Dough rheology, pasting property, and steamed bread quality of wheat flour as affected by the addition of sprouted wheat flour

ABSTRACT

Grain sprouting poses a significant global challenge, especially for wheat. Nonetheless, recent investigators have unveiled numerous benefits of germination. In this study, we incorporated various proportions of sprouted wheat flour (SF) into wheat flour to produce sprouted wheat steamed bread (SWSB). The impact of SF on the quality of flour and SWSB was evaluated, resulting a development of GABA-enhanced, green-healthy SWSB. With increased addition of SF, the falling number, pasting viscosity, and dough stability time of flour exhibited significant decreases, whereas the gluten index initially increased and then decreased. The textural properties, such as hardness, chewiness, adhesion, springiness, and cohesion, exhibited varying degrees of fluctuation with increasing SF levels. The specific volume of SWSB was optimal at an SF concentration of 6% and the sensory score was highest at 2%. Lightness of SWSB was comparable to that of the control at 4% SF addition. C-cell images revealed that the fineness of the SWSB texture initially increased and then decreased with increasing SF levels. Overall, an SF concentration of 4% was found to be optimal for dough properties, color, texture characteristics and sensory quality, providing a theoretical foundation for industrial production and application.

KEYWORDS:

• Sprouted wheat
• steamed bread
• properties
• quality

Introduction

Wheat (Triticum aestivum L.), following maize and rice, is one of the most extensively cultivated crops globally(FAO, 2014).^[1] Wheat flour plays a vital role as a critical primary ingredient in the production of various food products, such as bread, cookies, pasta, biscuits, cakes, noodles, and breakfast cereals.

Unfavorable weather conditions such as repeated and prolonged rainfalls, and abnormal temperature after physiological maturity impede the harvest and trigger germination of kernels in the parent plant in the field, known as preharvest sprouting (PHS). The PHS phenomenon is a widely recognized and prevalent problem issue, occurring once or twice per decade in several major wheat-producing areas worldwide. In some humid regions, PHS might occur annually or even more frequently.^[2,3] Furthermore, sprouting may occur in wheat with improper storage or inadequate dried drying after harvest.^[4]

Farmers and distributors, worldwide incur direct annual losses estimated to be as high as 1 billion dollars a year due to sprouting.^[3] The cereal-based food industry faces the challenge of adjusting to the unstable technological quality of raw wheat flour to meet the diverse consumer demands in the food process. Consumers, on the other hand, may encounter food products that deviate from their expectations, leading to high returns and complaints. Since sprouted wheat is generally unsuitable for food production and consumption,^[5] it is often downgraded for animal feed, resulting in a price reduction by about 20% to 50%.^[6]

From an academic perspective, wheat kernels, like other seeds, require the appropriate moisture and temperature to initiate germination.^[7] The release and synthesis of plant hormones such as abscisic acid, ethylene, and gibberellic acid occurs when the humidity reaches a critical level. These hormones stimulate the production of amylase, lipase, and proteases during wheat sprouting. The increase in amylase content leads to a reduction in the peak viscosity of the starch, affecting starch functionality. The elevation of proteases can potentially depolymerize gluten-forming proteins, leading to reduced dough consistency. The rise in lipase activity causes lipid breakdown and auto-oxidation, leading to off-flavors in the final product. Consequently, the resulting flour has poor process characteristics, such as rough bread, sticky buns, and an increased rate of noodle breakage.^[8,9]

The trend toward green and healthy food has sparked a growing interest in the potential nutritional benefits of sprouted grains. Recent studies have demonstrated substantial increase in specific nutrients, such as folic acid and gamma-aminobutyric acid (GABA) during the germination process. GABA, a non-protein amino acid also known as 4-aminobutanoic acid or 4-aminobutyric acid, is widely present in bacteria, plants, and vertebrate animals. In animals, it serves a crucial in various physiological functions, such as neurotransmission, blood pressure regulation, cell signaling, and hormonal regulation. Additionally, it exhibits protective effects against a wide range of diseases, including brain diseases, psychiatric diseases, cancer, cardiovascular diseases, and respiratory diseases.^[10] As a bioactive compound, GABA has been authorized for use in functional foods in China, the United States, Japan, and several European countries.^[11] While GABA production has been studied in brown rice, researchers have also observed variations in GABA content during the germination of wheat and barley.^[12]

Steamed bread, also known as Chinese mantou, is a traditional Chinese staple food with a rich history dating back 1,700 years and is widely consumed around the world.^[13] Its distinct taste and flavor, steamed bread has contributed to its popularity in certain European and American countries.^[14] To date, there has been limited research conducted on Chinese steamed bread prepared using wheat flour substituted with sprouted wheat flour (SF).

In this study, SF was utilized as a green raw material in the production of Chinese steamed bread, with the wheat flour supplemented by gamma-aminobutyric acid (GABA)-enhanced SF. The research aimed to investigate the effects of different doses of SF on the rheological properties, pasting characteristics, wet gluten, falling number (FN), color, texture, sensory, and inner structure of the steamed bread. Furthermore, the study determined the optimal amount of SF required to attain the highest quality of steamed bread. The findings of this study lay a theoretical foundation for future research on the potential application of sprouted wheat in the food industry, and highlights the potential to enhance the nutritional and commercial value of sprouted wheat for human consumption.

Materials and methods

Materials

The steamed bread wheat flour utilized in the study was provided by Hubei Fengqingyuan Grain and Oil Group Co., Ltd. and active dry yeast was purchased from the local market. Wheat grains of a particular variety Fu-wheat 1228# were purchased from the Agricultural Market. Unless specified otherwise, all reagents used in the experiment were of analytical grade.

Sprouted wheat and sprouted wheat flour (SF)

Wheat grains were cleaned and soaked in water with a ratio of 1:3 in a beaker for 6 hours at room temperature. The grains were subjected to a four-day germination period in a growth chamber under dark conditions,^[15] at a temperature of 20°C and a relative humidity of 80%. The treated sprouted grains were dried by hot air (DHG-9053A, Jinghong, Co., Ltd., Shanghai, China) until the moisture content was less than 12%, and then milled (YB-1000A, Sufeng, Co., Ltd., Yongkang, China) until the flour could pass through a 100 mesh sieve. Five different flour blends were prepared, regular flour was replaced with whole SF at levels of 2, 4, 6, 8, and 10 g/100 g, respectively. The GABA content of the SF was extracted by ELISA method (Nanjing Jiancheng Biological Engineering Research Institute, Co., Ltd., Jiangsu, China).^[16]

Physicochemical composition and characteristics of SF

Both cleaned wheat and sprouted wheat underwent a battery of physico-chemical quality analyses to determine their characteristics, including moisture content, protein content, starch, gluten, ash, lipid and γ-aminobutyric acid. The flour blends from the wheat samples were also subjected to analysis of their proximate composition by the methods outlined in AACC (2000) and previously reported by Shafi et al..^[17] Additionally, the falling number value (in seconds) was measured by a lab instrument (FN-1310, Falling Number Apparatus, Perten, Co., Ltd., Sweden) accredited with ISO-17025.

The Mixolab® (Chopin Technologies, Villeneuve La Garenne, Co., Ltd., France) was used to determine the rheology of flours by the standard “Chop+” protocol: initial equilibrium at 30°C for 8 min, heating to 90°C over 15 min (at a rate of 4°C/min), holding at 90°C for 7 min, cooling to 50°C over 5 min (at a rate of 4°C/min) and holding at 50°C for 5 min. The mixing speed was kept constant at 80 rpm. The flour with water was 75 g，target torque was 1.1 ± 0.05 N·m.^[18] The pasting properties were determined using a rapid visco analyzer (RVA) (RVA-super4, Newport Scientific, Warriewood, Ltd., Australia) following the AACC Method 76–21.

Sprouted wheat steamed (SWSB) production^[19]

Upon dissolution of 0.8% yeast in a suitable quantity of warm water (30°C), the resulting aqueous solution was added to the mixed flour. The dough was prepared after flour mixing for 10 min at a medium speed (120 rpm) with a mixing machine (J092, National MFG, Ltd., USA), with the appropriate amount of water determined based on the flour water absorption capacity. The homogeneous mixture was then formed into 120 g dough balls by hand, which were subsequently fermented in a controlled fermentation box (JXFD, East-food, Co., Ltd., Beijing, China) at 30°C and 85% relative humidity for 40 minutes. The fermented dough was then steamed for 25 minutes in a tray situated above boiling water and allowed to cool at 25°C or 1 hour before further analysis.

Color determination of SWSB

The sample was cut into 15 mm sheet, and the L*, a*, b * (lightness-darkness) value was determined using a colorimeter (CR-10, Shengguang, Co., Ltd., Suzhou, China). Each sample was tested three times.

Specific volume and sensory evaluation of SWSB

The specific volume of the cooled steamed bread was measured by a food volume detector (BVM-L370, Perten, Co., Ltd., Sweden). To evaluate the sensory properties of the steamed bread, ten trained panelists from Wuhan Polytechnic University assessed various attributes, including appearance, flavor, viscoelasticity, palatability, and internal structure. The sensory evaluation was carried out in accordance with the Chinese standard method GB/T 35,991–2018, with minor modifications. In Table 1, a numerical score between 0 and 100 was assigned to each attribute, and a mean score was computed for each steamed bread sample.^[20]

Instrumental texture analysis of SWSB

The texture properties of SWSB were determined by a texture analyzer (TA-XT plus, Stable Micro Systems, Co., Ltd., UK) equipped with a P-45 probe after 1 hour of cooling. Two slices of 25 mm thickness taken from the middle of SWSB were analyzed. The trigger force and the pressing height were 5.0 g and 50% of the original height of steamed bread, respectively. The pretest, test and posttest speeds were set to 1 mm/s, 1 mm/s and 1 mm/s, respectively, following the methodology described by Luo et al.,^[21] with some modification. The texture parameters such as hardness, cohesiveness, springiness, gumminess, and chewiness were measured and recorded.

Image analysis of SWSB

The SWSB was cooled for 1 h initially and then sliced transversely to obtain uniform slices of 15 mm thickness. Two slices taken from the center were tested by a food image analyzer（C-Cell, Perten, Co., Ltd., Sweden).

Statistical analysis

The experimental data were expressed as mean ± standard deviation (SD). One-way analysis of variance (ANOVA) was performed using SPSS statistical software (SPSS, Inc, USA). Duncan’s multiple range tests were used to compare means at a significance of 0.05.

Results and discussion

Chemical compositions of wheat flour and SF

The compositions of original wheat flour and SF used in this study is detailed in Table 2. The total protein, fat, starch, moisture, and ash contents of SF were found to be significantly lower than those of non-sprouted wheat (p < .05). Conversely, the GABA content of sprouted wheat increased by 49.57%. The increase in GABA content during sprouting is a universal phenomenon across grain species, which is consistent with the findings of Cornejo et al.^[22] Disregarding the impact of sprouting on the machining characteristics of grains, the rise in bioactive compound GABA content contributes the potential of sprouting production to be “functional foods.”

Table 1. Quality scoring system for SWSB.

Quality parameter	Full score	Scoring criteria
Specific volume	20	Specific volume ≥2.8 mL/g = 20; Specific volume ≤1.5 mL/g = 5; 2.8 mL/g ≤ Specific volume ≤1.5 mL/g, minus 1.5 score per 0.1 mL/g reduction
Width to height	5	Width to height ≤ 1.4 = 5; Width to height ≥ 1.6 = 0; 1.4 ≤ Width to height ≤ 1.6, minus 1 score per 0.05 increase
Elasticity	10	Rebound quickly, can be compressed more than 1/2 = 7–10; Rebound slowly or does not rebound = 3–6; Difficult to compress, very hard = 2–6
Surface color	10	White, milky white = 8–10; Light yellow, yellow = 6–7; Gloom = 4–5
Surface structure	10	Smooth = 8–10; Uneven, pliable, air bubble or concave = 4–7
Interior structure	20	Tiny pores, uniform = 18–20; Tiny pores, uniform with several vesicles = 13–17; Close pores, uniform or separated between the edges and the epidermis = 10–12; Large pores, rough structure = 5–9
Chewiness	10	Chewy = 7–10; Tender, crumble, low elasticity = 4–7
Stickiness	10	Does not stick to teeth = 8–10; Slightly sticky = 6–7; sticky = 4–5
Flavor	5	Wheat flavor, no peculiar flavor = 5; Bland flavor = 4; Peculiar flavor = 1–3
Total score	100	—

Table 2. Proximate composition of wheat flour and sprouted wheat flour^†..

	Moisture (%)	Protein (%)	Fat (%)	Starch (%)	Ash (%)	GABA (mg/100 g)
Wheat flour	12.08 ± 0.44^b	11.58 ± 0.18^b	4.29 ± 0.15^b	66.06 ± 0.82^b	1.22 ± 0.01^b	72.28 ± 0.50^a
Sprouted wheat flour	8.30 ± 0.13^a	10.37 ± 0.01^a	3.69 ± 0.13^a	64.02 ± 0.25^a	1.12 ± 0.00^a	108.11 ± 2.42^b

^†Reported results correspond to mean ± standard deviation. Different letters within the same column indicate significant differences (p < .05).

Gluten content, gluten index and falling number (FN)

As depicted in Figure 1, the wet gluten content of wheat flour exhibited no significant difference with the gradual increase of SF addition (p < .05). However, the gluten index displayed an initial ascending and then descending trend. The highest gluten index of the flour was achieved at the SF addition of 4%, implying that SF can improve the gluten quality to a certain extent. The addition of SF was found to facilitate the degradation of wheat gluten by the added proteases, as reported in previous studies.^[8,9] The results of wet gluten content and gluten index varied among different studies^[23] but were consistent with others. Caetano et al.^[24] reported that only a part of gluten protein was degraded by protease activity generated within 48 h of germination, resulting in higher elongation characteristics and structural deformation recovery ability of germinated wheat than ungerminated wheat. Moreover, the protein hydrolytic activity doubled, but remained at a low absolute level during germination, as suggested by Marti et al.^[25]

Figure 1. Gluten content, gluten index of flour with different additions of SF. ^a-d contrast values (means) associated with the same letter are not significantly different (p > .05).

The “falling number” (FN) test, recognized as an international standard method, is a simple, fast, and reliable method for the indirect determination of α-amylase activity in cereals (Hagberg^[26] and Perten^[27]). Figure 2 shows a decreasing trend of the FN as SF content increases. The FN of samples with 2% SF addition decreased by 58% compared to the blank, and the rate of decrease slowed down, ranging from 200 s to 100 s, reaching a minimum of 111s with the highest addition of 10% SF. It indicated that α-amylase activity is significantly affected by germination (p < .05). Appropriate levels of α-amylase are essential for dough fermentation and favorable bread structure. Marti et al.^[28] demonstrated that bread made from whole sprouted wheat flour has a shorter baking time and a larger specific volume. Therefore, SF addition was beneficial to the flour quality.

Figure 2. Falling number（FN）of flour with different additions of SF. ^a-e contrast values (means) associated with the same letter are not significantly different (p > .05).

Pasting property

Table 3 illustrates that most pasting properties were altered in a noticeable manner except the pasting temperature. The peak viscosity, trough viscosity, breakdown viscosity, final viscosity, and setback viscosity declined significantly as the SF amount increased, whereas the peak temperature remained relatively constant (p < .05). The α-amylase activity increased in SF facilitated the decomposition of the starch, resulting in a reduction of viscosities. This is consistent with Rathjen et al.^[29] The present study reveals that the addition of SF resulted in a significant decrease in breakdown viscosity and setback viscosity, which suggests that the dough thermal stability reduced and the dough aging process slowed down (p < .05).

Table 3. Pasting properties of wheat flour added with different amounts of SF^†..

Amount of SF (%)	Peak viscosity (RVU)	Trough viscosity (RVU)	Breakdown viscosity (RVU)	Final viscosity (RVU)	Setback viscosity (RVU)	Peak time (min)	Pasting temperature (℃)
0	2652.5 ± 0.7^f	1832.5 ± 2.1^f	820.0 ± 2.8^f	3102.5 ± 7.8^f	1266.5 ± 4.9^f	6.50 ± 0.04^f	70.20 ± 1.06^a
2	807.5 ± 3.5^e	198.5 ± 4.9^e	616.0 ± 1.4^e	506.5 ± 4.9^e	330.0 ± 2.8^e	4.93 ± 0.00^e	70.28 ± 0.18^a
4	470.0 ± 5.7^d	72.5 ± 0.7^d	397.5 ± 4.9^d	189.0 ± 5.7^d	117.5 ± 3.5^d	4.40 ± 0.10^d	70.60 ± 0.64^a
6	360.0 ± 2.8^c	50.5 ± 2.1^c	309.5 ± 0.7^c	112.0 ± 4.2^c	59.5 ± 4.9^c	4.00 ± 0.00^c	70.50 ± 0.57^a
8	324.5 ± 0.7^b	41.0 ± 1.4^b	283.5 ± 0.7^b	79.5 ± 2.1^b	38.5 ± 0.7^b	3.87 ± 0.00^b	70.98 ± 0.04^ab
10	274.5 ± 2.1^a	31.5 ± 0.7^a	243.0 ± 1.4^a	57.5 ± 0.7^a	26.0 ± 0.0^a	3.67 ± 0.00^a	71.38 ± 0.67^ab

^†Reported results correspond to mean ± standard deviation. Different letters within the same column indicate significant differences (p < .05).

Mixolab characteristics

The dough properties of wheat flour added with SF are presented in Table 4. With the increasing SF addition levels, the dough stability of wheat flour decreased. C2 torque indicates protein weakening (the lowest value of torque produced) when the dough is subjected to simultaneous increase of temperature and mechanical work.^[30] With the increased addition of SF, C2 torque decreased, indicating the increase of protein weakening. C3 and C3-C2 both reflect the starch gelatinization characteristic measured by heating and mechanical stirring. The parameters decreased with the increase of the SF amount, which proved the SF can reduce the peak viscosity of the dough. C4 and C4/C3 indicate the thermal stability of the starch and the dough respectively. As shown in Table 4, the addition of SF brought down the C4 and C4/C3 torque significantly (p < .05), indicating the decrease of starch gel stability and the increase of dough maturation degree.^[31] C5-C4 reflects the aging characteristics of starch, and the smaller the value, the less likely the starch is to retrograde. The C5-C4 value became smaller with the increase of SF, indicating that the addition of SF improved the anti-aging characteristics of the mixed flour dough.

Table 4. Mixolab characteristics of wheat flour added with different amounts of SF^†..

Amount of SF (%)	Stability（min）	C1 (N·m)	C2 (N·m)	C3 (N·m)	C4 (N·m)	C5 (N·m)
0	7.49 ± 0.30^d	1.11 ± 0.01^b	0.40 ± 0.01^d	1.62 ± 0.01^d	1.56 ± 0.02^f	2.50±0.06^e
2	6.66 ± 0.32^c	1.10 ± 0.00^ab	0.32 ± 0.01^c	1.45 ± 0.04^c	0.79 ± 0.01^e	1.14±0.03^d
4	6.42 ± 0.19^c	1.09 ± 0.01^ab	0.32 ± 0.01^c	1.37 ± 0.02^b	0.56 ± 0.04^d	0.85±0.00^c
6	6.15 ± 0.18^bc	1.09 ± 0.01^a	0.30 ± 0.01^b	1.34 ± 0.01^b	0.46 ± 0.03^c	0.68±0.09^b
8	5.63 ± 0.15^ab	1.10 ± 0.00^ab	0.28 ± 0.01^a	1.32 ± 0.01^b	0.37 ± 0.01^b	0.54±0.02^a
10	5.41 ± 0.06^a	1.11 ± 0.01^ab	0.27 ± 0.00^a	1.26 ± 0.00^a	0.30 ± 0.00^a	0.43±0.01^a
Amount of SF	C3-C2 (N·m)	C4/C3	C5-C4 (N·m)	α slope	β slope	γ slope
0	1.23±0.01^d	0.96±0.00^e	0.95±0.04^d	-0.078±0.00^ab	0.493±0.01^c	-0.011±0.00^c
2	1.13±0.02c	0.54±0.01^d	0.36±0.02^c	-0.075±0.01^ab	0.403±0.05^b	-0.077±0.01^ab
4	1.05±0.03b	0.41±0.02^c	0.29±0.04^bc	-0.106±0.02^a	0.389±0.00^b	-0.076±0.01^ab
6	1.05±0.01b	0.34±0.02^b	0.22±0.06^ab	-0.064±0.01^b	0.337±0.01^ab	-0.103±0.00^a
8	1.05±0.01b	0.28±0.00^a	0.17±0.01^a	-0.063±0.01^b	0.316±0.01^a	-0.072±0.00^b
10	0.99±0.00^a	0.24±0.00^a	0.13±0.01^a	-0.072±0.00^ab	0.337±0.04^ab	-0.096±0.01^ab

† Reported results correspond to mean ± standard deviation. Different letters within the same column indicate significant differences (p < .05).

Specific volume and sensory quality of SWSB

Specific volume is an important property of steamed bread that represents the degree of volume expansion and air retention capacity.^[32] Table 5 showed that the specific volume initially decreased, then increased, and then decreased again with the increasing SF content. On the one hand, the increase in α-amylase content in SF may destroy the gluten network structure of the dough, thereby reducing gluten quality, which led to a decrease in specific volume of the steamed bread. On the other hand, the presence of fermentable sugars released by amylase action improved the rising of the dough, resulting in an increase in volume of the steamed bread. Marti et al.^[28] reported that adding an appropriate amount of SF improved the quality of bread. When SF content was over 6%, which caused the dough gluten network breaking down and become unstable structurally, resulting in a decrease of specific volume due to the rise in protease content. The addition of SF reduced the width-to-height ratio of steamed bread, which did not show significant difference among different SF additions. The optimal sensory score of 86 for SWSB was achieved at an SF content of 2%, which was comparable to that of the control group.

Table 5. Specific volume, sensory quality and color of SWSB with different additions of SF^†..

Amount of SF (%)	Specific volume (mL/g)	Width to height	Sensory quality	L*	a*	b*
0	3.1 ± 0.02^b	1.49 ± 0.01^b	85 ± 0.25^d	78.6 ± 0.40^b	−2.1 ± 0.15^a	14.4 ± 0.29^a
2	2.8 ± 0.03^a	1.39 ± 0.02^a	86 ± 0.23^d	80.0 ± 0.15^c	−1.7 ± 0.15^bc	14.5 ± 0.06^a
4	3.0 ± 0.03^a	1.39 ± 0.01^a	85 ± 0.06^d	78.9 ± 0.72^b	−1.7 ± 0.06^c	14.7 ± 0.87^bc
6	3.2 ± 0.03^c	1.38 ± 0.01^a	80 ± 0.15^c	77.5 ± 0.10^a	−1.9 ± 0.15^ab	14.7 ± 0.35^bc
8	2.8 ± 0.02^a	1.37 ± 0.03^a	76 ± 0.46^b	77.7 ± 0.10^a	−1.1 ± 0.12^d	15.6 ± 0.44^d
10	2.8 ± 0.01^a	1.37 ± 0.01^a	73 ± 0.17^a	77.3 ± 0.06^a	−1.6 ± 0.15^c	15.4 ± 0.32^cd

*Reported results correspond to mean ± standard deviation. Different letters within the same column indicate significant differences (p < .05).

Color of SWSB

Table 5 shows the color characteristics of SWSB. The whiteness (L*) of SWSB increased initially and then decreased with the addition of SF, reaching a peak at 2% and not significantly differing from the control group at 4% (p < .05), indicating that the sensory properties of SWSB can be improved within a certain range of SF addition. The addition of 8% SF, which contains bran and dextrin, resulted in a darker color of SWSB, with a decrease in L* and an increase in b* (i.e. a decrease in whiteness and a more yellowish color). The sensory quality of SWSB was highly correlated with whiteness and decreased with increasing SF addition. The optimal SF addition was found to be 4% or less based on the results presented in Table 5.

Texture of SWSB

In order to evaluate the qualitative physical properties of food samples, the TPA (Texture Profile Analysis) test was conducted, which aims to simulate the chewing behavior of human teeth by measuring the time-dependent change in strength during two chewing sessions. This test enables the quantification and scoring of important parameters such as hardness, adhesiveness, elasticity, and chewiness. Table 6 presents the results of the TPA on SWSB samples with different amounts of SF. The addition of SF led to an increase in hardness, chewiness, adhesion, and springiness of SWSB, which subsequently decreased at higher levels of SF addition. Specifically, the hardness of the steamed bread significantly decreased from 1363.58 g (0% SF) to 863.61 g (6% SF) and then significantly increased to 1310.99 g (10%SF) (p < .05). The minimum chewiness was observed at 4% SF addition, while the minimum adhesion and springiness were observed at 2% SF addition. The reduction of gluten content caused by the addition of SF may be responsible for the observed changes in texture properties. The presence of α-amylase may have contributed to the breakdown of starch, providing nutrients for yeast growth and enhancing dough properties, leading to irregular texture properties. This finding is consistent with the work of Hanida et al..^[33] The decrease of adhesion indicates a decrease in toughness, which may improve the taste of the SWSB to a certain extent.

Table 6. TPA texture analysis of SWSB with different additions of SF^†..

Amount of SF (%)	Hardness/(g)	Chewiness/(g)	Adhesion/(g)	Springiness	Cohesion	Resilience
0	1363.58^c	1003.42^c	1073.21^d	0.94^c	0.79^c	0.42^d
2	1173.69^b	600.68^a	760.92^b	0.78^a	0.80^c	0.42^d
4	954.13^ab	596.93^a	862.33^bc	0.80^a	0.77^bc	0.36^c
6	863.61^a	697.15^ab	668.55^a	0.89^b	0.74^b	0.36^c
8	1177.71^b	774.49^b	900.20^c	0.88^b	0.69^a	0.32^b
10	1310.99^c	671.85^ab	804.17^bc	0.84^ab	0.68^a	0.30^a

^†Reported results correspond to means ± standard deviations. Different letters within the same column indicate significant differences (p < .05).

The cohesion reflects the internal tightness, and the resilience indicates the ability to rebound after pressing. The cohesion and resilience of SWSB increased with the addition of SF, peaked at 2% SF, and then decreased thereafter. This finding suggests that SF can enhance the internal tightness of SWSB, making it less prone to falling apart and with a good rebound ability within a certain range. In conclusion, the addition of a small amount of SF rarely changed the SWSB quality. When SF was added within 4%, the produced steamed bread possessed desirable characteristics such as softness, moderate stretchiness, chewiness, and low crumb detachment.

Image analysis of SWSB

Figure 3 provides C-Cell images of SWSB with different levels of SF. It can be seen that the texture fineness of the SWSB initially increased and then decreased with the increasing level of SF. Table 7 presents the effect of SF on various parameters related to the cell and slice information of SWSB analyzed by the C-Cell food image analyzer. The results indicate that the brightness of the slices, cell contrast ratio, cell number, hole volume, and mean cell extension initially increased and then decreased, while cell area, cell diameter, cell volume, rough cell volume and wall thickness decreased and then increased with the increase of the SF content. The number of cells and wall thickness are good indicators of proofing quality.^[34] When the addition of SF was up to 4%, the SWSB internal structure was characterized optimal by delicate texture. Furthermore, the slice brightness and the lightness of SWSB exhibited similar changing trend (Table 5), with a significant decline observed beyond the addition of 4% SF (p < .05). Moreover, a thin wall thickness was observed at the SF content from 0 to 4%. The mean cell extension revealed that cell elongation increased with the addition of SF. Lower brightness indicates larger or deeper cells and a darker interior.^[35] Additionally, cell contrast ratio, which represents the ratio of average brightness between cell and wall, reflects the depth, wall thickness and color of products, with a higher value indicating better quality.^[36] According to the results, it can be concluded that the optimal brightness, cell condition, and delicate internal texture were achieved at the addition of 4% SF.

Figure 3. C-Cell image of SWSB with different additions of SF (0%; 2%; 4%; 6%; 8%; 10%, respectively).

Table 7. C-Cell image analysis of SWSB with different additions of SF^†..

Amount of SF (%)	Slice brightness	Cell contrast ratio	Cell number	Cell area (mm^2)	Cell diameter (mm)	Cell volume (mm^3)	Rough cell volume (mm^3)	Hole volume (mm^3)	Wall thickness (mm)	Mean cell extension
0	131.90^d	0.8045^abc	2854^b	47.80^bc	10.945^bc	2.860^ab	6.440^a	16.80^a	3.015^d	1.585^a
2	135.65^f	0.8125^bc	3310^c	45.45^a	8.690^a	2.570^a	5.400^a	49.50^bc	2.585^ab	1.695^d
4	132.80^e	0.8190^c	2676^b	45.60^a	9.270^ab	2.805^ab	5.620^a	45.30^bc	2.680^abc	1.685^cd
6	128.75^c	0.7930^ab	2641^b	47.40^bc	10.400^abc	3.485^bc	7.175^ab	49.55^bc	2.755^bc	1.650^bc
8	125.30^b	0.8025^abc	2640^b	46.90^b	9.270^ab	3.005^ab	5.730^b	34.45^b	2.565^a	1.625^b
10	123.35^a	0.7860^a	2275^a	48.35^c	11.505^c	3.925^c	9.090^b	54.15^c	2.790^c	1.655^bc

^†Reported results correspond to means ± standard deviation. Different letters within the same column indicate significant differences (p < .05).

Conclusion

Different levels of sprouted flour were added to the wheat flour to produce Chinese steamed bread. With the increased addition of SF, the gluten indexes of the flour initially increased and then decreased, and the falling number (FN) decreased. The addition of SF significantly reduced peak viscosity, trough viscosity, breakdown viscosity, final viscosity and setback viscosity, while the pasting temperature remain constant. Moreover, the protein weakening increased as SF level increased. Steamed bread with 4% SF exhibited the highest quality characteristics. SWSB is a new value-added product of sprouted wheat, which can not only reduce waste, but also enhance the nutritional and commercial value of wheat products. Additionally, SF could be further explored by been combined with other varieties of wheat flour, as well as with rice flour, named rice bread. The sprouted wheat may play a quite different role in the industrial production and application.

Declaration of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Disclosure statement

No potential conflict of interest was reported by the author(s).