saitagaroon and co-workers (1985) used hydrochloric acid to hydrolyze copra meal polysaccharides.
The copra meal was pretreated with 36% acid (5 parts acid to 3 parts copra meal) or 3.5 hr. The mixture
was then diluted to reduce the acidity to 1 N and boiled under reflux for 5 hr. under these conditions, 51
mg reducing sugars were produced from 100 mg defatted copra meal. Considering the carbohydrate
content of the copra meal sample, the efficiency of the hydrolysis was 94%. The objective of their study
was to produce reducing sugars, especially mannose, for subsequent hydrogenation to sugar alcohol. Thus,
after recovery of the acid and neutralization, the precipitated proteins were just filtered off. They
suggested, however, considering using the protein as feed component. The reducing sugars were
hydrogenated to sugar alcohols; 81% of the carbohydrates were converted to sugar alcohols.
The Philippine Coconut Research and Development Foundation (PCRDF) also pretreated copra meal
with concentrated hydrochloric acid for 12 hr (unpub). After reducing the acidity to 1 N, the mixture was
stirred at room temperature for 1 hr. Then, it was boiled under reflux for 3 hr. Their objective was also to
produce sugar alcohols from copra meal. Before hydrogenating the monosaccharides produced from the
hydrolysis, these were purified. Work must still be done to increase the yield of sugar alcohols.
Copra meal can be hydrolyzed not only with acid but also with enzymes. Mannanases are enzymes
that can hydrolyze mannan, galactomannans, or even glucomannans into their component oligosaccharides
and monosaccharides. They have been isolated from animals, plants, and microorganisms (reviewed by
Dekker and Richards 1976). Before the composition of copra meal polysaccharide was determined, many
researchers had sought to increase the availability of the protein by hydrolyzing the copra meal with
microbial extract containing unidentified enzyme/s or with cellulose. Using cellulose from Stachybotrys
atra, 50% of the fiber was degraded (Ramamurti and Johar 1963). Rao (1969), on the other hand, used
enzymes from Trichoderma virdie (which could be mannanase and cellulose) and increased protein
extractability. Gerpacio et al. (1984), however, observed that the feeding value of copra meal was not
increased by treating it with cellulose. When an enzyme solution from a mannanase-producing
microorganism, Streptomyces sp., was added to copra meal, the crude fiber was reduced from 12.68% to
6.32% (50% reduction). This was fed to broiler chicks and higher weight gain in the chicks was observed.
This could be attributed to the increase in digestibility of dry matter, crude fat, crude fiber, and nitrogenfree extract of the meal, and increase in apparent metabolizable energy. These results support previous
ideas (Hagenmaier et al. 1973; Molina and Lachance 1973; Rama Rao et al 1964; Ramamurti and Johar
1963) that to increase utilization of the proteins in copra meals, the proteins have to be extracted from the
complex carbohydrates. The fat could also have been made more available because the lipid-proteinpolysaccharide complex was broken down (Teves et al. 1989).
Other mannanase-producing
microorganisms have also been shown to have the ability to hydrolyze copra meal. Actinomycetes strains
that exhibited high mannanase activity hydrolyzed copra mannan, yielding the following products:
mannose, mannobiose, small amounts of mannotriose, and other unidentified oligosaccharides (Takahashi
et al. 1983). Penicillium purpurogenum No. 618 hydrolyzed white copra meal into monosaccharide and
disaccharide (Kusakabe et al. 1987). Takahashi and his co-workers (1983) studied the products of the
Streptomyces sp. enzyme-mediated hydrolysis (as mentioned above) more closely. After 24 hr, the
products were mainly mannose and mannobiose, with mannooligosaccharides. PCRDF isolated and
identified copra-meal hydrolyzing isolates, from soil samples from the Philippine coconut plantations
(unpub.). These were Bacillus stearothermophilus, Bacillus coagulans, and Streptomyces sp. However,
optimization of copra meal hydrolysis using these isolates must still be done.
CONCLUSION
There remains a need to increase the economic value of copra meal. For every ton of coconut oil
extracted, approximately five hundred kilograms of copra meal is produced as by-product. Two groups are
now treating copra meal with enzymes from two different microorganisms and utilizing the hydrolyzate as
an improved feed component. With enzymatic hydrolysis, any further destruction of the protein is avoided.
For the production of mannose and mannooligosaccharides, however, chemical hydrolysis may be
advisable. It is less expensive and takes less time. Whether the proteins is acid-hydrolyzed copra meal can
still be used remains to be studied. In the face of increased competition in the vegetable oil market, the
Philippines would be better off if it maximizes its use of copra meal, the other side of copra.
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