Structure‐Functionality Changes in Starch Following Rough Rice Storage

The molecular‐level features of starch in relation to the changes in rice functionality during storage are not yet fully elucidated. This work investigated the effects of rough rice storage conditions on starch fine structures and physicochemical properties. Dried rough rice samples (medium‐grain Bengal and long‐grain Cypress) were stored at 4, 21, and 38°C in temperature‐controlled chambers and then periodically removed and evaluated after 1, 3, 5, 7, and 9 months. Flour (powdered head rice) and starch (extracted from head rice by alkali steeping) samples were evaluated for pasting and thermal properties. High‐performance size‐exclusion chromatography and high‐performance anion exchange chromatography were used to characterize starch molecular size and amylopectin chain‐length distribution, respectively. Significant changes in starch fine structure were observed primarily on the 38°C lots, and to some extent on the 21°C lots. The decreased amylose: amylopectin ratio, shortened amylopectin average chain length, and the shift in chain‐length distribution to shorter branch chains were implicative of molecular‐level starch degradation. The flour and starch samples showed inconsistent trends in pasting and thermal properties, thus suggesting the role of not only starch but also its interaction with non‐starch components in rice aging.     

Crystallinity and Rheological Properties of Pregelatinized Rice Starches Differing in Amylose Content

Three rice starches with different amylose contents (Glutinous: 1.4%, Jasmine: 15.0% and Chiang: 20.2%) were pregelatinized in a double drum dryer at 110, 117 and 123°C. Starch crystallinity was determined by X‐ray diffractometry and Fourier transform infrared (FTIR) spectrometry. Rheological properties were assessed by a Rapid Visco Analyser (RVA) and rheometer. Pregelatinized starches obtained from Glutinous (PGS) and Jasmine rice (PJS) gave an RVA pasting profile with cold peak viscosity. At drum temperature 110°C, PGS and PJS showed X‐ray patterns that were indicative of amorphous structures. However, pregelatinized Chiang rice starch (PCS) exhibited RVA hot peak viscosity and the presence of an amylose‐lipid complex with remaining granule structure. The PCS had a lower water absorption index (WAI) and water solubility index (WSI) than PJS and PGS. After pregelatinization at increased drum temperature (117, 123°C), the PGS had a lower WAI, whereas PCS showed an opposite trend indicating lower degree of granule disruption. In addition, the cold peak viscosity of PGS and PJS decreased with increasing drum temperature. For all drum temperatures, the apparent viscosity at 25°C for PGS and PJS decreased with increasing shear rate, indicating shear‐thinning behavior.     

Morphology and Microstructure of Maize Starches with Different Amylose/Amylopectin Content

The morphology and microstructure of maize starches with different amylose/amylopectin ratios (waxy: 0/100; normal maize: 23/77; Gelose 50: 50/50; Gelose 80: 80/20) were studied by microscopy with ordinary and polarized light, scanning electron microscopy (SEM) and X‐ray diffraction (XRD). Generally, the granules of the amylopectin‐rich starches were more regular in shape than those of the amylose‐rich starches, but the surfaces of the amylose‐rich starches were smoother than those of the amylopectin‐rich starches. The birefringence and particle size of the granules were waxy > normal maize > G50 > G80, which also corresponds with the trend of molecular weight. Waxy and normal maize starches showed typical A‐type patterns, while G50 and G80 show B‐type patterns. Crystallinity increases with increasing the amylopectin content.     

Aqueous Leaching of Derivatized Amylose from Hydroxypropylated Common Corn Starch Granules

Aqueous leaching of hydroxypropylated common corn starches at different times and temperatures was conducted. Results indicated that the greater the modification the easier it was for the amylose to leach out and that the preference for leaching of derivatized amylose decreased as MS of the whole starch increased.     

Comparison Between Granular Starch Hydrolyzing Enzyme and Conventional Enzymes for Ethanol Production from Maize Starch with Different Amylose: Amylopectin Ratios

The effect of enzyme treatments (granular starch hydrolyzing and conventional enzymes) and different amylose: amylopectin ratios of maize starch on ethanol production was evaluated. For starch treatments, amylose: amylopectin ratios were prepared by mixing commercially available Hylon VII (70% amylose and 30% amylopectin) and Amioca (˜100% amylopectin) starches. For maize treatments, waxy, high amylose and regular dent hybrids were used to represent varying amylose: amylopectin ratios. All hydrolyses followed by fermentations were conducted at 15% solids content. Differences were observed in ethanol yields among granular starch hydrolyzing and conventional enzymes. Differences also were observed in ethanol yields between different amylose: amylopectin ratios for pure starch and maize samples. For starch samples, final ethanol concentrations varied from 2.2 to 9.1% (v/v) for fermentation with granular starch hydrolyzing enzyme and from 6.7 to 9.3% (v/v) for conventional enzymes. Higher ethanol concentrations were observed for Amioca starch for both enzymes. For maize samples, final ethanol concentrations were highest for waxy maize for both granular starch hydrolyzing (8.2%, v/v) and conventional (8.2%, v/v) enzymes. Lowest ethanol concentrations were observed for high‐amylose maize samples for granular starch hydrolyzing (6.3%, v/v) and conventional (5.2%, v/v) enzymes.     

Analysis of Genotypic Diversity in the Starch Physicochemical Properties of Nonwaxy Rice: Apparent Amylose Content,Pasting Viscosity and Gel Texture

A total of 499 non‐waxy rice lines including 172 landraces (the landrace set) and 327 cultivars and breeding lines (the breeding line set) were used to study the genetic diversity of starch physicochemical properties, and the differences between the landrace set and the breeding line set were compared. All the rice lines were planted in the same season and at the same location in Hainan province. Wide diversities of starch physicochemical properties were found, e.g. apparent amylose content ranged from 7.9% to 33% in normal rice and up to 39.8% in an amylose extender mutant; peak viscosity ranged from 90.1 to 305.4 RVU, hot paste viscosity from 77.5 to 248.1 RVU, and cold paste viscosity from 111.4 to 412.6 RVU; gel hardness ranged from 9.4 to 61.1 g. The breeding line set had a wider range of physicochemical properties than the landrace set with a rare exception in gel hardness. The mean values of nearly all the parameters showed significant differences between the two sets of rice except for the setback ratio. The adhesiveness and cohesiveness of landrace starches were significantly lower than those of the breeding lines whereas the other parameters of the landrace set were higher than those of the breeding line set. Analysis of correlation among these parameters indicated that most of the traits were significantly correlated. The wide range of physicochemical properties among non‐waxy rice lines allows breeders to obtain breeding lines with desirable grain quality and food processors to select unique rice materials for specialty food processing, in addition to the applications in other processing industries.     

The Influences of Chain Length of Amylopectin on Resistant Starch in Rice (Oryza sativa L.)

Amylopectin is the principle component of starch. To elucidate the relationships between amylopectin and resistant starch content, six rice mutants with altered fine structure of amylopectin were selected for comparative studies with the primary wild type and two types of amylose‐extender (ae) mutants. Significant differences in resistant starch content were observed among mutants with similarity or differences in amylose levels. Mutants high in resistant starch had significantly increased proportions of short amylopectin chains with DP≤12, decreased levels of intermediate chains with size of 13≤DP≤36, and decreased fractions of long chains with DP≥37. Additionally, there was a mutant different to ae, which was characterized by an increased level of short chains with 8≤DP≤12 and 13≤DP≤24, and a decreased proportion of long chains with DP≥37. The increased contents of short chains with 8≤DP≤12 and decreased of intermediate and long chains with 24≤DP were clearly associated with the increase of resistant starch in rice.     

Characterization of Physical Properties of Flour and Starch Obtained from Gamma‐Irradiated White Rice

Physical and structural characteristics of rice flour and starch obtained from gamma‐irradiated white rice were determined. Pasting viscosities of the rice flour and starch, analyzed by using a Rapid Visco Analyser, decreased continuously with the increase in irradiation dosage. Differential scanning calorimetry showed that gelatinization onset, peak and conclusion temperatures of rice flour and starch changed slightly but the enthalpy change decreased significantly with increase of irradiation dosage. All irradiated starch displayed an A‐type X‐ray diffraction pattern like the native starch. Gel permeation chromatography showed that the blue value ratio of the first peak (amylopectin) to the second one (amylose) decreased with the increase of the irradiation dosage. The weight‐average molecular weight (M_w) and gyration radius (R_z) of amylopectin analyzed by using HPSEC‐MALLS‐RI (high‐performance size‐exclusion chromatography equipped with multiangle laser‐light scattering and refractive index detector) decreased gradually from 1.48×10⁹ (M_w) and 384.1 nm (R_z) of native rice starch to 2.36×10⁸ (M_w) and 236.8 nm of 9 kGy‐irradiated starch. The branch chain‐length distribution of amylopectins determined by HPAEC‐ENZ‐PAD (high‐performance anion‐exchange chromatography with amyloglucosidase post‐column on‐line reactor and pulsed amperometric detector) showed that gamma irradiation had no significant effect on the amylopectin branch chains with 13≤DP≤24 and 37≤DP, but produced more branch chains with 6≤DP≤12 when the irradiation dosage was less than 9 kGy. It might be deduced that gamma irradiation caused the breakage of the amylopectin chains at the amorphous regions, but had little effects on the crystalline regions of starch granules, especially at low dosage irradiation.     

甘薯淀粉糊的流变特性

通过考察甘薯淀粉糊在不同甘薯淀粉浓度和不同温度下的流变特性,结果表明甘薯淀粉糊是典型的非牛顿型、剪切变稀的和触变性流体,温度越高,浓度越低,甘薯淀粉糊的滞后性越小;同时用幂律方程和Cross方程来描述糊的流变特性,发现Cross方程比幂律方程拟合精度更高。而浓度很低的情况下(如2%),甘薯淀粉糊的触变特性与其他浓度不同,表现为下行线在上行线之上,更适合用Herschel-Bulkley方程来描述它的流变行为。甘薯淀粉糊的动态流变行为则表现为在将开始糊化时,储能模量G’、损耗模量G"和tanδ都急剧上升,在到达糊化顶峰时急剧下降,而在降温过程中G’和G"都呈上升趋势,tanδ则是在100～50℃时下降,50～20℃时上升。     

Rheological Properties of Rice Starch Dispersions in Dimethyl Sulfoxide

The steady and dynamic shear rheological properties of rice starches dispersed in dimethyl sulfoxide (DMSO) solution (90% DMSO‐10% water) were evaluated at various concentrations (7, 8, 9 and 10%, w/w). Rice starch dispersions in DMSO solution at 25°C showed a shear‐thinning flow behavior (n=0.44–0.60) and their consistency index (K) and apparent viscosity (η_a,100) increased with the increase in concentration. The apparent viscosity over the temperature range of 25–70°C obeyed the Arrhenius temperature relationship, indicating that the magnitudes of activation energy (E_a) were in the range of 11.7–12.7 kJ/mol. The Carreau model provided better fit on the shear rate‐apparent viscosity data than the Cross model. Dynamic frequency sweep test showed that both storage modulus (G′) and loss modulus (G′′) of rice starch dispersions increased with the increase in concentration. G′′ showed a higher dependence on frequency (ω) compared to G′ due to the higher G′′ slopes. All rice starch dispersions showed the plateau of G′ at high frequencies. Intrinsic viscosity of rice starch dispersions in DMSO was 104.1 mL/g.     

表观直链淀粉含量对小麦淀粉凝胶流变特性影响的研究

探讨表观直链淀粉在小麦淀粉凝胶的流变学特性中的作用,寻找表观直链淀粉含量与流变特性参数间的相关性。运用动态流变仪对9种不同品种小麦淀粉的糊化和短期回生进行分析,找出流变特性参数,并运用SPSS分析其相关性。在表观直链淀粉含量相差较大的情况下,结合糯小麦淀粉来考察,直链淀粉对于升温、降温、时间扫描和频率扫描等过程的流变特性有着重要的影响;当直链含量相差较小时,在8个普通小麦品种间,直链淀粉对与降温过程和凝胶形成强度有着决定性的影响。在整个短期回生过程中,表观直链淀粉含量直接决定凝胶的流变特性,但是在表征流变特性上有一定的局限性。     

Analysis of Variations in the Amylose Content of Grains Located at Different Positions in the Rice Panicle and the Effect of Milling

The results of the presented study indicated that the amylose content (AC) of individual rice kernels varied among grains in the same panicle and even in outer and inner layers of the same grain. The differences among the grains in panicles were 19.1% in the Indica variety “Zhenong 5” and 22.8% in the Japonica variety “Zhehu 9827”. The amylose content of the grains in the upper position or the first branches of panicles and of the early flowering grains or heavier grains was higher than that of others. Amylose content increases by 1.36% in Japonica rice variety “Zhehu 9827” and 1.92% in Indica rice variety “Zhenong 5”, when the degree of milling increases by 10%. The tendency of changes in AC was the same for grains of the Japonica and the Indica rice variety. Furthermore, for analyzing AC the grains in a panicle should carefully be selected. Errors coming from sampling could be decreased by using a multiplicity of grains rather than single‐grain samples.     

Rheological and Thermal Properties of Extruded Mixtures of Rice Starch and Isolated Soy Protein

Many foods gain new mechanical, thermal and textural properties after being processed due to interactions between carbohydrates and proteins. This effect is characteristic for each foodstuff. The properties of extruded isolated soy protein (ISP) and rice starch were studied considering the following extrusion variables: starch proportion with respect to ISP (0–100%), pH (3–9), moisture content (20–30%) and temperature (140–180ºC). The following characteristics were measured: Water absorption index (WAI), water solubility index (WSI), glass transition temperature (T_g), melting temperature (T_m), viscosity at 90ºC and at 50ºC, storage (G′), loss modulus (G′′) and tan δ. The results indicate that the extruded starch exhibits higher WAI and WSI values than untreated starch. For extruded ISP these values are much lower than for untreated ISP. Extrudates with higher starch proportion had higher T_g and T_m values; pH has a significant effect (p<0.05), at pH 3 higher T_g values were observed, and at pH 9 higher values of T_m. The highest viscosities at 90ºC and 50ºC were observed for extrudates with a higher starch proportion and pH 9. Extruded mixtures showed a more elastic than viscous behavior and an extruded 1:1 blend of starch‐ISP exhibited the behavior of a viscous liquid.     

不同添加物质对羟丙基木薯淀粉流变特性的影响

淀粉糊流变特性是影响淀粉类食品加工品质的主要因素。本文利用C-LTD80 RheolabQC流变仪测定了不同添加物质对羟丙基木薯淀粉流变特性的影响,结果表明：添加不同的物质均未改变羟丙基木薯淀粉糊的流体类型,各流变参数经Herschel-Bulkley模型进行拟合,拟合系数接近1。单甘酯、食盐、柠檬酸使羟丙基木薯淀粉糊的剪切应力不同程度降低,黏稠系数K减小,流变特性指数n增加;蔗糖酯、酪朊酸钠、黄原胶、CMC、瓜尔豆胶、蔗糖使羟丙基木薯淀粉糊的剪切应力明显提高,黏稠系数K增加,流变特性指数n减小。该结果对羟丙基木薯淀粉类食品深加工开发具有较大的指导意义。     

不同添加物对羟丙基木薯淀粉流变特性的影响

淀粉糊流变特性是影响淀粉类食品加工品质的主要因素。利用流变仪测定了不同添加物质对羟丙基木薯淀粉流变特性的影响,结果表明:添加不同的物质均未改变羟丙基木薯淀粉糊的流体类型,各流变参数经Herschel-Bulkley模型进行拟合,拟合系数接近1。单甘酯、食盐、柠檬酸使羟丙基木薯淀粉糊的剪切应力不同程度降低,黏稠系数减小,流变特性指数增加;蔗糖酯、酪朊酸钠、黄原胶、CMC、瓜尔豆胶、蔗糖使羟丙基木薯淀粉糊的剪切应力明显提高,黏稠系数增加,流变特性指数减小。     

Effect of Molar Substitution on Rheological Properties of Hydroxypropylated Rice Starch Pastes

The steady and dynamic shear rheological properties of hydroxypropylated rice starch pastes (5%, w/w) were evaluated at different molar substitution (MS, 0.030‐0.142). The swelling power (35.5‐52.8 g/g) and solubility (8.19‐10.7%) values of the hydroxyproylated rice starches were higher than those of native rice starch (26.6 g/g and 7.78%) and increased with an increase in MS. The hydroxypropylated starch pastes at 25°C showed a pronounced shear‐thinning behavior (n = 0.33‐0.40) with Casson yield stress (σ_oc = 15.9‐31.7 Pa). The consistency index (K) and yield stress (σ_oc) values of the hydroxypropylated starch pastes were lower than those of the native starch, and increased progressively with an increase in MS. The apparent viscosity (η_a,500) obeyed the Arrhenius temperature relationship over the temperature range of 10‐55°C; the activation energies (E_a) of the hydroxypropylated starch pastes were in the range of 14.8‐18.5 kJ/mol, i.e. higher than that (14.1 kJ/mol) of the native starch. Storage (G′) and loss moduli (G′′) of hydroxypropylated starch pastes increased with an increase in MS, while tan δ (G′′/G′) values decreased, indicating that G′ rose more strongly than G′′ with increased MS.     

不同链淀粉含量改性高链淀粉磁性微球制备及其结构的研究

本文研究了以链淀粉含量50％和70％的交联高链玉米淀粉为原料，利用氧化磁化工艺引入磁性粒子，对磁性淀粉中磁性粒子的生成、大小、分布和磁化效果进行了研究；利用喷雾干燥技术，制备功能性磁性药物微球，并对其结构作了详细研究。结果表明，不同链淀粉含量交联高链玉米淀粉在氧化磁化后，形成的磁性粒子可达到纳米级，颗粒形状其本不变，但表面结构都发生很大变化。磁化后淀粉颗粒表面出现空隙，且空隙直径远远大于形成的磁性粒子的直径，能很好地包埋磁性粒子。喷雾干燥制备的功能性磁性微球其粒径可达微米级，表面结构致密。     

湿热处理对不同直链淀粉含量大米淀粉多尺度结构和消化性能的影响

本文采用体外模拟法和现代化分析技术测定及考察了不同直链含量的大米淀粉经湿热处理后其多尺度结构和消化性能的变化情况,明晰了湿热处理后大米淀粉多尺度结构和消化性能的关系。结果表明,湿热处理体系中热能和水分子的协同作用,一方面对大米淀粉颗粒具有一定的破坏作用,使得其平均相对分子量降低、双螺旋含量降低、相对结晶度降低、半结晶片层的有序化程度降低,M_w2×10~7的高分子量片段区域逐渐向M_w1×10~6拓宽,且直链含量较低的大米淀粉破坏程度更为显著。另一方面,湿热处理促进了降解后的大米淀粉分子链自由运动,使淀粉分子发生重排和取向,形成新的单螺旋结构,有利于大米淀粉慢消化和抗消化性能的提高,且直链淀粉含量较高的大米淀粉提高的越明显。研究结果为加工淀粉及淀粉基营养健康食品提供了基础数据及理论支撑。     

Effect of Heat‐Moisture Treatment on Structural and Thermal Properties of Rice Starches Differing in Amylose Content

Starches from glutinous rice (1.4% amylose), Jasmine rice (15.0% amylose) and Chiang rice (20.2% amylose) were exposed to heat‐moisture treatment (HMT) at 100 °C for 16 h and at different moisture levels (18, 21, 24 and 27%). The effect of heat‐moisture treatment on structural and thermal properties of these three rice starches was investigated. The HMT did not change the size, shape and surface characteristics of rice starch granules. The A‐type crystalline pattern of rice starches remained unchanged after HMT. The relative crystallinity (RC) and the ratio of short‐range molecular order to amorphous (RSA) of heat‐moisture treated glutinous and Jasmine rice starches decreased with increasing moisture level of the treatments. In contrast, the RC of the treated Chiang rice starch remained practically unchanged. A peak of crystalline V‐amylose‐lipid complexes was clearly presented in all treated Chiang rice starches. The peak became progressively stronger with increasing moisture level of the treatment. Differential scanning calorimetry (DSC) of all treated rice starches showed a shift of the gelatinization temperature to higher values. Increasing moisture level of the treatments increased the onset gelatinization temperature (T_o) but decreased the gelatinization enthalpy (ΔH) of rice starches. A broad gelatinization temperature range (T_c‐T_o) with a biphasic endotherm was found for all treated Chiang rice starches and Jasmine rice starch after HMT₂₇ (HMT at 27% moisture level). Additionally the (T_c‐T_o) of treated Chiang rice starches increased linearly with increasing moisture level of the treatments.