Waxy Rice Starch Research Articles

Dynamic Rheological and Microstructural Properties of Normal and Waxy Rice Starch Gels Containing Milk Protein Ingredients

AbstractThe viscoelastic and microstructural properties of normal and waxy rice starch gels containing milk proteins, with concentration ranging from 0 to 10%, were investigated using dynamic rheological measurements and confocal microscopy observations. The gels were made by heating the starch dispersions (10%) in the presence of the milk protein ingredients, namely skim milk powder (SMP), milk protein concentrates (MPC), sodium caseinates (NaCAS) and whey protein isolates (WPI). It was found that qualitatively the rheological behaviour of the mixed gels was similar to that of the starch alone, indicating that the continuous phase was made of starch molecules. Furthermore, up to a concentration of 5%, all these ingredients could be considered as inert fillers, since they did not affect drastically the elastic modulus of the mixed gels. Only at high concentration was an effect observed, and it is believed that in the case of SMP and MPC, the effect could be attributed to the separation of the milk proteins and the starch molecules into separate phases, as shown by confocal microscopy. That heat induced gelation of WPI was also believed to be responsible for the large increase in the elasticity of the WPI/rice starch gels at high concentration of WPI.

Physicochemical characteristics of waxy rice starch influencing the in vitro digestibility of a starch gel

Starches were isolated from three waxy rice varieties: Koganemochi (Kog), Hakuchomochi (Hak), and Kantomochi 172 (K172). Forty percent starch gels were prepared and the extent of starch gel digestibility was determined by an in vitro method. The distribution of chain lengths of amylopectin was analyzed and differential scanning calorimetry was used to analyze gelatinization and retrogradation of waxy rice starch. The K172 gel had significantly higher resistance to hydrolysis than had the other gels. The K172 starch contained lower proportions of the short chains of amylopectin and showed higher gelatinization temperature and enthalpy. The retrogradation peak was measured using waxy rice starch gels stored for 1 and 7 days at 5 °C. The K172 gel was observed to retrograde more quickly and to have a greater extent of retrogradation than the other gels. The difference in amylopectin chain length distribution and recrystallinity contributed to the variation in the starch gel digestibility of waxy rice.

Influence of β-cyclodextrin on the short-term retrogradation of rice starch

Abstract The effect of β-cyclodextrin (β-CD) on short-term retrogradation of rice starch was studied. Retrogradation of normal rice starch was reduced more by β-CD than by glycerol monostearate (GMS). β-CD reduced the rate of retrogradation of amylose and normal rice starch but not waxy rice starch. Differential scanning calorimetry (DSC) detected a potential amylose-β-CD complex formation. DSC data were analysed using the Avrami equation. Results showed that β-CD significantly lowered the crystallizing rate ( k ) and increased the Avrami exponent ( n ) of amylose recrystallisation ( P 0.05). Molecular dynamics (MD) simulation indicated that the stability of the complex was primarily due to non-bonded interactions, such as Van der Waals (Vdw forces), electrostatic force, and hydrogen bonds formed in the presence of β-CD.

The pasting properties of sonicated waxy rice starch suspensions

The effect of sonication on the pasting properties of waxy rice starch solutions (5 wt%) was investigated. It has been found that the functionality of starch granules was significantly influenced by the length of sonication and the solution temperature. A comparison of the pasting behaviour showed that the peak and final viscosities of the starch dispersions sonicated at temperatures near the onset temperature of gelatinisation were lower than those of the non-sonicated dispersions. The particle size measurements showed that the size of the heated and sonicated granules were smaller than that of the heated non-sonicated starch granules. Scanning electron microscopy (SEM) observations showed that the starch granule surface was not affected by sonication, and the size exclusion chromatography did not show any reduction in the size of the starch molecules. Based on these observations, the change in the pasting behaviour is explained in terms of the solubilisation of the swollen starch granules and starch aggregates induced by sonication.

In vitro Digestibility of Hydroxypropylated and Cross‐linked Waxy and Non‐waxy Rice Starches

AbstractIn vitro digestibility of hydroxypropylated and cross‐linked waxy and non‐waxy rice starches was investigated to find the proper resistant starch (RS) assaying method for chemically modified starches. RS and total dietary fiber (TDF) content of hydroxypropylated and cross‐linked waxy and non‐waxy rice starches were measured using the approved AOAC RS assay procedure (AOAC method 2002.02) and the AOAC TDF assay procedure (AOAC method 985.29). Hydroxypropylation did not alter the RS content of waxy and non‐waxy rice starches (less than 1% of RS). Cross‐linking also did not change the RS content of waxy and non‐waxy rice starches (less than 1% of RS). It is interesting to note that non‐RS content decreased with increasing hydroxypropylation (97‐80%) and cross‐linking (99‐95%) in both waxy and non‐waxy rice starches. This indicates that some fraction of RS in hydroxypropylated and cross‐linked waxy and non‐waxy rice starches cannot be measured using approved AOAC RS and TDF assay procedures. Therefore, the RS and TDF assay procedures performed in this study are not appropriate to determine the RS content of chemically modified starch. Further investigation is needed to develop a method to determine the RS content of chemically modified starch.

수침에 따른 찹쌀, 찹쌀 가루 및 찹쌀 전분의 물리화학적 특성 변화

유과 품질에 큰 영향을 주는 수침 처리가 찹쌀, 찹쌀 가루 및 찹쌀 전분의 물리화학적 특성에 미치는 영향을 조사하였다. 수침처리는 세 가지 시료 모두의 등온흡습곡선에 큰 영향을 주었으나 특정한 경향을 나타내지는 않았다. 용해도는 세 가지 시료 모두 호화개시온도 이후 급격히 증가하였고 수침기간이 증가함에 따라 점차 증가하는 경향을 나타내었다. 팽윤력은 찹쌀 및 찹쌀가루의 경우 수침기간이 증가함에 따라 감소하였으나 찹쌀 전분의 경우 감소하였다가 증가하는 경향을 나타내었다. X-선 회절 분석 결과, 수침처리를 한 시료 모두 A형 결정형 형태를 유지하였고, 상대적 결정화도는 수침이 진행될수록 감소하였다. 이로 보아 수침 과정 동안 전분의 일부 결정형 영역이 분해된다는 것을 확인할 수 있었다. RVA 점도 특성을 분석한 결과, 찹쌀과 찹쌀 가루의 경우 유사한 경향을 나타내었고, 찹쌀 전분의 경우 이들과 다른 RVA 점도 특성을 나타내었다. 이처럼 Native 상태의 찹쌀, 찹쌀 가루와 찹쌀 전분의 RVA 점도 특성 차이는 수침 초기에 단백질과 지질 등이 용출되어 제거되는 것에 기인한 것으로 보이며, 점도가 감소하는 이유는 수침동안 일어나는 미생물의 생육작용에 의한 것으로 생각된다. The objective of this study was to investigate the effect of soaking time on physicochemical properties of waxy rice, waxy rice flour and waxy rice starch. Waxy rice (WR), waxy rice flour (WRF), waxy rice starch (WRS) were soaked at <TEX>$18^{\circ}C$</TEX> for 14 days and dried at <TEX>$40^{\circ}C$</TEX>. Dried samples were grounded and sieved using 180 mesh. Physicochemical properties of the three samples, such as swelling power, solubility, moisture sorption isotherms and pasting properties using rapid visco analyzer (RVA) and crystal pattern using X-ray diffractometer were determined. In all samples, soaking time greatly influenced moisture sorption isotherms but no typical pattern was shown. Swelling power was not greatly changed by soaking time in the three samples. Solubility increased with increasing soaking time in all three samples, indicating that some soluble particles were exuded during soaking. In RVA pasting properties, WR and WRF showed a similar pattern, while WRS showed different pasting properties, suggesting that rice protein plays a significant role in pasting properties. X-ray diffraction patterns of all three samples showed typical A-type crystal pattern suggesting that soaking did not affect crystalline region of samples.

Effects of different components in skim milk on high-pressure-induced gelatinisation of waxy rice starch and normal rice starch

The gelatinisation of starch in skim milk required higher pressures than did the gelatinisation of starch in water. This study examined the effects of various milk components on the pressure-induced gelatinisation of waxy rice starch and normal rice starch, in order to understand the differences between the gelatinisation characteristics of starch in skim milk and starch in water. Gelatinisation was retarded in skim milk, which was attributed to the effects of soluble milk minerals and lactose. The presence of these components may reduce the plasticising ability of the suspension medium. Direct interactions between the milk components and starch molecules may also contribute to retarded gelatinisation. Milk proteins (casein and whey protein) did not affect the degree of pressure-induced gelatinisation at the concentrations of these components in skim milk, at 10% total solids.

Effect of pH on complex formation between debranched waxy rice starch and fatty acids

Complex formations between debranched waxy rice starch (DBS) and fatty acids (FA) of different hydrocarbon chain lengths (8:0, 10:0, 12:0, 14:0, 16:0, and 18:0) were studied in an aqueous solution by measuring the blue colour stained with iodine. The objective of this study was to understand the effects of the solubility and hydrophobicity of guest molecules (FA) on the complex formation with DBS. Lauric acid (12:0) displayed the greatest complex forming ability with DBS by showing the least blue colour developed with iodine. The effect of pH (3–7) on the DBS/FA complex formation was evaluated by measuring the iodine-scanning spectra of the mixture. Short-chain FA (8:0) displayed less complex formation at pH ≥ 5, above the p K a of fatty acid (∼4.8), which suggested that the charge formation of the short-chain FA caused a lower partitioning of the FA into the hydrophobic cavity of the DBS single helix. On the contrary, FA of 10:0–18:0 displayed an increased complex formation at pH > 5, which could be attributed to increased solubility of these longer-chain FA at a dissociated and ionized form. The hydrocarbon chain length of the FA had an important impact on the extent of the complex formation. A FA that had a shorter hydrocarbon chain was more soluble in an aqueous solution and more readily formed a complex with DBS. At pH 6 and 7 (above the p K a), 10:0 formed less inclusion complexes with DBS than did 12:0. Iodine-scanning spectra showed that the absorbances of all iodine-stained DBS/FA solutions at higher wavelength were substantially lower than that of the iodine-stained DBS alone, suggesting that FA preferentially formed inclusion complexes with DBS of longer chains.

Fragmentation of Waxy Rice Starch Granules by Enzymatic Hydrolysis

ABSTRACTSmall starch particles were prepared by hydrolyzing waxy rice starch using α‐amylase and then ultrasonicating in ethanol. Differential scanning calorimetry (DSC) revealed that a mild hydrolysis for 3 hr increased the melting enthalpy of the starch, which might indicate that the hydrolysis was selective in the amorphous regions. Later, at 6–24 hr, the hydrolysis rate was reduced, with gradual decreases in DSC melting enthalpy, indicating that the crystalline regions were eroded simultaneously. X‐ray diffraction patterns revealed the same trend as the DSC results. Average diameter of starch granules or particles was decreased dramatically in both volume‐ and number‐based measurements (5.94→1.64 μm, and 0.45→0.18 μm, respectively) during the early stage of rapid hydrolysis (up to 3 hr). Native waxy rice starch exhibited a particle size distribution with a major peak at 5.6 μm. After hydrolysis for 3 hr, the volume distribution of starch granules changed to two major size peaks at 0.5 and 3.6 μm. The starch fragment of 0.5 μm was assumed to consist of crystalline blocklets. With excessive hydrolysis (24 hr) or ultrasonication, however, starch particle diameter was increased, indicating that the particles might be swollen or aggregated into clusters.

Two- and Multi-Step Annealing of Cereal Starches in Relation to Gelatinization

Two- and multi-step annealing experiments were designed to determine how much gelatinization temperature of waxy rice, waxy barley, and wheat starches could be increased without causing a decrease in gelatinization enthalpy or a decline in X-ray crystallinity. A mixture of starch and excess water was heated in a differential scanning calorimeter (DSC) pan to a specific temperature and maintained there for 0.5-48 h. The experimental approach was first to anneal a starch at a low temperature so that the gelatinization temperature of the starch was increased without causing a decrease in gelatinization enthalpy. The annealing temperature was then raised, but still was kept below the onset gelatinization temperature of the previously annealed starch. When a second- or third-step annealing temperature was high enough, it caused a decrease in crystallinity, even though the holding temperature remained below the onset gelatinization temperature of the previously annealed starch. These results support that gelatinization is a nonequilibrium process and that dissociation of double helices is driven by the swelling of amorphous regions. Small-scale starch slurry annealing was also performed and confirmed the annealing results conducted in DSC pans. A three-phase model of a starch granule, a mobile amorphous phase, a rigid amorphous phase, and a crystalline phase, was used to interpret the annealing results. Annealing seems to be an interplay between a more efficient packing of crystallites in starch granules and swelling of plasticized amorphous regions. There is always a temperature ceiling that can be used to anneal a starch without causing a decrease in crystallinity. That temperature ceiling is starch-specific, dependent on the structure of a starch, and is lower than the original onset gelatinization of a starch.

Effects of cellulose derivatives and carrageenans on the pasting, paste, and gel properties of rice starches

Effects of different cellulose derivatives and carrageenans on the pasting, rheological, and textural properties of normal (NRS) and waxy (WRS) rice starches were investigated. When suspensions of both NRS and WRS were heated in a Rapid Visco Analyser (RVA) in the presence of the hydrocolloids, increases in apparent pasting temperatures and peak and final viscosities in the following decreasing order were observed: methylcellulose (MC) > carboxymethylcellulose (CMC) for cellulose derivatives and λ- > í- > κ-carregeenan for carrageenans. Slight decreases in peak and final viscosities were observed when hydroxypropylmethylcellulose (HPMC) was the hydrocolloid. Dynamic viscoelasticity measurements indicated that NRS–hydrocolloid pastes were less solid-like than the control, as evidenced by their higher tan δ values, whereas tan δ values of WRS–hydrocolloid pastes were the same as that of the control. Steady shear rheological measurements showed that addition of the different hydrocolloids used increased the apparent viscosity ( η a,100) and consistency coefficient ( K) values of both starches with the same trend as that observed during pasting, whereas the opposite trend was observed for the flow behavior index ( n) values. The hardness and adhesiveness of NRS pastes were significantly increased by addition of κ- and í-carrageenans, but were unaffected by the other hydrocolloids. A similar effect was observed for WRS, with the exception of κ-carregeenan, in which the hardness of the mixed paste was decreased. The starch–hydrocolloid pastes exhibited a phase-separated microstructure in which amylose- and amylopectin-rich domains were dispersed in a hydrocolloid-rich continuous phase.

Effect of high-pressure treatment on normal rice and waxy rice starch-in-water suspensions

The effects of treatment pressure (⩽700 MPa), temperature at treatment (10–60 °C), and treatment duration (0–30 min) on the gelatinization of normal and waxy rice starches were investigated. Pressure-treated starch suspensions were examined for pasting behaviour, initial apparent viscosity ( η initial), degree of swelling, birefringence changes, and leaching of starch and amylose. The η initial measurements provided an objective and analytical means of determining the degree of pressure-induced gelatinization of starch. Both normal and waxy rice starches exhibited sigmoidal-shaped pressure-induced gelatinization curves. The degree of gelatinization was dependent on the type of starch, the pressure, the temperature, and the duration of treatment. Different combinations of these factors could result in the same degree of gelatinization. There was a linear correlation between the degree of swelling and η initial. After treatments at ⩾500 MPa, both starches lost all birefringence although they experienced different extents of change in η initial and the degree of swelling.

Enzymatic Synthesis and Properties of Highly Branched Rice Starch Amylose and Amylopectin Cluster

We enzymatically modified rice starch to produce highly branched amylopectin and amylose and analyzed the resulting structural changes. To prepare the highly branched amylopectin cluster (HBAPC), we first treated waxy rice starch with Thermus scotoductus alpha-glucanotransferase (TSalphaGT), followed by treatment with Bacillus stearothermophilus maltogenic amylase (BSMA). Highly branched amylose (HBA) was prepared by incubating amylose with Bacillus subtilis 168 branching enzyme (BBE) and subsequently treating it with BSMA. The molecular weight of TSalphaGT-treated waxy rice starch was reduced from 8.9 x 10(8) to 1.2 x 10(5) Da, indicating that the alpha-1,4 glucosidic linkage of the segment between amylopectin clusters was hydrolyzed. Analysis of the amylopectin cluster side chains revealed that a rearrangement in the side-chain length distribution occurred. Furthermore, HBAPC and HBA were found to contain significant numbers of branched maltooligosaccharide side chains. In short, amylopectin molecules of waxy rice starch were hydrolyzed into amylopectin clusters by TSalphaGT in the enzymatic modification process, and then further branched by transglycosylation using BSMA. HBAPC and HBA showed higher water solubility and stability against retrogradation than amylopectin clusters or branched amylose. The hydrolysis rates of HBAPC and HBA by glucoamylase and alpha-amylase greatly decreased. The k cat/ K m value of glucoamylase acting on the amylopectin cluster was 45.94 s(-1)(mg/mL)(-1) and that for glucoamylase acting on HBAPC was 11.10 s(-1)(mg/mL)(-1), indicating that HBAPC was 4-fold less susceptible to glucoamylase. The k cat/ K m value for HBA was 15.90 s(-1)(mg/mL)(-1), or about three times less than that for branched amylose. The k cat/ K m values of porcine pancreatic alpha-amylase for HBAPC and HBA were 496 and 588 s(-1)(mg/mL)(-1), respectively, indicating that HBA and HBAPC are less susceptible to hydrolysis by glucoamylase and alpha-amylase. HBAPC and HBA show potential as novel glucan polymers with low digestibility and high water solubility.

Viscosity, Swelling and Starch Leaching During the Early Stages of Pasting of Normal and Waxy Rice Starch Suspensions Containing Different Milk Protein Ingredients

AbstractThe effects of three milk protein ingredients, sodium caseinate (NaCAS), whey protein isolate (WPI) and skim milk powder (SMP), on the swelling and leaching behaviour of normal and waxy rice starch solutions, during the early stages of pasting, were investigated. It was found that the swelling onset temperature for both starches was increased by NaCAS and SMP but was not affected by WPI. Furthermore, onset temperature determined by the swelling measurements was lower than the onset temperature determined from viscosity measurements. However, the calculated viscometric onset temperature, using the Maron‐Pierce equation and the results of the swelling measurements, was found to be in very good agreement with the measured viscometric onset temperature. This study also showed that the quantity of leached polysaccharides during the early stages of starch pasting was very small, indicating that significant leaching of polysaccharides during pasting primarily occurs after the break‐up of the sheared starch granules.

Effect of minor addition of xanthan on cross‐linking of rice starches by dry heating with phosphate salts

AbstractEffects of xanthan on the crosslinking of normal and waxy rice starches using a mixture of phosphate salts (sodium trimetaphosphate and sodium tripolyphosphate, 99 : 1, dry solid basis) were investigated. The starch (158.4 g, dry solids) was dispersed in an aqueous solution containing xanthan and phosphate salts (1.6 and 0.6 g in 280 mL water, respectively), and the slurry was dried overnight at 45°C until the moisture content was less than 10%. The dry cake was then ground into powders and heated for 2 h at 130°C in a convection oven. The pasting viscosity, paste clarity, melting and in vitro digestion behaviors of the starches with modifying agents (xanthan and phosphate salts) were investigated. The heat treated starches displayed enhanced shear stability and reduced breakdown, as evidences of crosslinking. Xanthan (1.0% based on starch solids) enhanced the crosslinking effects in the viscosity profile. Waxy rice starch evidenced more profound viscosity changes than did normal rice starch, indicating it was more susceptible to the heat treatment. The waxy rice starch heated with the mixture of phosphate salts and xanthan exhibited a continuous increase in pasting viscosity without any breakdown. Under a DSC analysis, melting enthalpy decreased but melting temperature increased somewhat as results of the heat treatment with xanthan. In an in vitro digestion analysis, the starches treated with xanthan exhibited decreases in the maximum digestion level, and increases in the resistant starch (RS) content. Dry heating, however, increased the digestion rate and glycemic index (GI) regardless of the presence of phosphate salts or xanthan indicating that the starches were thermally degraded. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Effect of granular characteristics on the viscoelastic properties of composites of amylose and waxy starches

For elucidating the influence of granular properties on the viscoelastic characteristics of starch gel, in this study waxy corn and waxy rice starches pre-heated at different temperatures were mixed with amylose isolated from normal corn starch to form amylose–waxy starch composites. Rheological properties of the amylose, the waxy starches and the composites during aging at 25 °C were determined and compared. Results showed that the storage modulus ( G′) of amylose solution (2%, w/w) during aging was lower than 48 Pa, and the rheological properties during aging of waxy starches pre-heated at 60 °C were too weak to be detected. The G′ of waxy starches during aging decreased with increasing pre-heating temperature from 70 to 90 °C, and the decrement on G′ value was more obvious for waxy corn starch. The amylose–waxy starch composites had higher gel strength than that of amylose or waxy starch alone. The G′ of amylose–waxy corn starch composite increased with increasing pre-heating temperature from 60 to 80 °C and then decreased at 90 °C, however, the G′ of amylose–waxy rice starch composite increased with increasing pre-heating temperature from 60 to 90 °C. Waxy corn starch had lower hot paste and final viscosities, but higher breakdown than waxy rice starch. Waxy corn starch also showed a rapid increase on the swelling power at temperature above 70 °C, while waxy rice starch increased slowly. The rigidity and integrity of waxy corn starch granules was found lower than waxy rice starch at 90 °C. Results indicate that granule properties and interaction occurred between amylose and starch granules play important roles during gelation of starch.

Preparation and Properties of High Degree Substituted Acetylated Rice Starches and Preparation of Their Films Part 1

Starches from three varieties of rice of high amylose (indica), intermediate amylose (japonica) and almost negligible amylose (japonica waxy) were isolated. They were acetylated by using four times their weight of acetic anhydride (11% sodium hydroxide as 50% aqueous solution as catalyst) for 15, 30 and 60 min.The acetyl content varied from 30 to 41% and degree of substitution (DS) from 1.63 to 2.55. Under similar conditions of acetylation, waxy rice starch showed highest acetyl content and highest DS. Dimethyl formamide was the solvent used for dispersing these modified starches. Films of indica modified starch of 30% acetyl content and 1.63 DS showed highest strength compared to other varieties of modified starch. Glass transition temperature (Tg) was highest in waxy rice starch (~ 232°C) followed by japonica non-waxy and indica rice starch. After acetylation, the Tg values increased in waxy modified ones, remained almost same in indica modified ones, decreased to some extent in japonica non-waxy modified ones compared to their respective native starches. Difference in specific heat capacity between starting and ending of glass transition point of indica and its modified ones remained almost same, increased in japonica and its derivatized ones, decreased in waxy modified one compared to their respective native starches. Among the native starches, melting point was highest in waxy starch. Modification increased this property in all the starches under all periods of acetylation. Increment was highest in japonica waxy acetylated ones. Degradation or decomposition of these starches occurred at 3-10°C higher than their respective melting points. Heat evolution was very high in japonica native (~ 203 mJ mg-1) and heat absorption was highest in indica 15 min modified one (~ 265 mJ mg-1). Difficulties encountered while determining the dynamic viscosity using the equipment of the synthetic polymer have been explained

Effect of high-pressure treatment on various starch-in-water suspensions

This study investigated the high-pressure-induced gelatinization of different starches, namely normal rice, waxy rice, normal corn, waxy corn, tapioca and potato starches. The high-pressure-treated starch solutions were characterized by pasting behaviour, degree of swelling and changes in birefringence. Potato starch was found to be less affected by pressure treatment than the other starches, as it retained birefringence after a pressure treatment of 600 MPa for 30 min. Waxy and tapioca starches showed complete gelatinization after the same treatment, whereas normal starches were only partially gelatinized. The pasting curves of the normal starches showed an increase in the initial viscosity after pressure treatment, whereas the initial viscosities of the waxy starches after the 600 MPa for 30 min treatment were already equal to their respective peak viscosities.

Effect of milk protein products on the rheological and thermal (DSC) properties of normal rice starch and waxy rice starch

The effects of four milk protein ingredients, namely skim milk powder (SMP), milk protein concentrate (MPC), sodium caseinate (NaCN) and whey protein isolate (WPI), on the pasting behaviour of a 10% normal rice starch or waxy rice starch solution were assessed using rheological and differential scanning calorimetry (DSC) measurements and confocal scanning laser microscopy (CSLM). It was found that all these milk protein ingredients affected markedly and differently the pasting behaviour of the two rice starches. For instance, for normal rice starch, SMP and NaCN shifted the temperature of peak viscosity to higher temperatures, whereas MPC and WPI reduced the temperature of peak viscosity. For waxy rice starch, SMP, NaCN and WPI increased the temperature of peak viscosity, but MPC did not affect it. The value of the peak viscosity was also either increased or decreased, depending on the milk protein type and its concentration. The onset temperature measured by DSC correlated very well with that measured by rheology. However, there was no correlation between the peak temperature measured by DSC and that measured by rheology. This could have been due to, for example, phase separation between the milk proteins and the starch molecules, as clearly observed by CSLM for SMP/rice starch and MPC/rice starch mixtures.

Effects of molecular size and structure of amylopectin on the retrogradation thermal properties of waxy rice and waxy cornstarches

Starches from waxy rice and waxy corn were treated in anhydrous methanol with 0.36% HCl at 25 °C for 1–15 days to obtain starches with different molecular weights. The retrogradation thermal properties of the HCl–methanol-treated starches, after gelatinized and stored at 4 °C for 7 days, were determined by using differential scanning calorimetry, and effects of molecular size and structure of amylopectin on the retrogradation thermal properties were elucidated. Results indicated that the degree of retrogradation (DR%) of waxy starches increased with decreasing molecular weight. The DR% of waxy starches was found negatively correlated with the logarithmic value of its weight-average degree of polymerization (DP w ) ( r 2=0.847 for waxy rice and 0.951 for waxy corn). The increment of DR% with the decreasing DP w of waxy cornstarch (slope=−13.98) was profoundly lower than that of waxy rice starch (slope=−25.42). In spite of the botanical source of starch, the DR% and the melting temperature of retrograded waxy starch depended on not only the molecular size, but also the molecular structure such as average chain length and chain length distributions of amylopectin branch chains and its subfractions.