The corn seeds, soybean oil, commercial extruded snacks, and seasonings were procured from the local market in Rourkela, Odisha, India. Yellow PPI was purchased from MyFitFuel Pvt. Ltd., India, and phytosterol (predominantly containing 75% beta-sitosterol and 10% campesterol) was purchased from Thermo Scientific Pvt. Ltd., India.

In this study, soybean oil was selected for phytosterol dispersion based on the previous study conducted by Pavani et al. [41]. Initially, oil was heated at 90°C, and phytosterol in the solid form (1%, w/v) was added into the oil and continuously stirred for 15 mins until phytosterols were completely dissolved in the oil. The resulting oil was considered a functional oil throughout the study.

Prior to extrusion, the composite blends (I, II, and III) were prepared as shown in Table 1. The blends were mixed and maintained at a moisture content of 18%, wet basis. The hydrated blends were kept overnight at room temperature (~25°C) in air-tight containers before the extrusion experiments. A laboratory-scale twin screw extruder (Jinan Saibainuo Machinery Co., Ltd.) with a circular orifice die, and an aperture diameter of 3 mm was used for the extrusion process. The operating power was 14.5 kW, and the barrel length (L) to diameter (D) ratio of the extruder was 24.5. The extruder barrel consists of four zones as shown in Figure 1. The first three zones’ temperatures (T₁, T₂, T₃ from left to right side as shown in Figure 1) were maintained at temperatures of 30°C, 50°C, and 70°C, respectively, whereas the fourth zone temperature T₄ was varied from 130°C to 150°C. BB design was used with PPI, screw speed, and temperature of zone four (T) as process parameters (Table 2). A total of 17 experimental runs were carried out with five center points. The extrudates collected after each experiment were dried using a hot air oven at 40°C for 3 h or until constant weight was reached. The extrudates collected at optimum conditions (PPI of 2.78%, screw speed of 451 rpm, and T of 150°C) with a desirability value of 0.725 were selected for conducting sensory studies and are referred to as the functional extrudate (S₁) [42].

The phytosterol retention (PR) of the functional extrudates was calculated using the procedure of Araújo et al. [43]. Before analysis, the hydroethanolic extract was prepared by maceration of extruded powder with a solvent ratio of 2:10 (%; w/v) for 7 days. Liebermann-Burchard reagent was prepared by mixing 5 mL of sulfuric acid into acetic anhydride (50 mL). 100 mL of hydroethanolic extract which was initially dried at 40°C. Then, the residue was resuspended into 20 mL of chloroform, and the volume was adjusted to 50 mL using the same solvent. From the above solution, 10 mL was added with 2 mL of LB reagent, and absorbance was measured at 625 nm after adding the reagent. The phytosterol content was measured using equation 1:

Cs is the standard concentration, A_a is the absorbance of the sample, and A_s is the absorbance of the standard.

Before sensory evaluation, all panel members were requested to complete training that was provided on various sensory evaluation terminologies, sampling techniques, sensory scale scoring, selection of quality attributes, sensory scale, different scoring methods, and data interpretation to turn each response into a score.

Sensory evaluation of functional extrudates (S₁) and commercial samples (S₂, S₃, and S₄) were conducted to understand the acceptance or rejection of extrudates, similarity values, ranking, and consumer acceptability of the extrudates. Henceforth, functional extrudates (S₁) and commercial samples (S₂, S₃, and S₄) will be referred to as “samples” wherever they are mentioned together. The evaluation was conducted with fifteen panelists (nine men and six women between the ages of 25 and 35) from NIT Rourkela, Odisha, India. They were selected based on their interest in sensory evaluation, familiarity with snack products, and willingness to participate in the sensory evaluation. Panelists reported having no illness during the sensory evaluation. Before the experiment, extrudates were placed on paper plates and named randomly. Each panelist was asked to taste the extrudates and provide their preference by a tick mark (√) on the linguistic score sheet. Panelists rinsed their mouth with water between assessments of various extrudates to prevent fatigue and lingering taste.

The relationship between independent attributes, i.e., quality characteristics (color, flavor, taste, and mouthfeel), and output variables, i.e., panelist’s preference (acceptance or rejection, similarity values, and ranking), is numerically measured using the fuzzy logic technique. In this process, the score obtained from each panelist was mathematically converted and interpreted into a triangular membership function (MF). Then, each sample and its corresponding quality features were ranked in general and separately. The flow chart (Figure 2) shows the various steps involved in the sensory evaluation of extrudates using the fuzzy logic technique. Triplets of each sample and their corresponding quality attributes were calculated using a sensory scale followed by the overall sensory scores (SS) of samples and quality attributes in general. Next, overall MF values were calculated using a standard fuzzy scale (F). Finally, the similarity values, the ranking of the samples, and their quality parameters were measured.

Triangular MF distribution pattern of sensory scales is represented by a set of three numbers, called “triplet” [44]. Values of triplets associated with triangular membership distribution function for five-point sensory scale are shown in Figure 3. ∆ abc represents membership distribution function for the not satisfactory/not at all important (NI) category, ∆ ac₁d represents distribution function for fair/somewhat important (SI) category, etc. The first number of the triplet denotes the coordinate of abscissa at which the value of MF is 1. The second and third numbers of the triplet designate the distance to left and right respectively of the first number where the MF is zero.

The triplets for SS of the individual sample were assessed in terms of: (i) the sum of SS; (ii) triplets associated with the sensory scale; and (iii) number of panelists as shown in equation 2:

Where S indicates the triplets for the SS for particular samples (r) for a particular quality attribute (α); r denotes the samples (S₁, S₂, S₃, S₄); α denotes sample’s quality attributes, i.e., color (C), flavor (A), taste (T), and mouthfeel (M); n₁, n₂, n₃, n₄, and n₅ are the number of judges who rated particular sample (r) as unsatisfactory, fair, medium, good, and excellent, respectively on a five-point sensory scale.

Similarly, for a particular quality attribute (color, flavor, taste, and mouthfeel) of the samples in general, the values of triplets QC, QA, QT, and QM were calculated using equation 3:

Where β denotes quality attribute, i.e., color (C), flavor (A), taste (T), and mouthfeel (M); n₁, n₂, n₃, n₄, and n₅ represents the number of judges opting for specific linguistic scores for the quality attributes in general.

The triplets for the relative weights of the quality attributes were determined to find out the triplets for the overall SS of the samples. Equation 4 was used to calculate triplets for the relative weights for color:

Where Q_sum is the sum of the first digits of triplets of all the quality attributes, i.e., QC, QA, QT, and QM, whereas QC_rel is triplet for the relative weights for the color. Similarly, triplets for the relative weights for the flavor (QA_rel), taste (QT_rel), and mouthfeel (QM_rel) were calculated.

Overall SS of S₁ were calculated using equation 5:

Where SO₁ specifies the overall SS of S₁; S₁C, S₁A, S₁T, and S₁M are triplets of the SS of S₁ related to color, flavor, taste, and mouthfeel, respectively; QC_rel, QA_rel, QT_rel, and QM_rel indicates the triplet for the relative weight of the quality attributes of the samples in general. Each term on the right-hand side of equation 5 is a triplet, and the multiplication of the two triplets for e.g., triplet (p q r) and triplet (s t u) is done by following equation 6:

Where triplet is a combination of three integers which is used to represent the distribution patterns of triangular MF. Using the similar procedure, overall SS for other samples, i.e., SO₂, SO₂, and SO₄ were determined.

The triangular distribution pattern of 6-point sensory scale, which will be referred here as “standard fuzzy scale” is shown in Figure 4. The standard fuzzy scale represents six sensory scales namely F₁, F₂, F₃, F₄, F₅, and F₆ where the linguistic terminology for the scale factors has been modified to fit the case of sensory analyses. MF of each of the sensory scales follows triangular distribution pattern where maximum value of membership is 1. Values of MF of F_l through F₆ are defined by a set of 10 numbers, which are defined in equation 7:

Now the values of the MF of the overall SS of samples were determined on the standard fuzzy scale using the triplets of the SS calculated from equation 5. The triplet is a combination of three integers (a b c), which is used to represent the distribution patterns of triangular MF across sensory scale as shown in Figure 5. The value of MF is 1 when the abscissa x is “a” and zero when x is less than (a – b) or greater than (a + c).

For a given value of x on abscissa, value of MF, B_x was calculated using equation 8:

For each of the samples and its triplet associated with overall SS, the value of MF B_x at x = 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 was calculated using equation 8. The value of the MF of the overall SS of each sample on the standard fuzzy scale is also determined by a set of 10 numbers, which are the maximum values of B_x in the 10 intervals from 0 to 100 in the mentioned range of x between (a − b) and (a + c). Hence, ten intervals, where membership values of B_x are calculated, comprise “0 < x < 10, 10 < x < 20, 20 < x < 30, 30 < x < 40, 40 < x < 50, 50 < x < 60, 60 < x < 70, 70 < x < 80, 80 < x < 90, 90 < x < 100”.

The values of the MF of each sample, i.e., B₁, B₂, B₃, and B₄ were compared with the values of the MF of the standard scale, i.e., F₁, F₂, F₃, F₄, F₅, and F₆ given in equation 7. Each of the terms B₁, B₂, B₃, B₄, F₁, F₂, F₃, F₄, F₅, and F₆ represent a row matrix having 10 elements.

The similarity values of the samples B were calculated using equation 9 [44]. Afterward, the similarity values of four samples were compared, and then the sample with the higher similarity value was considered extremely important (EI):

Where S_m represents the similarity value of the sample B_x; F_j represents F₁, F₂, F₃, F₄, F₅; B_x is the MF value for sample x on the standard fuzzy scale; BxTandFjTare transposes of the matrix B_x and F_j. For example, for functional extruded samples (S₁): S_m(F₁, B₁), S_m(F₂, B₁), S_m(F₃, B₁), S_m(F₄, B₁), S_m(F₅, B₁), S_m(F₆, B₁) were calculated from equation 9 using the matrix multiplication rule. Similarly, similarity values of other commercial samples S₂, S₃, and S₄ were calculated. Similarity values under the 6-scale factors of standard fuzzy sensory scales are compared to find out the highest similarity value. The same procedure was followed to rank the quality attributes (color, flavor, taste, and mouthfeel) of the four samples in general.

A similar procedure was followed to find out the ranks of four quality attributes for each of the samples S₁, S₂, S₃, and S₄. The only difference is that Q_sum is obtained by calculating the average of the first digit of the triplets of QC, QA, QT, and QM.

Phytosterols are sterols derived from plants, similar to cholesterol in terms of structure. Their degradation mainly depends on factors including temperature, mositure, light, processing conditions, and storage. Various studies have shown that high-temperature processing techniques like heating, baking, and frying result in phytosterols’ degradation and form various free radicals. In this study, the PR of the extrudates ranged from 0.4832 g/100 g to 0.9532 g/100 g. The highest PR was observed at an extrusion temperature of 130°C, whereas the lowest was observed at a temperature of 150°C. This might be because phytosterols were unstable/degraded and oxidized at elevated temperature, generating free radicals [45]. In another study, vitamin B₁₂ in extrudates degraded at higher temperatures and lost completely at 190°C during the extrusion process [46]. Various food products fortified with phytosterol including cheese spread from goat milk, functional fermented maize yogurt, and fermented cereal products showed degradation of phytosterols at elevated extrusion temperature [16, 47, 48].

The sum of the SS given by panelists/judges and the triplets associated to the quality attributes of different samples are given in Table 3 and sum of the SS for the quality attributes for the samples in general is given in Table 4. The relative attributes of the samples were measured using five-point sensory scale factors. Sensory scale factors were used to calculate general quality attributes like NI, SI, important (I), highly important (HI), and EI. Next, the quality attributes and relative weights were determined using equation 3. Finally, the overall scores of the samples were estimated by multiplying the triplets of quality attributes of the samples and relative weights of quality attributes of the samples using the multiplication rule as given in equation 6. The overall SS of individual samples calculated in the form of triplets are given below:

SO ₁ = (51.1759 40.9537 34.2500)

SO ₂ = (73.8889 49.5833 38.1296)

SO ₃ = (72.9722 48.9722 33.2407)

SO ₄ = (74.5556 50.0000 33.1481)

Where SO₁, SO₂, SO₃, and SO₄ are the overall SS of the samples S₁, S₂, S₃, and S₄, respectively.

The values and symbols of the six-point scale MF are shown in equation 7.

The value of the MF of the overall SS of each sample on the standard fuzzy scale at x = 0 to 100 were calculated using equation 8, and the values are as shown below:

B ₁ = (0, 0.2388, 0.4829, 0.7271, 0.9713, 1, 0.7424, 0.4504, 0.1584, 0)

B ₂ = (0, 0, 0.1148, 0.3165, 0.5182, 0.7199, 0.9216, 1, 0.8397, 0.5775)

B ₃ = (0, 0, 0.1225, 0.3267, 0.5309, 0.7351, 0.9393, 1, 0.7886, 0.4877)

B ₄ = (0, 0, 0.1089, 0.3089, 0.5089, 0.7089, 0.9089, 1, 0.8358, 0.5341)

The similarity values (S_m) and the ranking of the food products indicate the comparative importance of all the quality characteristics that aid in acceptance/rejection. Similarity values of the samples were calculated by combining the MF values of the standard fuzzy logic scale (F’s) and the overall MF values of the SS (B’s) using equation 9 and the calculated values are shown in Table 5. For example, the similarity values of S₁ were calculated as 0, 0.0337, 0.3064, 0.6890, 0.6927, 0.2767, and 0.0224, which were not satisfactory, fair, satisfactory, good, very good, and excellent respectively. Thus, the overall SS of S₁ was good due to its high S_m value. Similarly, S₂, S₃, and S₄ were very good with S_m values of 0.6835, 0.6788, and 0.6952, respectively as shown in Table 5.

Similar procedure was used for ranking of quality attributes (color, flavor, taste, and mouthfeel) for the evaluation of the samples in general. Triplets of overall SS for quality attributes were calculated in equation 3. Using the method of computation mentioned earlier and denoting BC, BA, BT, and BM as overall SS on the standard fuzzy scale, for color, flavor, taste, and mouthfeel, respectively we get:

BC = (0, 0, 0, 0, 0.1333, 0.5333, 0.9333, 1, 0.5455, 0)

BA = (0, 0, 0, 0.2, 0.6, 1, 1, 0.5385, 0.0769, 0)

BT = (0, 0, 0, 0, 0, 0.1333, 0.5333, 0.9333, 1, 0.5)

BM = (0, 0, 0, 0, 0, 0, 0.3333, 0.7333, 1, 0.7143)

Similarity values, S_m of all the four quality attributes (color, flavor, taste, and mouthfeel) were calculated and are presented in Table 6.

Similarity values of the four quality attributes of each sample against six-point sensory scales, i.e., not satisfactory, fair, satisfactory, good, very good, and excellent were calculated using equations 7, 8, and 9. Using the method of computation mentioned earlier and denoting BC₁, BA₁, BT₁, and BM₁ as overall SS on standard fuzzy scale, for color, flavor, taste, and mouthfeel, respectively, for S₁ we get:

BC ₁ = (0.1708, 0.4646, 0.7584, 1, 0.9472, 0.6502, 0.3531, 0.0561, 0, 0)

BA ₁ = (0.0379, 0.3003, 0.5627, 0.8251, 1, 0.8985, 0.5941, 0.2897, 0, 0)

BT ₁ = (0, 0.1842, 0.4092, 0.6342, 0.8592, 1, 0.8986, 0.6275, 0.3564, 0.0853)

BM ₁ = (0, 0.0776, 0.2894, 0.5012, 0.7129, 0.9247, 1, 0.8082, 0.5105, 0.2128)

Similarly, overall SS for all the quality attributes of S₂, S₃, and S₄ were calculated and are given below.

For S₂:

BC ₂ = (0, 0, 0.1030, 0.3030, 0.5030, 0.7030, 0.9030, 1, 0.8654, 0.6041)

BA ₂ = (0, 0.1692, 0.4000, 0.6308, 0.8615, 1, 0.8896, 0.6135, 0.3374, 0.0613)

BT ₂ = (0, 0, 0.0601, 0.2558, 0.4514, 0.6471, 0.8428, 1, 0.9525, 0.7106)

BM ₂ = (0, 0, 0, 0.1340, 0.3196, 0.5052, 0.6907, 0.8763, 1, 0.9092)

For S₃:

BC ₃ = (0, 0, 0.0191, 0.2106, 0.4021, 0.5936, 0.7851, 0.9766, 1, 0.7106)

BA ₃ = (0, 0.1848, 0.4293, 0.6739, 0.9185, 1, 0.8109, 0.5273, 0.2437, 0)

BT ₃ = (0, 0, 0.1386, 0.3408, 0.5431, 0.7453, 0.9476, 1, 0.7870, 0.4995)

BM ₃ = (0, 0, 0, 0.1611, 0.3486, 0.5361, 0.7236, 0.9111, 1, 0.8386)

For S₄:

BC ₄ = (0, 0, 0, 0.1888, 0.3782, 0.5677, 0.7572, 0.9467, 1, 0.7535)

BA ₄ = (0, 0.1111, 0.3333, 0.5556, 0.7778, 1.0000, 1, 0.7248, 0.4495, 0.1743)

BT ₄ = (0, 0, 0.1386, 0.3408, 0.5431, 0.7453, 0.9476, 1, 0.7870, 0.4995)

BM ₄ = (0, 0, 0, 0.1888, 0.3782, 0.5677, 0.7572, 0.9467, 1, 0.7778)

The similarity values of each quality attribute of the samples S₁, S₂, S₃, and S₄ are shown in Table 7.

The sensory characteristics of functional extrudates were assessed based on their quality attributes, using the fuzzy logic technique. Before the sensory analysis was conducted, functional extrudates were developed by twin screw extrusion process of phytosterol enriched corn and pea protein. Functional extrudates (S₁) were compared with commercial samples (S₂, S₃, and S4). Among these, S₄ achieved the top rank, with a sensory scale labeled as “very good” and a similarity value of 0.6952. It was followed by S₂, then S₃, and finally the functional extrudates (S₁). The overall SS for the samples, as obtained from the similarity values are:

S ₁: mouthfeel (good) > taste (good) > color (satisfactory) > flavor (satisfactory)

S ₂: mouthfeel (very good) > taste (very good) > color (very good) > flavor (good)

S ₃: mouthfeel (very good) > color (very good) > taste (very good) > flavor (good)

S ₄: color (very good) > mouthfeel (very good) > taste (very good) >aroma (good)