Economically Useful Plants of Sri Lanka Part l V m Screening of Sri Lanka Plants for Tannins

Abstract : Several Sri Lankan plants have been assayed for their tannin content. Percenta~ e total tannins as determined by the hide powder method have been compared with the results obtained by the polyclar adsorption method. Infra-red spectroscopy has been used to classify the tannins isolated as either belonging to the condensed type or hydrolysable type. The barks of Carapa granata and Ceriops fagal have been identified as two new tannin rich sources.


Introduction
Tannins are polyphenolic substances widely distlibuted among higher plants.They are important economically as agents for the tanning of leather and they impart flavour to wines.Recently4 evidence has been obtained in support of their potential value as cytotoxic 01 anti-neoplastic agents.In addition, tannins are now being increasingly used2 in the manufacture of plastics, paints, ceramics and water softening agents.The demand for tannin is very great and hence a survey of new sources of plant materials for tannins has assumed increasing impo~tance.Within the overall programme5 of the Chemical Investigation of Economically usefi~l Plants of Sri Lanka, a survey of Sli Lanka plants for their tannin content was also undertaken.Two types of tannins are known.They are hydrolysable tannins and non-hydrolysable tannins.The leather tanning industry requires mainly watersoluble tannins.

Results and Discussion
In the present investigation, the ability of tannins to precipitate gelatin from solution3 has been used to test qualitatively the presence of tannins in plant extracts.The extracts which havave a positive gelatin-salt reagent and neutral ferric chloride tests were adjudged to contain tannins in detectable amounts.The plant extracts which gave positive qualitative tests wele analysed quantitatively.The methanol defatted extracts which had a yield of greater than twenty percent (dry plant weight basis) were subiected to adsorption with hide powder2 and the percentages of the material adsorbed wele regarded as indicating the amount of tannins in the respective plant extracts which could b: used in the tanning industry.The results have been compared with the yields of tannins obtained using adsorption on the polyamide3 polyclar.The Table 1 gives the list of 43 samples subjected to screening for tannins.The water solubility of the defatted methanol extracts is also given in the Table I .Since hydrolysable tannins ale esters and non-lyd~olysable (condensed) tannins are polymers of phenolic compounds, infrared sp~ctroscopy conld b-used to differentiate between the two major classes of tannins.Tannins isolated in tlte present study hsve bzen classified using this method and the results are included in the Table .The nuts of Ternlinalia chebtrls used in this country as a vegetable tanning material in the production of tanned leathx gave for one sample, a defatted methanol extract yield of 44.7 %.In this case, the total tannin yizld as determined by the hide powder and by the polyamide adsorption mcthods were 27.3% and 27.1% respectively.However, contrary to published results3 the tannin yields obtained by the two methods wzre not in agreement in many instances.Cassia aixriculata bark extracts are widely used in India as a vegetable tanning msteria1.lThe present study has shown that the tannins of Cas.~irr auriculafa are of the condensed type.The defatted methanol extracts of the bark of Ceriops tagal contain water-soluble tannins wh~ch are of hydrolysable typz.More than fifty p ~r c e n t of these defatted extiacts are capable of tanning leathel.In many instances the yield of tannin from the Sri Lankan mangrove species was low.C~irapa granata (Meliaceae) bark extract was found to be a good source of tannin.Even tl~ongh this tannin belongs to the condensed type, its solubility in water and adsorbability on chromed hide and po1yamid.ewould make it a suitable tanning material.This i s the first report on the tannin yields of several plant p a t s including the barks of Ceriops fagal and Curapa grcanata.

3, Experimental
The plant materials were collected from various localities in Sri Lanka, mainly in mangrove swamps.Infrared spectra of defatted lnethanolextracts with a yield of > 20% were obtained using a Perkin Elmer 257 spectrophotometer.Hide powdel was prepared fiom cattle skin purchased locally.The polyamide, polyclar, was purchased.

Qualitative test for Tannins
The powdered plant part (10 g) was extracted with methanol for about 2 hr.The extract was solvent evaporated and the dried lesidue was defatted by refluxing with light petroleum f o ~ about 4 hr.The residue was dried again.Hot distilled water (25 ml) was added to the residue and the mixture was stirred well.10% NaCl (3-4 drops) was added and the solution was filtered into 4 test tubes.To each tube the foIlowing reagents were added.
-. Percentage total tannin as determined by the hide powder method is given and the percentage total as determined by the polyclar adsorption method is given in parenthesis.

Plant Name and Family
1. 4-5 Drops of 1 % gelatin : 2. 4-5 Drops of gelatin-salt reagent (1 % gelatin + 10% NaC1); 3. Neutral felric chloride; 4. Used as a reference.If a piecipitate was obtained in tubes 1 and 2 and if tube 3 also gave a positive test, then tannins were considered to t e present in detectable amounts in the test extract.

Quantitative assay
The powdered plant part (10 g) was extracted ~i t h methanol and the extract was defatted as before.The defatted methanol extract yield was recorded.

Preparation of chrorned hide po~vdeu
De-haired cattle skin was dried well and was ground.The powder was sieved and the fine drq powder was used.Dry hide powder (3.12 g) was digested with ten times its weight of distilled water for 1 hr, k chiome alunz solutior, (3 % w/v) was added and the contents were frequently stirred for sever61 hours.After standing overniglxt the material was transferred to a cloth and was squeezed.The material was washed tholoughly wit11 watel to lemove excess alum.

Adsorption on clzromed hide
The defatted extract (0.185 g) was dissolved in distilled water (200 ml) and was filtered free of any insoluble matter.25 ml of this solution was evapo~ated to dryness and the weight of the residue &as noted.Another 50 ml of this solution was added to the prepaled chromed hide powder and was agitated f o ~ about 10 min.The contents wzre filtered through a cloth.Kaolin was thoroughly mixed with the filtrate and the mixture was filtered.25 ml of this filtrate was evaporated to dryness.From the weight of the residue, the amount of substance adsorbed onto the chromed hide was calculated.The tannin contents have been expressed as percentages and are given in the Table 1.

Adsorption 072 polyclar
The defatted extract (1.5 g) was dissolved in 50 rnl water. 25ml of this solution was treated with polyclar (3 g).The mixture was stirred for 4 11r and was filtered.Kaolin (2 g) was added to the filtrate and the mixture was stirred.The mixture was filtered and was evaporated to dryness.25 ml of the remaining aqueous solution of the defatted extract was also evaporated to dlyness.From the weight of the residues, the amount of tannin adsorbed onto the polyainide was obtained and the tannin contents have been expressed as percentages in Table 1.

Solubility determination
50 mg of the tannin was treated with cold water (1 ml).The insoluble matter was filtered and the percentage solubility was calculated.