Influence of defatted mango kernel seed flour addition on the rheological characteristics and cookie making quality of wheat flour

Abstract Defatted mango kernel seed flour was added to wheat flour for the production of cookies. The protein contents of the wheat‐mango kernel flour blend were optimized using optimal mixture design of response surface methodology. The farinograph analysis had acceptable mixing profile at 25%‐defatted mango kernel flour incorporation, after which the mixing profile was adversely affected. The pasting temperature was between 65.8 and 75.6°C; peak viscosity ranged between 448 and 521 BU while the final viscosity ranged between 594 and 709 BU. The flour blends had promising dynamic rheological characteristics; at 15% incorporation of defatted mango kernel flour, G’ was greater than G’’ while a stage was reached when G’ was equal to G’’ at 25% incorporation. At 50% incorporation, G’’ was greater than G’. The cookies produced showed high (>70%) quality in terms of physical properties, color, and sensory evaluation at 25% incorporation of defatted mango flour.

The increased researches into gluten-free food materials are yet to translate into production of gluten-free bread that is widely acceptable. This is as a result of challenges in developing gluten-free dough with appropriate viscoelastic and rheological properties suitable for bread production. For dough to be useful for bread production, it needs to pass the tests of descriptive empirical rheological techniques, which include amylograph and extensograph (Awolu, 2018;Dobraszczyk & Morgenstern, 2003;Weipert, 1990). Farinograph provides information that is vital to baking processes such as water absorption, mixing time and intensity, stability, and consistency (Weipert, 1990), while amylograph measures the apparent viscosity and gelatinization temperature (Dobraszczyk & Morgenstern, 2003).
The elastic and viscous components of complex viscosity are separately assessed using dynamic rheology (Weipert, 1990). Dynamic rheology is measured using viscometer and rheometers; both are versatile and efficient instruments which have opened new possibilities for studying viscosity-related problems in the science and processing of cereals (Gerth, 1980). Viscometer measures steady state flow while rheometer measures dynamic characteristics of the strain and temperature-dependent dough. Bread dough displayed viscoelastic properties with nonlinear shear thinning and thixotropic behaviors, and their flow properties are determined using a viscometer and a rheometer (Weipert, 1990). Shear thinning is most obvious in the viscosity curves of dough. At low strains, viscosity is high and dough structure seems to be intact. In contrast, high strains lead to a large disorientation and destruction of the dough's structure and, hence, led to reduced viscosity. Dynamic oscillatory rheometers, employed a sinusoidal oscillating deformation of known magnitude and frequency to calculate the phase lag angle between stress and strain, and elastic (storage modulus, G') and viscous (loss modulus or G'') components of a complex viscosity η* (Weipert, 1990).
Large amounts of food wastes are produced by the food industries (about 35%), and they have been identified as serious causes of environmental problems and economic losses if not utilized effectively (Jahurul et al., 2015). These food industry by-products can be good sources of potentially valuable bioactive compounds. Mango by-products, especially seeds and peels, are considered to be cheap sources of valuable food and nutraceutical ingredients. Mango kernel seeds are agro-industrial wastes with more than one million tons of mango seeds being treated as wastes annually (Karunanithi, Bogeshwaran, Tripuraneni, & Krishna Reddy, 2015). Mango kernel seeds have been shown to contain higher antioxidant activities and phenolic contents than the edible portions (Soong & Barlow, 2004). In fact, mango seed had over 70% of the total antioxidant and phenolic contents of mango fruits. Mango kernel seed flour is obtained by defatting mango seed kernels. Undefatted mango kernel seed had been shown to be rich in protein (7.53 g/100 g), fat (fiber (2.20 g/100 g), carbohydrate (69.77 g/100 g), and energy (421 KCal/100 g) and contained appreciable minerals contents (170 mg/100 g calcium, 210 mg/100 g magnesium, and 365 mg/100 g potassium) (Yatnatti, Vijayalakshmi, & Chandru, 2014).
Mango (Mangifera indica L.) is one of the most important fruits marketed in the world with global production exceeding 26 million tons in 2004 (FAOSTAT, 2006). It is grown naturally or cultivated mainly in tropical and subtropical regions and has been shown to be the second largest tropical fruit crop in the world (Joseph & Abolaji, 1997) behind only bananas (Jahurul et al., 2015). It is a rich source of antioxidants including ascorbic acid, carotenoids, and phenolic (Ribeiro, Barbosa, Queiroz, Knödler, & Schieber, 2008). Mango (Mangifera indica L.) polyphenols exhibit anti-inflammatory and cancer-cytotoxic properties in multiple cancer types, including malignancies of the colon and breast (Banerjee, Kim, Krenek, Talcott, & Mertens-Talcott, 2015;Masibo & He, 2008).
Research focus has been mainly on the utilization of the mango kernel seed oil and the undefatted mango kernel seed flour. The bioactive compounds in the defatted mango kernel seed flour and the protein are left unutilized. The extract yield of phytochemical from mango kernels ranged from 1.0% (hexane extraction) to 5% (ethanol extraction) (Devi & Arumughan, 2007). The implication of this is that the amount of phytochemicals in defatted mango kernel seed flour ranged from 95 to 99%. This defatted mango kernel flour has not been utilized for product development; hence, this research is focused on the utilization of defatted mango kernel seed flour blended with wheat flour in the production of cookies. The influence of the defatted mango kernel flour on the protein content and rheological characteristics of the blends was optimized and evaluated. Cookies were developed from the blends, and the effect of the incorporation of mango kernel seed flour on the cookies quality was evaluated.

| Experimental design
The experimental design for the optimization of the protein content was carried out using optimal mixture design (response surface methodology, design expert, DX 10). The independent variables were wheat flour (0-100 g/100 g) and mango kernel flour (0-100 g/100 g), while the dependent variable was the protein content.
The number of replicates is shown in Table 2.

| Determination of protein content
Protein content of the composite flour was determined using Flash 2000 N/Protein Analyzer (Thermo Scientific). About 3.5 mg sample was analyzed for the determination of the nitrogen content. The protein content was automatically evaluated by assuming a conversion factor of 6.25.

| Rheological characteristics of wheat flour (WWF)-defatted mango kernel flour (DMKF) blends
Blends of wheat flour and defatted mango kernel flour were prepared in the ratios 100:0 (W), 85:15 (X), 75:25 (Y), and 50:50 (Z) by replacing WWF with DMKF. was added from a buret until dough was formed. As the dough is mixed, the farinograph records a curve on the graph paper depicting the farinograph parameters (Awolu, 2018). Parameters measured include water absorption, dough development time, dough stability, and mixing tolerance index.

| Pasting characteristics
The pasting characteristics were determined by using Micro-Visco-Amylograph (model 803201 by Brabender, Germany) according to the standard AACC (2000) methods. About 15 g of the sample was mixed with 100 mL of water. The sample was placed inside the amylograph and allowed to run for about 27 min.

| Dynamic rheology
The dynamic rheology for wheat flour-defatted mango kernel flour blends was carried out by using modified method of Demirkesen et al. (2010) using Modular Compact Rheometer (NCR52, Anton Paar).
The position was set at 2.000 mm, temperature at 25.00°C while the measuring system was PP76. The dough samples were placed between the parallel plates and the edges were carefully trimmed with a spatula. The flow experiments were carried out under steady shear condition (Shear rate ranged from 1 to 50 1/s) while for the frequency sweep test, the strain rate was kept constant below 0.5%; the dough elastic modulus and complex viscosity were measured as a function of frequency (between 0.1 and 100 rad/s).

| Cookies preparation
The method of Sudha et al. (2007) was used to prepare cookies from the wheat flour-defatted mango kernel flour by slightly modifying the method. The composite flour composition for cookies production and the baking conditions is presented in Table 1. After baking, cookies were cooled to room temperature, packed in polypropylene pouches, and sealed till further evaluation.

| Physical characteristics
Method of Sudha et al. (2014) was used for the evaluation of spread (W), and thicknesses (T) of cookies were measured by placing them edge to edge and stacking, respectively. Cookies were rearranged, and measurements were made. The spread ratio W/T was calculated. The weight of the cookies was determined while the objective evaluation of texture expressed as breaking strength (g, force) was measured using the triple beam snap (three-point break) technique of Soma, Mahadevamma, & Sudha (2016) using a texture analyzer (TAHDi, Stable Micro Systems, Godalming, UK).

| Color measurements
The color (L, a, b, and dE) of the cookies was measured using Hunter

| Sensory evaluation
The sensory evaluation was carried out according to Sudha et al. (2014). Cookies were evaluated for color and appearance, texture, taste, and overall quality on a 9-point hedonic scale. The scores assigned in the scorecard for these parameters were as follows: excellent-9, very good-8, good-6, satisfactory-5, fair-3, poor-2, and very poor-1.

| Statistical analysis
The analysis of variance (ANOVA), the multifactor analysis of variance, and the multiple range test were done using the Statgraphic Centurion XVI, version 16.1.11 (StatPointInc). All analyses were carried out in triplicate. The results were expressed as mean ± standard deviation.
Duncan's test at significant level of p ≤ 0.05 was applied to the data to establish the significance of the differences between the samples.

| Protein content of wheat-mango kernel flour blends
The actual and predicted protein contents of wheat-mango kernel flour blends are presented in Table 2

| Pasting characteristics
The results of the pasting characteristics of the composite flour are presented in Table 3; however, the pasting profile is shown in
Higher G'' has been reported to indicate formation of weak gellike structure. It has been established that water added to doughs mainly has strong plasticizing effects, but does not modify the supramolecular organization of high molecular weight proteins (Berland & Launay, 1995). Berland and Launay (1995) also reported that increase in water content only leads to softening of the dough (G', G", and η* decrease) as observed in this work but does not alter dough structure. Bread dough has been shown to displayed viscoelastic properties with nonlinear shear-thinning and thixotropic behaviors (Weipert, 1990). So, the shear-thinning behavior obtained in this study could be said to be appropriate for bread production dough. In addition, low strains had been shown to produce high viscosity (dough structure seems to be intact), and vice versa. This study also had similar behavior with high viscosity at low strain (Figure 4).
Increase in the incorporation of mango seed flour (50%), however, reversed the dynamic rheology trend observed in 100% wheat flour. An equal G' and G'' were obtained as the angular frequency increased in sample Z (Figure 4c), while pure mango kernel flour, the G' was greater than G''. This indicates that mango seed incorporation would promote elasticity of wheat flour, especially when the water content of the dough is high. The complex viscosity has been reported to decrease with the frequency (Liu, Wang, Liu, Zhou, & Luo, 2015). The shear stress versus shear strain plot produced pseudoplastic (shear-thinning) curves (Figure 5a-c).

| Characterization of Cookies
The results of the physical characteristics of the cookies are presented in Table 4. There was no significant difference (p ≤ 0.05) in cookie diameter of samples W, Y, and Z; there was, however, a significant difference (p ≤ 0.05) in cookie diameter of sample X and others. There were significant (p ≤ 0.05) differences in the thickness of the cookies.
Wheat flour had the highest thickness; the incorporation of DMKF significantly (p ≤ 0.05) reduced the cookies thickness. The same trend was also observed in the weight of the cookies. However, cookies made from wheat-mango kernel flour blends had higher breaking strength. The breaking strength of cookies increased by twofold as the incorporation of DMKF increased from 15 to 50%. Breaking strength of cookies at 25% DMKF was close to wheat flour cookies.
The results of the color (Lab) measurement of the cookies are presented in Table 4. Positive L* represents lightness, positive a* represents redness, and positive b* represents yellow. The results indicated acceptable cookies color. Expected color for the cookies is golden Inclusion of defatted mango kernel flour up to 25% in the cookies had color properties reasonably comparable to whole wheat flour cookies.
The sensory evaluation (

| CON CLUS IONS
Incorporation of defatted mango kernel flour into wheat flour would be suitable for production of baked products. The protein content was nutritionally sufficient while the rheological evaluation showed that wheat-defatted mango flour blends up to 25% defatted mango flour addition were adequate; they displayed acceptable dough mixing and viscoelastic behavior. In fact, addition of defatted mango flour enhanced the elastic characteristic of the flour blends. The pasting properties of the blends were similar to 100% wheat flour, indicating a good starch heating properties. The cookies at 25% incorporation of defatted mango kernel flour showed an excellent (>70%) physical and sensory properties as well as acceptable measurement. The overall cookie quality acceptability at 25% defatted mango kernel flour incorporation was over 70%.

ACK N OWLED G M ENTS
The first author acknowledges the Department of Flour Milling,

Baking and Confectionery, CSIR-Central Food Technological
Research Institute, Mysuru, India, for providing equipment used for the analyses carried out in this work. In addition, the first author acknowledged TWAS for providing postdoctoral fellowship hosted by CSIR-CFTIR, Mysore, India.

CO N FLI C T O F I NTE R E S T
Authors declare there is no conflict of interests.

E TH I C A L R E V I E W
This study does not involve any human or animal testing.  Notes. Values in the parenthesis for sensory evaluation indicate maximum score; Values for a particular row followed by different letters as superscript differ significantly (p < 0.05). W-100% wheat flour; X-85% wheat flour + 15% mango kernel flour; Y-75% wheat flour + 25% mango kernel flour; Z-50% wheat flour + 50% mango kernel flour.