INTRODUCTION:

Mango is one of the most delicious tropical seasonal fruit in the Maharashtra which is belongs to the family Anacardiaceae¹. It is also called as “The king of the fruits”. After consumption or industrial processing of these fruits, considerable amounts of mango seeds are discarded as a waste². Disposable of mango seed waste is leads to imbalance of environment. Increasing research attention on materials from renewable resources like mango seed waste is due to globally increasing environmental awareness, and the possibility of increasing price and dwindling supply of petroleum-based products^3-4. The composition of wood and mango seed hard cover is almost similar such as cellulosic fibers. Cellulose, hemicellulose and lignin as the three main components of wood, straw, corn stalk, seed coat and other biomasses have been extensively investigated^5-6. Cellulose being one of the most abundant natural occurring polymers has a number of applications such as paper, packaging, lacquer technologies, pharmaceutical coatings etc. In addition, cellulose and its derivatives have also found biomedical applications as hemodialysis membranes, biosensors, coating materials for drugs and wound dressing.⁷ Lignin in wood fibres has been associated with the mechanical strength of the wood and its resistance towards microorganism attack. ⁸

The elucidation of the structure of lignin has been difficult, giving rise to controversies of its actual roles. Moreover, the structure of lignin has not been completely understood. However, lignins are generally classified into three major groups.⁸ They are (i) the gymnosperm lignin which is a dehydrogenated polymer of coniferyl alcohol, (ii) the angiosperm lignin which is a mixed dehydrogenated polymer of coniferyl and sinapyl alcohols and (iii) grass lignin which is composed of a mixed dehydrogenated polymer of coniferyl, sinapyl and p-coumaryl alcohols.

All lignin that have been isolated were found to have undergone a certain amount of structural modification either chemically or physically.⁹ As lignin is a complex polymer there is bound to be some structural deformation during extraction. There has been considerable work on the application of FT-IR spectroscopy in lignin analysis. FT-IR spectroscopy has been used to monitor the degradation of lignin in wheat straw and significant differences were found in the FT-IR spectra of the lignin in the region of 1400 – 1750 cm-¹.¹⁰ The absorption band at 1510 cm-¹ has been used as an internal standard for quantitative analysis of lignin content.¹¹ The de convolution of FT-IR spectra of lignin has enhanced the fine structures and resolutions helps to elucidate the differences between two lignin samples using FT-IR spectroscopy.¹²

The attempt is made to develop the lignin from mango seed hard cover and its FTIR study for commercial and chemical utilizations.

MATERIALS AND METHODS:

Materials:

Source: Ripened Alphanso Mango fruits were purchased from the local market of Ratnagiri and Thane district from Maharashtra; India, During March to April 2009 and 2010. In this study, the differences within the individual species were not considered. It was assumed to be less significant compared to the variations observed between the different types of plant species.

Preparation of sample:

Seeds from fruit were separated manually and sun dried for five weeks. Outer hard cover and inner kernel was separated, sun dried for two weeks. Hard cover was chopped and dried at 50⁰C¹³

(a) (b)

Image. 1. (a) Dry powder of mango seed hard cover (shell)

(b) Dry powder of Lignin from mango seed hard cover (shell)

Isolation of Lignin:

Lignin was isolated using the established Klason method¹⁴. Mango seed hardcover was ground to pass a 40-mesh sieve and dried in an oven at 107^oC for 24 h. Dried powder (10gm) was weighed into a cellulose extraction thimble. The thimble was placed in a Soxhlet extraction apparatus. Extraction was carried out with 95% ethanol-benzene, 1: 2 (v/v), for 8 h. The solvent was removed and air dried in a fume-cupboard. The sample was then digested in a beaker with hot distilled water (400 ml) at about l00^oC for 3 h. Filtered off and washed it with hot distilled water (100 ml), then rinsed with ethanol (50 ml) before being air dried. The partially digested mango seed hard cover was placed in a small beaker and 72% sulphuric acid (I5ml) was added slowly with stirring. The mixture was allowed to stand for 2 h in a water bath at 30^oC with frequent stirring. The mixture was transferred into l L flask and acidified with 3% sulphuric acid. The reaction mixture was refluxed for 4 h. The insoluble lignin was allowed to settled and filtered into a pre-weighed filtering crucible having porosity No.3. Crude lignin washed with hot distilled water to free from acid. The crucible and its contents were dried in an oven at 105°C for 12 h, cooled in a desiccators and weighed. The drying and weighing were repeated until the weight was constant. The lignin content was calculated as a percentage of the oven-dry unextracted sample.

FT-IR Analysis of Lignin:

Lignin samples were made into KBr discs. Approximately 2 mg of lignins were ground with 200 mg of KBr. The FT-IR spectra were carried out using Perkin Elmer 1600 FT-IR Spectrometer. Analysis of lignin in the powder sample was carried out using the multiple internal reflectance technique

RESULTS AND DISCUSSION:

Lignin is known to consist of polymeric substances that differ in composition from one species of plant to another as well as from tree to tree within individual species. Dry powder of mango seed hard cover is shown in image1. (a). Lignin is prepared by klason method is shown in image 1. (b). Factors affecting difference between dry powder of mango seed hard cover and its lignin are depend on local climatic conditions, soil composition, pH and the nature of the surrounding vegetation.

Klason lignin contents of mango seed hard cover was determined and compared with four different hardwoods reported in literature data^{15 (}Table 1). The Klason lignin contents was found in Selangan bam (Shorea sp.) and Kapur (Dl),obalanops sp.) types of reported wood were very similar while Belian (Eusideroxylon zwageri) having a slightly higher percentage of lignin than selangan batu and kapur. Rubber wood which is known to decay easily was generated only 18% lignin. The mango seed hard cover content was 29.80% lignin this value is match with the percentage of lignin with Belian (Eusideroxylon zwageri)which was earlier reported. This result indicates that a possible relationship between the lignin content of mango seed hard cover and its strength of might exist. FT-IR spectra of the Klason lignins were taken for mango seed hard cover shown in Fig.1.

Table 1. FT-IR absorption band shifts between 1612 and 1400 cm-¹

Wood type	Absorption Bands cm-¹
Belian	1612*	1510*	1457	_
Selangan batu	1609	1498	1458	1424
Kapur	1609	1499	1459	1424
Rubberwood	1604*	1499	1458	Should
Mango seed hard cover(shell)	1648.1	1561.4	1460.4	1421.9

Fig.1. FT-IR spectra of lignin from Mango seed hard cover obtained using KBr pellet cell.

The spectra of the lignins in the region from 1800 cm-¹ to 4000 cm-l did not provide much information other than broad hydroxyl and aliphatic GH absorptions. This observation was also noted by other researchers^{10, 11}. This region of the FT-IR spectra will not be considered further. The aromatic absorption region of the spectra contains bands assigned to lignin. Band assignment of the spectra between regions 1000 and 1800 cm-¹ is shown in Table 2. The FT-IR spectra of Klason lignin from the samples show a shift in the absorption bands between 1612 and 1500 cm-^1. Table 3 shows the corresponding band shifts in the four reported samples and mango seed hard cover studied. In addition to the absorption bands of lignin, there are extra bands observed. These bands, (1010 cm-¹), are most likely to be due to the presence of cellulose components of the material. The first was the absorption band of wave number between 1420 cm-¹and 1430 cm-¹ Fig.1. FT-IR spectra of lignin of Mango seed hard cover obtained using KBr pellet cell showed a relatively strong absorption at 1421.9 cm-¹. This absorption band is assigned to the aromatic skeletal vibration. This indicates that mango seed hard cover has almost a single type of aromatic ring while the other wood contains at least two types with a more or less similar concentration (Fig.1.). The absorption band at 1061 cm-¹ is assigned to the aromatic C-B in plane deformation of the guaiacyl type (5). This indicates that lignin in rubber wood and mango seed hard cover contain a higher proportion of guaiacyl group than those from belian, selangan batu and kapur.

Table.2. FT-IR absorption bands for Klason lignin.

Wave number (cm-¹)	Significance of bands.
1700 – 1744	C=O in acetyl, aliphatic ester or aldehyde groups
1600 – 1615	aromatic skeletal vibrations
1505 – 1515	aromatic skeletal vibrations.
1455 – 1490	C-H deformation asymmetric
1420 – 1430	aromatic skeletal vibrations
1320 – 1330	syringyl ring (4) breathing with C-O stretching
1270 – 1280	guaiacyl ring (5) breathing with C-O stretching
1220	syringyl ring (4) breathing
1160	aromatic C-H in plane deformation, guaiacyl type (5).
1120	aromatic C-H plane deformation of syringyl type (4).
1030	guaiacyl type (5) and C-O deformation of primary alcohol aromatic C-H in plane deformation

Table.3. Percentages of Klason lignin in some tropical

Woods and mango seed hard cover

Type of wood	% Lignin mean ± s.dev_
Belian (Eusideroxylon zwageri)	32.5 ± 0.42
Selangan bam (Shorea sp.)	31.2 ± 0.29
Kapur (Dl),obalanops sp.)	29.6 ± 0.92
Rubber (Hevea jrasiliensis)	18.2 ± 0.16
Mango seed hard cover( shell)	26.3 ± 1.68

CONCLUSION:

This study has shown that there are detectable differences in the FT-IR spectra of the extracted lignin. Further studies should be carried out to elucidate the applications and uses of this mango seed hard cover lignin. Separation of lignin components will be necessary to characterize the exact nature of each type of lignin in plants. Further application of this lignin is being complete in our laboratory.

ACKNOWLEDGEMENT:

The authors are thankful to Vidya Prasaral Mandal and Principal Dr. (Mrs.) M. K. Pejavar, B. N. Bandodkar College of Science. Thane – 400 601 for infrastructural facilities.

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Received on 02.07.2011 Modified on 15.07.2011

Asian J. Research Chem. 4(10): Oct., 2011; Page 1635-1637