The objective of this study was to determine bread slice medium part properties in relation to quality parameters with a focus on gluten strength. Since sensory evaluation of bread is time consuming, expensive and subjective in nature, computerized image analysis was applied as objective method of bread crumb quality evaluation. Gluten Index method was applied as fast and reliable tool for defining gluten strength of wheat. Significant (P90) Ana, Demetra, Klara, Srpanjka and Divana have shown trend to give unequal and bigger crumb grains while cultivars Golubica, Barbara, Žitarka, Kata and Sana with optimal gluten strength (GI= 60-90) have shown finer and uniform crumb grain.Cilj istraživanja bio je utvrditi povezanost parametara izgleda sredine kruha i kakvoće pšenice, s naglaskom na jačinu glutena. Budući da je senzorska procjena kruha vremenski zahtjevna, skupa i relativno subjektivna, u procjeni izgleda sredine kruha korištena je računalna analiza slike kao objektivna metoda. Jačina glutena pšenice određena je brzom i pouzdanom gluten indeks metodom. Statistički značajna (p90), Anu, Demetru, Klaru, Srpanjku i Divanu, karakterizira neujednačena poroznost sredine kruha s velikim šupljinama, za razliku od kultivara Golubice, Barbare, Žitarke, Kate i Sane s optimalnom vrijednošću gluten indeksa (GI= 60-90), čija je poroznost, s obzirom na manje šupljine, bila ujednačenija

D. Magdić

Daniela Horvat

G. Drezner

Gordana Šimić

Zorica Jurković

English

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1ISSN 1330-7142UDK =  633.11 : 664.6IMAGE ANALYSIS OF BREAD CRUMB STRUCTURE IN RELATION TO GLUTEN STRENGTH OF WHEATD. Magdić (1), Daniela Horvat (2), G. Drezner (2), Zorica Jurković (2), Gordana Šimić (2)Original scientific paperIzvorni znanstveni članakSUMMARYThe objective of this study was to determine bread slice medium part properties in relation to quality parameters with a focus on gluten strength. Since sensory evaluation of bread is time consuming, expensive and subjective in nature, computerized image analysis was applied as objective method of bread crumb quality evaluation. Gluten Index method was applied as fast and reliable tool for defining gluten strength of wheat. Significant (P<0.05) positive correlation was noticed between bread slice medium part properties and Gluten Index and bread appearance (h/d), while wet gluten content have shown negative influence on these properties. The cultivars with over strong gluten (GI>90) Ana, Demetra, Klara, Srpanjka and Divana have shown trend to give unequal and bigger crumb grains while cultivars Golubica, Barbara, Žitarka, Kata and Sana with optimal gluten strength (GI= 60-90) have shown finer and uniform crumb grain. Key-words: bread, image analysis, crumb structure, gluten strengthINTRODUCTIONThe technological properties of wheat flour are strongly dependent on total gluten quantity and quality. Quality gluten, describing by degree of strength and extensibility, allows sufficient expansion and good distribution of the gas cells within dough (Lasztity, R., 2003). For gluten strength evaluation different tests, including Gluten Index and physical dough properties determined by Brabender farinograph and extensograph, have been applied in Croatia (Jurković et al., 1996).Among bread making parameters accessed by flour and dough analysis and baking test, loaves volume and crumb quality are certainly the two most important for the end use quality. In evaluation of this attributes image analysis is confirmed as objective and high confidence method and has became almost standard crumb evaluation method in last decades (Zayas, 1993; Chtioui et al., 1996; Magdić, 1999), since sensory evaluation of bread is time consuming, expensive and subjective in nature. For applying image analysis in crumb quality evaluation bread loaves should be correctly sliced and slices must be properly lightening, captured by camera and digitized. Later image processing is optional and depends on necessity of cropping the rectangular medium part or all internal part of slice. Finally, main crumb texture attributes can be evaluated by computer programs based on different algorithms(Heijden, 1998; Zghal et al., 1999; Crowley et al., 2002; Gallagher et al., 2003).MATERIAL AND METHODSThe Prebasic seeds from ten winter wheat cultivars: Žitarka, Srpanjka, Barbara, Klara, Golubica, Kata, Ana, Demetra, Divana and Sana were analyzed. All cultivars were grown in the experimental field of Agricultural Institute Osijek, Croatia in years 2001 and 2002. The chemical composition and technological properties of flour were evaluated by standard research procedure published by International Association for Cereal Science and Technology (ICC). The crude protein content of sample grains was measured by Infratec 1241 (Foss Tecator) which is calibrated according to ICC _________________() PhD Damir Magdić – Faculty of Food Technology, Franje Kuhača 18, 31000 Osijek, (2) PhD Daniela Horvat, PhD Georg Drezner, PhD Zorica Jurković and MSc Gordana Šimić - Agricultural Institute Osijek, Južno predgrađe 17, 31000 Osijek2standard method No 105/2. All samples were milled into flour using a Brabender Quadrumat Jr. Mill, and flour was standardised for ash 0.55%. Wet gluten content and Gluten Index were determined according to ICC standard method No 155. Wet gluten in wheat flour is a plastic-elastic substance consisting of the proteins gliadin and glutenin, obtained after washing out the starch from wheat flourdough. Gluten separated from wheat flour is centrifuged to force wet gluten through a specially constructed sieve under standardized conditions. The percentage of wet gluten remaining on the sieve after centrifugation is defined as the Gluten Index. All analyses were done in duplicates. Baking test of all samples was done according to ICC standard method No 131. Baking test was done in the industry bakery ("Croatia", Osijek). A dough is made of flour (1000 g), water, according to farinographic water absorption, dry yeast (18 g), salt (15 g), sucrose (18.6 g), ascorbic acid (0,05 g). Dough pieces are scaled rounded, rested 30 min, sheeted and moulded, placed in tins, proofed 50 min and baked at 230C for 30 min. Dough handling properties were noted. The loaves were evaluated the followingday for volume, shape and crumb structure. The bread volume was measured by volumeter filled with millet grains. Statistical analysis of data was carried out with Statistica 6.0 (StatSoft software).In preparation for quality assessment by image analysis, bread loaves were sliced in the middle, providing two cross sections. Slices were properly illuminated (700 lux) by halogen, indirect illumination and images were captured. The acquired images represented surfaces with a size of 10 x 8 cm (960 pixels per cm2). Three loaves were produced from each of ten wheat cultivars and images of each half of a loaf were recorded as 8-bit bitmap file with 256 grey levels. The threshold value 128 was chosen and determined by the "trail and error" method in order to gain the best cell resolution. The same image processing operations were applied to all records (Fig. 1). After image pre-processing, evaluation of crumb texture appearance was performed. Slice texture analysis was done,calculated total area of cells (sum of all spots where more than 5 pixels were connected), number of cells bigger than 5 pixels, average cell area, average radius, perimeter, minimum and maximum radius and roundness of crumbs/cells (measure of roundness is in the range between 0 - not round and 1 -perfectly circular). The value was calculated as: roundness = 4  total area / perimeter squared) as the main crumb texture attributes. The attributes were evaluated by use of GLI/2 Scientific Imaging Software. Figure 1.  Original image and applied transformationsSlika 1. Izvorna slika i primijenjene transformacijeRESULTS AND DISCUSSIONTextural appearance of bread crumbs depends on flour protein quality and quantity (Magdić et al., 2002; Prabhasankar et al., 2002; Lasztity, R., 2003). The grain samples taken from two years were different in breadmaking quality and on average their crude protein content varied between 12.9% (Srpanjka and Ana) and 14.7% (Golubica). Quantity of gluten expressed as wet gluten varied between 29.8% (Srpanjka) and 43.4% (Golubica) (Table 1). It must be mentioned that protein and wet gluten content is not a measure of gluten quality. Gluten quality is defined by the degree of elasticity and extensibility. In accordance with our previous investigation strong correlation between the extensographic parameters and Gluten Index indicates that the Gluten Index can be accepted as fast and reliable tool for describing gluten strength of Croatian wheat flour (Jurkovic et al., 2000; Curic et al., 2001; Horvat et al., 2002). In the investigated cultivars Gluten Index values were ranged from 62 (Kata) to 99 (Srpanjka). According to the results of 3the baking test, the best loaf volume had cultivars Divana (573 cm3/100 g flour) and Klara                    (514 cm3/100 g flour).Table 1. The mean values of quality parameters of tested winter wheat cultivars Tablica 1. Srednje vrijednosti parametara kakvoće analiziranih kultivara pšeniceCultivarKultivariPa WG GI V h/dGI >90Srpanjka 12.9b 29.8 99 473 0.70Ana 12.9 30.7 98 455 0.80Demetra 13.2 32.3 97 466 0.77Klara 13.2 35.0 93 514 0.76Divana 16.5 42.2 93 573 0.88MeanProsjek13,5c 33.8 95 505 0,74GI <90Barbara 13.3b 39.5 84 490 0.70Žitarka 13.4 41.4 76 486 0.66Golubica 14.7 43.4 75 462 0.68Sana 12.6 34.2 71 499 0.70Kata 13.2 39.7 62 467 0.69MeanProsjek 13.0c 37.1 72 486 0,68aP=crude protein content of grains (%); WG=wet gluten (%); GI=Gluten Index; V=loaf volume (cm3/100 g flour); h/d = ratio of loaf height and diameter measured on a half of loaf length; bMean value (n=2 years); cMean value (n=10)aP=udio ukupnih bjelančevina u zrnu (%); WG=vlažni gluten (%); GI=gluten indeks; V=volumen vekne (cm3/100 g brašna); h/d=omjer visine i širine vekne mjeren na polovici dužine;bProsjek (n=2 godine); cProsjek (n=10)4The results obtained by digital image analysis demonstrated cultivars' specific differences (Table 2). Table 2.  Bread slice image analysis results (pixels)   Tablica 2. Rezultati analize slike kriške kruha (pikseli)CultivarKultivariAreaPovršinaRadius PolumjerPerimeterOpsegMin radius Min. polumjerMax radiusMaks. polumjerRoundness aOkruglostGI >90Srpanjka 21.07b 2.55 18.50 0.60 4.26 0.73Ana 20.19 2.54 19.44 0.57 4.29 0.68Demetra 17.87 2.13 17.67 0.64 3.67 0.77Klara 15.32 2.33 16.24 0.52 3.89 0.72Divana 17.16 2.37 17.43 0.59 3.97 0.71MeanProsjek 18,17c 2,36 17,74 0,59 3,98 0,73GI < 90Barbara 12.60b 2.16 14.77 0.47 3.63 0.74Žitarka 13.54 2.25 15.96 0.46 3.79 0.73Golubica 14.71 2.29 15.88 0.46 3.88 0.75Sana 12.40 2.17 15.44 0.42 3.75 0.69Kata 12.70 2.18 14.77 0.47 3.66 0.76MeanProsjek13.19c 2,21 15,37 0,46 3,74 0,73a Ratio of height and width of cell; bMean values (n=2 years), cMean values (n=10)a Omjer visine i širine šupljine; bProsjek  (n=2 godine), cProsjek (n=10)The cultivars Barbara, Žitarka, Golubica, Sana and Kata with Gluten Index value from 62 to 84 havegiven smaller crumbs on slice's area (12.4-14.71 pixels per crumb), while cultivars Srpanjka, Ana, Demetra, Klara and Divana with over strong gluten (GI>90) have given bigger crumbs (15.32-21.07pixels per crumb), even when differences in loaf volumes among cultivars were not noted. The most significant positive impact (P<0.05) on increasing of crumb texture attributes had Gluten Index.                  In accordance with other researchers (Scanlon et al., 2000; Zghal et al. 2001), we have found that the highest impact of Gluten Index was on total crumb area (r=0.84), crumb perimeter (r=0.82) and min radius (r=0.84) (Table 3).Table 3. Correlation between bread crumb texture properties and wheat quality  Tablica 3. Korelacije između parametara sredine kriške kruha i kakvoće pšeniceParametersParametriPa WG GI V h/dAreaPovršina-0.04 -0.63* 0.84* -0.11 0.49RadiusPolumjer0.09 -0.41 0.56 0.00 0.34PerimeterOpseg-0.04 -0.63* 0.82* -0.09 0.56Min radiusMin. polumjer0.18 -0.51 0.84* 0.08 0.66*Max radiusMaks. polumjer-0.11 -0.48 0.60 -0.06 0.34RoundnessOkruglost0.04 0.29 -0.18 -0.29 -0.345aP= crude protein content of grains (%); WG=wet gluten (%); GI=Gluten Index; V=loaf volume (cm3/100 g flour), h/d=ratio of loaf height and diameter measured on a half of loaf length; * P< 0.05aP=udioukupnih  bjelančevina (%); WG=vlažni gluten (%); GI=gluten indeks; V= volumen vekne (cm3/100 g brašna), h/d= omjer visine i širine vekne mjeren na polovici dužine;The most significant (P<0.05) negative impact on crumb area and perimeter had wet gluten (r=-0.63).On the other side, loaf appearance (h/d ratio) have shown positive correlation with crumb area(r=0.49), perimeter (r=0.56) and significant (P<0.05) positive impact on minimum radius (r=0.66)(Table 3).CONCLUSIONThe best loaf medium part porosity was found in bread loaves made of Žitarka, Kata, Golubica, Barbara and Sana. At the same time, these cultivars had optimal gluten strength. In this research the most significant positive impact on textural appearance of bread crumbs had Gluten Index, while the most significant negative influence had wet gluten content. Analyzing obtained results it could be concluded that the bread coarse area does not depend on a loaf volume. Crumb texture is a typical property of cultivar and according to crumb texture properties the cultivars can be recommended as a good choice for specific bakery products.REFERENCES1. Chtioui, Y., Bertrand, D., Dattee, Y., Devaux, M-F. (1996): Identification of seeds by colour imaging - comparison of discriminant analysis and artificial neural network. Journal of the Science of Food & Agriculture, 71:433-441.2. Crowley, P., Schober, T.J., Clarke, C. I., Arendt, E. K. (2002): The effect of storage time on textural and crumb grain characteristics of sourdough wheat bread. European Food Research & Technology. 214:489-496.3. Curic, D., Karlovic, D., Tusak, D., Petrovic, B., Dugum J. (2001): Gluten as a standard of wheat flour quality. Food Technology & Biotechnology, 39:353-361.4. Gallagher, E., Gormley, TR., Arendt, EK. (2003): Crust and crumb characteristics of gluten free breads. Journal of Food Engineering, 56:153-161.5. Global Lab Image/2 ver. 2.6, Data Translation Inc., Marlboro, USA6. Heijden, F. (1998): Image Operations in: Image Based Measurement Systems. University of Twente, The Netherlands, 69-129.7. Horvat, D., Jurković, Z., Sudar, R., Pavlinić, D., Šimić, G. (2002): The Relative Amounts of HMW Glutenin Subunits of OS Wheat Cultivars in Relation to Bread-Making Quality. Cereal Res. Comm., 30:415-422.8. Jurkovic, Z., Sudar, R., Drezner, G., Horvat, D. (2000): The HMW glutenin subunit composition of OS wheat cultivars and their relationship with bread-making quality. Cereal Res. Comm., 28:271-277.9. Jurković, Z., Sudar, R., Horvat, D., Drezner G. (1996): Kakvoća brašna OS kultivara pšenice. Poljoprivreda, 1-2:67-75. 10. Lasztity, R. (2003): Prediction of Wheat Quality-Succes and Doubts. Periodica politechnica. Ser. Chem. Eng., 46:39-49.11. Magdić D. (1999): Digital Image Analysis in: The Digital Image Analysis Algorithm of Bread Medium Part, Master thesis, FFT Zagreb, 65-68.12. Magdić, D., Horvat, D., Jurković, Z., Sudar, R., Kurtanjek, Ž. (2002): Chemometric Analysis of  High Molecular Weight Glutenin  Proportions and Image Data of Bread Crumb Structure from Croatian Wheat Cultivars. Food Technology and Biotechnology, 40:331-341. 13. Prabhasankar, P., Manohar, R. S., Gowda, L. R. (2002): Physicochemical and biochemical characterisation of selected wheat cultivars and their correlation to chapati making quality. Eur. Food Res. Technol., 214:131-137.614. Scanlon, M.G., Sapirstein, H.D., Fahloul, D. (2000): Mechanical properties of bread crumb prepared from flours of different dough strength. Journal of Cereal Science, 32:235-243.15. Zayas IY. (1993): Digital image texture analysis for bread crumb grain evaluation. Cereal Foods World, 38:760-766.16. Zghal, M.C., Scanlon, M.G., Sapirstein, H. D. (1999): Prediction of bread crumb density by digital image analysis. Cereal Chemistry, 76:734-742. 17. Zghal, M.C., Scanlon, M.G., Sapirstein, H.D. (2001): Effects of flour strength, baking absorption, and processing conditions on the structure and mechanical properties of bread crumb.Cereal Chem., 78:1-7.POVEZANOST RAČUNALNE ANALIZE SLIKE S JAČINOM GLUTENA PŠENICESAŽETAKCilj istraživanja bio je utvrditi povezanost parametara izgleda sredine kruha i kakvoće pšenice, s naglaskom na jačinu glutena. Budući da je senzorska procjena kruha vremenski zahtjevna, skupa i relativno subjektivna,u procjeni izgleda sredine kruha korištena je računalna analiza slike kao objektivna metoda. Jačina glutenapšenice određena je brzom i pouzdanom gluten indeks metodom. Statistički značajna (p<0,05) pozitivna korelacija utvrđena je između svojstava sredine kriške kruha i gluten indeksa te s oblikom vekne kruha (h/d), dok je  udio  vlažnoga glutena imao negativan utjecaj na ta svojstva. Kultivare s vrlo jakim glutenom (GI>90),Anu, Demetru, Klaru, Srpanjku i Divanu, karakterizira neujednačena poroznost sredine kruha s velikim šupljinama, za razliku od kultivara Golubice, Barbare, Žitarke, Kate i Sane s optimalnom vrijednošću gluten indeksa (GI= 60-90), čija je poroznost, s  obzirom na manje šupljine, bila ujednačenija. Ključne riječi: kruh, računalna analiza slike, struktura sredine kruha, jačina glutena(Received on 18 April 2006; accepted on 23 May 2006 - Primljeno 18. travnja 2006.; prihvaćeno 23. svibnja 2006.)

POVEZANOST RAČUNALNE ANALIZE SLIKE S JAČINOM GLUTENA PŠENICE

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