No abstract

Inoculation of a food product for use in subsequent validation studies typically makes use of a high concentration cocktail of microorganisms suspended in aqueous media. However, this inoculation method may prove difficult particularly when the food product is a low-moisture food containing antimicrobial compounds, such as some dried spices. In this study, a dry transfer method for inoculation of clove powder, oregano leaves, ginger powder, and ground black pepper with a five-serovar cocktail of Salmonella was developed and compared with a traditional aqueous inoculation procedure. Spices were inoculated at three levels, 10, 8, and 6 log CFU/g, by using both an aqueous suspension of Salmonella and a dry transfer of Salmonella from previously inoculated silica beads. At the highest inoculation level, the dry transfer method resulted in a significantly higher microbial load (P < 0.05) for ground cloves and oregano, but not for ginger and ground black pepper. At the intermediate inoculation level, differences were apparent only for ginger and black pepper. Inoculation levels of 6 log CFU/g resulted in recoveries below detection limits for both methods of inoculation. Additional examination on the survival of Salmonella on silica beads after inoculation and in clove powder after dry transfer from silica beads showed linear rates of decline, with a rate of -0.011 log CFU/g/day for beads and -0.015 log CFU/g/day for clove powder. The results suggest that dry transfer of Salmonella via inoculated silica beads is a viable alternative when traditional aqueous inoculation is not feasible.

In this study, commercial AZ31B magnesium alloy was used to compare the differences between the microstructure, texture, and mechanical properties of conventional solidification (as homogenized AZ31) and rapid solidification (as RS AZ31). The results demonstrate that a rapidly solidified microstructure leads to better performance after hot extrusion with a medium extrusion rate (6 m/min) and extrusion temperature (250 °C). The average grain size of as-homogenized AZ31 extruded rod is 100 μm after annealing and 4.6 μm after extrusion, respectively, but that of the as-RS AZ31 extruded rod is only about 5 μm and 1.1 μm, correspondingly. The as-RS AZ31 extruded rod attains a high average yield strength of 289.6 MPa, which is superior to the as-homogenized AZ31 extruded rod, and is improved by 81.3% in comparison. The as-RS AZ31 extruded rod shows a more random crystallographic orientation and has an unconventional weak texture component in <112¯1>/<202¯1> direction, which has not been reported yet, while the as-homogenized AZ31 extruded rod has an expected texture with prismatic <101¯0>/<1¯21¯0>//ED.

Low-temperature and high-speed extrusion of wrought magnesium alloy is an urgent problem. Mg-2.5Al-2Ca-1Sn alloys were extruded at 260 ℃ with different ram speeds (2.0,4.0 and 6.0 mm/s). The effects of extrusion speed on the microstructure and mechanical properties of the alloys were systematically investigated. It's worth noting that all the three extruded alloys were fully dynamic recrystallized (DRXed).With the increase of extrusion speed from 2 mm/s to 6 mm/s, the DRXed grain size are increased from 1.25 μm to 1.94 μm, average second phase particles are augmented from 0.79 μm to 0.89 μm and the volume fraction of second phase increases from 6.4% to 18.6%.The extruded alloys with three different extrusion speeds all show excellent comprehensive mechanical properties because of fine grain size, fully recrystallization and homogeneously dispersed second phase particles. The tensile yield strength (TYS) and ultimate tensile strength (UTS) decreased from 285 MPa,304 MPa to 217 MPa,264 MPa while the elongation increased from 11.4 % to 20 % when the ram speed rised from 2.0 mm/s to 6.0 mm/s.