Seung Taik Lim

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 in glass transition and enthalpy relaxation between native and gelatinized rice starches

Native and gelatinized rice starches were compared in their glass transition and enthalpy relaxation at various water contents using a differential scanning calorimetry (DSC). In a low moisture content range (8–18%), the glass transition temperature (Tg) of native starch was higher (up to 20°C) than that of gelatinized starch, and the difference became greater as the moisture content decreased. Heat capacity change (ΔCp) at Tg became substantially higher by gelatinization. Plasticizing effect of water on the glass transition in the low moisture content range followed the Couchman–Karasz equation. The glass transition temperature (Tg′) of native starch with sufficient moisture (40 or 60%) also appeared higher (−6.8 or −6.0°C) than that of gelatinized starch (−10.0 or −7.7°C), but ice-melting occurred in broader temperature range with smaller ΔH when the starch was gelatinized. Upon extended storage up to 14 days at 4°C, the gelatinized starch showed increased Tg′ but decreased ice-melting enthalpy due to the water incorporation in recrystallization of starch. Enthalpy relaxation appeared only when the moisture was <20% regardless of gelatinization. The relaxation peak increased in magnitude as the moisture content increased, and appeared as ‘Tg overshoot’ at a moisture content above 12% due to superimposed glass transition, whereas at a moisture content below 12%, it located in a temperature range far below glass transition, showing a ‘sub-Tg endotherm’.

Molecular Characterization of Corn Starch Using an Aqueous HPSEC-MALLS-RI System Under Various Dissolution and Analytical Conditions

ABSTRACT Molecular characteristics based on absolute weight-average molecular weight (Mw) and z-average radius of gyration (Rg) of normal corn starch were analyzed by high-performance size-exclusion chromatography (HPSEC) attached to multiangle laser-light scattering (MALLS) and refractive index (RI) detectors under different starch dissolution and analytical conditions. Autoclaving (121°C, 20 min) or microwave heating (35 sec) provided better HPSEC recovery and higher Mw for starch molecules than simple dissolution in hot water. The Mw for the autoclaved corn amylopectin and amylose fractions separated with a TSK G5,000 column at 60°C were 201 × 106 and 3.3 × 106, respectively. The specific volume for gyration (SVg) calculated from Mw and Rg could be used for the comparison of molecular compactness which was inversely related to the degree of branching. The SVg values of amylopectin and amylose fractions in the chromatogram (TSK G5,000, autoclaved for 20 min) were 0.092 and 0.529, respectively. But a por...

Starch-g-polycaprolactone copolymerization using diisocyanate intermediates and thermal characteristics of the copolymers

Starch-g-polycaprolactone copolymers were prepared by two-step reactions. The diisocyanate-terminated polycaprolactone (NCO-PCL) was prepared by introduc- ing NCO on both hydroxyl ends of PCL using diisocyanates (DI) at a molar ratio between PCL and DI of 2:3. Then, the NCO-PCL was grafted onto corn starch at a weight ratio between starch and NCO-PCL of 2:1. The chemical structure of NCO-PCL and the starch-g-PCL copolymers were confirmed by using FTIR and 13 C-NMR spec- trometers, and then the thermal characteristics of the copolymers were investigated by DSC and TGA. By introducing NCO to PCL (Mn: 1250), the melting temperature (Tm) was reduced from 58 to 45°C. In addition, by grafting the NCO-PCL (35-38%) prepared with 2,4-tolylene diisocyanate (TDI) or 4,4-diphenylmethane diisocyanate (MDI) onto starch, the glass transition temperatures (Tgs) of the copolymers were both 238°C. With hexamethylene diisocyanate (HDI), however, Tg was found to be 195°C. The initial thermal degradation temperature of the starch-g-PCL copolymers were higher than that of unreacted starch (320 versus 290°C) when MDI was used, whereas the copoly- mers prepared with TDI or HDI underwent little change.

Preparation, characterization and utilization of starch nanoparticles

Starch is one of the most abundant biopolymers in nature and is typically isolated from plants in the form of micro-scale granules. Recent studies reported that nano-scale starch particles could be readily prepared from starch granules, which have unique physical properties. Because starch is environmentally friendly, starch nanoparticles are suggested as one of the promising biomaterials for novel utilization in foods, cosmetics, medicines as well as various composites. An overview of the most up-to-date information regarding the starch nanoparticles including the preparation processes and physicochemical characterization will be presented in this review. Additionally, the prospects and outlooks for the industrial utilization of starch nanoparticles will be discussed.

Synthesis and characterization of pullulan-mediated silver nanoparticles and its antimicrobial activities

Synthesis of silver nanoparticles was achieved using pullulan as both a reducing and stabilizing agent. The effect of pullulan and silver nitrate amounts on the synthesis of silver nanoparticles (AgNPs) was investigated. The formation of nanoparticles was first screened by measuring the surface plasmon resonance peak at 420-430 nm using UV-vis spectroscopy. The morphology of the synthesized AgNPs was determined using TEM, which indicated that the AgNPs varied in shape and polydispersed with an average size of 2-30 nm. The presence of elemental silver and the crystalline structure of the AgNPs were confirmed by EDX and XRD analyses. The possible functional groups of pullulan responsible for the reduction and stabilization of AgNPs were evaluated using FT-IR. The pullulan-reduced AgNPs showed excellent antibacterial, antifungal, and antibiofilm activity against food and multidrug resistant bacterial and fungal pathogens. The results showed that pullulan could be used as a reducing as well as a capping agent for synthesizing AgNPs which had potent antimicrobial activity.

Effect of ultrasonic treatments on nanoparticle preparation of acid-hydrolyzed waxy maize starch

Waxy maize starch was dispersed (14.7% solids) in an aqueous sulfuric acid solution (3.16M), and hydrolyzed by stirring for up to 7 days at 40°C with ultrasonic treatments at different vibration amplitudes (20 and 40%) and durations (30 and 60min/day). The amount of starch nanoparticles in the hydrolyzates isolated after 7 days, measured by a dynamic light scattering detector, was raised from 20% to 70% by an ultrasonic treatment (20% amplitude, 30min). The aggregation of nanoparticles possibly occurring during the hydrolysis was effectively prevented by the ultrasonication. Alternatively, ultrasonic treatments were applied to the re-dispersed suspension of the large microparticles of starch hydrolyzates (2 days) precipitated by a mild centrifugation (500rpm, 10min). By an ultrasonic treatment at 60% vibration amplitude for 3min, the microparticles could be completely transformed to nanoparticles. The inherent crystalline structure of waxy maize starch (A-type in X-ray diffraction) remained after the ultrasonic treatments during acid hydrolysis, but it was disrupted by the ultrasonic treatments for the re-dispersed microparticles.

Preparation of crystalline starch nanoparticles using cold acid hydrolysis and ultrasonication

Waxy maize starch in an aqueous sulfuric acid solution (3.16 M, 14.7% solids) was hydrolyzed for 2-6 days, either isothermally at 40 °C or 4 °C, or at cycled temperatures of 4 and 40 °C (1 day each). The starch hydrolyzates were recovered as precipitates after centrifuging the dispersion (10,000 rpm, 10 min). The yield of starch hydrolyzates depended on the hydrolysis temperature and time, which varied from 6.8% to 78%. The starch hydrolyzed at 40 °C or 4/40 °C exhibited increased crystallinity determined by X-ray diffraction analysis, but melted in broader temperature range (from 60 °C to 110 °C). However, the starch hydrolyzed at 4 °C displayed the crystallinity and melting endotherm similar to those of native starch. The starch hydrolyzates recovered by centrifugation were re-dispersed in water (15% solids), and the dispersion was treated by an ultrasonic treatment (60% amplitude, 3min). The ultrasonication effectively fragmented the starch hydrolyzates to nanoparticles. The hydrolyzates obtained after 6 days of hydrolysis were more resistant to the ultrasonication than those after 2 or 4 days, regardless of hydrolysis temperatures. The starch nanoparticles could be prepared with high yield (78%) and crystallinity by 4 °C hydrolysis for 6 days followed by ultrasonication. Scanning electron microscopy revealed that the starch nanoparticles had globular shapes with diameters ranging from 50 to 90 nm.

Protective Effects of Kaempferol (3,4',5,7-tetrahydroxyflavone) against Amyloid Beta Peptide (Aβ)-Induced Neurotoxicity in ICR Mice

To determine the effects of kaempferol, rat pheochromocytoma cells (PC12) and Institute of Cancer Research (ICR) mice were utilized as neuronal models. Using in vitro assays, kaempferol was shown to have protective effects against oxidative stress-induced cytotoxicity in PC12 cells. Administration of kaempferol also significantly reversed amyloid beta peptide (Aβ)-induced impaired performance in a Y-maze test. Taken altogether, the results reported here suggest that further investigation is warranted of the influence of kaempferol on pathways related to Alzheimer’s disease.

Fragmentation of Waxy Rice Starch Granules by Enzymatic Hydrolysis

ABSTRACT Small 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...