Qunyi Tong

Effect of pullulan on the short-term and long-term retrogradation of rice starch☆

The effect of pullulan (PUL) on the retrogradation of rice starch (RS) was investigated by means of rapid visco-analyzer (RVA), rotational rheometer, differential scanning calorimetry (DSC), and X-ray diffraction (XRD). RVA results showed that addition of pullulan significantly decreased the breakdown and setback values, which meant that the short-term retrogradation of RS was inhibited. The dynamic time sweep of samples also proved the retarding effect of pullulan on the retrogradation of RS. DSC curves showed clearly that pullulan significantly reduced the retrogradation enthalpy of amylopectin, and the kinetics of retrogradation was analyzed using the Avrami model. XRD results showed that recrystallinity of RS was reduced from 11.565% to 8.841% with the addition of pullulan and this was in line with the DSC results. It could be concluded that the addition of pullulan apparently influenced not only the short-term retrogradation of amylose, but also the long-term retrogradation of amylopectin.

Mechanism study of Tween 80 enhancing the pullulan production by Aureobasidium pullulans

The influences of Tween 80 on the pullulan production, cell growth, glucosyltransferase activity and fatty acid composition of the cells were studied. The addition of Tween 80 to the culture medium significantly enhanced the pullulan production, but had no impact to biomass accumulation. Glucosyltransferase activity involved in pullulan synthesis was remarkable promoted with an increase of Tween 80 content. The ratio of unsaturated/saturated fatty acids contained in the cells was significantly higher in 0.5% Tween 80 in comparison with the absence of Tween 80. Results indicated that the increase of pullulan yield brought by Tween 80 was highly correlated with glucosyltransferase activity and fatty acid composition. Tween 80 was not degraded to serve as extra carbon source.

Drying process of pullulan edible films forming solutions studied by ATR-FTIR with two-dimensional correlation spectroscopy

Drying phenomenon of aqueous pullulan solutions at 50°C was investigated by ATR-FTIR spectroscopy and two-dimensional correlation infrared spectroscopy. Two-dimensional asynchronous spectrum at 1800-1500cm(-1) wavenumber was resolved into three separate bands, which were assigned to aggregated water with strong hydrogen bond (AW-S), aggregated water with moderately hydrogen (AW-M) bond, and free water (FW), respectively. Curve fitting results indicated that the quantities of the three species of water were constant during the first 55min of drying process. However, the area of the three bands (at around 1047, 1022 and 998cm(-1)) varied as drying progressed, implying the formation of more-ordered pullulan chains structure, as well as increased pullulan chain-chain interactions. Further analysis using 2D asynchronous correlation spectroscopy in 1200-950cm(-1) wavenumber regions revealed the sequence of spectral changes during the drying process.

Effect of pullulan on the water distribution, microstructure and textural properties of rice starch gels during cold storage

The effects of pullulan on the water distribution, microstructure and textural properties of rice starch gels during cold storage were investigated by low field-nuclear magnetic resonance (LF-NMR), scanning electron microscope (SEM), and texture profile analysis (TPA). The addition of pullulan reduced the transversal relaxation time of rice starch gels during cold storage. The microstructure of rice starch gel with 0.5% pullulan was denser and more uniform compared with that of rice starch without pullulan in each period of storage time. With regard to textural properties, 0.01% pullulan addition did not significantly change the texture of rice starch gels, while 0.5% pullulan addition appeared to reduce the hardness and retain the springiness of rice starch gels (P⩽0.05). The restriction effects of pullulan on water mobility and starch retrogradation were hypothesized to be mainly responsible for the water retention, gel structure maintenance, and modification of the textural attributes of rice starch gels.

Rheological properties of pullulan-sodium alginate based solutions during film formation.

During film formation, the rheological properties of pullulan, sodium alginate, and blends, dried at 50°C were studied using an oscillatory rheometer. According to the drying curves, the drying process of pullulan, alginate, and blend films was divided into three stages. At the first drying stage, four samples exhibited typical liquid-like viscoelastic behavior. As the drying proceeded (polysaccharide concentration up to 75%), pure pullulan chains formed an entangled network, whereas coupling of alginate molecules gave a weak gel. At this drying stage, complex viscosity data for 75% alginate and blends were fitted with the power law equation. The effects of drying on the mechanical properties of pullulan-sodium alginate based samples were analyzed using the generalized Maxwell model, and their relaxation spectra were determined. The rheological properties during drying obtained from this study is essential for understanding film-forming mechanism and predicting the properties of pullulan-sodium alginate based edible films.

Effect of ultrasonic treatment on total phenolic extraction from Lavandula pubescens and its application in palm olein oil industry.

The aims of the current study were to evaluate the best technique for total phenolic extraction from Lavandula pubescens (Lp) and its application in vegetable oil industries as alternatives of synthetic food additives (TBHQ and BHT). To achieve these aims, three techniques of extraction were used: ultrasonic-microwave (40 kHz, 50 W, microwave power 480 W, 5 min), ultrasonic-homogenizer (20 kHz, 150 W, 5 min) and conventional maceration as a control. By using the Folin-Ciocalteu method, the total phenolic contents (TPC) (mg gallic acid equivalent/g dry matter) were found to be 253.87, 216.96 and 203.41 for ultrasonic-microwave extract, ultrasonic-homogenizer extract and maceration extract, respectively. The ultrasonic-microwave extract achieved the higher scavenger effect of DPPH (90.53%) with EC50 (19.54 μg/mL), and higher inhibition of β-carotene/linoleate emulsion deterioration (94.44%) with IC50 (30.62 μg/mL). The activity of the ultrasonic-microwave treatment could prolong the induction period (18.82 h) and oxidative stability index (1.67) of fresh refined, bleached and deodorized palm olein oil (RBDPOo) according to Rancimat assay. There was an important synergist effect between citric acid and Lp extracts in improving the oxidative stability of fresh RBDPOo. The results of this work also showed that the ultrasonic-microwave assisted extract was the most effective against Gram-positive and Gram-negative strains that were assessed in this study. The uses of ultrasonic-microwave could induce the acoustic cavitation and rupture of plant cells, and this facilitates the flow of solvent into the plant cells and enhances the desorption from the matrix of solid samples, and thus would enhance the efficiency of extraction based on cavitation phenomenon.

Rapid, accurate, and simultaneous measurement of water and oil contents in the fried starchy system using low-field NMR

Fried starchy food is rich in oil that may pose a risk to health. For controlling of the oil uptake, a rapid and accurate method for the determination of oil content in the fried starchy food is important. In this study, low-field nuclear magnetic resonance (LF-NMR) was applied to simultaneously determine water and oil contents in the model fried starchy system. The proton signals from oil and water were verified and distinguished by desiccation at 105°C. There was no superposition between oil and water signals in the fried starch, making it possible for quantitative analysis of water and oil in a single test. Compared with Soxhlet extraction, the LF-NMR analysis provided a more accurate result of oil content in the fried starchy system, confirming the practicability of the application of LF-NMR technology as a fast and accurate method for the quantification of water and oil in the fried starchy system.

Effect of uracil on pullulan production by Aureobasidium pullulans CGMCC1234.

Effect of uracil on the pullulan production, biomass and uridine phosphorylase (UPase) activity was studied in this research. Uracil was found to enhance pullulan accumulation and the addition time of uracil was crucial to pullulan production. Pullulan yield of 49.07 g/L was achieved by adding 5mM uracil at 48 h, by comparison to 37.72 g/L obtained with the control. UPase activity could not be detected at early growth stage of Aureobasidium pullulans, but stimulated by added uracil at logarithmic phase and stationary phase. The time course study on the fermentation of pullulan demonstrates that pullulan production was not closely associated with biomass accumulation. Results indicate that the increased pullulan yield brought by uracil was correlated with UPase activity.

Why sucrose is the most suitable substrate for pullulan fermentation by Aureobasidium pullulans CGMCC1234

This paper studies the metabolic pathway of sucrose in pullulan fermentation by Aureobasidium pullulans. Because of its high pullulan production, sucrose proved to be the best carbon source for pullulan synthesis by A. pullulans CGMCC1234 (36.3g/L). Compared to other carbon sources, A. pullulans cells reached the stationary phase more quickly in the presence of sucrose. The specific sugar types and concentrations occurring during pullulan fermentation were detected using High Performance Liquid Chromatography (HPLC). HPLC results revealed that sucrose did not simply break down into glucose and fructose in the medium employed. Kestose (22.69g/L) also accumulated during early stages of fermentation (24h), which reduced the osmotic pressure of the extracellular fluid and diminished the inhibition of cell growth and pullulan production. β-Fructofuranosidase activity strongly depended on the carbon source. Sucrose was the best inducer of β-fructofuranosidase production. However, β-fructofuranosidase production did not directly and/or proportionally correlate with the growth of A. pullulans cells.

Understanding the influence of Tween 80 on pullulan fermentation by Aureobasidium pullulans CGMCC1234

In this paper, several new perspectives concerned with the effect of Tween 80 promoting pullulan production were presented. With the presence of Tween 80, the maximum pullulan yield increased by 41% (53.04 g/L). Meanwhile, the carbon source was consumed faster and the broth viscosity was higher. The lower final pH suggested that Tween 80 could protect the integrity of the mycelia. The dispersed filaments were not easily entangled with each other and less pellets were formed in the Tween 80 culture broth. FT-IR spectrum analysis indicated that the evaluated sample structure was coincided with commercial pullulan. The molecular weight of sample significantly dropped comparing with the control. The above findings indicated that Tween 80 facilitated the uptake of nutrient from surroundings to the microorganism and the release of pullulan into the extracellular fluid. These results were useful in better understanding the regulation and optimization of efficient pullulan fermentation.