Observation of microstructure change during freeze-drying by in-situ X-ray Computed Tomography

X-ray computed tomography technique was used to observe microstructure formation during freeze-drying. A specially designed vacuum freeze-drying stage was equipped at the X-ray CT stage, and the frozen and dried microstructures of dextrin solutions were successfully observed. It was confirmed that the many parts of the pore microstructures formed as a replica of the original ice microstructures, whereas some parts formed as a consequence of the dehydration dependent on the relaxation level of the glassy phases, suggesting that the post-freezing annealing is advantageous for avoiding quality loss that relates to the structural deformation of glassy matters. Keywords: freeze-drying; X-ray CT; ice microstructure; glassy state

Experimental investigation on pore size distribution and drying kinetics during lyophilization of sugar solutions

The pore structure is a decisive factor for the process efficiency and product quality of freeze dried products. In this work the two-dimensional ice crystal structure was investigated for maltodextrin solutions with different concentrations by a freeze drying microscope. The resulting drying kinetics was investigated for different pore structures. Additionally the three-dimensional pore structure of the freeze dried samples was measured by µ-computed tomography and the pore size distribution was quantified by image analysis techniques. The two- and three-dimensional pore size distributions were compared and linked to the drying kinetics.Keywords: pore size distribution; freeze drying; maltodextrin solution; freeze drying microscope

Influence of drying conditions on the acacia gum particle growth in fluidized bed agglomeration: in-line monitoring of particle size

Acacia gum is an important food emulsifier that presents poor instant properties which can be improved by fluidized bed agglomeration. This study investigated the influence of drying conditions on particle growth kinetics using an in-line particle size monitoring by spatial filter velocimetry. The drying conditions varied according to the binder flow rate and the fluidizing air temperature. The particle growth kinectis showed drying conditions dependence. At mild drying conditions the growth rate and the process yield were higher. The in-line particle size monitoring was useful to observe the influence of the drying conditions on the growth kinetics.Keywords: fluidized bed agglomeration; acacia gum; particle growth kinectis; in-line monitoring.

Effect of temperature and mode of drying on bioactive compounds and quality of germinated parboiled rice

Germinated parboiled rice (GPR) is recognized as a functional food because it is rich in bioactive compounds, especially gamma-aminobutyric acid (GABA). GPR was produced by soaking, incubating, steaming, and then drying using a high-precision hot air dryer. The results indicated that air flow mode and drying temperature had significant effects on the quality of GPR. Drying at higher temperatures and shorter times conserved GABA content. Using through-flow mode decreased drying time and prevented color change. However, a slightly lower percentage of head rice yield was observed. Moreover, using through-flow mode negatively affected the hardness loss after cooking.Keywords: Germinated parboiled rice; Drying mode; Gamma-aminobutyric acid; Head rice yield

Enhancing antioxidant property of instant coffee by microencapsulation via spray drying

This study is aimed to improve the antioxidant property of instant coffee by using microencapsulation technique and spray drying. Concentrated coffee extract was mixed with Konjac glucomannan hydrolysate (KGMH) and Maltodextrin (MD). The mixture of coating material and coffee extract was then spray dried at 160 - 180 °C inlet air temperature and at 85-90 °C outlet air temperature. KGMH can preserve retention of phenolic compounds, DPPH scavenging activity and antioxidant activity of FRAP (p<0.05 of instrant coffee better than other treatment. Keywords: Hydrolysed Konjac Glucomannan; Spray Drying; Microencapsulation; Instant Coffee, Antioxidant

Thermodynamic properties and moisture sorption isotherms of two pharmaceutical compounds

This investigation examines and compares the water sorption isotherms and the thermodynamic properties of two pharmaceutical preparations (Hypril and Azix) intended to be manufactured with the same process plant and equipment. The moisture equilibrium isotherms were determined at 50, 60 and 70 °C using a gravimetric technique. Five isotherm models were explored for their fitting to the experimental data. Azix showed sigmoid type II isotherms while Hypril showed type III isotherms according to the BET classification. All investigated models fitted well the water sorption isotherms of Hypril. By contrast, only GAB and Adam and Shove equations gave appropriate fit to the experimental data of Azix. For both formulations, the isosteric heat and the differential entropy decreased sharply with the increase of equilibrium moisture content to minimum values and thereafter remain constant. In the case of Azix, the integral enthalpy decreased with equilibrium moisture content while the integral entropy increased until reaching a constant value. Contrariwise, Hypril showed decreasing of the integral enthalpy and entropy with the equilibrium moisture content. Keywords: sorption isotherm, enthalpy, entropy, spreading pressure, pharmaceutical formulations

Investigation of influence of pre-treatment and low-temperature on drying kinetics, sorption properties, shrinkage and color of brown seaweeds (Saccharina Latissima)

Drying kinetics of Saccharina latissima (raw and blanched) at low temperatures (10.0, 25.0 and 38.0 °C) was studied. The effective moisture diffusivity coefficient varied due to temperature alterations in the range between 1.4 and 4.5 10-10 m2/s for raw and 0.91 and 2.56 10-10 m2/s for blanched seaweeds. Significant changes in structural properties and chemical composition resulted in a much longer drying time of blanched seaweeds, when compared with raw. Drying temperature of 38.0 °C resulted in more brown color, when compared with other samples. Sorption characteristics of dried raw seaweeds depended on salt content and showed high accumulation of moisture at relative humidity of air of 80.0 %. The blanched seaweeds showed linear accumulation of moisture within increasing of relative humidity of drying air from 20.0 to 80.0 %, but high level of hysteresis was determined between sorption and desorption isotherms. The shrinkage development within dewatering of blanched and raw samples was also studied. Keywords: brown seaweeds, drying kinetics, sorption isotherms, color

Drying behavior, diffusion modeling of cuminum cyminum L. undergoing microwave-assisted fluidized bed drying

In order to conserve cuminum cyminum L. during long storage periods, the drying kinetics of this seed undergoing microwave-assisted fluidized bed dryer at various microwave output power (300, 600 and 900w), air velocity (10, 15 and 20 m/s) and air temperatures (45, 55 and 65ᵒc) were studied. The main aim of this research is developing a mathematical model of mass transfer to investigate the microwave-assisted fluidized bed drying of cuminum cyminum L. seed. In this paper, we tried to discover a good model to evaluate moisture effective diffusivity (Deff). Keywords: cuminum cyminum L, microwave-assisted drying, mathematical modeling,

Improvement of pea protein isolate powder properties by agglomeration in a fluidized bed: comparison between binder solutions

This study aimed to compare the agglomeration process of pea protein isolate (PPI) using water and aqueous gum Arabic solution as binder liquids. Drying air temperature and binder flow rate were set at 75 °C and 3.1 mL/min, respectively. Moisture content, mean particle size, wetting time and flowability were analyzed. Using water as binder liquid, the responses were (4.0 ± 0.4)%, 316.13 ± 16.73 μm, 10 s and free flow, respectively. Aqueous gum Arabic solution provided (2.9 ± 0.5)%, 462.67 ± 51.23 μm, 3 s and free flow as responses. Gum Arabic solution showed to be a more promising binder.Keywords: Agglomeration; Pulsed fluidized bed; Pea protein isolate; Wetting time; Flowability

Effects of Assistance of High Frequency Dielectric and Infrared Heating on Vacuum Freeze Drying Characteristics of Food Model

By combining vacuum freeze drying combined with high-frequency dielectric and/or infrared heating, the drying time for frozen gels containing 1% agar with sucrose or sodium chloride was successfully shorten, and the drying time was influenced by the heating methods and by the additive component to the sample. Additionally, it was experimentally confirmed that the power consumption for freeze drying combined with electromagnetic wave heating could be reduced because of the shortened drying time. Consequently, this study could be a very important step for designing a vacuum freeze drying process optimally combining electromagnetic wave heating for each sample component.Keywords: freeze drying, electromagnetic wave heating, food model, sucrose, sodium chloride