Studies on Coconut Sapal

STUDIES ON COCONUT SAPAL

III. MANNAN IN THE DEVELOPING NUT[1]

J.R. Velasco and Chita J. Meimban[2]

© Philippine Journal of Coconut Studies. June 1989.

Mannan was determined in nuts of various ages by extracting the dried coconut meat successively with water, 0.4%, 4.0%, and 18.0% solution of sodium hydroxide. It was found that the 8-mo-old nut contained the highest amount of mannan (total weight of 68.3640 g per 100 g dried meat). The most effective extractant was the 18% solution of sodium hydroxide.

Prospects for the commercial uses of mannan were cited, and the role of mannan in metabolism was speculated on.

INTRODUCTION

In a previous paper, Velasco and Meimban (1986) commented that the carbohydrates of the coconut meat (solid endosperm) is largely a by-product of the coconut oil industry. In the dry process of oil rendering, it is a major constituent of the low-priced copra; in the wet process, it is a major part of the so-called sapal, which becomes “residue flour” (Hagenmaier et al. 1976) when it is dried and granulated. Residue flour has no established market. It is deemed important to search for uses of the carbohydrates because it is a major part of the meat. Moreover, if thrown away as waste, it may be a pollution hazard.

In preliminary study, Balleza and Sierra (1976) determined the proximate composition of the coconut meat at various stages of nut development. They found that the carbohydrates or nitrogen-free extract (NFE) was the highest at 53.09%, on dry weight basis, in the 8-mo-old nut. It progressively decreased at 14.70% in the 12-mo-old nut. Thereafter, it increased slightly to 22.80% in the 15-mo-old nut. They further reported that the crude fiber was highest in the 10-mo-old nut (5.92%), and lowest in the 15-mo-old nut (2.87%). Nambiar and Apacible (1976) estimated the NFE in the flour obtained by their oil-milling process at 55%-60%. Presumably, their flour came from 12-mo-old nuts. (In oil-milling, only nuts 12 mo or older are used.) Their percentage contrasts markedly with Balleza and Sierra’s 14.70%. The residue flour obtained by the Texas A&M process contained 68% NFE (Hagenmaeir et al. 1976). It was further reported that on oil-free and moisture-free basis, NFE came out to be 85%; crude fiber, 22%. On hydrolysis, the NFE yielded 78% mannose, 21% dextrose, and 5% unidentified simple sugars. A simple observation was made by Takahashi et al. (1983), who found that mannose constituted 70%-89.9% of their polysaccharide hydrolysate, while galactose accounted for 3%-6.6%. These findings tend to differ from the findings of Rao et al.(1961), and Mukherjee et al. (1962) who reported that their polysaccharide on hydrolysis yielded D-mannose and D-galactose. This led them to call their polysaccharide a galactomannan.

The present writers became interested in the polysaccharide contents of the nuts at various ages, and their findings are herein presented.

MATERIALS AND METHODS

Coconuts

Nuts at various ages or stages of development were used in this study. To estimate the age of the nut, the bunches were counted backwards from the bunch with the most recently fertilized button or nutlet, that is, nutlet where the droplet of water on its stigma had dried up. On the assumption that one bunch is produced each month, the next older bunch was estimated to be 1 mo old, and so on.

The nuts were cut into halves, and their meat was scopped. The meat was homogenized under alcohol in order to prevent the action of enzymes, and to keep the polysaccharide in the solid phase. The alcohol was drained off, and the solid was dried at 60 C.

Isolation of the Polysaccharide

The method of Rao et al. (1961) was adopted. In essence, it consists of extracting the oil with benzene plus alcohol (2:1); the polysaccharide was extracted successively with various solvents (water, 0.4%, 4.0% and 18.0% solution of sodium hydroxide) in an atmosphere of nitrogen; the extract was acidified with the acetic acid to ph 4-5; and the polysaccharide was precipitated by adding the extract dropwise to twice its volume of 95% ethyl alcohol. After removing the occluded matter, the crystals were dried at 40 C.

This method is similar to that of Takahashi et al. (1983), except the latter delignified the copra meal by treatment with acetic acid and sodium chlorite before extracting the mannan.

RESULTS AND DISCUSSION

There was very little meat in the 7-mo-old nut, hence, there was just enough material for one determination. While the data for this age may be indicative, they do not suffice as basis for a conclusion. Table 1 shows that the highest total mannan was obtained from the 8-mo-old nut, followed by that from the 10-mo-old nut. Total mannan from the 12-mo-old nut was less than one-half of that from the 10-mo-old nut.

Among the extractants used, water was the poorest. The 18% solution of the sodium hydroxide extracted the highest total mannan, while the 4% solution was a good second. Takahashi et al. (1983) extracted the copra meal with 24% solution of sodium hydroxide.

If the residue were to be considered as one criterion of results, the F-value of the mean square for extractant and for age-extractant interaction would be significant, while that of the mean square for age would be insignificant. On the other hand, if only the mannan yields were to be considered, the F-value of the mean square for extractant, age, and their interaction would be significant.

In spite of the statistics, the great variability among replications is still a matter of concern. More study may have to be undertaken in order to determine if the variability is due to poor technique, the heterogeneity of the biological material, or the tentative nature of the analytical procedure. One likelihood, as earlier suggested, was the various extent of polymerization of the mannose units, and the insolubility of each polysaccharide size in alcohol. Thus, the total of the weighs from the 7-mo-old nut was only 64g out of the original 100 g. On the other hand, recovery from the 8-mo to 12-mo-old nuts ranged from 94% to 97%. A large part of the polysaccharide in the former could have been of small size, and quite soluble in alcohol.

From the practical standpoint, the most likely source of mannan for commercial purposes would be the 8-mo and 10-mo-old nuts or those which have not yet attained full maturity. On the other hand, the most promising extractant is 18% solution of sodium hydroxide, or maybe even 24%, as used by Takahashi (1983). A market for mannan may be developed along the following uses:(1) as homogenizer, (2) as blood extender,(3) as mannitol, and (4) as an intermediate in some industrial processes.

While the search for new uses of the polysaccharide in the coconut meat is beyond doubt important, it may not be superfluous to explore some impractical (shall we say, theoretical) aspects of the whole subject matter. Thus, the transformation, of the material in the developing nuts seems intriguing. It may be recalled that the dominant sugar in the nut water (liquid endosperm) in the early stages of development is glucose, while the dominant polysaccharide in the meat is polymannose (mannan). To effect the transformation, from glucose to mannose, an isomerase enzyme must be involved. It may be curious to find if the enzyme is extracellular or endocellular. If the transformation is effected in the liquid endosperm, then the extracellular enzyme can be studied more conveniently.

Of course, it is further conceivable, that the mannan could be transformed into someother carbohydrates. This might be the reason for the drop in mannan content after the peak in the 8-mo-old nut.

All these speculations are meant to indicate that the developing nut is a promising material for the study of intermediary metabolism, and the enzymes which are involved.

REFERENCES

BALLEZA, C.F. and Z.N. SIERRA, 1976.Proximate analysis of the coconut endosperm in progressive stages of development. Phil. J. Coco.S. 1(2):37-44.

HAGENMAIER, R., D. M. GLISSENDORF, and K.F. MATTIL. 1976. The residue from aqueous extraction of fresh coconut: An analysis. Phil. J. Coco. S. 1(1):37-41.

MUKHERJEE, A.K. and C.V.N. RAO. 1962. A mannan from the kernel of coconut (Cocos nucifera L.) J. Indian Chem. Soc. 39:687

NAMBIAR,T.V.P. and A.R. APACIBLE. 1976. Alternative processing methods of producing coconut products. IV. Methods of processing coconuts. Phil. J. Coco. S. 1(2):31-36.

RAO, C.V.N., D.. CHOUDHURY, and P. BAGCHI. 1961. A water-soluble galactomannan from coconut (Cocos nucifera L.) Canadian J. Chem. 39:375.

TAKAHASHI, R. et al. 1983. Studies on mannanase of Actinomycetes. I. Some properties of extracellular mannanase. Japanese J. Tropical Agric. 27(3):140-148.

VELASCO,J.R.and C.J. MEIMBAN. 1986. Studies on coconut sapal I. Challenges and opportunities. Phil. J. Coco. S. 11(2): 40-44.

Age of Nut (mo) / Weight
Water / (g)
0.4% / 0.4% / 18.0% / Residue
NaOH / NaOH / NaOH
7 / 0.2265 / 4.8880 / 5.4197 / 11.7950 / 41.7
0.5139 / 4.5855 / 17.7547 / 44.1180 / 29.4
8 / 0.3540 / 5.7632 / 17.2101 / 49.1928 / 21.8
0.3787 / 4.3765 / 17.1931 / 43.6518 / 30.6
Ave. 0.4155 / 4.9084 / 17.3859 / 45.6542 / 27.3
0.1350 / 3.8379 / 20.1474 / 29.4660 / 39.2
10 / 0.2534 / 4.1583 / 21.7101 / 32.2635 / 35.4
0.2372 / 3.3735 / 21.9723 / 32.7000 / 37.7
Ave. 0.2085 / 3.7899 / 21.2766 / 31.4765 / 37.4
1.9936 / 0.5938 / 1.8422 / 18.9934 / 74.8
12 / 0.3735 / 1.5938 / 2.1743 / 22.2583 / 69.6
0.3928 / 1.8167 / 3.2288 / 27.3250 / 65.7
Ave. 0.920 / 1.3347 / 2.4151 / 72.8589 / 70.0

SMD = 1.13

TABLE 1. Weight in grams of mannan in 100 g of dried coconut meat (solid endosperm)

[1]This study was supported in part by the ASEAN- Australian Research Fund.

[2]Industrial Technology Development Institute, Department of Science and Technology, Manila, Philippines.