Hydroxypropylation of pigeon pea (Cajanus cajan) starch: Preparation, functional characterizations and enzymatic digestibility

Hydroxypropyl starch derivatives were prepared from pigeon pea starch (NPPS) which is an unconventional starch source. Functional parameters and characterization of both native and modified starches were carried out. The starch granules appeared oval or elliptical in shape with sizes ranging from 7 to 40 μm in width and 10 − 30 μm in length. Hydroxypropylation did not alter the shape of the starch granules in a pronounced way. Generally, the x-ray diffractograms of native pigeon pea starch showed the “A” pattern. However, slight reductions in the diffraction intensity of starches after modification were observed. At all temperatures studied (30-90 °C), swelling and solubility of hydroxypropylated starches were higher than the NPPS. Progressive increases in swelling capacity and solubility were observed as the molar substitution (MS) increased among the hydroxypropylated starches. Hydroxypropylation reduced starch paste turbidity on storage. Also, studies showed that syneresis reduced after hydroxypropylation. In addition, syneresis reduced as the MS of the hydroxypropyl starches increased. The results indicate that pasting temperature and peak temperature reduced after modification but peak viscosity increased in hydroxypropylated starch derivatives compared with the native starch. Setback reduced in hydroxypropylated starches compared with the native starch. Enthalpy of gelatinization and percentage retrogradation reduced after hydroxypropylation and progressive reductions were observed as the MS increased among the starch derivatives. Hydroxypropylation increased enzymatic digestibility.     

Starch hydroxyalkylation: Physicochemical properties and enzymatic digestibility of native and hydroxypropylated finger millet (Eleusine coracana) starch

Starch was isolated from finger millet (Eleusine coracana) and it was etherified with propylene oxide to produce hydroxypropylated derivative. The specific specie used in this study is African finger millet known as jeero. The yield of starch obtained from finger millet on dry weight basis was 52.4%. Progressive increases in molar substitution (MS) were observed as the volume of propylene oxide added to the reaction medium increased. The X-ray pattern of native finger millet starch conforms to the ‘A’ diffraction pattern characteristics of cereal starches. Prominent peaks were observed at around 2θ=15°, 17°, 18° and 23° and weaker peaks at around 2θ=20° and 26°. No pronounced differences were observed between the diffractograms of native starch and the hydroxypropyl derivatives. Hydroxypropylation improved the free swelling capacities of the native starch at all temperatures studied (30–90 °C). Turbidity of unmodified finger millet starch paste increased progressively as the days of storage increased. Turbidity reduced remarkably after hydroxypropylation and reduction in turbidity was observed as the MS of the modified starches increased. Hydroxypropylation reduced pasting temperature, increased peak viscosity but reduced setback value. In addition, hydroxypropylation reduced percentage syneresis of the unmodified starch. Retrogradation properties monitored with differential scanning calorimetry reveals that starch retrogradation reduced reasonably after hydroxypropylation. Carbon 13 NMR spectroscopy reveals that hydroxypropylation took place predominantly on carbon 6 on the anhydroglucose unit (AGU).     

高取代度羟丙基木薯淀粉流变特性研究(I)流变特征及羟丙基取代度的影响

研究了高取代度羟丙基木薯淀粉溶液（分子取代度ＭＳ＝１．６～４．５）的流变特性及羟丙基取代度对流变特性的影响规律。结果表明，高取代度羟丙基木薯淀粉呈现假塑性流体特征，符合幂定律τ＝Ｋγｍ。ｍ值在０．７～０．８范围，表明羟丙基化使木薯淀粉偏近牛顿流体。高取代度羟丙基木薯淀粉具有触变性和剪切稀化性质，并随溶液浓度升高而增大。羟丙基取代度对木薯淀粉流变特性有很大影响，当ＭＳ≤３．５时，溶液的表观粘度和剪切稀化现象随ＭＳ的增高而减小，当ＭＳ＞３．５时，溶液的表观粘度和剪切稀化现象随ＭＳ的增高而增大。这种变化规律符合羟丙基化反应机理。     

Substituent distribution within cross-linked and hydroxypropylated sweet potato starch and potato starch

Revealing the substituents distribution within starch can help to understand the changes of starch properties after modification. The distribution of substituents over cross-linked and hydroxypropylated sweet potato starch was investigated and compared with modified potato starch. The starches were cross-linked with sodium trimetaphosphate and/or hydroxypropylated with propylene oxide. The native and modified starches were gelatinized and hydrolysed by pullulanase, β-amylase, α-amylase and a combination of pullulanase, α-amylase and amyloglucosidase. The hydrolysates were analysed by HPSEC, HPAEC and MALDI-TOF mass spectrometry. Cross-linking had only a slight effect on the enzymatic hydrolysis, where hydroxypropylation evidently limited the enzymatic hydrolysis. The results obtained suggest that the hydroxypropyl substituents are not distributed regularly over the starch chains. Although the average substitution was around 2 hydroxypropyl groups per 10 glucose units, in the enzyme digests of hydroxypropylated starches, oligomer fragments of 10–15 glucose units, carrying 5–8 hydroxypropyl groups, were identified. It is hypothesised that higher levels of substituents are present in the amorphous regions and periphery of clusters of starch granules. This is the first time that the location of hydroxypropyl groups within sweet potato starch has been examined in this detail. Despite significant differences in granule architecture between starches from potato and sweet potato, similar patterns of hydroxypropylation have been found.     

Rheological properties and stability of low-in-fat dressings prepared with high-pressure homogenized yeast

The aim of present study was to investigate the feasibility of application high-pressure homogenized (HPH) yeast aqueous dispersions with low nucleic acid content for the formulation of low-in-fat dressings. The HPH treatment (1500 bar, 3 passes) in alkaline medium improved the protein dispersibility (>50%). Emulsions were prepared using sunflower oil (12.0% or 25% w/w oil), xhantan/guar gums (0.5% w/w), modified starch (0–4.0% w/w), salt, sucrose, acidulants, EDTA, and antimicrobial agents. All emulsions (pH 3.97 ± 0.27; a_w = 0.97 ± 0.01), whatever the starch content, behaved clearly as pseudoplastic fluids in steady flow measurements. Moreover, as the frequency sweep measurements were made they also exhibited a weak gel behavior. Although the presence of starch produced an increase of mean particle size (D_3,2 values), the rheological parameters (consistency index, proportionality coefficient and coordination number) also increased, so that the starch contributes to reinforce the three-dimensional network formed by oil droplets, protein aggregates and other polysaccharides. Yeast dressings were stable to coalescence after 28 days of quiescent storage (7.0 ± 0.5 °C) and only the highest starch concentration at 25% w/w oil was sufficient to maintain the stability of network.     

FLOW BEHAVIOUR OF CALCIUM COMPLEXED HYDROXYPROPYL RICE STARCHES

The flow behaviour characteristics of native, hydroxypropyl starches and their calcium complexes were determined at different levels of starch concentrations, temperatures and shear rates. Hydroxypropyl starch with different Molar Substitution (MS = 0.02–0.12) were used. Both native and hydroxypropyl starch were treated with varying amount of calcium (50–250 μg/g starch). Flow properties were affected due to hydroxypropylation and their calcium treatment. The flow properties were evaluated by power law equation.     

Evaluation of lower-starch diets for lactating Holstein dairy cows

The objective of this experiment was to measure ruminal and lactational responses of Holstein dairy cows fed diets containing 3 different starch levels: 17.7 (low; LS), 21.0 (medium; MS), or 24.6% (high; HS). Twelve multiparous cows (118 ± 5 d in milk) were assigned randomly to dietary treatment sequence in a replicated 3 × 3 Latin square design with 3-wk periods. All diets were fed as total mixed rations and contained approximately 30.2% corn silage, 18.5% grass silage, and 5.0% chopped alfalfa hay. Dietary starch content was manipulated by increasing dry ground corn inclusion (% of dry matter) from 3.4 (LS) to 10.1 (MS) and 16.9 (HS) and decreasing inclusion of beet pulp and wheat middlings from 6.7 and 13.4 (LS) to 3.4 and 10.1 (MS) or 0 and 6.8 (HS). In vitro 6-h starch digestibility of the diet increased as nonforage sources of fiber replaced corn grain (% of dry matter; 73.6, HS; 77.3, MS; 82.5, LS) resulting in rumen-fermentable starch content by 14.6, 16.2, and 18.1% for the LS, MS, and HS diets, respectively. Diets had similar neutral detergent fiber from forage and particle size distributions. Dry matter intake, solids-corrected milk yield, and efficiency of solids-corrected milk production were unaffected by diet, averaging 26.5 ± 0.8, 40.8 ± 1.6, and 1.54 ± 0.05 kg/d, respectively. Reducing dietary starch did not affect chewing time (815 ± 23 min/d), mean ruminal pH over 24 h (6.06 ± 0.12), acetate-to-propionate ratio (2.4 ± 0.3), or microbial N synthesized in the rumen (585 ± 24 g/d). Total tract organic matter digestibility was higher for HS compared with MS and LS diets (69.2, 67.3, and 67.0%, respectively), but crude protein, neutral detergent fiber, and starch digestibilities were unaffected. As dietary starch content decreased, in vitro ruminal starch fermentability increased and, consequently, the range between HS and LS in rumen-fermentable starch (3.5 percentage units) was less than the range in starch content (6.9 percentage units). Under these conditions, dietary starch content had no measurable effect on ruminal fermentation or short-term lactational performance of high-producing Holstein dairy cows.     

Preparation of a hydroxypropyl Ganoderma lucidum polysaccharide and its physicochemical properties

A hydroxypropyl Ganoderma lucidum polysaccharide (H-GLP) was prepared from a low-value water-insoluble polysaccharide from G. lucidum (GLP) using propylene oxide under an alkaline condition. The H-GLP was characterised for its chemical structure with IR and ¹³C NMR spectra and analysed for its mono-sugar composition, molecular weight, and hydroxypropyl content. H-GLP contained mannose, glucose, and galactose in a mole ratio of 1.0:36.5:3.59, respectively, with an average molecular weight of 788 kDa and a hydroxypropyl content of 12.05%. H-GLP also had an excellent water solubility of more than 50 mg/mL, suggesting that hydroxypropylation might serve as an effective approach to enhance water solubility of GLP. H-GLP was also compared to the original GLP and ascorbic acid for antioxidant properties. H-GLP showed much stronger free radical scavenging capacity against hydroxyl and superoxide anion radicals and hydrogen peroxide than GLP. These results suggested the potential of hydroxypropylation in developing water-soluble antioxidative polysaccharides from GLP to enhance the profitability of G. lucidum production and processing industries.     

乙酰化羟丙基淀粉改性次序及程度研究

为确定复合改性对淀粉性质的影响,从而为复合改性淀粉在食品中的应用提供参考。以玉米淀粉为原料,在羟丙基淀粉及乙酰化淀粉2种单一改性淀粉研究的基础上,采用分光光度法确定单一改性淀粉取代度,并以复合取代度为指标,探讨乙酰化羟丙基复合改性淀粉的改性次序及改性程度对复合改性淀粉制备的影响。结果表明:水解作用与空间位阻是影响复合改性效果的重要因素;乙酰化羟丙基复合改性淀粉合理的改性次序应为先羟丙基化后乙酰化,且在一定范围内,乙酰化反应不受羟丙基化程度的影响。     

Studies on the synthesis and properties of hydroxypropyl derivatives of cassava (Manihot esculenta Crantz) starch

Cassava starch was subjected to hydroxypropylation in three different media, which included water, water in the presence of a phase transfer catalyst, and 2‐propanol, all at 30 ± 2 °C for 24 h. Propylene oxide was used in four different concentrations (50, 100, 150 and 200 g kg^?1 of starch dry weight). The products were characterized by determining their molar substitution (MS), structural and functional properties. The analyses were done in triplicate and the data were analyzed using the statistical package 8.01. The MS of the products ranged from 0.26 to 1.41. The MS of the hydroxypropyl derivatives were found to be higher when the reaction was carried out in the aqueous medium in the presence of tetrabutylammonium bromide, a phase transfer catalyst, when compared to the reaction in 2‐propanol, which was found to be not very effective at 30 ± 2 °C. The etherification altered the granular properties of starch, as could be seen from scanning electron micrographs. Hydroxypropylation resulted in starch pastes which were stable and with higher swelling volume, solubility, light transmittance and water binding capacity as compared to native starch. The hydroxypropyl starches showed significantly lower pasting temperatures and setback viscosities. The enzyme digestibility of the derivatives was seen to decrease with increase in MS and there was a significant reduction in the syneresis of the starch pastes of hydroxypropyl derivatives. Texture profile analysis showed that hydroxypropylated starch gels exhibited higher hardness, springiness (elasticity) and gumminess and lower cohesiveness than the native starch. Copyright © 2007 Society of Chemical Industry     

Effect of cross-linking on the resistance to enzymatic hydrolysis of waxy maize starch and low-methoxy pectin

Gelatinised waxy maize starch and low-methoxy pectin mixtures were solubilised/dispersed in water and cross-linked with sodium trimetaphosphate (STMP). The polysaccharides were subjected to α-amylase, β-amylase or amyloglucosidase (AMG) hydrolysis for different times, and at two starch to pectin combination ratios (3:2 and 2:3). The extent of hydrolysis by porcine pancreatic α-amylase of the cross-linked (gelatinised) starch was 54.8–58.9% in comparison with gelatinised starch (for different incubation times), corresponding to 52.3–58.9% and 51.3–55.3% of the starch in the uncross-linked (UL) 3:2 and 2:3 starch to pectin ratios (for the same hydrolysis times). Blends of individually cross-linked starch to pectin ratios (3:2 and 2:3) were hydrolysed to 66.2–67.0% and 65.4–71.8%, respectively, compared with the corresponding UL counterparts. When the gelatinised starch was incubated for 0.5–36 h with β-amylase, hydrolysis ranged from 9.2% to 26.2%, and from 5.4% to 12.2% when the starch was cross-linked (corresponding to 40.0–58.7% of the gelatinised starch). For starch to pectin ratios of 3:2 or 2:3 blended after cross-linking, or by simultaneous cross-linking, hydrolysis represented 2.3–3.4% and 0.3–0.6% for the 3:2 ratio but only 1.2–2.0% and 0–0.3% for the 2:3 ratio. Hydrolysis with AMG using a 0.1 mg ml⁻¹ enzyme concentration caused 51.8% hydrolysis of gelatinised starch, which was lowered to 35.2% (i.e. by 68%) after cross-linking. At a higher enzyme concentration (1 mg ml⁻¹), the comparable figures were 91.7% and 71.9% (a reduction of 78.4%). For the UL 3:2 starch to pectin ratio and 0.1 and 1 mg ml⁻¹ enzyme concentrations, there was 27.8% and 56.5% hydrolysis of the polysaccharide which translated to 24.3% (87.4%) and 45.8% (81.1%), respectively, after cross-linking. Comparable figures for the 2:3 ratio (for the 0.1 and 1 mg ml⁻¹ enzyme concentrations) were 20.2% and 36.5% hydrolysis of the UL samples and 18.2% (90.1%) and 32.5% (89.0%) hydrolysis, respectively, after cross-linking.     

Crosslinking of interfacial layers in multilayered oil-in-water emulsions using laccase: Characterization and pH-stability

The enzymatic crosslinking of polymer layers adsorbed at the interface of oil-in-water emulsions was investigated. A sequential two step process, based on the electrostatic deposition of pectin onto a fish gelatin interfacial membrane was used to prepare emulsions containing oil droplets stabilized by fish gelatin-beet pectin membranes (citrate buffer, 10 mM, pH 3.5). First, a fine dispersed primary emulsion (5% soybean oil (w/v), 1% (w/w) gelatin solution) (citrate buffer, 10 mM, pH 3.5) was produced using a high pressure homogenizer. Second, a series of secondary emulsions were formed by diluting the primary emulsion into pectin solutions (0 - 0.4% (w/w)) to coat the droplets. Oil droplets of stable emulsions with different oil droplet concentrations (0.1%, 0.5%, 1.0% (w/v)) were subjected to enzymatic crosslinking. Laccase was added to the fish gelatin-beet pectin emulsions and emulsions were incubated for 15 min at room temperature. The pH- and storage stability of primary, secondary and secondary, laccase-treated emulsions was determined. Results indicated that crosslinking occurred exclusively in the layers and not between droplets, since no aggregates were formed. Droplet size increased from 350 to 400 nm regardless of oil droplet concentrations within a matter of minutes after addition of laccase suggesting formation of covalent bonds between pectin adsorbed at interfaces and pectin in the aqueous phase in the vicinity of droplets. During storage, size of enzymatically treated emulsions decreased, which was found to be due to enzymatic hydrolysis. Results suggest that biopolymer-crosslinking enzymes could be used to enhance stability of multilayered emulsions.     

Starch-gum Interactions: Formulations and Functionality Using Amaranth/Corn Starch and CMC

Formulations exploiting starch-gum interactions and using waxy amaranth starch and corn starch (1–5%), and CMC (0–1%) have been worked out. The combinations giving a Brookfield viscosity equivalent to 5% corn starch were found for both the starches. Amaranth starch CMC combinations showed higher viscosities than corn starch-CMC combinations. However, an efficient synergism was observed for corn starch, as seen from Brabender amylograph peak viscosity values. Freeze-thaw stability as well as stability under acidic conditions, retort conditions of 15psig/30min and mechanical shear improved admirably on interaction with CMC. No significant differences between corn and/or amaranth starch were observed when studied for functional properties after interaction with CMC. The only exeption was much better freeze-thaw stability for amaranth starch-CMC combination. This is explained to be due to inherently good freeze-thaw stability of waxy amaranth starch.     

Relationships between dry matter content,ensiling, ammonia-nitrogen,and ruminal in vitro starch digestibility in high-moisture corn samples

The objectives of the study were (1) to determine relationships between high-moisture corn (HMC) dry matter (DM), ammonia-N [% of crude protein (CP)], and soluble CP concentrations, and pH, with 7-h ruminal in vitro starch digestibility (ivStarchD), and (2) to evaluate the effect of ensiling on pH, ammonia-N, soluble CP, and ivStarchD measurements in HMC. A data set comprising 6,131 HMC samples (55 to 80% DM) obtained from a commercial feed analysis laboratory was used for this study. Month of sample submittal was assumed to be associated with length of the ensiling period. Data for month of sample submittal were analyzed using Proc Mixed in SAS (SAS Institute Inc., Cary, NC) with month as a fixed effect. Regressions to determine linear and quadratic relationships between ivStarchD and ammonia-N, soluble CP, pH, and DM content were performed using Proc Mixed. The ivStarchD increased by 9 percentage units from October to August of the following year. Similar results were observed for ammonia-N and soluble CP with increases from 1.8 to 4.6% of CP and 31.3 to 46.4% of CP, respectively, from October to August of the following year. Ammonia-N was positively related to ivStarchD (R² = 0.61). The DM content of HMC at silo removal was negatively related (R² = 0.47) to ivStarchD with a decrease of 1.6 percentage units in ivStarchD per 1-percentage-unit increase in DM content. The pH of HMC was negatively related to ammonia-N (R² = 0.53), soluble CP (R² = 0.57), and ivStarchD (R² = 0.51). Combined, ammonia-N, DM, soluble CP, and pH provided a good prediction of ivStarchD (adjusted R² = 0.70). Increasing pH, ammonia-N, soluble CP, and ivStarchD values indicate that HMC may need up to 10 mo of ensiling to reach maximum starch digestibility. Ammonia-N, DM content, soluble CP concentration, and pH are good indicators of ruminal in vitro starch digestibility for high-moisture corn.     

Influence of interfacial composition on oxidative stability of oil-in-water emulsions stabilized by biopolymer emulsifiers

The objective of this research was to evaluate the influence of storage pH (3 and 7) and biopolymer emulsifier type (Whey protein isolate (WPI), Modified starch (MS) and Gum arabic (GA)) on the physical and oxidative stability of rice bran oil-in-water emulsions. All three emulsifiers formed small emulsion droplets (d₃₂ < 0.5 μm) when used at sufficiently high levels: 0.45%, 1% and 10% for WPI, MS and GA, respectively. The droplets were relatively stable to droplet growth throughout storage (d₃₂ < 0.6 μm after 20 days), although there was some evidence of droplet aggregation particularly in the MS-stabilized emulsions. The electrical charge on the biopolymer-coated lipid droplets depended on pH and biopolymer type: −13 and −27 mV at pH 3 and 7 for GA; −2 and −3 mV at pH 3 and 7 for MS; +37 and −38 mV at pH 3 and 7 for WPI. The oxidative stability of the emulsions was monitored by measuring peroxide (primary products) and hexanal (secondary products) formation during storage at 37 °C, for up to 20 days, in the presence of a pro-oxidant (iron/EDTA). Rice bran oil emulsions containing MS- and WPI-coated lipid droplets were relatively stable to lipid oxidation, but those containing GA-coated droplets were highly unstable to oxidation at both pH 3 and 7. The results are interpreted in terms of the impact of the electrical characteristics of the biopolymers on the ability of cationic iron ions to interact with emulsified lipids. These results have important implications for utilizing rice bran oil, and other oxidatively unstable oils, in commercial food and beverage products.     

Ultrasound-assisted production of bioethanol by simultaneous saccharification and fermentation of corn meal

An ultrasound-assisted liquefaction as a pretreatment for bioethanol production by simultaneous saccharification and fermentation (SSF) of corn meal using Saccharomyces cerevisiae var. ellipsoideus yeast in a batch system was studied. Ultrasound pretreatment (at a frequency of 40 kHz) was performed at different sonication times and temperatures, before addition of liquefying enzyme. An optimal duration of the treatment of 5 min and sonication temperature of 60 °C were selected, taking into account glucose concentration after the liquefaction step. Under the optimum conditions an increase of glucose concentration of 6.82% over untreated control sample was achieved. Furthermore, the SSF process kinetics was assessed and determined, and the effect of ultrasound pretreatment on an increase of ethanol productivity was investigated. The obtained results indicated that the ultrasound pretreatment could increase the ethanol concentration by 11.15% (compared to the control sample) as well as other significant process parameters. In this case, the maximum ethanol concentration of 9.67% w/w (which corresponded to percentage of the theoretical ethanol yield of 88.96%) was achieved after 32 h of the SSF process. A comparison of scanning electron micrographs of the ultrasound-pretreated and untreated samples of corn meal suspensions showed that the ultrasound stimulated degradation of starch granules and release of glucose, and thereby accelerated the starch hydrolysis due to the cavitation and acoustic streaming caused by the ultrasonic action.     

Effect of calcium and hydroxypropylation on crystallinity and digestibility of rice starches

The digestibility of native and hydroxypropyl rice starches in the presence of calcium was investigated. Calcium interacted with native and hydroxypropyl rice starches and altered their relative crystallinity. Hydroxypropylation was measured in terms of molar substitution (MS) which in turn enhanced calcium binding. Depending upon the amount of calcium added (50–250 μg calcium per g dry starch) and levels of MS (ranging from 0·02 to 0·12), 25·4– 34·1 μg calcium was bound per g of hydroxypropyl starch. Native starch bound 25·4 μg calcium per g dry starch, which was much less than the hydroxy-propylated starches. Crystallinity decreased with the increase of MS and calcium concentration. Digestibility of ungelatinised hydroxypropyl starches increased with MS (2·5–4·1 mg reducing sugar released per g dry starch) and the trend is reversed in the gelatinised form. Calcium-induced amylolysis of the starches by porcine pancreatic α-amylase but somehow inhibited amyloglucosidase attack. © 1998 SCI.     

Acid thinned jicama and maize starches as fat substitute in stirred yogurt

Jicama and maize starches were hydrolyzed with HCl (1.5, 3.0 or 4.5 g/100 g of starch), at a temperature of 40 °C using two hydrolysis times (3 and 6 h). The acid degradation of both starches was not excessive as revealed by the positive blue value, amylose content, gel formation and gel thermo-reversibility. Jicama starches were more susceptible to acid hydrolysis than maize starches. Hydrolyzed jicama starches showed low values of gel strength and water solubility index, and high values of damaged starch, total sugar content and water absorption index. Stirred yogurt formulated with hydrolyzed starches showed different properties of syneresis index according to the starch type and hydrolysis conditions. Yogurt samples with hydrolyzed jicama starches added did not show significant differences in pH and viscosity. Sensorial testing showed that it is possible to produce yogurt with good functional and sensorial properties using hydrolyzed jicama starches as a fat substitute.     

Mild hydrolysis of resistant starch from maize

To investigate structural changes of resistant starch (RS) caused by mild-acid treatment, native maize starch, retrograded (RS3), and cross-linked (RS4) resistant starches, prepared from maize starch, were hydrolyzed with 0.1 M HCl at 35 °C for 30 days. The hydrolysis rate of RS3 was shown to be the highest, at 44.1% after 30 days of the hydrolysis. The hydrolysis rapidly progressed upto 10 days but gradually changed after that. Native starch and RS4 showed less than 5% of hydrolysis during the period of hydrolysis. As for the RS level of the residue after the hydrolysis, RS4 did not show any significant change, but RS3 exhibited an increase of up to 25.9% after 30 days, which led to 88% increase in comparison with 13.8% at the initial stage. As a result of examining the molecular weight (MW) of RS3 by the SEC-MALLS-RI system, the non-hydrolyzed RS3 exhibited three peaks, having MW 53.4 × 10⁶, 7.4 × 10⁶, and 0.8 × 10⁶, respectively, but the MW of the molecules decreased to 4.9 × 10⁶ and 0.6 × 10⁶ after 7 days of hydrolysis. It was difficult to verify the MW of RS4 because this was not dispersed in 1 M NaOH. The crystallinity of native starches, RS3 and RS4, by X-ray diffractometry of the residue hydrolyzed with 0.1 M HCl was equal to that of the non-hydrolyzed starch. The peak intensity at 2θ = 17° of RS3 increased sharply after hydrolysis.     

高取代度羟丙基木薯淀粉流变特性研究(I)不同因素对流变特性的影响

研究了浓度、温度和ｐＨ值对高取代度羟丙基木薯淀粉溶液流变特性的影响。结果表明，高取代度羟丙基木薯淀粉溶液在浓度为５％～３０％，温度为２０～４０℃，ｐＨ为３～１１的范围内，均呈现假塑性流体特征，符合幂定律τ＝Ｋγｍ。浓度和温度因素对高取代度羟丙基木薯淀粉的表观粘度有显著影响，浓度越高，粘度越大，温度越低，粘度越小，它们之间的关系可用η＝ＡＣＢ和η＝ＤＴＥ表示。ｐＨ值对高取代度羟丙基木薯淀粉的流变特性没有明显影响，木薯淀粉经高度羟丙基化后具有良好的耐酸耐碱稳定性。