Sensory analysis of microwave‐roasted fenugreek and coffee blend

Fenugreek is one of the well‐known legumes, used for its antimicrobial, antioxidant, nutritional, and pharmaceutical properties. It was aimed to obtain coffee by blending microwave (600 W)‐roasted fenugreek with coffee arabica and to determine the best roasting conditions (2 and 4 min), and blending ratios (20% and 50%) for fenugreek seeds by consumer sensory analysis. A voluntary, minimal‐trained consumer panel of 80 panelists was conducted. Coffee from roasted Arabica beans (100%) was used as a control. Cronbach's alpha values of 67.2% and 90.9% were obtained for the reliability of the first and second parts of the survey, respectively. The attributes “brown” color, “burnt,” and “bitter” taste, and “astringent” texture were significantly different between samples (p < 0.05), whereas oily appearance, green color, coffee, green/vegan, fruity, sour, sweet, nutty, caramel, cacao, caffeine and creamy flavor, and viscosity sensation were statistically the same. The Tamhane T2 post hoc test showed that the color of the control sample was more brownish, whereas the 50% blend of 4 min roasted fenugreek had a more burnt, bitter, and astringent taste. Appreciation scores for taste/aroma, appearance, and mouthfeel also differed significantly between samples, whereas odor was rated as the same by panelists. This study shows that sample with 20% mixture of fenugreek roasted for 4 min at 600 W had statistically the same scores as the control sample in terms of odor, appearance, aroma, taste, and mouthfeel. These findings were also supported by physical and antioxidative quality measurements such as color, pH, moisture content, total phenolic content, and antioxidant activity.

The reason why people like the taste and smell of coffee is the combination of more than 1000 compounds, including carbohydrates, lipids, nitrogenous compounds, vitamins, minerals, alkaloids, and phenolic compounds, which are produced as a result of a long chain of chemical transformations during roasting and brewing the coffee (Bae et al., 2014). One of the unique aroma compounds is caffeine, which is responsible for the stimulating effect. Arabica coffee beans contain 1% caffeine, whereas Robusta coffee beans contain 1.7% (Ashihara & Crozier, 2001).
There are controversial opinions about the health effects of caffeine. Caffeine is said to have antioxidant and anti-inflammatory effects (Iris et al., 2018;Li et al., 2021) and is thought to reduce the risks of cardiovascular diseases, obesity, diabetes mellitus, and certain cancers (Collado-Mateo et al., 2020;Machado et al., 2021) when consumed moderately. However, when consumed in excess, caffeine can cause an increased risk of heart disease and cancer, caffeine intoxication and addiction, nervous system restlessness, irritability, migraine, anxiety, insomnia, difficulty in sleeping, agitation, mental atrophy, and other side effects (Juliano & Griffiths, 2004). To avoid health problems, decaffeinated coffee has been produced in the industry. However, decaffeination is an expensive process and causes undesirable changes in the aroma of the product. Therefore, decaffeinated coffee is not consumed in large quantities. Due to the negative health effects caused by overconsumption of coffee, its expensiveness and its future extinction, researchers are interested in coffee substitutes obtained by roasting different beans that provide the coffee taste experience without caffeine.
In fact, different varieties of coffee-like substitutes such as chicory, malt, wheat, rye, barley, mung bean, and date seed (Alptekin & Bölek, 2020;Fadel et al., 2008;Gani et al., 2012;Majcher et al., 2013;Prohens et al., 2014;Vieira, 2013) have been studied in the literature to produce coffee-like beverages. However, there was no study in the literature on the use of fenugreek as coffee substitute in coffee blends and the impact of roasting time and blend ratio on consumer sensory analysis, physical and antioxidative properties. The flavor and fragrance analysis of fenugreek revealed that fenugreek imparts coffee aroma compounds. Fenugreek seeds were reported to contain 3-Amino-4, 5-dimethyl2(5H)-furanon, a strong flavor compound that contributes to the burnt sweet note of coffee (Pasricha & Gupta, 2014). Fenugreek is also reported to have maple-like aroma and bitter taste, but this can be eliminated by roasting (Dwivedi et al., 2019).
Fenugreek (Trigonella foenum-graecum) is a herbaceous legume species that belongs to the Leguminosae (Fabaceae) family and is one of the oldest medicinal plants used mainly in the countries of Eastern Mediterranean and Central Asian (Goyal et al., 2016;Ouzir et al., 2016). Fenugreek used as seeds is often included in the recipes of these countries, but it is also known to have been used therapeutically in the past (Altuntas et al., 2005). Fenugreek seeds are thought to have pharmacological effects such as antiviral, anti-tumor, and antioxidant activities. The seeds contain proteins rich in lysine and L-tryptophan, galactomannan that forms mucilaginous fiber, saponins, and sapogenins such as diosgenin and trigonelline, which are responsible for therapeutic effects such as inhibiting cholesterol and lowering sugar levels (Hamden et al., 2010;Kumar et al., 2014;Smith, 2003). However, one drawback of fenugreek seeds is their bitter taste and unpleasant odor, which limits their use in food formulations.
In this study, fenugreek seeds were not used directly as a coffee substitute because of their bitterness and unlikable odors. Therefore, to reduce these undesirable properties, fenugreek seeds were roasted and blended with regular coffee. As fenugreek seeds were roasted at 130 C for 7 min in an open pan, they exhibited higher 2,2-diphenyl-1-picrylhydrazyl (DPPH) content than the raw seeds (Saini et al., 2016). The beneficial effects of conventional roasting of fenugreek seeds have been studied by many authors, whereas information on phenolic and antioxidant changes after microwave roasting and the effect of roasting time are limited. In one study, roasted fenugreek seed flour was found to have the higher antioxidant capacity and phenolic content with less dietary fiber (Pandey & Awasthi, 2015). The phenolic content of roasted fenugreek seed flour was found to have 48.5 mg as opposed to 45.4 mg of gallic acid equivalents (GAE) per gram of sample, and the antioxidant activities of roasted and raw fenugreek seed flours were 32.0% and 18.1%, respectively.
The fact that fenugreek seeds contain coffee like components and that antioxidant capacity and phenolic compounds increase upon roasting suggests that a coffee-like beverage can be obtained from fenugreek seeds. Therefore, the aim of this study was to obtain an optimum blend formulation of fenugreek seeds and arabica coffee (20% and 50% roasted fenugreek seeds) and microwave roasting (600 W) time (2 and 4 min).
The roasting time of fenugreek beans was an important quality parameter in the production of coffee blends. Therefore, through sensory analysis of the resulting beverages, the mixing ratio and roasting time leading to the highest quality product were determined in comparison to regular coffee. During roasting, simultaneous formation of antioxidants due to Maillard reaction and release of phenolic compounds improves the color, flavor, and odor of coffee blend; thus, it is convenient to analyze sensory attributes, phenolic compounds, and antioxidant capacity together.

| Roasting
One hundred grams of fenugreek seeds was placed at the geometrical center of turntable as a single layer and roasted in a microwave oven (Bosch Built-in Oven HMT75M551B) at 600 W microwave power for 2, and 4 min. Roasting was repeated three times for each condition.
The roasted fenugreek seeds were mixed to assure uniformity, and they were blended with roasted coffee arabica with 20% and 50% (w/w) ( Table 1). The power supplied by microwave was calculated by IMPI (International Microwave Power Institute) 2 L test with three replications. Coffee prepared by 100% roasted coffee arabica was used as control (C5).

| Grinding
A grinder (Delonghi Coffee Grinder KG79) was used separately for roasted fenugreek and control coffee seeds to obtain medium size particles suitable for filter coffee. The grinding was carried out in three batches for coffee and fenugreek seeds individually. Particle size of the ground 2 min roasted fenugreek and coffee seeds was calculated by method described by Maille et al. (2021) by using ImageJ (National Institution of Health, Bethesda, Md., USA) as 0.73 ± 0.3 mm and 0.68 ± 0.3 mm, respectively.

| Brewing
Five grams of microwave-roasted fenugreek seeds and coffee arabica blend was added to 100 ml of 100 ± 2 C (IKEA Fantast Thermometer with Fork Kitchen Thermometer, Sweden) water. French Press (Bodum, Switzerland) was used to brew the samples for 5 min to obtain filter coffee. Totally, 4 L of each blend was prepared throughout the study. Coffee was served warm.

| Sensory analysis
A voluntary consumer panel was conducted with 80 semi-trained panelists over 18 years of age who were preferred coffee consumers and did not have chronic diseases. Care was taken to ensure that panelists were coffee lovers. Formal sensory evaluation training was conducted prior to analysis. The basic requirements of sensory evaluation were explained to the panelists such as what to do and what not to do, and they were informed about the description of sensory characteristics. The sensory panel was conducted at room temperature in a fluorescent-lit room between 09:00 and 15:00. Subjects were asked not to eat or chew gum for 1 h beforehand. Between tastings, the subjects were asked to wait 1 min and drink water as a mouth rinse. Five different coffees were served warm in clear plastic cups with a code name. The survey consisted of two parts. In the first part, subjects were asked to describe the appearance, taste, aroma, and mouthfeel. Sensory attribute definitions and descriptors for freshly brewed coffee samples from Chapko and Seo (2019) and Seninde and Chambers (2020) were used with minor modifications (Table 2). This definition was expressed on a 5-point hedonic sensing scale, ranging from 1 (not sensed at all) to 5 (extremely sensed). In the second part, a 5-point hedonic scale ranging from 1 (dislike extremely) to 5 (like extremely) was used to express whether subjects liked the look, smell, aroma, taste, and mouthfeel.

| Moisture content determination
Fenugreek-arabica blends and ground control coffee were dried in an electrical oven (Nuve ENO55, Ankara, Turkey) at 105 C up to the establishment of constant weight (Association of Official Analytical Chemists [AOAC], 1984). The calculation was done by using weight before they were placed into the oven and weight immediately after they were removed from the oven with two replications.

| pH measurement
The pH of the fenugreek blended and control coffee was determined by using an OHAUS ST 10 pH meter (OHAUS Corp., USA) with an accuracy of ±0.1. Average of two replications was considered.

| Color measurement
The color of roasted fenugreek-arabica blends was measured using (Konica Minolta Spectrophotometer, CM-5, Japan). Results were expressed in terms of CIE color coordinate system (L*, a*, and b*) where L* value represents "lightness," from zero (black) to 100 (white); a* value represents "+redness" or "Àgreenness"; and b* represents "+yellowness" or "Àblueness." For the homogeneity among the runs, three different measurements were performed with two replications.
To provide the same environmental conditions, no sunlight was allowed to pass into the laboratory.

| Total phenolic content (TPC) determination
Total phenols were determined as GAE mg/L according to the method described by Samsonowicz et al. (2019) and Waterhouse (2002).
Folin-Ciocalteu colorimetry was adapted for small sample volumes as microscale protocol. Twenty percent of Na 2 CO 3 was prepared by dissolving 200 g anhydrous sodium carbonate in 800 ml distilled water and brought to a boil. After cooling, crystals of sodium carbonate were added and allowed to stand at room temperature for 24 h. Then the solution was filtered through Whatman filter paper no. 1 and diluted to 1 L with distilled water. To prepare the gallic acid standard, 0.5 g gallic acid was dissolved in 10 ml ethanol and then diluted to 100 ml with distilled water (5 g/L). Dilutions of 0, 1, 2, 3, 5, and 10 ml of the solution were made to 100 ml with water to obtain 0, 50, 100, 150, 250 and 500 mg/L phenol concentrations. After solutions were prepared, 20 μl of coffee extracts (C1-C2-C3-C4-C5) was mixed with 1.58 ml of distilled water and 100 μl of Folin-Ciocalteu and then, the mixture was left at room temperature for 6 min. Three hundred microliters of 20% Na 2 CO 3 was added to the mixture. The samples were incubated for 2 h at room temperature in the dark, and the absorbance of blue-colored solutions was measured at 765 nm using spectrophotometer (T80+, UV/Vis. spectrometer, PG Instrument Ltd.). All measurements were replicated two times.

| Antioxidant activity determination
Percent ABTS (2,2 0 -azinobis (3-ethylbenzothiazoline-6-sulfonic acid)) radical inhibition was used to evaluate antioxidant activity based on the method of Re et al. (1999 where, AA is the ABTS radical inhibition, A s is the absorbance of sample, and A c is the absorbance of control. All measurements were replicated two times.   Table 3 with significant p values. The effects of blending ratio (%) (X 1 ) and microwave roasting time (min) (X 2 ) on quality parameters of fenugreek blends were expressed by mathematical models given by regression equations with adjusted coefficient of determination (R adj 2 ) in Table 4. The coefficient of determination was quite high for all the quality parameters.

| TPC
The TPC of the coffee samples mixed with fenugreek ranged from 930.9 ± 13.4 to 1262.2 ± 17.6 mg GAE/L. As the blend ratio of fenugreek seeds increased, the TPC increased linearly (Table 4).
Similarly, debittered fenugreek flour addition to flour increased the TPC levels (Dhull et al., 2020). TPCs of coffee blends C2 and C4 were higher than the TPC of individual fenugreek and arabica coffee seeds. This can be explained by the synergistic effect of fenugreek and coffee seeds. Similar findings were reported by Krishnaiah et al. (2012). They revealed that TPCs of sole Beta vulgaris L., sole Morinda citrifolia L., and the mixture of these fruit extracts were 0.0455, 0.2104, and 0.2534 mg of TAE/g of extract, respectively, which may be attributed to the synergistic effect of phenolic compounds. Contini et al. (2012) studied the effect of the addition of hazelnut skin waste to the espresso coffee brew on phenolic content of mixture in vitro and found that although hazelnut skin phenolics were in the range of 32.8-327.6 mg, hazelnut skin added to espresso coffee varied from 48.2 to 481.6 mg/serving due to additive effect of phenolics.

| Antioxidant activity
The antioxidant activity of coffee blend brews was measured using ABTS method (Table 3). This method is widely used to evaluate in vitro antioxidant activity of coffee (Jeszka-Skowron et al., 2016;Złotek et al., 2016). DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate) method was not preferred in this study because it is more appropriate for polar compounds, whereas ABTS assay can be used for both lipophylic and hydrophilic compounds (Dudonne et al., 2009). The antioxidant activity of fenugreek blended coffee samples ranged from 78.36 ± 0.0% to 83.485 ± 0.16%. These results were in the range of previous study of Priftis et al. (2015), who observed that percent inhibition by ABTS assay of green coffees roasted at different times was in the range of 33.4-135.0.
The antioxidant activity of 2 and 4 min microwave-roasted fenugreek seeds was 70.501 ± 0.16% and 72.551 ± 0.16%, respectively, whereas ABTS inhibition was 82.57 ± 0.16% for 100% coffee arabica brew. The results were close to the antioxidant activity of fenugreek seeds determined by Mashkor (2014) by DPPH assay ranging from 43.61% to 67.30% inhibition. Antioxidant activity of C1 and C3 was lower than that of C5 whereas the activity of C2 and C4 was higher than that of C5. Regression equation and coefficients show that the effect of blending ratio on the increase of antioxidant activity was greater than that of roasting time (Table 4). When fenugreek seeds were blended with arabica coffee 50%, the synergistic effect of antioxidants becomes highly effective 3.2 | Descriptive sensory analysis of fenugreekarabica blend coffee in comparison with arabica coffee In Figure 1, the mean and standard deviation of the descriptive sensory analysis results of volunteer panelists after tasting fenugreekarabica blend coffee and control coffee were presented. The reliability of the descriptive sensory analysis part was calculated as 67.2% by using Cronbach's alpha. For normality assumption, descriptive sensory data were tested by using Kolmogorov-Smirnov test and found that all the data were not distributed normally. Thus, the significant differences between the samples were evaluated by p values calculated by Kruskal-Wallis test (p < 0.05). Different uppercase letters on the columns indicate a statistically significant difference (p < 0.05) by the Tamhane T2's post hoc test (p < 0.05). Of the 17 sensory attributes used to describe physical appearance, aroma/flavor and mouth feel texture, brown color, burnt and bitter flavor, and astringent texture attributes were found to differ significantly between samples (p < 0.05). However, oily appearance, green color, coffee, fruity, green/vegan, sweet, sour, nutty, caramel, cacao, caffeine, creamy flavor, and viscosity feel were statistically the same between the coffee samples. Figure 1 shows that the amount of visible oil and green color observed by the panelists for fenugreek-arabica blend coffee samples obtained by different roasting times had the same intensity with the regular coffee. Fenugreek blended coffees' brown color intensity was found to be statistically same. Brown color intensity observed for C1

| Physical appearance
and C4 was less than control coffee. However, brown color observed by the panelists for C2 and C3 was statistically the same with control coffee, C5. Instrumental color analysis results highlighted C1 blend because ΔE values were closest to the value of C5.

| Flavor/aroma
Among the physical appearance, flavor/aroma, and mouth feeling, flavor/aroma has the most significant motivation in drinking coffee because flavor is a combination of retronasal aroma and taste. Retronasal perception is formed by the flow of food volatile stream from the back of the throat towards the nasal discharge. The volatile substances interact with the receptors and then processing the sensory information as odor recognition (Mombaerts, 2001). Consumers first perceive and describe the smell of flavor; thus, it is defined as the fragrant component of flavor (Petracco, 2001). In addition, roasting improves the taste and aroma (Nwadi et al., 2020). Thus, aroma substances and their components are primarily responsible for flavor diversity, and they are extremely important for complex products such as coffee (Murphy et al., 1977).
Among 127 sensory descriptors listed for coffee (Hayakawa et al., 2010), 12 sensory descriptors were selected. Figure 1 shows that coffee, fruity, green/vegan, sweet, sour, nutty, caramel, cacao, caffeine, and creamy flavor/aroma sensed by the panelists had statistically the same intensity in all the samples. Mean of the descriptive sensory analysis scores showed that brewed coffee aroma and caffeine flavor notes were sensed higher among other sensory F I G U R E 1 Sensory attributes of fenugreek blended arabica coffees. C1 = 20% blend + 4 min roasted, C2 = 50% blend + 4 min roasted, C3 = 20% blend + 2 min roasted, C4 = 50% blend + 2 min roasted, and C5 = 100% regular coffee. ***Significant at 0.1% level. **Significant at 1% level. *Significant at 5% level. No superscript means not significant. Error bars represent means ± standard deviation. respectively. Limitations of the study design include that the blend samples were brewed at 100 C with 2 C error margin because it has been found in the literature that the brewing temperature has a strong influence on the sensory perception of espresso (Andueza et al., 2003;Klotz et al., 2020).
When 4 min roasted fenugreek seeds blended 50% with arabica coffee (C2), burnt/acrid and bitter sensory attributes sensed by panel- ists were significantly higher than C1, C3, C4, and control coffee. This can be due to dark scorched taste of cooked or nearly burnt slightly sharp and acrid flavors arising from higher roasting time in microwave with higher blend ratio of fenugreek seeds. Instrumental analyses were also in agreement with this result, because as roasting time increased, a significant decrease in the pH values of the samples was observed due to release of acidic chemical compounds and Maillard reaction. Moreover, 50% blend of roasted fenugreek with coffee improved TPC and antioxidant activity, which may contribute to burnt/acrid and bitter sensory attributes.
It is known that ancient Egyptians consumed fenugreek as a vegetable, used its seeds to preserve mummies, and used roasted seeds as coffee and for medicinal purposes (Sarwar et al., 2020). However, in literature, its direct or partial use as a coffee has not been studied, so sensory attributes of fenugreek coffee have not been documented yet. Roasted fenugreek seeds were used as flour and incorporated in food formulations other than coffee, but its use is limited because of its distinctive pungent odor and unique taste (Snehlata & Payal, 2012).
In functional food research, fenugreek has been incorporated as a whole seed meal into different flours that can be used in the production of baked goods, including pizza, bread, and cakes (Afzal et al., 2016;Chauhan & Sharma, 2000;Hegazy & Ibrahium, 2009;Hooda & Jood, 2005a;Hooda & Jood, 2005b;Man et al., 2019). The bitter taste of foods containing fenugreek has been associated with fenugreek saponins, alkaloids, and volatile constituents (Khorshidian et al., 2016;Srinivasan, 2006). Shirani and Ganesharanee (2009) investigated the effects of fenugreek flour on the sensory quality of chickpea-rice-based extruded products and found that fenugreek flour percentage of more than 2% was not accepted because of its distinct bitter taste. Fenugreek flour was obtained in another study by roasting in an open pan at 130 C for 7 min and decreased the bitterness to a certain extent to make possible to use fenugreek in high amount in various preparations with an enhancement of TPC to 48.5 mg GAE/g sample and antioxidant activity to 32.0% (Pandey & Awasthi, 2015). Despite the stated health benefits of fenugreek, its bitter and astringent taste significantly reduces consumption of its flour. Adding it directly to products such as bread, cookies, and cakes in the form of food has caused unexpected changes in the taste and smell of these products.

| Mouth feel
Mouth-feeling also called the body or texture is also an important sensory descriptor for fenugreek blended coffee. Mouth feel affects the perception of taste and is affected by the interaction of mouth layer and food structure during consumption (Taylor & Roozen, 1996).
These perceptions typically include characteristics such as astringency and viscosity, which are more complex sensations resulting from the interaction of food components with the skin and mucous mem-

| Consumer acceptance test
Subjects were asked to evaluate the preference level for the fenu- greek blended coffee samples with regular coffee in the second part of the sensory analysis. The reliability of the consumer acceptance test was calculated as 90.9% by using Cronbach's alpha. The mean and standard deviation of the acceptance level of the samples were presented in Figure 2. Appearance, odor, aroma, taste, and mouth feel liking scores were found to change with respect to different coffee formulations. Figure 3 and Tamhane T2 results showed that the best result close to the scores of coffee control sample (C5) was C1 in terms of appearance, odor, aroma, taste, and mouth feel appreciation. The verification of the best formulation selection was done by the effectiveness index method of Degarmo et al. (1984) by the formulation below.
Value of effectiveness ¼ Treatment value À Worst value ð Þ = Best value À Worst value ð Þ : Effectiveness index showed that appearance, aroma, taste, and mouth feel liking scores of C1 were higher than all the other formulations, whereas in terms of odor, C3's score was slightly higher than C1.
Consumer acceptance results ( Figure 3) were in great agreement with instrumental analysis perspective. Higher TPC and antioxidant activity values were obtained for C2 and C4, which lead to unacceptable appearance, odor, aroma, taste, and mouthfeel by panelists.
While 50% of roasted fenugreek was added to coffee, it caused coffee to reach higher values than the current TPC and antioxidant levels; however, it was not accepted by sensory analyses due to the bitterness of fenugreek. Selection of C1 was also acceptable in terms of color, pH, TPC, and antioxidant activity measurements.

| CONCLUSION
In this study, the possibility to use fenugreek seeds in coffee blend was investigated. When control samples' (C5) L*, a*, and b* values were used as a base for the calculation of ΔE values of the fenugreekarabica blends, the lowest score was obtained by C1. The increase in microwave roasting time and blend ratio of fenugreek seeds decreased the moisture content and pH of samples significantly; thus, the closest results to the control coffee were obtained by sample C1.
As fenugreek was blended 50% with arabica coffee (C2 and C4), TPC and antioxidant activity were improved due to the synergistic effect of fenugreek with coffee.
The sensation scale of oily appearance, green color, coffee, fruity, green/vegan, sweet, sour, nutty, caramel, cacao, caffeine, creamy flavor, and viscosity feel of fenugreek-arabica blends was statistically the same as the control sample. Sensory perception results revealed that C2 sample's burnt/acrid and bitter sensory attributes sensed by panelists were significantly higher than C1, C3, C4, and control coffee.
These findings were consistent with the instrumental analysis. As a result, 4 min roasted fenugreek seeds blended 20% with arabica coffee resulted in higher acceptance score in terms of appearance, aroma, taste, and mouthfeel with a similar oily appearance, green color, coffee, fruity, green/vegan, sweet, sour, nutty, caramel, cacao, caffeine, creamy flavor, viscosity, and burnt/acrid and bitter taste with control coffee. Effectiveness index and instrumental analysis of pH, color, moisture content, TPC, and antioxidant activity also verified these findings. Considering the possibility of coffee bean depletion in the future, in this study, it was proved that roasted fenugreek can be incorporated into the formulation of coffee blends.

CONFLICT OF INTEREST
None.
F I G U R E 3 Liking scores in terms of appearance, odor, aroma, taste, and mouth feel appreciation