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.     

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.     

Determination of Optimum Conditions for Enzymatic Debranching of Cassava Starch and Synthesis of Resistant Starch Type III using Central Composite Rotatable Design

Cassava starch was debranched by treatment with isoamylase and pullulanase and the yield of resistant starch type III (RS III) optimized with respect to starch solids concentration (7.5‐15%, w/v), incubation time (8‐24 h) and enzyme concentration using central composite rotatable design. Higher concentrations of pullulanase (10‐35 U/g starch) compared to isoamylase (30–90 mU/g starch) were required to give a similar degree of starch hydrolysis within the experimental domain. A clear debranching end‐point was identifiable by following the reducing value, blue value and β‐hydrolysis limit of cassava starches debranched using isoamylase. It was difficult to define a debranching endpoint of pullulanase treatment by these parameters due to contaminating α‐D ‐(1→4) activity. The yield of RS III was significantly higher in isoamylolysates and increased steadily with increasing degree of hydrolysis to peak at 57.3%. Purification of the debranched material further increased the RS III yield to 64.1%. Prolonged (24 h) hydrolysis of cassava starch with high concentration of pullulanase (35 U/g) gave lower RS III contents in the purified (34.2%) and unpurified (36.2%) hydrolysates compared to 49.5 and 62.4%, respectively, at moderate pullulanase concentration (22.5 U/g) and incubation time (16 h).     

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.     

响应面试验优化晶种诱导-双酶复合法制备RS_3型籼米抗性淀粉工艺

以微波预糊化籼米淀粉为原料,自制RS_3型马铃薯抗性淀粉为晶种,研究RS_3型籼米抗性淀粉的晶种诱导-双酶复合法制备工艺。利用扫描电子显微镜对淀粉颗粒形貌进行表征并研究淀粉的抗酶解性。在单因素试验的基础上,固定其他酶解条件,以RS_3型籼米抗性淀粉产率为响应值,确定晶种添加量、异淀粉酶添加量、普鲁兰酶添加量和普鲁兰酶酶解时间作为影响产率的主要因素,进行Box-Behnken响应面优化试验。得到RS3型籼米抗性淀粉的最佳制备工艺条件为:晶种添加量5%、异淀粉酶添加量8 U/g、普鲁兰酶添加量8 U/g、普鲁兰酶酶解时间3.50 h。在此最佳制备工艺条件下,RS_3型籼米抗性淀粉产率为27.42%,RS3失去原有的淀粉颗粒形貌,表面变得粗糙,结晶结构致密,具有较强抗酶解能力。     

Chemical and Physical Characterisation of Grain Tef [Eragrostis tef (Zucc.) Trotter] Starch Granule Composition

Chemical and physical properties of starch granules isolated from five grain tef (Eragrostis tef) varieties were characterised and compared with those of maize starch. Endogenous starch lipids extracted with hot water‐saturated n‐butanol and total starch lipids extracted with n‐hexane after HCl hydrolysis were 7.8 mg/g (mean) and 8.9 mg/g (mean), respectively, slightly lower than in the maize starch granules. The starch phosphorus content (0.65 mg/g) was higher than that of maize starch but virtually the same as reported for rice starch. The starch granule‐swelling factor was lower than that of maize starch and extent of amylose leaching was higher. The starch X‐ray diffraction pattern was characteristic of A type starch with a mean crystallinity of 37%, apparently lower than the crystallinity of maize starch and more similar to that reported for rice and sorghum starches. The starch DSC gelatinisation temperature was high, like for other tropical cereals; T_o, T_p, T_c and ΔH were in the range 63.8—65.4, 70.2—71.3, 81.3—81.5 °C and 2.28—7.22 J/g, respectively. The lower swelling, apparently lower percentage crystallinity and lower DSC gelatinisation endotherms than maize starch suggest that the proportion of long amylopectin A chains in tef starch is smaller than in maize starch.     

Effects of gamma irradiation on starch digestibility of rice with different resistant starch content

Three rice cultivars (RS3M, RS4H and RS5L) differing in resistant starch contents but similar in genetic background were chosen to study the effects of gamma irradiation on starch physicochemical properties and digestibility. Irradiation increases the resistant starch content in all the three cultivars and in a dose‐dependent manner in rice with low‐resistant starch content (RS5L). Irradiation decreases apparent amylose content and gelatinisation temperature and changed the starch granule structure, while increasing V‐type crystallinity. Starch enzymatic hydrolysis rate was reduced following irradiation, and the effect of irradiation on reducing starch digestibility was negatively correlated with resistant starch content. Treatment with gamma irradiation has therefore a potential for increasing resistant starch content and producing low digestibility of starch in common rice.     

大米淀粉凝胶储藏过程中消化特性的变化

对大米淀粉凝胶储藏过程中消化特性的变化进行了研究，研究结果表明：在储藏早期，直链含量高的大米淀粉凝胶，随着直链凝皎网络的形成和稳定，淀粉体系中慢消化性淀粉和抗性淀粉含量显著增加，表明直链三维凝胶网络对酶有较强抗性。在后期的储藏过程中，随着储藏时间的延长，大米淀粉体系中慢消化性淀粉含量逐步增加，慢消化性淀粉含量增加的主要原因是由于支链淀粉的重结晶所引起。     

Resistant Starch Content and Structural Changes in Maize (Zea mays) Tortillas During Storage

Storage of maize products such as tortillas may cause starch retrogradation and lead to resistant starch (RS) formation. This study was carried out to determine if storage of maize tortillas under refrigerated conditions enhanced RS content and/or modified RS structure. Improved Costeño variety maize grain was nixtamalized and processed into tortillas which were stored for five and ten days at 5°C. Total resistant starch (TRS) and retrograded resistant starch (RRS or RS3) contents were determined on raw and nixtamalized maize grain and tortillas stored for zero, five and ten days. Differential scanning calorimetry (DSC), X‐ray diffraction (XRD) and near‐infrared (NIR) spectroscopy were use to evaluate structural changes in retrograded resistant starch isolated from each sample type. Total starch content was 67 ± 1.5% for all samples, TRS ranged from 3.3% in the raw grain at 7.2% in tortillas stored for ten days, while RRS starch content ranged from 0% in the raw grain to 3.2% in tortillas stored for ten days. DSC showed endothermic transitions corresponding to amylopectin and amylose retrogradation, at 31.9 and 139.7°C in RRS from tortillas stored for five days, and at 47.9 and 146°C in RRS from tortillas stored for ten days. These values agreed with the higher total RS content recorded after prolonged storage. XRD revealed a starch crystallinity of 13.7% in tortillas stored for five days and 15.3% in those stored for ten days. NIR spectroscopy analysis showed evidence of structural changes in polymeric order that were more pronounced in RRS of tortillas stored for ten days, due to increase in crystalline region.     

Rice Starch Molecular Size and its Relationship with Amylose Content

The composition and starch molecular structure of eight rice varieties were studied. Waxy and non‐waxy (long‐, medium‐, and short‐grain) rice varieties from California and Texas were used. The amylose contents were measured using the Concanavalin A method and were found to be related to the type of rice: waxy ≈ 1.0%, short and medium grain 8.7–15.4%, and long grain 17.1–19.9%. The weight‐average molar masses (M_w) of the starches varied from 0.52 to 1.96×10⁸ g/mol. As would be expected, a higher M_w of rice starch correlated to lower amylose content. The range of M_w of amylopectin was 0.82 to 2.50 ×10⁸ g/mol, and there was also a negative correlation of amylopectin M_w with amylose content. Amylose M_w ranged from 2.20 to 8.31×10⁵ g/mol. After debranching the amylopectin with isoamylase, the weight‐average degree of polymerization (DP_w) for the long‐chain fraction correlated positively with a higher amylose content. California and Texas varieties were significantly different in their amylose content, starch M_w (short‐ and medium‐grain only), and amylopectin M_w (p < 0.05).     

Starch of diverse Mexican rice cultivars: physicochemical,structural, and nutritional features

Structure‐function relationship of rice starch is scarce in the literature. Starch was isolated from diverse Mexican rice varieties and their swelling power (SP), soluble solids (ss), thermal and pasting properties, XRD pattern, in vitro starch digestibility, and AP chain‐length distribution were evaluated. Rice starches with low SP at 60°C had higher temperature and enthalpy of gelatinization. The peak viscosity of rice starches ranged between 2426 and 3519 cP, and the samples presented high values for setback due to the AM content. Rice starches presented the typical A‐type XRD pattern with crystallinity values between 32.7 and 36.3%. Rice starches presented high amounts of short chains (A and B1), and differences were found among the cultivars. AM content for rice starches ranged between 18.4 and 22.9%, and the main fraction recorded by HPSEC was the Fraction III (short chains) with values around 60%. The uncooked rice starch samples presented high values of slowly digestible starch (SDS) and rapidly digestible starch (RDS), and differences were found among the cultivars. In cooked samples decreased SDS and increased RDS and RS. Onset temperature and enthalpy of gelatinization were correlated with the percentage of A‐chains and an opposite pattern was found with the percentage of B1 chains. AP structural characteristics affect the functional, physicochemical, and digestibility properties of rice starches.     

The Significance of Starch Polymorphism in Commercially Produced Parboiled Rice

A study of eight commercial parboiled samples derived from two varieties of rice produced by four different processes has shown that depending on the parboiling process, the starch component itself can be present as native and/or retrograded starch in addition to the amylose-lipid complex. Further, it was demonstrated that the polymorphic states of starch can influence the texture and behaviour of cooked rice. The parboiled rice samples which had all three states of starch (i.e. ungelatinized and recrystallized amylopectin plus the amylose-lipid complex) possessed the hardest eating property but the lowest solubility. A negative linear relationship was demonstrated between the hardness and the solubility of cooked, parboiled rice. Overall, the observations suggest the existence of different forms of starch in parboiled rice which vary with the different parboiling protocols. The conditions governing their formation need to be established before investigating the specific functionality of individual forms within the rice. This study further confirmed that retrograded starch (amylopectin) in parboiled rice did not exhibit a B-tye X-ray pattern but mixed A+V patterns.     

Effect of Processing on Slowly Digestible Starch and Resistant Starch in Potato

The effect of a number of laboratory‐scale pretreatments on the proportions of rapidly digested (RDS), slowly digested (SDS) and resistant starch (RS) in raw and cooked potato has been examined using an in vitro digestion procedure. Potatoes of the variety Frisia were prepared in three states: raw, cooked, and cooked followed by a cold treatment (4°C, two days). Each preparation was then subjected in triplicate to freeze‐drying, coarsely mincing, pasting, freezing, dry‐milling after freeze‐drying, in 22 different combinations, before digesting. In raw potato, very little RDS and SDS (<5% total starch (TS)) were present, and the mechanical treatments of the potato did not affect the amounts of RDS and SDS. Cooking resulted in an almost complete conversion to RDS (>95% TS) in freshly‐cooked potato, but after post‐cooking cold treatment much of the RDS transformed to SDS, which reached a maximum of about 45% TS. SDS formation was independent of the degree of tissue disruption after cooking, and was generally associated with formation of RS, however, freezing after cooking allowed SDS formation without prolonged cold treatment and with very little associated RS (SDS 35% and RS 4% of TS). Freeze‐drying caused an increase in RS in most treatments of the cooked potatoes. The observed effects provided guidance for sample handling in potato research, but also suggested several approaches to the enrichment of SDS and/or RS, with a concurrent reduction in RDS, that could be used to improve the nutritional profile of potato products by decreasing RDS (lowered glycaemic impact), and increasing SDS (more sustained energy availability) and RS (prebiotic benefits).     

Digestibility of common native starches with reference to starch granule size,shape and surface features towards guidelines for starch-containing food products

Influence of diverse botanical sources (wheat, maize, waxy maize, cassava, potato, rice or waxy rice) on in vitro native starch digestibility has been investigated. Physicochemical properties (chemical composition, particles size and shape, surface features) of starch granules were determined with a view to explaining digestibility differences between samples. Rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS) contents were measured according to Englyst method. Potato starch was shown to be composed of large rounded granules having smooth surfaces, which explains its slow enzymatic breakdown. Potato starch displayed the highest RS (86%) content and the lowest RDS content (9.9%). Since RS positively influences health and SDS may result in cell, tissue and/or organ damages, potato starch is an ideal starch nutrient. Conversely, waxy rice starch was rich in amylopectin and displayed small diameters and angular shapes, which are both known to facilitate enzymatic starch hydrolysis. It exhibited a near-zero RS content (0.9%) and a high RDS fraction (60%). According to this study, potato starch exhibited the best nutrient profile, followed up in this order by cassava, waxy maize, wheat, maize and waxy rice starches.     

Varietal Differences in Physicochemical Properties of Waxy Rice Starch

High-gelatinization temperature (GT) waxy rice starch amylopectin has higher sedimentation coefficient than low-GT waxy rice amylopectin. Get filtration on Sepharose CL-2B and TSK-Gel G-6000PW also showed higher mean molecular weights for high-GT amylopectins than for low-GT amylopectins. The harder texture of cooked rice products from high-GT waxy rices, compared to the texture of products from low-GT waxy rices, may be due to the higher molecular weight of their amylopectins.     

Determination of amylopectin structure and physicochemical properties in rice endosperm starch of mutant lines derived from Malaysian rice cultivar MR219

BACKGROUND: Characterization of starch properties and functionality can apply breeding program selection for desirable traits such as eating, cooking and processing qualities to meet consumer preference. Low amylose content is generally preferred in Malaysia because of cohesive, tender and glossy cooked rice. Rice high in short‐chain amylopectin has a lower transition temperature of starch gelatinization. In the continuing search for improved starch quality in rice cultivars a study was carried out with new mutant lines MR219‐4 and MR219‐9, derived from MR219. RESULTS: MR219 and its mutant lines contain L‐type amylopectin, being high in amylopectin of intermediate chain length with degree of polymerization 12‐21. The apparent amylose content (AAC) in MR219‐4 had lower AAC value (19.2%) compared to other lines. A strongly negative correlation was found between chain‐length fraction of amylopectin and transition temperatures—onset temperature peak temperature, and conclusion temperature (0.992, 0.958, 0.950; P < 0.01)—with fraction b1 (fb1), respectively. CONCLUSION: The Malaysian lines studied contain L‐type amylopectin and offer a better understanding of grain quality improvement in terms of starch properties and functionality. This information will be directly applicable to select for desirable traits in future breeding programs. Copyright © 2012 Society of Chemical Industry     

Non-Starch Polysaccharides and in Vitro Starch Digestibility of Raw and Cooked Chick Peas

The effects of domestic and industrial cooking methods on the non-starch polysaccharides (NSP) content and in vitro starch digestibility of chick pea (variety “blanco lechoso”) have been studied. Total and soluble NSP increased, as did the slowly digestible starch (SDS), whereas the resistant starch (RS) fraction decreased after cooking, showing higher content in domestic than industrially cooked chick peas. The in vitro starch digestible rate index (SDRI) was similar in the cooked chick peas, as was the rapidly available glucose (RAG). Due to the low values of RAG, chick peas would give a slow post-prandial glycaemic response. Domestic cooked chick peas consumption would increase the intakes of RS in human diet, whereas the industrially cooked chick peas with lower content of RS would result in less flatulence problems.     

Characterisation of low‐digestible starch fractions isolated from amylosucrase‐modified waxy corn starch

Amylosucrase (AS) modification of starch increases the slowly digestible (SDS) and resistant starch (RS) fractions. However, the characteristics and formation mechanism of each fraction of AS‐modified starch have not been determined yet. Therefore, this study isolated SDS and/or RS from AS‐modified waxy corn starches and investigated their structural characteristics. The amount of SDS+RS and RS had a positive correlation with the proportion of the medium length (13–24 of degree of polymerisation) branched chains of amylopectin. The relative crystallinity increased in the order of AS‐modified starch < SDS+RS < RS, while maintaining the B‐type crystalline structure. The thermal transition temperature ranges of the isolated fractions were also higher than those of undigested starches. The medium branched chains of amylopectin were presumably the clincher for the SDS and/or RS formation in AS‐modified starches. The principal causes of SDS and RS formation were the chain length elongation and the subsequent retrogradation‐like process, respectively.     

Nutritionally Important Starch Fractions of Rice Cultivars Grown in Southern United States

Abstract: Dietary starches can be classified into 3 major fractions according to in vitro digestibility as rapidly digestible (RDS), slowly digestible (SDS), and resistant starch (RS). Literature indicates that SDS and/or RS have significant implications on human health, particularly glucose metabolism, diabetes management, colon cancer prevention, mental performance, and satiety. In this study, the nutritionally important starch fractions (RDS, SDS, and RS) in cooked rice were assayed in vitro, making use of 16 cultivars grown in 5 southern U.S. rice growing locations (Arkansas, Louisiana, Mississippi, Missouri, and Texas). RDS, SDS, and RS were 52.4% to 69.4%, 10.3% to 26.6%, and 1.2% to 9.0%, respectively, of cooked rice dry weight. Cultivar, location, and cultivar-by-location interaction contributed to the variations in RDS, SDS, and RS contents. Means pooled across locations indicated that SDS was higher for the Louisiana samples than those from Texas, whereas RS was higher for the Texas samples than those from Arkansas, Louisiana, and Mississippi. Some cultivars were identified to possess high levels of RS (for example, Bowman and Rondo) or SDS (for example, Dixiebelle and Tesanai-2) and were also stable across growing locations. Apparent amylose content correlated positively with RS (n = 80, r = 0.54, P ≤ 0.001), negatively with RDS (n = 80, r =−0.29, P ≤ 0.05), and insignificantly with SDS (n = 80, r = 0.21, P > 0.05). RS and SDS were not collinear (n = 80, r =−0.18, P > 0.05); it does not follow that a cultivar high in RS will also be high in SDS, and vice versa. The observed differences in RDS, SDS, and RS among the samples are indicative of wide genetic diversity in rice.     

Impact of Process Conditions on Digestibility of Pea Starch

This study investigated how process conditions affect the digestibility of pea starch from pea starch powder (PSP). The factors considered were resistant starch (RS), slow digestible starch (SDS) and rapidly digestible starch (RDS) content. The examined five process factors were: material/water ratio, cooking temperature, cooking time, soaking time, and heat dehydration time. Changes in process conditions mainly altered the content of RS and SDS. Analysis with Sephadex G-200 chromatography and differential scanning calorimetry revealed that RS was mainly from retrograded amylose and amylopectin, while SDS and RDS were mainly derived from amylopectin.