Physicochemical and Pharmaceutical Properties of Carboxymethyl Rice Starches Modified from Native Starches with Different Amylose Content

Carboxymethyl rice starches (CMRS) were prepared from nine strains of native rice starches with amylose contents of 14.7–29.1%. The reaction was conducted at 50°C for 120 min using monochloroacetic acid as a reagent under alkaline conditions and 1-propanol as a solvent. After determining the degree of substitution (DS), the physicochemical properties including water solubility, pH, and viscosity of 1% (w/v) solution, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses of the granules, as well as some pharmaceutical properties of CMRS powders and pastes were investigated. The DS range was 0.25–0.40. All CMRS dissolved in unheated water and formed viscous gel. A good positive correlation was observed between amylose content and DS (r = 0.9278) but not viscosity. SEM and XRD concurrently revealed significant physical alteration of CMRS granules compared with those of native starches, which reflected the changes in the properties of CMRS. At 3% (w/w), CMRS can function as tablet binder in the wet granulation of both water-soluble and water-insoluble diluents. The tablets compressed from these granules showed good hardness with fewer capping problems compared with those prepared using the pregelatinized native rice starch as a binder. In addition, most CMRS pastes formed clear films with varying film characteristics, depending upon the amylose content of the native starches. This type of modified rice starch can potentially be employed as a tablet binder and film-former for pharmaceutical dosage formulations.     

Structures of Four Waxy Rice Starches in Relation to Thermal,Pasting, and Textural Properties

Waxy rice starches from three japonica cultivars (Taichung Waxy 1 [TCW1], Taichung Waxy 70 [TCW70], Tachimemochi) and one indica cultivar (Tainung Sen Waxy 2 [TNSW2]) were characterized for chemical and physicochemical properties. The amylopectin structures were different for the four waxy rice starches in terms of degree of polymerization (DP), average chain length (CL), exterior chain lengths (ECL), and distribution of chains, indicating the existence of varietal differences. The order of swelling power was TCW1 > TCW70 > TNSW2 > Tachimemochi; the order of water solubility index was TCW70 > TNSW2 > Tachimemochi > TCW1. The low water solubility index of TCW1 might be ascribed to a high DP. All starches shared similar gelatinization temperatures and enthalpies but showed distinct retrogradation patterns. TNSW2 showed the highest retrogradation rate, followed by TCW2, Tachimemochi, and TCW70. TCW70 exhibited the highest overall pasting viscosity, followed by TNSW2, TCW1, and Tachimemochi. The hardness of waxy rice starch pastes from a Brabender amyloviscograph increased rapidly after storage at 5°C for one day and remained the same or slightly increased after seven days of storage, whereas the opposite trend was observed for adhesiveness. The lower degree of retrogradation of TCW70 was probably a result of a larger amount of A chain and a shorter ECL. The changes in hardness correlated with the amount of A and B1 chains. The texture attributes of waxy rice starch pastes were significantly affected by amylopectin retrogradation during storage.     

Effect of Steeping Treatment on Pasting and Thermal Properties of Sorghum Starches

Chemical treatments in wet milling could improve the physico‐chemical properties of starch isolated from high‐tannin sorghums. Sorghums Chirimaugute (medium‐tannin), DC‐75 (high‐tannin), and SV2 (tannin‐free) were steeped in water, dilute HCl (0.9%, v/v), formaldehyde (0.05%, v/v), and NaOH (0.3%, w/v) solutions before wet milling and starch separation. Pasting, textural, and thermal properties of starch were determined. Steeping in NaOH resulted in starches with higher peak viscosity (PV), cool paste viscosity (CPV), and setback than when water, HCl, and formaldehyde were used. The time to PV (P_time) and PV temperature (P_temp) were markedly reduced by treatment with NaOH. NaOH could have caused a degree of pregelatinization. HCl treatment gave starches with higher P_temp and P _time, presumably due to delayed granule swelling. Gel hardness was largely determined by the starch amylase content. The low hardness of DC‐75 starch gels was slightly improved in NaOH‐treated grains. Gelatinization temperatures of sorghum starches were generally low, regardless of steeping treatment. Starch from NaOH‐treated grain generally had slightly higher gelatinization temperatures than when water, HCl, or HCHO was used. Chemical treatments during steeping of sorghum grains greatly affected starch properties. Dilute alkali steeping during wet milling could be used to improve properties of starch isolated from tannin‐containing sorghums.     

Degree of Milling Effects on Rice Pasting Properties

The effects of degree of milling on pasting properties of medium‐grain (cv. Bengal and Orion) and long‐grain rice (cv. Cypress and Kaybonnet) were quantified using a Brabender ViscoAmylograph and a Rapid Visco Analyser. For all the cultivars tested, surface and total lipid contents decreased as the degree of milling increased. The peak viscosities for all rice increased with the degree of milling and the rates of increase were higher for medium‐grain than long‐grain cultivars. Degree of milling did not have a consistent effect on final viscosity for all the cultivars tested.     

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.     

Extrusion of Cross‐Linked Hydroxypropylated Corn Starches I. Pasting Properties

A series of cross‐linked (0, 0.014, 0.018, 0.024, and 0.028% POCl₃, dry starch basis) hydroxypropylated (8%) corn starches were extruded using a Leistritz micro‐18 co‐rotating extruder. Process variables included moisture, barrel temperature, and screw design. Differential scanning calorimetry and X‐ray diffraction studies showed the level of starch crystallinity decreased with increasing severity of extrusion conditions. Pasting properties of the extruded starches were examined using a Rapid Visco Analyser. Pasting profiles of starches extruded at different conditions displayed different hot paste viscosity and final viscosity. Increasing starch moisture content during extrusion and level of cross‐linking increased starch viscosity (P < 0.0001), whereas increasing extrusion temperature and shear decreased starch viscosity (P < 0.0001). Interactions were found between level of cross‐linking and screw design and between extrusion temperature and starch moisture content (P < 0.0001).     

Effect of Amylose Content on Gelatinization,Retrogradation, and Pasting Properties of Starches from Waxy and Nonwaxy Wheat and Their F1 Seeds

We studied the effect of amylose content on the gelatinization, retrogradation, and pasting properties of starch using wheat starches differing in amylose content. Starches were isolated from waxy and nonwaxy wheat and reciprocal F1 seeds by crossing waxy and nonwaxy wheat. Mixing waxy and nonwaxy wheat starch produced a mixed starch with the same amylose content as F1 seeds for comparison. The amylose content of F1 seeds ranged between waxy and nonwaxy wheat. Nonwaxy‐waxy wheat had a higher amylose content than waxy‐nonwaxy wheat. Endothermic enthalpy and final gelatinization temperature measured by differential scanning calorimetry correlated negatively with amylose content. Gelatinization onset and peak temperature clearly differed between F1 and mixed starches with the same amylose content as F1 starches. Enthalpy for melting recrystallized starches correlated negatively with amylose content. Rapid Visco Analyser measurement showed that F1 starches had a higher peak viscosity than waxy and nonwaxy wheat starches. Mixed starches showed characteristic profiles with two low peaks. Setback and final viscosity correlated highly with amylose content. Some of gelatinization and pasting properties differed between F1 starches and mixed starches.     

Gelatinizing,Pasting, and Gelling Properties of Potato and Amaranth Starch Mixtures

Physicochemical properties of mixtures of native potato and native amaranth (Amaranthus cruentus), heat‐moisture treated (HMT) potato and heat‐moisture treated amaranth, cross‐linked potato and cross‐linked amaranth, native potato and heat‐moisture treated amaranth, and heat‐moisture treated potato, and native amaranth were tested at different ratios. Two peaks were noticed in the pasting curves when large differences of swelling factor and amylose leaching existed between individual components in the mixture. It seems that amylose leaching from one starch in a mixture may affect the swelling and much of the granular break down of the other. The mixtures showed stabilities in hot pastes that were higher than the less stable components in a mixture. Some mixtures such as HMT potato and native amaranth showed very specific nonadditive pasting behavior. Mixing 10% of native amaranth to HMT potato starch caused a large reduction of peak viscosity and cold paste viscosity, resulting in a very soft gel. In the differential scanning calorimeter, each component of a mixture gelatinized independently, showing two peaks corresponding to the individual components. When transition temperatures of both components were similar in DSC, the result was a single endotherm. Dramatic changes of pasting and subsequent gel properties resulted when thermal transition of the two components occurred in the same temperature range. Retrogradation enthalpies as measured by DSC were between the two individual components in all tested mixtures.     

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.     

Effects of Granular Structures on the Pasting Behaviors of Starches

Japonica (Tainung 67 [TNu67]) and waxy (Taichung 70 [TCW70]) rice, normal and waxy corn, and cross-linked waxy rice and corn starches were used in an investigation of the influence of the granular structure on the pasting behavior of starch, using small amplitude oscillatory rheometry. Both normal corn and normal rice (TNu67) starches had the highest storage moduli (G′), followed by their cross-linked versions; native waxy corn and rice starches had the lowest. Native waxy starches showed paste characteristics (G′ < 500 Pa; tan δ > 0.2) at concentrations of up to 35%. However, cross-linked waxy starches exhibited gel behavior at 10% concentration (cross-linked TCW70) or higher (cross-linked waxy corn starch). The degrees of swelling power were in the order: TCW70 > native waxy corn > TNu67 ≅ cross-linked TCW70 ≅ normal corn ≅ cross-linked waxy corn starches. Solubilities were in the order: normal corn > TNu67 > native waxy > cross-linked waxy starches. The addition of 2% purified amylose from indica rice (Kaohsiung Sen 7) did not induce gelation of waxy corn starch. Swelling powers of normal corn, TNu67, and crosslinked waxy starches were similar, but normal corn and TNu67 had much higher G′ value. Such results implied that the formation of gel structure was governed by the rigidity of swollen granules and that the hot-water soluble component could strengthen the elasticity of the starch gel or paste.     

Impact of Proteins on Pasting and Cooking Properties of Nonparboiled and Parboiled Rice

The role of proteins in the pasting and cooking properties of non‐parboiled (npb) and parboiled (pb) rice was tested by means of a reducing agent dithiothreitol (DTT) and a protease (trypsin). DTT increased the swelling power and carbohydrate leaching of flour from npb rice flour but decreased its amylose leaching. Although DTT slightly increased the Rapid Visco Analyser (RVA) viscosity at the initial stages of the pasting process, it decreased RVA viscosity in the further phases of the experiment. Preincubation of flour with a trypsin decreased RVA viscosity along the whole temperature profile. Addition of DTT to the cooking water decreased water absorption and rice hardness and increased leaching of solids during cooking and stickiness of the cooked npb rice. Addition of DTT to the cooking water of flour from pb rice increased swelling power, carbohydrate leaching, and amylose leaching. Addition of DTT also increased RVA viscosity. Preincubation with trypsin had a similar effect but the changes were less pronounced. Addition of DTT increased stickiness of cooked pb rice and increased water absorption and leaching of solids during cooking. Taken together, the results provide evidence for the existence of a protein barrier affecting starch swelling, rheological, and cooking properties of both npb and pb rice.     

Changes in Retrogradation Properties of Rice Starches with Amylose Content and Molecular Properties

The increases in storage modulus (G′), retrogradation enthalpy change (ΔH) and ΔH‐related Avrami kinetic parameters of gelatinized rice starch dispersions at 25% (w/w) were investigated with respect to storage period, amylose content (AC), and molecular properties. Three high‐AC and five low‐AC rice cultivars were compared for understanding the multiple influences of AC and molecular properties involved. After refining the results of correlation analysis, the G′ of just‐cooled samples changed positively, mainly with AC and additionally with the average chain length of amylose (CL_AM) and the weight ratio of extra‐long plus long chains to short chains of amylopectin (AP) (r_APchain). The developed ΔH on short‐term storage (10 days) elevated with increasing AC and CL_AM and decreasing degree of polymerization of AP (DP_AP), but after long‐term aging for one to three months with increasing r_APchain, especially for the low‐AC cultivars examined. Greater Avrami rate constants for retrogradation could be attributed to the combination of a lower DP_AP and r_APchain or AP chain length and a greater CL_AM. The polynomials using these critical factors to describe the retrogradation parameters were elucidated and could account for 85–99.6% of data deviations.     

Key Proteins Causing Changes in Pasting Properties of Rice During Aging

Key components that cause changes in pasting properties of rice during storage aging were investigated in this work. The main nonstarch components in rice were sequentially removed from fresh and aged rice, the aging effect of the component was separated, and thus the aging contribution rate of the component (CACR) on rice aging could be deduced. The results showed that the largest contributor to rice aging was albumin with a CACR of 65%, followed by globulin and prolamin with the CACRs of 38 and 14%, respectively, and the CACR of glutelin was small (1%). In contrast, the CACRs of fat and crude starch were –7 and –11%, respectively. These findings suggest that albumin and globulin are predominantly responsible for changes in pasting properties of rice during storage aging. This conclusion directs future researchers to the changes occurring in albumin and globulin for disclosing the mechanisms of rice aging.     

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.     

Physicochemical Properties of Sonicated Mung Bean,Potato, and Rice Starches

Mung bean, potato, and rice starch solutions (5%, w/w) were sonicated for up to 5 min after heating, and their physicochemical properties were investigated. Alkaline viscosities, including the apparent and inherent viscosities of starches, decreased. The residues of the swollen starch granules after pasting and centrifugation were also reduced prominently by sonication. Average degree of polymerization did not change with sonication. The starch paste became more transparent, and the hot paste viscosity measured at 70°C decreased remarkably. Results indicate that changes in the physicochemical properties of starch were induced by the disruption of swollen granules rather than the breakage of glucosidic linkages with sonication.     

Properties of Starches from Several Low‐Amylose Rice Cultivars

The starch properties of five low‐amylose rice cultivars, Yawarakomachi, Soft 158, Hanabusa, Aya, and Snow Pearl, were compared with those of two normal amylose rice cultivars, Nipponbare and Hinohikari. There were no large differences in the distributions of the amylopectin chain length determined by high‐performance anion‐exchange chromatography, and the starch gelatinization properties determined by differential scanning calorimetry, between normal and low‐amylose rice cultivars. Results obtained using rapid viscosity analysis indicated that low‐amylose rice starches had lower peak viscosity, breakdown, and setback values than normal amylose rice starches. Starch granules from low‐amylose rice cultivars had a higher susceptibility to glucoamylase than those from normal amylose rice cultivars. The results of this study showed some differences between normal and low‐amylose rice starches in pasting properties and enzymatic digestibility.     

Effect of Alkaline‐Soluble Proteins on Pasting Properties of Nonwaxy Rice Flour

The pasting properties of rice flours and reconstituted rice flours from mixing a common starch with proteins extracted from different rice cultivars at different total protein content levels were studied. Results showed that not only the total protein content but also the protein composition had an effect on the pasting properties of the rice flours. Among the different strands of rice proteins, globulin had the strongest influence on the pasting properties, followed by glutelin, whereas prolamin had the least influence. At the subunit level of the proteins, proteins with a molecular weight of 17,000, most likely from globulin, had the strongest effect on the peak viscosity of the rice flour, followed by those of 33,000. In comparison with that of the rice starch, the influence of proteins in rice was limited. The effect of interactions between the rice proteins and the starch, such as the role of starch‐granule‐associated proteins, was not isolated in this study, and further investigation is required to quantify this effect.     

Molecular and Gelatinization Properties of Rice Starches from IR24 and Sinandomeng Cultivars

The differences in pasting properties involving gelatinization and retrogradation of rice starches from IR24 and Sinandomeng cultivars during heating‐cooling processes were investigated using a Rapid Visco Analyser (RVA)and a dynamic rheometer. The results were discussed in relation to the molecular structure, actual amylose content (AC), and concentration of the starches. Generally, both starches possessed a comparable AC (≈11 wt%), amylose average chain length (CL), iodine absorption properties, and dynamic rheological parameters on heating to 95°C at 10 wt% and on cooling to 10°C at higher concentrations. In contrast to Sinandomeng, IR24 amylose had a greater proportion of high molecular weight species and number‐average degree of polymerization (DP_n). IR24 amylopectin possessed a lower DP_n and greater CL, exterior CL (ECL), and interior CL (ICL). Comparing the results of RVA analysis and dynamic rheology, the gelatinization properties and higher retrogradation tendencies of IR24 starch can be related to the structural properties and depend on starch concentration. In addition, the exponent n of starch concentration for storage moduli at 25°C (G′₂₅ ∝ Cⁿ) increased linearly with increasing AC.