Copra Meal Hydrolysis: a Review

Copra Meal Hydrolysis: A Review

C.L.L. Banta[1]

INTRODUCTION

C

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).

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-D-mannosyl 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.

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 (1260 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 nitrogen-free 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-protein-polysaccharide 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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[1]Technical Supervisor, Philippine Coconut Research & Development Foundation, Inc. (PCRDF), 3F PCRDF Bldg., Pearl Drive, Ortigas Center, Pasig City 1600, PHILIPPINES.