Liming Che

Micronization and Hydrophobic Modification of Cassava Starch

In this study, the cassava starch was micronized in a vacuum ball-mill to make tiny granules of different particle sizes (the d 50 value from 7.9 μm to 24.0 μm). The properties of the micronized cassava starch, such as granularity, gelatinization properties, and dispersibility in organic solvent, have been evaluated. Then the micronized cassava starch has also been modified using a dry-method to improve its hydrophobic property, with aluminate coupling agent (ACA). The results suggest that the granularity of the starch decreases sharply through micronization in the vacuum ball-mill. The d 50 value of micronized starch was reduced from 24.0 μm to 7.9 μm with the milling time from 0 h to 54 h. The active sites increase as the size of the cassava starch is reduced. The micronized starch has been found to be more easily gelatinized, dispersed in organic solvent and modified. The gelatinization temperature of starch was reduced from 59° C to 23° C with the milling time from 0 to 54 h.

Effect of High-Pressure Homogenization on the Structure of Cassava Starch

Cassava starch suspension was homogenized at different pressures (0, 20, 40, 60, 80, and 100 MPa) with a high-pressure homogenizer. To investigate the effect of high-pressure homogenization on the structure of cassava starch, the samples were characterized using microscopy, laser scattering, and X-ray diffraction techniques, with native and heat gelatinized cassava starches as controlled samples. The temperature of starch suspension increased linearly with applied pressure at a rate of 0.187°C/MPa. Microscopy studies showed that cassava starch was partly gelatinized after high-pressure homogenization, and the degree of gelatinization increased with homogenizing pressure. Results of laser scattering measurements suggested a considerable increase in particle size after homogenization at 100 MPa as a result of granule swelling. The X-ray diffraction pattern showed that there was no evident change after homogenization suggesting that the crystalline structure of starch granules was resistant to high-pressure homogenization.

Convective Drying Kinetics of Single Droplets of Aqueous Glucose

The convective drying kinetics of single droplets of aqueous glucose was measured using a single droplet drying rig. The effects of air temperature and velocity were evaluated. It was found that the droplet of aqueous glucose shrank uniformly, retaining a nearly spherical shape during drying. The normalized volume (d/d0)3 of the droplet decreased linearly with its moisture content. A constant-drying-rate-like period occurred when the moisture content of the droplet was higher than an amount of about 1.0 kg kg−1 dry solid. The diameter of the droplet decreased sharply due to the evaporation of water, while its temperature remained at a wet-bulb-like temperature in this period. When the moisture content of the droplet was lower than the above-mentioned value, the drying transferred to a falling-drying-rate-period, during which the temperature of the droplet rose quickly and approached the air temperature as drying continued. The effect of air temperature on the drying of single droplets of aqueous glucose was more pronounced when compared with that of air velocity.

A Simple Nongravimetric Technique for Measurement of Convective Drying Kinetics of Single Droplets

In this article, a method is presented to measure the moisture content of single droplets/particles under air convection based on accurate measurement of the droplet/particle diameter and temperature. Experiments on droplets/particles of aqueous glucose were conducted as an example, and the results obtained support validity of such a method.

Nafion coated stainless steel for anti-biofilm application

Biofilms can adhere to most surfaces and have caused a wide range of problems in various industrial processes as well as daily life activities. In this work, the anti-biofilm ability of Nafion-coated stainless steel surface was investigated and our results showed that stainless steel discs coated with 1% Nafion can significantly reduce E. coli adhesion. Nafion has a large amount of negatively charged sulphonate groups, and the findings of this study suggest that the negative surface charge can greatly reduce bacterial adhesion through increasing the electrostatic repulsion between negatively charged bacterial cells and Nafion coated stainless steel surface. The roughness of coated and uncoated stainless steel discs made no significant differences while the hydrophobic of the discs increased after coated with Nafion.

Dairy milk particles made with a mono-disperse droplet spray dryer (MDDSD) investigated for the effect of fat

Mono-disperse droplet generation and subsequent drying in a spray-drying chamber, i.e., mono-disperse droplet spray dryer (MDDSD), provides a better-defined “flight experience” for liquid droplets. The related particle formation can be investigated more easily than that in the usual poly-disperse droplet spray dryer (PDDSD). Previously, skim milk, which is of high protein and high lactose content and is one of the two main dairy fluids that are processed into powder form for consumer markets, was subjected to this kind of investigation in Australia. Here, whole milk, which is the other main dairy fluid, has been spray-dried in a MDDSD set-up at Xiamen University (China). Because the initial droplet size is uniform, measurable, and the particle morphology after drying is consistent, it was possible to investigate the initial solids content effect upon shrinkage and inlet air temperature effect upon shrinkage. In contrast to what had been found for skim milk particles, the formation of the fat-containing (whole milk) particles does not follow the perfect shrinkage model as the skim milk does. This work has improved our quantitative understanding of the whole milk drying process. A fundamental analysis invoked with a modified one-dimensional modeling of spray drying has been given that has shown some further insight about the process.

Evaporation of Pure Droplets in the Convective Regime Under High Mass Flux

An analytical expression analogous to the D2 law was introduced, based on a mass transfer consideration, to describe the evaporation of pure droplets in the convective regime based on the Ranz-Marshall-type correlation for the Sh number. Comparison was made to single droplet drying experiments of pure water. It was found that the effect of mass transfer coefficient depression is significant under the high mass flux condition from the droplet. An expression was obtained to approximate the total time required for complete evaporation of a pure droplet. This expression can be used as a quick computation tool for more fundamental studies on droplet evaporation under controlled ambient conditions.

An Investigation in Microencapsulating Astaxanthin Using a Monodisperse Droplet Spray Dryer

Astaxanthin has stirred great interest in the research and health communities due to its antioxidant capacity and possible role in reducing the risk of some diseases. However, astaxanthin is a highly unsaturated molecule that can degrade and lose its bioactive properties during processing and storage. Microencapsulation is a possible preservation process and a product option. In this work, monodisperse astaxanthin-containing microparticles with high bioactivity retention were prepared using the monodisperse droplet drying technique. The morphology, microstructure, surface oil content, flowability, antioxidant capacity, and in vitro release properties of the microparticles were determined to test the reliability of the spray-drying technique. The results show that monodisperse astaxanthin-containing microparticles have smooth surface, low surface oil content, excellent flowability, prolonged release profile, and high antioxidant activity. The current work indicates that the monodisperse droplet spray-drying technique enhances both bioactivity retention and product properties of astaxanthin-containing microparticles.

Optimization of Supercritical Carbon Dioxide Extraction of Eucommia ulmoides Seed Oil and Quality Evaluation of the Oil

Supercritical carbon dioxide extraction (SC-CO2) technology was used to extract oil from Eucommia ulmoides seed. The optimum conditions and significant parameters in SC-CO2 were obtained using response surface methodology (RSM). The qualities of the extracted oil were evaluated by physicochemical properties, fatty acid composition, vitamin E composition. It was found that the optimum extraction parameters were at pressure of 37 MPa, temperature of 40°C, extraction time of 125 min and CO2 flow rate of 2.6 SL/min. Pressure, temperature and time were identified as significant parameter effecting on extraction yield. The importance of evaluated parameters decreased in the order of pressure > extraction time > temperature > CO2 flow rate. GC analysis indicated that E. ulmoides seed oil contained about 61% of linolenic acid and its fatty acid composition was similar with that of flaxseed oil and perilla oil. The content and composition of vitamin E was determined using HPLC. The E. ulmoides seed oil was rich in vitamin E (190.72 mg/100 g), the predominant vitamin E isomers were γ- tocopherol and δ- tocopherol, which accounted for 70.87% and 24.81% of the total vitamin E, respectively. The high yield and good physicochemical properties of extracted oil support the notion that SC-CO2 technology is an effective technique for extracting oil from E. ulmoides seed.

Drying kinetics study of irregular fibril materials in a “differential” laboratory rotary dryer: Case study for cut tobacco

ABSTRACT Rotary dryers are commonly used in the modern large-scale tobacco drying industry that consumes huge amounts of energy. In fact, rotary dryers are commonly used in chemical industry in general. It is difficult to investigate the drying behavior at industrial scale. A “differential” laboratory rotary dryer was therefore designed and tested. The large diameter of the industrial dryer was preserved, but the width was a section of the industrial dryer. The drying characteristics of cut tobacco from top leaves and bottom leaves with initial moisture contents (22.5 ± 1.0% on the wet basis) were studied in the “differential” dryer at air temperatures of 65, 85, 105, 125, and 145°C, respectively. The results show that increasing drying temperature accelerated the drying process, whereas the surface temperatures of the cut tobacco samples stayed in the temperature range of 48–71°C when their moisture contents were reduced to 12.0 ± 1.0% (wb). This 12.0% (wb) was required by commercial operations. Uniquely, the drying kinetics was captured using the reaction engineering approach (REA). Although different settings were applied, the model can be used to describe all the data well. The unique relationship between the normalized activation energy and the moisture content is approximated which is independent of the drying air temperature and the tobacco origin. The different drying behaviors for the cut tobacco from top leaves and bottom leaves can be attributed to their different equilibrium isotherms. Through controlling the drying time as predicted by REA model, the outlet moisture contents of cut tobacco from top leaves dried at 95°C/RH0.034/320 s and 115°C/RH0.017/250 s were shown to be 12.3 and 11.8% (wb), with the relative deviations of 2.5 and 1.7%, respectively, and these were within the industrial permissible range.