Rice Starch Isolation Research Articles

Starch fine molecular structures as driving factors for multiphasic starch gelatinization property in rice flour

AbstractBackground and ObjectivesAlthough the gelatinization property of isolated rice starch has been investigated in terms of its relationship to starch fine molecular structures, it remains unclear how these structures determine the gelatinization property of rice flour. The gelatinization properties of 10 rice flours with varying chain‐length distributions were thus studied.FindingsRice flours with larger amylose molecules, longer and higher amount of amylopectin intermediate chains showed double gelatinization peaks. The onset and peak temperatures of gelatinization for the peak having a lower gelatinization temperature showed a positive correlation with the molecular size of amylopectin. Conversely, the conclusion temperature of gelatinization for the peak with a higher gelatinization temperature exhibited a negative correlation with the molecular size of amylose and a positive correlation with the quantity of amylose and amylopectin intermediate chains. These correlations were largely different compared with those for rice flours with a single gelatinization peak.ConclusionsThese results supplied the first associations between gelatinization property of rice flour and starch fine molecular structures, which were different from those for pure rice starches.Significance and NoveltyThese results have the potential to assist the food industry in developing rice products with improved quality, depending on the molecular structure of the starch.

Isolated rice starch fine structures and pasting properties changes during pre-germination of three Thai paddy (Oryza sativa L.) cultivars

This research aimed to investigate fine structural changes and pasting properties of isolated rice starches during pre-germination. Three stages of pre-germinated brown rice (PGBR) and flour were prepared from three different Thai paddy cultivars. Changes in α-amylase activities of flour were determined. Starch was isolated from the flour by alkali extraction. The molecular size distributions, amylopectin branch chain length distributions, and pasting properties of three-stage PGBR starches were compared to ungerminated brown rice (UGBR) starches. During pre-germination, the α-amylase activities of PGBR flour from all rice cultivars were increased. Isolated UGBR starches from the three rice cultivars had higher starch yields than three-stage PGBR starches. HPSEC-RI results showed different molecular size distributions; the amylose contents of KDML105 and RD31were reduced from 15.5 to 12.7% and 18.6 to 15.8% at the 1st and 2nd stages of pre-germination, respectively. HPAEC-PAD results indicated that isolated three-stage PGBR starches from three rice cultivars had lower short A chains amylopectin branch chains than their UGBR starches. Pre-germination affected pasting properties in which the peak viscosities changed at the 1st stage of pre-germination for RD6 (3662 cP) and the 2nd stage of pre-germination for KDML105 (3860 cP) and RD31 (2279 cP) cultivars.

Changes in physicochemical properties of rice starch during steeping in the parboiling process

Isolated rice starch, milled rice, and paddy rice kernels of the same variety (18% amylose) were examined after steeping at temperatures (60–75 °C) below and above the onset of rice starch gelatinization temperature for different durations in a 2:1 (w/w) ratio of water to kernel or starch. Changes in gelatinization temperatures were greater for resultant isolated starch >> milled rice > paddy rice. Annealing above its original To caused partial gelatinization, loss of crystallinity, and birefringence of the isolated starch as determined by X-ray diffraction, differential scanning calorimetry, and light microscopy. However, starch granules in milled rice and paddy rice, which are surrounded by non-starch components, maintained their granule integrity. Scanning electron microscopy revealed morphological differences between starch granules within native and steeped rice kernels. Rice starch granules and kernel characteristics were significantly altered during steeping and changes in isolated starch differed from those inside the rice kernels.

Retrogradation properties of high amylose rice flour and rice starch by physical modification

A new physical modification applied to prevent the retrogradation of rice flour and rice starch was investigated. This study examined the retrogradation properties of treated rice flour or rice starch paste by three stirring or heating–stirring, or without. The results proved that the retrogradations of rice flour and rice starch were both not substantially affected by three stirring modifications. However, three heating–stirring treatments had a marked effect on retarding the retrogradation of rice flour, but did not affect that of isolated rice starch. In the differential scanning calorimetry (DSC) analysis, modified rice flour by three heating–stirring exhibited the lowest retrogradation enthalpy (3.04 J/g dry matter) as compared to the control RF (5.93 J/g dry matter) and by three stirring (5.08 J/g dry matter). Meantime, it had almost the least recrystallization of retrogradation by X-ray diffraction (XRD). It was also found through scanning electron microscopy (SEM) that the granule structure of this modified rice flour had a more honeycomb-like structure and the lowest crystallinity as compared to the others.

Structural modification and characterization of rice starch treated by Thermus aquaticus 4-α-glucanotransferase

Rice starch was modified using Thermus aquaticus 4-α-glucanotransferase (TAαGTase) in this study. The changes in the molecular structure and the effect on the starch retrogradation by TAαGTase treatment were investigated on isolated rice starch. By treating TAαGTase, molecular weight profile of amylopectins shifted to higher elution time from 1.0 × 10 8 to 2.4 × 10 7 or 0.8 × 10 7, depending on the level of enzyme dosage. Meanwhile, there were huge increases in the proportions of content corresponding to amylose size and even smaller molecules. On treating with TAαGTase, short branch chains (DP 1–8) increased, and longer branch chains (>DP 19) increased significantly as well, with a broader distribution up to DP 46 compared to the control rice starch. Amylose content decreased from 30.0 to 21.8–23.7%. This indicated that the amylose could be transferred to the amylopectin branch chain by the disproportionation of TAαGTase, resulting in lowering the amylose content and the formation of amylopectin with a broader branch-chain length distribution. TAαGTase modified rice starch showed that X-ray diffraction pattern of the B-type crystalline even before cold storage, and that a variety of cyclic glucans (DP 5–19) were produced by enzymatic reaction. In particular, the accelerated rate of starch retrogradation was clearly observed compared to the control due to an overall increase in the number of elongated long-branch chains, decrease in the amount of amylose–lipid complex, and the possible synergistic effects of these factors.

Effects of Alcalase/Protease N treatments on rice starch isolation and their effects on its properties

The effects of different protease treatments on rice starches and their properties were studied. The rice starches produced from protease N exhibited higher pasting viscosities than those produced from alcalase. The hot pastes of the starches produced from protease N also showed higher elastic moduli, zero-order Newtonian viscosities and yield stresses than those produced from alcalase. No differences were found in the crystalline pattern, thermal properties, granules appearance, and average molecular weight ( M w) of the rice starches between the two protease treatments. But the M w of the pasted starch produced from protease N was higher than that produced from alcalase. When additional protease was added to the isolated starches and the mixture pasted, the M w of the starches pasted with added alcalase was significant lower than that of the starches pasted with added protease N. The reduction in molecular weight suggested that alcalase had modified the starch molecules during pasting.

The effect of rice variety and starch isolation method on the pasting and rheological properties of rice starch pastes

The effect of rice variety and starch isolation method on the pasting and rheological properties of rice starches was evaluated. One waxy and three non-waxy rice varieties from California with a range of amylose contents of 1.6–26.5% and four methods of isolation were evaluated. A rotational rheometer (RR) was used to measure the pasting and rheological properties of starch dispersions (8% w/w). The RR pasting curves had similar shapes to those from a rapid visco-analyzer (RVA). The four treatments used for isolating starch were a protease, NaOH (0.1% and 0.4%), or sodium dodecyl sulfate (SDS) (1.0%). The NaOH (0.4%) and SDS treatments were found to reduce the peak pasting temperatures of the non-waxy starches as compared with the protease and NaOH (0.1%) treatments. The same trend of the treatments was found with the elastic moduli, low shear viscosities, and yield stresses of the non-waxy starch pastes measured at 65 °C, immediately after pasting. The elastic moduli of the waxy starch pastes appeared to be least affected by method of starch isolation, but the low shear viscosity and yield stress of the protease starch paste was significantly higher than the paste from the other three treatments. Overall, the method of rice starch isolation was found to affect the gelatinization and rheological characteristics of hot rice starch paste.

Effect of high-pressure treatment on rheological, thermal and structural changes in Basmati rice flour slurry

Rheological, thermal and structural changes in high pressure (HP) treated Basmati rice flour dispersions were studied as function of pressure level (350–650 MPa), slurry concentration (with 1:5, 1:3 and 1:2 flour-to-water ratios) and holding time (7.5–15 min). Rice flour dispersions exhibited a gradual liquid–solid gel transformation as they gelatinized and/or denatured and behaved as viscoelastic fluid following HP treatment. Mechanical strength ( G′) of pressurized gel increased with applied pressure and rice concentration. Differential scanning calorimeter (DSC) thermograms of rice slurry measured after pressure treatment indicated a reduction in peak enthalpy in proportion with the extent of gelatinization and/or denaturation of starch and proteins. Pressure-treated rice samples had a progressively lower gelatinization temperature. A 15 min pressure treatment at 550 MPa was found sufficient to complete gelatinization of protein free isolated rice starch while the slurry required 650 MPa. The presence of proteins might have been responsible for the slower starch gelatinization in the rice slurry during pressure treatment. The sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier-transform infrared (FTIR) spectroscopy results indicated some minor changes in protein subunits and secondary structure of rice protein. This study has provided complementary information on pressure-induced changes in physical (thermal stability, overall structure) and molecular level (secondary structure) of rice protein.

Rice starch isolation by neutral protease and high-intensity ultrasound

Abstract The efficacy of a neutral protease and combinations of neutral protease and high-intensity ultrasound for isolation of rice starch was investigated. Rice flour slurry (33%) was treated with a neutral protease at 0.01, 0.03, or 0.05% (on flour basis) or combinations of 0.03% neutral protease and high-intensity ultrasound at 25, 50, or 75% amplitude for 15, 30, or 60 min concurrently or sequentially. The starch yield using neutral protease alone ranged from 62.5 to 71.8% with 0.53–0.88% residual protein content and 0.99–1.81% damaged starch content. The starch yield greatly improved to 79.8–86.7% with 0.50–0.96% residual protein content and 0.98–1.87% damaged starch content when neutral protease treatment was combined with high-intensity ultrasound. Increasing sonication time at 50% amplitude during protease digestion improved the starch yield from 83.9 to 86.1%, but did not improve those treated at 75% amplitude. The preferred combination was neutral protease digestion for 2 h followed by sonication at 75 or 50% amplitude for 15 or 30 min. The starch structure analyzed by a high performance size-exclusion chromatography and scanning electron microscopy revealed no damage to the molecular structure or to the starch granule surface, however, the peak viscosities of rice starch increased after sonication. The combination of neutral protease and high-intensity ultrasound was an effective technique for isolation of rice starch without generating high salt wastes.

Application of High‐Intensity Ultrasound and Surfactants in Rice Starch Isolation

ABSTRACTHigh‐intensity ultrasound was evaluated as an alternative method to isolate rice starch without the use of chemicals as in the traditional alkaline steeping method. Surfactants, including sodium dodecyl sulfate (SDS), sodium stearoyl lactylate (SSL), and Tween 80, at 0.1, 0.3, or 0.5% combined with high‐intensity ultrasound were also investigated for rice starch isolation. A rice flour slurry (33%) was subjected to sonication for 15, 30, or 60 min at an amplitude of 25, 50, or 75% and at 40 or 50°C. The starch yield was not significantly affected by the treatment temperature and ranged from 46.7 to 76.2% (starch dry basis) after the sonication treatment; the protein and damaged starch contents of the isolated starches were 0.9–1.7% and 3.1–3.5% (dry basis), respectively. The combination of 0.5% SDS and high‐intensity ultrasound improved the starch yield to 84.9% with low residual protein, however, little improvement was observed with SSL or Tween 80. The pasting properties of isolated starch as measured by a Rapid Visco‐Analyser were affected by the treatment temperature and by the amount of residual protein and damaged starch. The thermal properties of the isolated starch were not changed by sonication and the amylose content remained unchanged. The surface of the isolated starch was not damaged by sonication as shown by scanning electron microscopy. High‐intensity ultrasound, alone or combined with SDS, showed a great potential for rice starch isolation in a short period of time without generating alkaline effluent.

Pasting and Crystalline Property Differences of Commercial and Isolated Rice Starch with Added Amino Acids

ABSTRACT This study compared effects amino acid structure and type on the pasting properties and crystallinity of rice starch isolated from flour. Amino acids were added at 2 and 6% of the starch (dry basis) for RVA analyses. Charged amino acids had more of an influence on pasting properties than neutral amino acids. Our results indicated that the negatively charged amino acids had a similar effect as that of the positive charged amino acids for decreasing cooking stability of the starch, but opposite effects on retrogradation tendency. Charged amino acids increased the crystallinity of the starch, potentially enhancing resistant starch nature.

Rice Starch Isolation from Newly Developed Rice Cultivars by the Improved Alkali Method.

A rapid and efficient rice starch isolation method was tested on two varieties of newly developed rice, Hoshinishiki (Kanto181) and Saikaimochi227 (a high-amylose and a high-yield waxy rice), and a reference rice variety, Nipponbare. Rice flour was stirred in 0.05 or 0.075 M aqueous sodium hydroxide for 3 h once or three times, neutralized with 1 M hydrochloric acid and washed with water. Isolated rice starch was compared with the starch isolated by the conventional method in terms of chemical and physical properties. The improved method reduced processing time to two days, while the conventional method required one to three weeks. The improved method lowered damaged starch and protein contents, but slightly lowered starch recovery. Non-waxy rice starches isolated by the two methods differed in physical properties upon testing by photopastegraphy and Rapid Visco Analyser (RVA), whereas no difference was observed in waxy rice. The phosphorus content in Nipponbare starch decreased during the isolation process due to degradation of the lysophospholipid, and the phosphorus content was the lowest in the starch isolated by the conventional method. Sodium content was high in the starch isolated by the improved method, although the influence of residual sodium on the viscosity of the paste was small. To reduce residual sodium in the starch isolated by the improved method, washing with water eight times after neutralization was needed. Thus, we propose the improved procedure for rice starch preparation. Rice flour is washed with 0.05 M aqueous sodium hydroxide three times, neutralized and then washed eight times with water. In the case of high-amylose or waxy rice flours, alkali washing can be reduced to once.

Pasting Property Differences of Commercial and Isolated Rice Starch with Added Lipids and β‐Cyclodextrin

ABSTRACTLipids are known to generally affect starch properties but the effects of lipid structure and β‐cyclodextrin (β‐CD) on different starches has not been investigated. This study compared the effects of lipids and β‐CD on pasting properties of isolated rice starch with commercial rice starch. Flour was defatted by Soxhlet extraction and deproteinated by alkaline protease digestion. Fatty acids, monopalmitin (MP), tripalmitin, lysophosphatidylcholine (LC), lysophophatidylethanolamine (LE), each added at 0.2 and 0.6% (starch db), and β‐CD added at 2 and 6% (starch db) were tested. Pasting temperature (PT) increased with added phospholipid, particularly in the commercial starch, while all lipids except tripalmitin increased final viscosity (FV) and total setback (TSB). Breakdown (BKD) was mainly affected and increased by up to 39 RVU for fatty acids while decreasing by up to 80 RVU for other lipids in both starches. TSB doubled by the addition of 0.6% MP but decreased to onethird by 0.6% LE or LC. Addition of β‐CD decreased minimum viscosity (MV) and FV while increasing BKD in isolate but decreased TSB in commercial starch.

Comparison of Protease Digestion at Neutral pH with Alkaline Steeping Method for Rice Starch Isolation

L'isolement de l'amidon de riz differe des autres methodes d'isolement, du mais, du ble au de la pomme de terre, en raison des proprietes differentes de ses proteines. Le procede par trempage alcalin presente un rendement de 73 a 85%, mais produit beaucoup d'eaux residuelles alcalines. L'efficacite d'une digestion par la protease acide, neutre ou alcaline a pH neutre est evaluee, cette technique ayant deja montre son efficacite sur l'amarante et l'avoine.

On the roles of protein and starch in the aging of non-waxy rice flour

Changes in pasting and thermal properties of non-waxy rice flour and its isolated starch during storage at 25, 35 and 45°C were compared. Aging had no apparent effect on the pasting behaviour of the isolated starch, but markedly affected that of the flour. Peak viscosity ( V p) of rice flour pastes generally increased with both temperature and time of storage, but reached a plateau within 4 weeks of storage at 45°C. Fresh flour paste exhibited lower V p, a slower rise in apparent viscosity, and much better stability than an isolated starch paste. The addition of isolated oryzenin to isolated rice starch resulted in pasting behaviour which more closely approximated that of an extensively aged flour. DSC scans of fresh flour at ∼13% moisture revealed a weak heat-irreversible endothermic event over the temperature range from 47 to 66°C which was attributed to the denaturation of oryzenin. This transition was shifted to higher temperatures with increasing storage temperature and time. It also became increasingly skewed and broadened until it was no longer detectable after the flour had been stored at 45°C for 8 weeks. Starch gelatinization characteristics of both flour and isolated starch, as determined by DSC, were apparently unaffected by aging. However, rice flour exhibited significantly higher onset temperature of gelatinization, but lower gelatinization enthalpy, than isolated rice starch. Similarly, pulsed NMR studies showed no apparent effect of aging on retrogradation behaviour of rice flour or starch gels. These results suggest that modification of the protein component, rather than starch, was primarily responsible for rheological changes associated with aging of rice flour.

Rice Starch Isolation by Alkaline Protease Digestion of Wet-milled Rice Flour

Alkaline protease digestion with a food-grade enzyme was used to produce rice starch from wet-milled rice flour (WMRF). In a 3×3 factorial modelling experiment, recoveries of starch and levels of protein contamination were determined at pH 8·5–10·0, protease levels of 0·5–1·5% (based on WMRF), and digestion times of 5·0–30·0 h. The following digestion conditions were kept constant; 55 °C with mild agitation, 34–37% (w/v) flour solids, and alkalinity to within ±0·2 pH units. Regression equations with the three variables explained 92% and 98%, respectively, of the variances in starch recovery and protein contamination. Upon digestion with 1·1% protease at pH 10·0 and 18·0 h, starch recovery was 95% and protein contamination was 0·5%. Most hydrolysis of rice protein occurred in the first 3–4 h of digestion as determined by the consumption of sodium hydroxide (NaOH). Rice starch also was isolated by extraction of WMRF with c. 2·5 parts of 0·05 m NaOH at c. pH 12. The recovery of starch was c. 10% higher with the protease method than with the NaOH method, and the effluents contained mostly amino acid salts as opposed to protein mixed with alkali. The rice starch isolated by protease digestion was lighter in appearance, contained more lipid, and gave a somewhat lower consistency after pasting. The raw materials used to isolate rice starch by the protease method were approximately twice as costly in 1996 as those in the NaOH method, principally because of the cost of the protease (55% of total).

Comparison of Protein Extraction Solutions for Rice Starch Isolation and Effects of Residual Protein Content on Starch Pasting Properties

Protein extraction solutions such as aqueous solutions of sodium hydroxide (0.1 and 0.2 %), sodium lauryl sulfate (SLS, 1.2 %) containing sodium sulfite (0.12 %), and dodecylbenzene sulfonate (DoBS, 1.2 %) containing sodium sulfite (0.12 %) were compared in their protein removal efficiencies during isolation of starch from a rice flour (Ilpumbyo, a nonwaxy Korean rice variety). In addition, the pasting properties of the isolated starch was compared. More than 80 % of the flour protein was extracted in 1 h by stirring the dispersion (1:3, w/v) at room temperature. Repeating the extractions (1 or 2 h for each step) with fresh solution significantly increased the protein removal efficiency. When the extraction in 0.2 % NaOH was repeated four times (1 h for each step) at 25°C, the residual protein content in the isolated rice starch was 0.9 % (DB), equivalent to 86 % removal of the rice protein. Raising the extraction temperature slightly increased the protein solubility, but starch loss also became significant. Among the solutions, DoBS was most effective in removing rice protein whereas SLS was least. The residual protein content had a critical role in determining the pasting characteristics of the isolated starch, showing a negative correlation to the peak viscosity of the starch paste, but a positive correlation to the pasting temperature.

Comparison of Protein Extraction Solutions for Rice Starch Isolation and Effects of Residual Protein Content on Starch Pasting Properties

Comparison of Protein Extraction Solutions for Rice Starch Isolation and Effects of Residual Protein Content on Starch Pasting Properties