Changing dietary patterns, heightened consumer awareness, and increasing prevalence of gluten-related disorders have driven the food industry toward the development of healthier, functional alternatives to traditional wheat-based products. As a result, the demand for gluten-free, microbiologically stable, low-glycemic-load food products has risen significantly [1,2]. This growing need is largely attributed to the rising incidence of celiac disease, type 1 diabetes, and obesity worldwide. While individuals with celiac disease comprise approximately 1% of the global population, up to 83% remain undiagnosed, underscoring the necessity of developing accessible and acceptable gluten-free options [3]. However, many gluten-free crops such as rice, cassava, and corn tend to have high glycemic loads due to low protein and fiber contents and elevated levels of reducing sugars, which may contribute to the development of chronic metabolic diseases [2,4].

Snack bars, particularly cereal-based or functional bars, offer a promising vehicle for delivering nutrient-dense, gluten-free alternatives for health-conscious and time-constrained consumers [5]. Their portability, convenience, and capacity to incorporate diverse functional ingredients make them ideal for bridging nutritional gaps. However, creating gluten-free snack bars that match the structural, textural, and sensory appeal of gluten-containing counterparts remains a technological challenge due to the absence of gluten’s viscoelastic properties [6,7]. To overcome this limitation, researchers have turned to the use of composite flours from underutilized, nutrient-rich sources such as cereals, legumes, and fruits.

Sorghum (Sorghum bicolor L. Moench) is a drought-tolerant, gluten-free cereal widely cultivated in Africa, Asia, and the Americas. It is rich in starch (comprising 75%-79% of its weight), dietary fiber, phenolic compounds, and micronutrients including iron, calcium, and phosphorus [8,9]. Despite its high carbohydrate content and antioxidant potential, sorghum’s protein quality is limited by its low lysine content due to the predominance of kafirin storage proteins.

Mung bean (Vigna radiata) is a nutrient-dense legume native to Southeast Asia but now grown in regions including West Africa, South America, and Australia. When sprouted, mung beans undergo enzymatic changes that enhance protein digestibility and micronutrient bioavailability while reducing antinutritional factors [10,11]. With a protein content ranging from 22% to 24%, low fat levels, and a rich mineral and vitamin composition, sprouted mung beans are a valuable addition to cereal-based products, particularly in combating malnutrition [12,13].

Date fruit (Phoenix dactylifera L.), locally known as dabino in Hausa, is a highly valued functional food widely consumed across arid and semi-arid regions. Dates are composed of about 70% carbohydrates, primarily glucose and fructose, and are rich in dietary fiber, potassium, magnesium, and vitamins of the B complex, such as thiamine, riboflavin, and folate [14,15]. Moreover, their low glycemic index and high antioxidant content make them suitable natural sweeteners in health-oriented formulations [16,17].

Combining malted sorghum, sprouted mung bean, and date fruit flour in snack bar formulations provides a synergistic blend of macronutrients, essential amino acids, antioxidants, and dietary fiber. Nevertheless, the success of such a product depends heavily on optimizing the ratios of these ingredients to ensure desirable physical properties such as spread ratio, bulk density, texture, and structural integrity, which are a part of ready, key evaluation indices by consumers and are important in offering a sense of commercial profitability to processors and marketers. In this regard, D-optimal mixture design, a variant of Response Surface Methodology (RSM), is a powerful statistical tool that enables efficient optimization of multicomponent formulations with a reduced number of experimental runs [18]. This method helps identify the best ingredient proportions by modeling the relationship between mixture components and product responses [19,20].

Therefore, the present study aims to optimize the blend formulation of gluten-free snack bars developed from malted sorghum, sprouted mung bean, and date fruit flour blends using D-optimal mixture design and to evaluate the resulting products’ physical properties. The outcome of this work will contribute to the formulation of nutritious, functional, and gluten-free snack bars utilizing locally available, underutilized crops, while addressing the dietary needs of gluten-sensitive individuals and promoting sustainable food innovation.

Source of Raw Materials

Grains of the improved sorghum variety (KSV-15) were obtained from the Seed Production Unit of the Institute of Agricultural Research (I.A.R), Ahmadu Bello University, Samaru, Zaria, and Kaduna State, Nigeria. Mung bean seeds were obtained, identified, and authenticated at the Department of Agronomy, Michael Okpara University of Agriculture, Umudike, Abia State, Nigeria, as Vigna radiata L. Wilczek species (NM 94 Variety). Dried date palm fruit was purchased from Nassarawa Market, Mbak Itam III, Akwa Ibom State, Nigeria, and was identified and authenticated as the Phoenix dactylifera L. species (Dabino in the Hausa variety) under the voucher number UUPH 8(h) at the University of Uyo Pharmacy Herbarium. Baking ingredients were bought from Etaha Itam Market in Itu Local Government Area. Akwa Ibom State, Nigeria. All the reagents used throughout the study were of analytical grade.

Processing of Malted Sorghum Flour

The method of Bello et al. [20] was used for malted sorghum flour production. Five (5) kg of sorghum grains were sorted to remove foreign matter and soaked for 12 h in potable water (w/v; 1:2). Soaked grains were drained and sprouted by spreading them out on a covered jute bag in a germination box. Water was sprinkled on it daily until sprouting began. After 48 h of sprouting, sprouted sorghum was dried in an oven (NAAFCO BS, OVH – 102, China) at 65°C for 6 h. Sprouts were removed by rubbing through palms. The dried malted sorghum was milled using a laboratory hammer mill (Cu-600 Glufex Medicals and Scientific, UK) and sieved through a 425 µm mesh sieve. The flour was cooled and packaged in a polyethylene bag for further use.

Processing of Sprouted Mung Bean Flour

Production of malted mung bean flour was carried out using the method described by Offia-Olua and Akubuo [21]. Three (3) kg of mung bean seeds were sorted, cleaned, and steeped in potable water for 12 hours. The steeped beans were spread on a moistened muslin cloth and sprinkled with water daily while allowed to sprout for 48 hours. The water sprinkled on the mung bean seeds contained a 0.1% concentration of sodium hypochlorite to destroy or discourage the growth of microorganisms while the seeds were allowed to germinate at 30°C in the germination box. After 48 h of sprouting, the sprouted seeds were kilned in an oven (NAAFCO BS, OVH – 102, China) at 65°C for 4 h to terminate germination; sprouts were removed on palm by abrasion and winnowing. The dried malted mung bean seeds were milled using a hammer mill (Cu-600 Glufex Medicals and Scientific, UK), sieved through a sieve-shaker, cooled, and packaged in an airtight container for further use.

Processing of Date Palm Fruit Powder

Three (3) kg of dried date fruits were cleaned, pitted, and then cut into small pieces and dried in the oven (NAAFSCO BS, OVH – 102, China) at 650°C for 4 h to obtain constant weight and then milled in a grinder (M-20, KA – Werke, GMBH and Co. KG, Staufen, Germany) to obtain date powder. The date powder was packaged in an airtight container for further use, as described by Oraby et al. [22].

Experimental Design for the Preparation of the Flour Blends

A D-optimal mixture design of Response Surface Methodology generated using Design Expert Software (Version 12.0.3.0, Stat-Ease Inc., Minneapolis, USA) was used for the formulation of the flour blends from malted sorghum flour, sprouted mung bean flour, and date fruit powder. The proportion of each flour was expressed as a fraction of the blend form to make the sum of the component ratios 100%. The independent variables and their constraint limits were malted sorghum flour (60% - 80%), sprouted mung bean flour (10% - 30%), and date fruit powder (5% - 10%). The responses were physical properties—weight, diameter, thickness, width, and spread ratio. The ranges used here were selected based on information obtained from literature and preliminary experiments. Table 1 shows the formulated mixture runs generated from the design.

Snack Bars Recipe Standard

Fourteen (14) snack bars were prepared following the respective ratios, each based on the corresponding composite flour generated. From each composite flour, which was mixed in a Kenwood mixer for 3 min to obtain a homogeneous mixture, 100 g of flour was weighed out. Also, 25 mL of egg, 80 mL of date syrup, 50 g of margarine, 5 g of powdered milk, 2 g of baking powder, 2 g of nutmeg powder, 5 mL of vanilla essence, and 0.2 g of salt were blended with 100 g of each composite flour. Each blend was mixed with 150 mL of potable water. The snack bars formulae varied only in the amount of malted sorghum flour, sprouted mung bean, and date fruit powder in the different ratios, but the ingredients remained constant for all the samples.

Table 1: Composite Flour Formulations of Malted Sorghum, Sprouted Mung Bean and Date Fruit Powder using D-Optimal Mixture Design

SMD 1-14 = Sorghum, Mung Bean, and Date Snack Bar.

Processing of Snack Bars

The snack bars were produced according to the method described by Edima-Nyah, et al. [23]. The dry ingredients were manually mixed together in a stainless-steel bowl for about 3 min to obtain a uniform mixture. The liquid ingredients (egg, date syrup, and vanilla essence) were added and mixed for 3 min. Water (150 mL) was incorporated slowly, and the entire dough was mixed thoroughly for about 2 min to obtain a uniform dough. The dough was transferred into greased aluminum pans and compressed in the pans using a spatula to give a uniform mass. The pan covers were placed over them to smoothen the tops and give the bars the desired shape. The dough was baked in an oven at 150°C for 25 min. They were allowed to cool, de-panned, and cut into bar sizes: 8 cm x 3 cm x 2 cm. The snack bars were cooled at ambient temperature (27 ± 2°C) and packaged in a high-density polyethylene pouch. The packaged snack bars were labeled, sealed using an electronic sealing machine, Double Leopard (Model: SP 200H, Taiwan), and stored at ambient temperature (27 ± 2°C) in the laboratory for various determinations.

Determination of Physical Characteristics of Snack Bars

The snack bar's diameter was determined by placing the snack bars horizontally (edge to edge) in a row, and the diameter was measured with a digital Vernier caliper with 0.01 mm accuracy [24]. The mean value was recorded as the diameter of the snack bars. Thickness and the width of the snack bars were determined by stacking the snack bars, one on top of another, and the average thickness and width were taken using a digital Vernier caliper with 0.01 mm accuracy [24]. The weight of the snack bars was determined by placing the snack bars on a digital weighing balance, and the weight was measured and recorded [25]. The spread ratio was calculated as the average diameter/thickness [26].

Statistical Analysis

Analysis of data was performed using IBM SPSS (version 23 software). One-way Analysis of Variance (ANOVA) was used to determine significant (p<0.05) differences between means, which were separated using the New Duncan multiple range test (NDMRT) to perform multiple comparisons between means at p<0.05. Response surface modeling and optimization were accomplished using Design Expert (12.0.3.0) software (Stat-Ease, Minneapolis, United States), with model adequacy check and selection criteria including a significant model at p < 0.05, a reasonably high coefficient of determination (R²) and adjusted R², an insignificant (p > 0.05) lack of fit, and a minimum adequate precision of 4.0.

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