Dough rheology and baking performance of wheat flour–lupin protein isolate blends

Food Research International 43 (2010) 1009–1016

Contents lists available at ScienceDirect

Food Research International journal homepage: www.elsevier.com/locate/foodres

Dough rheology and baking performance of wheat flour–lupin protein isolate blends A. Paraskevopoulou *, E. Provatidou, D. Tsotsiou, V. Kiosseoglou Laboratory of Food Chemistry and Technology, School of Chemistry, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece

a r t i c l e

i n f o

Article history: Received 20 October 2009 Accepted 19 January 2010

Keywords: Lupin protein Dough rheology Bread Texture

a b s t r a c t The impact of addition of two lupin protein isolates (LPI), enriched either in proteins belonging to globulin (LPI G) or to albumin (LPI A) fraction, on wheat flour dough and bread characteristics was investigated. LPI addition increased the dough development time and stability plus the resistance to deformation and the extensibility of the dough. The presence of LPI proteins in dough affected bread quality in terms of volume, internal structure and texture, while extra gluten addition to the blends to compensate for wheat gluten dilution, resulting from LPI addition, led to an improvement of bread quality characteristics. Generally, the incorporation of LP isolates to wheat flour delayed bread firming. The results obtained are discussed in terms of a possible action of LPI particles as a filler of the gluten network and partly in terms of possible interactions that take place between the gluten protein constituents and those of lupin. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction Legume seeds provide valuable proteins, which are considered to be increasingly important in human nutrition. In addition, legume proteins in the form of flour, concentrate or isolate, are a good supplement for cereal-based foods, since both legume and cereal proteins are complementary with regard to their essential amino acids. Legume proteins are rich in lysine and deficient in sulphur-containing amino acids, whereas cereal proteins are deficient in lysine, but have adequate amounts of sulphur amino acids (Eggum & Beame, 1983). Therefore, legume proteins can be successfully used in baked products, to obtain a protein-enriched product with improved amino acid balance. The potential use of legumes as protein-enriching agents of baked products, mainly in the form of protein flours, has been reported by several authors. Among the legume protein products tested were various soybean protein preparations (Ribotta, Arnulphi, León, & Anón, 2005a), chickpea flour (Gómez, Oliete, Rosell, Pando, & Fernández, 2008), germinated chickpea flour (Fernandez & Berry, 1989), germinated pea flour (Sadowska, Blaszczak, Fornal, Vidal-Valverde, & Frias, 2003) and lupin flour (Dervas, Doxastakis, Hadjisavva-Zinoviadi, & Triantafillakos, 1999; Doxastakis, Zafiriadis, Irakli, & Tananaki, 2002; Pollard, Stoddard, Popineau, Wrigley, & MacRitchie, 2002). Lupin (Lupinus) is a leguminous seed with high protein content (about 35% of dry matter), similar to that of soybean, low oil content (Duranti, Consonni, Magni, Sessa, & Scafaroni, 2008; Sujak, * Corresponding author. Tel.: +30 2 31 0 997832; fax: +30 2 31 0 997779. E-mail address: [email protected] (A. Paraskevopoulou). 0963-9969/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2010.01.010

Kotlarz, & Strobel, 2006), while, in comparison to other legumes, it has a lower content of the main anti-nutritional components. Moreover, lupin can be grown in more temperate to cool climates than soy. This legume appears to be particularly promising, since biological properties, including cholesterol and glucose-lowering capacities, as well as satisfactory functional properties, e.g. gelation, emulsification, of its proteins have been reported (Doxastakis et al., 2007; Duranti et al., 2008; Makri, Papalamprou, & Doxastakis, 2005; Mavrakis, Doxastakis, & Kiosseoglou, 2003). Its main proteins belong to the family of the storage proteins with the globulins representing about 90% of the total protein content. Bread is considered one of the major constituents in the human diet worldwide. The development of breads enriched in lupin proteins, by incorporating lupin flours, has been the subject of research conducted by Dervas et al. (1999) and Doxastakis et al. (2002). These workers demonstrated that substitution of wheat flour by full fat lupin flour, concentrated lupin flour and defatted concentrated lupin flour, at a 5% substitution level, increased the stability and the tolerance index of the dough, while a marked decrease was noted at higher levels (15%) of supplementation. In addition, the bread volume decreased as the level of lupin flour increased something that was primarily attributed to the dilution of the wheat gluten structure by the added protein. However, as wheat flour fortification was conducted only with lupin flour with a protein content ranging between  30% and 36%, it was not possible to appreciate the real impact of the proteins of lupin flour on the dough properties since other lupin flour constituents (mainly fiber) could, also, have an effect. Furthermore, no information was reported in these studies on the effect of lupin flour addition on the bread staling performance.

1010

A. Paraskevopoulou et al. / Food Research International 43 (2010) 1009–1016

This work was based on two lupin protein isolates (LPI) prepared from lupin flour by the method of isolelectric precipitation (LPI G) and ultrafiltration (LPI A) and enriched in proteins belonging to the lupin protein globulin and albumin fraction, respectively. The aim of the study was to assess the way the proteins of each one of the LP isolates affect the dough characteristics and the breadmaking properties of wheat flour (WF) following supplementation with lupin isolate at relatively high levels. 2. Materials and methods 2.1. Materials Wheat flour used in the study was obtained from a local milling company (Katerini, Greece). Its characteristics were in the range of typical values of medium strong flour, suitable for bread, i.e. protein and ash contents were 11.8% and 0.42%, respectively, both expressed on a 13.5% moisture basis (AACC, 2000). Two lupin protein isolates differing in the method applied for their preparation and enriched either in globulins (G) or albumins (A) were provided by the Fraunhofer Institut für Verfahrenstechnik and Verpackung (Freising, Germany). LPI A was prepared by extracting the albumins of defatted lupin flour with water of slightly acidic pH (5) at low temperature, followed by ultrafiltration and spray drying. The remaining protein fractions (globulins) were then extracted with water at a slightly alkaline pH (8) at a moderate temperature and recovered from the extract by acid precipitation followed by spray drying (LPI G). Their protein concentration was higher than 92% (w/w), while their fat content was less than 2% (w/w). According to Mavrakis et al. (2003) the protein solubility of both isolates is very high (about 80%) and depends on the pH and NaCl concentration. Active dry yeast, salt and powder gluten, used for breadmaking, were purchased from the local market. 2.2. Evaluation of dough properties The dough mixing and stretching properties of the different wheat flour/LPI blends were studied using farinograph and extensograph instruments (Brabender, Duisburg, Germany), The measurements were conducted according to AACC methods 54–21 and 54–10 (1995). From the farinograph curves, water absorption (percentage of water required to yield dough consistency of 500 BU), dough development time (DDT, time to reach maximum consistency), stability (time during dough consistency is at 500 BU) and elasticity (band width of the curve at the maximum consistency), were determined. The parameters obtained from the extensograph curves were expressed as: (a) resistance to constant deformation after 50 mm stretching (R50); (b) extensibility (Ex), which is the distance travelled by the recorder paper from the moment in which the hook touches the test piece until rupture of the test piece; (c) the ratio between the last two parameters (R50/Ex). 2.3. Baking test Breads were prepared as follows: 300 g WF or 300 g WF–LPI mixtures (5% or 10% in LPI), were first dry-mixed in the farinograph bowl for 1 min. Next, 6 g dry yeast and 6 g salt, previously dissolved in water, were added followed by the addition of water up to 500 BU consistency and the dough kneading process was continued for a total of 6 min. The resulting dough was left to rest for 5 min, kneaded for extra 2 min and placed in a proofing cabinet at 30 °C. After 45 min fermentation, the dough was punched down to remove gases, proofed for further 45 min, placed in 20 cm  7 cm aluminium baking pans and baked at 180 °C for 45 min. Each baking test was conducted in triplicate.

2.4. Evaluation of bread quality characteristics Evaluation of the baked loaves quality characteristics was carried out following cooling to room temperature for 2 h. To assess the effect of ageing on bread texture, slices (20 mm thickness) were cut from the centre of the loaves, wrapped with polyethylene film to prevent drying, and stored for up to 2 days at room temperature. The baking loss was determined by weighing breads before and 2 h after baking. The cross sectional area in the middle of the slab was determined according to Paraskevopoulou and Kiosseoglou (1997). The moisture content was determined after heating a 5 g sample at 130 °C for 2 h. Crumb cells were analysed by scanning two slices per loaf, 20 mm thick, on a flatbed scanner (Canon MP160). Subimages (30  30 mm) were analysed by UTHSCSA Image Tool programme (Version 3.0, University of Texas Health Science Centre, San Antonio, Texas). Total number of cells, number of cells smaller than 4 mm2, total cell area, number of cells per centimeter square and the cell area/total area ratio were calculated. The evaluation of texture of bread crumb was performed using a TA.XT2i texture analyser equipped with a 25 kg load cell (Stable Micro Systems, Surrey, UK) and Texture Expert software (v. 1.11) for data analysis. Texture profile analysis (TPA) was carried out using a cylindrical aluminium probe (2 cm diameter). Measurements were carried out on the crumb of bread slices at certain time intervals of 0, 1 and 2 days. Each slice was subjected to a double cycle of compression under the following conditions: crosshead speed 1 mm/s and maximum deformation 50%. One measurement was taken on the crumb of each slice at pre-selected location. Bread crumb hardness (g), cohesiveness (–), springiness (–), gumminess (g) and chewiness (g) were calculated from the force–time curves generated for each sample (Bourne, 2002). In addition to evaluation of texture, the mechanical properties of bread samples were determined by converting the force–time curves into compression stress (r) – Hencky strain (H) ones and employing the following equations (Van Vliet, 1999):

eH ¼ ln

LðtÞ L0

and

r¼

FðtÞ A

where L0 is the original sample height, L(t) is the sample height after a compression time t, F(t) is the compression force at time t and A is the compression surface area of the bread sample. Measurements of all the above quality parameters were performed in three replicates; two values obtained from the same loaf were averaged into one replicate. 2.5. Electrophoresis studies To search for possible interactions between the wheat gluten proteins and those of lupin in dough, a portion of about 25 g of dough was extensively washed under running tap water until the water ran clear (25 min). The recovered wet gluten was then freeze dried. A small quantity of the freeze-dried sample was dissolved in a 0.0625 M Tris buffer at pH 8.8 containing 2% SDS and 5% mercaptoethanol to obtain a protein solution containing 1– 2 mg of protein per mL. Gel electrophoresis was conducted, according to Laemmli (1970), using 3% and 10% acrylamide stacking and separating gels, respectively. The gel sheets were stained for protein with Coomassie brilliant blue G-250 and photographed with a Kodak digital camera. 2.6. Statistical analysis Data obtained during dough and bread quality measurements were subjected to analysis of variance (ANOVA) and Duncan’s test using the software program of Statistical Package for the Social

A. Paraskevopoulou et al. / Food Research International 43 (2010) 1009–1016

Sciences (SPSS, edition 16.0), in order to assess significant differences among samples. Differences were considered significant when p < 0.05. 3. Results and discussion 3.1. Effect of LPI incorporation on dough mixing properties The addition of both lupin protein isolates to wheat flour brought about some significant changes in its dough mixing behaviour as measured by the farinograph. Farinograph data of wheat flour (control) and those of the supplemented with LP isolate, at a 5% or 10% level, are shown in Table 1. Supplementation of wheat flour with LPI G increased the water required for optimum breadmaking absorption (p < 0.05), while this parameter remained unaffected when LPI A was added (p > 0.05). An increase in water absorption, following incorporation of various vegetable protein concentrates or isolates to wheat flour, has also been reported by other researchers who attributed the water absorbing capacity of these protein preparations to their ability to compete for water with other constituents in the dough system. According to these authors the ability of these proteins to absorb high quantities of water results in doughs which exhibit increased farinograph water absorption values (Dervas et al., 1999; Doxastakis et al., 2002; El-Adawy, 1997; El-Soukkary, 2001). The quantity of added water is considered to be very important for the distribution of the dough materials, their hydration and the gluten protein network development. The observed difference between the two isolates suggests that, during dough mixing, the proteins of LPI G require more water to become hydrated than those of LPI A. This is probably due to the highly water-soluble albumins present in the LPI A which require less water to become hydrated compared to the proteins of LPI G. The latter are mainly globulins which were prepared by isoelectric precipitation and hence constitute less soluble proteins (Mavrakis et al., 2003) that are more difficult to hydrate and as a result they are fully hydrated after higher water addition. The time required for the control dough to reach 500 BU consistency was also modified by LPI addition. During this phase of mixing, the water hydrates the flour components and the dough is developed. Dough development time (DDT) was significantly higher (p < 0.05) for all WF–LPI blends than control (1.5 min), while between LPI samples no significant difference was observed (p > 0.05) (Table 1). The increase in dough development time resulting from LPI addition could have been due to the differences in the physicochemical properties between the constituents of the LP isolates on the one hand and those of the wheat flour on the other, as has been previously reported by Morad, El-Magoli, and Afifi (1980) who studied the incorporation of lupin or defatted soybean flour in wheat flour. Probably, the lack of difference between the two isolates was the result of similar solubilities as reported in Section 2. Regarding dough stability, it appears that the dough samples containing LPI exhibited higher stability and resistance to mechan-

1011

ical mixing values than the control. In general, the stability value is an index of the dough strength, with higher values indicating stronger dough. The increase in the stability time was related to the amount of substitution. Thus, stability times of 3.77 and 10.15 min are observed for the dough supplemented with 5% LPI G and LPI A, respectively. The respective values for the dough supplemented with 10% LPI were 13.07 and 12.03 min, which were much higher than those of the control (1.40 min). This enhancing effect might be probably the result of lupin protein particle entrapment within the gluten network structure. As reported by Güemes-Vera, Arciniega-Ruiz Esperza, and Dávila-Ortiz (2004), who performed structural analysis of dough originating from mixtures of wheat flour with lupin flour as well as with lupin protein concentrates and isolates, the presence of the vegetable protein in the mixture led to the disruption of dough structure. Their study also revealed that the vegetable protein was present in the dough in the form of hydrated but not fully dispersed particles. One may, therefore, hypothesise that the not fully dispersed particles may behave as reinforcing fillers of a gluten network and this may explain the enhancement in the dough stability. On the other hand, the results of electrophoresis studies (Fig. 1) demonstrated that a small fraction of lupin proteins remained in the gluten fraction after extensive dough washing under tap water, indicating possible association between the gluten on the one hand and some of the proteins of lupin present possibly in the outer surface of the hydrated particles. The rest of the particle proteins were, however, readily washed away during dough treatment with water. Ribotta, León, Pérez, and Anón (2005b) also reported that gluten formation was interfered with soy proteins and suggested that this was the result of both non-covalent and covalent wheat–soy protein interactions. Doxastakis et al. (2002) and Dervas et al. (1999) came to a similar conclusion, while El-Adawy (1997) reported that the addition of sesame protein preparations reduced the stability periods of all the blends studied. The width of the farinograph curve is a measure of dough cohesiveness and elasticity. The elasticity of dough at 500 BU was decreased by LPI addition. Between the two isolates, the highest elasticity was observed at 5% (w/w) LPI A (87.5 BU) and the lowest at 5% (w/w) LPI G (70 BU) (Table 1). These results suggest that the proteins of the LPI G do not readily bind with those of gluten to enhance dough elasticity. Similar results were reported by Roccia, Ribotta, Pérez, and León (2009) who found that the substitution of wheat protein by soy protein decreased mixture elasticity, indicating dough network weakening. Maforimbo, Skurray, Uthayakumaran, and Wringley (2007) suggested that the weakening of wheat flour dough by soy protein was the result of increased SH concentration. One other reason for the weakening of dough strength resulting from vegetable protein addition could stem from the fact that the substitution of gluten proteins by the non-gluten-forming vegetable proteins causes a dilution effect and consequently weakens the dough. When gluten was added to dough formulations with 10% LPI to restore the gluten to the level to that of the control,

Table 1 Effect of 5% and 10% lupin protein isolate addition (LPI G and LPI A) and gluten (Gl) on farinograph characteristics of wheat flour (WF).A

A

Dough formulation

Water absorption (%)

Dough development time (min)

Dough stability (min)

Elasticity (BU)

WF WF WF WF WF WF WF

53.6 ± 0.11a 55.5 ± 0.16b 56.0 ± 0.06b 57.0 ± 0.15b,c 53.9 ± 0.08a 54.0 ± 0.08a 55.7 ± 0.11b

1.53 ± 0.21a 2.13 ± 0.25b,c 2.07 ± 0.06b 2.53 ± 0.31c 2.30 ± 0.24b,c 2.15 ± 0.24b,c 2.27 ± 0.25b,c

1.40 ± 0.40a 3.77 ± 0.85b 13.07 ± 1.43e 4.23 ± 0.15b 10.15 ± 1.66d 12.03 ± 0.06e 5.93 ± 0.40c

97.5 ± 9.6c 80.0 ± 14.1a,b 70.0 ± 0.0a 83.3 ± 5.8a,b,c 87.5 ± 9.6a,b 82.5 ± 9.6b,c 93.3 ± 5.8b,c

and and and and and and

LPI LPI LPI LPI LPI LPI

G(5) G(10) G(10) and Gl A(5) A(10) A(10) and Gl

Mean ± standard deviation of three replicates; values in the column followed by the same letter are not significantly different (p < 0.05).

1012

A. Paraskevopoulou et al. / Food Research International 43 (2010) 1009–1016

ST

1

2

3a

4a 5a 6a

7a 8a

3b 4b

5b 6b 7b

8b

97.2 66.4 55.6 42.7 34.6 27.0 20.0 14.7 6.3 Fig. 1. Electrophoretic patterns of proteins remaining in dough following extensive washing with water. Dough prepared with WF (control): Lanes 1 and 2; dough prepared with WF–LPI G (5%) mixture: Lanes 3a and 4a; dough prepared with WF–LPI G (10%) mixture: Lanes 5a and 6a; dough prepared with WF–LPI A (5%) mixture: Lanes 3b and 4b; dough prepared with WF–LPI A (10%) mixture: Lanes 5b and 6b. Lanes 7a–8a and lanes 7b–8b represent LPI G and LPI A proteins, respectively.

no significant differences were observed in the water absorption parameter and DDT between the supplemented with LPI flour samples (Table 1). This suggests that the increase in the values of these parameters resulting from LPI addition should be attributed to the presence of the lupin proteins rather than to the reduction in the gluten content of the flour. In straight contrast, the presence of extra gluten to supplemented with LPI flours influenced to a significant extent both the dough stability and elasticity, with the values of these parameters approaching those of the control. This is an indication that the gluten network structure has a greater effect on these two parameters than the presence of the lupin proteins. 3.2. Effect of LPI incorporation on dough extension properties Extensograph measurements provide useful information about the viscoelastic behaviour of dough. Data on the effect of added lupin protein isolates on the extensograph characteristics of wheat flour dough samples, throughout a 135 min resting time period, are presented in Table 2. The initial resistance to deformation

(R50) appeared to decrease or remain unaffected at 5% LPI addition, the result depending on the resting time while it increased when the level of LPI addition was 10%. Upon resting, the control dough exhibited the lowest resistance after a 90 min resting time with a remarkable increase at the end of the relaxing period. In contrast, the resistance of dough samples containing LPI continuously increased with time, showing the highest resistance after 135 min. The parameter R50 predicts the dough handling properties and the fermentation tolerance. As a result, the increase in this parameter value promoted by LPI addition suggests a good handling behaviour and a large dough tolerance in the fermentation stage. The R50 values appear to approach those of the control, when additional gluten was added to compensate for the wheat gluten dilution resulting from LPI addition, only in the case of the LPI A, probably due to the different physicochemical characteristics between the two isolates. Likewise, the extensibility of dough (Ex), an indicator of the dough processing characteristics, was reduced by LPI addition, with its value dropping to almost half of that of the control extensibility with the presence of LPI A plus gluten addition at 45 and

Table 2 Effect of 5% and 10% lupin protein isolate addition (LPI G and LPI A) and gluten (Gl) on extensograph characteristics of wheat flour (WF).A Dough formulation

Dough resting time (30 °C) 45 min Resistance to extension R50 (BU)

WF WF + LPI G(5) WF + LPI G(10) WF + LPI G(10) and Gl WF + LPI A(5) WF + LPI A(10) WF + LPI A(10) and Gl A

97 ± 20b 53 ± 11a 144 ± 2c

90 min Extensibility Ex (mm)

Ratio R50/Ex

126 ± 5d 93 ± 19b,c

0.77 ± 0.13a,b 0.58 ± 0.12a

101 ± 5c

1.42 ± 0.06c

93 ± 23b

88 ± 6b,c

1.05 ± 0.20b

64 ± 24a

80 ± 10b

0.78 ± 0.21a,b

192 ± 18d 51 ± 6a

104 ± 3c 61 ± 5a

1.86 ± 0.22d 0.83 ± 0.05a,b

135 min Extensibility Ex (mm)

Ratio R50/Ex

Resistance to extension R50 (BU)

Extensibility Ex (mm)

Ratio R50/Ex

120 ± 6d 109 ± 6c,d

0.67 ± 0.13a 0.87 ± 0.08a,b

100 ± 8a 140 ± 5b

97 ± 10a,b 111 ± 2c

0.98 ± 0.18a 1.26 ± 0.02b

166 ± 2b

102 ± 10c

1.65 ± 0.19c

205 ± 3c

101 ± 10a,b,c

2.05 ± 0.19c

147 ± 30b

101 ± 2c

1.46 ± 0.30c

215 ± 21c

107 ± 1b,c

2.00 ± 0.19c

91 ± 19a

87 ± 9b

1.04 ± 0.12b

105 ± 19a

92 ± 4a

213 ± 25c

107 ± 2c

2.01 ± 0.28d

222 ± 20c

109 ± 4c

72 ± 7a

1.07 ± 0.10b

102 ± 3a

Resistance to extension R50 (BU) 81 ± 19a 95 ± 6a

76 ± 4a

91 ± 1a

Mean ± standard deviation of three replicates; values in the column followed by the same letter are not significantly different (p < 0.05).

1.13 ± 0.16a,b 2.03 ± 0.20c 1.12 ± 0.03a,b

1013

A. Paraskevopoulou et al. / Food Research International 43 (2010) 1009–1016 Table 3 Cross sectional area, baking loss, moisture and texture characteristics of bread loaves 2 h after baking.A

A

Bread sample

Bread cross sectional area (cm2)

Baking loss (% w/w)

Moisture (% w/w)

Hardness (g)

Springiness (–)

WF WF + LPI WF + LPI WF + LPI WF + LPI WF + LPI WF + LPI

57.41 ± 1.15d 54.19 ± 2.19c 50.37 ± 0.65a,b 54.43 ± 1.79c 51.24 ± 1.07b 47.81 ± 1.48a 51.68 ± 2.81b,c

15.1 ± 0.50b 14.6 ± 0.40a,b 15.1 ± 0.37b 14.4 ± 0.68a,b 13.2 ± 0.42a 13.8 ± 0.37a 15.2 ± 0.71b

42.8 ± 0.30a 43.4 ± 0.33b 43.6 ± 0.06b 43.7 ± 0.23b 43.6 ± 0.10b 43.6 ± 0.10b 42.8 ± 0.30a

811 ± 40a 1264 ± 20c 1106 ± 78b 1213 ± 75c 1241 ± 44c 1452 ± 36d 1057 ± 42b

0.879 ± 0.006 0.892 ± 0.005 0.878 ± 0.005 0.883 ± 0.010 0.893 ± 0.005 0.862 ± 0.008 0.861 ± 0.004

G(5) G(10) G(10) + Gl A(5) A(10) A(10) + Gl

b c, d b b, c d a a

Cohesiveness (–)

Gumminess (g)

Chewiness (g)

0.752 ± 0.005d 0.715 ± 0.004b 0.684 ± 0.004a 0.730 ± 0.009c 0.710 ± 0.010b 0.694 ± 0.014a 0.682 ± 0.002a

604 ± 24a 902 ± 18d 838 ± 51c 705 ± 52b 896 ± 29d 937 ± 49d 721 ± 31b

524 ± 24a 795 ± 13c 748 ± 45c 620 ± 61b 777 ± 37c 859 ± 21d 620 ± 23b

Mean ± standard deviation; values in the column followed by the same letter are not significantly different (p < 0.05).

90 min resting times. However, the extensibility value was remained practically the same at the highest resting time. In the case of the control dough a clear decrease of this parameter value was detected (from 126 mm at 45 min to 97 mm at 135 min). The value of the R50/Ex ratio increased as the level of LPI substitution increased and appeared to be more pronounced after 90 min of resting time indicating a less extensible dough. The addition of LPI A led to the highest R50/Ex ratio value (2.0 vs. 0.7 in the control), which reveals a greater reinforcing effect of this sample, probably due to strongest interaction between the albumins of this isolate and the flour proteins. 3.3. Influence of LPI incorporation on bread properties The effect of the lupin protein isolate incorporation on the fresh bread characteristics is summarized in Table 3. The volume, as expressed by the cross sectional area, of the control bread sample was significantly higher than that of samples incorporating lupin proteins (p < 0.05). This effect is probably related to the decreased elasticity of dough resulting from LPI addition (Table 1). LPI addition at a 10% level promoted the greatest volume reduction (13% and 17% for G and A, respectively). Dervas et al. (1999) and Doxastakis et al. (2002) also reported a decrease in bread vol-

ume with increasing levels of lupin or soy flour and attributed this decrease to the dilution of the wheat gluten by the legume protein. The decrease in bread volume is also consistent with the findings of El-Adawy (1997) who worked with sesame seed protein preparations and reported that sesame protein isolate incorporation provided loaves with a lower specific volume, the extent of reduction depending on the substitution level. Extra gluten addition to the blends to compensate for wheat gluten dilution, resulting from LPI addition, led to an improvement of bread volume (p < 0.05), but the bread volume still remained lower compared to that of the control (Table 3). It appears, therefore, that the decrease in bread volume resulting from LPI addition is most likely due to the combined effects of gluten dilution and mechanical disruption of the gluten network structure by the lupin particles. The high resistance to extension exhibited by these systems (Table 2) may restrict expansion during fermentation and baking, especially in the case of 10% (w/w) LPI A addition. According to van Vliet, Janssen, Bloksma, and Walstra (1992), there is an optimum value for the resistance to deformation; too high resistance can induce a limited and slow expansion of the air cells during proofing. It can also be hypothesised that the lupin proteins suppress the amount of steam generated, as a result of their high water absorption capacity, leading thus to reduced loaf volume

Fig. 2. Images of control (WF) and LPI-enriched bread crumbs.

1014

A. Paraskevopoulou et al. / Food Research International 43 (2010) 1009–1016

Table 4 Gas cell characteristics of control (WF) and LPI-enriched bread crumbs.A Total number of cells/9 cm2

Number of cells < 4 mm2

Total cell area (mm2)

Cell to total area ratio

No. cells/cm2

WF WF + LPI WF + LPI WF + LPI WF + LPI

1290d 564b 653a 647a 701c

773c 416a 533b 437a 525b

284.5c 240.7b 280.4c 168.1a 269.0b,c

0.32c 0.27b 0.31c 0.19a 0.30b,c

143.33c 62.67a 72.56b 71.90b 77.90b

G G + Gl A A + Gl

Mean values of triplicates; values in the column followed by the same letter are not significantly different (p < 0.05).

was described in the case of the dough rheology (Tables 1 and 2). The texture profile analysis also revealed that bread samples containing LPI exhibited lower cohesiveness (p < 0.05) compared with the control. An increase in gumminess and chewiness values with LPI addition was also observed (p < 0.05). As the calculation of both parameters take into account the hardness data, the values of these parameters followed a similar to hardness tendency. The incorporation of additional gluten to the 10% (w/w) LPI-containing formulations resulted in the reduction of the values of bread crumb gumminess, chewiness and hardness (only in the case of LPI A addition) and it enhanced those of crumb cohesiveness. As a result of these changes the values of the above parameters approached those of the control. During bread storage, physicochemical changes lead to crumb firming, flavour deterioration and, generally, loss of sensory

(a)

100 80

Stress (kN/m 2)

and greater crumb firmness. Skendi, Biliaderis, Papageorgiou, and Izydorczyk (2009) observed that inclusion of b-glucan in wheat flour was accompanied by a decrease in loaf specific volume, the extent of decrease depending on b-glucan level. In addition, examination of the loaf internal structure revealed that the crumb of the LPI-containing bread contained a greater number of small gas cells compared to the control (Fig. 2). Image analysis, performed on scanned bread slices, provided a more detailed view of the bread crumb characteristics. According to Table 4 data the total cell area as well as cell to total area ratio of LPI-enriched breads was lower compared to the control. Large cells in wheat bread are due to gluten elasticity that allows cell expansion by gas pressure during fermentation and oven spring. LPI proteins are not as elastic as gluten, so they did not form a network and did not allow cell expansion, so the crumb appears more compact. This probably adversely affected bread volume suggesting that incorporation of LPI into wheat flour resulted in a dough with more stable gas cells which did not coalesced readily during baking. Theoretically, the lower values of the total cell area imply lower bread volumes given that the quantity of dough used to produce bread loaves was the same in all products. Bread made with extra gluten addition to LPI-enriched wheat flour exhibited again an increased number of large cells when compared with the bread of the LPI-enriched flour probably due to an enhancement of the gas retention capacity of the gluten network. Concerning baking losses, as can be observed in Table 3 the water retention capacity was to some extent enhanced by the incorporation of LPI in wheat flour bread formulations. Additionally, LPI-enriched breads had a slightly higher moisture content than the control due to a higher water addition during breadmaking (higher farinographic absorption) and because lupin proteins retain more water than gluten. Although there is a change in baking loss, this seems not to impair moisture content. The bread sample supplemented with LPI A and containing additional gluten to compensate for wheat gluten dilution resulting from the lupin protein addition, was the exception to this trend, since its moisture content was found to be equal to that of the control (Table 3). The mechanical properties of LPI-enriched breads were evaluated by conducting compression tests on bread crumb samples and the resulting strain–stress curves are presented in Fig. 3. The control bread exhibited lower stress values than the LPI-enriched breads, indicating that LPI addition yielded a more resistant to deformation crumb (Fig. 3a). This behaviour is reasonable considering that the control sample was prepared with wheat flour only that resulted in a stronger and more organised gluten network, due to its higher content of the gluten proteins. When extra gluten was added in the mix to compensate for the wheat gluten dilution resulting from LPI addition the tendency remained the same (Fig. 3b). Data on the effect of LPI incorporation on the texture profile parameters of bread are exhibited in Table 3. LPI addition brought about a marked increase in crumb hardness probably as a result of the thickening of the crumb walls surrounding the air cells and the strengthening of the crumb structure by the protein particles, as

48 h

60 40

2h

20 0 0.0

0.2

0.4

0.6

0.8

Strain (-)

(b)

100 80

Stress (kN/m 2)

A

Bread sample

48 h

60 40 2h

20 0 0.0

0.2

0.4

0.6

0.8

Strain (-) Fig. 3. Stress–strain curves obtained by compression of control (WF) and LPIenriched bread crumbs (a) and LPI-enriched bread crumbs with extra gluten addition (b) after storage for 2 h (open symbols) and 48 h (filled symbols) at room temperature. Key: h j, control; s d, LPI A; 4 N, LPI G. The LP isolate supplementation level was 10% w/w.

A. Paraskevopoulou et al. / Food Research International 43 (2010) 1009–1016

Hardness increase (%)

160 140 120 100

WF LPI G 5% LPI G 10% LPI G 10% (Gl) LPI A 5% LPI A 10% LPI A 10% (Gl)

80 60 40

b

C

C

References

B B A

a a

to an improvement of bread quality characteristics. Additionally, the incorporation of LP isolates to WF delayed bread firming, while this was even more evident in the case of LPI A, when this was combined with supplementary gluten, indicating a kind of synergistic effect between the two additives.

C

B

b

b b

1015

a

20 0 24h

48h

Storage period Fig. 4. Increase (%) in hardness of control (WF) and LPI-enriched bread crumbs after storage at room temperature. Values are means of three replicates; mean values for the first 24 h of storage with a different small letter are significantly different (p < 0.05) and mean values for the 48 h of storage with a different letter are significantly different (p < 0.05).

quality. Even though starch retrogradation has been shown to be the primary cause of bread firming, other components, particularly proteins, may also affect the staling rate (Davidou, Le Meste, Debever, & Bekaert, 1996; Zobel & Kulp, 1996). The effect of ageing on crumb hardness of the control and LPI-containing breads was assessed following storage for 24 and 48 h and the results, expressed as % hardness increase, are shown in Fig. 4. The increase in hardness after 24 h of storage, in the case of both the control as well of the LPI G and of the LPI A-containing samples at a 5% (w/w) level, was not significantly affected compared to the fresh samples (p > 0.05). On the other hand, LPI A at high addition level had a favourable influence on crumb hardness (p < 0.05) (Fig. 4), which was even more evident after 2 days of storage, something that could be attributed to its higher water retention capacity (Table 3) and a possible inhibition of the amylopectin retrogradation (Biliaderis, Izydorczyk, & Rattan, 1995). According to Skendi et al. (2009), water migration that occurs among bread components is possible to lead to the formation of a stiffer network involving bglucans. In general, the addition of LPI A delayed bread firming, while the increase in hardness with ageing was even lower when this was combined with extra gluten addition, indicating a kind of synergistic effect between the two additives. This result was also confirmed by conducting compression tests to bread crumbs 2 days after their preparations. As can be seen in Fig. 3b, the addition of extra gluten to LPI A–WF mixture induced a marked decrease in the stress values of the respective breads in comparison to LPI G-enriched samples, which were even lower than the control ones. In conclusion, it appears that the addition of both LP isolates to wheat flour modified the rheological properties of the dough as well as the characteristics of the produced bread. An increase in the farinograph water absorption of the dough was observed only in the case of LPI G addition, presumably due to greater water requirement of its proteins in order to become hydrated, compared to the highly water-soluble albumins present in the LPI A. The LPI addition increased the dough development time and stability as well as the extensograph parameter values of the dough. This was attributed mainly to LP particle entrapment within the gluten network structure, as well as to possible association between the gluten and some of the lupin proteins present possibly in the outer surface of the hydrated particles. Baking tests showed that LPI addition significantly impaired the volume, internal structure and texture of the breads. Extra gluten addition to the blends to compensate for wheat gluten dilution, resulting from LPI addition, led

AACC (2000). Approved methods of the American Association of Cereal Chemists (10th ed.). St. Paul: American Association of Cereal Chemists, Inc.. Biliaderis, C. G., Izydorczyk, M. S., & Rattan, O. (1995). Effect of arabinoxylans on bread making quality of wheat flours. Food Chemistry, 53, 165–171. Bourne, M. (2002). Principals of objective texture measurement. In M. Bourne (Ed.), Food texture and viscosity (pp. 107–187). London: Academic Press. Davidou, S., Le Meste, M., Debever, E., & Bekaert, D. (1996). A contribution to the study of staling of white bread: Effect of water and hydrocolloid. Food Hydrocolloids, 10, 375–383. Dervas, G., Doxastakis, G., Hadjisavva-Zinoviadi, S., & Triantafillakos, N. (1999). Lupine flour addition to wheat flour dough and effect on rheological properties. Food Chemistry, 66, 67–73. Doxastakis, G., Zafiriadis, I., Irakli, M., & Tananaki, C. (2002). Lupin, soya and triticale addition to wheat flour doughs and their effect on rheological properties. Food Chemistry, 77, 219–227. Doxastakis, G., Papageorgiou, M., Mandalou, D., Irakli, M., Papalamprou, E., D’Agostina, A., et al. (2007). Technological properties and non-enzymatic browning of white lupin protein enriched spaghetti. Food Chemistry, 101, 57–64. Duranti, M., Consonni, A., Magni, C., Sessa, F., & Scafaroni, A. (2008). The major proteins of lupin seed: Characterisation and molecular properties for use as functional and nutraceutical ingredients. Trends in Food Science and Technology, 19, 624–633. Eggum, B. O., & Beame, R. M. (1983). The nutritive value of seed proteins. In W. Gottschalk & P. H. Muller (Eds.), Seed protein biochemistry, genetics and nutritive value (pp. 499–531). The Hague: Junk. El-Adawy, T. A. (1997). Effect of sesame seed protein supplementation on the nutritional, physical, chemical and sensory properties of wheat flour bread. Food Chemistry, 59, 7–14. El-Soukkary, E. A. H. (2001). Evaluation of pumpkin seed products for bread fortification. Plant Foods for Human Nutrition, 56, 365–384. Fernandez, M. L., & Berry, J. W. (1989). Rheological properties of flour and sensory characteristics of bread made from germinated chickpea. International Journal of Food Science and Technology, 24, 103–110. Gómez, M., Oliete, B., Rosell, C. M., Pando, V., & Fernández, E. (2008). Studies on cake quality made of wheat–chickpea flour blends. LWT – Food Science and Technology, 41, 1701–1709. Güemes-Vera, N., Arciniega-Ruiz Esperza, O., & Dávila-Ortiz, G. (2004). Structural analysis of the Lupinus Mutabilis seed, its flour, concentrate, and isolate as well as their behavior when mixed with wheat flour. LWT – Food Science and Technology, 37, 283–290. Laemmli, U. K. (1970). Cleavage of structural proteins during the assembly of the head of bacteriophageT4. Nature, 227, 680–685. Maforimbo, E., Skurray, G., Uthayakumaran, S., & Wringley, C. (2007). Incorporation of soy proteins into the wheat–gluten matrix during dough mixing. Journal of Cereal Science, 47, 380–385. Makri, E., Papalamprou, E., & Doxastakis, G. (2005). Study of functional properties of seed storage proteins from indigenous European legume crops (lupin, pea, broad bean) in admixture with polysaccharides. Food Hydrocolloids, 19, 583–594. Mavrakis, C., Doxastakis, G., & Kiosseoglou, V. (2003). Large deformation properties of gels and model comminuted meat products containing lupin protein. Journal of Food Science, 68, 1371–1376. Morad, M. M., El-Magoli, S. B., & Afifi, S. A. (1980). Macaroni supplemented with lupin and defatted soybean flour. Journal of Food Science, 45, 404–405. Paraskevopoulou, A., & Kiosseoglou, V. (1997). Texture profile analysis of heatformed gels and cakes prepared with low cholesterol egg yolk concentrates. Journal of Food Science, 62, 208–211. Pollard, N. J., Stoddard, F. L., Popineau, Y., Wrigley, C. W., & MacRitchie, F. (2002). Lupin flours as additives: Dough mixing, breadmaking, emulsifying, and foaming. Cereal Chemistry, 79, 662–669. Ribotta, P. D., Arnulphi, S. A., León, A. E., & Anón, M. C. (2005a). Effect of soybean addition on the rheological properties and breadmaking quality of wheat flour. Journal of the Science of Food and Agriculture, 85, 1889–1896. Ribotta, P. D., León, A. E., Pérez, G. T., & Anón, M. C. (2005b). Electrophoresis studies for determining wheat–soy protein interactions in dough and bread. European Food Research and Technology, 221, 48–53. Roccia, P., Ribotta, P. D., Pérez, G. T., & León, A. E. (2009). Influence of soy protein on rheological properties and water retention capacity of wheat gluten. LWT – Food Science and Technology, 42, 358–362. Sadowska, J., Blaszczak, W., Fornal, J., Vidal-Valverde, C., & Frias, J. (2003). Changes of wheat dough and bread quality and structure as a result of germinated pea flour addition. European Food Research and Technology, 216, 46–50. Skendi, A., Biliaderis, C. G., Papageorgiou, M., & Izydorczyk, M. S. (2009). Effects of two barley b-glucan isolates on wheat flour dough and bread properties. Food Chemistry. doi:10.1016/j.foodchem.2009.08.030.

1016

A. Paraskevopoulou et al. / Food Research International 43 (2010) 1009–1016

Sujak, A., Kotlarz, A., & Strobel, W. (2006). Compositional and nutritional evaluation of several lupin seeds. Food Chemistry, 98, 711–719. van Vliet, T., Janssen, A. M., Bloksma, A. H., & Walstra, P. (1992). Strain hardening of dough as a requirement for gas retention. Journal of Texture Studies, 23, 439–460.

van Vliet, T. (1999). Rheological classification of foods and instrumental techniques for their study. In A. Rosenthal (Ed.), Food texture, measurement and perception (pp. 65–96). Gathersburg: Aspen Publishers. Zobel, H. F., & Kulp, K. (1996). The staling mechanism. In R. E. Hebeda & H. F. Zobel (Eds.), Baked goods freshness (pp. 1–64). New York: Marcel Dekker, Inc.