Improving the quality of nutrient-rich Teff (Eragrostis tef) breads by combination of enzymes in straight dough and sourdough breadmaking

Journal of Cereal Science 55 (2012) 22e30

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Improving the quality of nutrient-rich Teff (Eragrostis tef) breads by combination of enzymes in straight dough and sourdough breadmaking Ieva Alaunyte, Valentina Stojceska*, Andrew Plunkett, Paul Ainsworth, Emma Derbyshire The Manchester Metropolitan University, Department of Food and Tourism Management, Hollings Faculty, Old Hall Lane, Manchester M14 6HR, UK

a r t i c l e i n f o

a b s t r a c t

Article history: Received 21 October 2010 Received in revised form 4 July 2011 Accepted 22 September 2011

The growing interest in the benefits of wholegrain products has resulted in the development of baked products incorporating less utilised and ancient grains such as, millet, quinoa, sorghum and teff. However, addition of wholegrains can have detrimental effects on textural and sensory bread product qualities. Enzymes can be utilised to improve breadmaking performance of wholegrain flours, which do not possess the same visco-elastic properties as refined wheat flour, in order to produce a healthy and consumer acceptable cereal product. The effects of Teff grain on dough and bread quality, selected nutritional properties and the impact of enzymes on physical, textural and sensory properties of straight dough and sourdough Teff breads were investigated. Teff breads were prepared with the replacement of white wheat flour with Teff flour at various levels (0%, 10%, 20%, and 30%) using straight dough and sourdough breadmaking. Different combinations of enzymes, including xylanase and amylase (X þ A), amylase and glucose oxidase (A þ GO), glucose oxidase and xylanase (GO þ X), lipase and amylase (L þ A) were used to improve the quality of the highest level Teff breads. A number of physical, textural and sensory properties of the finished products were studied. The nutritional value of breads was determined by measuring chemical composition for iron, total antioxidant capacity, protein, fibre and fat. The obtained results were used to estimates intakes of nutrients and to compare them with DRIs. The incorporation of Teff significantly (P < 0.05) improved dietary iron levels as 30% Teff breads contained more than double the amount of iron when compared to corresponding wheat bread (6 mg/ 100 g v 2 mg/100 g). Addition of Teff also significantly (P < 0.05) improved total antioxidant capacity from 1.4 mM TEAC/100 g to 2.4 mM TEAC/100 g. It was estimated that an average daily allowance of 200 g of Teff enriched bread would contribute to DRIs in the range of 42e81% for iron in females, 72 e138% for iron in males; 38e39% for protein in males, 46e48% for protein in females; and 47e50% of fibre in adults. The major challenge was encountered in producing the highest level of Teff bread with good textural and sensory attributes. Increasing the level of Teff significantly (P < 0.05) increased dough development time, degree of softening, crumb firmness and bitter flavour whilst decreasing the dough stability, specific loaf volume and overall acceptability of the bread. Teff breads produced with the addition of enzyme combinations showed significant improvements (P < 0.05) in terms of loaf volume, crumb firmness, crumb structure, flavour and overall acceptability in both straight dough and sourdough breadmaking. Ó 2011 Elsevier Ltd. All rights reserved.

Keywords: Teff (Eragrostis tef) Breadmaking technology Enzymes Sour dough

1. Introduction Consumer awareness of the health benefits of wholegrains has led to a growing demand for healthier cereal products.

* Corresponding author. Tel.: þ44 161 247 2488; fax: þ44 161 247 6992. E-mail address: [email protected] (V. Stojceska). 0733-5210/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jcs.2011.09.005

Incorporation of nutrient-rich wholegrains into bread is a promising way of producing a healthy alternative staple food product. Teff (Eragrostis tef) is a nutritious cereal grain indigenous to Ethiopia. It is considered a superior grain due to its nutritional merits (National Research Council, 1996). Teff is rich in carbohydrate, fibre (National Research Council, 1996; USDA, 2007), and contains more iron, calcium and zinc than other cereal grains, including wheat, barley and sorghum (Abebe et al., 2007;

I. Alaunyte et al. / Journal of Cereal Science 55 (2012) 22e30

Mengesha, 1966). Hence, nutritional profile of Teff indicates that it could be used in producing a healthy cereal product. The physico-chemical properties of Teff indicate that there is a great potential to be used in a broad range of food applications. Teff flour has high water absorption capacity, which relates to higher swelling degree of gel phase of Teff starches and possibly small and uniform size of Teff starch granules, hence, providing larger surface area and the higher water absorption (Bultosa, 2007; Bultosa et al., 2002). Teff starch has a slow retrogradation tendency (Bultosa, Hall et al., 2002), hence, it could have a potentially positive impact on shelf life of baked products. Teff is preferred for making Ethiopian flatbread injera in terms of flavour quality, texture and softness (Taylor et al., 2003; Zegeye, 1997). A number of authors improved total and soluble dietary fibre, protein, zinc, selenium and antioxidant content of wheat bread by supplementation of wholegrain flours, such as oat, barley, buckwheat and amaranth (Flander et al., 2007; Holtekjolen et al., 2008; Lin et al., 2009; Tosi et al., 2002). The incorporation of wholegrains into bread is a challenging task for cereal technologists. Most ancient grains do not contain gluten-forming proteins, which are essential for producing leavened bread with a fine open structure. A number of different enzymes and sourdough technology have been used to improve the breadmaking properties of flours. Researchers have utilised enzymes to improve dough and bread quality parameters, such as dough development time, loaf volume and crumb firmness in wheat breads with added rye bran (Laurikainen et al., 1998) wheat bran (Katina et al., 2006; Sanz Penella et al., 2008), and in rice bread (Gujral and Rosell, 2004). Sourdough technology combined with enzyme treatments can be also used for nutritional and product quality implications. Sourdough fermentation is known to have a positive nutritional effect in terms of increased mineral bioavailability and vitamin stability, reduced postprandial glucose and insulin and possible prebiotic effect (Poutanen et al., 2009). Combination of sourdough and selective enzymes was shown to have positive effects on bread loaf volume, shelf-life and crumb structure (Di Cagno et al., 2003; Katina, Salmenkallio-Marttila et al., 2006; Martinez-Anaya et al., 1998). Teff was incorporated into straight dough breadmaking by several authors (Ben-Fayed et al., 2008; Mohammed et al., 2009). In all cases, addition of Teff in higher quantities had a detrimental effect on quality of breads. Breads produced with Teff flour up to the level of 30% in Ben-Fayed et al. (2008) and up to 20% in Mohammed et al. (2009) studies had lower specific volumes and higher crumb firmness. Furthermore, Teff breads had significantly lower sensory scores, as only 10% and 5% Teff breads had comparable acceptability scores compared to wheat bread in Ben-Fayed et al. (2008) and Mohammed et al. (2009) studies, respectively. The first objective of this research was to study the effects of Teff incorporation into straight dough and sourdough breadmaking on textural and sensory properties. The second objective was to determine effects of enzyme treatment on straight dough and sourdough teff bread quality. This research also aimed to study selected nutritional properties of incorporation of Teff into bread products and to compare estimated intakes of nutrients to the dietary reference intakes (DRIs). To the author’s knowledge there is no published work on nutritional properties of Teff breads and the impact on enzymes on the quality of Teff breads. 2. Materials and methods The ingredients used for bread making were: white wheat flour (Smiths Flour Mills, Worksop, UK), white Teff flour (Soil & Crop Improvement, Romhof, Holland), compressed yeast (Fermipan,

23

Gist-Brocades, Holland), vegetable fat shortening (Cardowan Creamers Ltd, Glasgow, UK), sugar and salt (purchased from a local supermarket in Manchester) and improver (Diamond, British Arkady, Manchester, UK). Commercial sourdough culture LV1 containing 98% yeast (Saccharomyces chevalieri), 2% bacteria (Lactobacillus casei, Lactobacillus brevis) were supplied by Fermex International Ltd (Worcester, UK). Four commercial enzymes, xylanase (Pentopan Mono) containing 2500 fungal xylanase units/g, a-amylase (Fungamyl) containing 2500 fungal a-amylase units/g, glucose oxidase (Gluzyme) containing 10,000 glucose oxidase units/g and lipase (Lipopan F) containing 25000 lipase units/g were supplied by Novozymes, Denmark. Dosage of enzymes used for combined form was, according to supplier’s recommendations, 15 ppm for xylanase, 1.5 ppm for amylase, 5 ppm for glucose oxidase and 15 ppm for lipase. The combinations were xylanase and a-amylase (X þ A), aamylase and glucose oxidase (A þ GO), glucose oxidase and xylanase (GO þ X), lipase and a-amylase (L þ A). 2.1. Flour blend characteristic measurements Farinograph measurements on the flour mixes (white wheat flour replaced by 0%, 10%, 20% and 30% Teff flour) were carried out using a Brabender Farinograph (mixer bowl 300 g, Brabender OHG, Duisburg, Germany) using official ICC method 115-1 (ICC, 1992). Measurements obtained from the Farinograph were: flour water absorption (WA), dough development time (DDT), dough stability time (DST) and degree of softening (DS) determined on 600 Brabender units (BU) line. Analysis was carried out in triplicate and a mean value calculated. Pasting properties of flour blends (with corrected values for moisture content) were measured using a Rapid Visco Analyzer RVA-4 (Newport Scientific Pty. Ltd, Warriewood, NSW, Australia). Experiments were performed according to an official AACC method 76e21.01 (AACC, 2010) for peak viscosity, hot past viscosity and setback viscosity. 2.2. The straight dough breadmaking The ingredients were added based on a % flour weight. Four types of breads were made: white wheat bread (control) and white wheat bread with flour substitution levels of Teff at 0%, 10%, 20% and 30%. The breadmaking formulation was as follows: flour, water (from Brabender Farinograph value), 2% salt, 6% sugar, 4% shortening and 3% dry yeast. Mixing of the ingredients was carried out in a Hobart mixer (Process Plant and Machinery Ltd, UK) to temperature of 30  C at speed 2 for 10 min. The dough was divided into 340 g pieces, moulded by hand and placed into pre-greased 454 g tins. The dough was proved for 55 min at 40  C with 85% relative humidity in a Foster RBC MK3 prover (Norfolk, UK) and baked in the oven (Teknitronic reel oven, Teknigas Ltd, UK) for 20 min at 200  C. 2.3. The sourdough breadmaking Sourdough bread formulations for wheat, 10, 20 and 30% Teff breads were used following the supplier recommended method. Sourdough starter consisted of 100% flour mix, 0.5% culture and 100% water. Ingredients were mixed and kept covered at 28  C for 24 h. Final dough consisted of 100% flour mix, 40% starter, 50% water, 1.5% yeast and 2% salt. The dough was left to ferment for 1 h. The processing conditions for sourdough breads were 55 min proving

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I. Alaunyte et al. / Journal of Cereal Science 55 (2012) 22e30

at 40  C and 85% humidity, breads were baked at 200 20 min.

C

for

2.4. Evaluation of bread quality The volume of the bread samples was measured after 24 h, using the rapeseed displacement method. Analyses were carried out in triplicate and specific loaf volume was calculated as volume/weight (ml/g). Crumb firmness was measured using a TA-XT2i texture analyser (Stable Micro Systems, Surrey, UK) fitted with a 25 mm cylinder probe using the AACC bread compression test 74-09 (AACC, 1998) to assess shelf-life over a period of 8 days. Image analysis of bread slices was carried out using a C-Cell analyser (Calibre Control International Ltd, Appleton, UK). Slice area (mm2), brightness, number of cells, wall thickness (mm), cell diameter (mm), cell volume (mm3) and fineness (cells/mm2) were studied.

2.5. Sensory analysis Sensory analysis was conducted on white wheat, 10%, 20%, 30% Teff breads and 30% enzyme supplemented Teff breads. Fifty panellists were asked to assess the bread for physical appearance, texture, mouthfeel, flavour, aftertaste and overall acceptability. The panellists marked a 10 cm line in accordance to their preference.

2.6. Nutritional analysis of breads 2.6.1. Iron Iron content of breads was determined using the 2,2 Dipyridyl method (AOAC, 1990). 2.6.2. Total antioxidant capacity The total antioxidant capacity of flours and breads was carried out using a Shimadzu UV-160A spectrophotometer according to the ABTSþ method (Re et al., 1999). Results were expressed in terms of Trolox equivalent antioxidant capacity (TEAC, mM Trolox equivalent per 100 g of sample). 2.6.3. Crude protein The protein content of Teff flour and all breads was estimated from the crude nitrogen content of the sample determined by the Kjeldahl method (N  6.25) (AOAC, 1984). 2.6.4. Fat Total fat content of Teff flour and all breads was determined by the Caviezel method (Gertz and Fiebig, 2000). 2.6.5. Total dietary fibre The total dietary fibre content of Teff flour and all breads was determined using Total Dietary Fibre Assay Kits TDF-100A and TDFC10 (SigmaeAldrich Inc, St Louis, MO, USA) using a combination of enzymatic and gravimetric methods (AOAC, 1997).

Fig. 1. Changes in bread crumb firmness during storage for 8 days in straight dough bread.

3. Results 3.1. The addition of Teff into straight dough breadmaking Teff was incorporated into straight dough breadmaking at the levels of 0, 10, 20 and 30%. The breads are shown in Fig. 1a. The quality evaluation of breads (Tables 1 and 2) showed that incorporation of Teff into breadmaking affected dough characteristics, final loaf volume, crumb firmness, crumb structure and taste attributes. 3.1.1. The effect of Teff on dough rheological parameters Rheological properties obtained by Farinograph and RVA of Teff blends are presented in Table 1. Water absorption (WA) of flours blended with Teff significantly increased (P < 0.05), which indicates higher water absorption capacity of Teff flour. Ben-Fayed et al. (2008) and Mohammed et al. (2009) found a similar trend for Teff supplemented doughs. This may be related to the small size of Teff starch granule, hence, larger surface area for the water to be absorbed. In addition, water absorption index of Teff starches was reported to be higher than maize (Bultosa, Hall et al., 2002), which confirms findings from this study. Higher WA probably affected dough development time (DDT), which significantly (P < 0.05) increased in Teff supplemented doughs. Similar findings were also obtained with amaranth flour supplemented wheat dough (Tosi, Re et al., 2002), which suggests that increased WA due to small size of amaranth and Teff grains might prolong DDT. Dough stability (DST) significantly (P < 0.05) decreased when Teff addition was at the highest levels (20 and 30%). Degree of dough softening (DS) has also significantly decreased (P < 0.05). As DST and DS values give an indication of dough tolerance and the rate of breakdown, this suggests that dough containing higher levels of Teff flour has less stability during the mixing phase and is more prone to early and rapid breakdown. Decrease in DST and DS values could be explained by the dilution of gluten-forming

Table 1 Some of the rheological properties of Teff supplemented doughs. Teff in dough (%)

2.7. Statistical analysis Differences in mean values of investigated factors were tested by Independent t-test and analysis of variance (ANOVA), significance levels were obtained with Tukey’s multiple range test using SPSS 16.0 (SPSS Inc., Chicago, Illinois, US). A significance level of P < 0.05 was used.

Farinograph Water absorption (%) parameters Dough stability (min) Dough development (min) Degree of softening (BU) Rapid visco Peak Viscosity (RVU) analyser Hot Paste Viscosity (RVU) parameters Setback Viscosity (RVU) aed

0%

10%

20%

30%

61.3 a 8.0 a 2.5 a 61.7 a 48.97 a 29.21 a 31.17 a

62.2 b 7.5 a,b 5.4 b 108.3 b 49.58 a 29.82 s 35.34 a

62.8 c 6.6 b 4.5 b 143.3 c 50.97 b 30.89 a 41.32 b

64.1 d 5.2 c 5.2 b 175.0 d 59.04 35.38 b 51.06 c

Different superscripts in the same row indicate that means were significantly different (P < 0.05).

I. Alaunyte et al. / Journal of Cereal Science 55 (2012) 22e30

25

Table 2 Physical, textural and sensory characteristics of straight dough Teff enriched wheat breads before and after enzyme treatments. Teff (%)/Enzyme combinations

Physical parameters

Sensory attributes

aed

Specific volume (ml/g) Slice area (mm2) Crumb brightness Number of cells Wall thickness, average (mm) Cell diameter, average (mm) Cell volume, average (mm3) Fineness (no cells/mm2) Crumb lightness Crumb softness Crumb elasticity Clearing mouthfeel Sweet flavour Bitter flavour Aftertaste Overall acceptability

Before enzyme combinations treatments

After enzyme combinations treatments

0%

10%

20%

30%

30% X þ A

30% A þ GO

30% GO þ X

30% L þ A

3.54 a 9123 a 148 a 5292 a 0.454 a 1.864 a 5.70 a 0.580 a 7.27 a 7.45 a 5.95 a 6.75 a 4.54 a 2.66 a 2.85 a 6.21 a

3.46 a,b 8997 a 126 b 4881 a,b 0.473 a,b 1.979 a,b 6.64 a,b 0.542 a 5.35 b 6.91 a,b 5.13 a,b 5.39 b 4.14 a 3.62 a 3.63 a 5.70 a

3.22 b 8468 a 115 c 4466 b 0.482 b 2.107 a,b 7.75 b,c 0.527 a 3.71 c 5.48 c,d 4.32 b 4.38 b,c 4.02 a 5.18 b,c 5.98 b 3.24 b

3.73 c 6753 b 103 d 3739 c 0.502 c 2.251 b 8.38 c 0.554 a 3.21 c 4.90 d 4.89 b 3.31 c 3.81 a 5.91 c 6.73 b 2.65 b

3.56 a 7418 b 116 c 4339 b 0.467 a 1.889 a 6.42 a 0.586 a 3.98 c 5.71 b,c 4.71 a,b 4.82 b 3.85 a 4.02 a 4.32 a 5.07 a

3.56 a 7608 b 117 c 4184 b 0.478 a 2.055 a,b 7.12 b 0.551 a 5.76 b 6.99 a,b 5.63 a,b 5.10 b 4.29 a 3.72 a,b 3.86 a 5.74 a

3.53 a 7476 b 118 c 4379 b 0.465 a 1.891 a 6.44 a 0.587 a 5.13 b 6.16 b,c 5.32 a,b 4.83 b 4.15 a 3.77 a,b 4.08 a 5.49 a

3.30 a,b 7283 b 115 c 3982 c 0.486 b 2.102 a,b 7.41 b,c 0.548 a 4.25 c 5.81 b,c 4.45 b 5.10 b 4.00 a 4.09 a 4.42 a 5.37 a

Different superscripts in the same row indicate that means were significantly different (P < 0.05).

proteins in the dough system by the addition of gluten-free Teff flour at the levels of 10e30% based on flour weight. Similar results were obtained by Salehifar and Shahedi (2007) where oat flour, which lacks gluten as well, was incorporated into white wheat bread, which increased degree of softening and decreased dough stability. Pasting profiles showed that there is a gradual increase in peak, hot paste and setback viscosities as the levels of Teff flour increased. Higher peak viscosity of Teff blends compared to wheat flour indicates higher water-binding capacity of the flour mixture (Newport Scientific, 2001), which also reflects higher water absorption readings from Farinograph values. The increase in hot paste viscosity of Teff flour blends show higher shear stress tolerance. However, high values of setback viscosity of Teff supplemented flour blend starches may indicate negative effects of starch retrogradation during product shelf-life period compared to bread made only from wheat flour. 3.1.2. The effect of Teff on bread quality Physical characteristics data, as presented in Table 2, showed that replacing wheat flour with Teff up to the level of 10% in straight dough breadmaking did not affect loaf volume, whereas incorporation of 20e30% had a detrimental effect. Addition of 20 and 30% Teff flour into the breadmaking formulation resulted in a significant decrease in loaf volume. Overall, the increase in the level of Teff flour in the breadmaking formulation was negatively associated with specific volume (r ¼ 0.83; P < 0.001). A similar trend was observed in other studies (Ben-Fayed et al., 2008; Mohammed, Mustafa et al., 2009). Both studies found a gradual decrease in loaf volume as the level of Teff flour was increased. Analysis of crumb structure (Table 2) revealed changes in cellular parameters. Slice area decreased in straight dough breads supplemented with Teff (r ¼ 0.84; P < 0.001). However, the significant decrease was only observed in the highest level of Teff bread. It could be suggested that lower specific volumes of Teff breads have contributed to lower slice area. Other cellular parameters, including cell wall thickness and cell volume significantly increased in 20 and 30% Teff breads, whilst the number of cells notably decreased. This resulted in a more open and coarse crumb structure with less cells, which have thicker walls and are larger in size. Slice brightness significantly decreased with increased levels of Teff flour (r ¼ 0.98; P < 0.001). As Teff flour is wholegrain flour, this would be expected, as bran particles would cause a darker crumb colour. Ben-Fayed et al. (2008) found breads containing

10e30% Teff flour to have significantly lower values for brightness, but higher values for yellowness and redness factors compared to corresponding wheat control bread. Sensory evaluation of studied breads, as shown in Table 2, revealed that increasing the level of Teff, the crumb lightness, softness and elasticity significantly (P < 0.05) decreased, whilst bitter flavour and aftertaste significantly increased (P < 0.05) for breads with 20 and 30% Teff flour when compared to the control bread. The overall acceptability was also significantly (P < 0.05) lower for 20 and 30% Teff breads, which had a strongest correlation with bitter flavour and aftertaste (r ¼ 0.62, P < 0.01). Similar findings were reported by Ben-Fayed et al. (2008) and Mohammed et al. (2009), as only levels of Teff up to 10 and 5%, respectively, were judged as acceptable. 3.1.3. Effects of Teff on shelf-life Initial crumb firmness (Fig. 1) was significantly higher in Teff breads and the increase was gradual with higher Teff supplementation. Loaf volume is considered to be a major determining factor of crumb firmness (Axford et al., 1968). In the present study, all Teff bread had lower volumes, and therefore, it could be suggested that increased crumb firmness is a direct effect of this. During the 8-day shelf-life period, all Teff breads had higher crumb firmness compared to white wheat bread, as level of Teff positively correlated with increased crumb firmness (r ¼ 0.96; P < 0.001). 3.2. The addition of Teff into sourdough breadmaking Teff flour replaced wheat flour at different levels in sourdough breads, which are shown in Fig. 1c. Addition of 0e30% Teff flour into the sourdough breadmaking formulation showed a gradual significant (P < 0.05) decrease in bread specific loaf volume (Table 2). This was expected as a similar trend was observed in straight dough Teff enriched breads. Similarly to straight dough breads, incorporation of Teff affected bread crumb parameters, as presented in Table 2. Slice area, crumb brightness and number of cells were significantly (P < 0.05) decreased as the level of Teff incorporation increased up to 20 and 30%. Similarly to straight dough bread, 10% sourdough Teff bread did not show significant changes in cellular parameters compared to wheat sourdough. Interestingly, other parameters, such as wall thickness, cell diameter and cell volumes were not affected by the addition of Teff in sourdough breads, which was opposite to the results obtained from straight dough breadmaking. This suggests

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I. Alaunyte et al. / Journal of Cereal Science 55 (2012) 22e30

Table 3 Physical and textural characteristics of sourdough Teff enriched wheat breads before and after enzyme treatments. Teff (%)/Enzyme combinations

Before enzyme combinations treatments

Specific volume (ml/g) Slice area (mm2) Crumb brightness Number of cells Wall thickness, average (mm) Cell diameter, average (mm) Cell volume, average (mm3) Fineness (no cells/mm2) aed

After enzyme combinations treatments

0%

10%

20%

30%

30% X þ A

30% A þ GO

30% GO þ X

30% L þ A

3.32 a 6845 a 131 a 4106 a 0.450 a 1.60 a 4.80 a 0.642 a

2.75 b 6059 a,b 116 b 4153 a 0.447 a 1.54 a 4.92 a 0.686 a

2.23 c,d 4947 d 100 c 3474 b 0.449 a 1.53 a 5.15 a 0.702 a

2.00 d 4229 e 89 d 3171 b,c 0.441 a 1.44 a 4.95 a 0.750 b

2.67 b 5743 b,c 101 c 3421 b 0.479 b 1.827 b 6.58 b 0.596 b

2.61 b 5668 b,c 101 c 3425 b 0.481 b 1.794 b 6.34 b 0.604 b

2.55 b 5655 c 102 c 3531 b 0.474 b 1.724 b 6.09 b 0.624 b

2.46 b,c 5393 c 105 c 3747 a,b 0.451 a 1.557 a 5.11 a 0.695 a

Different superscripts in the same row indicate that means were significantly different (P < 0.05).

that although volume of Teff breads was significantly reduced, sourdough breadmaking technology had a favourable effect on some crumb parameters, which might be due to the effects of acidification. Acidic conditions causes gluten to swell, which is known to increase softness and elasticity of the dough (Schober et al., 2003), hence, may have a possible favourable effect on crumb structure and uniformity as seen in the present study. 3.3. Nutritional evaluation of breads Teff flour was incorporated into breadmaking formula at the levels of 0%, 10%, 20% and 30%. Table 4 presents some of the nutritional properties of these breads. As a result of iron-rich Teff cereal incorporation, Teff breads contained significantly more iron compared to corresponding wheat bread. In fact, 30% Teff bread contained more than twice the amount of iron. This is in agreement with the majority of other researchers where Teff grain was compared with other cereal grains (Abebe, Bogale et al., 2007; Areda et al., 1993; Mengesha, 1966). Another nutritional property that has been significantly affected by the addition of Teff was total antioxidant capacity. Breads, containing 10%, 20% and 30% Teff flour, has significantly higher total antioxidant capacity compared with control wheat bread. Although, the research on the total antioxidant levels in Teff is very sparse, some researchers reported the content of phenolic compounds in Teff to be comparable to other wholegrain millets (McDonough and Rooney, 1985). Other researchers also improved antioxidant levels in bread when refined wheat flour was substituted with wholegrain barley flour (Holtekjolen et al., 2008) and unhusked buckwheat flour (Lin et al., 2009). In general, wheat and Teff breads did not differ significantly in their content of crude protein, fat and total dietary fibre. In the present study, the content of crude protein was similar in wheat and Teff breads; however, this value does not reflect the quality of protein in Teff enriched breads. Fat and dietary fibre content was similar in all breads. Wheat has similar levels of fat as Teff (Bultosa, 2007; National Research Council, 1996; USDA, 2007), therefore, this corresponds to similar values of fat in breads. This study results showed similar levels of total dietary fibre in all breads, although Teff flour contained a significantly higher level of

total dietary fibre. However, Teff is not as rich in fibre as some of the other wholegrain cereals; therefore, incorporation at the level of 10%e30% did not make a significant difference. Table 5 shows the contribution to Dietary Reference Intakes (DRIs), set by the Food and Nutrition Board of the National Research Council (Department of Health, 1991), of selected nutrients for wheat and Teff breads. The most noticeable difference in contribution between wheat and Teff breads was the dietary iron, which would be notably higher if Teff breads were incorporated as a part of habitual diet. 3.4. The effects of enzymes on Teff bread quality All enzyme combinations significantly (P < 0.05) improved specific volume, crumb firmness (Fig. 3) and sensory scores (Table 2) and some of the parameters were comparable to those of white wheat bread. Fig. 2 shows the images of straight dough and sourdough breads before and after addition of enzymes. The effect of xylanase and amylase (X þ A) was observed in straight dough and sourdough breads in terms of significantly (P < 0.05)increased specific volume, which influenced lower crumb firmness and better crumb structure compared to control 30% Teff bread. The positive effect on loaf volume and crumb firmness of X þ A supplementation was also reported by other researchers (Martinez-Anaya and Jimenez, 1997). Due to the possible synergistic effect of A þ GO on increased gas production by increasing the levels of fermentable sugars in the dough and stronger dough structure (Goesaert et al., 2006), favourable effects on increased loaf volume and decreased density were observed in Teff bread. A þ GO combination showed significant improvements in all bread quality parameters, which were comparable to white wheat bread (3.54 ml/g v 3.56 ml/g specific volume; 0.28 g/ml v 0.28 g/ml density; 3.60 N v 4.13 N crumb firmness; 6.21 v 5.74 overall acceptability for white wheat and A þ GO supplemented 30% teff bread, respectively). In this study, the best improvement in crumb cellular structure was also observed in A þ GO supplemented Teff bread. The crumb had a finer structure with a larger number of cells, which were small and had thin walls. Similar findings, in terms of improved dough handling

Table 4 Nutritional composition of breads. Iron content (mg/100 g) Wheat bread 10% Teff bread 20% Teffbread 30% Teffbread aec

2.39 3.13 4.08 5.62

   

0.27 0.50 0.80 1.22

a b c d

Total antioxidant capacity (mM TEAC/100 g) 1.39 2.03 2.14 2.41

   

0.07 0.08 0.07 0.04

a b b c

Crude protein content (g/100 g) 10.5 10.6 10.9 11.0

   

Different superscripts in the same row indicate that means were significantly different (P < 0.05).

0.25 0.35 0.07 0.02

a a a a

Fat content (g/100 g) 4.1 4.0 3.8 3.7

   

0.33 0.03 0.09 0.16

a a a a

Dietary fibre content (g/100 g) 4.1 4.2 4.3 4.5

   

0.35 0.41 0.44 0.32

a a a a

I. Alaunyte et al. / Journal of Cereal Science 55 (2012) 22e30 Table 5 Contribution of nutrients to the relevant DRIs consuming an average daily portion (5 slices, approx 200 g) of wheat and Teff breads. Nutrient

Protein Dietary fibre Iron

Gender

Male Female Adults Male Female

DRIs*

56 g/day 46 g/day 18 g/d 8.7 mg/d 14.8 mg/d

Contributions to DRIs (%) Wheat bread

10% Teff bread

20% Teff bread

30% Teff bread

38% 46% 46% 56% 33%

38% 46% 47% 72% 42%

39% 47% 48% 94% 55%

39% 48% 50% 129% 76%

properties, ovenspring, volume and texture were reported by other researchers in white pan bread with amylase and glucose oxidase supplementation (Haarasilta et al., 1991). Teff bread with A þ GO addition significantly reduced bitter flavour and aftertaste and was scored significantly more acceptable in the taste panel compared to unsuplemented 30% Teff bread. Teff bread supplemented with glucose oxidase and xylanase (GO þ X) combination showed a significant improvement in 30% Teff bread quality. Several researchers suggested a positive synergistic effect of glucose oxidase and xylanase (Laurikainen, Harkonen et al., 1998; Primo-Martin et al., 2005). The favourable effect was shown to be due to ability of both enzymes to diminish negative effects of each other. GO can limit water holding capacity of dough by gelation of water soluble arabinoxylans, which can make dough dry and stiff. Xylanase interferes with this by formation of smaller arabinoxylan fragments (Primo-Martin, Wang et al., 2005). In this study GO þ X Teff bread had significantly higher specific volume, reduced crumb firmness and a better crumb structure when compared to 30% unsupplemented Teff bread. Sensory evaluation showed significantly higher values for crumb softness, elasticity, sweetness and overall acceptability compared to control 30% Teff bread. Improvements in loaf volume, initial crumb firmness and sensory scores were observed in lipase and amylase (L þ A) combination Teff bread. Although the bread quality parameters were significantly better in L þ A Teff bread when compared to unsupplemented Teff bread, L þ A combination showed improvements to a lesser extent out of all enzyme combinations. Overall, doughs supplemented with different combinations of enzymes produced acceptable Teff breads, in terms of physical and sensory properties. Combinations of A þ GO and GO þ X, followed by X þ A and L þ A, showed the most noticeable changes in quality and sensory parameters.

27

4. Discussion Incorporation of Teff flour into breadmaking technology affected dough properties, bread physical characteristics and sensory attributes. Similar effects on bread quality was also reported by other authors, who used Teff and other wholegrain gluten-free cereal supplementation in breadmaking (Ben-Fayed et al., 2008; Mlakar et al., 2008a, 2008b; Mohammed, Mustafa et al., 2009; Oomah, 1983; Salehifar and Shahedi, 2007). Farinograph values, such as DDT, DST and DS, of Teff flour dough showed a decrease in dough quality parameters (Table 1). This trend was also reported by other researchers (Ben-Fayed et al., 2008; Mohammed, Mustafa et al., 2009). However, WA of Teff doughs increased, which is a positive effect in terms of higher yield of the final product. This was also supported by pasting profile analysis as 30% Teff flour blend has significantly higher peak viscosity. Increased WA values of Teff supplemented doughs were also found by other authors (Ben-Fayed et al., 2008; Mohammed, Mustafa et al., 2009). WA was also shown to be increased in wheat doughs supplemented with oat bran and amaranth flour (Krishnan et al., 1987; Mlakar, Turinek et al., 2008a). Higher bran proportion in wholegrain flours seems to be responsible for increased WA capacity of supplemented doughs, which explains the findings from this study. In this study, significantly lower specific loaf volumes and poorer crumb structure were also observed in straight dough and sourdough breads with higher substitution levels of Teff flour (Tables 2 and 3). This decrease in quality parameters might be attributed to dilution of functional gluten levels in dough, which was suggested in other studies where gluten-free crops were used for breadmaking (Krishnan et al., 1987; Mlakar, Turinek et al., 2008b; Salehifar and Shahedi, 2007; Tosi, Re et al., 2002). Additionally, lower bread quality of Teff breads could be explained by the disruption of the gluten matrix in the dough by the presence of bran particles in Teff flour. Lower loaf volume and poorer crumb grain were reported in oat supplemented breads due to large amounts of fine bran particles in dough (Zhang and Moore, 1999). Crumb firmness during the 8-day shelf-life period of Teff breads was significantly higher compared to control wheat bread (Fig. 1). However, it should be noted that after four days of shelf-life, crumb firmness of 10 and 20% Teff breads was not significantly higher than that of wheat bread. This indicates a possible positive effect on the rate of crumb firming. Indeed, research indicates that Teff starches have lower retrogradation tendency than maize or wheat starches (Bultosa and Taylor, 2004), and hence, have a possible favourable

Fig. 2. Images of breads prepared with wheat flour and different levels of Teff, and 30% Teff breads with enzyme addition using straight dough and sourdough technology. *Key: aStraight dough control wheat and Teff breads without enzymes; b- straight dough 30% Teff breads with different enzyme combinations; c- sourdough wheat and Teff breads without enzymes; d- sourdough 30% Teff breads with enzyme combinations.

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Fig. 3. Changes in crumb firmness of 30% Teff breads with and without enzymes during 8-day shelf-life storage.

effect on bread crumb firming rate. The results from this study indicate that addition of lower levels of Teff flour (10e20%) may have positive effects on slower crumb firming rate. At the highest level of Teff addition of 30% flour weight, crumb firmness during shelf-life however is negatively affected. This is also in agreement with pasting profile values as 30% Teff flour blend has significantly higher setback viscosity compared to white wheat flour. In the present study bitter flavour and aftertaste were the main contributors to the lower acceptability rating. Teff flour is wholegrain flour; therefore, higher levels of minerals and bran particles may contribute to the bitter taste and aftertaste. Phenolic compounds, found in cereal bran, are considered to be one of the main contributing factors to bitterness. High quantities of these compounds were shown to have a great impact on the perceived flavour bitterness and aftertaste in rye grain (Heinio et al., 2008). Furthermore, Heinio et al. (2008) concluded that, in particular, vanillic and veratric acids were related to cereal and intense aftertaste, whilst pinoresinol and syringic acid were associated with bitterness. Teff cereal contains one of the highest levels of vanillic and syringic acids compared to other millet grains (McDonough and Rooney, 1985), which suggests that bitter flavour and aftertaste in Teff breads observed in the present study was probably due to the high levels of these phenolic compounds. This is also in agreement with other researchers who suggested that bitter flavour of bread is caused by the higher levels of minerals and bran particles (Holtekjolen, Baevre et al., 2008; Mohammed, Mustafa et al., 2009; Salehifar and Shahedi, 2007). Teff breads in the present study contained high levels of dietary iron and antioxidants, which suggests that it might be one of the contributing causes to bitterness in flavour and aftertaste. In terms of Dietary Reference Intakes (DRIs) (Table 5), Teff breads would contribute to notably higher intakes of dietary iron and similar intakes of protein and fibre if 200 g of bread would be consumed daily. Higher dietary iron intake would be beneficial even more for iron deficiency susceptible population groups, such as children, female adolescents and childbearing age women, elderly and female athletes. Research indicates, that in the UK, an average female consumes 8.8 mg of iron a day (Henderson et al., 2004), which is significantly lower than recommended nutrient intake (RNI) of 14.8 mg/day (Department of Health, 1991). In fact, 200 g daily intake of 30% Teff bread would contribute over 75% of recommended female intake, which makes Teff bread a rich source of iron. Teff bread would also provide an adequate intake of protein and fibre. A number of researchers utilised single and combine enzyme treatments for improving quality of breads (Katina, SalmenkallioMarttila et al., 2006; Laurikainen, Harkonen et al., 1998). Research suggests that combined use of enzymes may have more notable effects on breadmaking properties, mainly due to the fact that

enzymes acting on different flour components can be utilised at once and some enzymes can diminish negative effects of one another (Caballero et al., 2007a, 2007b). This study results showed improvements in bread quality and sensory attributes by all enzyme combinations. In straight dough, Teff breads A þ GO and GO þ X were the most successful, closely followed by X þ A and L þ A, while in the sourdough breads, X þ A and A þ GO showed slightly more improvements. Xylanase sobulises non-starch polysaccharides (NSP) arabonixylans. Therefore, the strongest impact has been seen in whole wheat or bran supplemented doughs, which have higher levels of arabinoxylans (Katina, Salmenkallio-Marttila et al., 2006; Shah et al., 2006). Teff flour contains 1.9% arabinoxylans (Dal Bello and Arendt, 2008). This is comparable to wheat flour, which contains 1.5e2.5% (Courtin and Delcour, 2002). The positive effect on volume by amylase addition can be explained by the production of fermentable sugars in the dough and thereby higher rate of CO2 evolution by yeast (Kim et al., 2006). Therefore, the favourable effect of a combination of X þ A can be associated with increased dough resilience and increased extensibility due to reduced viscosity of dough by xylanase (Collar et al., 2000) and better gas production by the amylase (Goesaert, Gebruers et al., 2006). In this study, X þ A showed the greatest improvements in sourdough Teff bread whilst a lesser extent of improvement was obtained in straight dough bread. This might be explained by the fact that during sourdough fermentation, fibre components are broken down to the smaller particles (Corsetti and Settanni, 2007), therefore, the amount of substrate for the xylanase is greater and the effect of the enzyme is stronger. The positive effect of amylase and glucose oxidase (A þ GO) combination, which showed one of the greatest improvements for both straight dough and sourdough Teff breads in the present study, can be explained by each enzyme’s ability to act on separate functional flour components. Amylase breaks down starch into dextrins, which increases levels of fermentable sugars in the dough (Goesaert, Gebruers et al., 2006), and hence, increases bread volume. However, increased levels of gas cannot be retained unless dough gluten matrix is strong enough. Addition of glucose oxidase has a strengthening effect on dough by formation of additional bonds in the gluten network (Bonet et al., 2006). The favourable effect on flavour, aroma and taste of A þ GO Teff bread might have been influenced by increased formation of dextrins and maltose by amylase, which has an effect in the Maillard reaction. In fact, A þ GO bread had significantly higher scores for sweetness than control bread, which again can be attributed to higher levels of dextrins in the final product. This may also explain the effect of reduced bitter flavour and aftertaste in A þ GO supplemented Teff bread as increased sweetness may have masked bitter flavour and aftertaste. The synergistic effect of A þ L was suggested to be due to formation of more thermostable amyloseelipid complex (Leon et al., 2002). Also, lipase exerts a stronger positive effect in dough with added fat (Poulsen et al., 1998), which was used as an ingredient in this study for straight dough Teff bread production but not in sourdough breads. The secondary reactions of lipase is its effect on lipoxygenase, which has been shown to produce a whiter crumb colour (Castello et al., 1999), the effect that was observed in the present study. However, L þ A combination has improved bread quality to a lesser extent compared to other enzyme combinations. This is especially the case in sourdough Teff breads. The most plausible explanation would be that the sourdough recipe did not contain any added fat; hence, the effect of lipase in this combination was not was strong. Furthermore, Teff is a gluten-free cereal; therefore, supplementation with gluten network strengthening enzyme, such as glucose oxidase, had a greater effect on bread quality parameters.

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5. Conclusions Incorporation of Teff flour into breadmaking formulation at the level of 30% flour basis had a detrimental effect on loaf volume, crumb firmness, crumb structure and taste attributes. Bread containing 30% Teff had significantly lower specific volume, higher crumb firmness, less uniform and coarser crumb structure and lower overall acceptability due to bitter flavour and aftertaste. A similar trend was observed in sourdough Teff beads. The decrease in bread quality properties is probably due toweakening of the dough by the dilution of functional gluten proteins. Addition of enzyme combinations X þ A, A þ GO, GO þ X and L þ A to the straight dough and sourdough breadmaking resulted in significant improvements in loaf volume, crumb firmness, crumb structure and taste attributes. From the present study findings it can be concluded that a combination of enzymes could be used to improve quality of Teff enriched breads. Significant improvements were observed in terms of loaf volume and crumb firmness during shelf-life. Incorporation of Teff flour into the breadmaking formulation showed significant improvements in iron content and total antioxidant capacity, as well as adequate levels of protein, fat and fibre. These breads may contribute to the higher dietary intake of iron, which would be especially beneficial for more iron deficiency susceptible population groups, such as children, childbearing age women, pregnant and lactating women. According to the present study’s data, an average portion of 200 g of Teff bread a day could contribute to over 75% of DRIs for iron intakes in the female population. Teff breads would also contribute to higher levels of antioxidants, which have been shown to be beneficial in prevention of the formation of chronic diseases. Acknowledgements The authors wish to express their gratitude to Dr Frank Rittig from Novozymes, Switzerland for the technical advice and supplying enzymes and to Fermex International Ltd for kindly providing us with the sourdough starter cultures. References AACC, 1998. Method 74-09 American Association of Cereal Chemists (St Paul, Minnesota). AACC, 2010. Method 76-21.01 American Association of Cereal Chemists (St Paul, Minnesota). Abebe, Y., Bogale, A., Hambidge, K.M., Stoecker, B.J., Bailey, K., Gibson, R.S., 2007. Phytate, zinc, iron and calcium content of selected raw and prepared foods consumed in rural Sidama, Southern Ethiopia, and implications for bioavailability. Journal of Food Composition and Analysis 20, 161e168. AOAC, 1984. In: Williams, S. (Ed.), Official Methods of Analysis. Association of Official Analytical Chemists, Washington DC. AOAC, 1990. International Method 977.30, sixteenth ed. Association of Official Analytical Chemists, Washington DC. AOAC, 1997. International Method 985.29, sixth ed. Association of Official Analytical Chemists, Washington DC. Areda, A., Ketema, S., Ingram, J., Davis, R.H.D., 1993. The iron content of tef [Eragrostis tef (Zucc.) trotter] and its controversy. Ethiopian Journal of Science 16, 5e13. Axford, D.W.E., Colwell, K.H., Cornford, S.J., Elton, G.A.H., 1968. Effect of loaf specific volume on the rate and extent of staling in bread. Journal of the Science of Food and Agriculture 19, 95e101. Ben-Fayed, E., Ainsworth, P., Stojceska, V., 2008. The incorporation of Teff (Eragrostis tef) in bread-making technology. Cereal Food World 53, A84. Bonet, A., Rosell, C.M., Caballero, P.A., Gomez, M., Perez-Munuera, I., Lluch, M.A., 2006. Glucose oxidase effect on dough rheology and bread quality: a study from macroscopic to molecular level. Food Chemistry 99, 408e415. Bultosa, G., 2007. Physicochemical characteristics of grain and flour in 13 tef [Eragrostis tef (Zucc.) trotter] grain Varietis. Journal of Applied Science Research 3, 2042e2051. Bultosa, G., Hall, A.N., Taylor, J.R.N., 2002. Physico-chemical characterization of grain tef [Eragrostis tef (Zucc.) Trotter] starch. Starch-Starke 54, 461e468.

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