Electrochemical Analysis of Fatty Acids Obtained from the Natural Resource Seed of Perilla frutescens

 

Neelam Vaidya* and Rakesh Choure

Department of Chemistry, Dr. H. S. Gour University, Sagar-470 003, India

*Corresponding Author E-mail: neelam.vaidya15@rediffmail.com

ABSTRACT:

Perilla frutescens is grown as an oil seed crop in Sikkim. The saponifiable portion of fixed oil from the seeds of the tree has been analyzed using polarographic technique, which has revealed the presence of saturated fatty acids with  E_1/2/E_p values equal to 1: -0.56/-0.57 V, and 2: -0.62/-0.64 V vs S.C.E., corresponding to Palmitic acid (8.2%) and Stearic acid (5.73%) respectively. Whereas the unsaturated fatty acid mixture produced three waves Fig. III/IVB/IVB1 with E_1/2/E_p values equal to 1: -0.08/-0.08 V,  2:  -0.30/-0.32 V and 3: -0.48/-0.48 V Vs S.C.E., corresponding to Linolenic acid (64.4%), Linoleic acid (13.5%) and Oleic acid (8.06%)  respectively. The method has been successfully applied for the qualitative as well as quantitative analysis of fatty acids. Each of fatty acid present in the oil produced is well defined polarographic DCP and DPP Signals in 0.1M TMAB and 0.1M Cd²⁺ used as a supporting electrolyte as pH 4.0 ± 0.2.

 

KEYWORDS: Fatty acid, Polarographic analysis, Perilla frutescens.

 

INTRODUCTION:

Survey of literature reveals that so far, the organic chemists very much depended on the use of chromatographic methods viz. Thin layer chromatography, paper chromatography, gas liquid chromatography, HPLC etc., for the identification and separation of fatty acid present in the fixed oils ^1-4 R. Perilla frutescens (ornamental plant) was collected from Sikkim⁵ and authenticated by the Forest Department of Sikkim Government India. Yield of Perilla frutescens is 51 %. Seed oil content ranged from with 64.41 % Linolenic acid being the major part of fatty acid of the oil. The present communication reports the fatty acid composition of the fixed oil from the tree using a comparatively new electrochemical technique of polarography in the field of plant product. The present method is quick accurate and economic. The technique has been in use in this department ^6-8 and we have also presented part of this work ^9-11.

 

EXPERIMENTAL:

Crused seeds of Perilla frutescens were extracted by petroleum ether in soxhlet apparatus for 3 days. The extract, on removal of solvent, gave yellow colored oil.

 

Mixed fatty acids obtained by saponification of fixed oil. The saponifiable part of fixed oils contains a mixture of saturated and unsaturated fatty acids. On subjecting this mixture of fatty acids to the polarographic analysis a complicated polarogram is obtained. The half wave potentials of many components in the acid mixture may be so close as to superimpose the polarographic wave of other components. This disturbs an accurate analysis of the fatty acids. The saturated and unsaturated fatty acids of the fixed oils were separated (by Hilditch method) ¹². The separated mixtures of the two types of acids were dissolved in 70:30 (v/v) alcohol: water and subjected to polarographic analysis, using 70:30 (v/v) alcoholic solution of 0.1 M TMAB as supporting electrolyte at pH 4.0±0.2. For a better separation of polarographic waves the use of differential complexation ¹³ of fatty acids present in the mixture with a divalent ion e.g., Cd(II) was done 0.01 mM Cd(II) was therefore added to the test solution. Purified hydrogen gas was bubbled through the test solutions for 10 min before recording polarograms. For pH adjustments dil. Hydrochloric acid/dil. sodium hydroxide solutions were used. Current voltage curve for each acid at different concentrations, under the said experimental conditions was recorded by using authentic samples of the acids whose presence is indicated by the results of polarographic analysis of the saponifiable matter of the seed extracts of Perilla frutescens.

 

The polarograms were recorded on an Elico (India) micro processor based polarographic analyzer, model CL-362. The polarographic cell consisted of an electrode assembly having a dropping mercury electrode (DME), a coiled platinum wire electrode and a saturated calomel electrode (SCE). The capillary characteristics of the DME had a m^2/3 t^1/6 value of 2.5mg^2/3 sec^-½ at 60 cm effective height of mercury column. A systronics digital μ pH meter model- 361 was used for the pH measurements.

 

RESULTS AND DISCUSSION:

Figure 1a and1b clearly reveals the presence of  two waves/peaks relating to saturated fatty acids with  E_1/2/E_p values equal to 1: -0.56/-0.57 V vs S.C.E. and 2: -0.62/-0.64 V vs S.C.E., corresponding to Palmitic acid (8.2%) and Stearic acid (5.73%) respectively. Whereas the unsaturated fatty acid mixture produced three waves Figure 2a and 2b with E_1/2/E_p values equal to 1: -0.08/-0.08 V,  2:  -0.30/-0.32 V and 3: -0.48/-0.48 V Vs S.C.E., corresponding to Linolenic acid (64.4%), Linoleic acid (13.5%) and Oleic acid (8.06%) respectively. In Figures TMAB indicates-wave/peak of supporting electrolyte. The result of polarographic analysis of fatty acids have been shown in Table-1.

 

1

Figure 1a:  DCP of Mixture of saturated fatty acids obtained from Perilla frutescens seed in 0.1 M dm^-3 TMAB + 0.01 m M dm^-3 Cd²⁺ at 4.0 ± 0.2 pH.

	2

 

Figure 1b: DPP of Mixture of saturated fatty acids obtained from Perilla frutescens seed in 0.1 M dm^-3 TMAB + 0.01 m M dm^-3 Cd²⁺ at 4.0 ± 0.2 pH.

	3

 

Figure 2a: DCP of Mixture of unsaturated fatty acids obtained from Perilla frutescens seed in 0.1 M dm^-3 TMAB + 0.01 m M dm^-3 Cd²⁺ at 4.0 ± 0.2 pH.

	3

 

Figure 2b: DPP of Mixture of unsaturated fatty acids obtained from Perilla frutescens seed in 0.1 M dm^-3 TMAB + 0.01 m M dm^-3 Cd²⁺ at 4.0 ± 0.2 pH.

 

The presence of acids in the respective acid mixtures was confirmed by adding authentic samples of the acids to the analyte under similar experimental conditions and recording the polarogram. The resulting polarograms showed an increase of wave/peak height for the polarographic signal of each acid, without much difference in its E_1/2/Ep value. Thus confirming the usefulness of the DCP and DPP methods for qualitative and quantitative analysis of fatty acids present in the two mixtures. Besides, it also helps in avoiding the problem due to matrix effects.

 

The saturated and unsaturated fatty acids produce polarographic waves ¹⁴ at the dropping mercury electrode. In case of the saturated fatty acids the polarographic waves may be produced due to the discharge of hydrogen ions where as unsaturated fatty acids produce polarographic waves due to the reduction of double bond. An analysis of the wave indicates that the potential determining step involves one electron, which was calculated from the log plot slopes and (E _3/4-E_1/4) values ¹⁴. From the observed polarographic data of the fatty acids it is clear that, with the increase of carbon chain of the fatty acid, the discharge of hydrogen ions starts at a relatively lower potential and hence the E_1/2 value is also low.

 

Table - 1 : Polarographic data of saturated and unsaturated fatty acids present in fixed oil of Perilla frutescens seeds

S. No.		Name of fatty acids		E1/2 (volts)		Ep (volts)		id (uA)	Percentage in the group	Total percentage in the oil
Saturated acids
1.		Palmitic acid		-0.56		-0.57		0.5	59.04	8.2
2.		Stearic acid		-0.62		-0.64		0.3	40.95	5.73
Unsaturated acids
3.		Linolenic acid		-0.08		-0.08		3.4	74.89	64.41
	4.	Linoleic acid	-0.30		-0.32		0.5		15.7		13.5
	5.	Oleic acid	-0.48		-0.48		0.4		9.38		8.06

 

 

A similar explanation regarding the relation between the unsaturation and E_1/2 value may be given. It may be said that more the unsaturation in a compound, its reduction at the DME would take place at a relatively lower potential and hence the E_1/2 value would be accordingly low.

 

CONCLUSION:

The present method is significant as a complimentary tools for qualitative as well as quantitative analysis of fatty acids present in fixed oil obtain from the seed of Perilla frutescens with great accuracy and precision of determination. Besides the observed results are in good agreement with those reported in the literature.

 

ACKNOWLEDGMENTS:

In the last I am very thankful to my Department of Chemistry of Dr. H. S. Gour University Sagar, India for providing all facilities during my practical work.

 

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Received on 25.12.2010        Modified on 22.01.2011

Accepted on 28.01.2011        © AJRC All right reserved