Infrared Drying Characteristics of Long‐Grain Hybrid,Long‐Grain Pureline,and Medium‐Grain Rice Cultivars

The objective for this study was to investigate the effectiveness of scaled‐up infrared (IR) heating followed by tempering steps to dry freshly harvested rough rice. An industrial‐type, pilot‐scale, IR heating system designed to dry rough rice was used in this study. The heating zone of the equipment had catalytic IR emitters that provided heat energy to the sample as it was conveyed on a vibrating belt. The sample comprised freshly harvested rough rice of long‐grain pureline (Cheniere), long‐grain hybrid (6XP 756), and medium‐grain (CL 271) cultivars at initial moisture contents of 23, 23.5, and 24% wb, respectively. Samples at a loading rate of 1.61 kg/m² were heated with IR of radiation intensity 5.55 kW/m² for 30, 50, 90, and 180 s followed by tempering at 60°C for 4 h, at a product‐to‐emitter‐gap size of 450 mm, in one‐ and two‐pass drying operations. Control samples were gently natural air dried in an equilibrium moisture content chamber set at relative humidity of 65% and temperature of 26°C to moisture content of 12.5% wb. The effects of IR treatments followed by tempering on percentage points of moisture removed, head rice yield, energy use, rice color, and pasting characteristics were evaluated. For all cultivars, percentage point moisture removed increased with increase in IR drying duration. For all rice cultivars, one‐pass IR treatments for 180 s resulted in head rice yield significantly lower than that of rice dried with natural air in the controlled‐environment conditions (P < 0.05). Energy required to dry rice increased with increase in drying duration. Viscosity values of all the experimental samples were significantly greater (P value < 0.05) than that of the control samples for all the cultivars, except those treated with IR for 180 s. There was a significant difference (P < 0.05) in the color index (ΔE ) of treated milled samples and the controls. In conclusion, the study provided information crucial to understanding the effects of scaled‐up radiant heating and tempering of rough rice on drying rates and rice quality for long‐grain pureline, long‐grain hybrid, and medium‐grain rice cultivars.     

Effects of Controlled Ambient Aeration on Rice Quality During On‐Farm Storage

Rice (Oryza sativa L., ‘Cypress’) quality is highly dependent on its handling; hence, new storage treatments must be analyzed for their impact on rice quality. Rough rice from the 2000 season was harvested, dried, and stored in six farm‐scale bins. Three of the bins were aerated with a thermostatically activated controller, and three were aerated under traditional methods. Rice was sampled periodically over 12 weeks, and quality parameters were analyzed. The effects of bin sample position (spatial), bin sample depth, aeration treatment, and storage duration were investigated for their impact on rice quality factors: moisture content, head rice yield, pasting properties, and water absorption. For both aeration treatments at most sampling durations, rice sampled from the center of the bins had significantly lower head rice yield than that sampled from the north and south areas. Overall, moisture contents were not significantly affected by sampling position, although, in some specific sampling time and aeration treatment combinations, significant variation was noticed for moisture content as a function of sampling position. Sample depth within the bin did not cause any changes in the values of the rice properties. Throughout the storage duration, the physicochemical properties of the rice treated with controlled aeration were consistent with the trends of the rice treated with manual aeration. Storage duration significantly influenced (P < 0.05) water absorption, peak viscosity, head rice yield (HRY), and moisture content, with all but moisture content increasing over the storage duration. In contrast, the moisture content of the grain slightly decreased over the storage period.     

Physicochemical Properties of Rice Dried in a Single Pass Using High Temperatures

This study evaluated the physicochemical properties of high‐temperature, single‐pass dried rough rice. Pureline cultivars Wells (long grain) and Jupiter (medium grain) and hybrid cultivar CL XL729 (long grain), at initial moisture contents of 17.9–18.1% were dried in a single pass to approximately 12.5% moisture content with drying air temperatures of 60, 70, and 80°C and relative humidities of 13–83%. Immediately after drying, the samples were tempered for 1 h at the drying air temperatures in sealed plastic bags. Color, degree of milling, pasting viscosity, and thermal properties of the milled rice were evaluated. Results showed that color, degree of milling, and thermal properties were not affected by drying treatments. However, peak and final viscosities increased with increasing drying air temperatures in all three cultivars.     

Physicochemical Properties and In Vitro Starch Digestibility of Cooked Rice from Commercially Available Cultivars in Canada

The influence of amylose content, cooking, and storage on starch structure, thermal behaviors, pasting properties, and rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) in different commercial rice cultivars was investigated. Long grain rice with high‐amylose content had a higher gelatinization temperature and a lower gelatinization enthalpy than the other rice cultivars with intermediate amylose content (Arborio and Calrose) and waxy type (glutinous). The intensity ratio of 1047/1022 cm^–1 determined by Fourier Transform Infrared (FT‐IR), which indicated the ordered structure in starch granules, was the highest in glutinous and the lowest in long grain. Results from Rapid ViscoAnalyser (RVA) showed that the rice cultivar with higher amylose content had lower peak viscosity and breakdown, but higher pasting temperature, setback, and final viscosity. The RDS content was 28.1, 38.6, 41.5, and 57.5% in long grain, Arborio, Calrose, and glutinous rice, respectively, which was inversely related to amylose content. However, the SDS and RS contents were positively correlated with amylose content. During storage of cooked rice, long grain showed a continuous increase in pasting viscosity, while glutinous exhibited the sharp cold‐water swelling peak. The retrogradation rate was greater in rice cultivars with high amylose content. The ratio of 1047/1022 cm^–1 was substantially decreased by cooking and then increased during storage of cooked rice due to the crystalline structure, newly formed by retrogradation. Storage of cooked rice decreased RDS content and increased SDS content in all rice cultivars. However, no increase in RS content during storage was observed. The enthalpy for retrogradation and the intensity ratio 1047/1022 cm^–1 during storage were correlated negatively with RDS and positively with SDS (P ≤ 0.01).     

Properties of Flours and Starches as Affected by Rough Rice Drying Regime

Flours and starches from rough rice dried using different treatment combinations of air temperature (T) and relative humidity (RH) were studied to better understand the effect of drying regime on rice functionality. Rough rice from cultivars Bengal and Cypress were dried to a moisture content of ≈12% by three drying regimes: low temperature (T 20°C, RH 50%), medium temperature (T 40°C, RH 12%), and high temperature (T 60, RH 17%). Head rice grains were processed into flour and starch and evaluated for pasting characteristics with a Brabender Viscoamylograph, thermal properties with differential scanning calorimetry, starch molecular‐size distribution with high‐performance size‐exclusion chromatography (HPSEC), and amylopectin chain‐length distribution with high‐performance anion‐exchange chromatography with pulsed amperometric detection (HPAEC‐PAD). Lower head rice and starch yields were obtained from the batch dried at 60°C which were accompanied by an increase in total soluble solids and total carbohydrates in the pooled alkaline supernatant and wash water used in extracting the starch. Drying regime caused no apparent changes on starch molecular‐size distribution and amylopectin chain‐length distribution. Starch fine structure differences were due to cultivar. The pasting properties of flour were affected by the drying treatments while those of starch were not, suggesting that the grain components removed in the isolation of starch by alkaline‐steeping were important to the observed drying‐related changes in rice functionality.     

Effect of Ultrasonic Treatment of Brown Rice at Different Temperatures on Cooking Properties and Quality

This research studied developing quick cooking brown rice by investigating the effect of ultrasonic treatment at different temperatures on cooking time and quality. The medium grain brown rice was ultrasonically treated in water at temperatures of 25, 40, and 55°C for 30 min and then dried by air at 25°C to its initial moisture content (11.0 ± 0.6%, wb) before cooking. The microstructure of rice kernel surface, chemical composition, and optimal cooking time of treated brown rice were determined. The pasting and thermal properties and chemical structure of flour and starch from treated brown rice were also examined. The results showed that the optimal cooking times were 37, 35, and 33 min after treatment at 25, 40, and 55°C, respectively, compared to the control of 39.6 min. The ultrasonic treatment resulted in a loss in natural morphology of rice bran, allowing water to be absorbed by a rice kernel easily, particularly at high‐temperature treatment. Even through rice flour still maintained an A‐pattern in the pasting properties, the crystallinity significantly increased after treatment at 55°C. Ultrasonic treatment increased the peak, hold, and final viscosities and decreased the onset temperature (T_o) and peak temperature (T_p), significantly. Thus, ultrasonic treatment could be used for reducing cooking time of brown rice.     

Effects of Heat Treatments on the Milling,Physicochemical, and Cooking Properties of Two Long‐Grain Rice Cultivars During Storage

During storage, the milling, physicochemical properties, and eating quality of rice change, which is generally termed “aging.” Aged rice is preferred by processors because of better processing characteristics, and therefore there are attempts to develop accelerated aging processes. In this study, the effects of various heat treatments and their influences on the milling, physicochemical, and cooking properties of two long‐grain rice cultivars during storage were investigated with a randomized complete block design with an 8 × 5 × 2 full‐factorial treatment design. Two long‐grain rice cultivars, Wells and XP723, were treated with eight different heat treatments, including two levels of UV irradiation, two levels of autoclaving, three levels of convection oven heating, and one control, and then stored for 180 days at room temperature. The heat treatments significantly influenced all properties, including head rice yield (HRY), surface lipid content, peak gelatinization temperature, pasting properties, and cooked rice texture. All properties except HRY exhibited a significant two‐way interaction of cultivar and heat treatment. The severe autoclaving treatment resulted in rice of significantly different protein compositions when compared with the control. Storage impacted all properties except HRY and peak gelatinization temperature. Autoclaving (particularly severe autoclaving) produced samples with more distinct characteristics for most properties. Cooked rice hardness and stickiness exhibited not only significant main effects but also significant two‐ and three‐factor interactions.     

Effects of Rough Rice Storage Conditions on Gelatinization and Retrogradation Properties of Rice Flours

Changes in gelatinization and retrogradation properties of two rice cultivars, Bengal and Kaybonnet, during rough rice storage were studied using differential scanning calorimetry (DSC). The storage variables included two storage moisture contents (12 and 14%), three storage temperatures (4, 21, and 38°C), and four storage durations (0, 3, 9, and 16 weeks). Rough rice cultivar, storage temperature, moisture content, and duration affected (P < 0.05) the enthalpies and temperatures of gelatinization and retrogradation of rice flour. Bengal had a higher gelatinization enthalpy (P < 0.005) but lower gelatinization temperatures (P < 0.0001) than the long-grain Kaybonnet. Rice stored at 38°C exhibited higher gelatinization enthalpy and temperatures (P < 0.05) than those stored at 4 or 21°C. Storage duration affected the gelatinization and retrogradation properties through a higher order, rather than a linear, relationship.     

Effects of Rough Rice Storage Conditions on the Amylograph and Cooking Properties of Medium-Grain Rice cv. Bengal

Rough rice (cv. Bengal) was stored at four moisture contents (8.8, 10.7, 12.9, and 13.6% MC) and three temperatures (3, 20, and 37°C) for up to six months. The amylograph overall paste viscosity of the milled rice increased during storage. This increase was most apparent in all samples stored at 37°C. For rice stored at 20 and 37°C at all MC levels, a 30–50% increase in peak viscosity (PV) was observed during the first three months of storage. PV subsequently leveled off for rice stored at 12.9 and 13.6% MC but declined for samples stored at 8.8 and 10.7% MC. The final viscosities also increased during storage. The water-absorption ratio of the samples during cooking in excess water increased by an average of 15% over six months of storage. The amylograph and cooking properties were significantly affected (P < 0.05) by rough rice storage duration, temperature, MC, and their respective interactions.     

Development of Laboratory Techniques to Mimic Industrial‐Scale Nixtamalization

A laboratory nixtamalization process was developed to imitate larger scale cooking/steeping conditions. Corn (45 kg) was cooked in a pilot plant gas‐fired cook/steep tank and temperature was monitored every 30 sec. Cooling and heating rates were mimicked in the laboratory using a digital temperature programmable hot plate that adjusted grain‐water‐lime temperature changes at a specified rate. A Response Surface Central Composite Design was used to model pasting and thermal properties of nixtamal and masa as a function of cooking temperature (86–96°C), cooking time (20–40 min), and steeping time (3–11.77 hr). Nixtamal and masa moisture, dry matter loss, nixtamal and masa RVA peak temperature, shear thinning, nixtamal peak viscosity, masa final viscosity, nixtamal and masa DSC enthalpy peak and end temperatures, and nixtamal onset temperature were explained by the same regression terms for results obtained using both processes conditions. The intercept and slopes of the fitted models for the pilot plant and laboratory responses were not significantly different (P < 0.05). The laboratory method can be used to mimic larger scale processing over a wide range of nixtamalization conditions.     

Effects of Postharvest Elevated‐Temperature Exposure on Rice Quality and Functionality

Rapid drying with high‐temperature air has gained interest in the rice industry, but the effects of elevated‐temperature exposure on physicochemical properties of rice are of concern. This study investigated the effects of exposing rough rice to elevated temperatures for various durations without removing moisture. Physicochemical property response was evaluated in terms of head rice yield (HRY), germination rate (GR), milled‐rice yellowing, pasting properties, and gelatinization temperatures. Two long‐grain cultivars (pure‐line Wells and hybrid CL XL729) at initial moisture contents (IMCs) of 17.9 and 18.6%, respectively, and dried moisture content (DMC) of 12.5%, were hermetically sealed and exposed to 40, 60, and 80°C for various durations. Exposure to 80°C of IMC samples of Wells and CL XL729 resulted in a significant (2.3–2.5 percentage point) reduction in the HRYs. A 2 hr exposure of both cultivars at IMC level to 60°C completely inhibited GR, and exposure to 80°C of the cultivars at both moisture content (MC) levels immediately inhibited GR. Exposure to 80°C for almost all durations and 60°C for durations over 4 hr produced significant yellowing in both cultivars at IMC. Significant yellowing in both cultivars at DMC was also observed during a 28 day storage following 80°C exposure. In general, peak viscosities of both cultivars at IMC increased only after extended exposure to 40 and 60°C, but peak viscosities of the cultivars exposed to 80°C increased sharply and immediately upon exposure. No significant differences were observed in gelatinization temperatures of either cultivar at either MC level from elevated‐temperature exposure. Results from this study suggest that extreme‐temperature exposure of rough rice affects HRY, GRs, yellowing, and pasting properties of rice, but the extent of impact is MC dependent.     

Albumin Significantly Affects Pasting and Textural Characteristics of Rice Flour

The influence of albumin on the pasting and rheological properties of rice flour was investigated. Albumin was removed from the flour of three rice cultivars (Amaroo, Opus, and Langi) by water extraction and the pasting profile of the albumin‐depleted flour was analyzed using the Rapid ViscoAnalyser (RVA). Removal of albumin resulted in a significant (P < 0.5) decline in all the pasting parameters measured. When the extracted albumin was added to pure rice starch, exactly opposite trends occurred. The concentration of albumin in rice starch had a positive linear relationship with all pasting parameters measured. When the gels formed after RVA analyses were analyzed using the TA‐TX2 texture analyzer, the concentration of albumin had a positive linear relationship with hardness, but a near linear negative relationship with adhesiveness. The presence of albumin in rice starch slowed the uptake of water by starch in the initial stages of cooking, but the water uptake accelerated in later stages, and the final water absorption was higher in the samples containing albumin than in pure starch. The water‐soluble nature of albumin suggests that protein‐water‐starch interactions could be responsible for its effect on the physical properties of rice.     

Effect of Infrared and Conventional Drying Methods on Physicochemical Characteristics of Stored White Rice

The objective of this study was to investigate the effect of infrared (IR) drying followed by tempering and natural cooling on the change of physicochemical characteristics of white rice during up to 10 months of storage. The physicochemical characteristics of IR‐dried rice were also compared with those of conventionally dried rice. It took only 58 s to heat the rough rice from room temperature to 60°C with IR, and 2.17 percentage points of moisture was removed. After four months of storage, the increases in yellowness index, water uptake ratio, and volume expansion ratio of the rice dried with IR were 73.8, 63.9, and 55.3% those of rice dried with an ambient air drying method, respectively. IR drying slightly decreased the gelatinization temperature, enthalpy, and viscosities, reduced the changes in microstructure, and maintained cooking characteristics during storage. Therefore, the IR drying process is recommended to maintain the quality of white rice during storage.     

Effect of Extrusion Conditions on Pasting Behavior and Microstructure of Refabricated Rice: A Response Surface Analysis

The effects of moisture, screw speed, and barrel temperature on pasting behavior of refabricated rice grains were investigated in a corotating twin‐screw extruder with response surface methodology. The rice flour obtained from broken rice (≤1/8 of actual kernel size) of PR‐116 variety was used in the study. The screw speed was set at five levels between 49 and 150 rpm, barrel temperature between 59 and 110°C, and feed moisture between 31 and 45%. All pasting properties of refabricated grains evaluated—peak viscosity, hold viscosity, breakdown viscosity, final viscosity, and setback viscosity—were significantly (P < 0.01) affected by the three process variables. Barrel temperature was the most significant variable, with quadratic effect on all viscosity parameters. Response surface regression models were established to correlate the viscosity profile of refabricated rice grains to the process variables. The optimum moisture content, screw speed, and barrel temperature estimated by a response surface of desirability function for the production of refabricated rice were 36%, 130 rpm, and 89.5°C, respectively. Scanning electron microscopy also revealed that intermediate moisture and temperature along with high screw speed during extrusion could create a more realistic appearance of refabricated rice with less rupture of starch granules.     

Effect of Stabilized Rice Bran Fractions on the Formation of Rice Flour Pasting Properties

Rice flour composition played a key role in determining the changes in pasting properties of rice flour. The influence of incorporating defatted rice bran (DFRB), rice bran fiber (RBF), rice bran protein (RBP), and stabilized rice bran (SRB) fractions on the mechanism of rice flour pasting viscosities was investigated. Pasting properties of long‐ and medium‐grain rice flour substituted with 5, 10, 15, 20, and 100% bran fractions resulted in a significant decrease (P < 0.05) in rice flour pasting property values. Flour substituted with RBP had the lowest pasting property measurements compared with other fractions, and the greater the percentage substituted, the lower the pasting property values. DFRB and RBF were least affected properties when used as a replacement. Results were attributed to the contribution of rice starch in the mechanism of rice paste formation, in which decreasing starch in a rice flour sample, as a result of substituting with fractions of SRB, may have resulted in faster swelling of starch granules to the maximum extent and increased their susceptibility to be disrupted by shear, resulting in low paste viscosities. Results also suggested that protein structural integrity and the nature of starch–protein bonding affected rice flour pasting mechanism formation.     

Starch Pasting and Textural Attributes of Elbow Macaroni as Impacted by Dough Moisture,Dough Mixing Time,and Macaroni Cooking Time

The effects of dough moisture, mixing time, and cooking time on uncooked and cooked elbow macaroni by means of starch pasting and macaroni textural characteristics were investigated. In conventional elbow macaroni production, cooking time was found to have significant contributions to cooked macaroni starch pasting properties, indicating that degree of starch cook dependent on cooking time was the main influence on cooked macaroni starch pasting phenomena. Dough moisture also showed some significant (P < 0.05) relationships with cooked macaroni starch pasting properties; however, mixing time did not show significant effect. Cooked macaroni starch pasting properties showed significantly (P < 0.05) high correlations with cooked macaroni firmness and stickiness. Cooking time was the only major variable contributing to variations in cooked elbow macaroni starch and consequently in pasting and texture characteristics. Cooking time was highly related to firmness and stickiness of cooked elbow macaroni (P < 0.0001, R² = 0.8148; P < 0.0001, R² = 0.6215, respectively). In addition, dough moisture had a slight significant (P < 0.05) effect on cooked elbow macaroni firmness and stickiness. Cooked elbow macaroni firmness and stickiness were found to be highly correlated (P = 0.0001, R² = 0.8459). Increases in firmness increased cooked elbow macaroni stickiness. As a result, when elbow macaroni was cooked for shorter times, firmer and stickier macaroni was obtained.     

Storage Stability of Flour‐Blasted Brown Rice

Brown rice was blasted with rice flour rather than sand in a sand blaster to make microperforations so that water could easily penetrate the brown rice endosperm and cook the rice in a shorter time. The flour‐blasted American Basmati brown rice, long‐grain brown rice, and parboiled long‐grain brown rice samples were stored in Ziploc storage bags under atmospheric conditions and in vacuum‐packed bags. They were periodically tested for over 10 months for changes in water absorption, free fatty acid (FFA), peroxide value (POV), viscosity changes of flour using the Rapid ViscoAnalyser (RVA), and texture of whole cooked kernel using a texture analyzer during cooking. Flour‐blasted brown rice absorbed less water but needed less cooking time than its counterpart that was not flour‐blasted. There was an increase in FFA, POV, peak viscosity (PV), final viscosity (FV), breakdown viscosity (BD), and setback viscosity (SB) during storage of flour‐blasted brown rice for 300 days, but no change was observed in texture (hardness, gumminess) and water absorption. The combined coefficient of correlation (including all types of rice) between FFA and FV is r = 0.86 and between FFA and SB is r = 0.90 at P < 0.0001.     

Effect of Barley Flour on Development of Rice‐Based Extruded Snacks

This study was conducted to develop a ready‐to‐eat extruded food using a single‐screw laboratory extruder. Blends of Indian barley and rice were used as the ingredients for extrusion. The effect of extrusion variables and barley‐to‐rice ratio on properties like expansion ratio, bulk density, water absorption index, hardness, β‐glucan, L*, a*, b* values, and pasting characteristics of extruded products were studied. A central composite rotatable design was used to evaluate the effects of operating variables: die temperature (150–200°C), initial feed moisture content (20–40%), screw speed (90–110 rpm), and barley flour (10–30%) on properties like expansion ratio, bulk density, water absorption index (WAI), hardness, β‐glucan, L*, a*, b* values, and sensory and pasting characteristics of extruded products. Die temperature >175°C and feed moisture <30% resulted in a steep increase in expansion ratio and a decrease in bulk density. Barley flour content of 10% and feed moisture content of <20% resulted in an increased hardness value. When barley flour content was 30–40% and feed moisture content was <20%, a steep increase in the WAI was noticed. Viscosity values of extruded products were far less than those of corresponding unprocessed counterparts as evaluated. Rapid visco analysis indicated that the extruded blend starches were partially pregelatinized as a result of the extrusion process. Sensory scores indicated that barley flour content at 20%, feed moisture content at 30%, and die temperature at 175°C resulted in an acceptable product. The prepared product was roasted in oil using a particular spice mix and its sensory and nutritional properties were studied.