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Effect of hydrocolloids on physicochemical, sensory and textural properties of reconstructed rice grain by extrusion cooking technology Sara Ranjbar, Alireza Basiri, Amir Hosein Elhamirad, Akram Sharifi & Hossein Ahmadi Chenarbon Journal of Food Measurement and Characterization ISSN 2193-4126 Food Measure DOI 10.1007/s11694-018-9777-5 1 23 Your article is protected by copyright and all rights are held exclusively by Springer Science+Business Media, LLC, part of Springer Nature. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to selfarchive your article, please use the accepted manuscript version for posting on your own website. 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The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy Journal of Food Measurement and Characterization https://doi.org/10.1007/s11694-018-9777-5 ORIGINAL PAPER Effect of hydrocolloids on physicochemical, sensory and textural properties of reconstructed rice grain by extrusion cooking technology Sara Ranjbar1 · Alireza Basiri2 · Amir Hosein Elhamirad1 · Akram Sharifi3 · Hossein Ahmadi Chenarbon4 Received: 30 May 2017 / Accepted: 14 March 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Cracked or broken rice grains followed by lower rice efficiency during processing and milling of rice paddy are a major challenge contributing to the reduced economic productivity of this branch of industry. Therefore, the extrusion process for turning flour from broken rice or wastes into complete rice grains can bring about value-added for producers. In addition, an optimized formulation can improve product diversity and nutritional value. In this study, the effect of addition of Guar and Arabic gums on physicochemical, texture and sensory profiles of extruded rice grains was analyzed. Both gums were used in four concentrations (0.1, 0.2, 0.3 and 0.4 w/w %, d.b), and the effect of their different levels on properties of extruded rice was studied. Results from physicochemical tests on extruded rice samples showed that moisture content, water solubility index, water absorption index and bulk density were increased in samples containing higher concentration of Guar than Arabic gum and initial moisture content of 30% compared to no-gum samples, whereas lateral expansion, cooking loss, and total color change (ΔE) were reduced. Furthermore, results showed that higher levels of Guar than Arabic gum led to an improvement in sensory and textural properties. Keywords Extrusion · Rice grain · Arabic gum · Guar gum Introduction * Alireza Basiri bassiri@irost.ir; Ali_bassiri@yahoo.com Sara Ranjbar Sararanjbar89@gmail.com Amir Hosein Elhamirad ah_elhami@iaus.ac.ir; ah.elhami@gmail.com Akram Sharifi asharifi@qiau.ac.ir; akramsharifi76@gmail.com Hossein Ahmadi Chenarbon h.ahmadi@iauvaramin.ac.ir; h.ahmadi292@yahoo.com 1 Department of Food Science and Technology, Sabzevar Branch, Islamic Azad University, Sabzevar, Iran 2 Department of Chemical Technologies, Iranian Research Organization of Science and Technology (IROST), Tehran, Iran 3 Department of Food Science and Technology, Faculty of Industrial and Mechanical Engineering, Qazvin Branch, Islamic Azad University, Qazvin, Iran 4 Department of Agronomy, Varamin-Pishva Branch, Islamic Azad University, Varamin, Iran Rice is an annual plant belonging to the genus Oryza sativa L. and the family Gramminae with numerous species. It is regarded as the main source of nutritional energy for about half of the world population, particularly in Asia. Rice as a global staple food is obtained from the widely-used milling process to provide consumer-preferred properties [1]. It changes the texture and whiteness of rice, increases water-bonding capability and expansion ratio, improves digestibility, and reduces the cooking time [2]. Cracked or broken rice grains followed by lower rice efficiency during processing and milling of rice paddy are a major challenge contributing to the reduced economic productivity. Accordingly, the extrusion process in turning flour from broken rice or wastes into whole rice grains can improve the value added in the production process. In addition, this technique can be used to produce functional foods for niche groups based on additive different contents and types. Extrusion is a complex process made up of numerous operations including mixing, baking, making dough, cutting, forming and casting. The 13 Vol.:(0123456789) Author's personal copy S. Ranjbar et al. main objective of extrusion is to develop the diversity in daily foods through products with different shape, texture, colors and flavor. Advantages of the extrusion process include diversity in foods, reuse of food losses (e.g. converting broken rice into textured rice), lower process costs than other baking methods, more production, continuous process, and the possibility of automating the process. In addition, this technique has basically no waste and causes the least environmental pollution problems due to low water used. A set of factors affect the characteristics of extrusion products including temperature, pressure, mold hole size, shear forces, and food rheological properties [3]. Gums are a large group of polysaccharides with a good potential to become high-viscose products at low concentrations. Arabic gum is water soluble and unlike other gums, does not create the high viscosity at low concentrations due to its low molecular weight and highly branched structure. Furthermore, its viscosity varies with pH as a result of ionic changes within its structure. It should not be accompanied with certain food polymers like gelatin or sodium alginate. The main chain of this gum is D-galactopyranose bonded through β(1 → 3) links, and its sub-branches contain L-arabinose, L-rhamnose, and D-glucuronic. It is used as an emulsifier and a stabilizer in food systems as it curbs lipid movements and formation of two-phase fat emulsions in water [4]. Guar is made of hydrocolloid polysaccharides with high molecular weight. Its structure is similar to that seen in Karnoub as its main chain is made of β-D-mannopyranose attached by β(1 → 4) links. D-galactopyranose units are alternatively attached to the main chain via α(1 → 6) links. In general, its structure is like a galactomannan and is capable of forming a highly flexible film [5]. A study was conducted on physical, sensory and nutritional properties of extruded rice grains containing maize/wheat, sorghum/ wheat, and rice flour mixtures. Study treatments had a significant effect on extruded product color. The color of extruded products containing rice flour was highly similar to that of natural rice. The products of wheat/sorghum flour mixture had the highest cooking losses (13.4%) and water uptake (137.8%) and were significantly different from other treatments in terms of texture. At the same time, remaining vitamin C content of the product was low ranging between 4.3 and 27.6%, whereas iron and folic acid contents showed the highest stability [6]. A similar study investigated the effect of emulsifiers (glycerol monostearate, soy lecithin, and sodium stearoyl lactylate) and thickeners (arabic gum, sodium alginate and stick rice) on fast-cooked extruded rice products. The added emulsifiers increased the gelatinization and reduced the water-solubility of hydrocarbons, α-amylase sensitivity, solubility index in water, and cohesiveness. However, 13 addition of thickeners increased the gelatinization, bulk density, water-solubility of hydrocarbons, α-amylase sensitivity, solubility in water index, water uptake rate, and cohesiveness [7]. Another study analyzed the effect of three galactomannans on practical properties of extruded products containing rice-pea mixture. These products were produced with a base ratio of 70:30 (pea to rice) and were enriched with guar, Locust bean, and fenugreek gums (5–20%) and were finally extruded in an extruder under optimal conditions. Results showed satisfactory outputs for all three gums. A 5% addition of Guar and locust bean gums reduced the product hardness, whereas additions higher than 5% of Guar and locust bean gums as well as all levels of fenugreek gum led to an increased hardness. Fenugreek-containing samples were harder and more brittle than other treatments. Sensory analysis results showed that the use of all gums up to 15% concentrations could produce products with a satisfactory sensory profile. The glycemic index was dropped below 55 when the gum content increased by 15% and the guar gum showed a higher efficiency than others. In general, the use of all three galactomannans (< 15%) led to the development of products with satisfactory nutritional and organoleptic properties [8]. Another study investigated the effect of addition of rice bran (0–4%), Guar gum (0–10%), and extrusion conditions including moisture content (MC) (26–33%), screw speed (20–32 rpm), extruder temperature (70–120 °C) on physicochemical, texture, and nutritional profiles of rice. Results showed that the optimal process points included the addition of 4% rice bran, 30% MC, 26 rpm screw speed, and 95 °C temperature. At optimal conditions, total dietary fiber (16.61%), protein (9.4%), fat (3.68%), thiamine (0.68 µg/g), riboflavin (2.42 µg/g), and γ-oryzanol (16.07 mg/100 g) were obtained. Addition of the Guar gum improved color and texture of products, whereas its higher concentrations (> 10) led to producing harder products [9]. In another study, the cooking behavior of extruded rice flour improved with xanthan gum was evaluated. Long-grain rice flour with high amylose was extruded in a twin-screw extruder. Accordingly, the effect of screw speed (200–300 rpm), cylinder temperature (100–160 °C), and MC (16–22%) on a number of functional and physical properties, plasticity and digestibility of the extruded products was analyzed. According to regression analysis results, water absorption index (WAI) was significantly affected by all linear relationships, quadratic relationships and interactions. The maximum viscosity had a high correlation with the hot-paste viscosity and cold-paste viscosity. Moreover, it was shown that starch digestion was dependent on process conditions [10]. Against this background, the objective of the study was to obtain a rice synthesis technology to produce rice Author's personal copy Effect of hydrocolloids on physicochemical, sensory and textural properties of reconstructed… grains similar to natural ones and to improve qualitative and organoleptic properties by addition of Arabic and Guar gums, modified starch and mono- and diglycerides emulsifers using rice losses to create value-added. Materials and methods Materials The raw materials including broken rice grains (Avand Kala Co.), Arabic and Guar gums (Merck, Germany), mono- and diglycerides emulsifers (Pars Behbood Asia Co.), and titanium dioxide (Pars Behbood Asia Co.) were first purchased. The study treatments included extruded rice samples containing rice flour (68.9 and 100%) with mono- and di-glyceride emulsifiers (0.5%), modified maize starch (30%), titanium dioxide (0.1%), and different levels of Guar (0.1, 0.2, 0.3, and 0.4% dry matter) and Arabic gum (0.1, 0.2, 0.3, and 0.4% dry matter). The study treatments are given in Table 1. Physicochemical testing of rice flour The physicochemical profile of rice flour samples was determined using standard AOAC methods including moisture Table 1 Study treatments content [11], protein [12], fat [13], total fiber [14], ash [15], and amylose [16]. Extruded rice production methods To produce extruded rice, Sepid Rood broken rice grains were used due to their high amylose to amylopectin content. Broken rice grains were first crushed by a hammer mill and were passed through a 1 mm mesh sieve for grading purposes. Raw materials were then prepared and weighed for the extrusion cooking process. Excess water was added corresponding to the target MC (20–35%) by adding an amount of distilled water calculated through mass balance relation [10]. The mixing process was performed in a mixer at 365 rpm for 20 min to develop the paste [9]. The paste was then fed to an extruder with the number and diameter of openings of 24 and 1.8 mm, respectively, pressure of 25 MPa, the minimum and maximum screw speeds of 15 and 20 rpm, respectively, working temperatures of 75, 90, and 95 °C at 1st, 2nd, and 3rd levels, respectively, and the number of screws of 2 pcs. The device ran in an idle mode for 5–10 min and then the paste was fed. The feeding rate and screw speed were 12.5 kg/h and 150 rpm, respectively. Once leaving the extruder, the samples were conveyed via a tube towards a dryer. Different treatments were dried in a hot-air dryer with a single layer at 50 °C until reaching the Treatment codes Treatment types C B20 20-G1A4 20-G2A3 20-G3A2 20-G4A1 B25 25-G1A4 25-G2A3 25-G3A2 25-G4A1 B30 30-G1A4 30-G2A3 30-G3A2 30-G4A1 B35 35-G1A4 35-G2A3 35-G3A2 35-G4A1 Control sample 100% rice flour with 20% MC 0.1% Guar gum + 0.4% Arabic gum + additivesa with 20% MC 0.2% Guar gum + 0.3% Arabic gum + additives with 20% MC 0.3% Guar gum + 0.2% Arabic gum + additives with 20% MC 0.4% Guar gum + 0.1% Arabic gum + additives with 20% MC 100% rice flour with 25% MC 0.1% Guar gum + 0.4% Arabic gum + additives with 25% MC 0.2% Guar gum + 0.3% Arabic gum + additives with 25% MC 0.3% Guar gum + 0.2% Arabic gum + additives with 25% MC 0.4% Guar gum + 0.1% Arabic gum + additives with 25% MC 100% rice flour with 30% MC 0.1% Guar gum + 0.4% Arabic gum + additives with 30% MC 0.2% Guar gum + 0.3% Arabic gum + additives with 30% MC 0.3% Guar gum + 0.2% Arabic gum + additives with 30% MC 0.4% Guar gum + 0.1% Arabic gum + additives with 30% MC 100% rice flour with 35% MC 0.1% Guar gum + 0.4% Arabic gum + additives with 35% MC 0.2% Guar gum + 0.3% Arabic gum + additives with 35% MC 0.3% Guar gum + 0.2% Arabic gum + additives with 35% MC 0.4% Guar gum + 0.1% Arabic gum + additives with 35% MC Dry matter percentages are based on dry matter weight, and moisture percentage is based on wet weight a Additives 68.9% rice flour, 30% modified starch, 0.5% emulsifier, and 0.1% titanium oxide 13 Author's personal copy S. Ranjbar et al. target MC of 10–14% (w.b). The dryer had three levels, and its length was 15 m. The dried samples were then packed in polyethylene bags for different experiments [8]. Moisture content (MC) measurement The MC of samples was measured using the oven method at 105 °C for 24 h [11]. Color analysis Raw and extruded rice color analyses were conducted by determining three indices of a*, L* and b* using Minolta Hunterlab (C360, Japan) through the CIE method. The total color changes (∆E) were calculated using Eq. 2. √ (2) ΔE = (L − Lo )2 + (a − ao )2 + (b − bo )2 where: L0, a0 and b0 belong to the control sample. Bulk density (BD) measurement Textures analysis Following the drying of the extruded rice samples, rice grains were poured from a 15 cm height into a container with known volume. A ruler was then moved in a zigzag trajectory to align the rice surface with the container edge. The rice weight was determined inside the container, and its density (kg/m3) was calculated by dividing the stack mass to container volume [12]. Lateral expansion (LE) measurement This parameter in fact represents the lateral expansion of extruded rice grains, which is in turn a function of paste ingredients, and is determined using Eq. 1. L= d do (1) where, d0 is the die opening diameter (mm) and d is the extruded rice diameter (mm). The diameter of rice grains was measured by a digital caliper once the samples were cooled down to room temperature [9]. Water absorption index (WAI) and water solubility index (WSI) measurements For this experiment, a milled sample (2.5 g) with reduced particle size of 200–250 µm was immersed in distilled water, and the mixture was stirred for 30 min with a glass stirrer. The resulting dispersion was transferred to a centrifuge and was rotated at 4000 rpm for 15 min. The upper phase of the centrifuge tube was separated, and its solubility was determined. The precipitate phase was also weighed to determine its MC [8]. Cooking loss (CL) measurement A total of 100 g extruded rice was immersed in 400 g boiling water for 2 min. It was then drained. The drained water was heated for 20 h at 100 °C to determine the amount of remaining solids as cooking losses [6]. 13 Texture hardness of the raw and extruded rice samples was determined by Brookfield (Pro CT, USA). In this method, 40 g of the cooked samples was placed in a circular container and was pressed by a TA5 rod probe at 0.5 mm/s until reaching 60% of sample thickness. The related curves were drawn, and the hardness index for raw rice samples and the texture profile (e.g. hardness, adhesiveness, chewiness, gumminess, cohesiveness, and springiness) for the cooked samples were determined [9]. Organoleptic properties of cooked extruded rice samples The extruded raw rice was first boiled for 5 min (at 80 °C) (the raw rice was mixed with water at a 2:1 w/w ratio). It was then drained and cooked for 10 min at 100 °C. The sensory analysis was conducted by a total of ten trained panelists (20–30 years, male and female) based on the 9-point hedonic rating scale. In this way, features with very good and very bad evaluation were given 9 and 1, respectively. Items included color, flavor, texture, and total acceptance [8]. Statistical analyses Experimental data were analyzed using a completely randomized design with three replications. Means of variables were also compared by Duncan’s multiple-range test (α = 5%) in SPSS 16. Results and discussion Physicochemical analysis of extruded rice samples The moisture content, protein, fat, amylose, insoluble ash, total ash and total fiber of rice flour used in producing extruded rice were 9.18, 8.85, 1.77, 26.9, 0.4, 0.8 and 0.51%, respectively. Table 2 shows mean comparison results for the effect of different treatments on water solubility index (WSI), water absorption index (WAI), lateral expansion Author's personal copy Effect of hydrocolloids on physicochemical, sensory and textural properties of reconstructed… Table 2 Results from mean comparison of physicochemical analysis of extruded rice samples Treatments WSI (%) WAI (%) LE (%) BD (g/cm3) E (−)Δ MC (%) CL (%) B20 20-G1A4 20-G2A3 20-G3A2 20-G4A1 B25 25-G1A4 25-G2A3 25-G3A2 25-G4A1 B30 30-G1A4 30-G2A3 30-G3A2 30-G4A1 B35 35-G1A4 35-G2A3 35-G3A2 35-G4A1 C 13.42 ± 0.46i 14.13 ± 0.13h 14.26 ± 0.14gh 14.29 ± 0.12gh 14.43 ± 0.35g 15.10 ± 0.13f 15.72 ± 0.13e 15.59 ± 0.15e 15.62 ± 0.18e 15.51 ± 0.21e 16.52 ± 0.09d 17.07 ± 0.05c 17.12 ± 0.03c 17.16 ± 0.05c 17.19 ± 0.06c 17.65 ± 0.06b 17.98 ± 0.03a 17.96 ± 0.06a 18.03 ± 0.09a 18.09 ± 0.07a 17.15 ± 0.08c 2.443 ± 0.02jk 2.373 ± 0.01l 2.407 ± 0.01kl 2.417 ± 0.02jkl 2.423 ± 0.03jkl 2.687 ± 0.02g 2.470 ± 0.04ij 2.520 ± 0.01hi 2.530 ± 0.01h 2.537 ± 0.01h 2.797 ± 0.02f 2.650 ± 0.05g 3.017 ± 0.01d 3.383 ± 0.07b 3.040 ± 0.05d 2.910 ± 0.01e 2.837 ± 0.02f 3.103 ± 0.05c 3.720 ± 0.07a 3.113 ± 0.02c 1.943 ± 0.02m 182 ± 2.08a 149 ± 4c 142 ± 2.08d 138 ± 2.31e 130 ± 2.08gh 156 ± 1.73b 132 ± 0.58g 129 ± 1ghi 127 ± 1hi 126 ± 0.58i 148 ± 0.58c 126 ± 1.53i 120 ± 2.08j 119 ± 1j 113 ± 1k 135 ± 0.58f 120 ± 2.52j 122 ± 1.53j 120 ± 1j 113 ± 2.31k – 0.73 ± 0.01m 0.76 ± 0.02l 0.77 ± 0.01k 0.78 ± 0.01j 0.78 ± 0.02i 0.76 ± 0.02l 0.79 ± 0.01i 0.79 ± 0.01h 0.81 ± 0.01g 0.81 ± 0.02f 0.81 ± 0.02fg 0.85 ± 0.01d 0.86 ± 0.03d 0.86 ± 0.01d 0.87 ± 0.02c 0.82 ± 0.01e 0.86 ± 0.01d 0.87 ± 0.02c 0.87 ± 0.01c 0.88 ± 0.01b 0.89 ± 0.01a 15.93 ± 0.07a 5.21 ± 0.05d 5.20 ± 0.05d 5.17 ± 0.03d 5.19 ± 0.03d 15.84 ± 0.07ab 5.19 ± 0.02d 5.17 ± 0.03d 5.18 ± 0.02d 5.20 ± 0.05d 15.78 ± 0.18b 5.14 ± 0.03de 5.12 ± 0.04de 5.11 ± 0.02de 5.16 ± 0.05de 15.44 ± 0.13c 5.13 ± 0.02de 5.18 ± 0.04d 5.14 ± 0.05de 5.04 ± 0.04e – 9.89 ± 0.22j 9.90 ± 0.11j 10.56 ± 0.13hi 10.35 ± 0.26i 10.81 ± 0.12gh 10.84 ± 0.14gh 11.02 ± 0.35g 11.63 ± 0.21ef 11.72 ± 0.11e 12.03 ± 0.11d 11.36 ± 0.08f 11.40 ± 0.15f 12.12 ± 0.20cd 12.41 ± 0.15c 12.43 ± 0.27c 12.42 ± 0.22c 13.02 ± 0.07b 13.21 ± 0.23b 13.86 ± 0.12a 13.95 ± 0.13a 9.65 ± 0.03j 12.40 ± 0.05a 6.93 ± 0.04d 6.90 ± 0.04d 6.79 ± 0.01de 6.79 ± 0.01de 12.04 ± 0.06b 6.51 ± 0.05f 6.53 ± 0.04f 6.51 ± 0.02f 6.50 ± 0.01f 11.34 ± 0.1c 6.18 ± 0.02g 6.12 ± 0.03g 6.07 ± 0.04g 5.72 ± 0.47h 11.98 ± 0.01b 6.60 ± 0.01ef 6.56 ± 0.03f 6.52 ± 0.02f 6.50 ± 0.01f 2.89 ± 0.04i Different letters in the column indicate statistically significant differences (P < 0.05) WSI water solubility index, WAI water absorption index, LE lateral expansion, BD Bulk density, ∆E total color changes, MC moisture content, CL cooking loss (LE), bulk density (BD), total color changes (ΔE), moisture content (MC), and cooking loss (CL) of extruded rice samples. Effect of Arabic and Guar gums on MC of extruded rice samples According to Table 2, there was a significant difference between the different treatment levels in terms of the effect on MC (P < 0.05). The lowest MC belonged to B20 and natural rice (C), whereas the highest value was seen in 35-G4A1 and 35-G3A2 treatments. Results indicated that increased concentrations of Guar gum compared to Arabic gum were effective in increasing the final MC of the final product due to the higher water holding capacity of Guar than Arabic gum. In other words, the negative charges on Arabic gum surface led to delayed gelatinization and swelling of starch. Chaisawang and Suphantharika [13] also reported that guar gum could improve moisture holding capacity of paste and its quality. Shi and Bemiler [14] suggested that negatively charged gums (e.g. xanthan, alginate, carrageenan and arabic) caused a delay in the gelatinization and removal of amylose from paste. Effect of Arabic and Guar gums on WAI of extruded rice samples According to Table 2, there was a significant difference between the different treatment levels in terms of effect on WAI (P < 0.05). The lowest WAI belonged to 20-G1A4 and C, whereas the highest value was seen in 35-G3A2. Gums increased the gelatinization due to water absorption and swelling in starch. Moreover, an increased MC of the feed led to the gelatinization of starch granules and their degradation. The higher amylose to amylopectin content led to the higher water uptake due to the higher water absorption capability of starch. Note that 0.3% Guar gum in the starch-emulsifier-hydrocolloide matrix absorbed water easier than other concentrations. However, the negatively charged 0.2% Arabic gum failed to form a suitable film on starch, thus failed to curb its gelatinization, swelling and degradation. These results were in consistent with those reported by Ravindran et al. [8] who suggested that an increased concentration of guar and locust bean gums up to 5% had a significant effect on WAI, whereas their higher concentrations had an adverse effect. Becker et al. [15] showed that WAI increased at higher gelatinization level. 13 Author's personal copy S. Ranjbar et al. Effect of Arabic and Guar gums on WSI of extruded rice samples Effect of Arabic and Guar gums on LE of extruded rice samples According to Table 2, there was a significant difference between the different levels of treatments in terms of effect on water solubility index (WSI) (P < 0.01). The lowest WSI was in B20 and the highest amount was observed in 35-G4A1, 35-G3A2, 35-G1A4 and 35-G2A3. The presence of compounds from gelatinization could be effective in WSI. In this regard, high-MC feed could increase starch granule degradation. At the same time, different Arabic and Guar gum concentrations at 35% MC had no significant difference in terms of WSI of treatments. The interaction of emulsifier and gums with starch and formation of a new complex at 35% MC had also no significant effect on WSI (P ≥ 0.05). In other words, at 35% MC, the emulsifier glycerol monostearate and arabic and guar gums changed the hydrophilic-hydrophobic structure of extruded rice, resulting in increased WSI. The same results were reported by Wang et al. [7]. According to Table 2, there was a significant difference between the different treatment levels in terms of effect on lateral expansion (LE) (P < 0.05). The lowest LE belonged to and 30-G4A1, while the highest value was observed in B20. Generally, higher feed MC reduced the vapor pressure during the extrusion process. Increased MC of the paste reduced the elastic characteristic of the reconstructed rice grains, thus decreased LE. Higher concentrations of Guar gum than Arabic gum reduced LE and form a uniform structure in extruded rice samples creating highdensity structures with smaller cells. These are due to the ability of Guar gum to increase water holding capacity, create softer structure and reduce elasticity of grains. It was found that increasing feed MC from 26 to 33% significantly decreased LE in extruded samples [9]. Effect of Arabic and Guar gums on CL of extruded rice samples Effect of Arabic and Guar gums on BD of extruded rice samples Results showed that there was a significant difference between different treatment levels in terms of the effect on the bulk density (BD) (P < 0.05). The highest BD belonged to C, whereas the lowest value was seen in B20. In general, the change in extrusion conditions like increased mechanical and thermal energy (screw speed and extrusion temperature) increased the gelatinization of extruded products and reduced their density, whereas the formulation could leave various effects on their BD. High-amylose rice flour had a higher BD than low-amylose rice flour. By comparing 35-G4A1 with C, it was found that extrusion conditions (temperature, screw speed, pressure, blade speed, and feed MC) and formulation (emulsifier, gums, starch, and high-amylose rice flour) failed to form a sufficiently dense uniform texture in the products. This led to a small expansion in rice texture under different extrusion conditions, decreasing its BD. At the same time, 0.4% guar gum with 0.1% Arabic gum effectively increased water holding capacity, which in turn formed a softer amylopectin structure along with higher BD. Ravindran et al. [8] reported that higher concentrations of guar and fenugreek gums up to 20% led to an increase in BD. Zhuang et al. [16] suggested that BD decreased by increasing extruder temperature, whereas it showed no increase with increasing feed MC (from 28 to 36%) and screw speed (from 150 to 350 rpm). Wang et al. [7] reported that addition of emulsifiers like glycerol monostearate and addition of hydrocolloids like arabic gum could increase BD. 13 According to Table 2, there was a significant difference between the different treatment levels in terms of effect on cooking loss (CL) (P < 0.05). The highest CL belonged to B20, while the lowest value was seen in C. Extrusion conditions like mechanical and thermal energy (screw speed and extrusion temperature) increased the gelatinization of extruded products. Variations in feed MC, blade speed, and feeding rate also changed the extruded texture. In addition to process conditions, the formulation could also leave various effects on the texture of extruded products. During cooking of extruded rice samples, thermal denaturation and concentration of amino acids in the gum structure and thus formation of a weak lattice of compacted proteins inside rice grains prevented high swelling during water absorption and thus reduce cooking loss. Therefore, CL caused by developing a new product seems inevitable, which can be reduced down to a normal range by optimizing the process conditions and formulation. According to the results, the main factors in CL were 0.4% Guar gum and 0.1 Arabic gum, because of formation of a more cohesive structure and a stronger complex between amylose, emulsifier, and this gum ratio at optimal MC of 30% leading to a reduced CL. The results were in agreement with Lai [17] who reported that the amylose and emulsifier complex reduced CL in rice pastas. Yoo et al. [6] showed that wheat and sweet maize flours had higher CL than rice flour. Gujral et al. [18] found that addition of hydrocolloids and α-amylase to Chapati rice flour reduced CL, which in turn improved the texture quality. Author's personal copy Effect of hydrocolloids on physicochemical, sensory and textural properties of reconstructed… Effect of Arabic and Guar gums on ΔE of extruded rice samples rice flour by extrusion cooking. They suggested that increasing feed MC from 16 to 22% led to clearer sample colors. According to Table 2, there was a significant difference between treatments in terms of total color changes (ΔE) (P < 0.05). The lowest ΔE belonged to 35-G4A1, 30-G3A2, 30-G2A3, 35-G1A4, 30-G2A3, 35-G3A2 and 30-G4A1, while the largest amount was observed in B20 and B25. Generally, the formation of darker colors at higher temperatures was the result of the Maillard (browning) reaction, caramelization, protein degradation, and pigment decomposition following the extrusion process. The high temperature of extrusion and low water content clearly speeded up the Maillard reaction. Accordingly, a significant decrease (P < 0.05) in total color changes (ΔE) was observed by increasing the feed MC from 20 to 35%. At 30 and 35% MCs, samples containing Arabic and Guar gums showed significantly lower ΔE than that at 20 and 25% MCs due to higher water holding capacity of hydrocolloids and retardation of the Maillard reaction. Becker et al. [15] showed that different rice genotypes and extrusion conditions led to changes in color. In this regard, following the extrusion process, the extruded rice flour is darker with a reddish-yellowish color. Martinez et al. [19] also reported decreased ΔE in a study on modified Texture analysis of raw and cooked extruded rice samples Table 3 compares the mean values from texture analysis of raw and cooked extruded rice samples. Effect of Arabic and Guar gums on hardness of raw extruded rice samples According to Table 3, there was a significant difference between the different treatment levels in terms of effect on texture hardness of raw rice samples (P < 0.05). The lowest hardness belonged to B20, while the highest amount was observed in C and 35-G4A1. Considering the fact that LE reduced as MC increased leading to a denser lattice, a larger force was required to create the stress in the rice texture. Furthermore, 35-G4A1 had a significantly larger hardness than 30-G4A1. This showed that Guar gum had a better water holding capacity than Arabic gum. Accordingly, the gelatinization process of starch granules was accelerated at higher MCs, which contributed to higher hardness in rice texture Table 3 Results from mean comparison of texture analysis of raw and cooked extruded rice samples Treatments Hardness of raw rice (N) B20 20-G1A4 20-G2A3 20-G3A2 20-G4A1 B25 25-G1A4 25-G2A3 25-G3A2 25-G4A1 B30 30-G1A4 30-G2A3 30-G3A2 30-G4A1 B35 35-G1A4 35-G2A3 35-G3A2 35-G4A1 C 20.80 ± 0.29q 32.09 ± 0.49m 33.17 ± 0.20l 35.25 ± 0.73ij 33.99 ± 0.21k 23.26 ± 0.37p 34.76 ± 0.37jk 36.59 ± 0.35gh 37.86 ± 0.21ef 37.10 ± 0.13fg 25.04 ± 0.67° 35.95 ± 0.55hi 37.46 ± 0.28ef 40.33 ± 0.23c 40.57 ± 0.62c 28.50 ± 0.50n 37.95 ± 0.10e 39.36 ± 0.45d 40.52 ± 0.34c 42.87 ± 0.25b 52.22 ± 0.17a Hardness of cooked rice (N) Adhesiveness (mj) Cohesiveness (−) Springiness (mm) Chewiness (N) Gumminess (mj) 7.56 ± 0.35m 11.24 ± 0.26k 11.33 ± 0.26k 11.85 ± 0.18j 12.49 ± 0.43i 10.36 ± 0.20l 13.59 ± 0.26h 13.65 ± 0.44h 14.90 ± 0.08fg 14.41 ± 0.29g 12.69 ± 0.29i 14.76 ± 0.19fg 15.29 ± 0.28ef 17.71 ± 0.26d 19.40 ± 0.33b 14.76 ± 0.13fg 15.77 ± 0.1e 15.32 ± 0.27ef 18.76 ± 0.17c 19.08 ± 0.13bc 24.56 ± 0.8a 1.36 ± 0.38c 0.33 ± 0.06d 0.30 ± 0.10de 0.25 ± 0.04def 0.033 ± 0.06gh 1.93 ± 0.15b 0.16 ± 0.05defgh 0.13 ± 0.06efgh 0.11 ± 0.02efgh 0.056 ± 0.1fgh 2.16 ± 0.06a 0.10 ± 0.01efgh 0.11 ± 0.01efgh 0.10 ± 0.01efgh 0h 2.20 ± 0.1a 0.22 ± 0.07defg 0.12 ± 0.03efgh 0.066 ± 0.06fgh 0.033 ± 0.06gh 0h 0.54 ± 0.06l 4.51 ± 0.29de 5.16 ± 0.05c 5.65 ± 0.23b 6.05 ± 0.06a 0.45 ± 0.04l 3.77 ± 0.15hi 4.15 ± 0.05fg 4.75 ± 0.13d 5.49 ± 0.40b 0.47 ± 0.03l 3.28 ± 0.14j 3.76 ± 0.13hi 4.29 ± 0.20ef 4.62 ± 0.06d 0.69 ± 0.05l 3.63 ± 0.10i 3.80 ± 0.08hi 4.12 ± 0.10fg 3.92 ± 0.10gh 2.76 ± 0.10k 0.20 ± 0.02hi 0.25 ± 0.01efgh 0.27 ± 0.03defg 0.28 ± 0.01cdef 0.30 ± 0.04bcde 0.19 ± 0.03i 0.30 ± 0.01bcde 0.32 ± 0.02bcd 0.33 ± 0.02bc 0.36 ± 0.03ab 0.22 ± 0.02ghi 0.30 ± 0.01bcde 0.31 ± 0.01bcde 0.33 ± 0.02bc 0.40 ± 0.06a 0.23 ± 0.03fghi 0.31 ± 0.03bcde 0.32 ± 0.02bcd 0.35 ± 0.01ab 0.41 ± 0.02a 0.41 ± 0.02a 0.775 ± 0.04r 12.70 ± 0.02n 16.79 ± 0.01k 18.75 ± 0.02i 22.67 ± 0.05h 0.932 ± 0.01q 15.37 ± 0.02l 18.13 ± 0.02ij 23.36 ± 0.02g 28.48 ± 0.02c 1.321 ± 0.01p 14.53 ± 0.03m 17.83 ± 0.01j 25.07 ± 0.02f 35.85 ± 0.02a 2.342 ± 0.04° 17.75 ± 0.01j 18.66 ± 0.03i 27.07 ± 0.01e 30.69 ± 0.01b 27.80 ± 0.03d 1.439 ± 0.04t 2.815 ± 0.05r 3.061 ± 0.10q 3.319 ± 0.14p 3.748 ± 0.13n 2.076 ± 0.03s 4.078 ± 0.15m 4.368 ± 0.08l 4.918 ± 0.29g 5.188 ± 0.06f 2.792 ± 0.06r 4.429 ± 0.10k 4.742 ± 0.10j 5.845 ± 0.13e 7.761 ± 0.40c 3.395 ± 0.10° 4.894 ± 0.05i 4.909 ± 0.20h 6.572 ± 0.05d 7.833 ± 0.23b 10.07 ± 0.06a Different letters in the column indicate statistically significant differences (P < 0.05) 13 Author's personal copy S. Ranjbar et al. besides compounds like emulsifiers. Addition of Guar gum reduced retrogradation owing to its tendency to starch digestion. Ravindran et al. [8] found that increasing concentrations of Guar and locust bean gums up to 5% had a significant effect on reducing the hardness of samples, whereas, at higher concentrations, larger hardness values were observed. In a similar attempt, Wang et al. [7] suggested that rice samples had higher hardness at higher emulsifier concentrations. At the same time, increased concentrations of Arabic gum and other hydrocolloids led to lower sample hardness. Liu et al. [9] reported that increasing MC in extruder-shaped rice grains (from 26 to 34%) first increased the hardness and then reduced this parameter. They suggested that high protein content of rice could also increase hardness. By studying addition of Guar gum to extruded products containing maize, potato, rice and wheat flours, Parade et al. [20] found that its lower concentrations had no effect on starch digestion, however its 10% concentration improved starch digestion by 43% in wheat flour. They suggested that increased starch digestion reduced the sample hardness and viscosity. Effect of Arabic and Guar gums on hardness of cooked extruded rice samples According to Table 3, there was a significant difference between the different treatment levels in terms of effect on texture hardness of cooked rice samples (P < 0.05). The lowest hardness belonged to B20, while the highest amount was measured in C. Note that the C treatment showed a significant increase in the hardness compared to 35-G4A1. This increase suggested that the natural rice texture had a more homogeneous denser texture than the extruded rice samples. Liu et al. [9] found that optimized extrusion conditions, determined by response surface method (RMS), included 30% feed MC, 26.6 rpm screw speed, 95 °C extrusion temperature and 4% bran. They also reported that an increase in MC from 26 to 34% increased the hardness initially and then reduced this parameter. According to their results, increasing feed MC from 26 to 34% and reducing screw speed from 30 to 23 rpm led to the increased sample adhesiveness and reduced springiness. Additionally, high screw speed caused to the increased springiness and decreased adhesiveness. The gumminess increased from 44 to 67 g by increasing the extruder temperature (80, 95 and 110 °C). However, within this temperature range, the molecular cohesion increased initially from 0.18 to 0.4 and then decreased from 0.4 to 0.37. Effect of Arabic and Guar gums on texture adhesiveness of cooked extruded rice samples According to Table 3, there was a significant difference between the different treatment levels in terms of effect on texture adhesiveness of cooked rice samples (P < 0.05). The 13 lowest adhesiveness was observed in C, 30-G4A1, 35-G4A1, 20-G4A1, 25-G4A1, 35-G3A2, 30-G3A2, 35-G1A4, 30-G2A3, 25-G3A2, 35-G2A3, 25-G2A3 and 25-G1A4. The highest amount however was recorded for B35 and B30 treatments. The reason for this increase was that by increasing the feed MC from 20 to 30%, there was a higher chance of gelatinization of compounds, and increased amylose removal from starch structure led to higher sample adhesiveness. Note that the dewatering time and other extrusion conditions are effective in the adhesiveness [6]. Effect of Arabic and Guar gums on texture adhesiveness of cooked extruded rice samples There was a significant difference between the different treatment levels in terms of effect on texture cohesiveness of cooked rice samples (P < 0.05) (Table 3). The highest cohesion value was measured in C, 35-G4A1, 30-G4A1, 25-G4A1 and 35-G3A2, and the lowest amount belonged to B35, B30, B20 and B25. According to the results, treatments containing 0.4% Guar gum had a harder more cohesive structure than those with lower Guar content. These results are reasonable regarding to higher BD, lower LE and higher hardness of these treatments. In addition, a significant difference was observed between 20-G1A4 and B25. The lower cohesion index in treatments containing only flour was due to the weak structure and insufficient extruder pressure. Results of Yoo et al. [6] showed that wheat and maize flours caused less hardness in the texture than rice flour. It was also reported that the intermolecular cohesiveness of extruded textures containing maize-wheat mixture was lower than that in samples containing rice flour. Effect of Arabic and Guar gums on texture springiness of cooked extruded rice samples According to Table 3, there was a significant difference between the different treatment levels in terms of effect on texture springiness of samples (P < 0.05). The lowest springiness belonged to B20, B25, B30 and B35, while the highest value was observed in 20-G4A1. According to the results, higher Guar gum concentrations (0.4%) led to the increased springiness of extruded rice samples compared to treatments containing Arabic gum. This can be due to the larger effect of Guar gum on viscosity, and also its effect on the newly developed complex. Wang et al. [6] reported that the addition of emulsifiers increased the gelatinization degree and reduced the adhesiveness of samples, whereas the addition of hydrocolloids increased adhesiveness. They used 0–2% concentrations of glycerol monostearate as an emulsifier and suggested that increasing the emulsifier concentration could increase hardness in rice samples, whereas higher concentrations of Arabic gum and other hydrocolloids reduced Author's personal copy Effect of hydrocolloids on physicochemical, sensory and textural properties of reconstructed… this parameter. It was also reported that employing higher dewatering times led to a decreased hardness, chewiness and viscosity. Adhesiveness, however, increased during the first 5 min and then started to drop. At the same time, the springiness followed a rising trend at the first 7 min and then reduced during next 10 min. Effect of Arabic and Guar gums on texture chewiness of cooked extruded rice samples According to Table 3, there was a significant difference between the different treatment levels in terms of effect on texture chewiness of samples (P < 0.05). The highest value was measured in 30-G4A1 and the lowest value in B20. According to the results, 30-G4A1 had a significantly larger chewiness value for cooked extruded rice samples than 35-G4A1. This increase showed that mono- and diglyceride emulsifier limited the chewiness of structures giving a harder texture. In addition to hardness, cohesiveness was also effective in the chewiness of extruded rice samples. Results indicated that the complex containing 0.4% Guar gum, 0.1 Arabic gum, mono- and di-glyceride emulsifier and starch had a larger effect than increasing feed MC from 30 to 35%, representing that besides the extrusion process conditions, the formulation was also effective in the chewiness. Huang et al. [21] reported that chewiness of rice modified starch gel depended on hydrocolloid type and concentration and also rice starch type. Accordingly, gellan and carrageenan hydrocolloids can improve chewiness. Effect of Arabic and Guar gums on texture gumminess of cooked extruded rice samples According to Table 3, there was a significant difference between the different treatment levels in terms of effect on texture gumminess of samples (P < 0.05). The highest gumminess belonged to 35-G4A1 and the lowest value was measured in B20. Results indicated that increasing the feed MC from 20 to 35% increased the gumminess in only-flour treatments due to the increased water pressure and smaller expansion. Moreover, the treatment C showed a significant increase in the gumminess compared to 35-G4A1. That was because of the fact that natural rice texture had higher BD than extruded rice. Additionally, the cohesiveness of natural rice was higher than 35-G4A1. According to the results, Guar gum at 0.4% concentration and Arabic gum at 0.1% had a larger effect on gumminess than 0.3% guar and 0.2% Arabic gum concentrations. Note that increasing MC from 30 to 35% had no effect on gumminess. Yoo et al. [6] reported that the adhesiveness of the wheat-sweet maize flour was higher than rice flour. It should be noted that no changes were reported in springiness of samples, whereas chewiness and gumminess of the extruded products with rice flour were higher than those in samples containing wheatmaize flour. Sensory analysis of cooked extruded rice samples Table 4 compares the mean values from sensory analysis of cooked extruded rice samples. Sensory color analysis results for cooked extruded rice samples According to Table 4, there was a significant difference between the different treatment levels in terms of effect on color of cooked rice samples (P < 0.05). The highest score was recorded in C, 30-G4A1 and 30-G3A2, while the lowest score belonged to B20. Results indicated that increasing MC from 20 to 35% could delay the Maillard reaction and preserve color in extruded rice on the one hand, whereas, increasing Guar gum from 0.1 and 0.4% improved water absorption, on the other hand, which prevented the color change in the cooked rice. The results were in consistent with those in Martínez et al. [19] who reported that increasing MC from 16 to 22% improved the color quality. They Table 4 Results from mean comparison of sensory analysis of cooked extruded rice samples Treatments Color Flavor Texture Overall acceptability B20 20-G1A4 20-G2A3 20-G3A2 20-G4A1 B25 25-G1A4 25-G2A3 25-G3A2 25-G4A1 B30 30-G1A4 30-G2A3 30-G3A2 30-G4A1 B35 35-G1A4 35-G2A3 35-G3A2 35-G4A1 C 1 ± 0.2k 3 ± 0.3h 4.4 ± 0.2g 5.2 ± 0.3efg 4.6 ± 0.3fg 2.4 ± 0.4j 4.4 ± 0.4g 5.8 ± 0.3e 4.6 ± 0.3fg 6 ± 0.2de 2.5 ± 0.4ij 6.8 ± 0.5cd 7 ± 0.3c 8 ± 0.3b 8 ± 0.2b 2.5 ± 0.3ij 6 ± 0.3de 6.4 ± 0.4d 6.8 ± 0.3cd 6.8 ± 0.3cd 9 ± 0.2a 3 ± 0.3i 5 ± 0.5gh 4.8 ± 0.3h 6.8 ± 0.3ef 6.6 ± 0.5f 2.1 ± 0.5j 5 ± 0.4gh 6.8 ± 0.3ef 6.8 ± 0.2ef 7 ± 0.4def 4.8 ± 0.3h 7.3 ± 0.3d 8.5 ± 0.4b 8.5 ± 0.3b 8 ± 0.4c 4.8 ± 0.2h 7 ± 0.3def 8 ± 0.38c 8 ± 0.38c 7.3 ± 0.38d 9 ± 0.38a 2 ± 0.6j 6 ± 0.4gh 7.3 ± 0.4f 5.8 ± 0.4h 7.3 ± 0.4f 4 ± 0.5i 7.4 ± 0.3ef 7.6 ± 0.3d 7.4 ± 0.3de 7.6 ± 0.4d 5.8 ± 0.6h 7.8 ± 0.5c 7.8 ± 0.6c 7.8 ± 0.8c 8.1 ± 0.4b 4 ± 0.2i 7.6 ± 0.4d 7.6 ± 0.4cd 7.8 ± 0.3c 8.1 ± 0.3b 9 ± 0.2a 1.7 ± 0.5l 5.5 ± 0.5h 4.5 ± 0.5i 6.7 ± 0.4e 6 ± 0.5g 3.2 ± 0.5k 5.3 ± 0.5h 6.2 ± 0.4f 6.4 ± 0.6f 6.8 ± 0.6e 4.3 ± 0.3i 7.5 ± 0.7c 7.5 ± 0.7c 8.4 ± 0.6b 8.4 ± 0.5b 3.7 ± 0.5j 7.2 ± 0.6d 6.8 ± 0.5e 7.3 ± 0.5d 7.6 ± 0.7c 9 ± 0.5a Different letters in the column indicate statistically significant differences (P < 0.05) 13 Author's personal copy S. Ranjbar et al. were also in agreement with the results of Kohajdora [22], where addition of gums improved cake core color. Sensory texture analysis results for cooked extruded rice samples According Table 4, there was a significant difference between the different treatment levels in terms of effect on texture of cooked rice samples (P < 0.05). The highest score was recorded in C, 30-G4A1 and 35-G4A1, and the lowest score belonged to B20. Results indicate that addition of 0.4% Guar gum and 0.1% Arabic gum and increasing MC from 30 to 35% improved the texture of cooked samples. Note that the texture of the drained and cooked 30-G4A1 and 35-G4A1 treatments was better than other treatments due to higher BD, higher hardness and lower LE. Ravindran et al. [8] suggested that increasing guar gum to 20% had no significant effect on the sensory texture analysis of extruded flour mixture of rice and pea. Sensory flavor analysis results for cooked extruded rice samples According to the results in Table 4, there was a significant difference between the different treatment levels in terms of effect on flavor of cooked rice samples (P < 0.05) as the highest score was recorded in C, 30-G3A2 and 30-G2A3, and the lowest score belonged to B25. The findings showed that addition of Arabic and Guar gums can improve flavor of extruded samples. However, at 30 and 35% MC levels, the addition of 0.4% Guar gum led to a weaker flavor score than 0.3 and 0.2% cases. This can be due to the gumminess feeling in mouth. Rosell et al. [23] showed that gum addition improved flavor in cooked samples. Ravindran et al. [8] suggested that increasing Guar gum to 20% had no significant effect on improved flavor of extruded flour mixture of rice and pea. Sensory overall acceptability analysis results for cooked extruded rice samples According to Table 4, there was a significant difference between the different treatment levels in terms of effect on overall acceptability of cooked rice samples (P < 0.05). The highest score was recorded in C, 30-G4A1 and 30-G3A2, while the lowest score belonged to B20. Mean scores of overall acceptability showed that, at more than 20% MC levels, treatments containing Arabic and Guar gums were more acceptable to the panelists. Ravindran et al. [8] suggested that increasing Guar gum to 15% had no significant effect on overall acceptability of the extruded flour mixture of rice and pea. 13 Conclusion The textural, physicochemical and sensory properties of extruded rice grain were influenced by the hydrocolloids and the moisture content of the feeding material. 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