Structure and Properties of Starch in Rice Double Mutants Lacking Starch Synthase (SS) IIa and Starch Branching Enzyme (BE) IIb

Starch biosynthetic enzymes form multi-protein complexes consisting of starch synthase (SS) I, SSIIa, and starch branching enzyme (BE) IIb, which synthesize amylopectin clusters. This study analyzed the starch properties in two double mutant rice lines lacking SSIIa and BEIIb, one of which expressed an inactive BEIIb protein. The ss2a be2b lines showed similar or greater seed weight than the be2b lines, and plant growth was not affected. The ss2a line showed increased short amylopectin chains resulting in a lower gelatinization temperature. Starch granule morphology and A-type crystallinity were similar between the ss2a line and the wild type, except for a mild chalky seed phenotype in the ss2a line. However, the starch phenotype of the ss2a be2b lines, which was similar to that of be2b but not ss2a, was characterized by increased long amylopectin chains, abnormal starch granules, and B-type crystallinity. The similarity in phenotype between the ss2a be2b and be2b lines may be attributed to the inability of the be2b mutants to generate short amylopectin branches, which serve as primers for SSIIa. Therefore, the presence or absence of SSIIa hardly affected the amylopectin structure under the be2b background. The amylose content was significantly higher in the ss2a be2b lines than in the be2b lines. Starch crystallinity was greater in ss2a be2b lines than in be2b lines, despite the fact that starch crystallinity is generally negatively correlated with amylose content. This suggests that the formation of a double helix between long amylopectin chains and amylose affects starch crystallinity in the ss2a be2b mutants.     

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.     

Identification of a Point Mutation in the Granule-bound Starch Synthase I Gene (GBSSI) in a waxy Diploid Wheat Mutant and Design of Molecular Markers for Backcrossing

In cereals, granule-bound starch synthase I (GBSSI)-deficient mutants accumulate glutinous (amylose-free) starch in their storage tissues. The amylose-free starch produced by waxy (wx) mutants of hexaploid bread wheat (Triticum aestivum L.) is used in cakes and breads. However, wx mutants of diploid wheat (T. monococcum L.) have so far no commercial applications. In this study, we identified a mutation in exon 6 of GBSSI in a diploid wheat wx mutant that resulted in the replacement of Trp355 with a stop codon. Molecular markers were developed for the rapid screening of the mutation, which should allow the selection of heterozygous and homozygous plants during backcrossing. This will facilitate the improvement of the agricultural traits of the wx mutant and the generation of new amylose-free wx lines.     

Comparative Starch Synthase Activity of Indica and Japonica Developing Rice Grain

Developing grain of japonica rice had higher specific activity of granule-bound starch synthase than indica rice at the same growth stage, with indica-japonica hybrid having intermediate synthase activity. All were of similar amylose content in the mature grain. It supports an earlier speculation that for japonica rice to synthesize the same amount of amylose in its starch granule with a lower level of bound starch synthase, it must have a more efficient enzyme than indica.     

Partial Leaching of Granule‐Associated Proteins from Rice Starch during Alkaline Extraction and Subsequent Gelatinization

Starch granule‐associated proteins, including granule‐bound starch synthase (GBSS), were found to be partially lost during alkaline extraction of rice starch. Variability in amount of loss of GBSS and other granule proteins was found among different rice lines. Also, part of the GBSS and other granule proteins leached out during gelatinization of the alkali‐extracted rice starch. Confocal laser scanning microscopy revealed that some protein still existed in gelatinized starch granules prepared from starch isolated using alkaline extraction. The starch that retained more GBSS and other granule proteins after alkaline extraction tended to have more protein in the isolated gelatinized starch granules, indicating that proteins resistant to alkaline extraction also tended to resist leaching during gelatinization. The study suggests that leaching of granule‐associated proteins may contribute to variations in paste properties of alkali‐extracted starches.     

Starch Biosynthetic Protein Complex Formation in Rice ss2a be2b (+) Double Mutant Differs from Their Parental Single Mutants

Amylopectin, which consists of highly branched glucose polymers, is a major component of starch. Biochemical processes that regulate the elongation of glucose polymers and the generation and removal of glucose branches are essential for determining the properties of starch. Starch synthases (SSs) and branching enzyme (BE) mainly form complexes consisting of SSI, SSIIa, and BEIIb during endosperm development. Loss of BEIIb in rice is complemented by BEIIa, but the compensatory effects differ depending on the presence or absence of inactive BEIIb. To better understand these compensatory mechanisms, ss2a be2b (+) double mutant, which possessed truncated inactive SSIIa and inactive BEIIb, were analyzed. Soluble proteins separated by gel filtration chromatography showed that SSIIa and BEIIb proteins in the wild-type exhibited a broad range of elution patterns and only small amounts were detected in high molecular mass fractions. In contrast, most of truncated inactive SSIIa and inactive BEIIb from ss2a be2b (+) were found in high molecular mass fractions, and the SSI-SSIIa-BEIIb trimeric protein complex found in the wild-type was likely absent in ss2a be2b (+). Those SSIIa and BEIIb proteins in high molecular mass fractions in ss2a be2b (+) were also identified by mass spectrometry. Parental ss2a single mutant had negligible amounts of SSIIa suggesting that the truncated inactive SSIIa was recruited to high-molecular mass complexes in the presence of inactive BEIIb in ss2a be2b (+) double mutant. In addition, SSIVb might be involved in the formation of alternative protein complexes with < 300 kDa in ss2a be2b (+).     

大米淀粉的结构、组成与应用

本文对大米淀粉的结构、组成和应用进行了综述。较全面地概述了大米淀粉颗粒结构、分子结构特点和大米淀粉中的非淀粉组分(蛋白质和脂质)的性质及其对淀粉性能的影响；分析了大米淀粉和大米变性淀粉的性质及其开发应用情况；探讨了大米淀粉的潜在用途，包括大米多孔淀粉、抗消化淀粉、模拟脂肪和明胶替代物等；同时展望了大米淀粉工业的发展前景。     

Starch granule-associated proteins of hull-less barley (Hordeum vulgare L.) from the Qinghai-Tibet Plateau in China

BACKGROUND: The starch granule‐associated proteins (SGAPs) are the minor components of the starch granules and a majority of them are believed to be starch biosynthetic enzymes. The Qinghai‐Tibet Plateau in China, one of the centres of origin of cultivated barley, is abundant in hull‐less barley resources which exhibit high polymorphism in SGAPs. RESULTS: The SGAPs of hull‐less barley from Qinghai‐Tibet Plateau were analysed by one‐dimensional (1‐D) SDS‐PAGE, 2‐D PAGE and ESI‐Q‐TOF MS/MS. In the 1‐D SDS‐PAGE gel, four proteins including a 80 kDa starch synthase, actin, actin 4 and ATP synthase β‐subunit were identified as novel SGAPs. A total of six different bands were identified as starch granule‐bound starch synthase I (GBSSI) and the segregation of the novel GBSSI bands in F₁ and F₂ seeds derived from yf127 × yf70 was in accordance with Mendel's law. In the 2‐D PAGE gel, 92 spots were identified as 42 protein species which could be classified into 15 functional groups. Thirteen protein species were identified as SGAPs for the first time and multiple spots were identified as GBSSI. CONCLUSION: This study revealed novel SGAPs in hull‐less barley from the Qinghai‐Tibet Plateau in China and these will be significant in further studies of starch biosynthesis in barley. Copyright © 2011 Society of Chemical Industry     

Wheat Starch Modification Through Biotechnology

Natural mutations that affect the amylose/amylopectin ratio in starch are unlikely to develop naturally in wheat due to its allohexaploid genome (2n=6x; AABBDD). One of the strategies to modify wheat starch structure involves identification of germplasms with null alleles for starch biosynthetic genes, followed by exchange of functional alleles with the identified null alleles through classical plant breeding. This technique has successfully been used to combine the three null alleles for granule-bound starch synthase I (GBSSI) to develop a wheat line that produces amylopectin-rich (>95%) starch (waxy starch). Another strategy to alter expression levels of starch biosynthetic genes employs recent advances in molecular biology and genetic engineering of wheat. For this approach, various monocot vectors have been developed that drive expression of wheat starch branching enzyme I (SBEI) cDNA sequences in the anti-sense orientation. Several of the wheat cell lines transformed with the anti-sense vectors express branching enzyme (BE) activity at a significantly lower level than non-transformed cells. One transgenic wheat plant expressing the anti-sense SBEI RNA produces a ten-fold lower level of BE activity in kernels than wild-type wheat. Analysis of starch produced from the transgenic plant shows that starch structure and properties have been altered.     

Distinctive Sorghum Starch Granule Morphologies Appear to Improve Raw Starch Digestibility

Various factors, including starch granule channels, have been suggested to contribute to the control of sorghum starch digestibility for animal feed. Isolated starch from two normal sorghum lines (P721N, IS6986) and one high protein digestibility (HPD) mutant line (111) that differed in starch granule morphology were selected to study the influence of these factors on starch digestibility. Scanning electron micrographs were taken of raw and digested starches. Microscopy results confirmed that in all three sorghum lines channels in starch granules are the main route of enzyme penetration and the central cavity area is the starting point of enzyme digestion. Channel density was more pronounced in the HPD sorghum mutant line than in normal lines, which may have been responsible for its relatively high digestibility. Micrographs of IS6986 showed unique starch granule morphology with a collapsed ”doughnut‐shaped” structure in a portion of the granules. These unusual granules were rapidly digested and, unlike normal spherical granules, totally disappeared after 30 min of digestion. Amylases appeared to have fast access to the collapsed‐appearing starch granules. Digestion profiles, following incubation with pepsin and α‐amylase, showed that IS6986 and the HPD mutant (111) had the highest initial rate of starch digestion, followed by P721N. These findings provide insight as to how new sorghum cultivars might be developed with high starch digestibility for animal feed use.     

芋头淀粉的研究

本文研究了芋头淀粉的性质,实验采用电子显微镜拍摄了芋头淀粉颗粒的形态;运用X射线衍射仪测定了X-光衍射图样及结晶结构;通过重结晶法制得纯度较高的芋头直链淀粉和支链淀粉,利用高效液相色谱仪测定了芋头淀粉及其直、支链淀粉淀粉的重均聚合度、数均聚合度、分子量分布及分散度等,并与大米淀粉进行了比较.研究了芋头淀粉糊在不同质量分数、pH值以及不同蔗糖添加量的条件下,Micro Visco-Amylo-Graph黏度曲线的变化情况.本研究为进一步了解芋头淀粉的特性及应用开发提供了一定的理论依据.     

Retrogradation of Starch Mixtures Containing Rice Starch

ABSTRACT: Different starches often coexist in food systems. Starch retrogradation is the primary reason for quality deterioration of a food system during storage. This article addresses the retrogradation behaviors of several starch mixtures containing normal rice starch (NRS). Potato starch, tapioca starch, waxy corn starch, hydroxypropylated potato starch, hydroxypropylated tapioca starch, and acetylated tapioca starch were mixed with NRS. Starch suspensions were gelatinized and the relative solid content, (S′) measured by pulsed nuclear magnetic resonance, was used to characterize the retrogradation behavior of starch systems. The retrogradation behaviors of starch mixtures can be divided into two categories according to the additive or non‐additive nature of S′, for which the concept “regional moisture content” was introduced.     

添加淀粉对马铃薯米粉品质的影响

研究3种常用淀粉对马铃薯米粉品质的影响,为马铃薯米粉加工提供参考依据。分别将0%、5%、10%、15%、20%和25%的玉米、小麦和马铃薯淀粉添加到马铃薯全粉占比30%的米粉中,测定米粉蒸煮、色差、质构和拉伸性能指标的变化。结果:添加不同淀粉使得米粉的含水量显著减小(p<0.05);玉米、小麦以及5%~20%马铃薯淀粉可使米粉透射比显著增大(p<0.05);10%玉米淀粉能使碘蓝值显著增大(p<0.05);添加10%玉米、5%小麦以及5%~20%马铃薯淀粉,能使吐浆值显著减小(p<0.05);但3种淀粉对断条率影响均不显著。添加10%玉米、10%小麦和5%马铃薯淀粉能使米粉亮度L*显著减小(p<0.05),色度值a*和b*亦发生不同改变。5%~15%玉米淀粉可有效改善米粉硬度、峰值负载,但添加量达到20%时峰值负载形变量显著减小(p<0.05);小麦淀粉可改善弹性,添加10%~15%可有效改善硬度,15%和20%可改善峰值负载和咀嚼性;马铃薯淀粉可提高米粉硬度,但添加量达20%时米粉变得黏连。在实际生产中建议玉米和小麦淀粉添加量分别为5%和10%。     

不同品种大米理化性质及其淀粉结构对米饭食用品质的影响

米饭食味值和质构特性是评价大米食用品质的重要指标,为了探究不同品种大米的食味值、质构特性与其理化性质及淀粉结构的关系,以12种大米为研究样本,测定其食味值、质构特性、理化性质及淀粉结构特性,并分析内在相关性。结果表明,直链淀粉含量（质量分数）与米饭的硬度呈极显著正相关（P<0.01）,与米饭的凝聚性呈极显著负相关（P<0.01）;米饭食味值、质构特性与大米淀粉的糊化特性、热特性之间存在显著相关性,与结晶特性、淀粉颗粒表面有序度无显著相关性,表明淀粉的糊化特性决定了米饭的食味值、硬度、凝聚性和回复性。该研究可为后期优质稻米筛选培育以及大米适宜性加工提供理论基础。     

Effects of Cooking Methods and Starch Structures on Starch Hydrolysis Rates of Rice

This study aimed to understand effects of different cooking methods, including steamed, pilaf, and traditional stir‐fried, on starch hydrolysis rates of rice. Rice grains of 3 varieties, japonica, indica, and waxy, were used for the study. Rice starch was isolated from the grain and characterized. Amylose contents of starches from japonica, indica, and waxy rice were 13.5%, 18.0%, and 0.9%, respectively. The onset gelatinization temperature of indica starch (71.6 °C) was higher than that of the japonica and waxy starch (56.0 and 56.8 °C, respectively). The difference was attributed to longer amylopectin branch chains of the indica starch. Starch hydrolysis rates and resistant starch (RS) contents of the rice varieties differed after they were cooked using different methods. Stir‐fried rice displayed the least starch hydrolysis rate followed by pilaf rice and steamed rice for each rice variety. RS contents of freshly steamed japonica, indica, and waxy rice were 0.7%, 6.6%, and 1.3%, respectively; those of rice pilaf were 12.1%, 13.2%, and 3.4%, respectively; and the stir‐fried rice displayed the largest RS contents of 15.8%, 16.6%, and 12.1%, respectively. Mechanisms of the large RS contents of the stir‐fried rice were studied. With the least starch hydrolysis rate and the largest RS content, stir‐fried rice would be a desirable way of preparing rice for food to reduce postprandial blood glucose and insulin responses and to improve colon health of humans.     

加热时间对大米淀粉特性及抗性淀粉含量的影响

采用不同的加热时间对大米进行处理,并从加热处理过的大米中提取淀粉,采用电镜扫描仪、差示扫描量热仪、质构仪、流变仪等检测仪器研究加热时间对大米淀粉的颗粒形貌、热力学性质、凝胶特性、流变等性质的影响,采用酶解法测定加热处理过的大米中抗性淀粉的含量。结果表明：随着加热时间的延长,淀粉的膨润力与溶解度先增大后减小;加热时间在0～10min 时,抗性淀粉含量减少,其范围为18.01%～8.10%;淀粉颗粒由单个独立的颗粒逐渐膨胀至相互粘连,糊化焓值降低;硬度、延伸性等都有不同程度的变化;淀粉糊的剪切稳定性降低。     

大米淀粉及其不同取代度磷酸酯淀粉的糊化和流变特性

粳米淀粉与磷酸二氢钠发生酯化反应,通过改变反应温度得到取代度分别为0.028、0.049、0.073和0.14的磷酸酯淀粉。使用快速黏度分析仪和流变仪对比测定粳米淀粉及具有不同取代度的磷酸酯淀粉的糊化和流变特性。快速黏度分析仪测定的糊化特性显示PO43-与淀粉的结合降低了淀粉的糊化温度,升高了淀粉的峰值黏度,与粳米淀粉相比,磷酸酯淀粉更不易回生。流变仪测定的流变特性显示高取代度的磷酸酯淀粉抗剪切,随着取代度的增加,凝胶硬度降低,凝胶黏性增强。     

籼米中淀粉粒结合蛋白的分离鉴定及提取工艺优化

采用十二烷基硫酸钠（sodium dodecyl sulfate,SDS）缓冲体系分离提取碱洗籼米粉中的淀粉粒结合蛋白（starch granule-associated proteins,SGAPs）,经高效液相色谱-串联质谱法鉴定表明：碱洗得到上、中、下层籼米淀粉中的SGAPs均主要为淀粉合成酶I（granule-bound starch synthase I,GBSS I）,其他组分略有差别;其中以中层SGAPs含量最高,GBSS I达99.8%,谷蛋白质量分数仅为0.11%。采用响应面优化中层淀粉SGAPs的提取参数,得到最优条件为SDS添加量10.90%、煮沸时间4.10?min、MgSO4浓度0.90?mmol/L,此时SGAPs提取量为（1?028.61±0.05）μg/g。     

Acceptor Molecule of Granular-bound Starch Synthase from Sweet-potato Roots

In order to elucidate acceptor molecule of starch synthase bound to starch granules, the enzyme from sweet-potato roots was reacted with ADP- and UDP-[¹⁴C]-glucose, and the reaction products were structurally characterized. The radioactivity of the products was released as [¹⁴C]-maltose by β-amylase. The [¹⁴C]-glucose incorporation was found to be mostly in amylopectin component. However, approximately 30 and 20% of total radioactivity transferred from ADP- and UDP-[¹⁴C]-glucose, respectively, were also present in a molecule with a lower molecular weight than that of amylose component. The radioactivity was incorporated into the much longer unit-chains of amylopectin than into the usual chains. These results indicate that starch synthase bound to sweet-potato starch granules transfers glucose from ADP- and UDP-glucose into specific outer chains of amylopectin component, and that the incorporation of the glucose into a short-chain amylose molecule is simultaneously catalyzed by the starch synthetase.     

二氢杨梅素对大米淀粉回生的抑制作

淀粉是大米中的主要成分,其回生程度直接影响大米制品的品质与货架期。该研究将属于多酚类化合物的二氢杨梅素（Dihydromyricetin,DMY）添加到大米淀粉中,研究不同添加量的DMY与大米淀粉的相互作用以及DMY对大米淀粉的溶解度、膨胀度、回生焓值、微观结构的影响,以期改善大米淀粉的回生特性。结果表明,随着二氢杨梅素的添加,大米淀粉的溶解度从4.49%增加至12.83%,膨胀度11.41%降至10.12%;淀粉表面由原来的紧密结构变化为疏松多孔结构;红外光谱1 047 cm-1/1 022 cm-1的比值从0.87降至0.78。较未添加的DMY的大米淀粉相比,低浓度的DMY已经显著影响大米淀粉回生特性。当DMY的添加量为5%时,大米淀粉的回生焓值、回生率以及相对结晶度分别下降了68.75%、71.86%、59.07%。总体而言,二氢杨梅素可以抑制大米淀粉的回生。因此,在淀粉制品加工时,可考虑添加DMY来调控淀粉基食品的回生现象。