Optimization of Extrusion Cooking for Enhanced Physicochemical Properties in Jackfruit Seed (Artocarpus altilis) and Nixtamalized Maize (Zea mays L.) Flour Blend

Abstract

Extrusion is a key process in the production of ready-to-eat snacks, with a wide processing capacity of non-conventional raw materials such as jackfruit seed flour and nixtamalized corn, which improves the nutritional profile of the snacks. This study aims to optimize the extrusion cooking parameters of extrusion temperature (ET), moisture content (MC), and the ratio of jackfruit seed flour in nixtamalized maize flour (JSF/NMF) to enhance the physicochemical properties of ready-to-eat extruded products. The process parameters and JSF/NMF were optimized using a Box–Behnken design and response surface methodology. JSF/NMF and ET were found to significantly (p < 0.05) affect specific mechanical energy (SME), the expansion index (EI), hardness (H), the water absorption index (WAI), the browning index (BI), and overall acceptance (OA). The optimal conditions were an ET of 145.15 °C, MC of 22 g/100 g, and JSF/NMF of 70 g/100 g, which led to an extrudate with an SME of 273.38 J/g, EI of 1.12, H of 58.75 N, WAI of 6.14 g/g, BI of 61.68, OA of 4.56, protein content of 12.10 g/100 g, and fiber content of 4.86 g/100 g. It was demonstrated that the use of jackfruit seed flour and nixtamalized maize flour as non-conventional flour in the preparation of ready-to-eat snacks through extrusion was feasible in a single-screw extruder, obtaining favorable results in quality parameters that characterize extruded snacks.

1. Introduction

Snacks are usually considered unhealthy products since their long-term consumption is related to increases in health problems. Some consumers who are aware of the consequences of consuming unhealthy snacks prefer products that are made with natural ingredients; no artificial colors or flavors; low sodium, sugar, fat, and calories; high protein and fiber; and no gluten [1].

The development of new products with these characteristics requires certain techniques in food processing [2,3]. Extrusion serves as an alternative method for processing mixtures of flours where proteins and starch are fused in the presence of controlled humidity, high temperatures, and short residence time [3]. This process produces cooked products that have different shapes and are ready for consumption [4,5].

Extrusion cooking has benefits such as denaturing undesirable enzymes, inactivating some anti-nutritional factors (trypsin inhibitors, hemagglutinins, tannins, and phytates), improving the digestibility of starch and proteins, and preserving the natural colors and flavors of food [6].

The main role of starch and proteins is to provide structure, texture, mouth feel, volume, and many other desired characteristics for the finished product, as well as their nutritional properties [2,7,8,9,10].

Maize (Zea mays L.) is one of the most important cereals in the world since it provides necessary nutrients to the diet and is one of the most used cereals in extrusion due to its physical, nutritional, and sensory characteristics [8,11,12,13,14,15].

Nixtamalization is a traditional process that improves the nutritional and functional properties of corn, particularly in the production of corn flour and extruded products. This method involves soaking and cooking corn in an alkaline solution, which not only improves digestibility but also increases the bioavailability of niacin, calcium, and essential nutrients [13,14,15,16]. Furthermore, Colbert et al. [16] mention that consumers have shown a favorable response to nixtamalized products, indicating a strong market potential for these nixtamalized corn products. Nixtamalized corn flour could be complemented with jackfruit flour.

Jackfruit (Artocarpus altilis) is a fruit, and its seeds are an unconventional source of starch, dietary fiber, minerals, vitamins, and protein [17,18,19,20,21]. Jackfruit seeds are increasingly recognized for their potential in developing extruded snacks, offering a nutritious alternative to traditional ingredients. Its high carbohydrate (83.61%) and protein (15.32 g/100 g) content, along with low fat levels (6.46%), make jackfruit seed flour an ideal candidate for creating healthier snack options [22].

Incorporating jackfruit seed flour can improve the nutritional profile of snacks, addressing issues such as malnutrition and anemia through iron fortification [22]. Studies show that blending jackfruit seed flour with other flours, such as rice and soy flour, improves the expansion rates and antioxidant properties of extrudates [23,24]. However, no research has been conducted on the development of extruded snacks from mixtures of jackfruit seed flour and nixtamalized corn to enhance the nutritional value of the products obtained and give added value to these materials. The study aims to optimize the extrusion cooking parameters of extrusion temperature (ET), moisture content (MC), and the ratio of jackfruit seed flour to nixtamalized maize flour (JSF/NMF) to enhance the physicochemical properties of ready-to-eat extruded products.

2. Materials and Methods

2.1. Raw Materials

Jackfruit seed (Artocarpus altilis) was obtained in the municipality of Jalapa de Díaz Oaxaca, Mexico. Fruits that presented uniform brown coloration on the shell were selected to facilitate manual extraction of the seeds. The seeds were cut into slices (0.5 cm) and subjected to cooking (100 °C/3 min), dried at 60 °C/25 h, ground, and sieved (mesh No. 35 = 0.5 mm) [18,19]. Creole-type yellow maize (Zea mays L.) was obtained in the municipality of Jacatepec, Oaxaca, Mexico. The nixtamalized maize flour was obtained according to the procedure reported by Rodríguez-Miranda et al. [11].

2.2. Chemical Composition, Total Energy, and pH

The raw materials and the optimal product were chemically analyzed according to the AOAC [25] methods for moisture (925.10), ash (923.03), protein (920.87), crude fiber (925.08), and fats (920.39). The total carbohydrate content was obtained by difference (100 − moisture + ash + protein + crude fiber). The total energy was calculated according to Rivera-Mirón et al. [7], and the pH was measured by dispersing 1 g of sample in 10 mL of distilled water [8].

2.3. Degree of Gelatinization

The degree of gelatinization of the raw materials and the optimal product was determined according to the methodology described by Gandhi et al. [26].

2.4. Determination of Total Color Difference (ΔE) and Browning Index (BI)

Luminosity (L*), red–green chromaticity (a*), and yellow–blue chromaticity (b*) were measured using a Hunter Lab colorimeter (MiniScan Hunter Lab, model 45/0L, Hunter Associates Lab., Ind., USA). The total color difference (ΔE) and the browning index (BI) were calculated using Equations (1), (2a), and (2b), respectively. The color chart and color number were obtained with the help of the EasyRGB (http://www.easyrgb.com accessed on 10 December 2024) color search engine.

$$\Delta E={[{(L_s^{*}-L^{*})}^2+{(a_s^{*}-a^{*})}^2+{(b_s^{*}+b^{*})}^2]}^{1/2}$$

(1)

$$BI={\displaystyle \frac{\left[100*\left(\mathrm{X}-0.31\right)\right]}{0.17}}$$

(2a)

$$X={\displaystyle \frac{\left(a^{*}+1.75*L^{*}\right)}{\left(5.645*L^{*}+a^{*}-3.012*b^{*}\right)}}$$

(2b)

2.5. Extrusion Process

A Brabender brand single-screw laboratory extruder was used (Model E19/25 D, Brabender Instruments Inc., South Hackensack, NJ, USA). The temperature profile used was the following: zone 1: 60 °C; zone 2: 80 °C; zone 3: 120 °C; and zone 4: 120–180 °C (Table 2). The feed speed was 20 kg/h, the screw speed was 115 rpm, the screw compression force ratio was 3:1, the length/diameter ratio was 20:1, and the diameter of the output die was 3 mm.

2.6. Determination of Specific Mechanical Energy (SME)

SME (J/g) was calculated according to Pensamiento-Niño et al. [6] and according to Equation (3), as follows:

$$SME={\displaystyle \frac{\mathrm{\Omega }\times \mathrm{\omega }\times 60}{M_{feed}}}$$

(3)

where Ω is the torque exerted on the extruder impeller (N-m), ω is the angular velocity of the screw (rad/sec), and M_feed is the mass flow of the feed (g/min).

2.7. Analysis of Physical Characteristics

The expansion index (EI) was determined according to Navarro-Cortez et al. [12] and porosity (Φ) was determined according to Özer et al. [27]. Hardness (H) was determined by measuring the maximum compressive breaking strength [7] on a TA-XT2 texture analyzer (Texture Technologies Corp., Scarsdale NY/Stable MicroSystems, Haslemere, Surrey, UK) in compression mode using a Warner–Bratzler cutting blade with a test speed of 5 mm/s. The result is reported in Newtons (N). For each run, 15 repetitions were performed. The water absorption index (WAI) and the water solubility index (WSI) were determined according to the methodology described by Rodríguez-Miranda et al. [28].

2.8. Sensory Evaluation

A hedonic test was performed with 100 untrained panelists to assess overall acceptability (OA) [13]. The samples were coded with a random three-digit number, and the evaluation was carried out in three sessions. Extruded products were evaluated using a 7-point scale (from 1 = “extremely unpleasant” to 7 = “extremely liked”).

2.9. Experimental Design and Statistical Analysis

A Box–Behnken experiment design was performed with three independent variables using a commercial statistical package (Design-Expert 7.0.0, Statease Inc., Minneapolis, MN, USA) (Table 2). The independent variables were the extrusion temperature (ET), moisture content (MC), and ratio of jackfruit seed flour to nixtamalized maize flour (JSF/NMF). The response variables were SME, EI, Φ, H, WAI, WSI, pH, ∆E, BI, and OA. Experimental data were analyzed using the response surface methodology and a commercial statistical package (Statistica Version 10.0, StatSoft, Inc., Tulsa, OK, USA). The effect of the independent variables on the responses was interpreted using a second-order polynomial model. The statistical significance of the regression terms was examined using an analysis of variance for each response. The extrusion variables (ET and MC) and the JSF/NMF ratio were optimized. The optimization involved maximizing EI, Φ, and OA and minimizing SME and H, while the other responses remained in the found interval. Verification of the optimized conditions and characterization of the optimal product were carried out according to the determinations mentioned in the previous sections.

3. Results and Discussion

3.1. Chemical Composition, Total Energy, Degree of Gelatinization, and Color Parameter

Significant differences (p < 0.05) were found in all the determinations evaluated between raw materials (Table 1). The moisture content in both samples was below the level of 12% recommended by NOM-147-SSA1-1996 [29] to avoid deterioration due to microbial contamination, molds, and yeasts. JSF had higher (p < 0.05) protein, fat, crude fiber, and ash content, while NMF had the highest carbohydrate content (Table 1). The results obtained for JSF are superior to those reported by Oladunjoye et al. [17] and like those reported by Juárez-Barrientos et al. [19] and Goh et al. [20]. The protein, fiber, ash, and carbohydrate content found in NMF was like that reported by Cuj-Laines et al. [13].

The highest (p < 0.05) total energy was found for NMF due to the higher carbohydrate content, which provides higher calories than JSF (Table 1). The result found for JSF was within the range reported by Juárez-Barrientos et al. [19] (1660.96–1694.81 kJ/100 g). NMF showed higher percentage degrees of gelatinization, pH, and white coloration (L*), while JSF had higher values for parameters a* and b*. These color differences can be seen in the color chart (Table 1).

Table 1. Chemical composition, total energy, degree of gelatinization, pH, and color parameters for jackfruit seed flour (JSF), nixtamalized maize flour (NMF), and extruded mixtures (optimal conditions).

Component (g/100 g)	JSF	NMF	Extruded Mixtures (JSF/NMF) 1
Moisture	8.58 ± 0.06 b	7.25 ± 0.12 a	7.66 ± 0.33 a
Protein	13.20 ± 0.28 c	10.85 ± 0.33 a	12.10 ± 0.06 b
Fat	6.87 ± 0.73 a	3.69 ± 0.81 b	2.18 ± 0.30 c
Fiber	4.24 ± 0.36 b	1.80 ± 0.04 a	4.86 ± 0.37 c
Ash	3.78 ± 0.19 a	1.40 ± 0.01 b	2.94 ± 0.02 c
Carbohydrates	71.90 ± 1.26 a	82.30 ± 0.66 b	77.93 ± 0.42 c
Total energy (kJ/100 g)	1680.00 ± 13.35 a	1694.00 ± 17.49 a	1585.49 ± 10.51 b
Degree of gelatinization (%)	14.81 ± 0.17 a	17.86 ± 0.06 b	97.33 ± 0.79 c
pH	6.05 ± 0.00 a	7.76 ± 0.03 b	5.82 ± 0.06 c
L*	61.60 ± 0.01 a	79.80 ± 0.36 b	53.78 ± 0.34 c
a*	6.31 ± 0.01 a	0.41 ± 0.01 b	9.50 ± 0.44 c
b*	22.93 ± 0.02 a	15.45 ± 0.18 b	26.88 ± 0.07 c
# Color
Color primer	#AE906D	#D2C5A9	#9F7A53

The results are the average of three determinations ± standard deviation. Equal letters in the same row indicate significant differences (p < 0.05). Values are expressed on a dry basis, except moisture. ¹ Extruded at 145.15 °C, moisture content of 22 g/100 g, and JSF/NMF of 70 g/100 g. Source: authors based on experimental data.

Table 1. Chemical composition, total energy, degree of gelatinization, pH, and color parameters for jackfruit seed flour (JSF), nixtamalized maize flour (NMF), and extruded mixtures (optimal conditions).

Component (g/100 g)	JSF	NMF	Extruded Mixtures (JSF/NMF) 1
Moisture	8.58 ± 0.06 b	7.25 ± 0.12 a	7.66 ± 0.33 a
Protein	13.20 ± 0.28 c	10.85 ± 0.33 a	12.10 ± 0.06 b
Fat	6.87 ± 0.73 a	3.69 ± 0.81 b	2.18 ± 0.30 c
Fiber	4.24 ± 0.36 b	1.80 ± 0.04 a	4.86 ± 0.37 c
Ash	3.78 ± 0.19 a	1.40 ± 0.01 b	2.94 ± 0.02 c
Carbohydrates	71.90 ± 1.26 a	82.30 ± 0.66 b	77.93 ± 0.42 c
Total energy (kJ/100 g)	1680.00 ± 13.35 a	1694.00 ± 17.49 a	1585.49 ± 10.51 b
Degree of gelatinization (%)	14.81 ± 0.17 a	17.86 ± 0.06 b	97.33 ± 0.79 c
pH	6.05 ± 0.00 a	7.76 ± 0.03 b	5.82 ± 0.06 c
L*	61.60 ± 0.01 a	79.80 ± 0.36 b	53.78 ± 0.34 c
a*	6.31 ± 0.01 a	0.41 ± 0.01 b	9.50 ± 0.44 c
b*	22.93 ± 0.02 a	15.45 ± 0.18 b	26.88 ± 0.07 c
# Color
Color primer	#AE906D	#D2C5A9	#9F7A53

The results are the average of three determinations ± standard deviation. Equal letters in the same row indicate significant differences (p < 0.05). Values are expressed on a dry basis, except moisture. ¹ Extruded at 145.15 °C, moisture content of 22 g/100 g, and JSF/NMF of 70 g/100 g. Source: authors based on experimental data.

3.2. Specific Mechanical Energy (SME)

The highest SME (409.38 J/g) (Table 2) occurred at an ET of 120 °C, MC of 22 g/100 g, and JSF/NMF of 35 g/100 g. The lowest SME (209.03 J/g) occurred at an ET of 180 °C, MC of 20 g/100 g, and JSF/NMF of 70 g/100 g. Therefore, at higher temperature and JSF content, a decrease in SME was observed (Figure 1). ET and JSF/NMF presented a significant negative linear effect (p < 0.05) on SME (Table 3). The regression model of the experimental results showed a coefficient of determination (R²) of 0.876 as a significant regression model (p < 0.05) without a lack of adjustment. A reduction in SME with an increase in temperature is associated with a reduction in viscosity within the extruder [30].

The macromolecular transformations that decrease viscosity during the extrusion process are the gelatinization of starch and changes in protein structure [6]. This behaviour is similar to behavior reported by other studies [6,30]. The increase in the content of JSF in NMF produced a reduction in SME. The reason is the higher content of proteins and lipids in the mixture from JSF. It has been reported that the reduction in SME is promoted by the lipids and proteins along with an increase in temperature because the viscosity of lipids decreases with the increase in temperature [7]. Furthermore, a gel is formed during the denaturation of proteins, which reduces shear stress during the process of extrusion and decreases SME [31].

3.3. Expansion Index (EI) and Porosity (Φ)

The highest EI (1.89) and Φ (5.55) occurred at an ET of 150 °C, MC of 18 g/100 g, and JSF/NMF of 0 g/100 g (Table 1). Increasing JSF in NMF decreases EI and Φ (Figure 2A–F). The regression coefficient showed a significant negative linear effect (p < 0.05) for both responses (EI and Φ), with significant regression models (p < 0.05) showing R² values of 0.799 and 0.759, respectively, without a lack of adjustment (Table 3).

EI and Φ have a strong, positive correlation with higher expansion and higher porosity of the extruded product. Increasing JSF increased the protein, lipid, and fiber content, which probably caused an increase in the viscosity of the mixture during the extrusion process and decreased the expansion of the extrudates. The protein type, its content, and the fiber content in samples have been reported to decrease IE [14].

This occurs by increasing the protein and fiber present in the mixtures. Protein and fiber (a) decrease the content of the starch present, (b) affect the gelatinization of the remaining starch in the mixture, and (c) compete for water present in the matrix during the extrusion process. This limits the expansion of the material when exiting from the die and decreases IE and the Φ [28]. Felix-Medina et al. [14] mentioned that the fiber and protein of common beans affect the gelatinization of starch. The reason is that the non-starch polysaccharides of dietary fiber and the type of protein (globulins) can retain water more strongly than starch during the process of extrusion, thus reducing the expansion of the product.

Table 2. Experimental data of extruded snacks for response surface analysis.

Run	Independent Variables			Response Variables
	ET (°C)	MC (g/100 g)	JSF/NMF (g/100 g)	SME (J/g)	EI	Φ	H (N)	WAI (g/g)	WSI (%)	pH	ΔE	BI	OA
1	120 (−1)	18 (−1)	35 (0)	355.41	1.59	1.18	99.73	7.87	5.79	6.96	35.42	39.20	2.57
2	180 (1)	18 (−1)	35 (0)	235.27	1.57	1.36	38.30	7.30	5.34	7.08	37.63	43.36	3.13
3	120 (−1)	22 (1)	35 (0)	404.38	1.29	0.42	59.37	5.66	3.84	7.07	37.33	43.81	3.27
4	180 (1)	22 (1)	35 (0)	237.05	1.70	1.38	57.87	6.60	4.81	7.08	37.41	43.19	3.27
5	120 (−1)	20 (0)	0 (−1)	388.52	1.74	1.57	118.00	7.89	5.51	7.99	30.23	32.01	2.80
6	180 (1)	20 (0)	0 (−1)	321.48	1.33	0.17	83.04	7.62	5.39	8.05	32.21	35.44	2.97
7	120 (−1)	20 (0)	70 (1)	284.35	1.36	0.17	94.93	5.30	5.92	6.82	41.17	51.35	2.40
8	180 (1)	20 (0)	70 (1)	209.03	1.53	0.70	88.10	6.47	5.70	6.79	52.00	61.49	4.00
9	150 (0)	18 (−1)	0 (−1)	343.50	1.89	5.55	151.12	6.00	9.85	8.11	30.84	31.25	3.53
10	150 (0)	22 (0)	0 (−1)	378.79	1.88	2.10	99.69	7.54	4.98	8.04	32.35	32.74	3.37
11	150 (0)	18 (−1)	70 (1)	277.60	1.16	0.24	67.76	5.77	7.55	6.64	42.72	55.40	2.93
12	150 (0)	22 (1)	70 (1)	251.20	1.52	0.50	70.92	5.45	5.86	6.76	44.67	45.48	2.90
13	150 (0)	20 (0)	35 (0)	331.96	1.52	0.99	89.56	6.91	5.50	7.22	40.47	50.18	4.87
14	150 (0)	20 (0)	35 (0)	278.72	1.53	1.13	87.74	6.74	5.16	7.07	42.71	54.93	4.47
15	150 (0)	20 (0)	35 (0)	315.26	1.57	1.23	71.85	6.56	6.48	6.88	48.12	63.91	4.30
16	150 (0)	20 (0)	35 (0)	362.93	1.52	0.99	85.22	6.02	8.58	6.82	48.17	63.70	3.07
17	150 (0)	20 (0)	35 (0)	315.27	1.56	0.90	79.28	6.47	5.02	6.73	40.43	51.42	4.10

Numbers in parentheses are coded values. ET, extrusion temperature; MC, moisture content; JSF/NMF, jackfruit seed flour/nixtamalized maize flour; SME, specific mechanical energy; EI, expansion index; Φ, porosity; H, hardness; WAI, water absorption index; WSI, water solubility index; ΔE, total color difference; BI, browning index; OA, overall acceptability. Source: authors based on experimental data.

Table 2. Experimental data of extruded snacks for response surface analysis.

Run	Independent Variables			Response Variables
	ET (°C)	MC (g/100 g)	JSF/NMF (g/100 g)	SME (J/g)	EI	Φ	H (N)	WAI (g/g)	WSI (%)	pH	ΔE	BI	OA
1	120 (−1)	18 (−1)	35 (0)	355.41	1.59	1.18	99.73	7.87	5.79	6.96	35.42	39.20	2.57
2	180 (1)	18 (−1)	35 (0)	235.27	1.57	1.36	38.30	7.30	5.34	7.08	37.63	43.36	3.13
3	120 (−1)	22 (1)	35 (0)	404.38	1.29	0.42	59.37	5.66	3.84	7.07	37.33	43.81	3.27
4	180 (1)	22 (1)	35 (0)	237.05	1.70	1.38	57.87	6.60	4.81	7.08	37.41	43.19	3.27
5	120 (−1)	20 (0)	0 (−1)	388.52	1.74	1.57	118.00	7.89	5.51	7.99	30.23	32.01	2.80
6	180 (1)	20 (0)	0 (−1)	321.48	1.33	0.17	83.04	7.62	5.39	8.05	32.21	35.44	2.97
7	120 (−1)	20 (0)	70 (1)	284.35	1.36	0.17	94.93	5.30	5.92	6.82	41.17	51.35	2.40
8	180 (1)	20 (0)	70 (1)	209.03	1.53	0.70	88.10	6.47	5.70	6.79	52.00	61.49	4.00
9	150 (0)	18 (−1)	0 (−1)	343.50	1.89	5.55	151.12	6.00	9.85	8.11	30.84	31.25	3.53
10	150 (0)	22 (0)	0 (−1)	378.79	1.88	2.10	99.69	7.54	4.98	8.04	32.35	32.74	3.37
11	150 (0)	18 (−1)	70 (1)	277.60	1.16	0.24	67.76	5.77	7.55	6.64	42.72	55.40	2.93
12	150 (0)	22 (1)	70 (1)	251.20	1.52	0.50	70.92	5.45	5.86	6.76	44.67	45.48	2.90
13	150 (0)	20 (0)	35 (0)	331.96	1.52	0.99	89.56	6.91	5.50	7.22	40.47	50.18	4.87
14	150 (0)	20 (0)	35 (0)	278.72	1.53	1.13	87.74	6.74	5.16	7.07	42.71	54.93	4.47
15	150 (0)	20 (0)	35 (0)	315.26	1.57	1.23	71.85	6.56	6.48	6.88	48.12	63.91	4.30
16	150 (0)	20 (0)	35 (0)	362.93	1.52	0.99	85.22	6.02	8.58	6.82	48.17	63.70	3.07
17	150 (0)	20 (0)	35 (0)	315.27	1.56	0.90	79.28	6.47	5.02	6.73	40.43	51.42	4.10

Numbers in parentheses are coded values. ET, extrusion temperature; MC, moisture content; JSF/NMF, jackfruit seed flour/nixtamalized maize flour; SME, specific mechanical energy; EI, expansion index; Φ, porosity; H, hardness; WAI, water absorption index; WSI, water solubility index; ΔE, total color difference; BI, browning index; OA, overall acceptability. Source: authors based on experimental data.

3.4. Hardness (H)

H showed the highest value (151.12 N) in the extrudate obtained at an ET of 150 °C, MC of 18 g/100 g, and JSF/NMF of 0 g/100 g. The lowest value (38.30 N) occurred at an ET of 180 °C, MC of 18 g/100 g, and JSF/NMF of 35 g/100 g. The increase in temperature and JSF content produced a decrease in H (Figure 2G–I). As shown in Table 3, H was linearly affected (p < 0.05) by ET and linearly and quadratically affected by JSF/NMF in a negative way. Low extrusion temperatures have been reported to hinder the evaporation of water from the material during the process, resulting in a product with high mechanical resistance [32].

This also increases the hardness of the final product. At high temperatures, a decrease in the viscosity of the mixture occurs and produces a low-density product. Small bubbles with thin walls form, and the starchy component degrades, which results in products with lower values of H [12]. Therefore, increasing JSF/NMF increases the viscosity of the dough and promotes the formation and growth of bubbles in the extruded product. This reduces the hardness of the final product due to the increase in proteins in the mixture. Protein denaturation and increased starch degradation during the extrusion process have been reported to result in more brittle products [8,10].

3.5. Water Absorption Index (WAI) and Water Solubility Index (WSI)

The adjusted models for WAI and WSI were significant (p < 0.05), without presenting a lack of adjustment. The R² values were 0.742 and 0.960, respectively. The highest WAI (7.89 g/g) was obtained at an ET of 120 °C, MC of 20 g/100 g, and JSF/NMF of 0 g/100 g, while the lowest (5.30 g/g) occurred at an ET of 120 °C, MC of 20 g/100 g, and JSF/NMF of 70 g/100 g (Figure 3B, C). JSF/NMF presents a significant negative linear effect (p < 0.05) (Table 3, Figure 3A). For WSI, MC shows a significant negative linear effect (p < 0.05) and ET and JSF/NMF present a significant (p < 0.05) quadratic effect, with a positive effect for ET and a negative effect for JSF/NMF (Table 3). The lowest WSI (3.84%) was obtained at an ET of 120 °C, MC of 22 g/100 g, and JSF/NMF of 35 g/100 g, and the highest (9.85%) value was obtained at an ET of 150 °C, MC of 18 g/100 g, and JSF/NMF of 0 g/100 g (Figure 3D–F).

Gonzales et al. [33] mentioned that low WAI values are possible because the starch does not undergo a high degree of dextrinization during extrusion, depending on the conditions of the extrusion process. At high values, the opposite phenomenon occurs, which causes an increase in the water absorption capacity.

However, in this investigation, the formulation without JSF presented the highest WAI, so it may contain less starch content than the NMF, which is why WAI decreased when JSF was increased (Table 2). Increasing MC decreased WSI because the increase in moisture in the mixture reduces the friction of the mass in the extruder (Figure 3D), so the fragmentation of the material is limited. In addition, the lubricating effect provided by the water makes the sample pass faster through the extruder, and the sheer effect, temperature, and screw of the extruder are not enough to degrade the starch, resulting in a decrease in WSI [34]. Increasing ET increased WSI because the high temperature improves the degree of gelatinization of the starch, which increases the content of soluble solids (Figure 3E). This suggests a disintegration of the starch granules, which increases WSI [4,30]. However, increasing JSF/NMF decreased WSI (Figure 3F). This occurred because the molecular interactions between the degraded components such as starch, fiber, lipids, and proteins can increase the molecular weight of the complex formed and reduce the WSI of the final product [30].

Table 3. Coefficients estimated by multiple linear regression of the physicochemical characterization of extruded snacks using jackfruit seed flour (JSF) and nixtamalized maize flour (NMF) mixtures.

Coefficients	SME	IE	Φ	H	WAI	WSI	pH	ΔE	BI	OA
Intercept	307.214 *	1.553 *	1.277 *	85.736 *	6.623 *	5.878 *	7.282 *	37.831 *	42.894 *	3.094 *
Linear
ET	−53.727 *	0.004	0.033	−13.093 *	0.158	0.022	0.019	1.887	2.138	0.292
MC	7.454	−0.059	−0.490	−8.633	−0.215	−1.129 *	0.020	0.644	−0.498	0.079
JSF/NMF	−51.265 *	−0.220 *	−0.973 *	−16.267 *	−0.758 *	−0.088	−0.647 *	6.868 *	10.284 *	−0.054
Quadratic
ET2	6.182	0.017	0.352	5.068	−0.237	0.560 *	−0.032	1.443	2.646	1.046 *
MC2	0.220	−0.064	−0.370	4.389	0.078	−0.158	−0.019	2.074 *	4.573 *	0.975 *
JSF/NMF2	3.809	−0.034	−0.154	−11.710 *	0.096	−0.501 *	−0.203 *	1.096	3.232 *	0.983 *
Interactions
ET-MC	−11.799	0.088	0.196	14.983	0.378	0.355	−0.026	−0.533	−1.196	−0.142
ET-JSF/NMF	−2.069	0.064	0.481	7.033	0.361	−0.026	−0.023	2.214	1.676	0.358
MC-JSF/NMF	−15.421	0.110	0.926	13.649	−0.466	0.794	0.048	0.110	−2.851	0.033
R2	0.876	0.799	0.759	0.858	0.742	0.823	0.960	0.876	0.884	0.821
P of F (model)	0.000	0.001	0.030	0.002	0.001	0.022	0.028	0.015	0.014	0.040
p-value for lack of fit	0.1215	0.7030	0.0884	0.1224	0.8862	0.2661	0.3854	0.3548	0.4652	0.9950

* Bold numbers indicate significant parameter estimates (p < 0.05). SME, specific mechanical energy; EI, expansion index; Φ, porosity; H, hardness; WAI, water absorption index; WSI, water solubility index; ΔE, total color difference; BI, browning index; OA, overall acceptability. Source: authors based on experimental data.

Table 3. Coefficients estimated by multiple linear regression of the physicochemical characterization of extruded snacks using jackfruit seed flour (JSF) and nixtamalized maize flour (NMF) mixtures.

Coefficients	SME	IE	Φ	H	WAI	WSI	pH	ΔE	BI	OA
Intercept	307.214 *	1.553 *	1.277 *	85.736 *	6.623 *	5.878 *	7.282 *	37.831 *	42.894 *	3.094 *
Linear
ET	−53.727 *	0.004	0.033	−13.093 *	0.158	0.022	0.019	1.887	2.138	0.292
MC	7.454	−0.059	−0.490	−8.633	−0.215	−1.129 *	0.020	0.644	−0.498	0.079
JSF/NMF	−51.265 *	−0.220 *	−0.973 *	−16.267 *	−0.758 *	−0.088	−0.647 *	6.868 *	10.284 *	−0.054
Quadratic
ET2	6.182	0.017	0.352	5.068	−0.237	0.560 *	−0.032	1.443	2.646	1.046 *
MC2	0.220	−0.064	−0.370	4.389	0.078	−0.158	−0.019	2.074 *	4.573 *	0.975 *
JSF/NMF2	3.809	−0.034	−0.154	−11.710 *	0.096	−0.501 *	−0.203 *	1.096	3.232 *	0.983 *
Interactions
ET-MC	−11.799	0.088	0.196	14.983	0.378	0.355	−0.026	−0.533	−1.196	−0.142
ET-JSF/NMF	−2.069	0.064	0.481	7.033	0.361	−0.026	−0.023	2.214	1.676	0.358
MC-JSF/NMF	−15.421	0.110	0.926	13.649	−0.466	0.794	0.048	0.110	−2.851	0.033
R2	0.876	0.799	0.759	0.858	0.742	0.823	0.960	0.876	0.884	0.821
P of F (model)	0.000	0.001	0.030	0.002	0.001	0.022	0.028	0.015	0.014	0.040
p-value for lack of fit	0.1215	0.7030	0.0884	0.1224	0.8862	0.2661	0.3854	0.3548	0.4652	0.9950

* Bold numbers indicate significant parameter estimates (p < 0.05). SME, specific mechanical energy; EI, expansion index; Φ, porosity; H, hardness; WAI, water absorption index; WSI, water solubility index; ΔE, total color difference; BI, browning index; OA, overall acceptability. Source: authors based on experimental data.

3.6. pH

The pH of the extruded products depends on the initial pH of the raw materials. The lowest pH (6.64) was found at an ET of 150 °C, MC of 18 g/100 g, and JSF/NMF of 70 g/100 g, while the maximum value (8.11) was found at an ET of 150 °C, MC of 18 g/100 g, and JSF/NMF of 0 g/100 g (Table 2). Therefore, the most important variable was JSF/NMF, as increasing JSF decreases pH, as seen in Figure 3H,I. The adjusted regression model was significant, with R² = 0.960 without a lack of adjustment (Table 3). The pH was affected (p < 0.05) linearly and quadratically by JSF/NMF, presenting a negative effect (Table 3). Increasing JSF/NMF decreased the pH because JSF is the raw material with the lowest initial pH (6.05).

However, the treatment with the highest pH (8.11) had a greater pH than that provided by the materials (NMF of 7.76). This may be due to the extrusion process helping to release some free fatty acids present in the raw materials [12], which causes an increase in pH. Sriburi and Hill [35] and Pensamiento-Niño et al. [6] reported an increase in pH after an extrusion process.

3.7. Total Color Difference (ΔE) and Browning Index (BI)

The color of extruded products is crucial as it significantly influences consumer perception, product quality, and marketing. The ΔE and BI were linearly affected (p < 0.05) by JSF/NMF and quadratically affected by MC in a positive way. JSF/NMF in its quadratic form only positively affected BI, showing significant regression models (p < 0.05), with R² > 0.876 and no lack of adjustment (Table 3). As JSF/NMF increased, ΔE increased from 30.23 to 52 and BI increased from 31.25 to 63.91 (Table 2, Figure 4A–F). This indicates that when JSF increased, the color difference between the extrudates increased as BI increased, resulting in darker products. This is due to the degradation of pigments during the extrusion process and non-enzymatic blackening reactions, such as Maillard and caramelization reactions [14,34]. The increases in MC favored these reactions and affected the final product [6].

The differences observed between the treatments occurred because jackfruit is rich in sugars and β-carotene [36]. Therefore, heat treatment from extrusion and drying could influence the Maillard reaction and caramelization of reducing sugars and amino acids, leading to the formation of a brown color.

The Maillard reaction occurs between reducing sugars (such as glucose, maltose, etc.) and amino acids (e.g., lysine) and the thermal degradation of phenolic compounds that contribute to browning and flavor [37]. Felix-Medina et al. [14] mentioned that there is a direct correlation between low-molecular-weight molecules trapped in high-molecular-weight protein polymers (melanoidins) and the golden color of food.

3.8. Overall Acceptability (OA)

The OA of the extruded products ranged from 2.40 to 4.87 (Table 2). The highest OA was obtained at an ET of 150 °C, MC of 20 g/100 g and JSF/NMF of 35 g/100 g. The lowest was obtained at an ET of 120 °C, MC of 20 g/100 g, and JSF/NMF of 70 g/100 g. Increasing JSF decreased OA (Table 2, Figure 4H,I). However, the statistical analysis indicated that ET, MC, and JSF/NMF showed a significant (p < 0.05) quadratic positive effect on OA, with a significant regression model, R² = 0.821, and no lack of fit (Table 3). This occurred because, generally, an increase in temperature generates a greater expansion in the extruded products, which depends on the starch of the raw materials and the feed moisture content.

Do Carmo et al. [38] mentioned that the overall acceptance of extruded snacks from mixed peas and oats processed at a lower MC (11.2–16.8%) and lower ET (150–160 °C) were considered good in terms of both sensory aspects and texture. Raleng et al. [39] mentioned that the acceptability of extruded products despite color changes may be due to the crisp texture of a product. The perception of the panelists in this study indicated that the brown color was within the limit considered acceptable.

3.9. Optimization, Validation, and Characterization of the Optimal Product

A numerical optimization was carried out according to convenience and desirability. The criteria used are shown in Table 4. A desirability of 0.71 was found to have the lowest energy expenditure (273.38 J/g) and the greatest expansion (1.12), porosity (0.84), and acceptance (4.56) (Table 4). The predicted optimal conditions were determined at an ET of 145.15 °C, MC of 22 g/100 g, and JSF/NMF of 70 g/100 g. Validation of the predicted process conditions was carried out in triplicate, and the results were compared between predicted values and experimental values. No statistically significant differences (p < 0.05) were found for SME, H, pH, and OA, but differences (p < 0.05) were found for EI, Po, WAI, WSI, ΔE, and BI. These differences may be due to experimental error, low desirability, or lack of fit of the models.

The physicochemical characterization of the optimal product is shown in Table 1. The protein content (12.10 g/100 g) is higher than that reported in other investigations for mixtures of nixtamalized maize/pumpkin seed (11.74 g/100 g) [12], maize/common bean (6.59–10.04 g/100 g) [14], maize/rice/sorghum (8.25–9.48 g/100 g) [40], and rice/Kersting’s groundnut/lemon pomace (7.51–12.8 g/100 g) [4]. The contents of lipids and fiber were within the ranges reported for this type of product (lipids 0.51–4.44, fiber 2.68–14.18 g/100 g) [4,14,40]. The calorie content of this snack (1585.49 kJ/100 g) was lower than that reported by Borah et al. [41] (1696.612 kJ/100 g) and above that reported by Nascimento et al. [42] (927.38 kJ/100 g). The degree of gelatinization (97.33%) is in the range reported in the literature (48–99%) [26,43]. The degree of gelatinization could suggest good digestibility of the starch present in the snack [26]. The color chart shows the actual color of the JSF/NMF mix snack (Table 1).

Table 4. Optimum values of extrusion process parameters and responses for an extruded snack using jackfruit seed flour (JSF) and nixtamalized maize flour (NMF) mixtures.

Process Parameter	Importance	Target	Experimental Value		Optimum Value	Experimental Value
			Min	Max
ET (°C)	5	Range	120.00	180	145.15	145.15
MC (g/100 g)	5	Range	18.00	22.00	22.00	22.00
JSF/NMF (g/100 g)	5	Range	0.00	70.00	70.00	70.00
Responses
SME (J/g)	4	Minimize	209.03	404.37	311.21	273.38 ± 24.02 ns
EI	5	Maximize	1.16	1.74	1.62	1.12 ± 0.13
Φ	5	Maximize	0.17	5.55	1.21	0.84 ± 0.23
H (N)	4	Minimize	38.30	151.12	53.26	58.75 ± 8.20 ns
WAI (g/g)	4	Range	5.30	7.89	7.06	6.14 ± 0.12
WSI (%)	4	Range	3.84	9.85	5.95	9.37 ± 0.11
pH	4	Range	6.64	8.11	6.89	6.82 ± 0.06 ns
ΔE	4	Range	30.23	52.00	39.21	40.06 ± 0.24
BI	4	Range	31.25	63.91	62.46	61.68 ± 0.28
OA	4	Maximize	2.40	4.87	4.40	4.56 ± 1.06 ns

^ns, not significant; p < 0.05. ET, extrusion temperature; MC, moisture content; JSF/NMF, jackfruit seed flour/nixtamalized maize flour; SME, specific mechanical energy; EI, expansion index; Φ, porosity; H, hardness; WAI, water absorption index; WSI, water solubility index; ΔE, total color difference; BI, browning index; OA, overall acceptability. Source: authors based on experimental data.

Table 4. Optimum values of extrusion process parameters and responses for an extruded snack using jackfruit seed flour (JSF) and nixtamalized maize flour (NMF) mixtures.

Process Parameter	Importance	Target	Experimental Value		Optimum Value	Experimental Value
			Min	Max
ET (°C)	5	Range	120.00	180	145.15	145.15
MC (g/100 g)	5	Range	18.00	22.00	22.00	22.00
JSF/NMF (g/100 g)	5	Range	0.00	70.00	70.00	70.00
Responses
SME (J/g)	4	Minimize	209.03	404.37	311.21	273.38 ± 24.02 ns
EI	5	Maximize	1.16	1.74	1.62	1.12 ± 0.13
Φ	5	Maximize	0.17	5.55	1.21	0.84 ± 0.23
H (N)	4	Minimize	38.30	151.12	53.26	58.75 ± 8.20 ns
WAI (g/g)	4	Range	5.30	7.89	7.06	6.14 ± 0.12
WSI (%)	4	Range	3.84	9.85	5.95	9.37 ± 0.11
pH	4	Range	6.64	8.11	6.89	6.82 ± 0.06 ns
ΔE	4	Range	30.23	52.00	39.21	40.06 ± 0.24
BI	4	Range	31.25	63.91	62.46	61.68 ± 0.28
OA	4	Maximize	2.40	4.87	4.40	4.56 ± 1.06 ns

^ns, not significant; p < 0.05. ET, extrusion temperature; MC, moisture content; JSF/NMF, jackfruit seed flour/nixtamalized maize flour; SME, specific mechanical energy; EI, expansion index; Φ, porosity; H, hardness; WAI, water absorption index; WSI, water solubility index; ΔE, total color difference; BI, browning index; OA, overall acceptability. Source: authors based on experimental data.

4. Conclusions

The most influential variables in the extrusion process were the jackfruit seed flour/nixtamalized maize flour ratio (JSF/NMF) and extrusion temperature (ET). The optimal conditions, achieving the lowest energy expenditure (273.38 J/g) while maximizing expansion (1.12), porosity (0.84), and consumer acceptance (4.56), were determined to be an ET of 145.15 °C, moisture content (MC) of 22 g/100 g, and a JSF/NMF ratio of 70 g/100 g. Under these conditions, the gelatinization rate reached 97.33%, with a protein content of 12.10 g/100 g, a fiber content of 4.86 g/100 g, and an energy value of 1585.49 kJ/100 g. These findings confirm the feasibility of utilizing jackfruit seed flour and nixtamalized maize flour as non-conventional, gluten-free raw materials to produce ready-to-eat snacks via single-screw extrusion. The resulting product exhibited desirable physicochemical and sensory attributes, supporting the potential of jackfruit seed flour as an innovative, alternative starch source for gluten-free snack formulations, contributing to product diversification in the food industry.