OPTICAL CHARACTERISTICS OF BIOPOLYMER FILMS FROM PECTIN AND GELATIN

Transcription

1 Joural of Optoelectroics ad Advaced Materials Vol. 7, No. 3, Jue 5, p OPTICAL CHARACTRISTICS OF BIOPOLYMR FILMS FROM PCTIN AND GLATIN K. Nikolova *, I. Pachev, S. Saiov a Departmet of Physics, Uiversity of Food Techologies, 4 Plovdiv, 6 Maritza Blvd., Bulgaria a Cetral Laboratory of Optical Storage ad Processig of Iformatio, BAS, Acad. G. Bochev Str., bl., 3-Sofia, Bulgaria Biopolymer films from pecti with differet degree of esterificatio ad gelati have bee ivestigated. Data the effect of film thickess upo the spectral ad refractometric film characteristics with differet weight cotets have bee obtaied. A comparative aalysis of pecti films with a gelati film has bee carried out. The refractometric data are made for liquid phases with,.5 ad.5 % at 633 ad 79 m, usig He-Ne ad semicoductor lasers. O the base of the measured refractive idex the Sellmeier, s relatio is obtaied. (Received April, 5; accepted after revisio May 6, 5) Keywords: Refractio idex, Refractometry, Optical characteristics, Biopolymer, Pecti, Gelati. Itroductio Recetly, there is a icrease of ivestigatios o food coverigs obtaied from biopolymer solutios. Applied upo food raw materials or products the biopolymer films ca be looked upo as a part of their ow that ca be assimilated durig cosumptio. This fact together with some other advatages has a ecological impact, as well. The edible films protect the product from oxidatio, decrease the moisture- ad gas-diffusio, create a additioal mechaical protectio, colour protectio ad gloss. The matrix created from biopolymer macromolecules i the film allows to iclude additives havig a atimicrobial ad atioxidative effect. The actuality of the problem cocerig food coverigs improvemet is costatly icreasig, which imposes to perform ivestigatios upo the optical ad physical characteristics of films from polysaccharides ad proteis []. The purpose of this study is to ivestigate the optical characteristics of biopolymer solutios ad their films from apple ad citric pecti ad gelati by measurig their refractio idices (RI) ad their trasmissio spectra. A theoretical coectio has bee established betwee the sigleoscillatio models of Sellmeier [] ad Didomeiko ad Wemple [3], that allows to cout the specific oscillatio eergy ad the dispersio eergy d for each sample oly by meas of IR measuremet for two wavelegths.. xperimetal The refractive idex of water solutios of apple ad citric pecti, respectively with cocetratios of.5%,.5% ad % have bee ivestigated. The results for RI of the biopolymers studied have bee compared with the measured RI of gelati water solutio havig the same cocetratios. For each of the biopolymers studied films upo glass bases have bee applied. Durig water evaporatio at a ambiet temperature, homogeeous layers of apple ad citric pecti ad gelati have bee obtaied, respectively with cocetratios of.5% ad %. * Correspodig author: kr.ikolova@abv.bg

2 44 K. Nikolova, I. Pachev, S. Saiov The measuremet of RI of water solutios of ivestigatio biopolymers ad their films has bee doe with the laser refractometer descriptio i [4, 5] Because there is a close pheomeological coectio betwee the RI value, the theory of Maxwell ad the atomic structure of substaces, we cosider that it is iterestig to cout optical costats like specific, molecular refractio ad optical polarity for the liquid phase of apple ad citric pecti ad gelati at two wavelegths. For this purpose we use the depedecies give i []: r =, () + ρ M R = r. M =, () + ρ 4 R =,5. α p (3) where is RI at a give wavelegth, r is specific refractio, M is the molecular weight of the solutio, ad ρ is its desity. The refractive idex of the studied oe-percet biopolymer solutios have bee measured at t = 8 C for = 633m ad = 79m. Their desity has bee determied picometrically at the same temperature. For that purpose, the picometer with the studied ad the stadard liquid should be placed i a metal housig whose temperature is kept costat by meas of a thermostat. The molecular weight of the studied apple ad citric pecti ad gelati has bee determied by measurig the itrisic viscosity [ ] of the biopolymers studied i.5 µ NaC at t = 8 C, kept costat by meas of a thermostat [6]. As it is kow, IR ad the absorptio coefficiet are coected by meas of the Kramers- Kroig relatio. That is why, our study o the optical characteristics of the edible films from apple ad citric pecti ad gelati presets also the spectral depedecies of the optical trasmissio τ ( ). The measuremets have bee carried out o a spectrophotometer Carry 5, followig the methodology, preseted i [7, 8]. The sample studied is a film of the biopolymer discussed applied upo a glass substrate. Our study shows trasmissio spectra of edible films oly i the ifrared regio because i the visible regio they are all trasparet ad are of o sigificace. I our study we have established a relatio betwee the sigle-oscillatig models of Sellmeier (4) ad those of Didomeiko ad Wemple (5): s = + (4) s d = + ω (5) where ω is the photo eergy, is the specific oscillatig eergy ad d is the dispersio eergy. The parameter d is a measure of the stregth of itracoectio optical trasfers ad does ot deped o the type of coectio or the volume desity of valet electros. If we trasform the expressio (5), takig ito accout the relatios: π c π c = ω, ω =, ω =, = h π ad after simple trasformatios (5) oe gets (6).

3 Optical characteristics of biopolymer films from pecti ad gelati 44 d = + hc Whe we make a compariso betwee (6) ad (4) it is evidet that there is a simple coectio betwee the Sellmeier`s parameters s ad s ad the oscillatio eergies ad d. (6) π c h π c hc = ω = = = π d shc s = d = hc = s d hcs = s s hc = (7) We have calculated Sellmeier`s coefficiets S ad s i our study by measurig RI of biopolymer solutios of pecti ad gelati for two wavelegths. For each oe of them with the parameters S ad s from (7) system the eergy ad d valued have bee obtaied. 3. Results ad discussio The results give i Table have bee obtaied whe measurig RI of biopolymer solutios from apple, citric pecti ad gelati for = 633 m ad = 79 m ad of their films for = 633 m after the method of disappearig diffractio picture. Table. RI data of biopolymer solutios ivestigated ad the films obtaied from them. Type Liquid Phase, = 633 m Liquid Phase, = 79 m Solid Phase, = 633 m.5% apple pecti % apple pecti % apple pecti % citric pecti % citric pecti % citric pecti % gelati % gelati % gelati For each oe of the ivestigated biopolymers solutios, the coefficiets of Sellmeier have bee calculated ad through them from (7) system umerical values for the oscillatig eergies ad d have bee obtaied. The data are give i Table. As far as the studied biopolymers are cocered a polyom has bee obtaied from the first degree = f ( C% ) ad its correlatio coefficiet R has bee calculated. The aalytical expressios of the depedecies obtaied have bee give i Table 3.

4 44 K. Nikolova, I. Pachev, S. Saiov For all oe-percet solutios of the biopolymers studied o-optical costats-desities, itrisic viscosity [ η ] ad molecular weight M have bee measured which are ecessary for calculatig optical values, like specific, molecular refractio, polarity etc. for two wavelegths ad. The results have bee writte i Tables 4, 5 ad 6. Table. Sellmeier coefficiets values, dispersio ad oscillatig eergies of biopolymer solutios studied. Type s s,m, ev d,ev.5% apple pecti % apple pecti % apple pecti % citric pecti % citric pecti % citric pecti % gelati % gelati % gelati Table 3. Regressio depedecies of f ( C% ) = for the liquid phase of the biopolymers studied. Correlatio coefficiet R Type for the depedece of RI o the cocetratio = f ( C% ) Apple Pecti.98 Citric Pecti Gelati.99 Table 4. Specific desity of the solutios studied. Type 3 ρ, kg. m % apple pecti.749 % citric pecti.879 % gelati Table 5. Itrisic viscosity ad mea value molar weight of the biopolymers studied. Type [η], dl. g molecular weight, M Owes [9] Bert [] apple pecti citric pecti gelati.88 Table 6. Specific ad molecular refractios ad optical polarity of the solutios studied. Type 3 r, cm g. r cm 3,. g R 3,cm R 3,cm α 3,cm 4 α 3,cm 4 % apple pecti % citric pecti % gelati

5 Optical characteristics of biopolymer films from pecti ad gelati 443 From the data i Table it ca be see that the studied biopolymer solutios possess very ear RI while RI of the films obtaied from the same biopolymers are cosiderably differet. This fact shows that whe creatig a film from the biopolymer studied, additioal coectios appear that are o-existig i the solutio. By meas of the coefficiets of Sellmeier foud from Table, RI of the ie biopolymer solutios for the legth of the yellow sodium lie ( = 589.3m ) have bee calculated ad have bee compared with those measured by Abbe refractometer at the same wavelegth, at t = 8 C. The coicidece betwee the experimetal ad theoretically calculated data for RI is a good oe for the apple pecti it is a few uits ito the fourth sig, ad for gelati ad citric pecti it is 3. This fact allows by usig the dispersio parameters S ad s to calculate RI of each oe of the biopolymers studied i the visible regio of the spectrum ad to draw the dispersio depedece ( ) graphics. Fig. presets trasmissio spectra of oe-percet films from citric pecti ad gelati, take by meas of Carry 5 spectrophotometer. 86 gelati % citric pecti % T [%] wavelegth [m] Fig.. Trasmissio spectra of % Gelati ad % Citric Pecti i the Ifrared Regio. From Fig. it ca be see that gelati i the ifrared regio is less trasparet tha the citric pecti. Both biopolymers i the ear ifrared regio have a clearly expressed absorptio bad, while i the regio from 6 to 8 m they are maximally trasparet. From the trasmissio spectrum it ca be see that the citric pecti at m possesses the maximum of absorptio, ad the gelati the maximum of trasmissio that is due to the differet chemical groups cotaied i them. Table 7. Comparative data for RI (calculated ad measured). Type calculated measured.5% apple pecti % apple pecti % apple pecti % citric pecti % citric pecti % citric pecti % gelati % gelati % gelati

6 444 K. Nikolova, I. Pachev, S. Saiov 4. Coclusios Several coclusios ca be draw o the basis of the obtaied experimetal data:. The sigificat differece betwee RI of the studied biopolymer films as compared with their solutios witesses for the creatio of additioal coectios i the solid phase that are missig i the discussed material solutio.. There is a sigificat differece betwee o-optical costats itrisic viscosity ad desity of gelati ad both types of pecti. Gelati has the smallest desity ad itrisic viscosity, but have the greatest specific, molecular refractio ad optical polarity. Gelati solutios have a very close RI with those of apple pecti ad almost equal to it RI icremet. 3. From the trasmissio spectra τ() it ca be see that citric pecti is more trasparet i the ifrared regio tha gelati. 4. By determiig the dispersio parameters of Sellmeier S ad s it is possible to determie RI for each wavelegth from the visible regio of the spectrum with a comparatively high accuracy. The determiatio of oscillatig eergy d value, oly the sub-dispersio parameters S ad s allows for the quick ivestigatio of edible films chemical properties. 5. From all coclusios made by ow it follows that refractometric measuremets allow some iformatio to be obtaied, cocerig the structure of substaces ad aalysis of the processes that flow at a micro-level. That is of great importace for improvig physical parameters of the films that ca be used as a packig material of foodstuffs. Ackowledgemets The authors express their thakfuless to the Miistry of ducatio ad Sciece for the fiacial support by Cotract - - 6/4. Refereces [] J. J. Kester, O. R Fea, Food Techology 47 (986). [] B. Joffe, Refractometric Methods of Chemistry, Scietific ad Techical Publishig House for Chemical Literature, Leigrad (96). [3] S. H. Wemple, M. Didomeico, Physical Review B 3,338 (97). [4] S. Saiov, N. Dushkia, Appl. Opt. 9, 46 (99). [5] S Saiov, Rev. Sci. Istrum. 6, 36 (99). [6] G. Moravetz, Macromolecules i a Solutio, Publ.House Mir, Moscow (967). [7] I. Kostatiov, Tz. Babeva, S. Kitova, Appl. Opt. 37, (998). [8] Tz. Babeva, S. Kitova, I. Kostatiov, Appl. Opt. 4, (). [9] U. S. Owes, R. M. McCready, A. D. Shepherd, A. I. C. Report, 34 (95). [] G. Bert, H. Ager, D. Lexow, Die Nahrug 4, 59 (98).