Structure-retrogradation relationship of rice starch in purified starches and cooked rice grains: a statistical investigation

Amylose content and amylopectin chain length distribution, the two most commonly used structural parameters of starch, have significant effects on starch retrogradation. In the present work, starches were separated and purified from 18 rice cultivars. The amylopectin was purified from each starch. Amylopectin chain length distribution was analyzed by high-performance size-exclusion chromatography after debranched using isoamylase. The blue value was used to measure the amylose content before and after the defatting of starch. The amount of amylose associated with lipid was calculated. Pulsed nuclear magnetic resonance was used to follow the retrogradation of starch both in cooked rice grains and in the purified form. The Avrami equation was employed to describe the retrogradation kinetics of rice starch. To look into the relationship between the starch structure and retrogradation behavior, the structural parameters were correlated with retrogradation kinetics parameters using both Pearson and partial correlations. The results indicated the following: first, the retrogradation behavior of rice starch remains similar in both the purified form and cooked rice grains; second, the peak value of amylopectin short-chain length has a significant positive relationship with the amylopectin crystallization rate constant k; third, the amylose content after defatting has a significant positive relationship with the parameter k and a negative relationship with the Avrami exponent n; and fourth, the amount of amylose associated with lipid has a negative relationship with the parameter k.     

纳米级大米淀粉的制备及性质

为了探索纳米淀粉的新型制备方法及可行性,采用超高压均质和超微粉碎制备了纳米级大米淀粉,并研究了其颗粒粒度、吸湿性能、溶解度和膨胀率等理化性质.结果表明,超高压均质和超微粉碎能明显减小大米淀粉的颗粒粒度,成功制得纳米级大米淀粉,且随着大米淀粉粒度的减小,其吸湿性能、溶解度和膨胀率明显增加,说明纳米级大米淀粉的水合能力增强,体现了纳米级大米淀粉的表面效应和小尺寸效应.     

Thermal and physicochemical properties of rice grain, flour and starch

Three types of rices, namely, Thailand rice (Indica), Nipponbare (Japonica), and Himenomochi (Japonica waxy), in grain, flour, and starch forms have been studied for their thermal and physicochemical properties. In grain form, Indica was slender and Japonica rices were bold and thick. Indica had the highest protein and amylose equivalent. Protein contents in isolated starches varied from 0.2 to 0.9%. Cooked Indica grain was hardest and waxy rice was softest; stickiness was highest in Japonica rice. Glass transition temperature (T(g)) was highest in Indica rice flour (approximately 222 degrees C) and almost the same in Japonica rice flours. Melting point was highest for Japonica (approximately 264 degrees C) and almost the same for Japonica waxy and Indica rice flours. T(g) values of starches were almost the same in Indica and Japonica waxy (approximately 237 degrees C); defatting caused reduction in this property in all of the starches. Highest melting point was shown by Indica starch (approximately 276 degrees C) and was almost the same for the other two starches. Protein and fats play a critical role in glass transition and melting points of rice flours and their respective starches. Viscosities of the cooked pastes of flour and starch during cooking in an RVA instrument and their gel and other properties have been discussed.     

Comparison of physicochemical properties and starch structure of red rice and cultivated rice

Sixteen red rice accessions from the southern United States were studied for their physical, milling, pasting, and thermal properties, chemical composition, and starch fine structure relative to cultivated medium- and long-grain rice varieties. All red rice samples were medium-grain, but their physicochemical properties were different from those of Bengal, a cultivated medium-grain rice. Their apparent amylose and crude protein contents were generally higher, and their amylopectin structure consisted of a higher percentage of the shorter branch chains (DP6-24) and a lower percentage of the longer branch chains (DP25-65). Red rice starch pasting and thermal properties were similar to those of Wells, a long-grain rice cultivar. The red rice samples can be classified into two major clusters according to their kernel properties by hierarchical cluster analysis: one cluster with more resemblance to Wells and another cluster with more resemblance to Bengal. Starch structure and kernel physicochemical properties may offer an alternative way of classifying red rice in addition to phenotypic and genetic indices.     

Fine structures and physicochemical properties of starches from chalky and translucent rice kernels

This work compared the molecular structures and physicochemical properties of starches obtained from chalky and translucent kernels of six rice cultivars. Starch samples were prepared according to a modified alkali steeping method. Crystallinity, pasting characteristics, and thermal properties were studied by X-ray diffraction, rapid viscosity analysis, and differential scanning calorimetry, respectively. Starch molecular size fractions (amylopectin, amylose, and intermediate material) were estimated by high-performance size exclusion chromatography, and the chain length profiles of isoamylase-debranched amylopectin were evaluated by high-performance anion-exchange chromatography with pulsed amperometric detection. Starches from chalky kernels contained less amylose (more amylopectin) and more short branch-chain amylopectin (less long branch-chain amylopectin) compared with the translucent kernel starches. Differences in starch structural features significantly correlated with observed variation in grain translucency, starch X-ray diffraction patterns, thermal properties, and pasting characteristics. Starch synthesis in chalky kernels may slightly favor glucan chain branching over chain elongation.     

Far-infrared radiation increases the antioxidant properties of rice hull extract in cooked turkey meat

To determine the antioxidant effects of rice hull extract exposed to far-infrared radiation, the added extracts were compared with sesamol in cooked turkey breast. Rice hull extract showed antioxidant properties in cooked turkey breast by reducing lipid oxidation and volatile aldehydes. Far-infrared radiation increased significantly the antioxidant activities of rice hull extracts. Rice hull extract irradiated by far-infrared (FRH) had lower TBARS values and fewer volatile aldehydes (hexanal, pentanal, and propanal) than a non-irradiated extract (IRH) during the 3 days of aerobic storage. Addition of FRH at 0.2% (w/w) in turkey meat could reduce the amounts of volatile hexanal to 18-47% of the control during the storage. However, the antioxidant activities of rice hull extracts did not last as long as those of pure sesamol due to the relatively low concentration of phenolics, and the extracts had some peculiar odor. Addition of rice hull extracts also increased both a and b values of the samples due to its brown intensity.     

槲皮素对挤压大米淀粉结构及功能特性的影响

为改善挤压大米淀粉的功能特性,以米粉（rice, R）为主要原料,探究了不同槲皮素（quercetin, Q）添加量（0 ～ 10%）在挤压场下对米粉中淀粉的水溶性、吸水性、糊化特性等功能特性的影响。在此基础上,借助扫描电子显微镜（scanning electron microscopy）、X-射线衍射、红外光谱、及紫外可见光分光光度计揭示了Q在挤压场下对淀粉结构的演变规律。试验结果表明：当Q添加量为4%时,样品的吸水指数,碘结合能力均达到了最大值,且自由水弛豫时间提前;挤压体系中Q与淀粉通过氢键结合,颗粒结构变得更加立体、紧凑。与挤压米粉相比,槲皮素的添加延缓了淀粉的回生且提高了淀粉的热稳定性。根据以上结果可知,挤压体系中Q与大米淀粉复合,促进了淀粉分子链重排,进而改变淀粉的结构及功能特性,该研究可为开发抗回生的挤压大米淀粉基产品提供理论依据。     

拔节期追氮对春播和秋播糯玉米淀粉胶凝和回生特性的影响

以垦粘1号、苏玉糯1号和苏玉糯5号为材料,研究了拔节期追氮量(N 01、50和300 kg/hm2)对春播和秋播糯玉米淀粉胶凝和回生特性的影响,试验于扬州大学实验农牧场进行。结果看出,播期、品种和拔节期追氮量单因素及其互作对淀粉胶凝和回生主要特征值存在显著影响。糯玉米淀粉胶凝和回生特征值在拔节期追氮150 kg/hm2时和秋播条件下较优,即原淀粉具有较低的峰值温度、较高的热焓值,回生淀粉具有较低的回生值,且以垦粘1号表现较好。糯玉米淀粉胶凝和回生特征值之间存在一定的相关性。回生值分别与回生淀粉的热焓值、原淀粉的终值温度显著正相关,相关系数分别为0.82(P0.01)和0.47(P0.05);原淀粉的热焓值与峰值指数显著正相关,相关系数为0.53(P0.05),与原淀粉峰值温度、回生淀粉的终值温度显著负相关,相关系数分别为-0.53(P0.05)和-0.52(P0.05);回生淀粉的热焓值分别与回生淀粉起始温度、终值指数显著正相关,相关系数分别为0.46(P0.05)和0.66(P0.01)。综合考虑淀粉胶凝和回生特性在不同处理下的变化趋势,以秋播糯玉米淀粉在拔节期追N 150 kg/hm2处理下较优。     

Enzymatic synthesis and properties of highly branched rice starch amylose and amylopectin cluster

We enzymatically modified rice starch to produce highly branched amylopectin and amylose and analyzed the resulting structural changes. To prepare the highly branched amylopectin cluster (HBAPC), we first treated waxy rice starch with Thermus scotoductus alpha-glucanotransferase (TSalphaGT), followed by treatment with Bacillus stearothermophilus maltogenic amylase (BSMA). Highly branched amylose (HBA) was prepared by incubating amylose with Bacillus subtilis 168 branching enzyme (BBE) and subsequently treating it with BSMA. The molecular weight of TSalphaGT-treated waxy rice starch was reduced from 8.9 x 10(8) to 1.2 x 10(5) Da, indicating that the alpha-1,4 glucosidic linkage of the segment between amylopectin clusters was hydrolyzed. Analysis of the amylopectin cluster side chains revealed that a rearrangement in the side-chain length distribution occurred. Furthermore, HBAPC and HBA were found to contain significant numbers of branched maltooligosaccharide side chains. In short, amylopectin molecules of waxy rice starch were hydrolyzed into amylopectin clusters by TSalphaGT in the enzymatic modification process, and then further branched by transglycosylation using BSMA. HBAPC and HBA showed higher water solubility and stability against retrogradation than amylopectin clusters or branched amylose. The hydrolysis rates of HBAPC and HBA by glucoamylase and alpha-amylase greatly decreased. The k cat/ K m value of glucoamylase acting on the amylopectin cluster was 45.94 s(-1)(mg/mL)(-1) and that for glucoamylase acting on HBAPC was 11.10 s(-1)(mg/mL)(-1), indicating that HBAPC was 4-fold less susceptible to glucoamylase. The k cat/ K m value for HBA was 15.90 s(-1)(mg/mL)(-1), or about three times less than that for branched amylose. The k cat/ K m values of porcine pancreatic alpha-amylase for HBAPC and HBA were 496 and 588 s(-1)(mg/mL)(-1), respectively, indicating that HBA and HBAPC are less susceptible to hydrolysis by glucoamylase and alpha-amylase. HBAPC and HBA show potential as novel glucan polymers with low digestibility and high water solubility.     

Distribution of amylose,nitrogen, and minerals in rice kernels with various characters

The distribution of chemical constituents is known not to be even within a rice kernel. To improve the eating quality of rice or to give it some special traits by adjusting the milling intensity, we investigated the distribution of amylose, nitrogen (N), and specific minerals (P, K, Mg, Ca, and Mn) in rice kernels of 11 cultivars with various characteristics cultivated under similar conditions. The distributions of these constituents were determined using flour samples prepared consecutively by abrasive milling from the outer to the inner portions of hulled rice. In all the cultivars tested, N and the minerals were found to be more abundant in the outer than in the inner portion, but amylose was rich in the inner portion. P, Mg, K, and Mn were extremely rich in the outer portion, while N and Ca were only relatively rich there. Koshihikari, which is the most popular cultivar in Japan because of its excellent eating quality, showed the highest Mg/K ratio in the outermost portion of polished rice. The color of flour samples became pure white going from outside portions toward the center of the kernel, even if the sample was from red rice or purple-black rice because only the surface of hulled rice contains pigments. These findings suggest that the outer portion contains various compounds other than starch and the inner portion contains relatively pure starch. Rice palatability and other characteristics can be improved through controlling the degree of milling using the biased distribution of chemical constituents within a rice kernel.     

不同淀粉糊化及凝胶特性与粉条品质的关系

为了研究粉条加工过程中原料淀粉的糊化及凝胶特性对粉条品质的影响,该文对绿豆、红薯、马铃薯、大米和玉米等5种原料淀粉的糊化凝胶特性及其粉条品质进行了测定,并对淀粉糊化凝胶特性与淀粉粉条品质之间的关系进行探讨。结果表明:5种淀粉原料所制的粉条中,绿豆粉条的品质是较好,其次就是马铃薯粉条和红薯粉条,大米粉条和玉米粉条的品质较差;淀粉的糊化特性与粉条品质之间具有显著相关性,按显著程度的大小(P值大小)依次是:峰值黏度谷值黏度衰减值回生值、最终黏度;淀粉凝胶的硬度、弹性、黏性和咀嚼性对粉条品质的影响较大,按显著程度的大小(P值大小)依次是:硬度黏性咀嚼性弹性。在粉条加工原料选择及粉条品质改善中可以考虑用谷值黏度、回生值以及淀粉凝胶特性特征值回复性、咀嚼性和黏性作为考核衡量指标。研究结果为粉条生产中原料选择及品质改善提供参考依据。     

Analysis of genotypic and environmental effects on rice starch. 2. Thermal and retrogradation properties

Eight rice varieties with wide diversity in apparent amylose content (AC) were selected and planted in the early (HZE) and late season (HZL) in Hangzhou and in the winter season in Hainan (HN) for two consecutive years to study the genotypic and environmental effects on starch thermal and retrogradation properties of grain. Genotypic variation (all at P < 0.01) accounted for >56% of the total variation for onset (T(o)), peak (T(p)), and completion (T(c)) temperature, width at half-peak height (DeltaT(1/2)) of gelatinization, enthalpy (DeltaH(r)) of retrograded starch, percentage of retrogradation (R%), and 45.8% for enthalpy (DeltaH(g)) of gelatinization. Seasonal variation accounted for about one-fifth for T(o), T(p), and T(c) and one-third for DeltaH(g), but less for T(1/)(2), DeltaH(r), and R% of the total variation, indicating that T(o), T(p), T(c), and DeltaH(g) were highly affected by seasonal environment in addition to the genotypic variation. The T(o), T(p), T(c), and DeltaH(g) in HZL were much smaller than those in HZE and HN. Correlation analysis for the eight genotypes showed that AC was significantly correlated with DeltaH(g) (r = -0.83, P < 0.01) and R% (r = 0.734, P < 0.05). DeltaH(g) was also positively correlated with T(c) (r = 0.878, P < 0.05), but it did not have any correlation with DeltaH(r), whereas the latter was positively correlated with R% (r = 0.994, P < 0.001). The intercorrelation of T(o), T(p), T(c), and DeltaT(1/)(2) themselves was significant at P < 0.001. The correlation analysis results suggest that there are different molecular mechanisms to regulate thermal properties (T(o), T(p), T(c), and DeltaH(g)) and retrogradation properties (DeltaH(r) and R%) as affected by environmental conditions. The implications of the results for rice breeders and starch-based food processors are discussed.     

Lower weight gain and hepatic lipid content in hamsters fed high fat diets supplemented with white rice protein, brown rice protein, soy protein, and their hydrolysates

The physiological effects of the hydrolysates of white rice protein (WRP), brown rice protein (BRP), and soy protein (SP) hydrolyzed by the food grade enzyme, alcalase2.4 L, were compared to the original protein source. Male Syrian Golden hamsters were fed high-fat diets containing either 20% casein (control) or 20% extracted proteins or their hydrolysates as the protein source for 3 weeks. The brown rice protein hydrolysate (BRPH) diet group reduced weight gain 76% compared with the control. Animals fed the BRPH supplemented diet also had lower final body weight, liver weight, very low density lipoprotein cholesterol (VLDL-C), and liver cholesterol, and higher fecal fat and bile acid excretion than the control. Expression levels of hepatic genes for lipid oxidation, PPARα, ACOX1, and CPT1, were highest for hamsters fed the BRPH supplemented diet. Expression of CYP7A1, the gene regulating bile acid synthesis, was higher in all test groups. Expression of CYP51, a gene coding for an enzyme involved in cholesterol synthesis, was highest in the BRPH diet group. The results suggest that BRPH includes unique peptides that reduce weight gain and hepatic cholesterol synthesis.     

茶多酚对淀粉酯纳米颗粒及其稳定的Pickering乳液性质的影响

为探究茶多酚（Tea Polyphenols, TPs）对辛烯基琥珀酸酐（Octenyl Succinic Anhydride, OSA）酯化淀粉纳米颗粒（Starch Nanoparticles,SNPs）及其稳定的Pickering乳液性质的影响,该研究在制备OSA-SNPs的过程中添加TPs,研究TPs对OSA-SNPs的理化性质和乳化性能的影响。结果发现,添加TPs使OSA-SNPs的平均粒径增加、表面Zeta电位绝对值下降、接触角减小（P<0.05）。通过傅立叶红外光谱扫描发现,TPs与OSA-SNPs之间存在氢键和疏水相互作用。在TP-OSA-SNPs稳定的乳液中,增加TP-OSA-SNPs的质量浓度（从0.5 g/mL至2.0 g/mL）,乳滴平均直径明显减小（P<0.05）;当TP-OSA-SNPs的质量浓度增加至2 g/mL时,乳液形成了油滴紧密堆积的界面结构,能够抑制油滴迁移。通过加速氧化试验发现,与OSA-SNPs相比,TP-OSA-SNPs稳定的乳液中氢过氧化物值（Peroxide Value, POV）相对较低（P<0.05）,说明TP-OSA-SNPs具有延缓乳液中油脂氧化的作用。结果表明,这种新型具有抗氧化功能的食品级颗粒乳化剂,对构筑淀粉基Pickering乳液载体具有潜在价值。     

欧姆加热对米饭蒸煮过程能耗及其品质的影响

针对电饭煲蒸煮米饭存在电热转化效率低、温度不易控制等不足,该研究设计了一种加热速率和保温温度自动可控的欧姆加热试验系统,研究了浸泡时间（5、15、30、50、80 min）和水米比（1.25∶1、1.50∶1、1.75∶1、2.00∶1 mL/g）对水米混合物的电导率、欧姆蒸煮加热速率、能耗以及米饭品质（膨胀率、吸水率、物性值和颜色）的影响,并与电饭煲蒸煮米饭的能耗和品质进行比较。结果表明：浸泡能够增大水米混合物电导率,水米比越小电导率增加越快,有效提高欧姆加热蒸煮米饭加热速率;浸泡还有利于减少米饭蒸煮能耗（P<0.05）,促进米饭软化;因此大米浸泡处理30 min后采用欧姆加热蒸煮米饭可行。欧姆蒸煮加热速率越快,米饭硬度上升（P<0.05）,而黏性和弹性则略有减小（P<0.05）,加热速率在3～9 ℃/min范围内为宜;水米比可取1.25∶1～1.50∶1 mL/g。蒸煮相同质量的大米,欧姆加热所需能耗仅为电饭煲蒸煮的20%～25%;相较于电饭煲蒸煮,欧姆加热蒸煮米饭硬度最大可减小21%,且膨胀率和吸水率较大（P<0.05）、亮度L*值较小（P<0.05）。研究结果可为研发基于欧姆加热的快速高效米饭自动蒸煮装置提供技术支撑。