Effect of debittered fenugreek (Trigonella foenum‐graecum L.) flour addition on physical, nutritional, antioxidant, and sensory properties of wheat flour rusk

Fenugreek (Trigonella foenum‐graecum) is a unique legume crop having many pharmacological properties and health benefits attributed to its high soluble dietary fiber and phytochemicals. The main objective of this study was to evaluate selected functional and physical (color and pasting) properties of debittered fenugreek flour (DFF) and its addition on the nutritional value and acceptance of wheat flour rusk, prepared with 5%, 10%, 15%, and 20% DFF. The antioxidant potential and sensory attributes of DFF‐added rusks were also analyzed. The results revealed that with successive increase of DFF level, the nutritional, mineral, dietary fiber, and bioactive contents of the rusks were significantly (p ≤ .05) enhanced. The progressive replacement at 0% to 20% level significantly (p ≤ .05) improved the total phenolic content (157.5 to 455.8 mg GAE per 100 g), total flavonoid content (5.5 to 8.2 mg CE per 100 g), and antioxidant activity (20.4% to 45.5%). DFF incorporation significantly (p ≤ .05) increased the water and oil absorption capacity, whereas peak viscosity, breakdown viscosity, final viscosity, setback viscosity, and peak temperature were decreased. The color of rusks became darker, the loaf weight and hardness increased, whereas loaf volume and specific loaf volume values were decreased with DFF addition. Sensory attributes of rusks were slightly affected with DFF incorporation, and rusks with 15% DFF were found most desirable with significantly (p ≤ .05) enhanced nutritional, antioxidant, and sensory characteristics. The results of the present study demonstrated that incorporation of DFF at acceptable level could be achieved successfully for preparation of bakery product with enhanced nutritional and sensory quality.

The interest is increasing day by day in developing novel foods loaded with natural antioxidants derived from whole grains, oilseeds, fruits, vegetables, and their by-products (Dhull, Kaur, & Purewal, 2016).
Composite flours, in addition to extending the availability of wheat flour (WF), also supply essential nutrients and possess many bioactive substances of food science and biological values (Kaur, Kaur, & Purewal, 2018). Considering the health benefits of fenugreek, their incorporation as composite blends in the preparation of different food products may enhance nutritional and health status of consumers. Fenugreek incorporation in different baked products such as biscuits (Hegazy & Ibrahium, 2009;Hooda & Jood, 2005) and bread (Afzal, Pasha, Zahoor, & Nawaz, 2016;Chaubey et al., 2018;Maria Man et al., 2019) has been reported for improving their nutritional profile, dietary fiber, and antioxidant profile.
Although fenugreek owing to excellent neutraceutical properties has received significant recognition in recent years, however, its bitter taste limits the acceptability in food products prepared with its addition. Appropriate mitigation of this biggest limitation is always a product development challenge for the food researchers and culinologists.
Past research shows the use of different approaches (e.g., soaking, germination, and roasting) to address bitterness (Ertaş & Bilgiçli, 2012;Pandey & Awasthi, 2015). Further, the use of small amount of sugar (Sharafi, Hayes, & Duffy, 2013) and curd or yoghurt (Srinivasan, 2010) has been suggested to minimize the bitterness and pungent taste in traditional foods.
Considering the health benefits, low price, and ready availability of fenugreek, its incorporation as composite blends in the preparation of different food products may enhance its economic potential and consumption as well as nutritional and health status of consumers.
Though there are a number of previously published studies on the incorporation of raw fenugreek in different bakery products, studies regarding the use of debittered fenugreek in rusk preparation appear to be rather limited. Therefore, this study was undertaken with the main objective to investigate the effect of incorporation of debittered fenugreek flour (DFF) at 5%, 10%, 15%, and 20% levels on the nutritional, antioxidant, and sensory characteristics of rusks. The development of such nutritious bakery products would help to raise the availability of natural antioxidants and dietary fiber with demonstrated health benefits for the consumers.

| MATERIALS AND METHODS
Fenugreek seed cultivar HM-57 was purchased from Chaudhary Charan Singh Haryana Agriculture University, Hisar. Whole WF, curd, vegetable oil, sugar, and dry yeast were procured from a local market.

| Debittering of fenugreek seeds and preparation of blends
Fenugreek seeds were debittered using curd (1:1 in water) as per the procedure described by Chaubey et al. (2018), with a slight modification. After soaking in diluted curd for 12 hr, thoroughly washed and dried seeds were ground using a benchtop mill (Khera Mill, India) and passed through 70 mesh sieve to obtain DFF. The control consisted of 100% WF, whereas composite flour blends consisted of 5%, 10%, 15%, or 20% DFF in WF (these treatments were designated DFF-5, DFF-10, DFF-15, and DFF-20).

| Rusk formulation and preparation
The method described by Yaseen (2000), with some modifications, was used for preparation of rusks (with and without DFF). WF/DFFadded flour blends (100 g, passed through 60 BSS sieve), dry yeast (1.0 g), sugar (20 g), salt (1.0 g), vegetable oil (10 g), and fennel (0.5 g) were mixed in a pin mixer (12 min) with an adequate amount of water for preparing rusk dough. The dough was allowed to rest for 30 min, followed by fermentation of dough pieces (150 g, as per pan size) at 30 C for 90 min. The fermented loaves were then baked at 220 C for 25 min in revolving reel oven (National Mfg. Co., Lincoln, NE, USA) and then thoroughly cooled for easy slicing. The slices of about 1-cm thickness were then cut mechanically followed by roasting (200 C, 15 min) in an oven.

| Proximate composition, dietary fiber, and mineral estimation
The flour and rusk samples were analyzed for moisture, ash, fat, crude fiber, and protein (N × 6.25) contents using standard methods (AOAC, 2005). The samples were analyzed for SDF and IDF according to AOAC Methods 993.19 and 991.42, respectively (AOAC, 2005). Calcium (Ca), iron (Fe), zinc (Zn), and copper (Cu) contents were estimated in atomic absorption mode, whereas sodium (Na) and potassium (K) contents of seeds were estimated in emission mode using atomic absorption spectrophotometer (Model AA-7000, Shimadzu, Tokyo, Japan; AOAC, 2005).

| Functional properties
Bulk density was calculated as weight per unit volume of sample (g/ml) using a 10-ml graduated cylinder. Briefly, sample was filled in the cylinder and was gently tapped until no further diminution of the sample after filling to the 10-ml mark. Water absorption capacity (WAC) was measured by following the methods described by Sosulski (1962). Briefly, 0.5 g of sample was dispersed in 25 ml of distilled water, held for 30 min, and centrifuged (3,000 × g, 25 min), and supernatant was decanted. The sediment was weighed to calculate WAC, and results were presented as %. Oil absorption capacity (OAC) was measured by the method of Lin, Humbert, and Sosulski (1974). Briefly, 0.5 g of sample and corn oil (6 ml) was mixed, held for 30 min, and centrifuged (3,000 × g, 25 min), the separated oil was removed with a pipette, and the sediment was then reweighed. The flour samples were analyzed for their sedimentation value by following the method of Gupta, Bawa, and Semwal (2011). A 5-g portion of sample and 50-ml distilled water were mixed in a 100-ml stoppered graduated cylinder, shaken horizontally for 30 s initially followed by shaking at regular time intervals of 2 and 4 min. Then 50 ml of sodium dodecyl sulfate-lactic acid reagent was added, inverting the cylinder four times and further repetition of the inversion at 6-, 8-, and 10-min intervals. Finally, the contents were allowed to settle for 20 min, and the sedimentation values (ml) were recorded.

| Pasting properties
A starch cell of Modular Compact Rheometer (Anton Paar MCR-52, Austria) was used to measure the pasting properties of flour samples (Kaur & Singh, 2016). In an aluminum canister, flour sample (3.5 g) was mixed with 25-ml distilled water to measure the viscosity profile of the flour samples. All parameters, that is, the pasting temperature, peak viscosity, breakdown, setback, and final viscosity, were calculated from recorded data, using three replicates.

| Physical properties
After first baking and cooling, loaf weight and loaf volume (rapeseed displacement method) were measured. Specific loaf volume (ml/g) was calculated by dividing loaf volume with weight.

| Hardness
The rusk samples were analyzed for their hardness using TA-XT 2 Texture Analyzer (Stable Micro Systems, Haslemeres, England), and hardness was determined from force-time curves of the texture profile analysis using the method described by Baik, Powers, and Nguyen (2004).

| Color properties
Color measurement of flours was calculated using a Hunter Colorimeter fitted with optical sensor (Hunter Associates Laboratory Incorporation, Reston, VA, USA) on the basis of L * , a * , and b * color system. Total color difference (ΔE) was calculated by using the following equation:

| Total phenolic content
Total phenolic content (TPC) of the extracts was determined using Folin-Ciocalteu reagent, as described by Salar and Purewal (2017).
Absorbance of the extracts was recorded at 765 nm against a blank, and the results were expressed as gallic acid equivalent (GAE) from the standard calibration curve.

| Total flavonoid content
Total flavonoid content (TFC) was measured by the colorimetric assay developed by Zhishen, Mengcheng, and Jianming (1999), and absorbance of the mixture was determined at 510 nm versus water blank.
TFC of extract was expressed on a fresh weight basis as mg/g catechin equivalents (CE).

| DPPH assay
The DPPH radical scavenging capacity of the extracts was measured as described by Yen and Chen (1995) with some modifications.
Briefly, 3 ml of 100-μM DPPH was added to 100 μl of extract, and the changes in absorbance were recorded after 30 min at 517 nm. Percent (%) DPPH scavenging activity was calculated using the absorbance of control (A C ) and extracts (A E ): DPPH Scavenging Activity (%) = (A C − A E /A C ) × 100.

| Sensory properties
A semitrained panel evaluated the prepared rusk samples for various sensory characteristics such as color, aroma, taste, texture, and overall acceptability. A 9-point hedonic rating scale (9 = like extremely, 5 = neither like nor dislike, and 1 = dislike extremely; Meilgaard, Civille, & Carr, 1999 was used by the panel of 32 judges in the age group of 20 to 35 years, comprising students and faculty members of the department.

| Statistical analysis
The data recorded in triplicate values for all the quality parameters were analyzed by applying one-way analysis of variance (Snedecor & Cochran, 1994). Statistical analysis was carried out using statistical software package SPSS V.23 program.

| Proximate composition of flours
The results of proximate analysis are summarized in

| Antioxidant properties
Phenolics can act as antioxidant by inhibiting formation of free radicals, chelating metal ions, affecting the activity of prooxidative and antioxidizing enzymes and inhibiting the autoxidation chain reactions inside the body (Carocho & Ferreira, 2013). The results presented in    Table S1). This could be owed to the reducing properties of polyphenolic compounds in DFF, confirming their antioxidant potential.

| Functional properties of flours
Various functional properties of WF and DFF-added flour blends are summarized in

| Pasting properties
The pasting properties of WF and DFF-added flours blends are summarized in Table 4 ( Figure S1). These properties are generally associated with absorption of water, swelling, and further rupturing of starch granules in any system. Significant (p ≤ .05) difference in pasting properties of control (WF) and DFF-added flours were observed.

| Physical characteristics and hardness of rusks
Physical characteristics such as loaf volume, loaf weight, and specific loaf volume are significantly important parameters in defining the suitability of the raw materials used in rusk preparation. Loaf weight of breads prepared from WF and DFF-added flours at different levels, that is, 5%, 10%, 15%, and 20%, was recorded (Table 5). The loaf weight of different samples ranged from 160 to 168.2 g, the highest was of 20% DFF-added loaf, and the lowest was of control sample. A significant (p ≤ .05) increase in loaf weight was observed with each increment of non-WF (i.e., DFF), indicating that an extra amount of water was retained in breads after baking (Hooda & Jood, 2005). Also, increased weight of DFF-added loaf might be because of less retention of gas in the blended dough, hence providing a dense texture.
The results were comparable with the values reported in previous studies for fenugreek flour-added WF breads (Chaubey et al., 2018) and flaxseed flour-added WF rusks (Kaur et al., 2018). A significant (p ≤ .05) linear decrease in loaf volume of DFF-added rusks was observed with increase in DFF level from 5% to 20% (Table 5). The highest loaf volume (519.0 ml) was of control, whereas the lowest value (494.1 ml) was observed for 20% DFF-added loaf. It could be attributed to the dilution effect on gluten with the addition of non-WF to WF (Sivam, Sun-Waterhouse, Waterhouse, Quek, & Perera, 2011), and less retention of CO 2 gas caused the depression in loaf volume (Sharma & Chauhan, 2002) in rusk prepared from DFF-added flour. Specific loaf volume was obtained by dividing the loaf volume by the loaf weight, and results indicated a decrease in specific loaf volume on increasing levels of DFF compared with the control (Table 5).
The poor quality and quantity of gluten in cereal-pulse blended products may be responsible for dense structure of the fermented dough, resulting in low specific loaf volume. Some previous studies also reported a decrease in loaf volume for fenugreek flour-added bread (Chaubey et al., 2018) and flaxseed flour-added rusks (Kaur et al., 2018). The loaf weight was found positively correlated with WAC (r = .978, p ≤ .01). However, the loaf volume of DFF-added rusk was significantly (p ≤ .01) negatively correlated with WAC (r = −.975) but positively correlated with sedimentation volume (r = .993, Table S2), which confirmed the role of gluten in loaf volume. The viscoelastic properties of dough, which determines the size, shape of bread crumb, and its loaf volume, can be positively affected by protein addition (Aamodt, Magnus, & Faergestad, 2004).
The crumb hardness, that is, the force required to compress the sample, was measured using Texture Analyzer (the texture profile analysis is depicted in Figure S2), and the values are summarized in T A B L E 4 Pasting properties of wheat flour (WF) and debittered fenugreek flour (DFF)-added flour blends

| Color properties of rusks
The results for different color characteristics of control and DFFadded rusk samples are summarized in Table 5. The results showed that a progressive increase in the substitution of WF with DFF significantly (p ≤ .05) affected the color of the rusk samples (Figure 1), which is evident from the values of L * (lightness), a * (redness), b * (yellowness), and ΔE (total color difference) for control and DFF-added rusks (Table 5). There was a significant (p ≤ .05) decrease in the value of L * from 38. 52, 36.24, 31.15, 26.57, and 23.25 with progressive increment of DFF level (0%, 5%, 10%, 15%, and 20%, respectively). DFFadded rusk with low L * values showed reduced brightness, luminocity, and darker color as compared with the control (Figure 1)  and r = .967, p ≤ .01, respectively; Table S2). The increase in TPC, TFC, and antioxidant potential resulted in dark-colored rusk samples.

| Sensory properties of rusks
The replacement of WF with DFF at level of 5% to 20% significantly (p ≤ .05) affected the sensorial properties of rusks, and the results for appearance, aroma, taste, texture, and overall acceptability (OA) are reported ( Figure 2). All the sensory attributes of DFF-added rusk were negatively impacted with increasing level of DFF. Control (WF) rusk showed the highest values for all the sensory properties. Rusk with 20% DFF showed the lowest score for appearance (5.5), taste (6.5), aroma (5.0), and texture (6.0), thus the lowest OA score (5.5). The lowest sensory score for 20% DFF-added rusks may be due to its dark color, bitter taste, dense, and hard texture. The rusks with DFF at 15% level were found with desirable sensory score for appearance (8.5), aroma (8.0), taste (7.5), texture (8.0), and OA (8.0; Figure 2).
F I G U R E 1 Rusk prepared by incorporating debittered fenugreek flour (DFF) at different levels. Control represents rusk with 100% wheat flour. DFF-5, DFF-10, DFF-15, and DFF-20 represent rusks made with 5%, 10%, 15%, and 20% DFF, respectively F I G U R E 2 Sensory characteristics of rusk samples. Control represents rusk with 100% wheat flour. DFF-5, DFF-10, DFF-15, and DFF-20 represent rusks made with 5%, 10%, 15%, and 20% DFF, respectively 4 | CONCLUSIONS Partial replacement of WF with DFF had an impact on rusk quality and sensory characteristics. Rusks made with 15% DFF level had good nutritional and antioxidant profile with only minor reductions in sensory quality compared with a 100% WF control rusk. However, rusks made with 20% DFF were found more negatively affected. As DFF level increased, nutritional, dietary, mineral, and phytochemical profile of rusks was found to increase. At different levels of DFF inclusion (5%, 10%, 15%, and 20%), loaf volume and specific loaf volume were decreased, whereas loaf weight and hardness of DFF-added rusks were increased. All the pasting properties of DFF-added flours were negatively impacted as shown by higher degree of difference scores from the WF (control). The color of rusks became darker with the increase in the level of DFF. Of all the rusks made with DFF-added flour, the rusks made with 15% DFF had the most acceptable sensory and rusk quality characteristics.