The use of hydrogel structures in production of extruded rice and investigation of its qualitative characteristics

Abstract The aim of this study was to investigate the quality parameters of extruded rice containing hydrogel and comparing with natural rice (Hashemi variety rice). Extruded rice was produced with composite hydrogel (gellan, xanthan and sodium alginate) at the concentrations of 0.0 (control sample), gellan (0.5%)‐alginate (0.5%) (GA1), gellan (1%)‐alginate (1%) (GA2), gellan (0.5%)‐alginate (0.5%)‐xanthan (0.1%) (GAX 1%), and gellan (1%)‐alginate (1%)‐xanthan (0.2%) (GAX2%). The use of hydrogels had no significant effect on moisture content, ash content, cooking time, and color properties of extruded rice (p ≥ .05). In contrast, hydrogel significantly increased water absorption ratio (WAR), water solubility index (WSI), water absorption index (WAI), and textural properties (p ˂ .05) of extruded rice. This observation supports the highest score found for extruded rice containing GA2% and GAX2% in sensory properties, which were similar to natural rice. GA2% rice sample showed the similar texture characteristic, cooking feature, and color parameter to natural rice, ultimately, showing better organoleptic properties.


| INTRODUC TI ON
Rice is one of the main sources of food in the most populated regions of the world, such as China, India, Indonesia, the Philippines, Japan, etc.It is a rich source of macro and micro nutrients because during the rice grinding process, fat and bran layers which include vitamin and micronutrients are removed and white rice is produced (Budi et al., 2016;Ding et al., 2022;Rhowell et al., 2021).
Recently, extruded rice is popular because it can be used as a carrier of nutrients.In addition, replacement of cereals flour by legumes can increase protein content of grain.The extruded rice has desirable properties such as more digestibility, smooth texture, whiteness, delicate taste, and low fracture rate.Also, it is noteworthy that the use of natural broken rice in the extrusion process reduces the price of the product (Dilrukshi et al., 2022;Li et al., 2021;Tas & Shah, 2021).Extruded rice products are of great interest to develop the production of more nutritional foods with lower glycemic index (Guan et al., 2023).Ingredients such as lubricants, colorants, flavorings, and binders play an important role to produce extruded products of desired physicochemical and rheological properties (Forsido et al., 2021;Nateghi et al., 2021).
The types of extruders are divided into hot and cold extruder.
The cold extruder due to the lower temperature (below 100°C) of the fed chamber can decrease Millard reaction, disrupt the degradation of amino acids and vitamins, and reduce discoloration.
Due to constant temperature in the cold extruder chamber, it is appropriate for shaping and mixing of food like meat products and pasta.The hot extruder, due to high temperature, can eliminate microorganism contamination so that the cold extruded product does not need packaging by special properties (Choton et al., 2020;Shelar & Gaikwad, 2019).
Hydrogels are applied in food as drug delivery, packaging, and recently for the manufacturing of structured foods (Naji-Tabasi et al., 2023).Natural hydrocolloids are more interesting for creation hydrogels because of their various applications in domains such as delivery and creating structured foods.Researchers introduced hydrocolloids as one of the ingredients that have an effect on quality parameters like texture, rheological, cooking loss, and organoleptic properties of extruded rice.Hydrocolloids can create a threedimensional network that traps water molecules in this structure and prevent solid loss (Kraithong & Rawdkuen, 2020).Martínez et al. (2015) reported agar and carrageenan modified extruded wheat flour paste and gel properties.Zeng et al. (2021) found that xanthan and octenyl succinate anhydrate (OSA) starch improved by the twin-screw extrusion co-extruded XG-OSA due to better rheological properties and that resistance to environmental stresses is suitable for dysphasia products (Zeng et al., 2021).
In this investigation, the characteristics of extruded rice formulation were improved with cooperation of composite hydrogel.The effects of type and concentration of composite hydrogel (gellan, alginate and xanthan) were studied on physical, textural, and organoleptic properties of extruded rice.The properties of the extruded rice sample were compared to natural rice as a popular variety (Hashemi variety rice).
Calcium chloride was obtained from Merck Co. (Merck Co.).Sugar, sodium chloride salt, monoglyceride, and corn starch were bought from a local market (Mashhad, Iran).

| Extrusion process
To produce extruded rice, broken rice flour was used via the cold extruder method under a certain pressure condition at 40°C.Rice dough ingredients (based on flour weight) were as follows: 2% calcium chloride, 0.5% sodium chloride, 0.65% emulsifier, 0.5% sugar, and 15% corn starch mixed in dough mixer.Then, 60% hydrogel (based on flour weight) was added to the mixture.The dough was treated under a steam injection condition for 10 s (2 times).The total dough was kneaded for 10 min.Furthermore, it was put under pressure for feeding into barrel of extruder.Extruded product was dried at 40°C under air flow for ~6 h.After drying, extruded rice was immediately cooled to ambient temperature (25°C) and packed.In order to determine the hydrogel effect on rice grain properties (including GA1, GA2, GAX1, and GAX2), a control sample without hydrogel was prepared.
The quality properties of natural Hashemi rice were compared with the extruded rice.

| Moisture content
The moisture content was determined in triplicate according to the method described in AOAC (AOAC, 2005).After weighing, the samples were placed in an oven at 105°C to reach a constant weight and then placed in the desiccator.The moisture content was calculated as the difference between initial weight and final weight (AOAC, 2005).

| Ash content
The extruded rice sample (3 g) was poured into silica crucibles and incinerated on the burner.Then charred samples were heated in the furnace (Excition) at 550°C until the sample turned completely white.The samples were weighed after cooling in a desiccator.The ash concentration percentage was calculated as the difference between initial weight and final weight (AOAC, 2005).

| Optimum preparation time
Optimum preparation time (OPT) was determined in triplicate.Five grams of rice grains were hydrated in 150 mL boiling water.The OPT was matched to the moment of disappearance of the starchy core and soft tissue of the grains (Patria et al., 2020).

| Water absorption ratio
The water absorption ratio (WAR) was determined according to Patria et al. (2020) in triplicate.The hydrated samples after OPT were immediately cooled (20°C) and weighed.The water absorption capacity was calculated as follows: W 1 was weight of dry grain rice before cooking (OPT) and W 2 was weight of grains after cooking (Patria et al., 2020).

| Cooking loss
After cooking in OPT, 5 g of rice grain was rinsed with 100 mL of distilled cold water (20°C).Both the hydration water from cooking and the rinsing water were collected in a container and then evaporated in an oven at 105°C to constant weight.Cooking loss was calculated as the difference between weight of dry matter in cooking water (g) and initial weight of rice grain (g) (Patria et al., 2020).

| Lateral expansion
Lateral expansion was measured using the length of rice before and after cooking in OPT.Rice sample diameters were measured by a digital caliper once they were cooled (Saadat et al., 2019).

| Textural characteristics of rice
The rice grain before and after cooking was evaluated by a texture analyzer (TA-XT Plus Texture Analyzer).The cutting test was performed with blade probe (BLADE, HDP/BSW) at a test speed of 1 mm/s to retain 50% sample form.The measurement of hardness and adhesiveness of cooked and uncooked rice was performed at ambient temperature (25°C) (Bouasla & Wójtowicz, 2021).

| Color properties
The images of dry and cooked rice were scanned by a scanner (Canon scanner, LiDE220).Then Image J software (version 1.48 a) was used to measure color factors.The color properties of the samples were examined in the Lab color space.The values are L* (the luminance (0) or lightness (0-100)), a* (redness (+120) to greenness (−120)) and b* (yellowness (+120) to blueness (−120)) (Sun, 2016).∆E was calculated according to Equation 4 as a measure of the color difference between the extruded product and the Hashemi rice (Xiao et al., 2022).

| Sensory analysis
Sensory evaluation of rice was conducted after cooking in OPT.
Sensory analysis including color, aroma, texture, chewability, and overall acceptability was done with 22 trained panelists (the age range of 24-40 years).The panelists drank warm water during the test interval for each sample.The 5-point hedonic scale was used for sensory analysis (Naji-Tabasi et al., 2021).

| Statistical analysis
The results were analyzed by a completely randomized factorial design according to ANOVA.Then Duncan's multiple range test was applied to obtain the significant difference between means (p ≤ .05).

| Moisture content
Results showed no statistical significance (p > .05) between the moisture content of the hydrogel restructured rice compared to the control (restructured rice sample without hydrogel) (data not shown).According to experiment data, GA2% and control rice had the lowest moisture content, while the highest amount was observed in GA1% and GAX1% (p > .05).The moisture content of the

| Ash content
The hydrogel addition had no significant effect on the ash content of extruded rice (1.80%-2.25%) in comparison to the control sample (1.85%) (p > .05)(data not shown).However, the ash content of samples including GAX was more than other samples.Saadat et al. ( 2019) reported guar and Arabic gum (0.5% and 0.1%) increased the ash content of the samples which is caused due to the mineral ingredients in these gums (Saadat et al., 2019).Patria et al. (2021) reported galactomannan increased ash content of restructured rice using extruder (Patria et al., 2021).

| Cooking time
Figure 1a showed that the extruded rice containing hydrogels had no significant difference with cooking time (6-7 min) when compared to control sample without hydrogels (6.50 min) (p ˃ .05).However, it was expected that the presence of hydrocolloids delay the gelatinization of starch granules.Hydrocolloids prevent starch gelatinization and swelling due to the covering of starch grains.Gelatinization of tapioca was delayed due to the repulsion between starch and gum grains (both negatively charged).These studies made it clear that factors such as the molecular structure of hydrocolloids and the charges of starch and hydrocolloids have an important role in product rheological properties.The damaged starch leads to more starch granulation, swelling, and more moisture absorption (Chaisawang & Suphantharika, 2006).Maybe, using hydrogel instead of gum powder in formulation has a different effect, as there is no competition between hydrogel and starch in absorbing water.

| Water absorption ratio
The water absorption ratio in extruded rice including GA2 (326%) was significantly higher than rice without hydrogel (261%) (p ˂ .05),while other treatments had no significant difference compared to the control sample (p ˃ .05)(Figure 1b).This could possibly explain that  the gellan and alginate gums can increase water absorption in the extruded sample more than xanthan gum.However, extrusion processing has an important effect on gelatinization of rice starch granule so that when the rice is heated, grains rapidly absorb moisture (Detzel et al., 2016).Also reported is that due to the gums' intrinsic water absorption, using them in dough can affect the water absorption ratio, swelling, and gelatinization of grains (Srikaeo et al., 2018).

| Cooking loss
The effect of the gellan, alginate, and xanthan gum mixture in different concentrations on the cooking loss of extruded rice is presented in Figure 1c.The result showed that all of the treatments (9.28%-10.75%)had a significant effect on the reduction of the loss cooking compared to the restructure sample without hydrocolloid (10.95%) (p ≤ .05).Nevertheless, GA2% and GAX2% treatments (9.28%) significantly decreased solid loss (p ≤ .05).The higher cooking loss of samples including lower concentration (GA1% and GAX1%) or without hydrocolloids (control sample), indicates more leaching out during extruded rice cooking, which can increase the turbidity of cooking water.More hydrogen bonding between hydrocolloids and starch molecules can decrease cooking loss (Ismail et al., 2017;Kraithong & Rawdkuen, 2020;Wang et al., 2016).Kraithong and Rawdkuen (2020) investigated the effect of guar, carboxymethyl cellulose, and xanthan gum on extruded rice.The results showed lower cooking loss in sample including guar gum and carboxymethyl cellulose compared to that of xanthan.They explained lower cooking loss may be due to less expansion ratio and higher crystallinity of hydrocolloids (Kraithong & Rawdkuen, 2020).

| Lateral expansion
The lateral expansion results are shown in Figure 1d.The hydrocolloids had no significant effect on lateral expansion of restructured rice compared to that of the control sample (79%-81%) (p ˃ .05).Although, the results showed higher lateral expansion in extruded rice containing hydrocolloids compared to control sample.Gelatinization of hydrocolloids decreases the bulk density and elasticity and as a result increases the lateral expansion (Awolu & Akintade, 2021;Mirzaei et al., 2021;Naji-Tabasi & Mohebbi, 2015).In this present study, it was observed that samples containing GA and GAX slightly increased the height of rice.Although fat protects starch grains against gelatinization to reduce their gelatinization, expansion decreased (Boopathy et al., 2021;Yoo et al., 2013).
In general, as the temperature of the extruder chamber increases, the bulk density decreases as a result of the elastic force and insufficient vapor pressure.Electron microscope images showed that by increasing the extrusion temperature, looser granules are formed inside the molten material, which is able to create a microporous structure with gas bubbles, which ultimately reduces the apparent density (Gulati et al., 2020;Zhuang et al., 2010).

| Water absorption and solubility index (WSI)
The highest value of water absorption index was observed in GA1 sample (2.72 g/g) and the lowest in GAX2 (2.33 g/g) and control (2.51 g/g) (Figure 2a).Loubes et al. (2016) reported guar gum increased water absorption (58.7%) of modified rice compared to xanthan gum (Loubes et al., 2016).Also, Mirzaei et al. (2021) reported that adding hydrocolloids such as carboxymethylcellulose and locust bean gums in flour increased water absorption of extruded rice (Mirzaei et al., 2021).
The highest water solubility index (WSI) value was obtained in GA1 treatment (1.33 g/g) (Figure 1b).The alginate and gellan gum increased WSI in the GA1% extruded sample compared to the control (p ≤ .05).The WSI value coresponding to starch molecule behaviour during gelainazation and play important role in leaching.Intrinsically, amylose plays a more important role in water solubility index than amylopectin (Cai et al., 2015).Sandhu et al. (2015) reported gums decreased leaching out the amylose and amylopectin during gelatinization.These authors explained that the solubility index decreased due to gums complex with amylose.Nevertheless, their result showed leaching out of starch compound in cooked products including guar gum was more compared to that of xanthan gum.These authors attributed this result due to repulsing between starch granules phosphate groups and negative charge of anionic gum.In addition, gums can absorb water in a swell granule that decreased both starch swelling and water absorption of the rice grain (Raungrusmee et al., 2020;Sandhu et al., 2015).

| Color attributes
The color attribute of rice grain was analyzed according to L*, a*, and b* space.As shown in Figure 3, lightness of all the extruded samples including hydrogels was significantly (p ≤ .05)higher than the control sample.Naji-Tabasi and Mohebbi (2015) reported using hydrocolloids increases water distribution that affects Maillard and caramelization reactions, thus increasing the lightness of products.
The results showed no considerable difference in a* and b* index of all the extruded samples (p ≤ .05).

| Textural properties
The textural properties results of samples before and after cooking are shown in Table 1.In terms of samples before cooking, the control rice hardness (1108.75g) was significantly higher than other samples containing hydrogel (436.65-637.39g) (p ≤ .05).Temperature can increase the degree of crystallinity of extruded rice and organization of amylose complex with other ingredients that, in this case, due to the cooking temperature, hydrocolloids had a strong intermolecular bonding with starch molecules which increased rice hardness after cooking (Budi et al., 2016;Yang et al., 2020).After cooking, hardness of samples containing GA1% (8.66 g) and GA2% (8.87 g) was higher than other extruded samples (p > .05).In the other word, xanthan in the hydrogel restructure rice decreased texture hardness.These results may be due to lower solid loss and higher crystallinity of the rice noodle in which starch chain is stronger (Jafari et al., 2018;Kraithong et al., 2019).Liu et al. (2022) reported when the inulin were added to extruded mixture, it bound to water molecules through hydrogen bonds.In this way, inulin act as stabilizer and decreased mobility of water molecules between other molecules and decreased water loss of extruded flour.It is hypothesized that the reduced water accessibility of starch would increase the cross-links between starch chains and non-starch materials, which would subsequently increase hardness (Liu et al., 2022).As reported in WAR results, GA2% and GA1% had higher water absorption compared to other treatments in this work.Li et al. (2017) found adhesiveness is due to leaching of starch molecules and decreasing crystalline structure.Also, they confirmed that heat can disrupt the network structure and increase the leaching of starch molecules (Li et al., 2017).

| Sensory properties
Sensory properties of extruded rice containing hydrogels (GA1%, GA2%, GAX1%, and GAX2%) are shown in Table 2.In terms of color  2020) reported xanthan in gluten-free noodles had the highest score in overall acceptability.Also, it was reported that gellan, carrageenan, and glucomannan improve mouthfeel of rice starch (Huang et al., 2007).Ranjbar et al. (2018) found that guar and Arabic gums increase the overall acceptability of extruded rice.

| Comparison of selected restructured rice with Hashemi rice
In order to develop extruded rice containing hydrogel as a substitute product for natural rice, selected samples (GA2% and GAX2%) were selected and compared to Hashemi rice.
In compared to Hashemi rice color characteristics, extruded rice samples containing GA2% and GAX2% had the higher lightness and lower a* and b* (Table 3).This confirms that non-starch hydrocolloid distribute water in the starch structure and create lighting grain.Total color difference (∆E) values between GA2% and GAX2% with Hashemi rice were 12.13 and 12.20, respectively (Table 3).
Producing sample through cold extruder causes low color difference in compared with the original rice.
In terms of cooking characteristics, the extruded samples had lower cooking time, which was due to the degradation of starch structure in extruder (Table 3).The water absorption ratio increased due to more water absorption of hydrogel in restructured rice, where the water absorption ratio of extruded rice containing GA2% was highest (326%) and the Hashemi rice was lowest (201%) (Table 3).In terms of cooking loss, there is no significant difference between the selected extruded rice samples (9.29% and 9.28%) and Hashemi rice (9.21%).About lateral expansion after cooking, the height of optimum extruded grains (81% and 80%) was similar to Hashemi rice (80%).
Hashemi rice had the highest hardness in the extruded rice (Table 1).The extruded rice containing GA2% had higher stiffness (8.87 g) value compared to Hashemi rice and GAX2%.However, there was no significant difference before cooking (p ˃ .05) in hardness of   selected extruded rice samples (637.39 and 521.54 g) and Hashemi rice (633.89g).The amount of adhesiveness in the GAX2% sample was more than the other samples (Table 1), which due to increment in gums, adhesiveness increased.
The result showed no significant difference between the sensory characteristics of optimum extruded samples and Hashemi rice (Table 2).Nevertheless, our result showed that extruded rice containing GA2% sample can be a good alternative for Hashemi rice.

TA B L E 3
Cooking and color properties of optimum extruded rice and Hashemi rice.
2.6.3 | The water absorption index (WAI) and the water solubility index (WSI) Water absorption index and WSI were determined according to the method described by Patria et al. (2020) in triplicate.The sample flour (2 g) was diluted in 20 mL of distilled water and poured in centrifuge tubes.The solution was centrifuged at 865 g for 20 min.Then, the supernatant was poured in an aluminum container and dried in oven at 105°C for 24 h.The weight of the gel and dried supernatant was recorded.WAI and WSI were calculated as follows (Equations 2 and 3; Patria et al., 2020): E 1 Cooking properties of rice samples containing different concentrations of hydrogel (GA, gellanalginate; GAX, gellan-alginate-xanthan) (cooking time (min) (a), water absorption ratio (%) (b), cooking loss (%) (c), and lateral expansion (d)).
characteristics, there was no significant difference between the samples (4.10-4.78)(p > .05).The control sample and GAX1% obtained the lowest scores in terms of appearance, taste, aroma, and texture, although the difference was not significant (p > .05).As a result, the lowest overall acceptance score was obtained by the control (3.20) and GA 1% (3.30) samples (p ≤ .05).In a similar study, Raungrusmee et al. (
(Ranjbar et al., 2018)reased with the increment of gellan gum concentration (p > .05).But alginate gum content had no influence on moisture content.Maybe, the negative charges on the alginate gum surface led to a delay in gelatinization and starch swelling.The anionic gums, such as xanthan, alginate, carrageenan, and Arabic gum, can delay gelatinization and prevent the disappearance of amylose from the dough(Ranjbar et al., 2018).
According to the results, addition of different levels of gellan-alginate and gellan-alginate-xanthan gum hydrogel network had different effects on the texture, color, and physical parameters of the produced structured rice.The use of hydrogels in the rice structure significantly reduced the cooking loss and increased the water absorption ratio.Note: Means ± standard deviation.Different letters in each column indicate statistically significant differences (p ≤ .05).Textural properties of extruded rice before and after cooking.Sensory properties of extruded rice and Hashemi rice.Note: Means ± standard deviation.Different letters in each column indicate statistically significant differences (p ≤ .05).Note: Means ± standard deviation.Different letters in each row indicate statistically significant differences (p ≤ .05).
samples have less cooking time and stiffness.But they had more water absorption and desirable color.Investigation of sensory properties did not show a significant difference between structured samples and Hashemi rice.According to the results, structured rice containing GA2% and GAX2% hydrogels improved acceptable quality.TA B L E 1