Bansal, A K

Gupta, K K

Singh, P J

IACS Institutional Repository

l„J,an J. Phys. 76B (3), 283-287 (2002)U P  Ban international journalDielectric relaxation studies of four (Afferent varieties of rapeseed- mustard oil at differei^ temperaturesA K Bansal, K K Gupta, F* J Sinj|h* and K S Sharma Department of Physics. M S J College, Bjjjaratpur, Rajasthan, IndiaReceived I March 2001, accepted 15 March 2002Abstract Dielectric properties of four rapeseed-mustard oil samples of crop year 1998 having difTcrent percentage composition of different fatty acids have been studied at 100 KHz, 8.93 GHz and optical frequency of the D-Iincs of sodium. Temperature variation of dielectric properties has also been investigated in the temperature range from 303 to 333 K and both are decreasing with increase in temperature, for each sample under investigation. However, variation of e '  with temperature exhibits the prc.sence of cither a peak or a valley at some temperature in all the four samples, though less prominent in the sample . PCC-2 This may be attributed to the modification in the packing of dipoles at this temperature cither due to increase in the overall dipolar correlation or due to reduction in the overall dipolar correlation The macroscopic iclaxation time and various thermodynamic parameters have also been calculated for the dielectric relaxation process Negative values of molar entropy of activation indicate the existence of cooperative orientation of molecules arising out of stcric forces No specific dependence of dielectric parameters on constituent fatty acids is observ'edKc> words Dielectric properties, temperature variation, rapeseed-mustard oilPAC S Nos.I. IntroductionAmong the studies on the interaction between electro­magnetic fields and living matters, microwave spectroscopy of agriculture and biological substances is one of the increasing importance. The extensive use of domestic and industrial devices for food preparation, such as microwave ovens and defrosting apparatus etc., justifies the need for an even better knowledge of the effects of EM radiation on the food stuff. Microwave spectroscopy can be a useful technique for investigating some properties of tissues or proteins, and seems potentially able to give diagnostic information [1].Recently, dielectric behaviour of albumin and yolk of avian egg was studied by Lokhahde et al [2], soya bean oil and mustard oil by Khanna and Upadhyay [3], biologically and pharmaceutically important low molecular weight ethylene glycols by Sengwa and Kaur [4], Human Sera and Erythrocytes by Bianco et al [5].Corresponding AuthorHowever, little information is available for many agri­food materials. Rapeseed-mustard oil is one of the most important edible oils being consumed largely in India and elsewhere. Rapeseed-mustard group of oils are comprised of different varieties having different fatty acid composition. Except for minor amount of impurities, dietary fats and oils consist of triglycerides or esters of glycerol and high molecular or long chain aliphatic acids, both saturated or unsaturated [6], known as fatty acids. The value and suitability of mustard oil for nutritional or industrial uses are determined by its fatty acid composition. Low erucic acid rapeseed oil is more suitable for edible purposes. The HEAR [High Erucic Acid Rapeseed] oil was for a long time under use for domestic lighting. Other industrial uses came into being at a later stage. It can be used as a Lubricant or as a diesel fuel substitute. It is under limited use for the latter purpose, in view of cheapness of the diesel oil. Absence of essential fatty acids like linoleic acid in the diet results in hair fall,© 2002 lACS284 A K Bansal, K K Gupta, B ./ Sin^^h and K S Sharm aeczema like  skin eruptions, slow healing o f  wounds and dry scaly skin. Because o f  the ir importance the W H O  has recommended that at least 3?o o f  the diet should contain lin o le ic  acid [6 ].In the present study, we have determ ined d ie lectric  properties o f  d iffe ren t varieties o f  rapeseed-mustard o il having d iffe re n t percentage com position o f  fa tty  acids, along w ith  re laxation tim es and therm odynam ica l parameters.The m acroscopic re laxation lim e ( r,„), m olar free energy o f  activa tion  (A F ^  ), m o la r entropy o f  activation (A^V,) and m ola r cn tlia lp y  o f  activa tion  (A //^  ) have also been worked out fo r these samples, which may provide valuable infonnation fo r fu ture research in th is fie ld .2. M a te r ia l and e xp e rim e n ta l de ta ilsFor the present investigations, d iffe ren t samples o f  rapeseed- mustard o f  crop year 1998 nam ely H yola-401, M -21, PCC- 2, PYS-842, have been procured from  N ational Research Centre on rapeseed-mustard located at Sewar, Bharalpur (Ind ia ). Fresh o il from  these seeds was obtained by using a baby expelier. Th is o il was then filte red  by fine filters. To get the fa tty  acid p ro file  one drop o f  o il was taken in capped glass test tube. To it 1 m l o f  petroleum  ether (60 8 0 'C) was added and m ixed  w ith  very s lo w ly  A fte r keeping fo r one hour at room  temperature, 1.5 m l o f  0.05 M  sodium m ethoxide was added to it and kept at room temperature fo r one hour. Then 1.5 m l o f  8% sodium ch lo ride  so lu tion was added to it. L.aycrs were separated. I p i from  upper layer was injected on G .L .C . (N U C O N  5765 model). Fatty acid p rofiles were obtained using SP-2300 (2% )  ^ ,SP-2310 (3"^o) stainless steel co lum n using flam e ion iza tion  detector (F ID ). The oven temperature was m ainta ined at 240 ''C  and the in jector and the detector were both m ainta ined at 290"C.The d ie lec tric  constant (^ o )  at 100 K H z  was measured by using a d ipo le  m eter by d irec tly  measuring the capacitance and ca lib ra ting  it fo r standard liqu ids. The d ie lectric  constant at optica l frequency was obtained by squaring the re fractive  index measured at the frequency o f  the D -lines o f  sodium , measured w ith  the help o f  an A b be ’ s refractom eter. The measurements o f  wavelength in the d ie lectric  and that o f  vo ltage standing wave ra tio  were made at frequency 8.93 G H z  using a slotted wave-guide and a short c ircu ited  p lunger. The ca lcu la tion  o f  d ie lectric  p e rm ittiv ity  ( e ’ ) and d ie lec tric  loss (e^") were made fo llo w in g  the m ethod o f  Heston e t a l  [7 ] adopted fo r short-c ircu ited  term inations. The values o f  e '  and e'" so obtained are accurate w ith in  ± 1% and ±5%  respective ly. A l l  these measurements were made at fo u r tem peratures, viz. 303, 313, 323 and 333 K  using a tem perature regu la ting  system and a constant temperature w ater bath.1'he macroscopic re laxation tim e is determ ined by usint> the equation'  "  ° ' l+ . /w r , „  ’where e ' is the com plex p e rm ittiv ity  at angular frequency(0.On using e * - { e '  y > " ) ,  and separating real andim aginary parts, we get€= ~ e ,., -f ^0 “ ^  I 4- (O-T), (I)and{^0 “^ iOT,,Substituting the values o f  eo, e \  and co in cq. (I),wc may obtain the value o f  (m acroscopic re laxation time) M o la r free energy o f  activation is determ ined by E yring ’s equation f8 | fo r the d ie lectric  re laxationr , ,  -  ( / l / r ) c . \ p (  A f ;  IRT)\ AF, = A ll, -  TAS, (3)where A = ///A, R " gas constant and temperature (K), and AF, is the m olar free energy o f  activa tion, A / / ,  is the m ola r enthalpy o f  activeition and AS^ is the m o la r entrop) o f  activation3’hc slopes o f  the straight lines obtained by p lo tting  lop ( r „ ;7 )  versus ( I / / ’ ), when m u ltip lied  w ith  gas constant R gives the value o f  .1 //, Know ing the value oi'AF^ and J / / , , we can get the values o^'AS^ using eq. (3).3. Results and d iscussionfab le  I shows the com positions o f  fa tty  acids in different samples under study. The fatty ac id -com position  is obtained by tak ing  chrom atograms o f  the d iffe ren t samples under investiga tion . Chrom atogram  o f  one such sample ic P ('C -2  is g iven fo r example (F igure 1). Peaks corresponding to d iffe ren t retention tim es arc o f  d iffe re n t fa tty  acids'I 'ab lc  I.  r a t t y  acid c()!ii|)0.sition (°i>) in dif feren t s am ples  o f  rapcscal* mus tard  oil (crop year 19^)8)Variety Palmitic Stearic Oleic Liriolcic Linoicnic+hicosenoicP.rueic16 0* 180* 18 1* 18.2* 18.3* + 20.1*22 rIIyola-401 3.87 Tr 63 19 21.00 11.10 O.XIM-21 3 88 1.17 33 03 35.56 15 39 11 44PCC-2 2 94 Tr.** 14 25 17 90 20.34 44 54PYS-842 2.27 Tr ** 11 75 14 76 13.62 57 59These denote number of carbon atoms to number of double bonds in the corresponding fatly acids **'Tracc only.Dielectric relaxation studies o f four different varieties o f rapeseed-mustard oil etc 285present in these samples. Table 2 shows different fatty acids corresponding to different retention time (in minute). Table 3 shows the values of dielectric constants at 100 KHz, 8.93 GHz and at optical frequency of sodium D-lines along with loss factor e"' at 8.93 GHz for different varieties of rapesecd-mustard oil at 303, 313, 323 and 333 K. At anytemperature from 303 to 333 K experimental values of €q, e \  e ” and e<» are not giving any indication regarding the systematic variation of dielectric data with percentage composition of any fatty acid present in the samples under investigation. This may be attributed to the complexity of triglyceride structure, as the characteristics and particularly the physical properties of a fat are considerably dependent up0n how the fatty acids are distributed within the glyceride m|>Iecules and what arc their chain lengths [9].1Tat>le 2. Retention time (min ) of ditTcrent fatly acidsFatty acids Retention time (min)4 ' ' 2 2 L ffigure I, Chromatogram of PCC-2. table 3. experimental values of eo, e \  e"PalmiticStearicOleicLinoleici.inoicnicFicosenoicF>ucic3.45 5 81 6.49 7.69 9 44 11 14 19.34Gx, and AS  ^ for diOerent samples at 303, 313, 323 and 333 K.Icrnp (K) 0^ r»(x I0'2) Sec (K Cal/ mole)AHe (K.. Cal/ mole)AS^(Cal/moledeg.)3031133233333033133233333033133233333033133233333 6625 3 .6 1 2 0  3 5812 3.54373.2175 3 18753.1562 3.12753.23123.21253.16873.15623.0618 3.0250 2.9812 2 96252 4556 2 5025 2 5380 2.51242.4798 2.4927 2.4992 2.48302.45752.4798 2.5290 2.57312.43682.38612.42002.45120 2400 0 2440 0.2998 0.32350 2756 0 1934 0.2146 0 16130.22700.20220.17270.22290.22780.31930.26820.3029Hyola-401 2 1963 2 1874 2.1785 2.1720M-21 2 2052 2.19922.19332.1844PCC-22 .2 0 2 22.19632.19042.1815PYS-8422.1933 2.18922.1844 2 175638.433.430.331.029.227.426.1 26.131.0 28.624.521.728.732.127.524.23 3060 3.3480 3.4130 3.55403 1410 3.2250 3.3170 3 44003.17703.25203.27603.31803.13003.32303.35103.39000.8660.1501.8080.674-8.05-7.92-7.88-8.07-9.87-9.82-9.80-9.87-4.51-4.61-4.54-4.53- 8.10-8 .46-8.28286 A K Bansai K K Gupta, P J  Singh and K S SharmaFigures 2 and 5 show the behaviour of and €« for all the four samples, at temperatures ranging from 303 to 333 K. Both eo and are decreasing with increase inI3 7500 3 7000 3 6500 I 3 6000 '3 5500 ;3 5000 '3 4500 3 4000 :3 3500 I 3 3000 3 2500 1 3 2000 i 3 1500 I 3 1000 .3 0500 ;3 0000 I 2.6500 ^2 6000 ; 2.8500 2 8000 3001Hyota-401M-21PCC-2PY8-M2310 320 330Temperature (K)340Figure 2. Dielectric constant { eq) of the foui samples at frequency 100 KIb as a function of temperature.Hyoia^OM.21PCC'2PYS-442shape either to become spherical or to become elongated at some temperature. Elongated shape may be containing dipoles in a parallel alignment that enhances the value of e ‘Hyot«-401M.21PCC-2PY8-M2Figure 4. Doss factor (e") of the four samples at frequency 8.93 GH? as a function of icmppraturcHyoto.401M-21 PCC-2 PYS S42Figure 3. Dielectric constant (6*) of the four samples at frequency 8.93 GHz as a function of temperaturetemperature for each sample under investigation. The increase in temperature may cause decrease in overall dipolar correlation and so both eo and e„ decrease progressively at higher temperatures. However, in these samples, e ' does not show regular variation with change in temperature from 303 to 333 K as shown in Figure 3. In this figure, we find the presence of either a peak or a valley at some temperature in the samples under investigation. This strongly indicates about m^difleation in the packing of dipoles which alter itsFigure 5. Dielectric constant ( e») of the,four samples at optical frequency of sodium light as a function of temperature.while spherical shape contains reduced overall dipolar correlation. This behaviour is exhibited by all the samples, though less prominent in one sample i.e, PCC-2. Figure 4 shows the behaviour of for all the four samples with increase in temperature from 303 to 333 K. Behaviour of also docs not show a systematic variation with change in temperature from 303 to 333 K. Similar results for e ' an d  €** were reported by Venkatesh el al [10]. These w o rk e r s  determined e ' and for tylose (complex food material)Diek’clric relaxation studies o f four different varieties of rapeseed-mustard oil etc 287e th ano l a n d  e th a n o l /h e x a n c  m ix tu r e  a n d  r e p o r te d  s im ila r  b e h a v io u r  o f  e '  a n d  e "  w ith  c h a n g e  in  te m p e r a tu r e  w h e re  for s o m e  t e m p e r a tu r e  r a n g e  e '  a n d  e "  a re  d e c re a s in g  with in c re a s e  in  t e m p e r a tu r e  w h i le  f o r  o th e r  te m p e ra tu re  um ges th e s e  a r e  e i th e r  c o n s ta n t  o r  in c re a s in g  w ith  in c re a s e  III te m p e ra tu re .  S e n g w a  a n d  K a u r  [4 ] h a v e  a ls o  r e p o r te d  s im ila r r e s u l ts  in  o l ig o m e r s  o f  e th y le n e  g ly c o l  s h o w in g  n o  reg u la r v a r ia t io n  in  e '  a n d  e "  w ith  te m p e r a tu r e  in  th is  ire q u e n c y  r a n g e .  It is a ls o  s e e n  f ro m  th e  s a m e  ta b le  th a t  m a c ro .sc o p ic  r e l a x a t i o n  t im e  (r ,„ )  f o r  e a c h  s a m p le  is d e c re a s in g , in  g e n e r a l ,  w ith  in c re a s e  in  te m p e ra tu re  fro m  103 to  3 3 3  K . T h is  s h o w s  m o re  c o m p a c t  c lu s te r in g  o f  m o le c u le s  a t  lo w  t e m p e r a tu r e  d u e  to  w h ic h  m o re  t im e  is lakcn in r e o r ie n ta t io n  p ro c e s s .  It is a ls o  s e e n  f ro m  th e  s a m e  lable th a t  th e r e  is n o  s y s te m a t ic  t r e n d  in  th e  v a r ia t io n  o f  m a c ro sc o p ic  r e la x a t io n  t im e  w ith  in c re a s e  in  te m p e ra tu re  w h ich  c a n  b e  a t t r ib u te d  to  lo n g  c h a in  in t r a m o le c u la r  in te ra c tio n s  in  th e  t r ig ly c e r id e  m o le c u le s  o f  th e  s a m p le s  und er in v e s t ig a t io n .T a b le  3 a ls o  s h o w s  th e  c a lc u la te d  v a lu e s  o f  m o la r  f re e  e n e rg y  o f  a c t i v a t i o n  ( A F c )  f o r  e a c h  s a m p l e  u n d e r  in v e s tig a tio n . A F c  v a lu e s  fo r  e a c h  s a m p le  a r e  in c re a s in g  twill in c re a s e  in  t e m p e r a tu r e  f ro m  3 0 3  to  3 3 3  K . 'f h i s  c a n  be e x p la in e d  o n  th e  b a s is  th a t  a s  th e  t e m p e r a tu r e  in c re a s e s ,  the rm al a g i ta t io n  in c re a s e s  a n d  th e  m o le c u le s  r e q u ir e  m o re  en erg y  to  c o m e  to  th e  a c t iv a te d  s ta te . F ro m  th e  s a m e  ta b le , ii IS a lso  e v id e n t  th a t  f o r  a ll  th e  s a m p le s  u n d e r  in v e s t ig a t io n ,  the A H ^  v a lu e s  a re  le ss  th a n  th e  c o n -e s p o n d in g  AF^  v a lu e s , resu ltin g  in n e g a t iv e  m o la r  e n t r o p y  o f  a c t iv a t io n ,  .l.S’c \ allies. T h is  in d ic a te s  th e  e x is te n c e  o f  c o o p e r a t iv e  o r ie n ta t io n  iif the  m o le c u le s  a r i s in g  o u t  o f  s te r ic  f o r c e s  [1 1 ]  to  y ie ld  m ore o rd e r e d  s ta te .AcknowledgmentsT h e  a u th o r s  a rc  th a n k fu l  to  th e  H e a d  o f  th e  d e p a r tm e n t  o f  P h y s ic s  a n d  P r in c ip a l .  M . S .1. C o lle g e ,  B h a ra tp i i r  fo r  p ro v id in g  la b o ra to ry  fa c i l i t ie s . O n e  o f  th e m  (A  K. B a n s a l)  is in d p b te d  to  th e  U n iv e rs i ty  G ra n ts  C o m m is s io n ,  N e w  D e lh i f o r  p ro v id in g  te a c h e r  f e l lo w s h ip  to  h im . A u th o rs  a rc  a lso  th a p k fu l  to  th e  D ire c to r ,  N a t io n a l  R e s e a rc h  C e n tr e  o n  R a |te s e e d -M u s ta rd  fo r  p ro v id in g  th e  f a c i l i t ie s  to  w o rk  o n  ( i .  L .  C ,Kcftrcnfcs[11 (' G Lssc\, r H (irant, U. J Shcppaicl. G V South, M S Symonds, (i L Mills and J Slack Ann ;V ) A cad  Sa  AV> 303 M2 (1977)[2] M P l.okhandc, H R Arbad, M Ci 1 ondge and S ( ' Mchiolra Indian  J liioc/tcni lUophys 33 I5h(1^^96)[3] R k Khanna and S K Upadlivay Indian J Pure Appl Phys 37 404 (I W )[4] R J Sengua and Kul\mdcr kaur Indian J  lUochem Biophys 36 325 (19^0)«[5] lirunt) liianco. (iian Paolo Drago, Michele Marchesi Claudio Marlinu, Chusebbe Sandro Mela and Sandro Ridclla It'EP 7fans Insfnmi Measurcmenl lM-28 (No-4) (1979)|6| (i Nagaray Q uality and U tility of O d S e e d s  (Oirectoralc ofOilsced Research (ICAR), Ihderabad) p51 (1995)17] W M Heston (Jr) A 1) Pianklin. I' J Henncl> and ( ’ I* Smyth J \m (hem So, 11 3443 (1950)18] S Cilasslonc, k J Laidler and H I vring Pheory o f Rate P rocesses  (Newyork and I ondon Mt(irav\ iiill) Cdiap 9 (19tl)|9j F<aymond V Krik and Donald I Oihmer F ncylopedia  of ( h e m ita l  leehnoloffy, the in tersu en ce  en cycloped ia  IS C  S cm  )o tk  (MARli/LN Compan\ Limned. lokyo, Japan) Vol. 6 pl41 (1951)110] M S Vcnkalcsh, St I* Denis, G S V Raghuvan, Akyci C and I' Vandc Voort (Asia Paeil’ie Miciowave Conicrenee. New Delhi) p387 (1996)|1 11 F H Hranin (Jr) and C P Smyth J  Chem Phys 20 1121 (1952)

Dielectric Relaxation Studies of Four Different Varieties of Rapeseed-Mustard Oil at Different Temperatures

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Dielectric Relaxation Studies of Four Different Varieties of Rapeseed-Mustard Oil at Different Temperatures

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