Retrogradation of Rice Starches Studied by Differential Scanning Calorimetry and Influence of Sugars, NaCl and Lipids

In waxy and nonwaxy rice starch gels the retrogradation process was a function of time. The enthalpy for rice starch gel with high amylose content was higher than those for low amylose content or for waxy starch samples. In all rice starch gels, samples stored under 25°C had lower enthalpy and higher endothermic onset temperature. In presence of sucrose, extent of retrogradation increased, while in presence of NaCl, it decreased. Effects of maltose, glucose and lipids were dependent on rice starch gel and storage temperature.     

Dependence of physiochemical,functional and textural properties of high‐resistant starch rice on endogenous nonstarch polysaccharides

To investigate the possibility of improving the quality of rice rich in resistant starch through operation of nonstarch polysaccharides, the high dietary fibre (7.24%) mutant cw and its wild‐type R7954 were selected to study the physiochemical characteristics of starch before and after removal of nonstarch polysaccharides. Results showed that hydrolysed or partially hydrolysed nonstarch polysaccharides in cw decreased the resistant starch content significantly, from 15.23% to 10.8%. Nonstarch polysaccharides had significant influences on the gelatinisation temperature, RVA parameters of R7954, but no significant influences on that of cw. For cw, removal of cellulose increased swelling power and adhesiveness, decreased the hardness significantly, from 0.3 to 0.23 N, while the resistant starch content was still as high as 13.72% and showed no significant difference from the wild type. This suggests that the influences of nonstarch polysaccharides on starch properties depend both on the type of rice and the nonstarch polysaccharides. Operation on nonstarch polysaccharides for obtaining rice with lower glycemic index is feasible, but operation on nonstarch polysaccharides may also be an alternative way of improving the palatability for rice high in resistant starch.     

Physical Basis for Separation of Rice Starch using Various Density Gradient Systems and its Effect on Starch Recovery,Purity, and Pasting Properties

A 32% waxy and non waxy rice flour slurry containing starch‐protein agglomerates was physically disrupted in presence of water by use of high pressure homogenizer called Microfluidizer®. Microfluidized rice flour slurry from passes 2 and 4 was collected followed by isolation of starch using three different density gradient solutions/systems (CeCl, NaCl/sucrose and ZnSO₄·7H₂ O). Complete deagglomeration was obtained after passing the rice flour slurry four times through the Microfluidizer®. The recovery of isolated starch varied from 76.28% to 91.20% for different density gradient systems. The degree of deagglomeration did not seem to affect recovery but affected the purity of the isolated starches. All starches produced from pass 4 rice slurry resulted in starches with residual protein below 0.5%. Higher density of the gradient solution resulted in higher recovery and purity of starch. The isolation method had a significant effect on the pasting properties of the isolated starch. Residual protein in isolated starch had a negative correlation with peak viscosity and setback of pass 2 waxy and nonwaxy starches. The salts were retained in purified starch despite rigorous washing (at least 75 times greater than the control) and could affect starch properties.     

Effects of Na2CO3 and NaOH on Pasting Properties of Selected Native Cereal Starches

ABSTRACT: Using a Rapid Visco Analyzer (RVA), it was revealed that 2 alkalizing agents (Na2CO3 and NaOH) had a far larger effect on pasting properties of nonwaxy starches (wheat, corn, rice) compared with their effect on waxy starches (waxy corn and waxy rice). It was hypothesized that the alkalizing agents have a greater propensity to attack the amorphous regions of the nonwaxy starch granules, thereby causing increased leaching of amylose molecules and possibly also some hydrolysis of starch chains. As a result, the RVA pasting profile of a nonwaxy starch, in the presence of alkali, was drastically altered to one that more closely resembled that of its waxy counterpart without added alkali.     

Physicochemical Properties of Starch of Intermediate-Amylose and Waxy Rices Differing in Grain Quality

Starches from two crops of 7 intermediate-amylose and 7 waxy milled rices differing in eating qualities were characterized. Among the nonwaxy rice starches, those of softer cooked rice had gelatinization temperature of ≥ 70°C, medium to soft gel (110 mg/2 ml) consistency, low alkali viscograph peak viscosity, and greater Amylograph breakdown and lower Amylograph setback and consistency than low gelatinization temperature starches. Among waxy starches, gels of low gelatinization temperature samples had greater freeze-thaw stability than gels of high gelatinization temperature samples. A 12% paste gave better differentiation in Amylograph viscosity than 10% paste of intermediate-amylose milled rice. Water-extractable substances that suppressed the Amylograph viscosity of milled waxy rices were lipids and polysaccharides.     

Phosphorus and Amylose Branching in Rice Starch Granules

Phosphorus content of rice starch granules prepared by DoBS extraction of milled rice protein was lowest and was mainly 6-phosphoglucose for 2 waxy rices. For 6 nonwaxy rices it was highest and predominantly phospholipid P based on choline content. Defatting with water-saturated butanol reduced both choline and P content of nonwaxy rice starch. Once recrystallized amylose of 7 rices had 72–84% β-amylolysis limit, DP 532–793 glucose units per reducing end, CL 101–157 glucose units per nonreducing end and 3.4–7.5 branches/molecule.     

Non-starch polysaccharide compositions of rice grains with respect to rice variety and degree of milling

The chemical compositions of cell wall materials (CWM) in brown and milled rice were investigated using four rice varieties, Taichung Sen 10 (TCS10, indica), Tainung 67 (TNu67, japonica), Taichung Sen Waxy 1 (TCSW1, indica waxy), and Taichung Waxy 70 (TCW70, japonica waxy). The yield of CWM preparation, equivalent to total dietary fiber content, followed the order of TNu67 > TCS10 > the waxy cultivars. This order also held for the water solubility and pectic substance content of the CWM preparations and the compositional ratio of arabinose to xylose of all CWM samples. Comparatively, the nonwaxy CWM were rich in pectic substances and glucans; whereas the waxy CWM counterparts were dominant with hemicellulose plus cellulose and arabinoxylan-related polysaccharides. These results were more significant for the hot-water-soluble than insoluble parts and mainly dependent of rice variety rather than the degree of milling.     

Comparison of Thermal and Viscoelastic Properties of Four Waxy Starches and the Effect of Added Surfactant

The waxy starches used in this investigation (maize (WM), barley (WB) and two rice starches RD4 and IR29) showed different gelatinization temperatures (GT) and enthalpies (ΔH_G) measured with differential scanning calorimetry (DSC). The differences in GT and ΔH_G could only partially be related to X-ray crystallinity. The high GT waxy starches WM and RD4 retrograded to a greater extent measured with DSC and the order of increased retrogradation agreed well with the order of X-ray crystallinity of the retrograded waxy starches. The melting temperature (T_C) of the retrograded waxy starches in contrast to GT was very similar for all starches. This indicates that the temperature of the glass transition (T_g) of the amorphous regions in the starch granules controlled the onset GT and perhaps also the extent of retrogradation. Addition of cetyl trimethyl ammonium bromide (CTAB) decreased the extent of retrogradation more than 45% compared to the melting enthalpy (ΔH_C) of the waxy starches without CTAB addition. The rice starch RD4 was most affected by the CTAB addition, and the WM starch the least. The viscoelastic behaviour in the temperature interval 25–90°C of 12%(w/w) gels differed between the waxy starches. The WB starch gels showed the highest storage modulus (G′) value and the lowest phase angle (δ), i. e. strongest and least viscous gels. The WM starch gels showed the lowest G′ value and the highest δ. The rice starches were in between with the RC4 starch (high GT) showing higher G′ value and lower δ than the IR29 (low GT). The viscoelastic parameters changed only slightly with increased temperature. The addition of CTAB to the waxy starch gels changed the viscoelastic behaviour of the stronger and less viscous starch gels of the WB and RD4 as their G′ value decreased and δ increased with increased temperature. The effect on WM and IR29 was only small.     

Characteristics of Gel-chromatographic Fractions of Starch in Relation to Rice and Expanded Rice-Product Qualities

Starch from waxy and nonwaxy rices was separated on Sepharose. In nonwaxy rice, the major (void volume) fraction stained a varying shade of blue with iodine depending on the sample. The water-insoluble amyolose content as estimated in milled rice flour was highly positively correlated with the λ_max of the iodine colour as well as with the „amylose”︁ content of the fraction. Debranching with pullulanase showed that the fraction had the dual character of being both amylopectin and amylose. A second fraction was for the most part true amylose. The volume of expanded rice product seemed to increase with average molecular weight of starch. The highest average molecular weight of starch corresponded to analytical values of water-insoluble amylose as estimated in rice flour and the same corresponded to the greatest expansion volume.     

Rice Starch Diversity: Effects on Structural,Morphological, Thermal,and Physicochemical Properties—A Review

Abstract: Rice starch is one of the major cereal starches with novel functional properties. Significant progress has been made in recent years on the characterization of rice starches separated from different rice cultivars. Studies have revealed that the molecular structure and functional properties are affected by rice germplasm, isolation procedure, climate, agronomic conditions, and grain development. Morphological studies (microscopy and particle size analysis) have reflected significant differences among rice starch granule shapes (polyhedral, irregular) and in granule size (2 to 7 μm). Nonwaxy and long‐grain rice starches show greater variation in granular size than the waxy starches. Rice starch granules are smaller than other cereal starches with amylose contents varying from virtually amylose‐free in waxy to about 35% in nonwaxy and long‐grain rice starches. Amylose content appears to be the major factor controlling almost all physicochemical properties of rice starch due to its influence on pasting, gelatinization, retrogradation, syneresis, and other functional properties. Waxy rice starches have high swelling and solubility parameters, and larger relative crystallinity values than nonwaxy and long‐grain starches. However, nonwaxy rice starches have a higher gelatinization temperature than the waxy and long‐grain starches. The bland taste, nonallergenicity, and smooth, creamy, and spreadable characteristics of rice starch make it unique and valuable in food and pharmaceutical applications. This review provides recent information on the variation in the molecular structure and functional properties of different rice starches.     

Effects of cooking methods on starch hydrolysis kinetics and digestion-resistant fractions of rice and soybean

In this study, we investigated the effects of cooking methods and digestion-resistant fractions on the starch hydrolysis kinetics of rice and soybeans. The RS1 contents in unheated rice and soybeans were found to be high at 5.3 and 4.9%, respectively. After heating, the RS1 levels of the rice and soybeans were significantly reduced to 0.4 and 2.4%, respectively. The total nonstarch polysaccharide (NSP) content was not significantly different according to heat treatment, but the heat treatments affected the amounts of water insoluble nonstarch polysaccharides (WISNSP) and water soluble nonstarch polysaccharides (WSNSP). The level of WISNSP in the unheated samples was higher than the WSNSP of both samples; however, the WISNSP level showed a reducing trend after heating. Also, total pentosan and water soluble pentosan contents showed similar trends with total NSP and WSNSP. The hydrolysis indices (HI) of the unheated rice and soybeans were low (36.2 and 40.3%), while the heated group had high levels (89.5 and 45.0%). Among the cooking methods, the highest kinetic constants (0.284 and 0.199) were found with autoclaving for both rice and soybeans, followed by electric cooker (0.282 and 0.170), microwave oven (0.256 and 0.155), and stone pot (0.238 and 0.167). Particularly, all soybean samples appeared to have lower starch hydrolysis kinetics than the rice samples. The RS contents of the rice and soybeans were highest in the samples that were cooked in the stone pot, at 1.2 and 3.8%, respectively.     

Waxy Gene Factor and Residual Protein of Rice Starch Granules

Residual protein of rice starch granules prepared from milled rice by protein extraction with sodium dodecylbenzene sulfonate or alkaline protease treatment was related to amylose content. SDS-polyacrylamide disc gel electrophoresis confirmed that the major protein in nonwaxy starch granules was the Wx gene product with subunit molecular weight of about 60,000 daltons. The Wx gene product was absent in waxy starch granules.     

Thermal Properties of Sorghum Starch

The differential scanning calorimeter (DSC) was used to measure thermal properties of sorghum starch and flour. DSC gelatinization temperatures of 24 nonwaxy sorghum varieties were: T_o (onset temperature): 71.0 ± 1.0°C; T_p (peak temperature): 75.6 ± 0.9°C and T_e (end temperature): 81.1 ± 1.1°C, respectively. The gelatinization energies ranged from 2.51 to 3.96 cal/g. There were no consistent relationships between DSC gelatinization temperatures or gelatinization energies and grain characteristics or physicochemical starch properties. DSC gelatinization temperature for nonwaxy, heterowaxy and waxy sorghum tended to increase as the number of waxy alleles (wx) increased. However, it appeared that at least a difference of two waxy alleles was required before differences in thermal properties of the samples were significant.     

Structure-viscosity relationships for starches from different rice varieties during heating

The effects of starch particle size and leached amylose on the viscosity of rice starch dispersions and changes of short-range structure and amylose content in starch granules of different rice varieties during heating were investigated. It was found that starch granule swelling increased rice starch dispersion viscosity during heating. The viscosities of the starch dispersions during heating were principally dependent on granular volume fraction and independent of starch variety. A distinct correlation between the amount of leached amylose and swelling of starch granules was also found. High initial amylose concentrations in starch granules reduced swelling during heating, thereby reducing rice dispersion viscosities. Fourier-transform IR spectroscopy indicated that the loss of short-range order was significant when the temperature reached the pasting onset temperature. The short-range order of waxy and medium grain rice starches was higher than that of long grain rice starches before gelatinization. The loss of order of waxy and medium grain rice starches was greater than that of long grain rice starches during heating, which was due to the presence of amylose, restraining the swelling and disruption of starch granules during heating.     

Studies on Starch Phosphates. Part 3. On the Esterified Phosphates in Some Cereal Starches

Some cereal starches were investigated whether glucose phosphate residues were in the polysaccharides. Significant amounts (6–15 ppm, as P) of glucose 6-phosphate were found in the acid hydrolysates of corn, waxy corn, rice and waxy rice starches. After the extensive action of bacterial α-amylase on these starches phosphorylated oligosaccharide (α-LPD) was recovered in reasonable yield by a DEAE-Sephadex column chromatography. The α-LPDs prepared from two sources of waxy rice starch contained 81.8 and 94,3% of P₀ at the 6th position of glucose residues and the rest of P₀ at the 2nd and/or 3rd positions of glucose residues. All these results show that these starches have glucose phosphate residues. In wheat starch, however, no evidence for the presence of glucose phosphate residues has been obtained.     

Comparative Acid Modification of Various Starches

Eight starches (maize, sorghum, finger millet, waxy and nonwaxy rice, chick pea, tapioca and potato) were acid modified with 0.5N HCl at 50°C. Alkali fluidity number (AFN) increased progressively with time of modification, and was highest in cereal followed by root, legume, and tuber starches. However, reduction in the number average molecular weight (M̄_n) was in the reverse order. Potato starch had the highest M̄_n, among the nonwaxy native starches and showed the greatest fall upon modification, whereas cereal starches had the least M̄_n in native form and showed the least fall. In fact, there was a clear proportionality between the M̄_n, of native starch and the extent of its hydrolysis under any given set of conditions. This relationship could be expressed by two intersecting lines, one for grains and one for root and tuber starches. When acid modified starches were recovered and dried without neutralization, hydrolysis still continued strongly in potato starch and slightly in tapioca, finger millet and sorghum starches. Other starches showed no change.     

蜡质大米淀粉性质的研究

对蜡质大米淀粉的性质进行了研究，结果发现：与普通大米淀粉相比，蜡质大米淀粉的透明度要高，透明度随时间的稳定性要好；在几种介质中，蜡质大米淀粉均无沉降现象发生，常温稳定性较好；在蒸馏水中，蜡质大米淀粉在蒸馏水中经过两次冻融循环的析水率较高，在其他介质中均表现出了较好的冻融稳定性；淀粉糊为假塑性流体，不抗剪切，几种介质对粘度产生了不同的影响。     

Digestibility and Pasting Properties of Rice Starch Heat‐Moisture Treated at the Melting Temperature (Tm )

Non‐waxy and waxy rice starches adjusted to 20% moisture (wet based, w.b.) were heated in a differential scanning calorimeter to determine the optimum parameters for producing slowly digestible starch (SDS). Starches heated to the temperature of melting (T_m) and held for 60 min in the calorimeter showed a slow digestibility compared to unheated samples. Digestibility decreased by 25 and 10%, respectively, for non‐waxy and waxy rice starches relative to non‐treated starches. Heat‐moisture treatment of waxy corn, non‐waxy corn and wheat starches at the T_m determined for non‐waxy rice starch did not result in significant decreases in digestibility. For waxy rice starches heat‐treated in microwave or conventional ovens at the T_m , there were slight but significant increases in digestibility of the treated starches compared to non‐treated starches at all incubation times. Digestibility was higher for starches heated for 30 min than for 60 min. Non‐waxy rice starches did not show any significant changes in digestibility. Heat‐moisture treatment at the T_m and the holding time of sample at that temperature in a differential scanning calorimeter were found to be significant to the formation of slowly digestible heat‐moisture treated starch.     

大米糊化特性曲线探讨

本文利用Brabender淀粉粘度仪,详细研究了糯型与非糯型大米样品在特殊情况下的糊化特性,并证明有明显差别。在糊化特性曲线上发现糯米型最高粘滞峰值低于籼米型。这两种类型大米的最高粘滞峰值与它们的酶含量成负相关,与直链淀粉含量和糊化温度成正相关。     

A Comparative Study on Retrogradation of Rice Starch Gels by DSC,X-Ray and α-Amylase Methods

The degree of retrogradation (DR) of 10 and 50% rice starch gels, which were stored at refrigerator, room temperature and freezer for 1, 3 and 6 days, were investigated by DSC, X-ray diffractometry and α-amylase-iodine methods. Besides being affected by moisture content and storage conditions applied, the nonwaxy rice starch gels were retrograded faster and higher than the waxy ones. DR of 50% starch gels was higher than that of 10% starch gels. In case of 50% starch gels DR increased in the following order: refrigerated < room temperature < frozen. For 10% starch gels, no typical X-ray pattern of the retrograded starch was shown, while DSC and α-amylase-iodine method gave information on DR of starch gels. Due to interpretative sensitivity of the data obtained, α-amylase-iodine method was suggested as an adequate mens for the DR of starch gels.