A whole grain kernel encloses the germ, endosperm, and bran. The outer coating of bran is rich source of fiber and whereas the inner germ comprises minerals, vitamins, phytochemicals (phenolic acids and phytosterol compounds), and lignans. Pulses are part of a healthy, balanced diet and have been shown to have an important role in preventing illnesses such as cancer, diabetes, and heart disease. Pulses are a low-fat source of protein, with a high fiber content and low glycemic index. The grinding process is a unit operation that reduces the size of the material. It plays a major role in many aspects of the food industry. Many food processes frequently require size reduction, which is accomplished by applying diverse forces to create particles with certain sizes and shapes. All the raw materials were de-hulled by a versatile dhal mill to separate the germ, cotyledons, and husk. The raw materials were powdered and passed through 60 60-mesh BSS sieve.
Proximate plays an important role in knowing the nutrients present in the sample. The protein content is not only a useful parameter for determining nutritional value but also gives important technological indications. Protein content provides an idea of the quantity of water absorbed for a certain level of dough consistency and helps to predict the amount of time required for development, stability, and softening. The constant percentage of acacia gum at 1.0% is used in the formulations due to its function as a thickening agent and stabilizer to complete the characteristics of gluten-free flour (Gambuś, Sikora, & Ziobro, 2007).
The moisture content of food materials before grinding is a significant parameter for the powder to exhibit good flowability. For many food materials, the initial moisture content is the most principal variable determining the size distribution of particles and the grinding time. Thus, controlling the moisture content with such pre-treatments as drying or adding moisture is imperative before grinding.
Multigrain Semolina preparation
The gluten-free instant multigrain semolina was prepared using three different flour formulations. Four different flours (rice, ragi, cowpea, and black gram) were used in the formulations (Fig. 5).
It was found that the addition of acacia gum improves the functional properties of the final product. (Rodge, Sonkamble, Salve, & Hashmi, 2012) stated that the addition of gums results in dietary fiber increase and decreases caloric value by diluting the moisture content.
Table 2
Proximate composition of multigrain Semolina
(g/100g)
|
S1-AG
|
S2-AG
|
S3-AG
|
S1 + AG
|
S2 + AG
|
S3 + AG
|
Wheat
|
Moisture
|
5.91 ± 0.09
|
6.44 ± 0.14
|
7.15 ± 0.21
|
9.29 ± 0.27
|
7.43 ± 0.29
|
6.56 ± 0.33
|
8.19 ± 0.47
|
Ash
|
2.40 ± 0.03
|
2.42 ± 0.06
|
2.44 ± 0.03
|
2.43 ± 0.06
|
2.38 ± 0.03
|
2.23 ± 0.03
|
0.91 ± 0.06
|
Fat
|
0.35 ± 0.08
|
0.85 ± 0.02
|
0.31 ± 0.01
|
0.42 ± 0.03
|
0.73 ± 0.30
|
1.59 ± 0.04
|
0.90 ± 0.07
|
Protein
|
12.41 ± 0.42
|
12.96 ± 0.59
|
14.37 ± 0.44
|
12.25 ± 0.28
|
14.05 ± 0.90
|
14.32 ± 1.35
|
10.65 ± 0.04
|
Carbohydrates
|
78.93 ± 0.57
|
77.33 ± 0.55
|
75.73 ± 0.39
|
75.16 ± 1.97
|
75.41 ± 0.79
|
76.31 ± 1.65
|
79.34 ± 0.49
|
Calories
|
368.49
|
368.83
|
363.18
|
355.23
|
364.42
|
372.79
|
368.06
|
The prepared semolina was analyzed for its proximate composition (Table 12). The moisture content of different semolina samples ranges from 5.91–9.29% depending upon the blending ratio. Moisture percentage showed a significant difference between control (wheat semolina) and multigrain semolina products. There is a gradual increase in the moisture content from 5.91–7.15% in S1-AG to S3-AG (semolina without acacia gum) which is reversed in S1 + AG to S3 + AG (semolina with acacia gum) which decreases from 9.29–6.56%. The highest moisture content was observed for S1 + AG (9.29%) and the lowest for S1-AG (5.91%). The increase in moisture content of semolina with acacia gum might be due to increased water retention with gum which acts as a bind-enhancing agent. The lower moisture in semolina without acacia gum might be due to the adsorption of moisture by flour formulation. The data revealed that the moisture content of semolina decreased with the addition of acacia gum. There is a variation in the protein content of different semolina. The protein content varies from 12.25–14.37%. S1-AG and S2 + AG show an increase in the protein content compared to their formulations F1-AG and F2 + AG. Except for semolina S1-AG and S2 + AG, other semolina samples reported a decrease in protein content after steaming of particular flour formulations. But there is not much variation in the protein content of formulation F3 + AG (14.65%) and the semolina, S3 + AG (14.32%). This could be due to the higher content of protein in cowpea and black gram. (Abioye, Ade-Omowaye, Babarinde, & Adesigbin, 2011) also reported higher protein content of composite flour is due to the high protein content in soybean. However compared to multigrain semolina, wheat has reported less protein content (10.65%).
There is no much difference in the ash content of semolina with and without acacia gum which varies from 2.23–2.43%. Ash content was highest in multigrain semolina compared to wheat semolina (0.91%). this indicates the presence of high mineral content in the product. The ash content showed slight changes in semolina with and without acacia gum. The highest ash content (2.44%) belonged to the semolina with 45% pulse flour without acacia gum and the lowest (2.22%) to the semolina with 45% pulse flour with acacia gum. The addition of pulse flour might improve the mineral contents of the semolina.
The steaming plays a major role in the fat content of flour formulation. The fat content was found to reduce upon steaming. However, except for S3 + AG, the fat content of other semolina S1-AG to S3-AG and S1 + AG to S2 + AG was reduced compared to their respective flour formulations. Among the semolina with gums, gradual increase values were noticed with the addition of acacia gum. This might be due to the probable binding of pulse flour with polysaccharide-rich gum (Savary, Hucher, Bernadi, Grisel, & Malhiac, 2010) at the expense of proteins. The carbohydrate content in semolina ranges from 75.16–78.93%.
Agglomerated products were analyzed for their size by particle size analyzer. The particle size distribution of semolina is presented in Table 13. More than 95% of the flour is of 150 µm size. Increasing the cowpea flour from 20 to 40% increased the coarse particle size distribution in the semolina.
Table 3
Particle size distribution of multigrain Semolina
Particle size (µm)
|
S1 + AG
|
S2 + AG
|
SF3 + AG
|
S1-AG
|
S2-AG
|
S3 -AG
|
Wheat
|
40
|
100.00
|
100.00
|
100.00
|
100.00
|
100.00
|
100.00
|
100.00
|
60
|
100.00
|
99.93
|
99.92
|
100.00
|
100.00
|
100.00
|
100.00
|
100
|
99.50
|
98.67
|
98.77
|
100.00
|
100.00
|
100.00
|
100.00
|
150
|
97.44
|
95.94
|
96.03
|
99.60
|
99.61
|
99.87
|
100.00
|
Wheat semolina showed 100% for 40–150µm flour fractions. Compared to wheat semolina, semolina with acacia gum reported 100% for 40–100µm. While in semolina with gum, the percentages decrease by reducing the flour particle size. The majority of the particles of semolina without acacia gum shared a common particle size range (100%) which could give uniform hydration levels during dough formation and drying. The products were sieved to obtained an average particle size of 150, 60, and 40 µm corresponding to medium, medium coarse, and coarse semolina respectively.
Bulk density is a very important technological attribute of solid bulk products to evaluate product size, particle shape, smoothness, particle surface area, and void fraction. The bulk density of granular products increases with the increase in the size of granules due to low surface area and void fraction between particles.
Table 4
Physical properties of semolina
|
Bulk density (g/cm3)
|
Tap density (g/ml)
|
Swelling capacity (ml)
|
S1-AG
|
0.571 ± 0.01
|
0.60 ± 0.01
|
21 ± 0.31
|
S2-AG
|
0.588 ± 0.01
|
0.59 ± 0.01
|
22 ± 0.51
|
S3-AG
|
0.588 ± 0.01
|
0.57 ± 0.01
|
22 ± 0.48
|
S1 + AG
|
0.667 ± 0.01
|
0.67 ± 0.01
|
25 ± 0.34
|
S2 + AG
|
0.645 ± 0.01
|
0.63 ± 0.01
|
23 ± 0.41
|
S3 + AG
|
0.588 ± 0.01
|
0.57 ± 0.01
|
19 ± 0.51
|
Wheat
|
0.769 ± 0.01
|
0.81 ± 0.01
|
20 ± 0.34
|
The bulk density (g/cm3) is the density of sample measured without the impact of any compression. The bulk density of semolina diverges from 0.571 g/cm3 to 0.666 g/cm3. S1 + AG (0.666 g/cm3) and S2 + AG (0.645 g/cm3) reported the highest bulk density (Table 14). The bulk density of granular products increases with the increase in the size of granules due to low surface area and void fraction between particles. It was found that bulk densities of control samples (0.769 g/cm3) were a little higher than different semolina. This may be due to porous form and small particle size in different semolina samples. The difference between the bulk densities of flour and semolina was due to the difference in their particle sizes. Theoretically, when the particle size decreases, the surface area and void between particles increase, therefore bulk density decreases.
Swelling capacity (SC) is attributed to the capacity of starch molecules to hold water within their structure through hydrogen bonding (Ahmad et al., 2016). SP is vital for the manufacturing and structure retention of different bakery products. SP of flour is associated with the presence of flexible protein molecule that tends to decrease the surface tension of water (Sathe et al., 1982).
The swelling capacity of semolina samples ranges from 19.00–25.00 ml. It is clear from data that the lowest swelling capacity was detected in S3 + AG (19.00 ml) however the highest was reported for S1 + AG (25.00 ml) (Table 14). The swelling power of samples depends on the types of variety, size of particles, and types of processing methods or unit operations. The result reported the semolina sample has high swelling power as compared to its formulations. The swelling capacity of semolina increased with the incorporation of acacia gum. It is explicit that the swelling capacity of semolina is affected by the addition of acacia gum because acacia gum is gelatinized and forms strong binding. This specifies that acacia gum has a positive effect on swelling capacity.
Color plays an important quality parameter for consumers. Based on the composition of different flour, the L*, a*, and b* values has been changed (Table 15).
Table 5
Color intensity of semolina
|
Color
|
Semolina
|
L* (lightness)
|
a* (red)
|
b* (yellow)
|
S1-AG
|
44.95 ± 1.21
|
6.45 ± 0.27
|
12.45 ± 0.20
|
S2-AG
|
53.46 ± 0.79
|
5.46 ± 0.09
|
12.40 ± 0.07
|
S3-AG
|
56.96 ± 0.50
|
4.78 ± 0.05
|
13.83 ± 0.10
|
S1 + AG
|
57.96 ± 0.53
|
5.15 ± 0.20
|
13.02 ± 0.17
|
S2 + AG
|
63.54 ± 0.51
|
4.25 ± 0.08
|
12.08 ± 0.02
|
S3 + AG
|
62.06 ± 0.28
|
4.41 ± 0.10
|
13.04 ± 0.29
|
Wheat
|
72.97 ± 1.43
|
5.39 ± 0.13
|
33.82 ± 1.52
|
Color values (L*, a*, b*) of the various semolina were significantly altered (Table 15). The L* (lightness) values of the samples (with and without acacia gum) increased from 44.95 to 62.06 increased with the increased addition of cowpea flour. The a* and b* values of different flours varied between 4.41 to 6.45 and 12.08 to 13.83, respectively. The a* values were positive, thus indicating the predominance of red color over green color. A reducing trend was noticed in Redness (a*) in all the semolina without gum which ranges from 6.45–4.78. The b* value (yellowness) of the flour increased with increase in cowpea flour. Yellowness (b*) values of control (wheat semolina) were higher than multigrain semolina, representing a strong predominance of the yellow coloration, compared to multigrain semolina. However, variations in the yellowish (b*) were observed in semolina with and without gum. It is well known that the yellow color is correlated both to pigment content and enzymatic reactions, while the red index is strictly related to the development of Maillard reaction products (Oliver, Blakeney, & Allen, 1993).
3.1. Functional atttribures of semolina
Protein solubility (nitrogen solubility) in water and NaCl
Protein solubility of semolina with water and NaCl at pH 7.0 is reported in Table 16.
Table 6
Protein solubility of semolina
Flours
|
Protein soluability (%)
|
|
Water, pH 7.0
|
0.5 M NaCl, pH 7.0
|
S1 + AG
|
126.21 ± 2.36
|
6.72 ± 0.31
|
S2 + AG
|
270.65 ± 13.62
|
10.11 ± 0.13
|
S3 + AG
|
165.21 ± 1.63
|
12.27 ± 0.33
|
S1-AG
|
120.79 ± 1.43
|
6.84 ± 0.24
|
S2-AG
|
89.56 ± 5.45
|
8.75 ± 0.42
|
S3-AG
|
177.49 ± 6.32
|
8.56 ± 0.32
|
Wheat
|
167.38 ± 4.81
|
19.91 ± 0.15
|
The highest protein solubility of 270.65 ± 13.62% was recorded for S2 + AG followed by S3-AG S3-AG with 177.49 ± 6.32%. However, the protein solubility of all the semolina was found to enhance compared to its formulations. The least solubility of 89.56 ± 5.45% was observed in S2-AG in 0.5 m NaCl solution. Protein solubility was found to be reduced in NaCl compared to water extract in all the semolina samples. However, the protein solubility of these three formulations was increased compared to raw flour except ragi flour. Semolina with acacia gum has reported the highest protein solubility compared to semolina without gum.
Water absorption capacity is the interaction of nutrients and bioactive compounds of samples with water. The WAC is found to be more in multigrain semolina samples compared to control wheat semolina. WAC of semolina with and without acacia gum ranged from 189.81-234.09% (Table 17).
Water absorption capacity is the interaction of nutrients and bioactive compounds of samples with water. The WAC is found to be more in multigrain semolina samples compared to control wheat semolina. WAC of semolina with and without acacia gum ranged from 189.81-234.09% (Table 17).
Table 7
Functional properties of multigrain semolina
|
Semolina without acacia gum
|
Semolina with acacia gum
|
Wheat
|
|
S1-AG
|
S2 -AG
|
S3 -AG
|
S1 + AG
|
S2 + AG
|
S3 + AG
|
WAC (%)
|
234.09 ± 1.78
|
196.30 ± 0.96
|
206.72 ± 0.61
|
231.92 ± 1.68
|
194.47 ± 1.72
|
189.81 ± 0.19
|
103.86 ± 1.81
|
WSI (g/100g)
|
3.55 ± 0.78
|
5.82 ± 0.61
|
4.69 ± 0.82
|
4.76 ± 0.77
|
5.59 ± 0.73
|
8.01 ± 0.23
|
4.31 ± 0.59
|
OAC (%)
|
87.37 ± 0.58
|
94.35 ± 0.18
|
98.84 ± 0.90
|
88.20 ± 1.26
|
86.35 ± 1.01
|
85.30 ± 0.81
|
58.19 ± 0.40
|
FC (%)
|
0.80 ± 0.00
|
0.80 ± 0.00
|
4.00 ± 0.00
|
0.80 ± 0.00
|
0.80 ± 0.00
|
0.80 ± 0.00
|
5.33 ± 0.46
|
FS (%)
|
0.00 ± 0.00
|
0.00 ± 0.00
|
0.00 ± 0.00
|
0.00 ± 0.00
|
0.00 ± 0.00
|
0.00 ± 0.00
|
0.00 ± 0.00
|
EA( %)
|
1.64 ± 0.03
|
3.45 ± 0.00
|
3.45 ± 0.06
|
1.68 ± 0.02
|
3.45 ± 0.06
|
1.72 ± 0.00
|
3.28 ± 0.05
|
ES (%)
|
100.00 ± 0.00
|
50.00 ± 0.00
|
50.00 ± 0.00
|
100.00 ± 0.00
|
50.00 ± 0.00
|
100.00 ± 0.00
|
100.00 ± 0.00
|
WAC-Water absorption capacity (%), WSI-Water solubility index (g/100g), OAC-Oil absorption capacity (%), FC (foaming capacity), FS (foaming stability), EA (emulsion activity) and ES (emulsion stability).
The ability of multigrain semolina significantly increases with cowpea flour than the control sample (wheat semolina). This could be due to the higher dietary fiber content in multigrain semolina that might effectively contribute to increasing water holding capacity (Juliano & Villareal, 1993); (Petitot, Boyer, Minier, & Micard, 2010). These results are consistent with those reported for soy flour (Petitot et al., 2010). The high carbohydrate contents of flour are also attributed to the high WAC of foods (Anthony et al., 2014). From the outcomes, the semolina samples exhibited agreeable WAC thus creating appropriate functional ingredients for the development of ready-to-eat food products.
OAC was found to increase from S1 to S3 in the presence of acacia gum (Table 17). In addition to acacia gum, the increase in the cowpea flour concentration from S1 to S3 might have contributed to high oil absorption capacity. High OAC is due to the presence of several non-polar amino acids that bind the hydrocarbon chains of fats (Sathe, Deshpande, & Salunkhe, 1982). The proteins in the sample improve hydrophobicity by revealing more non-polar amino acids to the fat to take up oil (Awolu, Osemeke, & Ifesan, 2016). The OAC shows the increasing level of cowpea flour in semolina is directly proportional to the presence of acacia gum whereas the interactive effect of multigrain semolina in the absence of acacia gum is negative.
The foaming and emulsion properties of multigrain semolina with and without acacia gum are shown in Table 17. From the analysis conducted, it is seen that the foaming capacity of (S3-AG) was 4.0% compared to (S1-AG) and (S2-AG), while foaming stability was 0.00. The emulsion capacity was found to be similar in S2-AG and S3-AG with 3.45% compared to S1-AG with 1.64%. However, emulsion stability was found to be 100% in S1 + AG and 50% in S2 + AG and S3 + AG. The data proves that S3-AG has a high foaming capacity and emulsion activity compared to semolina with acacia gum. Foam capacity plays an essential role in manufacturing and sustaining the structure of different food products like ice creams and bakery products. Due to its high foaming capacity, it will be good in bakery product preparations.
The LGC measures the lowest quantity of flour needed to custom a gel in a measured volume of water. It varies from sample to sample based on the comparative ratios of lipids, protein, and carbohydrates.
Table 8
Least gelation concentration of multigrain semolina.
|
Percentage (g sample/100g H2O)
|
|
Samples
|
2
|
5
|
10
|
15
|
20
|
25
|
30
|
S1-AG
|
-
|
-
|
+
|
+
|
+
|
+++
|
+++
|
S2-AG
|
-
|
-
|
+
|
+
|
+
|
+++
|
+++
|
S3-AG
|
-
|
-
|
+
|
+
|
++
|
+++
|
+++
|
S1 + AG
|
-
|
-
|
+
|
+
|
++
|
+++
|
+++
|
S3 + AG
|
-
|
-
|
+
|
+
|
++
|
+++
|
+++
|
S3 + AG
|
-
|
-
|
+
|
+
|
++
|
+++
|
+++
|
Each value represents the mean of three determinations. -= no gelation, += mobile gel, ++ = firm gel, +++ = very firm gel.
S1-AG = Semolina 1 without gum; S2-AG = Semolina 2 without gum; S3-AG = Semolina 3 without gum; S1 + AG = Semolina 1 with gum; S2 + AG = Semolina 2 with gum; S3 + AG = Semolina 1 with gum.
Firm gel formation is seen at 20% concentration for S3-AG and all the semolina with gum (Table 18). Semolina with and without gum forms a very firm gel at a concentration of 25% and above. Protein and starch content are abundant in pulse/legume flours. The physical competition for water between protein and starch gelatinization plays a major role in gelation capacity of samples (Kaushal, Kumar, & Sharma, 2012). The incorporation of acacia gum in composite flour increased the gelling properties. The low gelation concentration may be used for the formation of curd or as an additive to other gel-forming materials in food products.
Phenolics provide vital responsibilities in the reproduction and growth of plants by acting as defense mechanisms. Phenolic substances also provide health benefits associated with reduced risk of chronic diseases and contribute to antioxidant activity (Liu, 2007). TPC and TFC were determined as mg gallic acid and mg catechin/100 g sample, respectively. The hydrothermal treatment during the preparation of foods may affect the content of phytochemicals (Towo, Svanberg, & Ndossi, 2003); (Zieliński, Michalska, Piskuła, & Kozłowska, 2006).
Table 9
Phenolic indexes its bioactivity of individual and composite flours
Samples
|
Total phenolic content (TPC)
|
Total flavonoid content (TFC)
|
Proanthocyanidin content (PAC)
|
Antioxidant activity (%)
|
S1-AG
|
23.88 ± 0.85
|
2.64 ± 0.03
|
1.57 ± 0.03
|
89.03 ± 0.12
|
S2-AG
|
20.10 ± 0.38
|
2.67 ± 0.07
|
1.39 ± 0.20
|
88.37 ± 0.40
|
S3-AG
|
40.25 ± 2.03
|
1.75 ± 0.10
|
1.06 ± 0.12
|
88.34 ± 0.58
|
S1+AG
|
26.13 ± 0.26
|
2.59 ± 0.13
|
1.62 ± 0.27
|
88.66 ± 0.46
|
S2+AG
|
26.74 ± 0.77
|
2.68 ± 0.10
|
1.80 ± 0.19
|
88.12 ± 0.45
|
S3+AG
|
14.40 ± 0.20
|
1.97 ± 0.05
|
3.13 ± 0.27
|
86.49 ± 0.37
|
Wheat
|
14.26 ± 0.21
|
0.50 ± 0.06
|
3.42 ± 0.26
|
88.74 ± 0.40
|
TPC, TFC, and PAC in multigrain semolina were significantly different from the control wheat semolina (Table 19). Semolina without acacia gum (S3-AG) reported higher TPC (40.25mg/g) compared to other samples. In the presence of acacia gum, the values were found to decrease from 26.13 to 14.40mg/g. This may be due to a decrease in the content of ragi flour from F1 to F3.
Steaming of composite flours leads to applicable changes in phenolic indexes. Although steaming decreased the polyphenolic content of S1-AG and S2-AG, The semolina prepared without acacia gum (S3-AG) showed the highest total phenolic content (40.25 ± 2.03mg/g) among different semolina.
Semolina with acacia gum (S2 + AG) reported the second-highest phenolic content (26.74 ± 0.77 mg/g). The steaming also reduced the total flavonoids and proanthocyanidins content in different semolina compared to composite flours. Similar results were reported by (Zhang, Chen, Li, Pei, & Liang, 2010) buckwheat flour. A similar decrease in the polyphenol content of pinto and black beans after steam treatment was reported (Xu & Chang, 2009). The decrease in the content of polyphenols, flavonoids, and proanthocyanidin might be due to the polymerization of polyphenols and decarboxylation of phenolic acids that occur during thermal treatment (Krystyjan, Gumul, Ziobro, & Korus, 2015). The total flavonoid content of F3-AG flour extracts declined from 6.87 ± 0.43 to 1.79 ± 0.03 mg/g and the total phenolics in S3-AG increased from 17.38 ± 1.65 to 40.25 ± 2.03 mg/g. The changes in the total flavonoid content of semolina could be due to the thermal degradation, oxidation of phenolics in the presence of oxygen and moisture, polymerization, and depolymerization of high molecular weight phenolics (Shahidi & Chandrasekara, 2015). (Hithamani & Srinivasan, 2014) have reported a reduction of the total flavonoid content of finger millet four by 68 and 10%, after hydrothermal treatments.
When composite flour was processed by steaming, the hydroxyl radical scavenging activity increased from 74.41–88.34%. DPPH scavenging activity ranges from 88.12-89.0% in different semolina samples. This might be due to the thermal destruction of cell wall polymers. This reduces the heat-sensitive phenolic compounds and releases insoluble-bound phenolic which increases the antioxidant activities of the semolina extracts.