Factors That Influence the Microwave Expansion of Glassy Amylopectin Extrudates

The microwave expansion of glassy, unexpanded amylopectin pellets was studied. Amylopectin was extruded at three levels of specific mechanical energy (483, 809, and 846 kJ/kg), and 35–40% moisture content, without expansion at the die. Glassy pellets were obtained by drying and equilibrating the extrudates at five water activities (a_w 0, 0.11, 0.33, 0.67, and 0.75). The pellets were characterized by measuring volume, porosity, and moisture content. The pellets were then expanded in a constant power microwave oven to determine the degree of expansion. When subjected to microwave heating, regardless of extrusion condition and initial a_w, the pellets expanded from the center where the highest temperature was recorded and then expansion advanced in the whole volume. Maximum expansion was reached after 30 sec of heating, after which samples started to burn from the center. Samples simultaneously expanded and lost moisture, both processes being faster and more intense for pellets of higher initial a_w. No expansion was observed for the pellets stored at a_w 0, while collapse was observed for pellets stored at a_w 0.73. A linear correlation between pellet expansion temperature and glass transition temperature was obtained. A hypothesis for the microwave expansion of glassy extrudates was formulated and represented on a state diagram.     

Glassy State Transition and Rice Drying: Development of a Brown Rice State Diagram

The effect of moisture content (MC) on the glass transition temperature (T_g) of individual brown rice kernels of Bengal, a medium‐grain cultivar, and Cypress, a long‐grain cultivar, was studied. Three methods were investigated for measuring T_g: differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and dynamic mechanical analysis (DMA). Among these methods, TMA was chosen, because it can also measure changes in the thermal volumetric coefficient (β) of the kernel during glass transition. TMA‐measured T_g at similar MC levels for both cultivars were not significantly different and were combined to generate a brown rice state diagram. Individual kernel T_g for both cultivars increased from 22 to 58°C as MC decreased from 27 to 3% wb. Linear and sigmoid models were derived to relate T_g to MC. The linear model was sufficient to describe the property changes in the MC range encountered during rice drying. Mean β values across both cultivars in the rubbery state was 4.62 × 10^‐4/°C and was higher than the mean β value of 0.87 × 10^‐4/°C in the glassy state. A hypothetical rice drying process was mapped onto the combined state diagram generated for Bengal and Cypress.     

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).     

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.     

Effect of Specific Mechanical Energy on Properties of Extruded Protein‐Starch Mixtures

The effect of the specific mechanical energy (SME) during extrusion of a protein‐starch mixture was studied by analyzing the glass transition temperature (T_g) and starch gelatinization. We found that the SME values of 344 to 2108 kJ/kg did not significantly change the T_g of the product. To explain the insensitivity of T_g to SME in spite of reported fragmentation taking place during extrusion, we studied the effect of the molecular weight (MW) on T_g in a model system consisting of dextrans of varying molecular weights. We found that the effect of the molecular weight on the T_g reached a plateau at 6.7 × 10⁴. Because the reported size of the fragments created during the extrusion process is larger than this, we were able to explain the apparent insensitivity of T_g to SME in the protein‐carbohydrate matrix studied. However, we found that starch gelatinization varied with SME, the degree of gelatinization being higher for systems exposed to higher SME.     

Effects of Waxy Rice Moisture Content and Rate of CO2 Injection on Characteristics of Extruded Pellets and Vacuum‐Puffed Yukwa (a Korean Traditional Snack)

Extrusion with CO₂ injection was developed to simplify the process of producing vacuum‐puffed yukwa (rice snacks). The effects of feed moisture content and CO₂ injection on the characteristics of extruded pellets (maximum viscosity and degree of gelatinization) and vacuum‐puffed yukwa (expansion ratio, bulk density, hardness, and color) were investigated. Higher feed moisture increased the size of vacuum‐puffed yukwa and the degree of gelatinization, whereas the maximum viscosity decreased. Maximum viscosity and gelatinization degree of extruded pellets were highly correlated with expansion ratio, bulk density, hardness, and color values of vacuum‐puffed yukwa. Increasing feed moisture content significantly increased expansion ratio but decreased bulk density and hardness. CO₂ injection decreased bulk density and hardness of vacuum‐puffed yukwa.     

Genotype and Environmental Influences on Pasting Properties of Rice Flour

The pasting behavior of flour from several Australian rice (Oryza sativa L.) cultivars, differing in amylose content and grown in three different locations and three seasons, were determined using the Rapid Visco Analyser. Genotype, growth season, and growth location all affected the pasting behavior of rice flour. The amylose content of the same cultivar was significantly higher in the coolest growing season, resulting in RVA traces with lower peak viscosity and higher setback than samples with lower amylose content. When the same cultivar of rice was grown in different locations in the same season, there were no significant differences in the total starch, protein, lipid, and amylose content of the flour, but there were significant differences in the pasting behavior. This indicates that environmental as well as genetic factors influence the pasting behavior of rice flour. Flour from parboiled and quick‐cooking rice did not paste and had low viscosities compared with unprocessed rice. Results from this study showed that the pasting behavior of rice flour was related to genotype and was influenced by environmental factors that brought about subtle changes in the grains that were not picked up by chemical analyses.     

Effect of Cultural Management Practices on Grain Quality of Two Rice Cultivars

To reduce fuel and labor costs and increase profits, farmers are trying new ways of growing rice (Oryza sativa L.). This includes changing crop rotations, tillage systems, and fertilization levels. There is little information on how these changes affect the cooking quality of rice. We therefore looked at the parameters associated with cooking and processing quality (apparent amylose, gelatinization temperature, lipid and protein contents, and pasting properties) of two U.S. long grains (Cybonnet and Wells) that were grown using two different tillage systems, standard rate and high rates of fertilization, and different crop rotations (continuous rice R‐R, rice after soybeans R‐SB, and rice after corn R‐C). No differences in quality traits were observed among any of the tillage systems. Rice grown in continuous rice rotation had the lowest protein content of brown and milled rice (8.6 and 8.1%, respectively) as compared to the highest levels observed in the rice‐soybean rotation (9.3 and 8.6%, respectively). Rice grown in continuous rice rotation also had higher peak viscosity than other crop rotations. Increasing the fertilization rate increased the protein content of brown rice and decreased peak, trough, and final viscosities. Apparent amylose content, gelatinization temperature, and lipid content were not affected by crop rotation or fertility; however, they were influenced by cultivar. Although the results indicated statistical differences for some quality parameters, the differences were small enough that they are unlikely to have a major impact on processing quality of long grain rice if co‐mingled.     

挤压加工参数对重组米生产过程及产品膨胀度的影响

为了考察重组米生产过程中挤压加工变量对几种系统参数与产品膨胀度的影响,试验以杂交籼米（9?718品种）为原料,利用响应面模型,以螺杆转速、进料速度、进料含水率以及末端机筒温度为输入变量,以挤压系统参数（物料温度、模头压强、扭矩、比机械能和产品含水率）和重组米膨胀度为响应变量,探索在重组米生产过程中加工变量与系统参数及产品膨胀度的关系。结果表明,压强、比机械能和产品膨胀度都受到4个挤压变量的显著影响,但是物料温度受进料速度影响不显著,马达扭矩受末端机筒温度影响不显著,产品含水率仅受进料含水率的显著影响。比机械能与螺杆转速正相关,与进料速度、进料含水率和末端机筒温度负相关。所得二次回归模型均拟合良好,建立的挤压数学模型可应用于重组米生产,为重组米工业化生产的过程预测和产品性质预测提供参考。     

Influence of Early and Delayed Transplantation of Paddy on Physicochemical,Pasting, Cooking,Textural, and Protein Characteristics of Milled Rice

Milled rice of four indica cultivars (PR114, PR116, PR118, and PAU201) obtained from early (June 5 and 15) and delayed (June 25 and July 5) transplanted paddy was evaluated for physicochemical, pasting, cooking, and protein characteristics. During the grain‐filling and development stage, early transplanted paddy experienced average maximum and minimum temperatures of 32.8 and 22.3°C, respectively, against 30.8 and 15°C, respectively, for delayed transplanted paddy. Lightness (L*) value, protein content, and lipid content of milled rice were lower, whereas apparent amylose content, cooked grain hardness, final viscosity, and setback viscosity were higher in the delayed transplanted paddy. Whiteness of milled rice of PR114, PR116, and PR118 from delayed transplanted paddy was lower than milled rice from early transplanted paddy. PAU201 did not show any change in whiteness with delayed transplantation. Cooked rice of PAU201 showed exceptionally higher adhesiveness and lower hardness compared with other cultivars. Protein profiling showed a lower accumulation of prolamines in milled rice from PR114 and PAU201 upon delaying the transplantation from June 5 to July 5, whereas PR116 and PR118 showed a decrease in prolamine accumulation from transplantation on June 25. The changes in milled rice caused by delayed transplanting of paddy might be because of cool nighttime air temperature that affected the accumulation of starch, protein, and lipid.     

Heat Treatments of Milled Rice and Properties of the Flours

The effects of autoclave and oven treatments on the gelatinization of rice flour and on the rheological characteristics of its pastes were studied by differential scanning calorimetry (DSC), rapid viscoanalysis (RVA), and rotational viscometry. Flours from autoclave‐treated rice (ATR) and oven‐treated rice (OTR) were prepared, respectively, by heating at 120°C for 60 min and 160°C for 60 min followed by drying (ATR sample), and grinding at 2.2–12.9% moisture content. The rice flour dispersions were adjusted between pH 6.3 and 2.8 using 0.2M citrate buffer. The retort processing of rice flour in water pastes were done at 120°C for 20 min either once or twice. The gelatinization peak temperature (PT and T_o) and the peak temperature corresponding to the amylose‐lipid complexes (T_p3) of ATR increased at pH 6.3 and 2.8 compared with OTR and UTR flour. This indicates that the internal structures of the starch granules in ATR became more stable to heat and acid, even though the damaged starch content of ATR was 23% compared with 16 and 7%, respectively, for untreated rice flour (UTR) and OTR. The OTR flour pastes showed a gel‐like behavior at pH 4.5 after retort processing in water at 120°C for 20 min; however, the ATR mixture behaved more like a liquid paste. Decreases in the reducing sugar content of OTR and ATR pastes suggested that enzymes in the heat‐treated rice were denatured, which retarded the hydrolysis of glucose chains and the rupture of starch granules during pasting.     

Chemical and Physicochemical Properties of Maize Starch After Industrial Nixtamalization

Processing conditions similar to traditional nixtamalization are now used by the industry in the production of dry maize flours (DMF). The objective of this investigation was to evaluate the effect of industrial nixtamalization on maize starch. Thus, dent maize grains were sampled from storage silos and the starch isolated (S). From the same batch of maize, DMF was obtained and the starch isolated (S‐DMF). The amylose content in the starches was quite similar (21.5–23.4%) and characteristic of a dent maize. However, nixtamalization increased the calcium content in S‐DMF. The starches investigated exhibited the typical A‐type diffraction pattern after 40 days of storage at 11–84.1% rh. However, the differential scanning calorimetry (DSC) results showed that annealing of maize starch occurred during storage at 30°C. On the other hand, industrial nixtamalization has both a melting and annealing effect on maize starch. Thus, the operative glass transition temperature (T_g), and the DSC parameters that define starch gelatinization (T_p and ΔH) showed that the proportion between crystalline and amorphous regions within the starch granule and the extent of physical damage to starch were modified by nixtamalization. As an example, T_g for S was between 60 and 62.5°C, while the S‐DMF had a T_g of 45–55°C for damaged starch and 65–70°C for annealed starch. Additionally, the extraction of the nonconstitutive starch lipids provided starches with more consistent thermal properties, particularly in the behavior of gelatinization at different water content. This last observation might have important implications in the consistency of starch physicochemical properties and, consequently, in the quality of maize products such as tortillas.     

Categorizing Rice Cultivars Based on Cluster Analysis of Amylose Content,Protein Content and Sensory Attributes

Presently, rice cultivars are categorized according to grain dimensions, amylose content, and alkali spreading value (gelatinization temperature type). Categorization of rice cultivars based on total sensory impact is needed. This work endeavors to divide world rices into groups based on amylose, protein, flavor, and texture properties. Ninety‐one rice samples representing 79 different cultivars and seven growing locations were separated into seven groups with Ward's Cluster Analysis. Cluster 1 included a third of the rice samples and had cultivars with a large diversity of grain shapes and amylose contents. Mean attribute scores for this cluster were near the grand mean for the collective rice samples for nearly every sensory attribute. Cluster 2 included conventional U.S. short‐ and medium‐grain cultivars. Cluster 3 included conventional U.S. medium cultivars that were produced in Louisiana. Mean sensory scores for this cluster characterized these cultivars as having relatively undesirable flavor and texture attributes. Cluster 4 included Japanese premium quality cultivars and U.S. medium‐grain cultivars developed for the Japanese market. Cluster 5 included high‐amylose, indica types that had relatively firm textural properties. Cluster 6 included relatively soft cooking, aromatic cultivars. Cluster 7 included waxy cultivars and other soft cooking grains. In several cases, the production environment (location, weather effects, etc.) influenced flavor and texture characteristics and resulted in the cultivar falling into an unexpected cluster. This categorization serves as a catalyst for indexing rice cultivars for cooking and processing qualities.     

Effects of Postharvest Parameters on Functional Changes During Rough Rice Storage

The expansion of value‐added uses for rice has created a demand for quantitative models of functional changes during postharvest handling. Consequently, this study evaluated the effects of postharvest parameters on the functional properties of long‐grain (cvs. Cypress and Kaybonnet) and medium‐grain (cv. Bengal) rice. The experimental treatments included rough rice drying conditions (low vs. high temperature drying), storage moisture content (10, 12, and 14%), storage temperature (4, 21, and 38°C), and storage duration (up to 36 weeks). Milling, cooking, and amylograph pasting properties were analyzed. Polynomial models (up to third‐order) were developed to describe the effects of postharvest factors on the functional properties. Drying treatments, storage moisture content, and storage duration affected (P < 0.05) all of the functional properties. Storage temperature influenced (P < 0.01) cooking and pasting properties, but not milling properties. Overall, there were significant interactions among the postharvest parameters. Additionally, these factors were related to the functional properties by higher‐order relationships.     

Preparation of High‐Quality Protein‐Based Extruded Pellets Expanded by Microwave Oven

The aim of this work was to study the effects of extrusion barrel temperature (75–140°C) and feed moisture (16–30%) on the production of third‐generation snacks expanded by microwave heating. A blend of potato starch (50%), quality protein maize (QPM) (35%), and soybean meal (SM) (15%) was used in the preparation of the snacks. A laboratory single extruder with a 1.5 × 20.0 × 100 mm die‐nozzle and a central composite routable experimental design were used. Expansion index (EI) and bulk density (BD) were measured in expanded pellets, viscosity at 83°C (V₈₃), thermal properties, and relative crystallinity were measured in extruded pellets. EI increased and BD decreased when the barrel temperature was increased, while the feed moisture effect was not significant. V₈₃ increased when feed moisture increased. Extrusion modified the crystalline structures of the pellets and the X‐ray data suggests the formation of new structures, probably due to the development of amylose‐lipid complexes. The maximum expansion of pellets was found at barrel temperatures of 123–140°C, and feed moisture of 24.5–30%. It is possible to obtain a functional third‐generation snack with good expansion characteristics using a microwave oven, and this snack has health benefits due to the addition of QPM and SM.     

Evaluation of Compatibility of Rice Starch and Pectins by Glass Transition and Sub‐Tg Endotherms and the Effect of Compatibility on Gel Viscosity and Water Loss

Differences in molecular structure and hydrophilicity may affect the compatibility of food components in a highly concentrated solution. Mixtures of TNuS19 rice starch (RS) and pectins with three different degrees of esterification (22, 64, and 92%) were used as a model system to evaluate the components' compatibility in a low‐moisture system. When analyzed individually by differential scanning calorimetry (DSC), RS, low methoxyl pectin (LMP), intermediate methoxyl pectin (IMP), and high methoxyl pectin (HMP) showed the presence of a glass transition temperature (T_g) at 75.2, 96.2, 96.4, and 93.5°C, respectively. Among mixtures, the compatible RS‐HMP exhibited only a single T_g between the T_g values of the two components, whereas the incompatible RS‐LMP showed two T_g values that were close to those of the individual components. The sub‐T_g endotherms of all three mixtures (1:1) were lower than the means of the corresponding components. The degree of decrease was more pronounced in the RS‐HMP mixture than in the others. The above results imply that the interaction, which led to close contact between side chains of the two components, was more intense in the compatible RS‐HMP mixture than in the RS‐IMP and RS‐LMP mixtures. The decrease of the sub‐T_g endotherm can be used as an index to evaluate the degree of compatibility as well as the interaction occurring between the two molecules. The above findings were further verified by dynamic mechanical analyses. Both viscosity and water retention of the compatible RS‐HMP mixed gel were significantly higher than those of the RS‐IMP and RS‐LMP mixed gels. This evidence further suggests that RS and HMP are compatible and exhibit a strong intermolecular interaction that increases gel viscosity and decreases water loss during high‐temperature heating.     

广西早籼品种(组合)的稻米品质状况及改良目标

广西多数早籼品种(组合)的糙米率、精米率、粒长、粒形、糊化温度、胶稠度、蛋白质含量等指标。达到了农业部(NY122-86)二级优质食用稻米标准。但完整米率的达标率偏低,胚乳的垩白程度偏大,垩白粒率偏高,直链淀粉含量偏高,米粒的蒸煮延长性差。今后,早籼稻的品质育种应把提高完整米率,降低直链淀粉含量和提高胚乳的透明度作为品质改良的主攻目标。     

Correlation Between Starch Retrogradation and Water Mobility as Determined by Differential Scanning Calorimetry (DSC) and Nuclear Magnetic Resonance (NMR)

Starches from nine varieties of rice, including four indica, three japonica, and two waxy cultivars, were used for the investigation of the correlation between retrogradation and water mobility. Retrogradation and water mobility were analyzed by differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) and expressed as enthalpy change (ΔH) and differential relaxation rate (ΔR₂) for water‐¹⁷O. Water contents were measured by DSC and Karl‐Fischer methods. The results indicated that three different profiles, based on amylose content, were observed for the ΔH changes of rice starch cooks during storage. They fit well to the nonlinear regression equations of exponential rise to maximum and exponential growth models. The water content, as measured with DSC, decreased during storage but increased as measured with the Karl‐Fischer method. This discrepancy might be attributed to the different characteristics of water measured by the two methods. The ΔR₂ of rice starch cooks showed an increasing trend during storage but was more complicated than the ΔH trend. The nonlinear regression models were also applied to fit the changes of ΔR₂ for indica varieties in the initial six days and for waxy varieties up to 24 days. This resembled the ΔH changes.     

Separation and Characterization of Barley Starch Polymers by a Flow Field‐Flow Fractionation Technique in Combination with Multiangle Light Scattering and Differential Refractive Index Detection

Flow field‐flow fractionation (flow FFF) with frit inlet and frit outlet mode (FIFO) was coupled online to multiangle light scattering (MALS) and refractive index (RI) detectors to investigate the molecular characteristics of normal and zero amylose barley starch polymers. Application of two different cross‐flows, 0.35 mL/min followed by 0.1 mL/min, and constant channel and frit flows of 0.1 and 1.0 mL/min, respectively, permitted a complete separation of amylose and amylopectin. The improved signals from the detectors due to application of the FIFO mode enabled the proper characterization of the small molecular weight species, as well as significantly enhanced the reproducibility of the measurements. The weight‐average molecular weight (M_w) and zaverage root‐mean‐square (RMS) radii of gyration (R_g) values for amylose and amylopectin in the normal starch samples were 2.3 × 10⁶ and 280 × 10⁶, and 107 and 260 nm, respectively. The M_w and R_g of amylopectin in the zero amylose starch samples were 360 × 10⁶ and 267 nm, respectively. The slopes (α) obtained by plotting log M_w versus log R_g for amylose and amylopectin were 0.6 and 0.3, respectively. These results are in good agreement with the theoretical prediction of the molecular conformation of amylose and amylopectin.