Comparative Study on the Influence of Various Drying Techniques on Drying Characteristics and Physicochemical Quality of Garlic Slices.

Effects of vacuum freeze drying (VFD), air impingement drying (AID), hot air drying based on temperature and humidity control (TH-HAD), pulsed vacuum drying (PVD), and medium- and short-wave infrared radiation drying (MSIRD) on the drying characteristics and physicochemical properties of garlic slices were investigated in the current work. Based on the experimental results, the Weibull model fitted the experimental results better (R2 > 0.99) than the Wang and Singh model. Samples dried with PVD showed the smallest color difference (ΔE*), better rehydration capacity and desirable reducing sugar content. In response to thermal effects and pressure pulsations, the cell walls gradually degraded, and the cell and organelle membranes ruptured. The allicin and soluble pectin contents of garlic slices treated with PVD were higher by 8.0-252.3% and 49.5-92.2%, respectively, compared to those of the samples dried by other techniques. VFD maintained a complete garlic slice structure with the minimum shrinkage and the best appearance. The MSIRD process produced the densest structure, and caused an additional loss of color and phytochemical contents. The findings in current work implied that PVD could be a promising drying technique for garlic slices.

Synthesis and characterization of tannic acid-PEG hydrogel via Mitsunobu polymerization.

Tannic acid (TA) based materials have received significant interest owing to their broad spectrum of chemical and biological properties. Herein, a novel tannic acid based hydrogel, TA-PEG hydrogel, was synthesized via Mitsunobu polymerization/polycondensation, in which TA and polyethylene glycol (PEG) were simply crosslinked together by ether linkages. This method was performed in one pot, straightforward, metal free and robust, ignoring the strong ionic/hydrophobic interactions between tannic acid and PEG. Bearing catechol and pyrogallol units from TA, TA-PEG hydrogel did not only reduce the silver and gold precursor, but also served as a capping agent and stabilizer for the in situ formed Au and Ag nanoparticles (NPs). Furthermore, the antioxidant activity of the hydrogel was excellent (94%) in the case of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging. TA-PEG hydrogel also showed antibacterial activity against Staphylococcus aureus and Escherichia coli. This work suggested a new method leading to polyphenol based soft materials rather than a complex coacervated microstructure. The resulting TA-PEG hydrogel has potential application in biomedical materials.