Determining the gelation temperature of ß-lactoglobulin using in situ microscopic imaging.

Evolution of microstructure during heat-induced gelation of ß-lactoglobulin (ß-LG) was investigated in situ using confocal laser scanning microscopy at various gel-preparation conditions: pH=2, 5, and 7; protein content=5, 10, and 15%; and salt (NaCl) content=0, 0.1, and 0.3 M. The number and area of evolving ß-LG clusters were observed as a function of time and temperature and the data were fitted to a log-normal model and sigmoid model, respectively. The gelation temperature (Tgel) of the ß-LG system was determined from both the number (Tgel/N) and total area (Tgel/A) of ß-LG clusters versus temperature data. The range of Tgel/N and Tgel/A values for all the cases was 68 to 87°C. The effect of pH was the most dominant on Tgel/N and Tgel/A, whereas the effects of ß-LG and salt contents were also statistically significant. Therefore, the combined effect of protein concentration, pH, and salt content is critical to determine the overall gel microstructure and Tgel. The Tgel/N and Tgel/A generally agreed well with Tgel determined by dynamic rheometry (Tgel/R). The correlations between Tgel/N and Tgel/A versus Tgel/R were 0.85 and 0.72, respectively. In addition, Tgel/N and Tgel/A values compared well with Tgel/R values reported in the literature. Based on these results, Tgel/N determined via in situ microscopy appears to be a fairly good representative of the traditionally measured gelation temperature, Tgel/R.

Characterization of Low-Molecular-Weight Collagen from Korean Native Chicken Feet Hydrolyzed Using Alcalase.

The aims of this study were to optimize the preparation of low-molecular-weight collagen using a proteolytic enzyme (alcalase) derived from the feet of Korean native chickens, and to characterize the process of collagen hydrolysis. Foreign bodies from chicken feet were removed using ultrasonication at 28 kHz with 1.36 kW for more than 25 min. The hydrolytic pattern and molecular weight distribution of enzyme-treated collagen from chicken feet were analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-performance liquid chromatography, respectively. Ideally, chicken feet should be treated at 100°C for 8 h to obtain a high collagen content using hot water extraction. The collagen content of the chicken foot extract was 13.9 g/100 g, and the proportion of low-molecular-weight collagen increased with increasing proteolytic enzyme concentration and reaction time. When treated with 1% alcalase, the average molecular weight of collagen decreased rapidly to 4,929 Da within 5 h and thereafter decreased at a slower rate, reaching 4,916 Da after 7 h. Size exclusion chromatography revealed that low-molecular-weight collagen peptides of approximately 1,000-5,000 Da were obtained after hydrolysis with 1% alcalase for 1 h.

Physicochemical and Gelatinization Properties of Starches Separated from Various Rice Cultivars.

UNLABELLED: Morphological, viscoelastic, hydration, pasting, and thermal properties of starches separated from 10 different rice cultivars were investigated. Upon gelatinization, the G' values of the rice starch pastes ranged from 37.4 to 2057 Pa at 25 °C, and remarkably, the magnitude depended on the starch varieties. The rheological behavior during gelatinization upon heating brought out differences in onset in G' and degree of steepness. The cultivar with high amylose content (Goami) showed the lowest critical strain (γ(c)), whereas the cultivars with low amylose content (Boseokchal and Shinseonchal) possessed the highest γ(c). The amylose content in rice starches affected their pasting properties; the sample possessing the highest amylose content showed the highest final viscosity and setback value, whereas waxy starch samples displayed low final viscosity and setback value. The onset gelatinization temperatures of the starches from 10 rice cultivars ranged between 57.9 and 64.4 °C. The amylose content was fairly correlated to hydration and pasting properties of rice starches but did not correlate well with viscoelastic and thermal characteristics. The combined analysis of hydration, pasting, viscoelastic, and thermal data of the rice starches is useful in fully understanding their behavior and in addressing the processability for food applications. PRACTICAL APPLICATION: Rice flour has potential applications in various food products. The physicochemical properties of rice flour are dependent on its variety, which affects the quality of the final products. In this study, the combined analysis including hydration, pasting, viscoelastic, and thermal properties of rice flour could afford information for preparing a particular product such as bread and noodle.