Effect of buckwheat flour addition to wheat flour on acylglycerols and fatty acids composition and rheology properties

Effect of buckwheat flour addition to wheat flour on acylglycerols and fatty acids composition and rheology properties

LWT - Food Science and Technology 44 (2011) 650e655 Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: ww...

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LWT - Food Science and Technology 44 (2011) 650e655

Contents lists available at ScienceDirect

LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt

Effect of buckwheat flour addition to wheat flour on acylglycerols and fatty acids composition and rheology properties Nada Nikoli c a, *, Marijana Saka c b, Jasna Mastilovi cb a b

Faculty of Technology, University of Nis, Bulevar oslobodjenja 124, 16 000 Leskovac, Serbia and Montenegro Institute for Food Technology, Novi Sad, Serbia

a r t i c l e i n f o

a b s t r a c t

Article history: Received 13 February 2009 Received in revised form 4 July 2010 Accepted 31 August 2010

In this paper, the rheological properties and lipids composition with an emphasis on acylglycerols and fatty acids composition of dough with various portions of buckwheat flour (BWF) are investigated. The results show lipids from wheatebuckwheat flour mixture has higher ratio of total unsaturated to saturated fatty acids content (3.77e4.78 g/100 g) than those of wheat flour only (3.71 g/100 g). The value of dough water absorption (WA), development time (DT), dough stability (DSt), gelatinization temperature (Tmax) and maximal pasta viscosity (hmax) increases when content of free fatty (FFA) acids increases, i.e. when buckwheat flour portion in flour mixtures increases, so FFA content has a proper influence on these dough properties. Dough with buckwheat flour has higher WA (54.3e56.0 ml/100 g), Tmax (82.0e84.1  C) and hmax (630e860 AU), longer Dst (0.7e4.6 min) and lower Dsf (82e90 FU) than dough with wheat flour only, whose appropriate values are 54.3 ml/100 g, 81.2  C, 480 AU, 0.3 min and 90 FU, respectively. So, the flour mixture with buckwheat flour of at least 5 g/100 g can be considered good quality flour. Ó 2010 Elsevier Ltd. All rights reserved.

Keywords: Buckwheat Wheat Dough Lipids composition Rheology

1. Introduction Buckwheat (Fagopyrum esculentum Moench) is not a cereal but usually grouped with cereals due to its way of cultivation and because the main nutritional value of buckwheat is similar to that of cereals. The importance of buckwheat is that it is a gluten-free food. Buckwheat is abundant in nutritive, such as protein, essential amino acids, dietary fiber, starch, vitamins B1 and B2, C and E (Watanabe, 1998; Wijngaard & Arendt, 2006) and it is also a good source of trace elements (Ikeda & Yamashita, 1994; Pomeranz, 1983). In comparison to cereals, buckwheat protein is of high nutritional quality due to relatively high levels of lysine and arginine (Watanabe, 1998) and well-balanced amino acids composition (Pomeranz & Robbins, 1972). In buckwheat seed protein, the salt-soluble globulin represents the major Osborn fraction (Belozersky, 1975), classified as a legumelike storage protein (Derbyshire, Wright, & Boulter, 1976). Buckwheat seed also contains antioxidants, where rutin and quercetin are the main antioxidants (Oomah, Campbell, & Mazza, 1996; Watanabe, Ohshita, & Tsushida, 1997). Different cultivars of buckwheat may have different content of rutin (Ohsawa & Tsutsumi, 1995) and most rutin is accumulated in the inflorescence, up to 12 g/100 g based on dry weight base (Hagels, 1999). * Corresponding author. E-mail address: [email protected] (N. Nikoli c). 0023-6438/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2010.08.017

Due to these components and high fiber content of 20 g/100 g (Bonafaccia, Marocchini, & Kreft, 2003; Farrell, 1978), retrograded starch (Kreft & Skrabanja, 2002) and dietary selenium (Stibilj, Kreft, Smrkolj, & Osvald, 2004), buckwheat is an important functional food: it appears to be a suitable component of food products and serviceable raw material for bakery products as the most important foods consumed by a large population (Holasova et al., 2002) and in many forms in foods (noodles, spaghetti, pancakes, etc.) in Japan, Russia, Central and Eastern Europe. Due to its effectiveness in controlling blood vessels buckwheat has been mentioned in preventing edema, hemorrhagic diseases and stabilizing high blood pressure (Havsreen, 1983; Xiaoling, Xie, Na, & Jinliang, 1992). In general, lipids comprise a small part of cereals and pseudo cereals, but have an important physiological role and role in food quality. In buckwheat lipids are concentrated in the embryo. The total lipids content in whole buckwheat grain depends on cultivar and it ranges from 2.6 to 3.2 g/100 g. The major fatty acids are palmitic (16:0), oleic (18:1) and linoleic (18:2) (Mazza, 1988). In buckwheat lipids, stearic, oleic, linoleic, linolenic, arachidic, behenic and lignoceric acids were also detected (Dorrell, 1971). As the fatty acids are not distributed uniformly, the type of tissues included in the flour affects directly its composition while the lipids in buckwheat affect proteins thermal properties (Chuan, 2007).

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There are rheological properties data about gelatinization temperature and water absorption for samples with 100, 90, 80, 70 and 60 g/100 g buckwheat flour based on wheat flour (Yoo, Kim, Yoo, Oh, & Ham, 2007) as well as capability of CO2 retention and baking behavior of buckwheat dough as gluten-free dough (PruskaKedzior, Kedzior, & Goracy, 2008). The addition of buckwheat flour and bran affected the spaghetti sensor properties (Chillo, Lavrse, Falcone, Protopapa, & Del Nobile, 2008), extrusion and cooking quality (Manthey, Yalla, Dick, & Baraddin, 2004) and tarhana chemical and functional properties (Nermin, 2009). Hromádková, Stavová, Ebringerova, and Hirch (2007) have reported that buckwheat hull hemicelluloses addition of 0.5 g/100 g has considerable effect on bread flour quality in relation to the resistance, extension and fermentation of dough and improved sensory properties of fresh bread and high scores for overall acceptability. As rheological properties have great relevance in predicting the product quality such as mixing behavior, sheeting and baking performance (Dobraszczyk & Morgenstern, 2003) and no data is available about development time (DT), dough stability (DSt), degree of softening (DSf), energy (E), resistance (R), extensibility (Ex), gelatinization temperature (Tmax) and maximal pasta viscosity (hmax), these rheological properties of wheat and buckwheat flours mixtures were investigated. The present work has been undertaken with the following objectives: (1) to prepare wheatebuckwheat flour mixtures with buckwheat flour portion in range from 3 to 30 g/100 g, (2) to investigate the effect of buckwheat flour addition on rheological properties, on fatty acids and acylglycerols composition with an emphasis on total saturated fatty acids (TS), total monounsaturated fatty acids (TMUS), total polyunsaturated fatty acids (TPUS) and total unsaturated fatty acids content (TU) and (3) to find the correlation coefficients (between some rheological properties and lipids components) and Euclidean distances (between flours and flours mixtures). 2. Materials and methods 2.1. Flour and mixtures The wheat flour (WF) and whole grain buckwheat flour (BWF) were bought from the local market. A 291, 285, 270, 240 and 210 g of wheat flour and 9, 15, 30, 60 and 90 g of buckwheat flour, respectively, were used to make 300 g of flour mixture with buckwheat flour portion of 3, 5, 10, 20 and 30 g/100 g, without adding additives. 2.2. Methods 2.2.1. Flour analysis Flour protein content was determined by the Kjeldahl method (N5.95). The ash content was determined by 920.153, AOAC 1995 method and the moisture content by 985.14, AOAC 1995 method. 2.2.2. Lipids content The lipids content was determined by n-hexane duplicate extraction, for the same sample, by using reflux (1: 20 w/v at boiling temperature, 60 min). The extracts were combined and 3 ml were dried at 110  C to a constant weight and the dry residue content was read out on the analyzer display (Scaltec SMO 01, Scaltec instruments, Germany). For lipids isolation, the rest of combined n-hexane extracts was evaporated under vacuum.

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absorption values (WA value in ml/100 g), development time (DT in minutes), dough stability (DSt in minutes), degree of softening (DSf in FU) and farinograph quality number (QN) determination. For extensograph measurement, the Brabender extensograph (Brabender, Model 8600-01, Duisburg, Germany) and test procedure ISO 5530-2 were used. The samples were prepared from flour, distilled water and salt, and data for energy (E in cm2), resistance (R in EU), extensibility (Ex in mm) and ration number (R/Ex) were recorded on extensograph curve. To obtain amylograph data such as gelatinization temperature (Tmax in  C and gelatization maximum hmax in AU), the amylograph (Brabender Model PT 100, Duisburg, Germany) and ISO 7973 test procedure was used. 2.2.4. HPLC analysis For HPLC analysis, Hol capek, Jandera, Fisher, and Prokes (1999) modified HPLC method and the Agilent 1100 High Performance Liquid Chromatograph, a Zorbax Eclipse XDB-C18 column: 4.4 m  150 mm  5 mm (Agilent Technologies, Wilmington, USA) and a UV/ViS detector were used. The flow rate of binary solvent mixture (methanol, solvent A, and 2-propanol/n-hexane, 5:4 by volume, solvent B) was 1 ml/min with a linear gradient (from 100% A to 40% Aþ 60% B in 15 min). The column temperature was held constant at 40  C. The components were detected at 205 nm. The monoacylglycerols (MAG), diacylglycerols (DAG) and triacylglycerols (TAG) were identified by comparing the retention times of the lipids components with those of standards. The samples of the reaction mixture were dissolved into a mixture of 2-propanol:n-hexane, 5:4 v/v and filtered through 0.45 mm Millipore filters. 2.2.5. GC analysis For GC analysis, fatty acids methyl esters were prepared. The lipids were alkaline hydrolyzed and methylated by methanol and BF3 as catalysts. The final fatty acids methyl esters concentration was about 8 mg/ml in heptane. For obtaining a methyl esters GC spectra, the HP 5890 SERIES II GAS-CHROMATOGRAPH, HP with FID detector and 3396 An HP integrator was used. Column was ULTRA 2 (25 m  0.32 mm  0.52 mm) (Agilent Technologies, Wilmington, USA), injector temperature of 320  C, and injector volume of 0.4 ml. The carrier gas was He at a constant flow rate of 1 ml/min. The flame ionization detector was at 350  C and split ratio was 1:20. Oven temperature was initially 120  C and was maintained at 120  C, for 1 min, then increased by 15  C/min until 200  C, increased by 3  C/min until 240  C, increased by 8  C/min until 300  C and maintained at 300  C for 15min. The fatty acids were identified by comparison of retention times of the lipids components with those of standards. 2.2.6. Statistical analysis STATISTICA, version 5.0 software was used to perform the statistical analysis: the means and standard deviations, the correlation coefficients and cluster analysis. The means and standard deviations were obtained by Descriptive Statistics, marking the Median & Quartiles and Confirm Limits for Means. In order to classify flours and mixtures of wheat flour with different buckwheat flour portion into groups, the cluster analysis and the Euclidean method with the complete linkage was used. 3. Results and discussion 3.1. Flour properties

2.2.3. Rheology measurement The Brabender farinograph (Brabender Model 8 10 101, Duisburg, Germany) according to ISO 5530-1 test procedure, was used for water

The wheat flour was B2 quality number (QN), and had protein content (PC) of 9.8  0.3 g/100 g, ash content (AC) of 0.5  0.04 g/100 g,

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Table 1 Rheological properties of wheat flour (WF) and wheatebuckwheat flour mixtures with variousportions of buckwheat flour obtained at Brabender farinograph, extensograph and amylograph. WF Farinograph data WA (ml/100 g) DT (min) DSt (min) DSf (FU) QN Group Extensograph data E (cm2) R (EU) Ex (EU) R/Ex Amylograph data Tmax( C) hmax(AU)

3 g/100 g

5 g/100 g

10 g/100 g

20 g/100 g

30 g/100 g

54.3 1.0 0.3 90 52.8 B2

    

0.6 0.2 0.1 3 2

54.3  1.0  0.7  90  44.8  B2

0.6 0.2 0.1 3 2

54.3  1.0  1.7  88  49.2  B2

0.6 0.2 0.2 2 2

55.1 1.1 2.2 84 54.6 B1

    

0.6 0.2 0.2 2 2

55.7 1.2 3.5 82 62.2 B1

    

0.6 0.2 0.3 2 2

56.0 1.5 4.6 82 67.8 B1

    

0.6 0.2 0.3 2 2

67.8 345 126 2.5

   

3 15 10 0.2

67.0 295 126 2.2

   

3 10 10 0.2

63.5 285 119 2.4

   

3 10 10 0.2

51.9 280 117 2.6

   

3 10 10 0.2

33.8 225 107 2.1

   

2 10 5 0.2

32.4 222 106 2.1

   

2 10 5 0.2

81.2  3 480  15

82.7  3 630  20

82.0  3 650  20

83.5  3 655  20

84.1  4 695  25

83.0  4 860  25

Value are the means and standard deviation (n ¼ 3) obtained by descriptive statistics and marking the Median & Quartiles and Confirm Limits for Means. WA e water absorption; DT e development time; Dst e dough stability; DSf e degree of softening; QN e quality number; E  energy; R e resistance; Ex eextensibility; R/ Ex e ratio R to Ex number. Tmax e gelatinization temperature; hmax e gelatization maximum.

lipids content (LC) of 1.9  0.1 g/100 g and gluten content (GC) of 24.6  0.4 g/100 g. The protein content in buckwheat flour was 10.6  0.5 g/100 g, the ash content was 1.9  0.05 g/100 g, the lipids content was 2.2  0.1 g/100 g and it is gluten free. The values are the averages of triplicate measurements of the same sample and followed by standard deviation. 3.2. Results of rheology measurement Farinograph, extensograph and amylograph data of flours and five flour mixtures with different portions of buckwheat flour are given in Table 1. Farinograph data depended on the buckwheat flour portion in flour mixtures. The water absorption increased from 54.3 to 56.0 ml/100 g with increasing buckwheat flour portion in mixtures. As the main dough component responsible for water absorption is gluten and as the buckwheat flour is gluten free, but with higher protein content than wheat flour (10.6e9.8 g/100 g), the good absorption properties are probably due to other protein components such as globulin and albumin (Pomeranz & Robbins, 1972). Similar effect was reported by Manthey et al. (2004) when buckwheat bran flour addition to spaghetti increased water absorption, too. The differences for dough development time among flour mixtures with different buckwheat flour portions, were insignificant, and the development time ranged from 1 to 1.2 min when buckwheat flour portions ranged from 1 to 20 g/100 g and it was 1.5 min when buckwheat flour portion was 30 g/100 g. On the other side, the dough stability for these doughs was considerably higher, especially in dough with buckwheat flour portion of 30 g/100 g, where it was 4.6 min compared to dough with wheat flour only, where this value was only 0.3 min.

The degree of softening decreased for maximal value of 8 FU with increasing portion of buckwheat flour (based on from Table 1, 90-82 ¼ 8FU). The buckwheat flour addition in portion of at least 5 g/100 g had positive influence on quality group of flour mixtures: it was B1 instead B2. Quality group is determined by the triangle area on farinograph curves and quality groups are A1 (0e1.4 cm2), A2 (1.5e5.5 cm2), B1 (5.6e12.1 cm2), B2 (12.2e17.9 cm2), C1 (18.0e27.4 cm2) and C2 (27.5e50.0 cm2) (Djakovic, 1980 pp. 47e49). Data for five flour mixtures with different portions of buckwheat flour obtained on extensograph, showed that all doughs with buckwheat flour had lower values for energy and dough resistance in comparison to dough made of wheat flour only and they decreased with increasing buckwheat flour portions. The extensibility of dough with buckwheat flour in ranged from 106 to 126 EU and those values were lower than extensibility of dough with wheat flour only. The ration number, R/Ex, varied and it ranged from 2.1 to 2.6. By amylograph data, doughs with buckwheat flour had higher Tmax than dough with wheat flour only, and this value was higher when buckwheat flour portion was higher. These results are compatible with Yoo et al. (2007) results for mixtures with higher buckwheat flour portion which ranged from 60 to 100 g/100 g. The maximal pasta viscosity increased from 630 to 860 AU when buckwheat flour portion increased, and the highest maximal pasta viscosity was when the buckwheat flour portion was 30 g/100 g. Then, maximal pasta viscosity value was nearly twice as higher as maximal pasta viscosity value for wheat flour only. As buckwheat contains special resistant starch (Wijngaard & Arendt, 2006), it can be the reason for increasing of maximal pasta viscosity. The buckwheat and rice flour are gluten-free food and their addition to wheat flour have the same influence on rheological

Table 2 The lipid (LC), free fatty acids (FFA), methyl esters (ME), monoacylglycerols (MAG), diacylglycerols (DAG) and triacylglycerols (TAG) content (g/100 g lipid solids) in wheat flour (WF), buckwheat flour (BWF) and in wheatebuckwheat four mixtures with various portions of buckwheat flour (BWF). Flours and mixtures

LC

WF BWF 3 g/100 g 5 g/100 g 10 g/100 g 20 g/100 g 30 g/100 g

1.9 2.2 1.9 1.9 1.9 1.9 2.1

FFA       

0.1 0.1 0.1 0.1 0.1 0.1 0.1

12.0 66.1 13.6 14.7 17.4 20.1 28.2

ME       

0.4 1.3 0.6 0.5 0.2 1.2 1.3

23.8 3.0 23.2 22.8 21.7 19.6 17.6

MAG       

1.3 0.2 1.4 0.7 0.3 1.2 1.2

2.2  1.0  2.2  2.1  2.1  2.0  1.8 

DAG 0.2 0.1 0.1 0.2 0.1 0.1 0.1

13.5 6.7 13.3 13.2 12.8 12.2 11.5

TAG       

0.9 0.6 0.5 0.2 1.2 1.2 1.1

Value are the means and standard deviation (n ¼ 3) obtained by descriptive statistics and marking the Median & Quartiles and Confirm Limits for Means.

48.6 23.1 47.8 47.3 46.1 43.5 40.9

      

1.5 0.8 1.3 1.3 1.3 1.3 1.3

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Table 3 Fatty acids composition of lipid from wheat flour (WF), buckwheat flour (BWF) and wheatebuckwheat flour mixtures with various portions of buckwheat flour obtained by GC analysis. Component (g/100 g of flour or flour mixture)

WF

Palmitic acid (16:0) Stearic acid (18:0) Behenic acid (22:0) Oleic acid (18:1) Linoleic acid (18:2) Phthalic acid TS TMUS TPUS TU TU/TS

19.45 1.36 0.26 20.23 57.91 0.68 21.07 20.23 57.91 78.14 3.71

Buckwheat flour portion in flour mixture

BWF

         

0.45* 0.14* 0.06* 0.21* 0.72* 0.08* 0.45* 0.21* 0.72* 0.93*

13.47 1.98 e 32.13 41.74 e 15.45 32.13 41.74 73.87 4.78

3 g/100 g 19.27 1.38 0.25 20.58 57.42 0.66 20.90 20.58 58.08 78.66 3.77

 0.40*  0.16*  0.62*  0.86*    

0.6* 0.6* 0.6* 0.6*

5 g/100 g 19.15 1.39 0.25 20.83 57.09 0.63 20.79 20.83 57.72 78.55 3.79

10 g/100 g 18.85 1.42 0.23 21.40 56.26 0.61 20.50 21.40 56.87 78.27 3.86

20 g/100 g 18.25 1.49 0.21 22.61 54.68 0.54 19.95 22.61 55.22 77.83 3.98

30 g/100 g 17.65 1.55 0.18 23.80 53.05 0.48 19.38 23.80 53.53 77.33 4.12

TS e total saturated fatty acids content; TMUS e total monounsaturated fatty acids content; TPUS e total polyunsaturated fatty acids content; TU e total unsaturated fatty acids content; TU/TS e ratio total unsaturated fatty acids content to total saturated fatty acids content. * values are the means and standard deviation (n ¼ 3) obtained by descriptive statistics and marking the Median & Quartiles and Confirm Limits for Means.

properties, except on WA. By comparing results for buckwheat flour to those obtained for white and brown rice flour (Nikoli c et al., 2008), it can be concluded that buckwheat and rice flours increase DT, DSt, QN, Tmax and hmax and decrese Dsf, E, R and Ex. 3.3. Acylglycerols and fatty acids composition The lipids profile analysis (free fatty acids, methyl esters, mono-, di- and triacylglycerols content) of wheat flour, buckwheat flour and wheatebuckwheat flour mixtures, obtained by HPLC analysis, is presented in Table 2 and fatty acids composition, obtained by GC analysis is presented in Table 3. Based on HPLC analysis, the content of components was determined by measuring the peak area at 1.76 min for FFA, peak area at 2.152 min for ME, peaks area in the range of 3.445e4.580 min for MAG, peaks area in the range of 5.276e8.677 min for DAG and peaks area in the range of 10.907e15.815 min for TAG. The lipids from buckwheat flour had higher FFA content (66.1 g/100 g lipids) and lower TAG content (23.1 g/100 g) than lipids from wheat flour (12.0 and 48.6 g/100 g, respectively). The content of MAG and DAG was twice as higher in wheat flour as the corresponding content in buckwheat flour. The content of FFA in mixtures had the same changing tendency as buckwheat flour portion: it increased when the buckwheat flour portion in flour mixtures increased, while the content of MAG, DAG and TAG had opposite changing tendency: they decreased when the buckwheat flour portion in flour mixture increased. The properties of dough such as WA, DT, DSt, Tmax and hmax had the same dependency on buckwheat flour portions as the content

of FFA, so it is seemed FFA had a proper influence on those dough properties, while the content of MAG, DAG and TAG had a proper influence on E, R and Ex dough properties. GC analysis showed that lipids from wheat flour contained 78.14 g/100 g of total unsaturated fatty acids, mainly consisting of linoleic (57.91 g/100 g) and oleic acid (20.23 g/100 g). Total polyunsaturated fatty acids content in lipids were at a higher rate (57.91 g/100 g) than monounsaturated fatty acids content (20.23 g/100 g). The lipids from this flour contained 21.07 g/100 g of total saturated fatty acids where the main fatty acid was palmitic acid with the content of 19.45 g/100 g, the stearic acid content was 1.36 g/100 g, while behenic and phthalic acid content was lower than 1 g/100 g. So, the content of total unsaturated fatty acids was nearly four times (3.7) higher than the total saturated fatty acids content (78.14e21.07 g/100 g). Lipids from buckwheat flour contained 73.87 g/100 g of total unsaturated fatty acids, composed of linoleic acid with content of 41.74 g/100 g and oleic acid with content of 32.13 g/100 g. The palmitic acid and stearic acid were detected as saturated fatty acid with content of 13.47 and 1.98 g/100 g, respectively. These results are similar to results reported by Mazza (1988) where linoleic acid was the content of content of 37.0 g/100 g, oleic, 36.3 g/100 g, palmitic 14.0 g/100 g and stearic acid in the range of up to 2.1 g/100 g. Other fatty acids were not detected even though Mazza (1988) reported that in lipids from buckwheat flour linolenic acid was in range 1.3e4.2 g/100 g and arachidic acids in range 0.1e1.7 g/100 g as well as 20:1, 22:0 and 24:0 fatty acids which ranged from 0.2 to 3.7 g/100 g. Comparing to wheat flour fatty acids composition, the biggest differences was in the content of total saturated fatty acids, which

Table 4 Correlation matrix for wheat and five wheatebuckwheat flour mixtures obtained by basic statistics and correlation matrices (correlations are significant at p < 0.05, N ¼ 12).

SA OA LA MAG DAG TAG WA DSt Ex Tmax

hmax

PA

SA

OA

LA

MAG

DAG

TAG

WA

DSt

Ex

Tmax

0.41 0.91 0.99 0.98 0.91 0.99 0.68 0.89 0.95 0.55 0.82

0.75 0.53 0.34 0.13 0.49 0.81 0.72 0.30 0.57 0.69

0.96 0.87 0.72 0.95 0.86 0.98 0.83 0.65 0.91

0.97 0.87 0.99 0.75 0.94 0.93 0.59 0.87

0.93 0.97 0.61 0.87 0.95 0.56 0.82

0.89 0.42 0.73 0.87 0.35 0.71

0.73 0.93 0.94 0.58 0.86

0.86 0.67 0.59 0.66

0.86 0.70 0.92

0.56 0.71

0.62

PA e palmitic acid content; SA e stearic acid content; OA e oleic acid content; LA e linoleic acid content; MAG emonoacylglycerols content; DAG ediacylglycerols content; TAG e triacylglycerols content; WA e water absorption; DSt e dough stability; Ex e extensibility; Tmax e gelatinization temperature; hmax e gelatization maximum.

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N. Nikolic et al. / LWT - Food Science and Technology 44 (2011) 650e655

Fig. 1. Dendrogram of wheat flour (WF), buckwheat flour (BWF) and flour mixtures with buckwheat flour portion of 3, 5, 10, 20 and 30 g/100 g, based on lipid parameters obtained by cluster analysis, using Euclidean distance and complete linkage method.

was 1.36 (21.07/15.45) times as higher in wheat flour as in buckwheat flour. Such fatty acids flour composition in buckwheat flour had influence on fatty acids composition in wheatebuckwheat flour mixtures, so the content of total saturated fatty decreased when the buckwheat flour portion in flour mixture increased.

3.4. Statistical analysis data The correlation coefficients between parameters (palmitic, stearic, oleic and linoleic acid content, MAG, DAG and, TAG content, WA, DSt, Ex, Tmax, and hmax) of wheat flour and wheatebuckwheat flour mixtures are presented in Table 4. The sample size was twelve (N ¼ 12, 6  2): wheat flour and five wheatebuckwheat flour mixtures with two measurements for each one. Only the correlations which were above absolute value of 0.8 were taken into consideration. There were 63.6% of correlations, among which 38.2% were proper, and 25.4% were opposite correlations. High oleic acid content was associated with low palmitic acid content, while high linoleic acid content was associated with high palmitic acid and low oleic acid content. The high MAG content went with high palmitic acid and linoleic acid content and low oleic acid content. It can mean that MAG mainly consists of palmitic and linoleic acid. Analog data indicated that the high DAG and TAG content went along with high palmitic acid and linoleic acid content, and high TAG content went along with low oleic acid content. So, DAG and TAG mainly consist of palmitic and linoleic acid, too. The WA was associated only with high stearic and high oleic acid content, while DSt was associated with eight parameters: in proper correlation with oleic acid content, WA and hmax and in opposite correlations with palmitic acid, linoleic, MAG and TAG content. There were also seven correlations above absolute value of 0.8 for Ex with given parameters: five proper, with palmitic acid, linoleic acid, MAG, DAG and TAG content, and two opposite correlations, with oleic acid content and DSt. Based on these data, it is clear that dough Ex depends on acylglycerols content, regardless whether they are MAG, DAG or TAG. Dough hmax depends on palmitic acid, oleic acid, linoleic acid, MAG and TAG content and on DSt: high hmax is associated with high oleic acid content and high DSt value and with low palmitic acid, linoleic acid, MAG and TAG content. Correlation matrix also shows Tmax had no correlations with above absolute value of 0.8, with any given parameters. By cluster analysis, based on multiple variables, wheat and buckwheat flour and their mixtures were classified into groups.

Number of variables were seven: wheat and buckwheat flour and five wheatebuckwheat flour mixtures (with buckwheat flour portions of 3, 5, 10, 20 and 30 g/100 g); number of cases i.e. parameters were seven: TS, TU, palmitic acid, stearic acid, oleic acid, linoleic acid and lipids content. Linkage distances for wheat, buckwheat flour and their mixtures were obtained and presented by dendrogram in Fig. 1. The mixtures with buckwheat flour portion of 3 and 5 g/100 g are joined with WF at the same distance level of 0.8 and make the first group; the mixtures with buckwheat flour portion of 10 and 20 g/ 100 g are joined with WF flour at the distance level of 1.3 and make the second group, while the mixture with buckwheat flour portion of 30 g/100 g is joined with WF at distance level of 4.33 and make the third group. BWF is joined with flour mixtures with buckwheat flour portion at the highest linkage distance of 15.6. The cluster analysis based on flour lipids characteristics, shows that when buckwheat flour portion in mixtures increases the linkage distance between BWF and flours mixtures decreases, while the linkage distance between WF flour and flour mixtures increases. 4. Conclusions Dough rheological properties and lipids profile data (fatty acids, mono-, di- and triacylglycerols composition) depend on buckwheat flour portion in the mixtures. The buckwheat flour addition has positive influence on the quality number. The wheatebuckwheat flour mixtures have higher ratio of total unsaturated to saturated fatty acids content than those in wheat flour. Dough extensibility depends on mono-, di- and triacylglycerols content and hmax depends on palmitic, oleic and linoleic acid content, mono- and triacylglycerols content. The wheatebuckwheat flour mixtures have higher water absorption, gelatinization temperature and maximal pasta viscosity, longer stability and lower degree of softening and extensibility than wheat flour only. So, wheatebuckwheat flour mixtures with buckwheat flour portion of at least 5 g/100 g can be considered good quality flour mixture. Acknowledgements This work was supported under the project No 20068 by the Ministry of Science and Technology of the Republic of Serbia. References Belozersky, M. A. (1975). Isolation and characterization of buckwheat seed 13S globulin. In Biosynthesis of storage proteins (pp. 152e156). Moscow: Nauka.

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