Journal of Cereal Science 51 (2010) 284–291 Contents lists available at ScienceDirect Journal of Cereal Science journal homepage: www.elsevier.com/locate/jcs Effect of hydrothermal treatment of rice flour on various rice noodles quality Supawadee Cham, Prisana Suwannaporn* Department of Food Science and Technology, Kasetsart University, 50 Paholyothin Rd., Jatuchak, Bangkok 10900, Thailand a r t i c l e i n f o a b s t r a c t Article history: Received 22 September 2009 Received in revised form 7 January 2010 Accepted 8 January 2010 The rice noodle industry in Thailand is facing problems regarding rice flour quality. This research aims to study the effects of hydrothermally modified rice flour on improving rice noodle quality. High-amylose rice flour (Chai Nat 1 variety) was modified using heat–moisture treatment (HMT) and annealing (ANN). Response surface methodology (RSM) with face-centered central composite design (FCCD) was applied to optimize the hydrothermal treatment condition. The effects of treatment conditions – moisture content; heating temperature and heating time on pasting; rheology; and textural properties of rice flour gel – were observed. A contour plot showed that all responses using HMT increased when moisture content and heating temperature increased. But heating time had no significant effect on response variables. ANN showed a lower response than HMT for all parameters. The optimum modified conditions were then matched with those of commercial flour for fresh, semi-dry and dry rice noodles; this showed no significant differences in texture or cooking quality (P0.05). The storage modulus (G0 ) after cooling of HMT (19,100 Pa) was much higher than that of ANN (5490 Pa). The differences in rheological properties of both treatments supported their proper uses to achieve various rice noodle qualities. Ó 2010 Elsevier Ltd. All rights reserved. Keywords: Hydrothermal treatment Rheological properties Rice noodle Optimization 1. Introduction The rice noodle industry in Thailand is facing problems with overuse of additives to enhance eating quality (Thailand Research Fund, 2009). Native rice flour has poor resistance to shear force, and low elastic gel-forming ability. Most native starches have a marked tendency to lose their viscosity and thickening power during cooking. Rice gel quality is greatly dependent on grain variety, amylose content and aging period (Pitiphunpong and Suwannaporn, 2009; Takahashi et al., 2005). Rice cultivars with high amylose content, low gelatinization temperature and high gel consistency are suitable for rice noodle making (Yoenyongbuddhagal and Noomhorm, 2002). Rice of intermediate amylose content yields a softer product with higher cooking loss, while flour from lowamylose rice has no potential for making usable rice noodles (Jayakody and Hoover, 2008; Jobling, 2004). In commercial practice, chemically modified starch (such as by cross-linking or acetylation) Abbreviations: ANN, annealing; cP, centipoise; DCp, heat capacity; FCCD, face centered central composite design; G0 , storage modulus; G00 , loss modulus; DH, enthalpy; HMT, heat–moisture treatment; Mc, moisture content; Pa, Pascal; R2, coefficient of determination; RSM, response surface methodology; Tc, conclusion temperature; Tg, glass transition temperature; Tgel, gelatinization temperature; To, onset temperature; Tp, peak temperature. * Corresponding author. Tel.: þ66 2 562 5038; fax: þ66 2 562 5021. E-mail address: [email protected] (P. Suwannaporn). 0733-5210/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jcs.2010.01.002 together with various hydrocolloids are widely used in the rice noodle industry. There is an increasing interest in more natural treatments of rice flour. Two hydrothermal treatments which are commonly used in modifying the physicochemical properties of starch are annealing (ANN) and heat–moisture treatment (HMT). In general, treatment of starch with excess water (>60% w/w) is referred to as ‘‘annealing,’’ whereas ‘‘heat–moisture treatment’’ is applied to starch with low moisture content (<35% w/w). Both physical modifications should apply at temperatures above the glass transition temperature (Tg) but below the gelatinization temperature (Tgel) (Jacobs and Delcour, 1998; Stute, 1992; Tester and Debon, 2000). Hydrothermal treatment is known as a process which increases starch crystallinity and its perfection (Jacobasch et al., 2006; Tester and Morrison, 1990), granule rigidity (Jacobs et al., 1995), polymer chain realignment, partial crystallite melting (Stute, 1992), and starch chain associations (amylose–amylopectin and or amylopectin–amylopectin) (Ozcan and Jackson, 2003). These hydrothermal treatments could suppress granule swelling, retard gelatinization and increase starch paste stability. Starch gel structure is altered and gel hardness increased (Chung et al., 2000; Jacobasch et al., 2006; Lii et al., 1996; Lim et al., 2001; Liu et al., 2000). Yoenyongbuddhagal and Noomhorm (2002) reported that HMT of rice flour could enhance the cooking and textural qualities of rice noodles. Hormdok and Noomhorm (2007) applied HMT and ANN of rice starch for noodle making, and revealed the possibility of utilizing these S. Cham, P. Suwannaporn / Journal of Cereal Science 51 (2010) 284–291 starches in composites with poor quality rice flour to produce noodles of acceptable quality. Different types of rice noodles exhibit different eating qualities, and hence require different treatment conditions. In this study, response surface methodology (RSM) was designed to optimize the hydrothermal treatment conditions for fresh, semi-dried and dried rice noodles in order to improve their qualities and reduce the use of additives. Pasting, rheological and textural properties of rice flour gel were studied and compared to those of commercial rice noodle flours in order to match different rice noodle qualities. 2. Experimental 2.1. Raw materials High amylose rice flour was used in this study on account of its good gel forming property that is suitable for rice noodle making. Moreover, it exhibited lower breakdown value, which reflected higher stability of the starch granule and less soluble starch (Suwannaporn et al., 2007). High amylose rice (Chai Nat 1 cultivar) was obtained as paddy rice from the Thailand Rice Research Institute. The paddy rice was dehusked using a McGill sample sheller (Rapsco, Brookshire, TX), and the rice bran removed using a McGill No. 2 mill. Samples were milled to a constant degree of milling (DOM¼90). The DOM was measured using a Satake Milling Meter MM-1B (Satake Engineering Co., Ltd., Tokyo, Japan). Polished rice grains were steeped in water for 4 h and then wet-milled using a double-disk stone mill (locally made in Thailand). Rice slurry was centrifuged using a basket centrifuge type H-130 G (Kokusan Ensinki Co., Ltd., Tokyo, Japan). The rice cake was then dried in a tray dryer at 455 C until the moisture content reached 10–12%. Rice flour of particle size 100 mesh was obtained using a hammer mill (Ultra-Centrifugal Mill, Type ZM 1; Retsch GmbH, Haan, Germany). Samples were packed in polyethylene bags, sealed, and kept at 4 C (Gullapanayutt, 2004). 2.2. Methods 2.2.1. Calorimetric profile of rice flour A differential scanning calorimeter (DSC) (DSC StarÒ System; Mettler Toledo AG, Greifensee, Switzerland) was used for calorimetric measurements. The instrument was calibrated with indium and zinc standards before taking sample measurements. All measurements were conducted under a nitrogen atmosphere. For glass transition temperature (Tg) measurement, starch samples (10–14% mc) were heated from 25 to 95 C at a rate of increase of 1 C/min. The samples were immediately cooled with liquid N2 to 5 C at a rate of 20 C/min, and then reheated at an increase of 1 C/min. The Tg was determined as the peak point on the first derivative curve of the heat-capacity thermogram. The temperature at the midpoint of the change in slope of the DSC heatcapacity thermogram was taken as the glass transition temperature (Tg) (Chung and Lim, 2004; Zhong and Sun, 2005). For calorimetric profile measurement, rice flour slurry (70% mc) was equilibrated for 1 h at room temperature. The samples were then scanned in a temperature range of 25–95 C at a heating rate of 5 C/min, using an empty pan as a reference. Onset temperature (To), peak temperature (Tp), conclusion temperature (Tc) and enthalpy of gelatinization (DH) were determined (Adebowale and Lawal, 2003). Each experiment was done in triplicate. 2.2.2. Experimental design 2.2.2.1. Heat–moisture treatment. The face-centered central composite design (FCCD) – with three levels of treatment temperature, heating time and moisture content – was assigned. 285 The FCCD was applied to estimate the relationship between variables on pasting, rheological and textural properties of rice flour gel. The FCCD consisted of eight factorial points, six axial points and six center points, leading to 20 sets of experiments. The experiments were run in random order to minimize the effects of unexpected variability in the observed responses due to extraneous factors. In HMT, the moisture content of rice flour was adjusted from 18% to 27% (X3; 1 to þ1 level). The mixture was incubated overnight in sealed aluminum foil bags, and then heated in a tray dryer at temperatures of 90–120 C (X1; 1 to þ1 level) for 1–3 h (X2;1 to þ1 level). Variables, levels and code values are presented in Table 1. 2.2.2.2. Annealing. The FCCD was selected using three levels of heating temperature and time. It consisted of six factorial points, two axial points and five center points, leading to 13 sets of experiments. The variables, levels and code values applied for the annealing process in this study are presented in Table 1. Rice flour was annealed in excess water at a temperature slightly above the glass transition temperature and below the gelatinization temperature: 60–70 C (X1; 1 to þ1 level) for 12–36 h (X2; 1 to þ1 level). After that, samples were centrifuged to remove excess water, and then dried using a tray dryer at 455 C until its moisture content reached 10–12%. According to the statistical method, a second-order polynomial function Eq. (1) was assumed to approximate the response under consideration (Khuri and Cornell, 1987). Where Y was the response variable, B0, Bi, Bii, Bij were the regression coefficients of variables for intercept, linear, quadratic and interaction terms, respectively. Xi and Xj were independent variables. The data reported in the table were the average value of triplicate observations. Contour Table 1 Variables, levels and code values employed in a central composite design for hydrothermal treatment. Experiment HMT Temperature ( C) (X1) Heating time (h) (X2) Moisture content (%) (X3) Code value Real value Code value Real value Code value Real value 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15–20 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 90 120 90 120 90 120 90 120 90 120 105 105 105 105 105 1 1 1 1 1 1 1 1 0 0 1 1 0 0 0 1 1 3 3 1 1 3 3 2 2 1 3 2 2 2 1 1 1 1 1 1 1 1 0 0 0 0 1 1 0 18 18 18 18 27 27 27 27 22.5 22.5 22.5 22.5 18 27 22.5 Experiment ANN 1 2 3 4 5 6 7 8 9–13 Temperature ( C): X1 Tempering time (h): X2 Code value Real value Code value Real value 1 1 1 1 1 1 0 0 0 60 70 60 70 60 70 65 65 65 1 1 1 1 0 0 1 1 0 12 12 36 36 24 24 12 36 24 286 S. Cham, P. Suwannaporn / Journal of Cereal Science 51 (2010) 284–291 plots were obtained by using Statistica (version 8) (StatSoft, Inc., USA). Predicted values of rice noodle qualities were obtained using Eq. (1). Y ¼ b0 þ 3 X bi Xi þ i¼1 3 X i¼1 bii Xi2 þ 2 3 X X Bij Xi Xj þ e (1) i ¼ 1 j ¼ iþ1 The relationships between the responses (pasting, rheological and textural properties) were judged by correlation coefficients of determination (R2). The significance or P-value was decided at a probability level of 0.05. The calculation of the optimum condition was performed using a multiple response optimization method. Condition variables were optimized compared to commercial rice noodle flour (National Starch & Chemical Co., Ltd., Bangkok, Thailand). 2.2.3. Pasting properties Pasting properties of modified rice flour were determined by a Rapid Visco Analyzer (model RVA3D; Newport Scientific, Warriewood, NSW, Australia) according to AACC standard method No. 61-02.01 (AACC, 2000). Rice flour samples were run in duplicate. First, 25 ml of distilled water was added directly to a metal RVA canister. Then 3.000.01 g of rice flour was weighed, added to the water, and immediately measured by RVA. These measurements were made using the standard Newport Scientific rice profile. An initial 10 s of high-speed (960 rotations min1) stirring was used to disperse the sample prior to the beginning of the measuring phase at 160 rotations min1. Temperature was held at 50 C for 1 min; then raised to 95 C in 3.5 min; held for 2.5 min; cooled to 50 C in 3.5 min; and held for 5 min. The RVA instrument provided the following parameters: peak viscosity (PV), the highest viscosity during heating; trough (T), the lowest viscosity; breakdown (BD), PV minus T; final viscosity (FV), the viscosity at the completion of the cycle; and setback (SB), FV minus PV. All values were reported in cP. Water absorption ¼ Cooking loss ¼ profile analysis was done using a TA.XT2 texture analyzer (Stable Micro Systems, Ltd., Godalming, Surrey, UK) using a stainless steel punch probe (P/6, 6.0 mm diameter). Distance was set at 10 mm and pretest speed at 1.0 mm/s. Hardness, adhesiveness and springiness were determined. 2.2.6. Preparation of rice noodles Rice noodles were prepared using optimized hydrothermal treatment conditions obtained in Sections 2.2.2.1 and 2.2.2.2. Control samples were prepared from commercial rice noodle premix, flour codes SP1, SP2 and SP3 (National Starch & Chemical Co., Ltd., Bangkok, Thailand), for fresh, semi-dried and dried noodles, respectively. Rice flour was mixed with water to obtain a concentration of 40% (w/w). The rice flour slurry was equilibrated for 1 h; then 50 ml of the rice slurry was spread evenly on a stainless steel plate, steamed for 5 min to complete gelatinization, and cooled down to room temperature. Fresh rice noodles were prepared by scraping the noodle sheet into thicknesses of approximately 1.0 mm, and then cutting into strips of 10 mm width. Semi-dry noodles (or ‘‘pad Thai’’ style noodles) were prepared from retrograded fresh noodle sheets by hot-air drying at 150 C for 10 min, and then cutting into small strips of 3 mm width. Dried rice noodles were prepared by prolonged drying of noodle strips until the moisture content reached 10–12%. 2.2.7. Determination of rice noodle qualities 2.2.7.1. Cooking qualities. Cooking qualities were determined according to AACC standard methods No. 66-50.01 and No. 5450.01 (AACC, 1999a,b): 5 g of dried rice noodle was boiled in 150 ml distilled water for 4 min, drained for 5 min, and then weighed. Cooking water was evaporated and dried at 105 C to a constant weight. Cooking loss was expressed as a percentage of dry matter lost during cooking to dry sample weight. The water absorption was the percentage of weight increase in cooked rice noodles compared to dried samples. ðWeight of cooked noodle Weight of dried noodleÞ 100 Weight of dried noodle ðWeight of dry matterÞ 100 Weight of dried noodle 2.2.4. Rheological properties Rice flour suspension was measured using a dynamic rheometer (Physica MCR 300 Series; Anton Paar, Graz, Austria). Rice flour suspension (20% w/w) was loaded on the parallel plate of the rheometer, and a thin layer of low-density silicon oil was gently applied to the edge of the exposed sample to prevent moisture loss. Rheological properties of rice flour paste were measured using a dynamic rheometer equipped with a parallel plate system (50 mm diameter). The gap size was set at 1000 mm. The strain and frequency were set at 0.5% and 1 Hz, respectively. Samples were heated from 25 to 95 C and cooled down at a rate of 2 C/min. Samples were run in triplicate. Data related to dynamic viscoelastic properties during gelatinization were used to obtain the storage modulus (G0 ). 2.2.5. Textural properties Rice flour gel was prepared by suspending 20% (w/v) of rice flour in distilled water and gelatinizing in a boiling water bath for 30 min. Rice gel was then placed in a cylinder tube, cooled and equilibrated at room temperature for 4 h. The rice gel obtained had a dimension of 20.0 mm in diameter and 20.0 mm height. Texture 2.2.7.2. Textural properties. Dry and semi-dry rice noodles were soaked in water for 10 min, boiled in water for 3 min, and immediately cooled in tap water. Cooked noodles were drained on a stainless steel screen and measured immediately. Fresh noodles were measured immediately after cooling down to room temperature. Tensile strength of the noodles was measured following the method of Stable Micro Systems and Bhattacharya et al. (1999). The noodle strand was wound around the parallel rollers of a spaghetti/ noodle tensile grip analyzer (TA.XT; Stable Micro Systems, UK) to anchor the sample ends and reduce any slippage. The maximum force (g) referred to the resistance to breakdown of the noodle. The distance (mm) at which the strand started to break indicated extensibility. A cooked noodle strand of 1 mm thickness was compressed by a cylinder probe (35 mm diameter) until the deformation reached 75% at a speed of 1 mm/s. The pause between the first and second compressions was 0.5 s. From the force/time curve of the texture profile, textural parameters including hardness and adhesiveness were obtained. Ten measurements were made for each sample. S. Cham, P. Suwannaporn / Journal of Cereal Science 51 (2010) 284–291 287 storage modulus (G0 ) were selected for a further predictive model. These responses were mainly affected by temperature, moisture content and time (P0.05). Similarly, the work of Hoover and Vasanthan (1994) found that a gradual increase in moisture content and treatment temperature could allow polymer chain motion, which consequently had a greater effect on enhancing setback, gel hardness and storage modulus of flour. Therefore, the contour plots for HMT were generated as a function of temperature and moisture content, with time held as a constant factor. Both ANN and HMT apparently increased setback, and storage modulus of starch gel when temperature, moisture content and time increased (Fig. 1). The increase in final viscosity and setback after modification supported the fact that the modification process tended to increase the region of crystallinity, as a result of the reorientation of starch granules and their tendency to re-associate to form a precipitate or gel (Adebowale and Lawal, 2003; BeMiller and Whistler, 1996). The highest gel hardness (160 g) was obtained from ANN of rice flour at 65–70 C for 24 h. Even higher gel hardness (280 g) was obtained when HMT rice flour was exposed at a temperature between 105 and 115 C and a moisture content around 18–22.5%. Temperature and moisture content were the dominant factors affecting starch granules. Liu et al. (2000) reported that the higher the temperature and moisture content, the more perfect the crystalline starch granules. These phenomena suggested that starch granule swelling was restricted by hydrothermal treatment. Each treatment caused a different alteration of the granular structure. During HMT, the increase in rheological properties was attributed to the increase in cross-linking between starch chains. This allowed the formation of more junction zones in the continuous phase of the gel, resulting in an increase of gel hardness, final viscosity, setback, and storage modulus (Eerlingen et al., 1996; Hoover and Manuel, 1996; Shih et al., 2007; Takahashi et al., 2005). In the case of ANN, temperature and time were the dominant factors affecting gel hardness. The increase in crystalline perfection of granules by the ANN technique affected starch gel properties. Crystalline perfection resulted from an increase in mobility of the amorphous part which facilitated the ordering of 3. Results and discussion 3.1. Glass transition temperature of rice flour According to the data obtained from the DSC, the glass transition and gelatinization temperatures of rice flour were 58 C and 75 C respectively. At low moisture content (14%), water was absorbed and bound with starch in amorphous phase. Tg was observed as the temperature at which the molecular mobility of the amorphous compound became apparent (Blanshard and Lillford, 1993; Huang et al., 1994; Roos, 1995a,b). It was revealed that the heat capacity (DCp) of rice flour was distinctly different between the glassy and gelatinized states. The glass transition of rice flour produced very small DCp (0.03 J/g), whereas that of the corresponding gelatinized starch exhibited a substantially higher value (15.07 J/g). The gelatinization endotherm is affected by the crystalline and amorphous transition. On the other hand, the glass transition endotherm is affected only the amorphous region which precedes the melting of crystallites (Roos, 1995a,b). The glass transition and gelatinization temperatures of rice flour obtained in this study were applied to determine the ANN and HMT process conditions applied in our experimental design. Both physical modifications should apply at temperatures above the glass transition temperature (Tg) but below the gelatinization temperature (Tgel) (Jacobs and Delcour, 1998; Stute, 1992; Tester and Debon, 2000). 3.2. Effect of hydrothermal treatment on rice flour gel The lack-of-fit test measuring the fitness of the model showed no significant lack-of-fit, together with a high R2 (Table 2). This indicated that the model was sufficiently accurate for predicting the responses of: final viscosity, setback, gel hardness, and storage modulus of both HMT and ANN. The equation coefficients of ANN and HMT conditions that affect responses are shown in Table 2, together with their R2. The responses studied were better explained by a second-order model. Responses with high fitting (R20.85); final viscosity, setback, gel hardness and Table 2 Regression equations and coefficients of determination of the effects of hydrothermal treatment conditions on rice flour gel qualities. Hydrothermal treatment condition Coefficient ANN Constant Linear Quadratic Interaction Response b0 b1 b2 b11 b22 b12 Lack of fit HMT 2 Coefficients of determination R Constant Linear b0 b1 b2 b3 b11 b22 b33 b12 b13 b23 Quadratic Interaction Lack of fit Coefficients of determination *Significantly different at a 95% confidence level. ns Not significantly different at a 95% confidence level. R2 Final viscosity (cp) Setback (cp) 16,862.6* 492.7* 22.4* 3.0* 0.7* 0.01ns 10,565.3* 280.0* 4.9* 1.3* 0.5* 0.2ns Gel hardness (g) 1709.32* 54.96* 6.83* 0.47* 0.03* 0.110ns Storage modulus (Pa) 19,692.1* 480.0* 93.5* 3.1* 0.3* 1.2ns 0.385ns 0.269ns 0.955ns 0.249ns 0.913 0.901 0.856 0.871 8605.02* 55.71* 62.91ns 317.71* 0.21* 17.36ns 7.18* 0.54ns 0.88ns 3.30ns 2096.75* 78.63* 131.3ns 545.51* 0.52* 60.27ns 9.54* 2.10ns 1.69ns 9.13ns 3531.84* 72.09* 80.51ns 16.57* 0.33* 18.80ns 0.59* 0.40ns 0.09ns 0.88ns 63,010.2* 170.6* 771.8ns 3555.1* 2.4* 654.5ns 34.8* 20.8ns 14.3ns 58.3ns 0.494ns 0.605ns 0.079ns 0.317ns 0.927 0.899 0.849 0.826 288 S. Cham, P. Suwannaporn / Journal of Cereal Science 51 (2010) 284–291 Fig. 1. Contour plot of hydrothermal treatment conditions on physicochemical properties of rice flour and its overlaid of (a) ANN fresh noodle, (b) HMT semi dried rice noodle, (c) HMT dried rice noodle. S. Cham, P. Suwannaporn / Journal of Cereal Science 51 (2010) 284–291 289 Table 3 Comparison of the observed and predicted values of the response variables in various rice noodle qualities using a t-test. Rice noodle Response variables Commercial rice flour Hydrothermally treated rice flour Fresh noodle Final viscosity (cp) Setback (cp) Hardness (g) Storage modulus (Pa) 2100–2600 1700–2200 130–160 12,000–14,500 2565.30 2145.80 153.93 14,204.00 2550.77105.11 2048.53171.34 150.19000.69 14,000.00120.24 Semi-dried noodle Final viscosity (cp) Setback (cp) Hardness (g) Storage modulus (Pa) 3500–4000 1400–1800 260–290 10,000–12,000 3702.76 1516.35 274.32 11,883.78 3650.14112.24 1418.54065.34 270.85019.15 11,500.15 184.05 Dried noodle Final viscosity (cp) Setback (cp) Hardness (g) Storage modulus (Pa) 4000–4500 1900–2500 260–290 13,000–15,000 4317.91 2067.28 280.73 13,644.40 4255.12000.55 2250.48011.34 275.15010.77 14,350.00124.19 Predicted valuens Observed valuens ns Not significantly different at a 95% confidence level in the same row. double helices and probably greater ordering primarily in the amorphous regions (Lin et al., 2008). Rice gel became harder because of the more ordered rearrangement of starch molecules during the ANN process. Moreover, hydrothermal treatment allowed the leached starch molecules to form a more continuous gel (Biliaderis, 1998; Chung et al., 2000; Lii et al., 1996; Tester et al., 1998). proportional to the granule rigidity and inversely proportional to the swelling ratio. Hydrothermal treatments are known to suppress granule swelling and retard gelatinization (Takahashi et al., 2005). At a constant shear-rate applied after peak, G0 of native rice flour dropped at a higher rate than that of hydrothermally treated flour due to shear-thinning phenomena. This indicates more rigid and thermally stable starch granules in hydrothermally treated flour. 3.3. Optimization of hydrothermal treatment conditions 3.4.2. During cooling On the contrary, G0 during cooling – which indicated gelling behavior at a lower temperature – increased to a greater extent and more rapidly in hydrothermally treated flour (Fig. 2). This demonstrated a strong interaction during cooling which caused aggregation between starch granules, and perfection formed due to starch chain associations during gel storage (Rao and Tattiyakul, 1999). G0 at this point was an index for rice noodle quality similar to the set back value obtained from a Rapid visco-analyzer (Suwannaporn et al., 2007). It was used to verify that an elastic and extensible sheet of rice flour gel could be obtained. At 25 C, G0 of HMT rice flour gel (19,100 Pa) was much higher than that of ANN (5490 Pa). ANN was the modification of flour slurry in excess water (>60%) at temperatures below gelatinization (<70 C); as a consequence, starch chains were free to move resulting in the mobility within the amorphous region. The ANN process only improves the crystallinity The optimization of HMT and ANN treatment conditions for various rice noodles was determined using their texture and cooking quality. Conditions that obtained pasting, textural and rheological properties comparable to commercial rice noodle flour were selected (Fig. 1). Data points within the optimized area of each noodle product were selected and run in triplicate for validation purposes. Results in Table 3 show that there was no significant difference between predicted value and observed value (P0.05). Rice flour gel prepared by hydrothermal modification gave similar qualities to those of commercial rice flour gel. 3.4. Rheological properties of hydrothermally treated rice flour The rheogram in Fig. 2 shows the temperature-dependent storage modulus (G0 ) of hydrothermally treated and native rice flour during heating from 25 to 95 C and cooling to 25 C. Storage modulus (G0 ) and loss modulus (G00 ) were determined in dynamic measurements related to the elastic behavior of the dual nature of the polymer melt, which was partly elastic solid and partly viscous fluid. Measurements of G0 and G00 provide information on polymer structure and might be related to molecular weight distribution or cross-linking (Rao and Tattiyakul, 1999). 3.4.1. During heating G0 of native and hydrothermally treated rice flour had similar patterns (Fig. 2). G0 started to increase dramatically at temperatures around 65 C and reached its peak at 85 C, indicating that both starch granules could swell and begin to gelatinize at the same temperature. Hsu et al. (2000) reported that the initial increase in G0 was caused by starch granules swelling progressively and becoming closely packed in the suspension. The increase in G0 was a result of structural changes, an irreversible swelling of starch granules, melting of crystallites, or a leaching of components of starch granules (Rao and Tattiyakul, 1999). However, G0 of native rice flour was higher than that of hydrothermally treated flour because hydrothermal treatment could retard the swelling power of starch granules. Lii et al. (1996) found that the rigidity of the gel was Fig. 2. Rheogram to show storage modulus (G0 ) of hydrothermal treatment rice flour during heating and cooling. 290 S. Cham, P. Suwannaporn / Journal of Cereal Science 51 (2010) 284–291 Table 4 Cooking and textural qualities of various rice noodles. Noodle sample Tensile strength (g) Hardness (g) Adhesiveness (g.s) Cooking yield (%) Cooking loss (%) Fresh noodle ANN 21.17a SP1Ò 25.60a 134.35a 135.98a 3.40a 2.16b 98.78a 99.81a 7.85a 6.50a Semi-dry noodle HMT 39.20b SP2Ò 43.82b 200.11b 205.85b 2.34b 1.09c 260.65b 265.70b 10.25c 9.85c Dry noodle HMT 51.19c SP3Ò 54.31c 215.03c 216.90c 3.29a 1.94b 420.50c 435.65c 8.85b 8.45b a-c Means in the same column followed by the same lowercase superscript letter are not different at P > 0.05. SP1Ò, SP2Ò and SP3Ò are commercial rice flours (National Starch & Chemical Co., Ltd.). of existing helices, thereby ‘‘perfecting’’ the starch crystallites without formation of additional helices. HMT was the modification of flour above the gelatinization temperature (100–120 C), and at restricted moisture content (<30%). On the other hand, HMT resulted in a partial melting of the crystallites, followed by a realignment of the polymer chains (Eerlingen et al., 1996). It has been reported that the number of double helices was increased during HMT. Moreover, the formation of additional helices was also promoted (Stute, 1992). Therefore, HMT improved the crystallinity of starch granules to a greater extent than ANN. The differences in rheological properties of such treatments support better uses of hydrothermal treatment for different rice noodle qualities. Strong and elastic gel forming, with low shear thinning, were required characteristics for rice noodle flour. However a softer texture was required for fresh noodles, whereas a stronger and more elastic gel was suitable for semi-dry and dry noodles. 3.5. Cooking and textural quality of rice noodles Cooking and textural qualities of rice noodles made by either hydrothermal modification or from commercial rice noodle flour were not significantly different (P0.05) (Table 4). Tensile testing, which assessed the breaking strength of noodles, correlated well with noodle quality (Bhattacharya et al., 1999). Hardness of rice flour gel has been reported to be a dominant factor in rice noodle quality (Bhattacharya et al., 1999; Ozcan and Jackson, 2003; Surojanametakul et al., 2002; Yoenyongbuddhagal and Noomhorm, 2002; Yunt et al., 1996). Semi-dried and dried noodles had higher tensile strength and gel hardness than fresh noodles because of the more retrograded gel induced after the drying process. These types of rice noodles were difficult to break down, and were more stretchable after cooking. A more pronounced effect on tensile strength was obtained by HMT-treated rice flour. On the contrary, fresh rice noodles required a softer texture with comparatively low tensile strength after cooking, which could be obtained by ANN. Moreover, all rice noodles made from hydrothermally treated rice flour showed lower adhesiveness, which indicated less surface stickiness of cooked noodles. It gave a ‘‘clean and smooth’’ texture which was a required quality in rice noodles. Since hydrothermal treatment created more intact starch granules with a more orderly crystalline starch matrix, this resulted in a relatively low degree of amylose leaching (Tester and Debon, 2000). 4. Conclusion Hydrothermal treatments using HMT and ANN could be offered as an alternative for the rice noodle industry. Rice noodles prepared by these methods resulted in similar eating quality to noodles made from commercial rice flours, but with a safe and completely natural product concept. Fresh rice noodles require a softer texture, which could best be obtained by ANN. Semi-dried and dried noodles need higher tensile strength and gel hardness, for which HMT was more appropriate. The low amylose leaching in hydrothermally treated rice flour gave a ‘‘clean and smooth’’ noodle surface, which is instrumental in the quality of rice noodles. Acknowledgements This research was funded by the Kasetsart University Research and Development Institute (year 2007). Partial student funding was obtained from the Graduate School, Kasetsart University. The authors would like to thank the Thailand Rice Research Institute, the Department of Agriculture, and the National Starch & Chemical Co., Ltd. (Thailand) for their information and support. References Adebowale, K.O., Lawal, O.S., 2003. Microstructure, physicochemical properties and retrogradation behaviour of Mucuna bean (Mucuna pruriens) starch on heat moisture treatments. Food Hydrocolloids 17, 265–272. AACC, 1999a. Method 66-50.01, Pasta and noodle cooking quality–firmness. In: AACC International Approved Methods of Analysis, eleventh ed. AACC International, St. Paul, MN, U.S.A. AACC, 1999b. Method 54-50.01, Determination of the water absorption capacity of flours and of physical properties of wheat flour doughs, using the consistograph. In: AACC International Approved Methods of Analysis, eleventh ed. AACC International, St. Paul, MN, U.S.A. AACC, 2000. Method 61-02.01, Determination of the Pasting Properties of Rice with the Rapid Visco Analyser. In: AACC International Approved Methods of Analysis, eleventh ed. AACC internation, St. Paul, MN, U.S.A. BeMiller, J.N., Whistler, R.L., 1996. Carbohydrates. In: Fennema, O.R. (Ed.), Food Chemistry, third ed. Marcel Dekker, New York, pp. 157–224. Bhattacharya, M., Zee, S.Y., Corke, H., 1999. Physicochemical properties related to quality of rice noodles. Cereal Chemistry 76, 861–867. Biliaderis, C.G., 1998. Structures and phase transitions of starch polymers. In: Walter, R.H. (Ed.), Polysaccharide Association Structures in Food. Marcel Dekker, New York, pp. 57–68. Blanshard, J.M.V., Lillford, P.J., 1993. The Glassy State in Foods. Nottingham University Press, Loughborough UK. Chung, H.-J., Lim, S.-T., 2004. Physical aging of glassy normal and waxy rice starches: thermal and mechanical characterization. Carbohydrate Polymers 57, 15–21. Chung, K.M., Moon, T.W., Chun, L.K., 2000. Influence of annealing on gel properties of mung bean starch. Cereal Chemistry 77, 567–571. Eerlingen, R.C., Jacobs, H., Van Win, H., Delcour, J.A., 1996. Effect of hydrothermal treatment on the gelatinization properties of potato starch as measured by differential scanning calorimetry. Journal of Thermal Analysis and Calorimetry 47, 1229–1246. Gullapanayutt, O., 2004. Improvement of ready-to-eat rice noodles in pouch by pasteurization. M.S. Thesis [in Thai], Kasetsart University, Bangkok. Hoover, R., Manuel, H., 1996. The effect of heat–moisture treatment on the structure and physicochemical properties of normal maize, waxy maize, dull waxy maize and amylomaize V starches. Journal of Cereal Science 23, 153–162. Hoover, R., Vasanthan, T., 1994. The effect of annealing on the physicochemical properties of wheat, oat, potato and lentil starches. Journal of Food Biochemistry 17, 303–325. Hormdok, R., Noomhorm, A., 2007. Hydrothermal treatment of rice starch for improvement of rice noodle quality. Journal of Food Science and Technology 61,1–9. Hsu, S., Lu, S.C., Huang, R.M., 2000. Viscoelastic changes of rice starch suspensions during gelatinization. Journal of Food Science 65, 215–220. Huang, R.M., Chang, W.H., Chang, Y.H., Lii, C.Y., 1994. Phase transition of rice starch and flour gels. Cereal Chemistry 71, 202–207. Jacobasch, G., Dongowski, G., Schmiedl, D., Mu¨ller-Schmehl, K., 2006. Hydrothermal treatment of Novelose 330 results in high yield of resistant starch type 3 with beneficial prebiotic properties and decreased secondary bile acid formation in rats. British Journal of Nutrition 95, 1063–1074. Jacobs, H., Eerlingen, R.C., Clauwaert, W., Delcour, J., 1995. Influence of annealing on the pasting properties of starches from varying botanical sources. Cereal Chemistry 72, 480–487. Jacobs, H., Delcour, J.A., 1998. Hydrothermal modifications of granular starch, with retention of the granular structure: a review. Journal of Agricultural and Food Chemistry 46, 2895–2905. Jayakody, L., Hoover, R., 2008. Effect of annealing on the molecular structure and physicochemical properties of starches from different botanical origins – a review. Carbohydrate Polymers 74, 691–703. Jobling, S., 2004. Improving starch for food and industrial applications. Current Opinion in Plant Biology 7, 210–218. S. Cham, P. Suwannaporn / Journal of Cereal Science 51 (2010) 284–291 Khuri, A.L., Cornell, J.A., 1987. Response Surfaces: Designs and Analyses. Marcel Dekker, New York. Lii, C., Tsai, M., Tseng, K., 1996. Effect of amylose content on the rheological property of rice starch. Cereal Chemistry 73, 415–420. Lim, S.T., Chang, E.H., Chung, H.J., 2001. Thermal transition characteristics of heat– moisture treated corn and potato starches. Carbohydrate Polymers 46, 107–115. Lin, J.H., Wang, S.W., Chang, Y.H., 2008. Effect of molecular size on gelatinization thermal properties before and after annealing of rice starch with different amylose contents. Food Hydrocolloids 22, 156–163. Liu, H., Corke, H., Ramsden, L., 2000. The effect of autoclaving on the acetylation of ae, wx and normal maize starches. Starch 52, 353–360. Ozcan, S., Jackson, D.S., 2003. A response surface analysis of commercial corn starch annealing. Cereal Chemistry 80, 241–243. Pitiphunpong, S., Suwannaporn, P., 2009. Physicochemical properties of KDML 105 rice cultivar from different cultivated location in Thailand. Journal of the Science of Food and Agriculture 89 (13), 2186–2190. Rao, M.A., Tattiyakul, J., 1999. Granule size and rheological behavior of heated tapioca starch dispersions. Carbohydrate Polymers 38, 123–132. Roos, H.Y., 1995a. Phase Transition in Foods. Academic Press, New York. Roos, H.Y., 1995b. Glass transition-related physicochemical changes in foods. Food Technology 65, 91–102. Shih, F., King, J., Daigle, K., An, H.-J., Ali, R., 2007. Physicochemical properties of rice starch modified by hydrothermal treatments. Cereal Chemistry 84, 527–531. Stute, R., 1992. Hydrothermal modification of starches: the difference between annealing and heat–moisture treatment. Starch 44, 205–214. 291 Surojanametakul, V., Tungtakul, P., Varanyanond, W., Supasri, R., 2002. Effects of partial replacement of rice flour with various starches on the physicochemical and sensory properties of ‘‘sen lek’’ noodle. Kasetsart Journal (Natural Science) 36, 55–62. Suwannaporn, P., Pitiphunpong, S., Champangern, S., 2007. Classification of rice amylose group using discriminant analysis. Starch/Starke 59, 171–177. Takahashi, T., Miura, M., Ohisa, N., Kobayashi, S., 2005. Modification of gelatinization properties of rice flour by heat-treatment. Journal of the Society of Rheology 33, 81–85. Tester, R.F., Debon, S.J.J., Karkalas, J., 1998. Annealing of wheat starch. Journal of Cereal Science 28, 259–272. Tester, R.F., Debon, S.J.J., 2000. Annealing of starch – a review. International Journal of Biological Macromolecules 27, 1–12. Tester, R.F., Morrison, W.R., 1990. Swelling and gelatinization of cereal starches. II. Waxy rice starches. Cereal Chemistry 67, 558–563. Available from: Thailand Research Fund, 2009. TRF News: thirty two rice noodle factories and the Thailand Research Fund cooperated to develop safe noodles http://www.trf.or.th (accessed 04.08.09). Yoenyongbuddhagal, S., Noomhorm, A., 2002. Effect of physicochemical properties of high-amylose Thai rice flours on vermicelli quality. Cereal Chemistry 79, 481–485. Yunt, S.H., Quail, K., Moss, R., 1996. Physicochemical properties of Australian wheat flours for white salted noodles. Journal of Cereal Science 13, 181–189. Zhong, Z., Sun, X.S., 2005. Thermal characterization and phase behavior of cornstarch studied by differential scanning calorimetry. Journal of Food Engineering 69, 453–459.
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