44 ISSN 1120-1770 online, DOI 10.15586/ijfs.v34i4.2253 P U B L I C A T I O N S CODON Effect of seven non-conventional starch rich sources on physico-chemical and sensory characteristics of extruded snacks Syed Zameer Hussain1, Rumaisa Gaffar1, Bazila Naseer1*, Tahiya Qadri1, Uzma Noor Shah2#, Monica Reshi1 1Division of Food Science and Technology, Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir, J&K, India; 2Department of Life Sciences, School of Sciences, Jain University, Banglore, India #The author has helped and contributed in revising the manuscript and language editing. *Corresponding Author: Bazila Naseer, Division of Food Science and Technology, Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir, J&K, India. Email: sheikhbazila@gmail.com Received: 27 June 2022; Accepted: 5 December 2022; Published: 29 December 2022 © 2022 Codon Publications OPEN ACCESS PAPER Abstract Starch-rich foods, such as cereal sources (rice, maize, and barley), are commonly used raw materials for extrusion cooking due to their excellent expansion characteristics. Other nonconventional starch sources like green banana, water chestnut, and potato can also be employed for extrusion cooking. The main aim of the study was to evaluate the extrusion behavior and sensory acceptability of nonconventional starch-rich food sources like rice, maize, barley, wheat, water chestnut, potato, and green banana. Maize, rice, wheat, potato, water chestnuts, barley, and green banana flour samples were evaluated for various physicochemical, pasting, and morphological properties, and were subjected to extrusion cooking at the moisture content of 15%, screw speed of 300 rpm, and barrel temperature of 125°C. The developed extruded snacks from selected crops were also evaluated for various physicochemical, pasting, and morphological properties. Potato flour and green banana flour recorded the highest starch content of 78.27 and 76.61%, respectively. The highest peak viscosity (6025 cp), trough viscosity (2968 cp), breakdown viscosity (3057 cp), pasting temperature (92°C), and minimum peak time (4.67 min) were recorded in the case of green banana flour. The structural assessment of all the flour samples was done through scanning electron microscopy. The highest expansion ratio (5.06), as well as overall acceptability (4.28), was recorded in the case of corn-based snacks. The highest bulk density and hardness were recorded in the case of barley-based snacks. The highest values of water absorption index and water solubility index were recorded in the case of green banana flour–based snacks. Keywords: starch rich, green banana, potato, extrusion cooking, scanning electron microscopy, pasting properties, sensory evaluation Introduction Snacks, being an indispensable part of the modern diet, are an effective carrier to improve the nutrition-based needs of the population. With the growing knowledge about a healthy diet, snacks can readily be consumed to improve overall nutrition. Snacks are primarily made from starch-rich materials due to their good puffing and expansion characteristics. Extrusion is the most com- monly employed multidimensional processing technique for developing snacks (Liu and Hsieh, 2008). It changes the molecular conformation of starch, which then inter- acts with other macromolecules by simultaneous appli- cation of high temperature and pressure. Although starch-based materials like corn, rice, wheat, potato, barley, and water chestnut have been explored for the development of snacks through extrusion either solely or in combination with other food materials (Hernandez-Díaz et  al., 2007; Kaur et  al., 2015); Reddy et  al., 2014) the comparative evaluation of these starch- based food materials for the development of snacks has Italian Journal of Food Science, 2022; 34 (4): 44–56 Italian Journal of Food Science, 2022; 34 (4) 45 Utilization of non-conventional starch sources in extrusion cooking Physicochemical analysis of flour samples Moisture content Moisture content was determined by the AOAC method 930.04 (AOAC, 2005). Five grams of the sample was weighed and dried at 60–70°C for 6–8 h, to constant weight. The loss in weight was determined to calculate the percent moisture content. Crude protein Crude nitrogen was determined by Kjeldahl method (AOAC, 1995). Half a gram of the sample in powdered form was placed in Kjeldahl tubes and 5 g of digestion mix- ture (potassium sulfate + ferrous sulfate + copper sulfate in the ratio of 5:0.5:0.25) was added. After adding 10 mL of concentrated H2SO4, the mixture was heated till the color changed to green. Then, tubes were cooled and 10 mL of distilled water was added to each sample. Then 40–50 mL of NaOH (40.00%) was added to it till the color changed to brown. Tubes were fitted in assembly, subjected to steam distillation, and ammonia released from the tubes was collected in the flask fitted in assembly containing 25 mL boric acid (4%) and 5 mL red indicator. Flask containing boric acid and indicator results in the formation of ammo- nium borate, which was titrated with 0.1 N HCl till color changed to brown. The resulting nitrogen content was multiplied by a factor of 5.95 to get crude protein content. Nitrogen Titere value Normality of HCl Weight of sample (g) (%) � � �14 ��100 (1) Crude protein = Crude nitrogen × 5.95 (2) Crude fiber Crude fiber was determined by following a gravimetric procedure of AOAC (1995). One gram of sample was subjected to acid hydrolysis with 2.5 N HCL followed by alkali digestion with 0.1 N NaOH. The residue obtained was then washed with double distilled water and ignited in a muffle furnace at 600°C for 6 h. At high tempera- ture, the organic matter in the residue got oxidized and inorganic residue was left behind. The difference in the weight before and after was determined to calculate the percentage crude fiber as: Crude fiber W (%) � � � W W1 2 100 (3) Where W1: weight of crucible with dry residue (g) W2: weight of crucible with ash (g) W: weight of sample (g) not been studied so far. In addition to this, green banana offers a significant potential to be used as a base material for the development of snacks due to its high starch con- tent and excellent nutritional profile (Kaur et  al., 2015). India is the second largest producer of bananas (FAO STAT, 2017) and very limited research is documented on the processing and utilization of green bananas. Moreover, the ripening of green banana is a very tedious practice and an appreciable quantity of bananas is wasted during post-harvest handling. Thus, there exists a pos- sibility of exploring green banana as a base material for the development of processed products like snacks. Therefore, the present study was envisaged to evaluate and compare different starch-based materials for the development of snacks with a broader aim to explore a nonconventional source of starch like green banana for extrusion processing. Material and Methods Raw materials Maize (var. C-7), rice (var. Jhelum), and wheat (var. Shalimar wheat 2) were procured from Mountain Research Center for Field Crops, Khudwani, Sher- e-Kashmir University of Agricultural Science and Technology of Kashmir (SKUAST-K), India; potato (var. Shalimar potato-1) from the Department of Vegetable Sciences, SKUAST-K; water chestnuts were harvested from Wular lake of Kashmir, India, which is Asia’s larg- est lake. Barley (a land race of Kargil, namely, “Naas”) was procured from Mountain Agriculture Research and Extension Station, Kargil, SKUAST-K and green banana (var Grand Naine) from the Department of Fruit Science, Sher-e-Kashmir University of Agricultural Science and Technology of Jammu, India. Flour preparation Maize, rice, wheat, and barley were ground in a labora- tory mill (3303, Perten, Hagersten, Sweden). Potatoes were washed, peeled, sliced, and dried in a tray drier (NSW-154, S-Narang, Scientific works New Delhi) at 40 ± 5°C. Before flour preparation, the usual practice is to dry the whole water chestnuts over traditional chul- las (made of mud) for about 10–12 days after which the flour is made from kernels extracted from these water chestnuts. Green banana (var Grand Naine) was peeled and sliced to 0.5 to 1 cm thickness. The slices were dried in a tray drier at 40 ± 5°C. Dried potato slices and green banana slices were ground to flour in a lab mill (3303, Perten, Hagersten, Sweden). All the seven flour samples were kept in separate polybags and stored at room tem- perature for further analysis. 46 Italian Journal of Food Science, 2022; 34 (4) Hussain SZ et al. ready-to-eat snacks. The temperature at the feed zone, compression zone, and die zone were maintained at 60°C, 80°C, and 125°C, respectively, throughout the experiment and the screw speed was kept constant at 300 rpm. Earlier, the moisture content of the flour samples was adjusted to 15% through pre- conditioning. The extruder was equipped with a torque indicator, which showed the percent of torque in proportion to the current drawn by the drive motor. The extruded samples were collected in trays, cooled, and packed in high density polyethylene (HDPE) pouches for further analysis. Determination of product responses for developed snacks Extruded snacks developed from maize, rice, wheat, potato, water chestnuts, barley, and green banana flour were evaluated for below mentioned parameters. System parameter Specific mechanical energy (SME) is the ratio of net mechanical energy input (after no load correction) to mass flow rate and was calculated as per the following equation (Pansawat et al., 2008): SME(kWh/Kg) Actual screwspeed (rpm) Rated screwspeed (rpm) tor � � % qque motor power rating (kWh) mass flowrate (Kg/h) 100 1000� �% (7) Product characteristics Bulk density Bulk density (BD) was measured using the volumetric displacement method as described by Singh et al. (2016). A known weight of the sample (extrudates) was taken into a pre-weighed (W1) measuring cylinder and the weight of the filled cylinder (W2) as well as the volume of the sample (V1) was noted. The BD was expressed using the following equation: BD (ρb) = W2 – W1 ÷ V1 (8) Water absorption index (WAI) and water solubility index (WSI) WAI and WSI were determined as per standard proce- dure given by Singh et  al. (2016). One gram of the sam- ple (W1) was mixed with 10 mL distilled water and kept at ambient temperature for 30 min and centrifuged for 10 min at 2000 rpm. Then final weight was taken (W2), Water absorption capacity was expressed as percent water bound per gram of the sample. Crude fat Crude fat analysis was done using Soxtec 2045 (Pelican India) (AACC, 2000). Sample for oil extraction was taken in thimble and put inside an extraction cup. The extraction cups were initially dried in oven at 130°C for 15 min and the weight of empty cups was noted. After cooling, the cups were filled with 70 mL of petroleum ether, which acted as solvent for fat extraction and the thimble containing the sample was placed inside the cup. The extraction cups were then mounted on the heating plate of the instrument and the temperature raised. After attaining the required temperature, the petroleum ether was allowed to boil for 30 min till the fat was dissolved in the petroleum ether. The solvent was then recovered for 20 min. The recovered ether was collected and the fat contained in extraction cups was estimated using the fol- lowing formula: Fat Weight of fat (g) Weight of sample (g) (%) � �100 (4) Ash content Standard AACC procedure (AACC, 2000) was followed. Five grams of the sample was put in a pre-weighed silica dish, charred on the hot plate, and incinerated in a muffle furnace at a temperature of 550 ± 10°C for about 3 h. The dish was cooled, weighed, and ash content was expressed as percent ash as given below: Ash Weight of ash (g) Weight of sample (g) (%) � �100 (5) Carbohydrate content Carbohydrate content was estimated by the difference method using the below given equation (AOAC, 1995). Total Carbohydrate content (%) [100 %(protein content fat � � � � � � � � content moisture ash crude fiber)] � � � � � � � � (6) Extrusion processing Extrusion cooking was carried out in a twin-screw extruder (Basic Technology Pvt. Ltd., Kolkata, India) with a 2.5 mm barrel diameter and 8:1 length to diam- eter ratio. The extruder was fitted with a die nozzle of 0.42 mm diameter. The preliminary trials were con- ducted to determine the best extrusion conditions (i.e., barrel temperature and screw speed) and moisture content of the feed material for the development of Italian Journal of Food Science, 2022; 34 (4) 47 Utilization of non-conventional starch sources in extrusion cooking breakdown viscosity (peak viscosity – hold viscosity), and set back viscosity (—FVhold viscosity) Scanning electron microscopy Scanning electron microscopy (SEM) was used to study the morphology of the flour samples. The samples were glued onto a sample holder using double-sided cel- lophane tape and then coated with gold. The coated samples were photographed using a scanning electron microscope (Hitachi S-300H-Tokyo, Japan), at an accel- erator potential of 5 kV to visualize the microstructure. Statistical analysis Statistical analysis of data was conducted using SPSS software (version 21). All the experiments were carried out in triplicate and data were analyzed using design factorial in completely randomized design (CRD). The significance of microwave heating was assessed by one factorial CRD at 5% level of significance. A p-value of less than 0.05 was used to designate the statistical signifi- cance in all the tested parameters. Results and Discussion Physicochemical analysis of different flour samples Table 1 illustrates the proximate composition including the starch content of flour different samples. The mois- ture content of flour different samples was in the range of 7.56% (for potato flour) to 12.20% (for rice flour). The highest percentage of crude fiber (5.54%) was recorded in barley flour followed by wheat flour (4.51%), whereas the least crude fiber content recorded in corn flour (0.42%) was statistically at par with that of rice flour (0.62%). The highest protein content recorded in the case of barley flour (11.83%) was found to be statistically at par with that of wheat flour (11.79%), whereas the least protein content was recorded in water chestnut flour (2.82%). The highest carbohydrate content (82.04%) recorded in the case of potato flour was found statistically at par with that of green banana flour (81.74%) and water chestnut flour (81.50%). At the same time, the highest starch con- tent (78.27%) recorded in potato flour was statistically at par with that of green banana flour (76.61%); however, the least carbohydrate content (67.39%) and starch content (62.40%) were recorded in the case of barley flour. The highest fat content (3.10%) was recorded in corn flour followed by barley flour (2.05%), whereas the least fat content recorded in rice flour (0.23%) was statistically at par with that of water chestnut flour (0.28%), which was further at par with that of potato flour (0.35%) (Table 1). WAC ( ) W W % � � �1 2 1 100 W (9) WSI was determined from the amount of dried sol- ids received by evaporating the supernatant from the water absorption index test described above. WSI was expressed as follows: WSI Weight of dissolved solids in supernatant Weight of dry sol (%) � iids �100 (10) Expansion ratio The expansion ratio (ER) was calculated as the ratio of extrudate thickness and the die diameter by using a dig- ital Vernier caliper of 0.001 mm accuracy (Jyothi et  al., 2009). Hardness Hardness was determined using TA-XT2i Texture Analyzer by applying a compression force (CF) using a P50 compression probe (50 mm. dia. cylinder aluminum) (Singh et al., 2016). Sensory evaluation Sensory evaluation of the samples was done by semi- trained panelists. A panel of 30 semi-trained judges selected from the scientific staff of Division of Food Science and Technology, SKUAST-K, Shalimar, carried out the sensory evaluation in the laboratory of Food Science and Technology. Noise-free and well illumi- nated sensory space was used for the test. Judges were also acquainted with rating method, specific terminology used, and different sensory characteristics. Coded sam- ples were presented to the panelists in plastic cups cov- ered with lids. Each coded sample was evaluated thrice by judges in a randomized manner. The panelists were provided with a glass of water to rinse their mouths and were given a 10 min break post each assessment. Sensory evaluation was done on a 5-point scale (1-extremely dislike and 5-extremely like) for various attributes (i.e., appearance, color, texture, flavor, and mouthfeel). The overall acceptability of each sample was calculated as the average of scores obtained for selected sensory attributes (Naseer et al., 2021). Pasting properties Pasting properties were determined with a Rapid Visco analyzer (RVA Starch TM, New Port, Scientific Warrie Wood, Australia) in accordance with the methods described by Kaur et  al. (2015). The different recorded parameters were pasting temperature (PT), peak time, peak viscosity, hold/trough viscosity (TV) (minimum viscosity at 95°C), final viscosity (FV) (viscosity at 50°C), 48 Italian Journal of Food Science, 2022; 34 (4) Hussain SZ et al. tuber flour gelatinizes at relatively low temperature, with rapid and uniform swelling of granules. Higher PT of green banana flour may be attributed to its strong inter- molecular forces within the flour matrix due to the closely packed smaller starch granular arrangement (Figure 1F). Peak viscosity (PV) of flour samples ranged from 362 to 6025 cp (Table 2). The lowest PV was recorded for water chestnut flour (362 cp) and the highest for green banana flour (6025 cp), which suggests the possible use of banana flour as a thickener in food application. PV indicates the water holding capacity of flour suspension and is attained before the structural breakdown of swollen starch gran- ules takes place (Hussain et  al., 2014). Disintegrated starch structure in water chestnut flour (as was evi- dent in Figure 1G) restricts swelling of starch granules, which leads to lower PV. As far as product quality is con- cerned, high PV is always desirable (Bhattacharya and Corke, 1996). Higher starch content (76.61%) of green banana flour together with its higher PT (92°C) may be the possible reason for its high PV. TV of flour samples ranged from 325 to 2968 cp (Table 2). The lowest TV was recorded for water chestnut flour (325 cp), whereas the highest was recorded for green banana flour (2968 cp). The high TV of green banana flour suggests its high hold- ing strength during cooling. Interaction of starch with The highest ash content was recorded in the case of water chestnut flour (2.38%), which was statistically at par with that of banana flour (2.06%), whereas the least ash content recorded in the case of potato flour (0.43%) was statistically at par with that of rice flour (0.47%) and wheat flour (0.53%). These results are in accordance with the results reported by Qamar et  al. (2017) for protein, ash, and carbohydrate contents of corn flour; by Onwuka et al. (2015) for fat, moisture, and ash contents of banana flour; by Hussain et al. (2019) for protein, fat, and crude fiber contents of barley and water chestnut flour. Pasting characteristics of different flour samples Pasting profile depicted in Table 2 demonstrates the wide range of viscosity parameters for different flour samples. PT), which indicates the onset of rise in viscosity, was found in the range of 60.9–92°C for different flour sam- ples. The lowest PT of 60.9°C was recorded for potato flour and the highest (92°C) for green banana flour (Table  2). Lower PT of potato flour can be attributed to the tendency of large swollen starch granules to gelatinize, which was evident in the SEM micrograph (Figure  1A) as well. Danbaba et  al. (2014) reported that Table 1. Physicochemical analysis of different flour samples. Parameters Flour samples Moisture (%) Fat (%) Ash (%) Crude fiber (%) Protein (%) Starch (%) Carbohydrate (%) Rice 12.20a ± 1.16 0.23a ± 0.11 0.47a ± 0.02 0.62a ± 0.08 8.03a ± 0.91 73.03a ± 7.21 78.45a ± 4.25 Wheat 12.15ba ± 1.15 1.70b ± 0.24 0.53ba ± 0.02 4.51b ± 0.04 11.79b ± 1.35 65.18b ± 4.25 69.32b ± 6.33 Corn 10.72c ± 1.08 3.10c ± 0.51 1.69c ± 0.24 0.42ca ± 0.03 8.23c ± 1.02 72.82ca ± 5.12 75.84c ± 6.42 Barley 11.95dab ± 1.38 2.05d ± 0.11 1.24d ± 0.17 5.54d ± 0.18 11.83db ± 1.22 62.40d ± 3.42 67.39d ± 7.86 Potato 7.56e ± 0.76 0.35e ± 0.02 0.43eab ± 0.03 2.33e ± 0.01 7.29e ± 0.56 78.27e ± 4.56 82.04e ± 5.65 Green banana 10.34f ± 1.18 0.62f ± 0.01 2.06f ± 0.20 1.49f ± 0.03 3.75f ± 0.21 76.61fe ± 1.86 81.74fe ± 2.21 Water chestnut 9.68g ± 0.84 0.28gae ± 0.01 2.38gf ± 0.07 3.34g ± 0.00 2.82g ± 0.02 70.50gc ± 6.95 81.50gef ± 4.87 Data are expressed as mean ± SD; values in the same column with different superscripts are statistically different. Table 2. Pasting properties of different flour samples. Parameters Flour samples Peak viscosity (cp) Trough viscosity (cp) Breakdown viscosity (cp) Final viscosity (cp) Setback viscosity (cp) Peak time (min) Pasting temperature (°C) Rice 2940a ± 17 1727a ± 12.76 1213a ± 17.69 4343a ± 25.51 2616a ± 12.66 5.13a ± 0.07 80.90a ± 2.57 Wheat 2106b ± 11.15 1292b ± 11.23 814b ± 20.15 3332b ± 11.01 2040b ± 11.67 5.60b ± 0.05 77.45b ± 1.69 Corn 2205c ± 17.15 1329c ± 10.96 876c ± 23.54 3403c ± 16.01 2074c ±17.03 5.64cb ± 0.1 73.28c ± 1.74 Barley 2915d ± 24 925d ± 12.58 1990d ± 6.80 3744d ± 8.73 2819d ± 15.01 5.70dbc ± 0.04 85.07d ± 2.28 Potato 3817e ± 13.65 2490e ± 11.50 1327e ± 9.84 5474e ± 11.53 2984e ± 8.45 6.87e ± 0.05 60.9e ± 2.81 Green banana 6025f ± 22.54 2968f ± 13.15 3057f ± 21.51 3302f ± 12.22 334f ± 5.50 4.67f ± 0.03 92.00f ± 2.79 Water chestnut 362g ± 9.01 325g ± 15.27 37g ± 3.05 452g ± 7.63 127g ± 9.01 4.90g ± 0.1 71.65g ± 1.28 Data are expressed as mean ± SD; values in the same column with different superscripts are statistically different; cp: centipoise. Italian Journal of Food Science, 2022; 34 (4) 49 Utilization of non-conventional starch sources in extrusion cooking Figure 1. SEM micrographs of (A) rice flour, (B) wheat flour, (C) corn flour, (D) barley flour, (E) potato flour, (F) green banana flour, and (G) water chestnut flour. (A) (B) (D) (F) (G) (C) (E) 50 Italian Journal of Food Science, 2022; 34 (4) Hussain SZ et al. starch granules reflect the crystalline and ordered molec- ular arrangement of rice flour. Reddy and Bhotmange (2013) also reported the presence of intact crystalline starch granules in basmati rice flour. The microstructure of wheat flour shown in Figure 1B depicts a compact structure of irregularly shaped particles of different sizes. Massive starch arrangement embedded within the gluten matrix was evident in Figure 1B, wherein gluten possi- bly acted as a cementing material in forming a compact and dense structure. Sakhare et  al. (2014) also reported the highly compact packed structure of wheat kernels. The micrograph shown in Figure 1C indicates that some- what spherical shaped large and small starch granules are present in corn flour. Loosely packed starch arrange- ment within protein and lipid matrix was also observed in Figure  1C. A large part of the shapeless cracked sur- face observed in corn flour can be attributed to the pres- ence of soluble starch remnants (Haros et al., 2006). Some crater-like depressions and eroded starch surfaces were seen in Figure 1C, which indicates kernel breakage due to milling. Hall and Sayre (1970) also reported the pres- ence of crater-like small indentations on polygonal starch structures in pearl corn. The scanning electron micro- graph depicted in Figure 1D demonstrates that barley flour consists of numerous round and polygonal shaped edged starch granules. The small and large starch granules with smooth surfaces in Figure 1D confirm the presence of both A- and B-type starch granules in barley flour. Densely packed clusters of starch embedded in flour matrix and a small amount of protein adhered to densely packed starch granules were also observed in Figure 1D. Nair et  al. (2011) also reported the presence of large (A-type) and small (B-type) starch granules surrounded by the protein matrix in barley flour. Sullivan et al. (2010) also reported bimodal distribution of starch granules in barley flour. The SEM micrograph depicted in Figure 1E indicated the presence of oval and polygonal starch granules in potato flour. The small and immature starch granules were seen adhered to the large starch granules (Figure  1E). Similar observations were reported by Horovitz et  al. (2011) for potato starch granules. The SEM micrograph depicted in Figure 1F indicates that green banana flour consists of elongated, round, and oval-shaped starch granules. A large number of smooth, small, and intact starch gran- ules without any rupture were evident in Figure 1F. Babu et al. (2014) also reported the presence of oval and elon- gated smooth starch structures in green banana flour. The micrograph depicted in Figure  1G demonstrates that in water chestnut flour starch granules are somewhat irregu- lar and asymmetric in shape with a rough surface. Rough granular structures indicated that starch was highly dam- aged, which can be attributed mainly to hydrothermal pre-conditioning of water chestnuts before flour prepa- ration. The fissures seen on the surface of granules were probably due to the drying of water chestnut kernels before milling (Figure 1G). soluble fibers in unripe banana might be responsible for its high TV (Mota et  al., 2000). Breakdown viscos- ity (BDV) of flour samples was found in the range of 37 to 3057 cp (Table  2). BDV depicts the potential of flour suspension to withstand high temperature under contin- uous shear conditions (Hussain et  al., 2014). High BDV is desirable for the production of snacks (Bhattacharya and Corke, 1996). Water chestnut flour had the lowest breakdown viscosity (37 cp), which can be attributed to its lowest peak viscosity. The highest BDV (3057 cp) recorded for green banana flour indicates its high sus- ceptibility to shear-induced degradation. FV indicates the ability of the flour to form a viscous paste after cooking and cooling and was found in the range of 452–5474 cp. The lowest FV was recorded in the case of water chestnut flour (452 cp) possibly because of its high damaged starch content (Figure 1G) which has a low tendency to develop viscous pastes. At the same time, highest FV of potato flour (5474 cp) can be attributed to its highest starch con- tent (78.27%) (Table 1) and large-sized starch granules (Figure  1E). Setback viscosity (SBV), which denotes the tendency of cooked starchy material to re-associate and retrograde upon cooling (Hussain et  al., 2014), ranged from 127 to 2984 cp (Table 2) for different flour samples. Lower SBV (127 cp) recorded for water chestnut flour demonstrates lower syneresis of cooked starch pastes during storage. However, the higher SBV of potato flour (2984 cp) indicates its high retrogradation tendency and ability to form a cohesive gel upon cooling. The peak time of flour samples indicates the time required to reach the peak in viscosity and ease of cooking a particular sam- ple. The peak time of flour samples ranged from 4.67 to 6.87 min (Table 2). The minimum peak time of 4.67 min was recorded for green banana flour and the highest (6.87 min) for potato flour. The minimum peak time of banana flour demonstrates its easy cooking ability and can be attributed to its soft and smaller starch granular structure (Figure 1F). At the same time, the high peak time of potato flour can be attributed to the high swell- ing degree of its starch granules due to their large gran- ular structures (Figure 1E). The peak time of wheat flour (5.60  min), corn flour (5.64  min), and barley flour (5.70 min) were found to be statistically at par with each other. Scanning electron microscopy of different flour samples The microstructure analysis of different flour samples showed a disparity in the starch granular arrangement within the flour matrix, which can be attributed to vari- ation in genotype, climatic conditions as well as process- ing variability. SEM micrograph depicted in Figure  1A shows closely packed starch granules of distinct shapes with fused smaller and larger starch granules in rice flour. Intact starch granules with some rough surfaces were evi- dent in the SEM micrograph of rice flour. These intact Italian Journal of Food Science, 2022; 34 (4) 51 Utilization of non-conventional starch sources in extrusion cooking Effect of different raw material on product characteristics of developed extrudates Bulk density and hardness BD is a measure of the degree of expansion undergone by the melt as it exits the extruder (Meng et  al., 2010). BD and ER are important parameters of extruded snacks as far as consumer acceptability is concerned. Lightweight and puffed snacks are preferred by the consumers. Table 3 shows that the BD of different extrudates ranged from 51.79 to 79.68 kg/m3. The highest BD was recorded in barley-based snacks (79.68kg/m3), while the low- est BD (51.79 kg/m3) was recorded in the case of corn- based snacks followed by rice-based snacks (55.11 kg/m3) (Table 3). These findings demonstrate that out of all types of snacks, barley-based snacks were the most dense, whereas corn-based snacks were lighter followed by rice- based snacks. The higher fiber content of barley flour (5.54%) (Table 1) could be the possible reason behind the higher BD of barley-based extrudates and lower BD of corn- and rice-based extrudates. Similar results have been reported by Kirjoranta et al. (2015) for barley-based extrudates and Reddy et  al. (2014) for corn-based extrudates. Hardness is associated with the expansion and cell struc- ture of the extrudates. The more is the force needed by the probe to penetrate into the extrudate, the higher is the hardness of extrudates (Meng et al., 2010). Hardness values of different extrudates were significantly (P < 0.05) different and were found in the range of 17.05–51.55 N (Table 3). Among all types of snacks, the highest hardness value (51.55 N) was recorded in the case of barley-based snacks followed by wheat-based snacks (43.24 N), whereas the least hardness value (17.05N) was recorded for corn-based snacks. Several studies reported a highly positive correlation between BD and hardness (Altan et  al., 2008; Bhattacharya, 1997; Hussain et  al., 2017); Effect of different raw materials on system parameter of extruded snacks Specific mechanical energy SME, the mechanical energy delivered to the unit mass of the material by motor drive in the extruder, measures the work done by the motor per unit mass in the extru- sion system (Prabhakar et  al., 2017). The mechanical energy facilitates the starch conversion and correlates well with the physical attributes of extrudates such as expansion, density, and texture characteristics (Altan et  al., 2008). Thus, the higher is the SME, the higher is the degree of starch gelatinization and thus the extru- date expansion (Hussain et  al., 2017). Table 3 depicts that SME values of extrudates developed from different samples were found in the range of 50.86–85.46 Wh/kg (Table 3). The highest SME (85.46Wh/kg) recorded for potato-flour-based extrudates was statistically at par with that of corn flour–based extrudates (83 Wh/kg), and green banana flour–based extrudates (82.39 Wh/kg) while the lowest SME (50.86 Wh/kg) was recorded for wheat-based extrudates, which were statistically at par with that of barley-based extrudates (52.16 Wh/kg). Meuser et  al. (1990) reported that SME increases with the increase in starch content of the feeding material. Thus, the higher starch content (78.20%) of potato flour was the possible reason for its higher SME. Gropper et al. (2002) reported that protein and fat content affect the SME inversely by forming thermoplastic complexes with water, which restricts the fragmentation of starch granules. However, the nonsignificant difference in SME of wheat-based and barley-based snacks viz-a-viz that of potato-, corn-, and green-banana-based snacks demon- strate the nonsignificant effect of protein and fat content on SME in the present study. An almost similar range of SME has also been reported by Singh et  al. (2019) for corn-based snacks, and by Pansawat et al. (2008) for rice-based extrudates. Table 3. System and product responses of extrudates prepared from different flour samples. Parameters Flour samples SME (Wh/kg) Bulk Density (kg/m3) Expansion ratio Hardness (N) WAI (g/g) WSI (%) Rice-based snacks 80.45a ± 0.12 55.11a ± 0.11 4.82a ± 0.02 21.72a ± 0.21 4.24a ± 0.09 29.84a ± 0.05 Wheat-based snacks 50.86b ± 0.12 73.20b ± 0.10 2.84b ± 0.05 43.24b ± 0.36 3.47b ± 0.07 21.70b ± 0.08 Corn-based snacks 83.00ca ± 0.32 51.79ca ± 0.09 5.06c ± 0.06 17.05c ± 0.11 5.35c ± 0.05 32.68c ± 0.06 Barley-based snacks 52.16db ± 0.07 79.68d ± 0.07 1.96d ± 0.03 51.55d ± 0.16 3.07d ± 0.11 19.03d ± 0.06 Potato-based snacks 85.46ec ± 0.05 62.51e ± 0.07 3.97e ± 0.01 33.24e ± 0.1 3.73e ± 0.08 27.56e ± 0.08 Green-Banana-based snacks 82.39face ± 0.08 59.29f ± 0.08 4.11fe ± 0.03 27.84f ± 0.24 5.50f ± 0.15 35.07f ± 0.09 Water-chestnut-based snacks 73.25g ± 0.11 68.58g ± 0.08 3.05g ± 0.04 37.61g ± 2.23 3.85g ± 0.05 23.21g ± 0.05 Data are expressed as mean ± SD; values in the same column with different superscripts are statistically different; SME: specific mechanical energy; WAI: water absorption index; WSI: water solubility index. 52 Italian Journal of Food Science, 2022; 34 (4) Hussain SZ et al. reported that the higher is the starch content of the feed material, the higher will be the WAI of extrudates due to greater exposure of hydrophilic groups of starch to water molecules, thereby allowing better moisture penetration into the porous extrudate structure. At the same time, higher protein and fiber content are known to reduce WAI due to their dilution effect on starch (Singh et  al., 2007). Jones et  al. (2000) reported that fiber, starch, and protein have a conjugation effect on WSI. Lower starch and higher protein and fiber content affect the extent of gelatinization and dextrinization, which reduces WAI and WSI. The highest starch content recorded in the case of potato flour (78.2%) was found statistically at par with that of green banana flour (76.61%), whereas pro- tein content and crude fiber content of potato flour were significantly (P < 0.05) higher than that of green banana flour (Table 1), which justifies the highest WAI and WSI of green-banana-flour-based extrudates compared to potato-flour-based extrudates as well as other extru- dates. Likewise, the least WAI and WSI of barley-flour- based extrudates were possibly due to the lowest starch content (62.40%), highest protein content (11.83%), and crude fiber content (5.54%) of barley flour compared to other flour samples. Similar WAI and WSI values were reported by Reddy et  al. (2014) for corn-based extrudates; Ding et  al. (2005) for rice-based extrudates; Hernandez-Díaz et al. (2007) for wheat-based extrudates; and Gamalth (2008) for banana-based extrudates. Sensory evaluation of different flour-based extrudates Sensory characteristics of different flour-based extru- dates are presented in Figure 2. Mouthfeel, described as a sensation recognized by the nervous system in the cavity of the mouth (Singh et  al., 2019), was found in a range of 3.00–4.35. Green-banana-based snacks recorded the highest mouthfeel score (4.35) followed by corn-based snacks (4.10) while the least mouthfeel scores were recorded for rice- and barley-based extrudates. The high- est mouthfeel score of green-banana-based snacks was possibly due to their fruity taste while the presence of an appreciable amount of soluble sugars in corn (Zilic et al., 2011) was the possible reason for the high mouth- feel score of corn-based extrudates. At same the same, the presence of tannic acids in barley (Niffenegger, 1964) possibly had a negative effect on the taste of the snacks developed from it, while the bland taste of rice could be the possible reason for the lower mouthfeel score of rice- based extrudates. Sharma et al. (2012) also reported that a bitter taste was noticed in barley-based muffins due to the presence of phenolics. The highest visual color score was recorded for rice-based extrudates (4.66) followed by corn-based extrudates (4.20), while green-banana-based snacks recorded the Meng et  al., 2010), thus, low-density products naturally offer low hardness. These results are in agreement with the findings of hardness reported by Kirjoranta et  al. (2015) for barley-based extrudates; by Singh et al. (2016) for corn-based extrudates; and by Ding et  al. (2006) for wheat-based extrudates. Expansion ratio During extrusion cooking, the sudden drop of pressure at the exit die causes a flash off of material moisture (Arhaliass et  al., 2009) because of which air pockets are formed within the sample, which leads to the formation of porous and puffed snacks (Yanniotis et  al., 2007). As far as consumer acceptability is concerned, high ER is desirable (Hussain et  al., 2017). ER of snacks developed from different flour samples ranged from 1.96 to 5.06 (Table  3). Highest ER (5.06) was recorded in the case of corn-based snacks followed by rice-based snacks (4.82) and green-banana-based snacks, whereas the lowest ER was recorded in the case of barley-based snacks (1.96) (Table  3). However, ER of green-banana-based snacks (4.11) was statistically at par with that of potato-based snacks (3.97) (Table 3). Since ER and BD are inversely related (Meng et  al., 2010), higher fiber content of bar- ley could be the possible reason behind lower ER of bar- ley-based snacks viz-a-viz lower fiber content of corn, rice, and green banana flour justifies the higher ER of extrudates developed from them. These results were found in accordance with the results of ER reported by Reddy et  al. (2014) for corn-based snacks; Ding et  al. (2005) for rice-based snacks; Hernandez-Díaz et  al. (2007) for wheat-based extrudates; and Gamalth (2008) for banana-based extrudates. WAI and WSI WAI is a measure of the water holding capacity of starch and gives the weight and volume occupied by starch gel formed upon interaction with water (Kaur et  al., 2015) while WSI indicates the extent of polysaccha- rides leached from starch granules in the presence of excess water and measures the amount of soluble solids present in the extrudates as a result of starch degrada- tion during extrusion cooking (Ding et  al., 2005). Thus, higher WSI and WAI are desirable as far as extrudate quality is concerned (Anderson, 1982). Both WAI and WSI values of different flour-based extrudates were sig- nificantly different (P < 0.05) and were found in the range of 3.07–5.50 g/g and 19.03–35.07%, respectively. Highest WAI (5.50 g/g) as well as WSI (35.07%) was recorded in the case of green-banana-flour-based extrudates, while least WAI (3.07g/g) and WSI (19.03%) were recorded for barley-based extrudates. Delgado-Nieblas et  al. (2014) Italian Journal of Food Science, 2022; 34 (4) 53 Utilization of non-conventional starch sources in extrusion cooking appearance as well as for texture was recorded by rice- based snacks followed by corn-based extrudates while the least scores were attained by barley-based snacks for both the sensorial parameters. Due to the relatively higher starch content and the lower crude fiber content (Table 1) of rice and corn flour, the expansion (Table 2) was maximum in snacks developed from them compared to other snacks, which could be the reason behind their maximum textural and appearance scores. Likewise, the low starch content and the high percentage of crude fiber in barley flour (Table 1) limited the expansion of the barley-based snacks, which led to harder snacks with undesirable appearance. Overall acceptability of differ- ent snacks varied from 2.89 to 4.28 (Figure 2E). Corn- based snacks were found to be highly acceptable with an overall acceptability score of 4.28 followed by rice (4.23) lowest color scores (2.66) (Figure 2B). The comparatively bright and white color of rice-based snacks and the desir- able yellow color of corn-based extrudates could be the possible reasons for their high visual scores. A low color score of green banana snacks can be ascribed to their inordinate sugar content (Li et  al., 2018), which leads to the formation of brown pigments through the caramel- ization of sugars during extrusion cooking (Adubofuor et  al., 2016). Gomes et  al. (2016) also reported an increase in the darker color of bread when the level of green banana flour in the formulation was increased. The scores for appearance and texture of different extru- dates varied from 2.83 to 4.70 and 2.73 to 4.56, respec- tively. Appearance implies the visual characteristics of the extruded product including its size as well as tex- ture and shape (Singh et al., 2019). The highest score for 0 2 4 6 Rice based snacks Wheat based snacks Corn based snacks Barley based snacks Potato based snacks Green Banana based snacks Water chestnut based snacks 0 1 2 3 4 5 Rice based snacks Wheat based snacks Corn based snacks Barley based snacks Potato based snacks Green Banana based… Water chestnut based… 0 1 2 3 4 5 Rice based snacks Wheat based snacks Corn based snacks Barley based snacks Potato based snacks Green Banana… Water chestnut… 0 1 2 3 4 5 Rice based snacks Wheat based snacks Corn based snacks Barley based snacks Potato based snacks Green banana… Water chestnut… 0 1 2 3 4 5 Rice based snacks Wheat based snacks Corn based snacks Barley based snacksPotato based snacks Green banana snacks Water chestnut based snacks Figure 2. Sensory evaluation of extrudates prepared from different flour samples. (A) Mouthfeel, (B) Color, (C) Appearance, (D) Texture, and (E) Overall acceptability. (A) (B) (C) (D) (E) 54 Italian Journal of Food Science, 2022; 34 (4) Hussain SZ et al. snacks. The outcome of the present study will provide a basic guideline for food processors and researchers in the selection of suitable base materials for the development of extruded snacks. References AACC (American Association of Cereal Chemists), 2000. International approved methods of analysis. 11th ed. AACC International, St. Paul, MN. Adubofuor, J., Amoah, I. and Osei-Bonsu, I., 2016. Sensory and physicochemical properties of pasteurized coconut water from two varieties of coconut. Food Science and Quality Management 54: 26–32. Altan, A., McCarthy, K.L. and Maskan, M., 2008. Extrusion cook- ing of barley flour and process parameter optimization by using response surface methodology. Journal of Science of Food and Agriculture 88(9): 1648–1659. https://doi.org/10.1002/jsfa.3262 Anderson, R.A. (1982). 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Conclusion Evaluation of viscous behavior of starch through Rapid Visco Analyzer (RVA) as well as understanding its struc- ture through SEM was deemed essential to predict the extrusion behavior of starch-rich materials. The differ- ent starch-rich materials selected in the present study showed diverse pasting profiles, starch structures as well as extrusion behavior. The highest starch content (78.2%), as well as carbohydrate content (82.04%), was recorded in potato flour, which was statistically at par with that of green banana flour. However, the lowest starch content (62.40%) as well as carbohydrate content (67.39%) was recorded in the case of barley flour. The highest peak viscosity (6025 cp), TV (2968 cp), breakdown viscosity (3057 cp), PT (92°C), and minimum peak time (4.67 min) were recorded in the case of banana flour, which was in conformity with its elongated, round, and oval-shaped starch granules revealed through SEM (Figure 1F) as well as higher values of extrusion characteristics such as WAI and WSI. In addition to starch content, it was observed that crude fiber also had a major influence on the phys- ical characteristics of snacks. Despite the lower starch content of corn and rice flour than potato and green banana flour, the highest ERER, overall acceptability, and lower BD and hardness were recorded in the case of corn-based snacks followed by rice-based snacks, which was possibly due to lower crude fiber content of corn and rice flour. 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