Year : 2009 | Volume
: 5 | Issue : 18 | Page : 159--164
Variations in Tannin and Oxalic acid Content in Terminalia arjuna (Arjuna) Bark
AK Pandey, DC Kori
Tropical Forest Research Institute, (Indian Council of Forestry Research and Education), P.O. RFRC, Mandla Road, Jabalpur 482 021, M.P, India
A K Pandey
Tropical Forest Research Institute, (Indian Council of Forestry Research and Education), P.O. RFRC, Mandla Road, Jabalpur 482 021, M.P
Terminalia arjuna (Arjuna), belonging to family combretaceae, grows along the streams or rivers and often in the shallow streambeds and riverbeds in central India. It has been considered by the Ayurvedic physicians as well as by the modern practitioners as a cardiac tonic. Clinical evaluation indicated that it has been found beneficial in the treatment of coronary artery disease, heart failure, and possibly hypercholesterolemia. It has also been found to possess antibacterial, antimutagenic and antioxidant activities. Demand for T. arjuna bark, both in India and abroad has been increasing rapidly for over a decade. About 95 percent of the requirement is met from the wild and collected in a pattern that is not concomitant with sustainable harvesting practices. The quality of the bark is directly dependent on harvesting technique and time. There is also a clear relationship between the part of the plant harvested, harvesting method used, and the impact of these on the plant. Keeping above into consideration it has been planned to carry out systematic study on phytochemical investigation of Arjuna bark collected from various parts of the tree at different harvesting time. The bark samples were analyzed for tannin and oxalic acid. The tannin and oxalic acid content varied from 6.75 to 14.82 % and 7.66 to 20.05 % respectively in various samples of T. arjuna bark collected from various places of Madhya Pradesh. The middle-aged trees having GBH around 130 cm were found to contain more amount of tannin. The study gives important information to obtain better quality of T. arjuna bark on sustainable basis.
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Pandey A K, Kori D C. Variations in Tannin and Oxalic acid Content in Terminalia arjuna (Arjuna) Bark.Phcog Mag 2009;5:159-164
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Pandey A K, Kori D C. Variations in Tannin and Oxalic acid Content in Terminalia arjuna (Arjuna) Bark. Phcog Mag [serial online] 2009 [cited 2022 May 17 ];5:159-164
Available from: http://www.phcog.com/text.asp?2009/5/18/159/57975
Terminalia arjuna L. (Combretaceae) is a large deciduous tree found throughout India growing to a height of 20-25 metres. It commonly grows on banks of rivers, streams and dry watercourses in sub-Himalayan tract, Central and South India and West Bengal; also planted for shade or as ornamental tree in avenues and parks. It has been a common observation that the Arjun tree thrives better in areas with sandy soils or areas with shallow soil layer. Therefore ecologically it can be said that the natural abundance of Arjun is due to higher water table in the area. Our inquiries with the local people revealed that no one has planted Arjun specifically. Also there has not been any religious reason for abundance of Arjun trees. Nevertheless people are aware about its medicinal properties. Local people use the fallen leaves as manure and the woody fruits as a fuel. In addition Arjun serves as minor timber in making agricultural implements. In the case of Arjun trees on tank bunds and field bunds, it was the local people who planted them. Profuse seeding is another character of the Arjun tree. The seeds are wind dispersed. Farmers replant the germinated seedlings and saplings growing in their cultivation lands onto the bunds.
Bark of T. arjuna is flat or slightly curved, external surface pink or flesh colored with a mealy coating; inner surface reddish brown, finely striated, peeling out in thin flakes, odorless, gritty and astringent. The bark has been used in India's native Ayurvedic medicine for centuries, primarily as a cardiac tonic. Clinical evaluation of this botanical medicine indicates that it can be beneficial in the treatment of coronary artery disease, heart failure, and possibly hypercholesterolemia , . It has also been found to possess antibacterial, antioxidant and antimutagenic activities. The pharmacology of T. arjuna have been discussed  and pharmacological activities are mainly due to the tannins present in their barks.
Demand for T arjuna bark, both in India and abroad has been growing rapidly for over a decade. Presently the bark of T. arjuna is being extracted through unscientific and destructive harvesting practices. Presently the collectors harvest the bark by making a blaze too deep and wide, damaging the cambium and ray cells responsible for the transport of nutrient and water from the roots to other parts of the tree. This is evident by many injured trees in natural habitat. About 95 percent of the requirement is met from the wild and collected in a pattern that is not concomitant with sustainable harvesting practices. Harvesting commercial quantity of bark can also affect tree population.
Although it is commonly believed that most tree species completely regenerate their bark after it has been damaged. T. arjuna trees are thick-barked and withstand fire damage, but are vulnerable to fungal or borer attack once their bark is removed. The ability to withstand bark damage offered the potential for sustainable harvesting of T. arjuna bark.
A fair amount of chemical work has been done on this plant. The major active constituents include tannins, triterpenoid saponins (arjunic acid, arjunolic acid, arjungenin, arjunglycosides), flavonoids (arjunone, arjunolone, luteolin), oxalic acid, gallic acid, ellagic acid, oligomeric proanthocyanidins (OPCs), phytosterols, calcium, magnesium, zinc, and copper , . It contained unusually, large quantities of calcium salts with small amounts of aluminum and magnesium salts; about 12% of tannins, consisting mainly pyrocatechol tanning; an organic acid with a high melting point and a phytosterol; some coloring matters, and sugars, etc. T. arjuna bark has been found to be a potent source of oxalic acid , . Many factors such as soil composition, water stress, temperature and humidity can affect levels of phenolics present in plants  . Tannin content altered during the development of the plant and also as a response to the environmental changes ,, . These variations influence directly the quality of the plant for medicinal use.
The quality of the bark is directly dependent on harvesting technique and time. There is also a clear relationship between the part of the plant harvested, harvesting method used, and the impact of these on the plant. Keeping above into consideration this study was carried out to find out the variation in tannin and oxalic acid content in T. arjuna bark.
Materials and Methods
The surveys were conducted to different areas of Madhya Pradesh to select Arjun growing areas. Arjun trees of different age group and girth size were selected for extraction of bark. The experiments were laid out in the forest areas of Balaghat and Jabalpur as well as in the farmer's field on randomized block design for the extraction of bark. The girth of selected trees at breast height (GBH) ranged between 77-228 cm. Trees of less than 60 cm GBH were rejected. Care was taken not to include trees with pollarded crown, broken branches or those infected with fungi and insects.
The bark of Arjuna was harvested by putting blazes of different sizes e.g.,19x30, 24x30, 30x30, 22.5x45, 25x45, 30x45, 32x45, 28x60, 30x60, 37.5x60, 41x60, 45x60, 38x90, 42x90, 57x90, 31x120, 45x120, 46x120 cm etc. The sizes of blaze were according to GBH and age of tree. The breadth of the blaze was 1 / 4 or 1 / 3 of the girth of the trunk at breast height. However, the length of the blazes was 30,45,60,90 and 120 cm. The harvested bark was brought to laboratory for chemical analysis. The Fresh and dry weights of the bark were recorded. Data on regrowth (regeneration of bark) was recorded on quarterly basis. The physical appearance of bark regrowth was also recorded. The bark's regenerative properties were determined by the time taken to regenerate the bark.
Tannin content in the bark was estimated by Folin-Denis Method  and oxalic acid content by using methods of Bhatia  .
Estimation of tannins: By Folin-Denis method
0.5 g of the powdered bark was taken in a 250 ml conical flask. 75-m1 distilled water was added in it. The flask was gently heated and boiled for 30 minutes. Centrifuged at 2000 rpm for 20 minutes and filtered. The supernatant liquid was collected in 100 in( volumetric flask and the volume was made up 100 ml. 1 ml of the sample extract was transferred to a 100mI volumetric flask containing 75-m1 distilled water. Added 5 ml of Folin-Deins reagent, 10 ml of 35% sodium carbonate solution and diluted to 100 mt with distilled water. The solution was shaken well and the absorbance was read at 700 mm after 30 minutes. Blank was prepared with water instead of the sample. Standard graph was also prepared by using 0 - 100μg tannic acid. The tannin content of the samples as tannic acid equivalents from the standard graph was calculated.
Determination of Oxatic acid
One part of the air-dried, water-extracted T. arjuna bark was treated with three parts of 20% H Z SO 4 acid at boiling temperature for one hour. After acid treatment the material was filtered while hot and the bark chips washed with hot water till free of acid (usually 3-4 washings). The filtrate was left overnight at room temperature when most of the calcium sulphate with some quantity of oxalic acid separated and was isolated by filtration. The filtrate was concentrated over a water-bath to a density of 1.15 or when the colour of the liquor just changed from red to dark red. At the stage oxalic acid crystals started appearing. The liquid was allowed to cool and oxalic acid crystals appeared in bulk. These crystals were separated by filtration and the filtrate was further concentrated to obtain a second crop of the oxalic acid crystals. A subsequent crop was also likewise obtained. The material obtained in the beginning with calcium sulphate and in 1 st , 2 nd and 3 rd crops was dissolved in water; a pinch of activated carbon was added to the solution and the solution was warmed over water-bath. The solution was filtered and concentrated to obtain crystals of oxalic acid. Total oxalic acid was recrystallized using distilled water.
Results and Discussion
The bark of T. arjuna was analysed for their tannin and oxalic acid content. The data pertaining to tree, blaze size, tannin and oxalic acid content is depicted in [Table 1]. Minimum and maximum girth of the trees selected for study was 77 cm and 228 cm respectively. Bark thickness at breast height ranged from 8.12 to 20.96 mm. Mean bark thickness at breast height in Arjuna trees was 15 mm. Mean thickness of bark varied from trees to trees. It is irrespective from the age/girth of tree. Mean bark yield per square centimeter ranged between 0.22 gm to 1.14 gm and found varying from tree to tree. The tannin content ranged from 6.75 to 14.82 gm per 100 gms. The amount of oxalic acid in the bark ranged between 7.66 gm to 20.05 gms per 100 gms. The variation was observed in tannin and oxalic acid content with season and age of the tree. The variation in protein, phenol, tannin, nitrate, oxalate in addition to vitamin C, anthocyanin and chlorophyll in the leaves was reported by Srivastava et at. 1997  . Seasonal variations in leaf tannins have already been reported for deciduous trees such as: Qpercusrobur  and Betulapubescens . These variations occurred during leaf growth and development, from spring to fall, and were related with herbivore resistance of plants. In the present study only bark tannins were evaluated and they also showed seasonal variations. Bark (inner bark is the potent part, and contains more tannin in comparison to dry inactive outer portion to the bark. Variation in tannin and oxalic acid content may be due to variation in climatic conditions (rainfall, humidity and mean temperature). Barks collected in the March contained higher amount of tannins (14.82%) followed by the bark collected in November.
Tannin and oxalic acid content in terms of girth/age of the tree is depicted in [Table 2]. The data revealed that there is direct relationship between tannin and oxalic acid content in terms of the girth of the tree. The trees of girth size 40 cm contained minimum amount of tannin (7.56%) and oxalic acid (11.54%) white trees of girth size 116 cm and 100 cm contained higher tannin (14.25 %) and oxalic acid (20.05 %).
Barks of different plant parts e.g. trunk, branch and twigs were also analysed for tannin and oxalic acid content. The data presented in [Table 3] revealed that the trunk bark contains maximum amount of tannin (13.03 %) and oxalic acid (18.46%), whereas lowest tannin (6.32 %) and oxalic acid (10.08 %) content was determined from the bark of the twigs.
Remove only 1 / 4 or 1 / 3 of the mature bark on total girth of the tree. Remove only outer and middle bark leaving the inner bark for regeneration. The bark should be dried in sun before storage. Regular field observations were taken on the recovery of bark. The stage of bark recovery (regrowth) varied from tree to tree. After one year, the stripped trees exhibited an average of 42% recovery based on surface area covered with fresh bark. Findings of studies conducted elsewhere indicated that some other factors like temperature, relative humidity and time of stripping influences wound heating in woody species. The trees in which the bark was harvested on 25 th December 2003 by putting blaze size (30X30cm) showed almost complete bark recovery nearly after two years. However, few trees showed partial recovery of bark. The study shows that the technique of making of blaze on the tree also plays an important role in the recovery of bark. If the blaze is sharp the recovery is faster whereas if the blaze (cut) is not sharp the recovery is slow. The study shows that bark regeneration in Arjuna depends on the extent of damage on the cambium layer. With damaged cambium when the wound extends beyond the cambium and into the wood, the cut may not heal or if it does, very slowly, exposing it to fungal and insect attack. Some insect and fungal infestations were observed on the blazes. Exposed part of the trunk was attached by the insects, but the damage was not severe. In some trees gums oozed out from the blazes. We did not observe any adverse trend on the overall development of tree. No tree was found to die after harvesting of bark. Although Arjuna shows remarkable bark regrowth in moist sites but this would be very early to predict at this stage of study.
Research needs to be undertaken on the selection of fast growing, high active-ingredient yielding T. arjuna c u ltivars.
Authors are thankful to Dr. A. K. Mandal, Director, Tropical Forest Research Institute, Jabalpur for providing necessary facilities to carry out work and M. P. M.F.P. Federation, Bhopal for financial assistance.
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