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Influence of flour particle size on quality of gluten-free rice bread
LWT - Food Science and Technology 54 (2013) 199e206
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Influence of flour particle size on quality of gluten-free rice bread Esther de la Hera 1, Mario Martinez 1, Manuel Gómez* Food Technology Area, E.T.S. Ingenierías Agrarias, Valladolid University, 34004 Palencia, Spain
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 January 2012 Received in revised form 16 April 2013 Accepted 19 April 2013
In recent years there has been growing interest in gluten-free bakery products. However, few studies have analyzed the influence of flour properties on the quality of these products. This study analyzes the influence of the type of rice, flour particle size and the water content of the dough used in gluten-free bread-making, and the microstructure of the doughs. Behaviour during proofing and the characteristics of the final bread are also described. The finest flours lead to poorest retention of the gas produced during fermentation and produce breads with a lower specific volume in both formulations, although this effect was more pronounced in the bread with 80 g of water per 100 g of flour. Flours obtained from short-grain rice produced breads with higher specific volumes and lower firmness in breads with 80 g of water per 100 g of flour. In breads with 110 g of water per 100 g of flour, the type of rice used had a greater effect on the texture than on the specific volume of the breads. Analysis of dough microstructure showed a film formed of water, hydrocolloid and starch granules fragmented during milling and kneading that covered the larger particles not broken during processing. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Coeliac Bakery quality Microstructure Rice flour quality Water content
1. Introduction Coeliac disease (CD) is a digestive tract disease that damages the small intestine and interferes with the absorption of nutrients from food. The ingestion of proteins present in some cereals such as wheat, barley and rye causes a loss of the intestinal villi, leading to reduced nutrient absorption. CD has now become one of the most common lifelong disorders, affecting 1% of the population worldwide (Catassi & Yachha, 2009). The only effective treatment for coeliac disease is to maintain a strict gluten-free diet, which leads to recovery of the intestinal mucosa (Farrell & Kelly, 2002; Green & Jabri, 2003). Some of the problems that persons with CD have to face are a lack of gluten-free bakery products, the poor quality (poor crust characteristics, rapid staling and poor mouth feeling and flavour) of the ones that do exist (Gallagher, Gormley, & Arendt, 2004) and the high price of gluten-free products (Arendt, Morrisey, Moore & Dal Bello, 2008). Furthermore, commercial gluten-free breads are mainly starch-based, leading to a nutritionally unbalanced diet due to a lack of fibre, vitamins and nutrients in coeliac diets (Kinsey, Burden, & Bannerman, 2008). Improvement in the quality of gluten-free products is therefore a challenge for modern society.
* Corresponding author. Tel.: þ34 9 79 108359; fax: þ34 9 79 108302. E-mail address: [email protected] (M. Gómez). 1 Tel.: þ34 9 79 108495; fax: þ34 9 79 108302. 0023-6438/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.lwt.2013.04.019
Wheat-gluten plays an essential role in bread-making, as it is responsible for the formation of a cohesive, extensible and elastic dough that is able to retain the gas produced during fermentation (Gan, Ellis, & Schofield, 1995; Singh & MacRitchie, 2001). This fact makes it difficult to achieve high-quality bread without the presence of gluten, and different approaches have therefore been investigated in attempts to improve the quality of gluten-free bread. First, it is essential to incorporate hydrocolloids as they act as gluten-substitutes, leading some authors to try to improve bread characteristics by comparing the effect of different hydrocolloids in gluten-free bread formulations (Lazaridou, Duta, Papageorgiou, Belc, & Biliaderis, 2007; Mezaize, Chevallier, Le Bail, & de Lamballerie, 2009). Other studies have looked at the use of additives such as emulsifiers (Nunes, Moore, Ryan, & Arendt, 2009), acidic food additives (Blanco, Ronda, Pérez, & Pando, 2011) and prebiotics (Korus, Grzelak, Achremowicz, & Sabat, 2006), as well as enzymes (Gujral, Guardiola, Carbonell, & Rosell, 2003; Gujral, Haros, & Rosell, 2004; Moore, Schober, Dockery, & Arendt, 2004; Renzetti & Arendt, 2009) and sourdough (Schober, Bean, & Boyle, 2007; Wolska, Ceglinska, & Dubicka, 2010). Overall, the objective of those studies was to improve batter consistency in order to achieve greater gas retention during proofing and baking. A number of authors have looked at the influence of flour processing on gluten-free bread-making. Brites, Trigo, Santos, Collar, and Rosell (2010) studied the differences in bread quality according to the variety of maize used and the milling process employed. Kadan, Bryant, and Miller (2008) compared different milling
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processes, concluding that the excess of fine particles in rice flours led to greater collapse of the breads, producing a lower volume. Some authors developed formulae by mixing different proportions of gluten-free flours and starches in order to improve bread volume or texture properties. For example, Sanchez, Osella, and de la Torre (2002) determined the optimum percentages for composite bread based on cornstarch, rice flour and cassava starch. Others, such as Minarro, Normahomed, Guamis, and Capellas (2010), compared the characteristics of flour-based and starch-based gluten-free formulae after the addition of unicellular proteins, reporting better results with the starch-based formulae. However, there has been little research into the influence of other flour parameters, particularly particle size and grain type, on bread characteristics. Only Araki et al. (2009) studied the effect of particle size on rice-bread, but their formula was supplemented with wheat-gluten and their main objective was to study differences in the milling process. The aim of the present study was to investigate the effect of different rice-grain types and flour-particle size on dough microstructure, dough behaviour during fermentation and the final quality of gluten-free bread (specific volume and texture).
2. Materials and methods
Table 1 Flour characterization parameters. Grain type
Particle size interval (mm)
Median particle size (mm)
Protein (g/100 g)
Starch (g/100 g)
Amylose (g/100 g)
Water hydration capacity (mL/g)
Short Short Short Short Long Long Long
>180 106e180 80e106 <80 >106 80e106 <80
126.43 d 121.32 cd 92.38 b 50.74 a 110.97 c 92.66 b 48.24 a
8.56 7.46 6.41 6.70 7.59 6.89 7.45
72.3 76.4 77.9 75.4 75.5 75.7 72.6
21.41 22.84 22.75 21.56 23.71 25.51 23.67
134.7 136.3 138.8 140.1 133.9 134.7 145.9
c b a a b a b
a bc c b b b a
a b b a c d c
a a b b a a c
Values with different letters in the same parameter are significantly different (p < 0.05). Values are the mean of two measures.
with screens of 80, 106 and 180 microns, we achieved four different particle-size fractions for short-grain rice flour (<80, 80e106, 106e 180, >180 mm), and three fractions for long-grain rice flour (<80, 80e106, >106 mm); an insufficient volume of the largest particle size long-grain rice flour was available for use in the study. Salt, sugar and sunflower oil were purchased from the local market. Dry yeast (Saf-instant, Lesaffre, Lille, France) and hydroxypropyl methylcellulose (HPMC) (Methocel K4M, Dow Chemical, Midlesex, UK) were used.
2.1. Materials 2.2. Methods Two different types of rice flour were used, one from short-grain and one from long-grain rice. The flours were supplied by Harinera Castellana S.A., (Medina del Campo, Valladolid, Spain). Sifting the two flours for 15 min in a Bühler MLI 300B mill (Uzwil, Switzerland)
2.2.1. Flour measurements Flours were analysed following AACC methods (AACC, 2010) for water hydration capacity (WHC) (AACC method 88-04) and protein
Fig. 1. Environmental scanning electron microscope photomicrographs of the flours: (a) short grain, 106e180 mm; (b) short grain, <80 mm; (c) long grain, 106e180 mm. Footnote: Arrow 1: Disintegrated starch granules within the protein matrix. Circles 2: Whole compound starch granules. Arrow 3: Smooth and compact surface.
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content (AACC method 46-30, performed with a Leco TruSpecÒN nitrogen/protein analyser, St. Joseph, Michigan, USA). Flour particle size was measured using a laser diffraction particle-size analyzer (Heros & Rodos, Sympatec, Clausthal-Zellerfeld, Germany). The total starch and amylose content were measured by the polarimetric method (AACC, 76-20). 2.2.2. Gluten-free bread making A straight-dough process was employed, using a Kitchen-Aid Professional mixer (KPM5, KitchenAid, St. Joseph, Michigan, USA) with either a wire whip (K5AWWC) or dough hook (K45DH), depending on water content. Two different formulae were tested. The following ingredients (as g/100 g on flour basis) were used in both formulae: sunflower oil (6 g/100 g), sugar (5 g/100 g), salt (2 g/ 100 g), instant yeast (3 g/100 g) and HPMC (4 g/100 g). In one formula the amount of water added was 80 g/100 g of flour whereas in the other it was 110 g/100 g. In both cases, the instant yeast was first rehydrated in half the amount of water. The kneading of the dough with 80 g water/100 g flour was done with a dough hook and the mixing of the batters with 110 g water/100 g was done with wire whip, both for a period of 8 min at speed 2. Each dough was prepared in duplicate. The doughs were moulded into aluminium pans of 232 108 43.5 mm: 350 g into each pan in the case of the dough with 80 g water per 100 g flour, and 250 g in the case of the dough with 110 g of water per 100 g of flour due to greater expansion during proofing. Pans were placed into a proofing chamber at 30 C and 90% relative humidity for 40 min. After proofing, the breads were baked in an electric oven for 40 min at 190 C. After baking, breads were demoulded, cooled for 50 min at room temperature and packed into sealed polyethylene bags to prevent dehydration.
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2.2.3. Rheofermentometer analysis The effect of the different flours on dough proofing was determined using a rheofermentometer (Chopin, Villeneuve-la-Garenne, France), obtaining information on dough development and gas production during fermentation (Czuchajowska & Pomeranz, 1993). In contrast to the traditional method, the weight of dough was reduced to 200 g and the weights were removed from the piston due to the weakness of this kind of dough compared to one prepared with wheat flour. The dough used in the analysis was elaborated using the same method as described above. Proofing temperature was set at 30 C, as in the bread making. The proofing conditions were therefore as similar as possible to those used for the doughs that were baked. 2.2.4. Evaluation of bread quality The evaluation of bread quality was done 24 h after baking. Bread volume was determined using a laser sensor with the BVM-L 370 volume analyser (TexVol Instruments, Viken, Sweden). The bread specific volume was calculated as the ratio between the volume of the bread and its weight. Weight loss was measured as the difference between the weight of the dough moulded and the weight of the bread after baking. Measurements were performed in duplicate. Crumb texture was determined using a TA-XT2 texture analyser (Stable Microsystems, Surrey, UK) with the “Texture Expert” software. A 25-mm diameter cylindrical aluminium probe was used in a ‘Texture Profile Analysis’ (TPA) double compression test to penetrate to ½ of the depth at a speed of 2 mm/s and with a 30s delay between the first and second compressions. Firmness (N), cohesiveness, springiness and resilience were calculated from the
Fig. 2. Environmental scanning electron microscope photomicrographs of the doughs: (a) 80 g water/100 g flour, short grain, <80 mm; (b) 80 g water/100 g flour, short grain, 106e 180 mm; (c) 110 g water/100 g flour, short grain, 80e106 mm; (d) detail of the hydroxypropyl methylcellulose and water network. Footnote: Arrow 1: Starch compound particles disintegrated and mixed with HPMC, protein and water, covering larger particles which had not been disaggregated during kneading. Arrow 2: Large air spaces. Arrow 3: WaterHPMC gel structure linking the different particles of the dough.
202
Dough development (mm)
a)
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3. Results and discussion 80
3.1. Flour characteristics
70 60 40 30 20 10 0 0:00
0:30
1:00
1:30
2:00
2:30
3:00
Time (hh:mm:ss)
b) 120 Dough development (mm)
Rice-flour characteristics are shown in Table 1. Median particle size revealed finer fractions than those estimated by sifting, as the mesh screen indicates the maximum size. It is noticeable that there was a much greater difference between the finest fraction and the following fraction (80e106 mm) than between each of the other fractions. There were significant differences in the protein content between the finest fractions of the flours from the two types of rice, being higher in short-grain rice flour. The fraction over 180 mm had the highest protein content, which could be due to residues of bran and the aleurone layer, as protein concentration is highest in the superficial layers of the rice kernel and decreases towards the centre (Champagne, Wood, Juliano, & Bechtel, 2006). When the starch content of the rice flours was analysed, the trend was reversed; this is because starch granules and protein content constitute approximately 97 g/100 g of milled rice grain (Fitzgerald, 2006; Shih, 2006). Short-grain rice flour had a higher starch content than the longgrain variety, and the intermediate fractions were those that presented the highest values. Regarding amylose content, the highest values were detected in the long-grain flours, as previously indicated by Moldenhauer, Gibbons, and McKenzie (2006). Rice variety was not found to have any clear effect on water holding capacity (WHC). Fractions below 80 mm showed higher ability to hydrate than those over 106 mm, and a significant correlation was observed between median particle size and WHC (p < 0.01; r ¼ 0.6), possibly due to the greater surface area of the smaller flour particles. Differences in flour microstructure may be seen in Fig. 1. Photographs 1a and 1b show two different fractions of short-grain rice. In photograph “a”, the 106e180 mm fraction, the particles appear much larger and there are whole starch granules. In photograph “b”, showing the <80 mm fraction, a large number of small, disintegrated starch granules can be seen within the protein matrix, together with a number of spherical compound granules. Fig. 1c shows a photograph of long-grain rice flour with a particle size of 106e180 mm. The particles look smoother and more compact than with the short-grain flour, which indicates that greater mechanical work will be necessary for disaggregation. In contrast, in Fig. 1a, short-grain particles show a rougher surface with loose starch granules that will separate more easily needing less mechanical work and so on suffering less damage. Moreover, this easily disaggregation could imply better water hydration and interaction when the rest of ingredients while bread-making.
50
100 80 60 40 20 0 0:00
0:30
1:00
1:30
2:00
2:30
3:00
Time (hh:mm) Fig. 3. Dough development curves from the rheofermentometer analysis of shortgrain breads. (a) 80 g water/100 g flour (b) 110 g water/100 g flour. Legend: ( ) ) Short grain, 80e106 mm; ( ) Short grain, 106e180 mm; Short grain, <80 mm; ( ) Short grain, >180 mm. (
TPA graph. Measurements were made on two central slices (20 mm thickness) from two breads from each dough. 2.2.5. Electron microscope photomicrographs Flour and dough photomicrographs were taken with a Quanta 200FEG (Hillsboro, Oregon, USA) environmental scanning electron microscope (ESEM), fitted with a backscattered electron detector (BSED). 2.2.6. Statistical analysis Differences between the parameters were studied for the flours and the breads by analysis of variance (ANOVA). Fisher’s least significant difference (LSD) was used to describe means with 95% confidence intervals. The statistical analysis was performed with the Statgraphics Plus V5.1 software (Statpoint Technologies, Inc., Warrenton, USA). Correlations were obtained using the same program.
3.2. Dough properties Fig. 2 shows the dough microstructures in photomicrographs taken with the ESEM. Fig. 2a and b show doughs elaborated with
Table 2 Physical properties of rice breads elaborated with 80 g of water per 100 g of flour. Grain type
Particle size interval (mm)
Specific volume (cm3/g)
Weight loss (g/100 g)
Firmness (N)
Cohesiveness
Springiness
Resilience
Short Short Short Short Long Long Long
>180 106e180 80e106 <80 >106 80e106 <80
3.11 3.47 2.40 1.71 2.13 2.08 1.63
13.87 13.75 13.90 15.46 14.40 13.48 14.72
4.33 a 3.36 a 12.37 b 35.94 c 34.49 c 38.09 c 50.89 d
0.37 0.39 0.44 0.43 0.35 0.29 0.29
0.54 0.56 0.76 0.70 0.61 0.67 0.54
0.16 0.18 0.23 0.25 0.12 0.15 0.18
d e c a b b a
a a a b ab a ab
Values with different letters in the same parameter are significantly different (p < 0.05). Measurements of specific volume and weight loss were performed in duplicate. Measurements of textural properties were made on two central slices from two breads of each dough.
a a a a a a a
a a b ab ab ab a
a a a a a a a
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Table 3 Physical properties of rice breads elaborated with 110 g of water per 100 g of flour. Grain type
Particle size interval (mm)
Specific volume (cm3/g)
Weight loss (g/100 g)
Firmness (N)
Cohesiveness
Springiness
Resilience
Short Short Short Short Long Long Long
>180 106e180 80e106 <80 >106 80e106 <80
3.93 4.09 5.10 4.13 4.75 4.65 3.04
21.87 21.13 21.20 21.06 20.70 21.53 21.72
1.40 a 1.62 a 0.99 a 2.29 a 1.13 a 2.60 a 15.61 b
0.47 0.47 0.60 0.53 0.29 0.31 0.31
0.57 0.62 0.91 0.93 0.86 0.85 0.86
0.22 0.20 0.35 0.30 0.11 0.10 0.12
b c e c d d a
a a a a a a a
b b d c a a a
a b d d c c c
b b d c a a a
Values with different letters in the same parameter are significantly different (p < 0.05). Measurements of specific volume and weight loss were performed in duplicate. Measurements of textural properties were made on two central slices from two breads of each dough.
80 g water/100 g flour. It may be observed that during kneading some of the starch compound particles had disintegrated and mixed with the HPMC, some protein particles and water, covering larger particles which had not been disaggregated during kneading. In Fig. 2b (coarse fraction), particles that had not disintegrated look coarser than those in doughs elaborated with finer fractions (Fig. 2a). In the case of long-grain rice (harder than the short-grain variety), there was less disintegration of the grains during kneading than in doughs elaborated with short-grain flours, and this will affect the final dough (Figure not shown). Fig. 2c, showing the dough elaborated with 110 g of water per 100 g of flour, reveals a similar structure to the doughs with 80 g of water per 100 g of flour. This structure is formed by simple starch granules mixed with HPMC, some protein particles and water, covering the larger flour
particles. However, the larger amount of water made the structure smoother, and large air spaces may be seen in these types of dough. These spaces do not disappear during proofing or baking, and they will be present in breads as large holes in the crumb. This fact has already been explained by McCarthy, Gallagher, Gormley, Schober, and Arendt (2005), who stated that as water and HPMC content increase, the gas cells coalescence to form larger cells. The waterHPMC gel structure linking the different particles of the dough may be observed in Fig. 2d. The graph in Fig. 3a shows the dough-development curves of doughs with 80 g of water per 100 g of flour during fermentation in the rheofermentometer. Only the curves of short-grain rice flour are presented as similar trends were observed with long-grain flour. As particle size increases, the dough-development curves
Fig. 4. Crumb detail of finished bread elaborated with 80 g water/100 g flour and 40 min proofing. Legend: Short grain, <80 mm; Short grain, 80e106 mm; Short grain, 106e180 mm; Short grain, >180 mm.
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rise higher. This would suggest that the breads will have a greater volume. With both types of flour, the coarsest fraction showed significant differences with respect to the other fractions. It may be clearly seen that the <80-mm fraction did not increase in volume, indicating that the gas produced was not retained. Fig. 3b shows the behaviour of short-grain rice-flour dough with 110 g of water per 100 g of flour. In this case, the <80-mm fraction did show development, but the structure broke up after approximately 90 min of fermentation, allowing the retained gas to escape and causing the curve to fall. There were no significant differences between the other fractions until after 2 h of fermentation, which is not typically reached in gluten-free bread-making. Development was greater in the case of breads with 110 g water/100 g flour and the dough had a better tolerance to excess proofing as, after 2 h, the curves continue to rise whereas, with the other formulation, they start to fall. The finer the flour particle size, the higher their surface area within the dough, meaning that a larger amount of water and HPMC will be necessary to link the dough; this probably explains why dough with larger amounts of water behave better. Although the mixture of water, HPMC and starch particles will weaken as water content increases, the 4% of HPMC used in this study was sufficient to maintain dough properties even with the higher water content. 3.3. Bread properties The properties of bread elaborated with 80 g water/100 g flour are listed in Table 2. The lowest specific volume of these breads was found with the finest fractions. When fractions over 80 mm were used, the short-grain rice flours were found to achieve higher
specific volumes than long-grain flours, and the highest specific volume was reached with short-grain flour with a 106e180 mm particle size. Lower specific volumes were found with doughs that expanded less during proofing (Fig. 3a). The differences between the specific volumes of the breads elaborated with the finest fractions and those elaborated with other fractions are therefore mainly due to differences in gas retention during fermentation. In the case of the >180-mm short-grain fraction (with the largest median particle size), the specific volume of the bread was lower than that of the bread elaborated with the fraction with a particle size between 106 and 180 mm, contrasting with the findings on the rheofermentometer curves. This would suggest that, in this particular case, the differences in specific volume were due to changes during baking. The physical properties of breads elaborated with 110 g water/100 g flour are shown in Table 3. The specific volumes in all these cases were higher than those of less hydrated breads, due to greater development of the doughs during proofing. As occurred with less hydrated breads, the fraction with a particle size <80 mm produced breads with a lower specific volume due to poorer development of the dough during proofing. Differences in the rheofermentometer curves between this fraction and coarser fractions were observed after 70 min. However, proofing times in this study, determined on the basis of previous studies (Kadan, Robinson, Thibodeux, & Pepperman, 2001; Pruska-Kedzior et al., 2008), were of less than 70 min and the rheofermentometer curves cannot therefore be compared directly with the specific volume values as dough development continued during the initial stages of baking. Based on these results, some fractions would have tolerated longer proofing times and would thus have achieved
Fig. 5. Crumb detail of finished bread elaborated with 80 g water/100 g flour and 40 min proofing. Legend: Long grain, <80 mm; Long grain, 80e106 mm; Long grain, >106 mm.
E.de la Hera et al. / LWT - Food Science and Technology 54 (2013) 199e206
better volume results. Another aspect to be taken into account is that gluten-containing breads are considered to have a longer shelflife when longer proofing times are used (Gomez, Oliete, Pando, Ronda, & Caballero, 2008). Higher volumes are achieved with long-grain rice-flour fractions >80 mm and with the 80e106-mm fraction of the short-grain flour. These fractions had a median particle size between approximately 90 and 120 mm (Table 1). Short-grain rice-flour fractions >106 mm were associated with lower specific volumes, as was observed with the largest particle size in breads with 80 g water/100 g flour. However, the negative effect of the coarsest fraction was more pronounced in the more hydrated breads. As no differences were observed during proofing, finding could have been due to changes in bread structure during baking. In addition, in both formulations, the finest particles did not behave well, probably due to a lack of gas retention during proofing. The specific volumes were lowest in the breads elaborated with these fractions, in agreement with the findings reported by Kadan et al. (2008) when studying the effect of different milling processes on flour properties. Choosing the wrong characteristics of the flours (type of flour and particle size) may lead to a loss of up to 40% in the specific volume in the case of breads elaborated with 110 g water/ 100 g flour, and of more than 50% in the case of the formulation with 80 g water/100 g flour. Analysis of weight loss showed no clear trends between the two types of rice or between flour-particle sizes. Formulations with 110 g water/100 g flour showed greater weight loss, probably due to the larger amount of water and also to the higher specific volume, which produces a greater surface area for evaporation. Regarding textural characteristics, breads with the 110 g water/ 100 g flour had lower firmness values due to their higher specific volumes and less compact structure. The only significant difference in firmness between the more hydrated breads was found with the finest fraction of the long-grain rice flour (highest firmness), and this bread also had the lowest specific volume. In the case of less hydrated breads, it was the amylose content rather than specific volume that had the greatest influence on firmness. Long-grain rice flour gave rise to higher firmness values than the short-grain flours. This effect may occur because long-grain flour has a higher amylose content, which produces more retrogradation phenomena (Singh, Kaur, Sandhu, Kaur, & Nishinari, 2006) and, therefore, firmer textures. The cohesiveness, springiness and resilience values depended on the formulations. There was hardly any difference in springiness between the formulations with 80 g water/100 g flour, and no differences in cohesiveness or resilience. The differences in springiness may be attributable to particle size, but no trend was observed. On the other hand, grain type and particle size were found to be important in the formulations with 110 g water/100 g flour. Breads of long-grain rice flour were not affected by particle size whereas those of short-grain flour showed significant differences between the different fractions. The highest values of cohesiveness, springiness and resilience were detected with the finer fractions, as was true for the only case which differences were detected in the less hydrated breads. Final crumb characteristics are determined by the combined amylose and amylopectin content. While amylose is required for crumb setting, due to its rapid retrogradation, amylopectin may counteract this effect, causing fresh bread to be softer (Schober, 2009). In Figs. 4 and 5 are shown the crumb detail of finished breads elaborated with 80 g of water per 100 g of flour for both short and long grain. Those breads elaborated with 110 g of water per 100 g of flour, although achieved greater specific volumes, were too weak and lost its consistency while slicing. This is the reason why photographs were not the spitting images of reality and so on are not shown. Overall, long grain bread slices seem lower than those from short grain. In addition, finest fraction, in both short and long grain
205
type, show the closest pore structure, more compact and harder as showed firmness texture parameter. 4. Conclusions This study demonstrates that the characteristics of the rice flour used in gluten-free bread-making have a marked influence on the processing and quality of the products obtained. This influence is attributed mainly to their effects on dough microstructure. It will therefore be necessary, both in industry and in research, to clearly define the characteristics of the flour, using parameters such as particle size or the amylose/amylopectin ratio, in order to achieve consistent results. Effects vary depending on the formulation and, in particular, on the water content. Although proofing times in studies of gluten-free bread are typically less than 60 min, the rheofermentometer analysis has shown that, depending on the characteristics of the flour and the dough, an increase in fermentation times could lead to an improvement in bread volume, shelflife and sensorial characteristics. These aspects of the final bread should be evaluated in future studies. Acknowledgements This study was supported by a grant from the Spanish Ministry of Science and Innovation (Grant: AGL2011-23802) The authors are grateful to Harinera Castellana (Medina del Campo, Valladolid, Spain) for supplying the raw materials, and to Agro-Technical Institute- ITACYL (Castile and Leon, Spain) and to Esteve Santiago S.A. (Cabezón de Pisuerga, Valladolid, Spain) for protein and particle size measurements. References AACC. (2010). In Approved methods of the American Association of Cereal Chemists, methods 44-15.02 (moisture), 46-30.01 (protein), 61-02.01 (pasting properties), 10-91.01 (cake symmetry and volume index) (11th ed.) St. Paul, Minnesota, USA: American Association of Cereal Chemists. Araki, E., Ikeda, T., Ashida, K., Takata, K., Yanaka, M., & Iida, S. (2009). Effects of rice flour properties on specific loaf volume of one-loaf bread made from rice flour with wheat vital gluten. Food Science and Technological Research, 15, 439e448. Arendt, E. K., Morrissey, A., Moore, M. M., & Dal Bello, F. (2008). Gluten-free breads. In E. K. Arendt, & F. Dal Bello (Eds.), Gluten-free cereal products and beverages (pp. 289e311). Minnesota, USA.: Academic Press. Blanco, C. A., Ronda, F., Pérez, B., & Pando, V. (2011). Improving gluten-free bread quality by enrichment with acidic food additives. Food Chemistry, 127, 1204e1209. Brites, C., Trigo, M. J., Santos, C., Collar, C., & Rosell, C. M. (2010). Maize-based glutenfree bread: influence of processing parameters on sensory and instrumental quality. Food and Bioprocess Technology, 3, 707e715. Catassi, C., & Yachha, S. K. (2009). The epidemiology of celiac disease. In E. K. Arendt, & F. Dal Bello (Eds.), The science of gluten-free foods and beverages (pp. 1e13). Minnesota, USA.: Academic Press. Champagne, E. T., Wood, D. F., Juliano, B. O., & Bechtel, D. B. (2006). The rice grain and its gross composition. In E. T. Champagne (Ed.), Rice chemistry and technology (3rd ed.) (pp. 77e108) St. Paul, Minnesota, USA: American Association of Cereal Chemists. Czuchajowska, Z., & Pomeranz, Y. (1993). Gas-formation and gas retention. 1. The system and methodology. Cereal Foods World, 38, 499e503. Farrell, R. J., & Kelly, C. P. (2002). Celiac sprue. New England Journal of Medicine, 346, 180e188. Fitzgerald, M. (2006). Starch. In E. T. Champagne (Ed.), Rice chemistry and technology (3rd ed.) (pp. 109e142) St. Paul, Minnesota, USA: American Association of Cereal Chemists. Gallagher, E., Gormley, T. R., & Arendt, E. K. (2004). Recent advances in the formulation of gluten-free cereal based products. Trends in Food Science and Technology, 15, 143e152. Gan, Z., Ellis, P. R., & Schofield, J. D. (1995). Gas cell stabilization and gas retention in wheat bread dough. Journal of Cereal Science, 21, 215e230. Gomez, M., Oliete, B., Pando, V., Ronda, F., & Caballero, P. A. (2008). Effect of fermentation conditions on bread staling kinetics. European Food Research and Technology, 226, 1379e1387. Green, P. H. R., & Jabri, B. (2003). Coeliac disease. The Lancet, 362, 383e391. Gujral, H. S., Guardiola, I., Carbonell, J. V., & Rosell, C. M. (2003). Effect of cyclodextrinase on dough rheology and bread quality from rice flour. Journal of Agricultural and Food Chemistry, 51, 3814e3818.
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Gujral, H. S., Haros, M., & Rosell, C. M. (2004). Improving the texture and delaying staling in rice flour chapati with hydrocolloids and alpha-amylase. Journal of Food Engineering, 65, 89e94. Kadan, R. S., Bryant, R. J., & Miller, J. A. (2008). Effects of milling on functional properties of rice flour. Journal of Food Science, 3, 151e154. Kadan, R. S., Robinson, M. G., Thibodeux, D. P., & Pepperman, A. (2001). Texture and other physicochemical properties of whole rice bread. Journal of Food Science, 66, 940e944. Kinsey, L., Burden, S. T., & Bannerman, E. (2008). A dietary survey to determine if patients with coeliac disease are meeting current healthy eating guidelines and how their diet compares to that of the British general population. European Journal of Clinical Nutrition, 62, 1333e1342. Korus, J., Grzelak, K., Achremowicz, K., & Sabat, R. (2006). Influence of prebiotic additions on the quality of gluten-free bread and on the content of inulin and fructooligosaccharides. Food Science and Technology International, 12, 489e495. Lazaridou, A., Duta, D., Papageorgiou, M., Belc, N., & Biliaderis, C. G. (2007). Effects of hydrocolloids on dough rheology and bread quality parameters in gluten-free formulations. Journal of Food Engineering, 79, 1033e1047. McCarthy, D. F., Gallagher, E., Gormley, T. R., Schober, T. J., & Arendt, E. K. (2005). Application of response surface methodology in the development of gluten-free bread. Cereal Chemistry, 82, 609e615. Mezaize, S., Chevallier, S., Le Bail, A., & de Lamballerie, M. (2009). Optimization of gluten-free formulations for French-style breads. Journal of Food Science, 74, 140e146. Minarro, B., Normahomed, I., Guamis, B., & Capellas, M. (2010). Influence of unicellular protein on gluten-free bread characteristics. European Food Research and Technology, 231, 171e179. Moldenhauer, K. A. K., Gibbons, J. H., & McKenzie, K. S. (2006). Rice varieties. In E. T. Champagne (Ed.), Rice chemistry and technology (3rd ed.) (pp. 49e76) St. Paul, Minnesota, USA: American Association of Cereal Chemists.
Moore, M. M., Schober, T. J., Dockery, P., & Arendt, E. K. (2004). Textural comparisons of gluten-free and wheat-based doughs, batters, and breads. Cereal Chemistry, 81, 567e575. Nunes, M. H. B., Moore, M. M., Ryan, L. A. M., & Arendt, E. K. (2009). Impact of emulsifiers on the quality and rheological properties of gluten-free breads and batters. European Food Research and Technology, 228, 633e642. Pruska-Kedzior, A., Kedzior, Z., Goracy, M., Pietrowska, K., Przybylska, A., & Spychalska, K. (2008). Comparison of rheological, fermentative and baking properties of glutenfree dough formulations. European Food Research and Technology, 227, 1523e1536. Renzetti, S., & Arendt, E. K. (2009). Effects of oxidase and protease treatments on the breadmaking functionality of a range of gluten-free flours. European Food Research and Technology, 229, 307e317. Sanchez, H. D., Osella, C. A., & de la Torre, M. A. (2002). Optimization of gluten-free bread prepared from cornstarch, rice flour, and cassava starch. Journal of Food Science, 67, 416e419. Schober, T. J. (2009). Manufacture of gluten-free specialty breads and confectionery products. In E. Gallagher (Ed.), Gluten-free food science and technology (pp. 130e 180). Oxford, UK: Wiley-Blackwell. Schober, T. J., Bean, S. R., & Boyle, D. L. (2007). Gluten-free sorghum bread improved by sourdough fermentation: biochemical, rheological, and microstructural background. Journal of Agricultural and Food Chemistry, 55, 5137e5146. Shih, F. F. (2006). Rice proteins. In E. T. Champagne (Ed.), Rice chemistry and technology (3rd ed.) (pp. 143e162) St. Paul, Minnesota, USA: American Association of Cereal Chemists. Singh, N., Kaur, L., Sandhu, K. S., Kaur, J., & Nishinari, K. (2006). Relationships between physicochemical, morphological, thermal, rheological properties of rice starches. Food Hydrocolloids, 20, 532e542. Singh, H., & MacRitchie, F. (2001). Application of polymer science to properties of gluten Source. Journal of Cereal Science, 33, 231e243. Wolska, P., Ceglinska, A., & Dubicka, A. (2010). Production of bread using sourdoughs from gluten-free cereals. Zywnosc-Nauka Technologia Jakosc, 17, 104e111.
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LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Influence of flour particle size on quality of gluten-free rice bread Esther de la Hera 1, Mario Martinez 1, Manuel Gómez* Food Technology Area, E.T.S. Ingenierías Agrarias, Valladolid University, 34004 Palencia, Spain
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 January 2012 Received in revised form 16 April 2013 Accepted 19 April 2013
In recent years there has been growing interest in gluten-free bakery products. However, few studies have analyzed the influence of flour properties on the quality of these products. This study analyzes the influence of the type of rice, flour particle size and the water content of the dough used in gluten-free bread-making, and the microstructure of the doughs. Behaviour during proofing and the characteristics of the final bread are also described. The finest flours lead to poorest retention of the gas produced during fermentation and produce breads with a lower specific volume in both formulations, although this effect was more pronounced in the bread with 80 g of water per 100 g of flour. Flours obtained from short-grain rice produced breads with higher specific volumes and lower firmness in breads with 80 g of water per 100 g of flour. In breads with 110 g of water per 100 g of flour, the type of rice used had a greater effect on the texture than on the specific volume of the breads. Analysis of dough microstructure showed a film formed of water, hydrocolloid and starch granules fragmented during milling and kneading that covered the larger particles not broken during processing. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Coeliac Bakery quality Microstructure Rice flour quality Water content
1. Introduction Coeliac disease (CD) is a digestive tract disease that damages the small intestine and interferes with the absorption of nutrients from food. The ingestion of proteins present in some cereals such as wheat, barley and rye causes a loss of the intestinal villi, leading to reduced nutrient absorption. CD has now become one of the most common lifelong disorders, affecting 1% of the population worldwide (Catassi & Yachha, 2009). The only effective treatment for coeliac disease is to maintain a strict gluten-free diet, which leads to recovery of the intestinal mucosa (Farrell & Kelly, 2002; Green & Jabri, 2003). Some of the problems that persons with CD have to face are a lack of gluten-free bakery products, the poor quality (poor crust characteristics, rapid staling and poor mouth feeling and flavour) of the ones that do exist (Gallagher, Gormley, & Arendt, 2004) and the high price of gluten-free products (Arendt, Morrisey, Moore & Dal Bello, 2008). Furthermore, commercial gluten-free breads are mainly starch-based, leading to a nutritionally unbalanced diet due to a lack of fibre, vitamins and nutrients in coeliac diets (Kinsey, Burden, & Bannerman, 2008). Improvement in the quality of gluten-free products is therefore a challenge for modern society.
* Corresponding author. Tel.: þ34 9 79 108359; fax: þ34 9 79 108302. E-mail address: [email protected] (M. Gómez). 1 Tel.: þ34 9 79 108495; fax: þ34 9 79 108302. 0023-6438/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.lwt.2013.04.019
Wheat-gluten plays an essential role in bread-making, as it is responsible for the formation of a cohesive, extensible and elastic dough that is able to retain the gas produced during fermentation (Gan, Ellis, & Schofield, 1995; Singh & MacRitchie, 2001). This fact makes it difficult to achieve high-quality bread without the presence of gluten, and different approaches have therefore been investigated in attempts to improve the quality of gluten-free bread. First, it is essential to incorporate hydrocolloids as they act as gluten-substitutes, leading some authors to try to improve bread characteristics by comparing the effect of different hydrocolloids in gluten-free bread formulations (Lazaridou, Duta, Papageorgiou, Belc, & Biliaderis, 2007; Mezaize, Chevallier, Le Bail, & de Lamballerie, 2009). Other studies have looked at the use of additives such as emulsifiers (Nunes, Moore, Ryan, & Arendt, 2009), acidic food additives (Blanco, Ronda, Pérez, & Pando, 2011) and prebiotics (Korus, Grzelak, Achremowicz, & Sabat, 2006), as well as enzymes (Gujral, Guardiola, Carbonell, & Rosell, 2003; Gujral, Haros, & Rosell, 2004; Moore, Schober, Dockery, & Arendt, 2004; Renzetti & Arendt, 2009) and sourdough (Schober, Bean, & Boyle, 2007; Wolska, Ceglinska, & Dubicka, 2010). Overall, the objective of those studies was to improve batter consistency in order to achieve greater gas retention during proofing and baking. A number of authors have looked at the influence of flour processing on gluten-free bread-making. Brites, Trigo, Santos, Collar, and Rosell (2010) studied the differences in bread quality according to the variety of maize used and the milling process employed. Kadan, Bryant, and Miller (2008) compared different milling
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processes, concluding that the excess of fine particles in rice flours led to greater collapse of the breads, producing a lower volume. Some authors developed formulae by mixing different proportions of gluten-free flours and starches in order to improve bread volume or texture properties. For example, Sanchez, Osella, and de la Torre (2002) determined the optimum percentages for composite bread based on cornstarch, rice flour and cassava starch. Others, such as Minarro, Normahomed, Guamis, and Capellas (2010), compared the characteristics of flour-based and starch-based gluten-free formulae after the addition of unicellular proteins, reporting better results with the starch-based formulae. However, there has been little research into the influence of other flour parameters, particularly particle size and grain type, on bread characteristics. Only Araki et al. (2009) studied the effect of particle size on rice-bread, but their formula was supplemented with wheat-gluten and their main objective was to study differences in the milling process. The aim of the present study was to investigate the effect of different rice-grain types and flour-particle size on dough microstructure, dough behaviour during fermentation and the final quality of gluten-free bread (specific volume and texture).
2. Materials and methods
Table 1 Flour characterization parameters. Grain type
Particle size interval (mm)
Median particle size (mm)
Protein (g/100 g)
Starch (g/100 g)
Amylose (g/100 g)
Water hydration capacity (mL/g)
Short Short Short Short Long Long Long
>180 106e180 80e106 <80 >106 80e106 <80
126.43 d 121.32 cd 92.38 b 50.74 a 110.97 c 92.66 b 48.24 a
8.56 7.46 6.41 6.70 7.59 6.89 7.45
72.3 76.4 77.9 75.4 75.5 75.7 72.6
21.41 22.84 22.75 21.56 23.71 25.51 23.67
134.7 136.3 138.8 140.1 133.9 134.7 145.9
c b a a b a b
a bc c b b b a
a b b a c d c
a a b b a a c
Values with different letters in the same parameter are significantly different (p < 0.05). Values are the mean of two measures.
with screens of 80, 106 and 180 microns, we achieved four different particle-size fractions for short-grain rice flour (<80, 80e106, 106e 180, >180 mm), and three fractions for long-grain rice flour (<80, 80e106, >106 mm); an insufficient volume of the largest particle size long-grain rice flour was available for use in the study. Salt, sugar and sunflower oil were purchased from the local market. Dry yeast (Saf-instant, Lesaffre, Lille, France) and hydroxypropyl methylcellulose (HPMC) (Methocel K4M, Dow Chemical, Midlesex, UK) were used.
2.1. Materials 2.2. Methods Two different types of rice flour were used, one from short-grain and one from long-grain rice. The flours were supplied by Harinera Castellana S.A., (Medina del Campo, Valladolid, Spain). Sifting the two flours for 15 min in a Bühler MLI 300B mill (Uzwil, Switzerland)
2.2.1. Flour measurements Flours were analysed following AACC methods (AACC, 2010) for water hydration capacity (WHC) (AACC method 88-04) and protein
Fig. 1. Environmental scanning electron microscope photomicrographs of the flours: (a) short grain, 106e180 mm; (b) short grain, <80 mm; (c) long grain, 106e180 mm. Footnote: Arrow 1: Disintegrated starch granules within the protein matrix. Circles 2: Whole compound starch granules. Arrow 3: Smooth and compact surface.
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content (AACC method 46-30, performed with a Leco TruSpecÒN nitrogen/protein analyser, St. Joseph, Michigan, USA). Flour particle size was measured using a laser diffraction particle-size analyzer (Heros & Rodos, Sympatec, Clausthal-Zellerfeld, Germany). The total starch and amylose content were measured by the polarimetric method (AACC, 76-20). 2.2.2. Gluten-free bread making A straight-dough process was employed, using a Kitchen-Aid Professional mixer (KPM5, KitchenAid, St. Joseph, Michigan, USA) with either a wire whip (K5AWWC) or dough hook (K45DH), depending on water content. Two different formulae were tested. The following ingredients (as g/100 g on flour basis) were used in both formulae: sunflower oil (6 g/100 g), sugar (5 g/100 g), salt (2 g/ 100 g), instant yeast (3 g/100 g) and HPMC (4 g/100 g). In one formula the amount of water added was 80 g/100 g of flour whereas in the other it was 110 g/100 g. In both cases, the instant yeast was first rehydrated in half the amount of water. The kneading of the dough with 80 g water/100 g flour was done with a dough hook and the mixing of the batters with 110 g water/100 g was done with wire whip, both for a period of 8 min at speed 2. Each dough was prepared in duplicate. The doughs were moulded into aluminium pans of 232 108 43.5 mm: 350 g into each pan in the case of the dough with 80 g water per 100 g flour, and 250 g in the case of the dough with 110 g of water per 100 g of flour due to greater expansion during proofing. Pans were placed into a proofing chamber at 30 C and 90% relative humidity for 40 min. After proofing, the breads were baked in an electric oven for 40 min at 190 C. After baking, breads were demoulded, cooled for 50 min at room temperature and packed into sealed polyethylene bags to prevent dehydration.
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2.2.3. Rheofermentometer analysis The effect of the different flours on dough proofing was determined using a rheofermentometer (Chopin, Villeneuve-la-Garenne, France), obtaining information on dough development and gas production during fermentation (Czuchajowska & Pomeranz, 1993). In contrast to the traditional method, the weight of dough was reduced to 200 g and the weights were removed from the piston due to the weakness of this kind of dough compared to one prepared with wheat flour. The dough used in the analysis was elaborated using the same method as described above. Proofing temperature was set at 30 C, as in the bread making. The proofing conditions were therefore as similar as possible to those used for the doughs that were baked. 2.2.4. Evaluation of bread quality The evaluation of bread quality was done 24 h after baking. Bread volume was determined using a laser sensor with the BVM-L 370 volume analyser (TexVol Instruments, Viken, Sweden). The bread specific volume was calculated as the ratio between the volume of the bread and its weight. Weight loss was measured as the difference between the weight of the dough moulded and the weight of the bread after baking. Measurements were performed in duplicate. Crumb texture was determined using a TA-XT2 texture analyser (Stable Microsystems, Surrey, UK) with the “Texture Expert” software. A 25-mm diameter cylindrical aluminium probe was used in a ‘Texture Profile Analysis’ (TPA) double compression test to penetrate to ½ of the depth at a speed of 2 mm/s and with a 30s delay between the first and second compressions. Firmness (N), cohesiveness, springiness and resilience were calculated from the
Fig. 2. Environmental scanning electron microscope photomicrographs of the doughs: (a) 80 g water/100 g flour, short grain, <80 mm; (b) 80 g water/100 g flour, short grain, 106e 180 mm; (c) 110 g water/100 g flour, short grain, 80e106 mm; (d) detail of the hydroxypropyl methylcellulose and water network. Footnote: Arrow 1: Starch compound particles disintegrated and mixed with HPMC, protein and water, covering larger particles which had not been disaggregated during kneading. Arrow 2: Large air spaces. Arrow 3: WaterHPMC gel structure linking the different particles of the dough.
202
Dough development (mm)
a)
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3. Results and discussion 80
3.1. Flour characteristics
70 60 40 30 20 10 0 0:00
0:30
1:00
1:30
2:00
2:30
3:00
Time (hh:mm:ss)
b) 120 Dough development (mm)
Rice-flour characteristics are shown in Table 1. Median particle size revealed finer fractions than those estimated by sifting, as the mesh screen indicates the maximum size. It is noticeable that there was a much greater difference between the finest fraction and the following fraction (80e106 mm) than between each of the other fractions. There were significant differences in the protein content between the finest fractions of the flours from the two types of rice, being higher in short-grain rice flour. The fraction over 180 mm had the highest protein content, which could be due to residues of bran and the aleurone layer, as protein concentration is highest in the superficial layers of the rice kernel and decreases towards the centre (Champagne, Wood, Juliano, & Bechtel, 2006). When the starch content of the rice flours was analysed, the trend was reversed; this is because starch granules and protein content constitute approximately 97 g/100 g of milled rice grain (Fitzgerald, 2006; Shih, 2006). Short-grain rice flour had a higher starch content than the longgrain variety, and the intermediate fractions were those that presented the highest values. Regarding amylose content, the highest values were detected in the long-grain flours, as previously indicated by Moldenhauer, Gibbons, and McKenzie (2006). Rice variety was not found to have any clear effect on water holding capacity (WHC). Fractions below 80 mm showed higher ability to hydrate than those over 106 mm, and a significant correlation was observed between median particle size and WHC (p < 0.01; r ¼ 0.6), possibly due to the greater surface area of the smaller flour particles. Differences in flour microstructure may be seen in Fig. 1. Photographs 1a and 1b show two different fractions of short-grain rice. In photograph “a”, the 106e180 mm fraction, the particles appear much larger and there are whole starch granules. In photograph “b”, showing the <80 mm fraction, a large number of small, disintegrated starch granules can be seen within the protein matrix, together with a number of spherical compound granules. Fig. 1c shows a photograph of long-grain rice flour with a particle size of 106e180 mm. The particles look smoother and more compact than with the short-grain flour, which indicates that greater mechanical work will be necessary for disaggregation. In contrast, in Fig. 1a, short-grain particles show a rougher surface with loose starch granules that will separate more easily needing less mechanical work and so on suffering less damage. Moreover, this easily disaggregation could imply better water hydration and interaction when the rest of ingredients while bread-making.
50
100 80 60 40 20 0 0:00
0:30
1:00
1:30
2:00
2:30
3:00
Time (hh:mm) Fig. 3. Dough development curves from the rheofermentometer analysis of shortgrain breads. (a) 80 g water/100 g flour (b) 110 g water/100 g flour. Legend: ( ) ) Short grain, 80e106 mm; ( ) Short grain, 106e180 mm; Short grain, <80 mm; ( ) Short grain, >180 mm. (
TPA graph. Measurements were made on two central slices (20 mm thickness) from two breads from each dough. 2.2.5. Electron microscope photomicrographs Flour and dough photomicrographs were taken with a Quanta 200FEG (Hillsboro, Oregon, USA) environmental scanning electron microscope (ESEM), fitted with a backscattered electron detector (BSED). 2.2.6. Statistical analysis Differences between the parameters were studied for the flours and the breads by analysis of variance (ANOVA). Fisher’s least significant difference (LSD) was used to describe means with 95% confidence intervals. The statistical analysis was performed with the Statgraphics Plus V5.1 software (Statpoint Technologies, Inc., Warrenton, USA). Correlations were obtained using the same program.
3.2. Dough properties Fig. 2 shows the dough microstructures in photomicrographs taken with the ESEM. Fig. 2a and b show doughs elaborated with
Table 2 Physical properties of rice breads elaborated with 80 g of water per 100 g of flour. Grain type
Particle size interval (mm)
Specific volume (cm3/g)
Weight loss (g/100 g)
Firmness (N)
Cohesiveness
Springiness
Resilience
Short Short Short Short Long Long Long
>180 106e180 80e106 <80 >106 80e106 <80
3.11 3.47 2.40 1.71 2.13 2.08 1.63
13.87 13.75 13.90 15.46 14.40 13.48 14.72
4.33 a 3.36 a 12.37 b 35.94 c 34.49 c 38.09 c 50.89 d
0.37 0.39 0.44 0.43 0.35 0.29 0.29
0.54 0.56 0.76 0.70 0.61 0.67 0.54
0.16 0.18 0.23 0.25 0.12 0.15 0.18
d e c a b b a
a a a b ab a ab
Values with different letters in the same parameter are significantly different (p < 0.05). Measurements of specific volume and weight loss were performed in duplicate. Measurements of textural properties were made on two central slices from two breads of each dough.
a a a a a a a
a a b ab ab ab a
a a a a a a a
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203
Table 3 Physical properties of rice breads elaborated with 110 g of water per 100 g of flour. Grain type
Particle size interval (mm)
Specific volume (cm3/g)
Weight loss (g/100 g)
Firmness (N)
Cohesiveness
Springiness
Resilience
Short Short Short Short Long Long Long
>180 106e180 80e106 <80 >106 80e106 <80
3.93 4.09 5.10 4.13 4.75 4.65 3.04
21.87 21.13 21.20 21.06 20.70 21.53 21.72
1.40 a 1.62 a 0.99 a 2.29 a 1.13 a 2.60 a 15.61 b
0.47 0.47 0.60 0.53 0.29 0.31 0.31
0.57 0.62 0.91 0.93 0.86 0.85 0.86
0.22 0.20 0.35 0.30 0.11 0.10 0.12
b c e c d d a
a a a a a a a
b b d c a a a
a b d d c c c
b b d c a a a
Values with different letters in the same parameter are significantly different (p < 0.05). Measurements of specific volume and weight loss were performed in duplicate. Measurements of textural properties were made on two central slices from two breads of each dough.
80 g water/100 g flour. It may be observed that during kneading some of the starch compound particles had disintegrated and mixed with the HPMC, some protein particles and water, covering larger particles which had not been disaggregated during kneading. In Fig. 2b (coarse fraction), particles that had not disintegrated look coarser than those in doughs elaborated with finer fractions (Fig. 2a). In the case of long-grain rice (harder than the short-grain variety), there was less disintegration of the grains during kneading than in doughs elaborated with short-grain flours, and this will affect the final dough (Figure not shown). Fig. 2c, showing the dough elaborated with 110 g of water per 100 g of flour, reveals a similar structure to the doughs with 80 g of water per 100 g of flour. This structure is formed by simple starch granules mixed with HPMC, some protein particles and water, covering the larger flour
particles. However, the larger amount of water made the structure smoother, and large air spaces may be seen in these types of dough. These spaces do not disappear during proofing or baking, and they will be present in breads as large holes in the crumb. This fact has already been explained by McCarthy, Gallagher, Gormley, Schober, and Arendt (2005), who stated that as water and HPMC content increase, the gas cells coalescence to form larger cells. The waterHPMC gel structure linking the different particles of the dough may be observed in Fig. 2d. The graph in Fig. 3a shows the dough-development curves of doughs with 80 g of water per 100 g of flour during fermentation in the rheofermentometer. Only the curves of short-grain rice flour are presented as similar trends were observed with long-grain flour. As particle size increases, the dough-development curves
Fig. 4. Crumb detail of finished bread elaborated with 80 g water/100 g flour and 40 min proofing. Legend: Short grain, <80 mm; Short grain, 80e106 mm; Short grain, 106e180 mm; Short grain, >180 mm.
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rise higher. This would suggest that the breads will have a greater volume. With both types of flour, the coarsest fraction showed significant differences with respect to the other fractions. It may be clearly seen that the <80-mm fraction did not increase in volume, indicating that the gas produced was not retained. Fig. 3b shows the behaviour of short-grain rice-flour dough with 110 g of water per 100 g of flour. In this case, the <80-mm fraction did show development, but the structure broke up after approximately 90 min of fermentation, allowing the retained gas to escape and causing the curve to fall. There were no significant differences between the other fractions until after 2 h of fermentation, which is not typically reached in gluten-free bread-making. Development was greater in the case of breads with 110 g water/100 g flour and the dough had a better tolerance to excess proofing as, after 2 h, the curves continue to rise whereas, with the other formulation, they start to fall. The finer the flour particle size, the higher their surface area within the dough, meaning that a larger amount of water and HPMC will be necessary to link the dough; this probably explains why dough with larger amounts of water behave better. Although the mixture of water, HPMC and starch particles will weaken as water content increases, the 4% of HPMC used in this study was sufficient to maintain dough properties even with the higher water content. 3.3. Bread properties The properties of bread elaborated with 80 g water/100 g flour are listed in Table 2. The lowest specific volume of these breads was found with the finest fractions. When fractions over 80 mm were used, the short-grain rice flours were found to achieve higher
specific volumes than long-grain flours, and the highest specific volume was reached with short-grain flour with a 106e180 mm particle size. Lower specific volumes were found with doughs that expanded less during proofing (Fig. 3a). The differences between the specific volumes of the breads elaborated with the finest fractions and those elaborated with other fractions are therefore mainly due to differences in gas retention during fermentation. In the case of the >180-mm short-grain fraction (with the largest median particle size), the specific volume of the bread was lower than that of the bread elaborated with the fraction with a particle size between 106 and 180 mm, contrasting with the findings on the rheofermentometer curves. This would suggest that, in this particular case, the differences in specific volume were due to changes during baking. The physical properties of breads elaborated with 110 g water/100 g flour are shown in Table 3. The specific volumes in all these cases were higher than those of less hydrated breads, due to greater development of the doughs during proofing. As occurred with less hydrated breads, the fraction with a particle size <80 mm produced breads with a lower specific volume due to poorer development of the dough during proofing. Differences in the rheofermentometer curves between this fraction and coarser fractions were observed after 70 min. However, proofing times in this study, determined on the basis of previous studies (Kadan, Robinson, Thibodeux, & Pepperman, 2001; Pruska-Kedzior et al., 2008), were of less than 70 min and the rheofermentometer curves cannot therefore be compared directly with the specific volume values as dough development continued during the initial stages of baking. Based on these results, some fractions would have tolerated longer proofing times and would thus have achieved
Fig. 5. Crumb detail of finished bread elaborated with 80 g water/100 g flour and 40 min proofing. Legend: Long grain, <80 mm; Long grain, 80e106 mm; Long grain, >106 mm.
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better volume results. Another aspect to be taken into account is that gluten-containing breads are considered to have a longer shelflife when longer proofing times are used (Gomez, Oliete, Pando, Ronda, & Caballero, 2008). Higher volumes are achieved with long-grain rice-flour fractions >80 mm and with the 80e106-mm fraction of the short-grain flour. These fractions had a median particle size between approximately 90 and 120 mm (Table 1). Short-grain rice-flour fractions >106 mm were associated with lower specific volumes, as was observed with the largest particle size in breads with 80 g water/100 g flour. However, the negative effect of the coarsest fraction was more pronounced in the more hydrated breads. As no differences were observed during proofing, finding could have been due to changes in bread structure during baking. In addition, in both formulations, the finest particles did not behave well, probably due to a lack of gas retention during proofing. The specific volumes were lowest in the breads elaborated with these fractions, in agreement with the findings reported by Kadan et al. (2008) when studying the effect of different milling processes on flour properties. Choosing the wrong characteristics of the flours (type of flour and particle size) may lead to a loss of up to 40% in the specific volume in the case of breads elaborated with 110 g water/ 100 g flour, and of more than 50% in the case of the formulation with 80 g water/100 g flour. Analysis of weight loss showed no clear trends between the two types of rice or between flour-particle sizes. Formulations with 110 g water/100 g flour showed greater weight loss, probably due to the larger amount of water and also to the higher specific volume, which produces a greater surface area for evaporation. Regarding textural characteristics, breads with the 110 g water/ 100 g flour had lower firmness values due to their higher specific volumes and less compact structure. The only significant difference in firmness between the more hydrated breads was found with the finest fraction of the long-grain rice flour (highest firmness), and this bread also had the lowest specific volume. In the case of less hydrated breads, it was the amylose content rather than specific volume that had the greatest influence on firmness. Long-grain rice flour gave rise to higher firmness values than the short-grain flours. This effect may occur because long-grain flour has a higher amylose content, which produces more retrogradation phenomena (Singh, Kaur, Sandhu, Kaur, & Nishinari, 2006) and, therefore, firmer textures. The cohesiveness, springiness and resilience values depended on the formulations. There was hardly any difference in springiness between the formulations with 80 g water/100 g flour, and no differences in cohesiveness or resilience. The differences in springiness may be attributable to particle size, but no trend was observed. On the other hand, grain type and particle size were found to be important in the formulations with 110 g water/100 g flour. Breads of long-grain rice flour were not affected by particle size whereas those of short-grain flour showed significant differences between the different fractions. The highest values of cohesiveness, springiness and resilience were detected with the finer fractions, as was true for the only case which differences were detected in the less hydrated breads. Final crumb characteristics are determined by the combined amylose and amylopectin content. While amylose is required for crumb setting, due to its rapid retrogradation, amylopectin may counteract this effect, causing fresh bread to be softer (Schober, 2009). In Figs. 4 and 5 are shown the crumb detail of finished breads elaborated with 80 g of water per 100 g of flour for both short and long grain. Those breads elaborated with 110 g of water per 100 g of flour, although achieved greater specific volumes, were too weak and lost its consistency while slicing. This is the reason why photographs were not the spitting images of reality and so on are not shown. Overall, long grain bread slices seem lower than those from short grain. In addition, finest fraction, in both short and long grain
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type, show the closest pore structure, more compact and harder as showed firmness texture parameter. 4. Conclusions This study demonstrates that the characteristics of the rice flour used in gluten-free bread-making have a marked influence on the processing and quality of the products obtained. This influence is attributed mainly to their effects on dough microstructure. It will therefore be necessary, both in industry and in research, to clearly define the characteristics of the flour, using parameters such as particle size or the amylose/amylopectin ratio, in order to achieve consistent results. Effects vary depending on the formulation and, in particular, on the water content. Although proofing times in studies of gluten-free bread are typically less than 60 min, the rheofermentometer analysis has shown that, depending on the characteristics of the flour and the dough, an increase in fermentation times could lead to an improvement in bread volume, shelflife and sensorial characteristics. These aspects of the final bread should be evaluated in future studies. Acknowledgements This study was supported by a grant from the Spanish Ministry of Science and Innovation (Grant: AGL2011-23802) The authors are grateful to Harinera Castellana (Medina del Campo, Valladolid, Spain) for supplying the raw materials, and to Agro-Technical Institute- ITACYL (Castile and Leon, Spain) and to Esteve Santiago S.A. (Cabezón de Pisuerga, Valladolid, Spain) for protein and particle size measurements. References AACC. (2010). In Approved methods of the American Association of Cereal Chemists, methods 44-15.02 (moisture), 46-30.01 (protein), 61-02.01 (pasting properties), 10-91.01 (cake symmetry and volume index) (11th ed.) St. Paul, Minnesota, USA: American Association of Cereal Chemists. Araki, E., Ikeda, T., Ashida, K., Takata, K., Yanaka, M., & Iida, S. (2009). Effects of rice flour properties on specific loaf volume of one-loaf bread made from rice flour with wheat vital gluten. Food Science and Technological Research, 15, 439e448. Arendt, E. K., Morrissey, A., Moore, M. M., & Dal Bello, F. (2008). Gluten-free breads. In E. K. Arendt, & F. Dal Bello (Eds.), Gluten-free cereal products and beverages (pp. 289e311). Minnesota, USA.: Academic Press. Blanco, C. A., Ronda, F., Pérez, B., & Pando, V. (2011). Improving gluten-free bread quality by enrichment with acidic food additives. Food Chemistry, 127, 1204e1209. Brites, C., Trigo, M. J., Santos, C., Collar, C., & Rosell, C. M. (2010). Maize-based glutenfree bread: influence of processing parameters on sensory and instrumental quality. Food and Bioprocess Technology, 3, 707e715. Catassi, C., & Yachha, S. K. (2009). The epidemiology of celiac disease. In E. K. Arendt, & F. Dal Bello (Eds.), The science of gluten-free foods and beverages (pp. 1e13). Minnesota, USA.: Academic Press. Champagne, E. T., Wood, D. F., Juliano, B. O., & Bechtel, D. B. (2006). The rice grain and its gross composition. In E. T. Champagne (Ed.), Rice chemistry and technology (3rd ed.) (pp. 77e108) St. Paul, Minnesota, USA: American Association of Cereal Chemists. Czuchajowska, Z., & Pomeranz, Y. (1993). Gas-formation and gas retention. 1. The system and methodology. Cereal Foods World, 38, 499e503. Farrell, R. J., & Kelly, C. P. (2002). Celiac sprue. New England Journal of Medicine, 346, 180e188. Fitzgerald, M. (2006). Starch. In E. T. Champagne (Ed.), Rice chemistry and technology (3rd ed.) (pp. 109e142) St. Paul, Minnesota, USA: American Association of Cereal Chemists. Gallagher, E., Gormley, T. R., & Arendt, E. K. (2004). Recent advances in the formulation of gluten-free cereal based products. Trends in Food Science and Technology, 15, 143e152. Gan, Z., Ellis, P. R., & Schofield, J. D. (1995). Gas cell stabilization and gas retention in wheat bread dough. Journal of Cereal Science, 21, 215e230. Gomez, M., Oliete, B., Pando, V., Ronda, F., & Caballero, P. A. (2008). Effect of fermentation conditions on bread staling kinetics. European Food Research and Technology, 226, 1379e1387. Green, P. H. R., & Jabri, B. (2003). Coeliac disease. The Lancet, 362, 383e391. Gujral, H. S., Guardiola, I., Carbonell, J. V., & Rosell, C. M. (2003). Effect of cyclodextrinase on dough rheology and bread quality from rice flour. Journal of Agricultural and Food Chemistry, 51, 3814e3818.
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