Jung Ah Han

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.

Effect of γ-irradiation on pasting and emulsification properties of octenyl succinylated rice starches

Octenylsuccinylated (OS) starches from waxy rice or high-amylose rice (28.1% amylose) (DS 0.023 and 0.025, respectively) were gamma-irradiated at 10, 30, or 50 kGy and their pasting and thermal properties, crystallinity, and emulsification property were examined. When the OS starches were irradiated, the degrees of substitution gradually decreased as irradiation dose increased. A significant decrease in pasting viscosity was observed with an increase in irradiation dose, indicating the presence of chain degradation induced by the radiation. The melting temperature and enthalpy determined by differential scanning calorimetry increased slightly by irradiating at 10 or 30 kGy. Little change in crystallinity was observed in the X-ray diffraction analysis for the OS high-amylose rice starch regardless of irradiation doses, whereas a decrease in crystallinity was observed with the OS waxy starch irradiated at 50 kGy. Chain degradation induced by irradiation occurred mainly in the amorphous regions, but some loss of crystallinity occurred when the irradiation was excessive. The OS starches showed greater emulsion capacity and stability than the native counterparts due to their amphipathic nature. The irradiation further improved the emulsification properties of OS starches. The irradiation at 10 kGy was optimal, and treating at higher doses decreased the emulsion capacity and stability of the OS starches.

Self-enhancement of GABA in rice bran using various stress treatments

Gamma-aminobutyric acid (GABA) may be synthesized in plant tissues when the organism is under stressful conditions. Rice bran byproduct obtained from the milling of brown rice was treated under anaerobic storage with nitrogen at different temperatures (20-60 °C) and moisture contents (10-50%) up to 12h. For the GABA synthesis, the storage at 30% moisture content and 40 °C appeared optimal. Utilisation of an electrolyzed oxidizing water (EOW, pH 3.3) for moisture adjustment and addition of glutamic acid increased the GABA content in rice bran. The maximum GABA content in rice bran (523 mg/100g) could be achieved by the anaerobic storage at 30% EOW for 5h at 40 °C after an addition of glutamic acid (5mM). This amount was approximately 17 times higher than that in the control (30 mg/100g). The use of EOW also prevented bacterial growth by decreasing the colony counts almost by half.

Improvement in antioxidant functionality and shelf life of yukwa (fried rice snack) by turmeric (Curcuma longa L.) powder addition.

The physico-chemical, oxidative and sensory characteristics of fried rice snack, yukwa with different amounts of turmeric powder (Curcuma longa) were investigated. The moisture content of the pallet ranged from 16.47% to 19.84%. After frying the pallet, a slight decrease in the degree of expansion was obtained with increasing turmeric powder content. The textural properties of yukwa were not changed until the turmeric powder content reached 5%; however, over 8% addition induced a decrease in the hardness and an increase in the crispiness. Oxidative deterioration was effectively inhibited by turmeric powder addition, and more turmeric powder in yukwa led to higher free radical scavenging activity. Based on the sensory characteristics, a 5% addition of turmeric powder was the most acceptable for the yukwa product. In the correlation results among variables, the moisture content of the pallet proved to be the most important factor for yukwa quality.

Enhancement of Antioxidant Activity of Onion Powders by Browning during Drying Process

Drying process was applied to increase the antioxidant activity of onion powder: freeze-drying or air-drying at 50, 70, and 90°C and onion extracts were obtained from each powder using water or aqueous ethanol (50%) at 25°C and 60°C. In the color analysis, the freeze-dried powders showed higher L* and lower a* and b* values than did the air-dried ones. The browning index of powders air-dried at 90°C was significantly higher than that of freeze-dried powders or those air-dried at temperatures below 90°C. Phenolic content in the extracts was 4.02-23.12 mg gallic acid equivalent/g sample, and was the highest in the extract from the sample air-dried at 90°C, regardless of the extraction condition. The highest antioxidant activity, measured by 2,2-azinobis-3-ethylbenzothiazoline-6-sulfonic acid and 1,1-diphenyl-2-picrylhydrazyl methods, was found in the powder air-dried at 90°C, which induced browning. These findings indicate that antioxidant activity depends more on browning during drying than on extraction conditions.