Determination of effective moisture diffusivity and assessment of quality attributes of banana slices during drying

The influence of drying temperatures on the moisture diffusivity and quality attributes of the dried banana slices in terms of volatile compound, shrinkage, color, texture and microstructure were studied. Bananas with peel color index of 5 corresponding to yellow color with green tip were sliced into 3 mm thickness, dipped into ascorbic acid solution and dried at four temperatures of 70, 80, 90 and 100 °C. Drying rate of banana slices can be divided into two sub-drying periods, first and second falling rate periods. The effective diffusivity estimated by the optimization technique was found to decrease sharply with moisture content in the first falling rate period and changed slightly in the second falling rate period. High-temperature drying seems to provide lower loss of volatile compounds in the dried sample. Moreover, the dried banana was very porous, resulting in remarkably lower hardness value than that obtained from the low-temperature drying whilst the crispiness was not significantly different amongst the samples obtained at various drying temperatures. Although the textural property could be improved at high temperature, the product color was brown as manifested by the low L- and hue values in particular at the drying temperature of 100 °C.     

Modeling heat and mass transfer–induced stresses in germinated brown rice kernels during fluidized bed drying

A study of stress distribution inside a germinated brown rice (GBR) kernel during drying is important to understand the fissure formation of GBR and hence control the drying process in order to improve the quality of GBR. In this study, a finite element method performed in three dimensions in conjunction with the heat and mass balance of the drying system was developed to describe moisture, temperature, and stress distributions inside GBR kernels during fluidized bed drying. The modeling was carried out using the coupling of heat and mass transfer and validated with experimental data at 90–150°C. The results of moisture and temperature predictions agreed well with the experiments. During drying, tensile stress occurred at the layers close to surface and compressive stress occurred at the inner portion of a kernel. The tensile and compressive stresses increased to the highest value at about 30 s of drying, corresponding to the highest moisture gradient, and then decreased afterwards. The tensile and compressive stresses were higher at a higher drying temperature. These stress prediction results corresponded to the experiments, which show more severe GBR fissuring at higher drying temperatures.     

Modeling of Diffusion with Shrinkage and Quality Investigation of Banana Foam Mat Drying

A diffusion model including shrinkage has been developed for predicting the change of moisture content in banana foam mats during drying. Two solution methods, moving boundary using variable grid and immobilizing boundary using the Lagrangian referential coordinate, were used in exploring their capabilities to predict the moisture change. Banana foam mats with initial foam densities of 0.3, 0.5, and 0.7 g/cm³ were dried at 60, 70, and 80°C and superficial air velocity of 0.5 m/s. The qualities of the final products in terms of texture and microstructure were determined. The moving boundary method can predict the moisture content more accurately than the immobilizing boundary method especially in the case of low-density foam. The quality determinations showed that the initial foam density strongly affected hardness, crispness, and morphology of dried banana foam mats, whereas the drying temperature had no significant effect on those qualities.     

Effects of heating method and temperature in combination with hypoxic treatment on γ-aminobutyric acid,phenolics content and antioxidant activity of germinated rice

Heat and hypoxic treatments were combined with soaking to enhance γ-aminobutyric acid (GABA) production in germinated paddy (GP). Effects of heating temperature, heating techniques, that is, impinging stream drying (ISD) and tray drying (TD), and germination time on the GABA content, phenolics content and antioxidant activity were also investigated. Heating temperature had a significant effect on the GABA content; both ISD and TD helped increase the GABA content when the post-treatment grain temperature was 38–40.5 °C. Within this grain temperature range, soaking in combination with heat and hypoxic treatments (S-ISD-H and S-TD-H) yielded GP with higher GABA content than soaking (S) and soaking in combination with hypoxic treatment (S-H). However, ISD was noted to be more suitable than TD. Phenolics content and antioxidant activity of GP prepared by S-ISD-H at different heating temperatures and S-H were not significantly different but were higher than those of the GP prepared by S.     

3D mesoporous bioactive glass/silk/chitosan scaffolds and their compatibility with human adipose-derived stromal cells

Human adipose-derived stem/stromal cells (hASCs) have been popularly studied as cell-based therapy in the field of regenerative medicine due to their ability to differentiate into several cell types. In this study, in order to improve the mechanical strength and bioactivity of scaffolds for bone tissue engineering, three types of mesoporous bioactive glasses with different shapes and compositions were dispersed in the silk fibroin/chitosan (SF/CS)-based scaffolds, which were fabricated with a combination of freezing and lyophilization. The characteristic and physical properties of these composite scaffolds were evaluated. The biocompatibility was also assessed through hASCs in vitro tests. Both Alamar Blue® and Live/Dead assay® revealed that the spherical mesoporous bioactive glass doped scaffolds enhanced cell viability and proliferation. Furthermore, the addition of spherical mesoporous bioactive glass into SF/CS scaffolds encouraged hASC osteogenic differentiation as well. These results suggested that this composite scaffold can be applicable material for bone regeneration.     

Effects of foaming agents and foam density on drying characteristics and textural property of banana foams

The technique of foaming has proved effective in creating a porous structure, which is an important requirement for crisp food. Foam density and the type of foaming agent indeed play a key role in determining the drying kinetics and textural property of the foamed food. The influences of the foam density and the types of foaming agents on the moisture diffusivity as well as the quality in terms of microstructure, texture and volatile losses of banana foams were therefore investigated. Three foaming agents, i.e., fresh egg albumen (EA), soy protein isolate (SPI) and whey protein concentrate (WPC) were used. The experimental results showed that WPC banana foam could retain more open structure during drying. This morphology provided less shrinkage and led to higher values of the effective diffusivity as compared with that of SPI and EA banana foams. In terms of the textural properties, WPC and EA banana foams were spongy and less crisp than SPI banana foam. Samples with lower foam densities exhibited higher values of the effective diffusivity, smaller hardness and lower crispness than those with higher foam densities. The losses of volatile substances were substantial during all processing steps, but the major losses were during the foaming step.