Article
Optimization of corn, rice and buckwheat formulations for gluten-free wafer production Ismail Sait Dogan1, Onder Yildiz2 and Raciye Meral1
Abstract Gluten-free baked products for celiac sufferers are essential for healthy living. Cereals having gluten such as wheat and rye must be removed from the diet for the clinical and histological improvement. The variety of gluten-free foods should be offered for the sufferers. In the study, gluten-free wafer formulas were optimized using corn, rice and buckwheat flours, xanthan and guar gum blend as an alternative product for celiac sufferers. Wafer sheet attributes and textural properties were investigated. Considering all wafer sheet properties in gluten-free formulas, better results were obtained by using 163.5% water, 0.5% guar and 0.1% xanthan in corn formula; 173.3% water, 0.45% guar and 0.15% xanthan gum in rice formula; 176% water, 0.1% guar and 0.5% xanthan gum in buckwheat formula. Average desirability values in gluten-free formulas were between 0.86 and 0.91 indicating they had similar visual and textural profiles to control sheet made with wheat flour.
Keywords Gluten-free wafer, corn flour, rice flour and buckwheat flour, optimization Date received: 13 July 2015; accepted: 14 September 2015
INTRODUCTION Celiac disease in the individuals with a genetic predisposition is a disease characterized by malabsorption associated with ingestion of foods containing gluten (Mulder and Cellier, 2005). The disease develops as a result of sensitivity to wheat, barley, rye and oats glutens causing damage in the intestinal mucosa (Weisser, 2007). After removal of cereal grains such as wheat, rye and oat from the diet, the clinical and histological improvement in the celiac patients is observed (Ciclitira et al., 2001), but symptoms occur again with the addition of that grains into daily diets (Michael et al., 1999). Cereal gluten, the most common cause of gastrointestinal malabsorption in childhood, affects children and adults for a lifetime. Typically, it is characterized by chronic diarrhea, growth retardation, poor appetite, abdominal distension and by muscle weakness. Food Science and Technology International 22(5) 410–419 ! The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1082013215610981 fst.sagepub.com
The removal of gluten found in wheat, rye and barley for lifetime diet is the main therapy (Go¨kog˘lu, 2007). Production of gluten-free products has been increased with functional alternatives and new technology. The basic approach in the manufacture of these products is the employment of gluten-free flours containing various protein sources as alternatives to wheat flours. However, the lack of compliance with taste, lack of easy accessibility and insufficiency of gluten-free products in the market are also ongoing. The majority of gluten-free products are concentrated on bread; however, the studies on the production and optimization of commonly consumed gluten-free snack baked goods such as cakes, wafers have been very limited. 1 Department of Food Engineering, Faculty of EngineeringArchitecture, Yuzuncu Yıl University, Tu¸sba Van, Turkey 2 Department of Food Engineering, Faculty of Engineering, Igdır ˘ dır, Turkey University, Ig
Corresponding author: Ismail Sait Dogan, Department of Food Engineering, Faculty of Engineering-Architecture, Yuzuncu Yıl University, Tu¸sba Van 65080, Turkey. Email:
[email protected]
Dogan et al. In the preparation of gluten-free baked products for celiac sufferers, rice flour and starch are widely used instead of wheat flour. Rice products have the proper flavour and colour and are often preferred because of the gluten-free formulation contains digestible protein (Eliasson and Larsson, 1993). Very few studies for the production of corn bread as gluten-free foods have been carried out because of corn’s own distinctive flavour. Therefore, the use of corn products in gluten-free foods is not common (Arendt and Bello, 2008; De la Hera et al., 2013). However, the properties of gluten-free foods obtained from corn have similar quality attributes compared to the foods made from wheat flour. Quality criteria such as crumb porosity and bread volume of gluten-free bread produced using corn starch, commercial zein and HPMC is said to have similar properties to bread made with wheat flour (Schober et al., 2008). In other study, effects of various sizes of different flours including yellow maize, yellow semolina and white corns in combination with HPMC were investigated in terms of the dough rheological properties and gluten-free bread qualities. The coarser maize flours provided breads with more volume and less firmness than the finer flour breads due to the higher availability of dough to retain gas produced during fermentation and that increased bread volume (De la Hera et al., 2013). Wafer has little in common with the other sorts of biscuits in regard to the formulation and processing steps. Wafer is a low moisture product having crispy and crunchy texture, and made with a liquid batter consisting of a mixture of flour and water, with small amounts of butter, sugar, salt and sodium bicarbonate (Dogan, 2006; Martinez et al., 2004). Sometimes butter is removed from the formula. Wafer batter normally has a water content of more than 130 parts per 100 parts of wheat flour. However, biscuit is baked out of stiff dough in the oven. The obtained wafer sheets are sandwiched with cream containing shortening, starch and milk powder and cut with a special slicing device. Wafers are cereal foods consumed by all age, especially liked better by 6–12 age groups (Dog˘an et al., 2004). Very few studies on wafer production and quality evaluation have been done in recent years. These studies are related to shelf life of wafer; mainly physical ageing of wafer and water sorption and plasticization in wafer (Living et al., 1997; Martinez-Navarrete et al., 2004) because of crunchiness or crispness is considered primary textural feature of wafer. Some physical and chemical properties of wafer samples obtained from the market were investigated. The study showed that analyzed wafer samples were not produced according to quality standards, and their chemical compositions were statistically different from each other (P < 0.05). They concluded that in order to
make in the high-quality wafers it is necessary to obtain standardization in production and effective control by the official authority (Meral and Dog˘an, 2004). Although the production and consumption is high, we have not found any studies on the gluten-free wafers to be consumed by celiac patients. The aim of this study is to optimize gluten-free wafers using corn, rice and buckwheat flours as an alternative product for celiac sufferers.
MATERIALS AND METHODS Materials Special-purpose wheat flour used in the production of standard control wafer sheets was obtained from Bafra Eris Flour and Feed Industry Pty Ltd. (Samsun, Turkey). In the production of gluten-free wafer, corn and rice flour obtained from Aron-Tech Ltd. (Izmir, Turkey), buckwheat flour from Ecology Markets (Istanbul, Turkey) and potato starch, xanthan (the viscosity of 1% aqueous solution of ranged from 1300 to 1700 cP in 1% KCl) and guar gum (the viscosity of 1% aqueous solution of ranged from 2000 to 3000 cP) from (Adler Food Company Pty Ltd. (Istanbul, Turkey) were used. Table salt and sodium bicarbonate were obtained from local market. Methods Batter preparation and baking process. The batter components and their proportions used in the production of wheat flour (control) and gluten-free wafer sheets are given in Table 1. Upper and lower limits of the water level used in the experimental formulas were determined by preliminary testing to obtain desired water absorption and the batter consistency for given solid content. Water was first added into a laboratorytype wafer mixer with a 5-L capacity (Feza Mechanic, Karaman, Turkey). Salt and NaHCO3 were fully dispersed in water for 10 s. Then, flour was added when the mixer was running. Total mixing time of the batter was 4 min. Laboratory-type wafer baking plates (Feza Mechanic) was used to bake rectangular wafer sheets of 3 mm thick, 382 mm long and 282 mm wide. A 125 5 g portion of the batter was fed as a suspension onto the centre of the surface of the lower plate before quickly closing the upper plate and locking the lid. The upper and lower plate’s temperature were independently controlled and adjusted to 170 C (Dogan, 2006). Laboratory-type wafer toasts (baking plates) (Feza Mechanic Co., Karaman, Turkey) was used to bake wafer sheets of 3 mm thick, 382 mm long and 282 mm wide. The temperature of the upper and lower toasts was independently monitored with digital thermocouples. Baking plates (toasts) was heated before and 411
Food Science and Technology International 22(5) Table 1. The ratios of formula components used in the control and gluten-free wafer sheets (%)a Components Wheat flour Corn flour Rice flour Buckwheat flour Patoto starch Water Sodium bicarbonate (NaHCO3) Salt Xanthan gum Guar gum
Standard (Control)
Corn formula
Rice formula
Buckwheat formula
100 70 70
150 0.7 0.7
30 138.8–181.2 0.7 0.7 0.14–0.7 0.14–0.7
30 165–194.4 0.7 0.7 0.14–0.7 0.14–0.7
70 30 155.9–184.1 0.7 0.7 0.14–0.7 0.14–0.7
a
The level of all formula components other than wheat flour are given wheat flour weight bases (fwb).
maintained at the temperature of experimental baking trials.
prob after fracture (mm) were also considered as parameters of fragility.
Wafer batter density. Batter density (g/ml) of experimental wafer batters was obtained by dividing the batter weight to the weight of an equal volume of water according to AACC Method 55-50.01 (AACC, 2000). The measurement was obtained at the ambient temperatures.
Colour measurement of wafer sheet. A flatbed scanner was used to capture the colour image of wafer samples. The images were saved as TIFF files. The colour was analysed quantitatively (in terms of L, a, and b) using Photoshop software (Adobe Systems, 2000). Wafer sheet colours (in terms of L, a, and b values) were converted to L ¼ 0–100, þa ¼ 0–60, þb ¼ 0–60 as described by Dog˘an (2002).
Viscosity measurement of wafer batter. Viscosities of wafer batters were determined using Rapid ViscoAnalyzer (RVA-4, Newport Scientific Pty. Ltd., Warriewood, NSW, Australia). A viscosity measurement unit was expressed as RVU unit (1 RVU corresponds to about 12 cP). Viscosity measurement was performed for each of wheat flour substitution based on the experimental design. Dry blends of formula (flour, potato starch and gum, etc.) of 3 g (based on 14% moisture) were used for viscosity measurement; deionized water was added to stirring vessel according to the design and stirred at 30 C and 160 r/min. Texture analysis of wafer sheets. The experimental wafer sheets were conditioned for 24 h before testing to obtain moisture equilibration within sheets. A texture analyser (TA.XT Plus; Stable Micro Systems Ltd., Godalming, Surrey, UK) was used to measure the hardness and resistance of wafer sheet to snap using a three-point bending test attachment fitted with a 5 kg load cell (as described in BIS4-3PB method). A piece of 4 cm 4 cm sheet was cut out and loaded at the center of the unit until the fracture occurred. A stainless steel plunger (100 dia ball) was employed at a displacement rate of 3 mm/s before and during testing. Post-test speed was 10 mm/s. The force at the fracture point was registered as hardness value (g). The distances of 412
Statistical analysis. Formula optimization of glutenfree wafer sheet was performed using response surface method (RSM). Optimum levels of modified components in each wafer sheet formulation were determined using Response Surface Methodology. The effects of water level and gum combinations in corn, rice and buckwheat formula as wheat flour replacement were tested with ‘‘central composite’’ model using the (2^2 þ star). Two replications were made for each reported measurements for the control wafer attributes. To produce wafer sheets having similar attributes to wheat flour wafer, the tested water absorption levels (%), the ratio of guar and xanthan gam combinations as experimental factors are given in Table 2. The effects of each factor, including in the model were evaluated to observe their effects on each given quality attributes. It was aimed to reduce uncontrollable variance by randomizing the experimental trials. The attributes of gluten-free wafer sheets were compared with control formula, and the obtained data were analyzed using StatGraphics Centurion 15.1 (StatGraphics, 2006). Significant difference between group averages was determined using Duncan multiple comparison tests at the level P < 0.05. The appropriate response values for each formulation were determined.
Dogan et al. Table 2. Tested water levels and gam ratios for corn, rice and buckwheat formulas Corn formula
Rice formula a
Trail
Water (%)
Gum
1 2 3 4 5 6 7 8 9 10 11
175.00 145.00 160.00 160.00 181.21 160.00 145.00 160.00 175.00 160.00 138.79
1 1 1.41 0 0 0 1 0 1 1.41 0
Buckwheat formula a
Water (%)
Gum
194.14 165.86 180.00 180.00 190.00 190.00 180.00 180.00 170.00 180.00 170.00
0 0 0 1.41 1 1 0 0 1 1.41 1
Water (%)
Guma
180.00 160.00 160.00 170.00 184.14 170.00 170.00 170.00 170.00 155.86 180.00
1 1 1 0 0 0 1.41 1.41 0 0 1
a (1 ¼ 0.1 guar and 0.5 xanthan; 0 ¼ 0.3 guar and 0.3 xanthan; 1 ¼ 0.5 guar and 0.1 xanthan; 1.41 ¼ 0.14 guar and 0.7 xanthan; 1.41 ¼ 0.7 guar and 0.14 xanthan).
Table 3. The characteristics of wheat flour (WF) wafer sheets as control Attributes
Values
Batter density (g/ml) Hardness (g) Fragility (mm) L a b
1.18 0.12 283.32 43.43 65.54 0.36 85.53 1.94 20.18 0.65 52.60 2.14
adversely affected causing difficulties. In order to eliminate negative flavour and fragility of the product and to improve functionality in the process, we have investigated the possibilities of usage and ratio of potato starch in the preliminary trials and have obtained positive results. Comparable wafer sheets in terms of appropriate taste, texture (brittleness, crispiness) and spread rate (uniformity) were obtained with 30% potato starch replacement level to each gluten-free substitution (corn, buckwheat or rice) as indicated in Table 1. Gluten-free batter attributes
RESULTS Wheat flour (control) wafer sheets The batter components and their proportions given in Table 1 were used to produce wheat flour sheets as control. Analyses of control wafer sheets are given in Table 3. These values are considered as reference values for determining the quality of experimental gluten-free wafer sheets. Potato starch in gluten-free formula In the preliminary trials, we encountered some difficulties with wheat flour substitutes (corn, rice and buckwheat flour) when we formulated at the 100% substitution rate in the study in terms of unpleasant taste in corn, higher fragility in rice and low spread rate to baking plate in buckwheat flour. Briefly the product’s taste profile changed, and wafer processing were
In terms of determination the appropriate water level and gum combinations to produce gluten-free wafer sheet using corn (CF), rice (RF) and buckwheat (BF) formulas, the evaluated levels of water and gums are given in Tables 1 and 2. The goal was to produce wafer sheets having similar attributes to wheat flour wafer. Batter density. Densities of wafer batters prepared with CF, RF and BF as a replacement of wheat flour were 0.87–0.91 g/ml, 0.85–1.19 g/ml, and 0.95–1.07 g/ml, respectively (Figure 1). Lowering water level and higher guar level in gum blend slightly increased batter density. Only interaction effect of different water and gum levels on density of CF dough was statistically significant (P < 0.05). In RF, the effect of water level and interaction effect of water and gum levels on density was statistically significant (P < 0.01). The effect of water level was only found significant In BF (P < 0.01). The regression coefficients (r2) of the model were 84.30, 89.66 and 89.66, respectively. The suggested models, including linear, quadratic and 413
Food Science and Technology International 22(5)
Rice Formula
Corn Formula 0.91
1.0
0.90
0.91
1.0
1.00
1.02
1.04
1.0 0.9
0.98
1.1
0.5
0.90
0.5 1.0
0.90
1.04 1.04
0.9
0.0
0.89
1.02
1.00 0.96
0.89
0.0
1.04 1.02
1.0 1.1 1.2
Gum (Coded)
0.9
1.0
0.88
0.89
0.5
Buckwheat Formula
1.1
1.2
0.87
0.89
0.0 0.98
1.1 1.0 0.89
–0.5
0.88
–1.0
0.87 0.89
0.88
0.87 0.90
140
–0.5
0.88
0.89
145
150
0.90
155
160
165
1.1 1.3
1.04
0.9
170
175
1.06
1.02
1.00
0.9
1.04
0.96
180
170
175
Water Level (%)
180
185
1.06
0.98
–1.0 1.0
1.2
0.85
0.89
1.02
1.00 0.96
–0.5
–1.0 0.86
0.9
1.2
1.08
160
190
165
Water Level (%)
170
175
180
Water Level (%)
Figure 1. Effect of water level and gums in CF, RF and BF on batter specific weight (g/ml).
Corn Formula
Rice Formula 1400
2000
3000
3000
600
1200
1400
1000
1.0
Buckwheat Formula
1400
0
1000
800
1.0
2500
1.0
2500 2500
2000
2000
1000 1500
2000 1400
Gum (Coded)
0.5
1200
0.5
2000
1000
1000
0.5 2500
2000
3000 1400
0.0
0.0
1500
1200
1600
0.0
4000
3000 2000
–0.5
2000 2500
3000
–0.5
–0.5
1200
1400
1500
1600
–1.0
4000
–1.0
2000
1000 1400
145
150
155
160
165
Water Level (%)
170
175
180
170
175
2000
1500
1200
1800
140
–1.0 2500
1600
3000
180
185
190
160
165
Water Level (%)
170
175
180
Water Level (%)
Figure 2. Effect of water level and gums in CF, RF and BF on batter viscosity (cP).
interaction effects of water level, xanthan and guar blend level on batter density explains 84.30% of changes in CF, 89.66% in RF, and 84.30% in BF. Batter viscosity. Batter viscosities for experimental gluten-free batters varied between 728.0 and 4165.0 cP for CF, 895.0 and 1682.0 cP for RF, 1156.0 and 3114.0 cP for BF batters (Figure 2). The suggested model, including linear, quadratic and interaction effects of water level, xanthan and guar levels in the blend explains 95.20% (r2: 95.20), of changes in batter viscosity for CF, 71.44% (r2: 95.20) for RF, 71.75% (r2: 95.20) for BF. Increasing water level in the formula significantly lowered batter viscosity (P < 0.01 in CF; P < 0.05 in RF and BF). Increasing the level of guar in gum blend slightly reduced the batter viscosity, but was not statistically significant. The quadratic and interaction effects of water level, xanthan and guar level in the blend for all formulas were not also significant (P > 0.05). 414
Gluten-free wafer attributes Wafer sheet fragility. Gluten-free wafer sheet fragility changed between 65.80–66.51 mm for CF, 65.32– 66.08 mm for RF, 64.83–65.81 mm for BF batters. Change interval was relatively small and had a value close to control wafer sheet made with wheat flour (Figure 3). Increasing the amount of water added to the formulas slightly increased fragility, but the changes in the gum blend didn’t affect the fragility. The linear, quadratic and interaction effects of water level, xanthan and guar level on fragility for CF and RF were not significant (P > 0.05); however, the quadratic effects of water level on fragility for BF were significant for CF (P < 0.05). Wafer sheet hardness. Sheet hardness of gluten-free wafer prepared with corn, rice and buckwheat formulas as a substitute of wheat flour were 130.45–291.71 g, 175.13–265.30 g, and 184.81–320.23 g, respectively
Dogan et al.
Rice Formula
Corn Formula
Buckwheat Formula 65.8
65.8 66.2 66.0
1.0
65.8
65.6
65.4
65.8
65.6
65.6
1.0
65.6
1.0 65.6
65.6
65.6
65.4
65.4 65.2
0.5
66.2
66.4
0.5
Gum (Coded)
66.0
65.6
65.6
65.8
65.0
0.5 65.2
65.4
65.2
65.0 66.0
0.0
0.0
65.0
0.0
65.4
66.0 66.2
66.4
65.6
65.6
66.2
–0.5
65.8
65.2
65.8
–0.5
65.4
65.2
–0.5
65.4
65.0
66.4
66.0 65.8 66.4
–1.0 66.2
66.6 66.8
140
66.2
66.0
66.0
66.6 –1.0
66.0
150
155
160
165
170
175
180
170
175
Water Level (%)
180
65.2
66.2
66.0
66.4
145
65.6
–1.0
65.8
185
65.4
160
190
165
Water Level (%)
65.6
170
175
65.8
180
Water Level (%)
Figure 3. Effect of water level and gums in CF, RF and BF on wafer sheet fragility (mm).
Rice Formula
Corn Formula 250
250 260
200
250
240
150
1.0
1.0
250
1.0
220
260
300
0.5
Gum (Coded)
Buckwheat Formula
280
300
200
220 240
150
0.5
200
200
0.5
200
200 240
180
0.0
0.0
–0.5
–0.5
220
220
240
250
200
200
180
240
150
250
0.0
220
200
200
–0.5
250
300
250
200 250
–1.0
240
–1.0 200
200
220
350 220
240
260
300
140
145
150
155
160
165
Water Level (%)
170
175
180 –1.0
180
170
175
180
185
300
200
190
250
250 300
160
Water Level (%)
165
170
175
180
Water Level (%)
Figure 4. Effect of water level and gums in CF, RF and BF on wafer sheet hardness (g).
(Figure 4). The suggested model, including linear, quadratic and interaction effects of water level, xanthan-guar blend level explains 98.84% (r2: 98.84) of changes in batter viscosity for CF and 79.34% (r2: 79.34) for RF. The effect of that tested factors on hardness of BF wafer sheet was found insignificant. Linear effect of water level in CF formula was significant on wafer hardness value (P < 0.001); Quadratic effect of water level also found significant (P < 0.01 in RF; P < 0.05 in BF). Lowering the amount of water added to the formulas dropped wafer hardness. Wafer sheet colour. Colour lightness values (L) of gluten-free wafer sheet changed between 80.75 and 86.80 for CF, 85.59–92.95 for RF and 80.40–86.55 for BF wafer sheets (Figure 5). L values of CF and BF were close to L values of control wafer sheet made with
wheat flour. L values of wafer sheets produced from RF were higher than the control value. Increasing the amount of water and xanthan gum in gum combination slightly increased sheet lightness value (L) for all formulas. However, linear, quadratic and interaction effects of water level, xanthan and guar level on lightness value for all formulas were not significant (P > 0.05). Gluten-free wafer sheet colour a values changed between 17.89 and 20.31 for CF, 16.46–18.78 for RF and 20.01–21.16 for BF wafer sheets (Figure 6). Linear, quadratic and interaction effects of water level, xanthan and guar level on colour a value for all formulas were not significant (P > 0.05). Colour b values were 54.04–61.10 for CF, 35.87– 42.25 for RF and 40.32–42.64 for BF wafer sheets (Figure 7). The effects of that tested factors on RF 415
Food Science and Technology International 22(5)
Corn Formula 78
Rice Formula
82
88
80
1.0
Buckwheat Formula
86
84
86
1.0
88 86
82
86 84
88
0.5
Gum (Coded)
88
84
1.0
86
82
86
0.5
84
90
0.5
84
88 86
0.0
92
0.0
86
86
82
86
90 90
0.0 84 82
92
90 86
–0.5
90
–0.5
–0.5
90 90
–1.0
90
–1.0
86
84
88
–1.0
86
84 86
88
90
86
Figure 5. Effect of water level and gums in CF, RF and BF on wafer sheet color (L) value.
Rice Formula
Corn Formula
Buckwheat Formula
17.5
20
18.5
18
21
20.0 19.5 19.0
19 18.0
1.0
1.0
20
20.6
20.6 20.6
0.5
17.5
17.5
19
Gum (Coded)
20.2 20.4
18.0
17.5
0.5
0.5
20.0
20.6
1.0 18.5
18
19.8
20.2 20.4
20.8
20.8
21.0
17.0 19
0.0
0.0
0.0
21.0 20.8
16.5
–0.5
–0.5
20.8
21.0
–0.5
17.0
20.6
20.6
20.4 20.2
–1.0
–1.0 18
20.8
–1.0
17.5
21.0
20.0
20.4
20.6
140
145
150
155
160
165
170
175
180
170
175
180
20.0
185
190
160
165
Water Level (%)
Water Level (%)
19.8 19.6 19.4
20.2
17.5
170
175
180
Water Level (%)
Figure 6. Effect of water level and gums in CF, RF and BF on wafer sheet color (a) value.
Rice Formula
Corn Formula 42
40
41
60
62
1.0
Buckwheat Formula
42
56
42.0
41
41
1.0
58 56
41.5
41.0
41.0
40
40
42.0
40 60
0.5
41.5 39
39
0.5
0.5
41.5
Gum (Coded)
40 42.5
39
58
58
38
38
0.0
0.0
42.0
41
0.0
39
41.5 41.5
38
56
40
–0.5
–0.5
41.5
1.0
40
–0.5
42.0
42.5
41.0 41.0
38
56
39
39
40.5
38
–1.0
–1.0
54
–1.0 41.5
56 58
140
145
150
155
39
52
58
38
42.5
42.0
160
165
Water Level (%)
170
175
180
170
175
180
185
190
160
Water Level (%)
Figure 7. Effect of water level and gums in CF, RF and BF on wafer sheet color (b) value.
416
41.0
40.5
170
175
40.0
40
165
Water Level (%)
180
Dogan et al. and BF wafer sheet colour b values were found insignificant (P > 0.05); however it was found significant in CF giving higher yellow tones (higher b values) in wafer sheet colour. The suggested model for CF wafer sheet colour b value including linear, quadratic and interaction effects of water level, xanthan-guar blend level explains 91.78% (r2: 91.78) of changes in colour b value for CF. Gluten-free wafer sheet optimization One of the most popular methods preferred in product development for improving the quality is the optimization of multiple factors and the use of desirability values. For this purpose, multiple response optimizations are widely used (Dogan and Yildiz, 2010). The average desirability value is obtained when all the factors are evaluated together and that ranges from 0 to 1. This value is the geometric mean of desirability value of each factor (Dog˘an et al., 2012). Quality criteria of control wafers are used to optimize each gluten-free formula. Considering all evaluated quality criteria, the best CF wafer sheet was produced using 163.5% water level, 0.5% guar and 0.1% xanthan gum (fwb). The attributes of this formula combination yielded similar wafer sheet to the control. Average desirability value of gluten-free CF wafer sheet was 0.905. Wafer sheet having attributes close to the control was produced using 173.3% water level, 0.45% guar and 0.15% xanthan gum (fwb) in RF. Average desirability value of RF wafer sheet was 0.861. BF wafer sheet having attributes close to the control was produced using 176% water level, 0.1% guar and 0.5% xanthan gum (fwb). The attributes of this formula combination yielded similar wafer sheet to the control. Average desirability value of RF wafer sheet was 0.858. The wafers produced by experimental formulations are depicted in Figure 8.
Wheat
Corn
Rice
Buckwheat
Figure 8. Wafer samples produced from experimental formulas.
DISCUSSION In the study, density of wafer batters prepared wheat flour was 1.18 g/ml. Densities of the experimental batters varied from 0.85 to 1.19 g/ml depending on type of gluten-free flours, i.e. corn, rice and buckwheat flour. Densities close to the control were 0.9 g/ml for CF, 1.07 g/ml for RF and 1.11 g/ml for BF. They were often lower than the control values. Lowering water content in the formula and increasing guar level in the gum blend, on way or another, altered batter density. Water and gum interactions effect in CF, water level and water and gum interactions in RF, water level in BF were statistically significant (P < 0.05). Presence of substances such as increased water level and gums altered wafer batter consistency at different levels. In the earlier study, wafer batter densities varied between 1.11 and 1.19 g/ml (Dogan, 2006). The batter density should be in a narrow range (1.14–1.15 g/ml) (Wade, 1988) to facilitate precise volumetric deposition onto baking plate to obtain sheets having similar textural properties such as crispiness and fragility. The study showed that measurement of batter viscosity was more important than density to obtain desirable batter consistency. The water level included in the each formula significantly affected batter viscosity. Xanthan in the gum blend increased the viscosity values somewhat. Batter viscosity should be controlled to obtain complete and crispy sheets (Beckett et al., 1994; Dogan 2006). Batter viscosity should be carefully controlled to improve spreadibality on the baking plate depending on what substitutes to be used instead of wheat flour in wafer production. The batter holding time is meanwhile critical before depositing onto baking plate. In the earlier study, it was also observed that temperature and batter viscosity are critical after mixing and during pouring onto hot-plate (Dogan, 2006). Therefore, to obtain a homogeneous quality in the wafer production, many variables must be monitored and controlled throughout the wafer production steps (Beckett et al., 1994; Dogan, 2006). Wafer sheet colours are affected by batter components and baking plate temperature. Light-coloured wafer sheet (higher L value) is desirable (Dog˘an et al., 2004). L value of 85.53, a value of 20:16, and b value of 52.59 were determined as colour values of wafer batters prepared wheat flour. The colour L, a, and b values of gluten-free wafers nearest to the control were 85.38, 18.50 and 57.58 for CF; 88.35, 17:44 and 40.00 for RF; 85.00, 20:33 and 40.58 for BF, respectively. Although there is a slight increase in the lightness value (L) with increased water content and increased xanthan in the combination, this increase were not found significant (P > 0.05). On increasing the 417
Food Science and Technology International 22(5) amount of water used in the formula only the changes in colour b value of CF wafer sheet were found statistically significant (P < 0.05). According to Dogan (2006) among the colour values of the wafer produced with wheat flour L values were between 74.80 and 88.42, a values were between 0.36 and 10.60, and b values were between 22.11 and 40.07. For acceptable wafer sheet suggested colour L, a, and b values were 82 2, 4 2 and 32 2, respectively. In general, the fragility slightly increased with increasing the amount of water used in the formula; variations of gum type in the blend however did not affect this value. A significant variation in fragility was only observed in BF with increased water content. In an earlier study, a digital penetrometer was used to measure the fragility and crispiness of the wafer sheet. The wafer sheet was punched and the distance to travel was recorded at one-tenth of a millimetre. The effects of water level, gluten content and baking temperature on penetrometer values were found significant (P < 0.01). The most important factor was found baking plate temperature. Wafer colour was darker and more fragile when baked at the higher temperature of 175 C (Dogan, 2006).
CONCLUSIONS The amount of water, type and amount of gum added to the flour in ensuring the desired batter consistency are very important in gluten-free wafer production. Measurement of batter viscosity is more important than density in controlling deposition of batter, completeness of wafer sheets, providing desirable crispness and controlling fragility. Amounts of water to be used for the production of wafer sheets with similar properties to the control product ranged from 164 to 176% in all three formulas. Furthermore, the type and amount of gum in the blend is varied depending on wheat flour substituents used. The amount of gum to be used for the desired wafer characteristics must be adjusted depending on each formula. Ensuring optimum wafer batter consistency is critical in terms of wafer processing and final wafer properties. Therefore, the main components must be optimized in each formula, separately. Fragilities of gluten-free wafer sheets containing rice, corn and buckwheat had similar texture as compared to the control. However the hardness of wafer sheet made with buckwheat flour yielded the highest in terms of hardness. DECLARATION OF CONFLICTING INTERESTS The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
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FUNDING The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this _ article: This work was funded by a Grant (2012-MIM-B010). The authors would like to thank Chairmanship of Scientific Research of Yuzuncu Yil University for financial support.
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