An Application of Image Analysis and Colorimetric Methods on Color Change of Dehydrated Asparagus (Asparagus maritimus L.)

Transcription

1 ORIGINAL SCIENTIFIC PAPER 233 An Applition of Imge Anlysis nd Colorimetri Methods on Color Chnge of Dehydrted Asprgus (Asprgus mritimus L.) Jsmin LUKINAC ( ), Stel JOKIĆ, Mirel PLANINIĆ, Dmir MAGDIĆ, Drko VELIĆ, An BUCIĆ-KOJIĆ, Mte BILIĆ, Srećko TOMAS Summry Shpe nd olor re key ftors in qulity evlution of fresh sprgus (Asprgus mritimus L.). Typil green olor of sprgus omes from the hlorophyll, pigment whih hs een degrdted during drying proess. The im of this pper ws to ompre olor hnges of sprgus dried in lortory try drier equipment t different tempertures (40 C, 50 C, 60 C nd 70 C) t irflow veloity of 2.75 ms -1. Color hnges were otined y digitl imge nlysis in RGB olor model nd y hrommeter in L * * * olor model. Bsi elements of imge nlysis system were low voltge hlogen lmps with refletor, digitl mer nd progrms for imge pre-proessing nd nlysis. Men vlues of olor prmeters, olor hnges nd orreltion oeffiients for sprgus were lulted for oth olor models. An nlysis showed sttistilly signifint influene of drying temperture on hue ngle nd totl olor hnge for oth hosen olor models of dehydrted sprgus. Represented results show tht there ws no sttistilly signifint differene ording to olor hnges etween drying t 50 C nd 60 C. Clulted orreltion oeffiient etween olor hnges for used models ws found to e Key words imge nlysis, olor, sprgus, dehydrtion University J.J. Strossmyer of Osijek, Fulty of Food Tehnology, Deprtment of Proess Engineering, F. Kuh 18, Osijek, Croti e-mil: jsmin.lukin@ptfos.hr Reeived: Otoer 23, 2008 Aepted: Mrh 4, 2009 ACKNOWLEDGEMENTS This work ws finnilly supported y Ministry of Siene, Edution nd Sports of the Repuli of Croti, projets nd Agriulture Conspetus Sientifius Vol. 74 (2009) No. 3 ( )

2 234 Jsmin LUKINAC, Stel JOKIĆ, Mirel PLANINIĆ, Dmir MAGDIĆ, Drko VELIĆ, An BUCIĆ-KOJIĆ, Mte BILIĆ, Srećko TOMAS Introdution Fresh sprgus is gining populrity due to its unique texture nd flvor (Lu et l., 2000) ut lso it is n extremely perishle vegetle. Freshly hrvested sprgus deteriortes rpidly leding to short shelf life (An et l., 2008). The very short shelf life of sprgus is minly relted to its high respirtory tivity whih ontinues fter hrvesting (Alnese et l., 2007). Dehydrtion, i.e. drying, of sprgus provides long term onservtion nd mrketility of this produt. In reent yers, muh ttention hs een pid to the qulity of dried foods. For the food tehnologil properties suh s olor, shpe (shrinkge) nd rehydrtion pity re determinnt for the qulity of the dried produt (Fernndez et l., 2005). Similr to other vegetles, hnges in olor, hemil nd texturl properties of sprgus our during therml tretment suh s drying. Color is n importnt qulity ttriute of fruit nd vegetle whih ours in the intertion mong light, oserved ojet nd oserver (Ym nd Ppdkis, 2004). To define nd disply olor it is neessry to selet olor spe whih is mthemtil representtion of set of olors. The three most ommon olor spes re: RGB (used for television, omputer sreens, snners nd digitl mers), CMYK (used y the printing industry) nd the CIE L spe (used in lortory olorimeters) (Fernndez et l., 2005). Colorimeters mesure olor prmeters on smll rounded re nd give non-ojetive results of olored smples with igger different olor re thn mesured re. Imge nlysis method n e pplied on totl re of nlysed smples to ensure more ojetive results euse lmost 100 % of totl surfe is ptured in n imge. Color hnges mesured in RGB olor model n e seprted in olor hnnels with intensity vlues for red, green nd lue olor from 0 to 255 (Mgdić nd Doričević, 2007). Severl studies hve een rried out to investigte the drying hrteristi of the A. offiinlis (Strhm nd Flores, 1994; My et l., 1997; Nindo et l., 2003). Generlly, in ville sientifi ppers, there seems to e no pulished work on the olor ehviour of dehydrted rre wild speies of sprgus (Asprgus mritimus L.). The ojetive of this investigtion ws to determine nd ompre olor hnges oserved y imge nlysis system in RGB olor model nd hrommeter in L * * * olor model of sprgus dried t four different tempertures. Mterils nd methods Mteril Rw wild sprgus (Asprgus mritimus L.) ws otined in My 2008, from the ostl re of the Adriti Se nd stored t +4 C. After stiliztion on room temperture, the sprgus ws ut into 10 m long slies efore drying nd nlysis. Moisture ontent nd olor of ll smples were mesured efore nd fter drying. Drying Asprgus smples were dried in pilot plnt try dryer (UOP 8 Try Dryer, Armfield, UK). The dryer enles the ontrol of temperture nd irflow veloity. The drying tempertures of sprgus smples vried from 40 C, 50 C, 60 C nd 70 C (±0.5 C). The dryer ws operted t onstnt ir veloity of 2.75 ms -1. The ir flowed prllel to the horizontl drying surfes of the smples. The drying proess ws strted when the required drying onditions were hieved. The fifty sprgus smples were rrnged on trys nd pled into the tunnel of the dryer, t whih point the mesurements were strted. Dehydrtion lsted until the required moisture ontent of round 9% (wet se) ws hieved. Determintion of dry mtter ontent Dry mtter ontent of the sprgus smples ws determined y drying the milled smples (~10 g) t 105 ±0.5 C to onstnt mss. Anlyses were done in duplite nd the verge dry mtter ontent (w d ), expressed in perents (%), ws lulted using the following eqution: m 2 w d(%)= 100 (1) m1 where m 1 is the mss of sprgus smples efore drying (g) nd m 2 is the mss of sprgus smples fter drying (g) Color mesurement In this pper olor of rw nd dehydrted smples ws mesured using digitl imge nlysis system nd hrommeter CR-400 (Minolt). The sprgus slies were milled in offee grinder to otin fine nd homogeneous powder. Anlyses of olor vlues were done twenty times for eh rw nd dehydrted sprgus smple. RGB olor mesurement Color hnges in RGB olor model were followed y imge nlysis. Bsi elements of imge nlysis system shown in Figure 1 were lightening hmer with low voltge hlogen lmps with refletor (provided illumintion of smple re of 760±5 Lux), kground from whih piture of smple ws tken with digitl mer (Pnsoni Lumix DMC-FZ30) nd softwre for imge pre-proessing nd nlysis (IrfnView, Adoe Photoshop, Glol L Imge/2). Smples for imging were pled t 60 m distne from mer (whih hs the following settings: Aperture F/5, Exposure Time 1/5 se). Imges were stored in itmp (BMP) grphi formt with 8-it Windows System pllet (2 8 = 256 olors) nd fter tht were proessed nd nlyzed. This grphi formt stores informtion out olors in RGB-triplets for every pixel on the imge where red (R), green (G) nd lue (B) re intensities of mentioned olors in rnge from 0 to 255. Progrm Glol L Imge/2 lulted men vlues of perentge for red (R), green (G) nd lue (B) olor on smple re. The hue ngle defined s (Preuil, 1953) R B hrgb 60 1 if G > R B G B (2) Agri. onspe. si. Vol. 74 (2009) No. 3

3 An Applition of Imge Anlysis nd Colorimetri Methods on Color Chnge of Dehydrted Asprgus (Asprgus mritimus L.) 235 Men vlues of olor nd olor hnges of sprgus smples were lulted for oth olor models. Sttistil nlysis One-wy nlysis of vrine (ANOVA) nd multiple omprisons (post-ho LSD) were used to evlute the signifint differene of the dt t p < Dt ws expressed s mens ± stndrd devition. Experiments were replited five times for sttistil purpose. Figure 1. Imge nlysis system (1) Lightning hmer, (2) Light soure, (3) Digitl mer, (4) Bkground for smple, (5) Smple for nlysis, (6) Computer Results nd disussion Tles 1 nd 2 show the results of the olor mesurement of rw nd dehydrted sprgus smples for oth RGB nd L * * * olor model. Sttistil nlysis (ANOVA, post-ho LSD, p = 0.05) showed tht drying tempertures hd sttistilly signifint influene on ll prmeters nd olor vlues on dehydrted sprgus smples for oth olor models, while only prmeter * (L * * * olor model) of dehydrted sprgus smples did not show sttistilly signifint hnge. ws lulted from R, G nd B vlues nd expressed in degrees: 0 (red), 60 (yellow), 120 (green), 180 (yn), 240 (lue) nd 300 (mgent). An verge shre of eh olor on smple surfe ws presented s the finl result. Color hnges in RGB olor model were defined s: E = R-R + G-G + B-B RGB where R 0, G 0 nd B 0 indite olor prmeters of rw sprgus smples. L olor mesurement Three prmeters, L * (lightness), * (redness) nd * (yellowness), were used to study olor hnges in the L * * * olor model. L * refers to the lightness of the smples nd rnges from lk (L * = 0) to white (L * = 100). A negtive vlue of * indites green, while * positive one indites red-purple. Positive * vlue indites yellow nd negtive * lue. The hue ngle, defined s (Little, 1975; MGuire, 1992; Voss, 1992): 1 h L tn when 0 nd 0, (4) 1 h L 180 tn when 0 ws lulted from * nd * vlues nd expressed in degrees: 0 (red), 90 (yellow), 180 (green), 270 (lue). The totl olor differene (ΔE) ws lulted s follows (Hunter, 1975): 2 * * * * * * (3) E 2 2 = L L L (5) where L* 0, * 0 nd * 0 indite olor prmeters of rw sprgus smples. Rw sprgus smples were used s the referene nd higher ΔE represented igger olor hnge. Tle 1. RGB olor prmeters of rw nd dehydrted sprgus smples Smple R G B Rw ± ± ± C ± ± ± C ± ± ± C ± ± ± C ± ± ± 3.07 dehydrted,, - groups whih differed sttistilly signifint from one to nother ording to drying temperture Tle 2. L * * * olor prmeters of rw nd dehydrted sprgus smples Smple L * * * Rw ± ± ± C ± ± ± C ± ± ± C ± ± ± C ± 0.34 d ± ± 0.26 d dehydrted,,, d - groups whih differed sttistilly signifint from one to nother ording to drying temperture Figure 2 shows the totl olor hnges of dehydrted sprgus smples t different drying tempertures for oth olor models. An ANOVA nlysis showed the existene of three groups whih differed signifintly from one to nother (p = 0.05; post-ho LSD), one of them orresponding to smples dried t 40 C, nother for the smples dried t 50 C nd 60 C, nd third one orresponding to 70 C. Clulted orreltion oeffiient etween olor hnges for used models ws found to e Color hnge from green to olive green or yellow green, is the result of the onversion of hlorophyll to pheophytin, Agri. onspe. si. Vol. 74 (2009) No. 3

4 236 Jsmin LUKINAC, Stel JOKIĆ, Mirel PLANINIĆ, Dmir MAGDIĆ, Drko VELIĆ, An BUCIĆ-KOJIĆ, Mte BILIĆ, Srećko TOMAS E (men SD) RGB olor model L 40 C 50 C 60 C 70 C Figure 2. Totl olor hnges (ΔE) of dehydrted sprgus smples t different drying tempertures for oth olor models h (men SD) rw 40 C 50 C 60 C 70 C d RGB e olor model through the mgnesium sustitution of the hlorophyll y hydrogen (Woolfe, 1979) during heting of green vegetles suh s sprgus. Figure 3 shows hue ngle vlues of olor of rw nd dehydrted sprgus smples t different drying tempertures for oth olor models expressed in degrees. An ANOVA nlysis for hue ngle of RGB olor model showed the existene of five groups whih differed signifintly from one to nother (p = 0.05; post-ho LSD) ording to different drying tempertures. By L * * * olor model three groups were found tht differed signifintly from one to nother. Hue vlues for oth used models hve trnsition diretion from green to yellow olor. L Figure 3. Hue ngle ( ) of olor of rw nd dehydrted sprgus smples t different drying tempertures for oth olor models Correltion oeffiient etween hue ngle vlues lulted for oth used models ws found to e Averge olor vlue of smple in eginning ws in RGB model R = 140, G = 188, B = 107 nd in L * * * model L * = 21.42, * = -2.77, * = Men olor hnges in RGB olor model were ΔE RGB = 37.56, nd in L * * * olor model were ΔE L = Conlusion Sttistilly omprtion of lulted dt etween olor hnges of sprgus dried t different tempertures ws investigted pplying imge nlysis system in RGB olor model nd hrommeter in L * * * model system. An ANOVA nlysis showed sttistilly signifint influene of drying temperture on hue ngle nd totl olor hnge for oth hosen olor models (ΔE RGB = ; h RGB = nd ΔE L** = ; h L** = ) of dehydrted sprgus. Represented results show tht there were no sttistilly signifint differenes ording to olor hnges etween drying t 50 C nd 60 C. Convetive drying t tempertures lower thn 45 C results in higher miroil ount (Mrtinov et l., 2007). It mens, the drying temperture should e ove this level. Previous studies onfirmed tht higher drying temperture results in lower energy input (Müller, 1992). Beuse of this nd the very similr olor hrteristis of mteril dried t 50 nd 60 C, the optiml temperture in this se is 60 C. Consumers selet their food in supermrkets sed on, primrily, visul pereption, nd often this is the only diret set of informtion s reeived from the produt. Aording to lulted results (high oeffiient orreltion etween hosen olor models), it ws found tht imge nysis method s well s olorimetry method n e used to oserve the olor hnges of dried sprgus smples. During drying it is very importnt to retin the originl olor of the sprgus s muh s possile, espeilly if dried sprgus re used, for exmple, in instnt soups or sues. Furthermore, the influene of drying on other qulity hrteristis of sprgus, like rehydrtion hrteristis, should e investigted in further studies. Referenes Alnese D., Russo L., Cinqunt L., Brsiello A., Di Mtteo M. (2007). Physil nd hemil hnges in minimlly proessed green sprgus during old-storge. Food Chem. 101: An J., Zhng M., Wng S., Tng J. (2008). Physil, hemil nd miroiologil hnges in stored green sprgus spers s ffeted y oting of silver nnoprtiles-pvp. LWT 41: Fernndez L., Cstillero, C., Aguiler, J.M. (2005). An pplition of imge nlysis to dehydrtion of pple diss. J. Food Eng 67: Hunter R. S. (1975). Sles for the mesurements of olor differene. In the Mesurement of Apperne. John Willy & Sons, New York, Lu M.H., Tng J., Swnson B.G. (2000). Kinetis of texturl nd olor hnges in green sprgus during therml tretments. J Food Eng 45: Agri. onspe. si. Vol. 74 (2009) No. 3

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