Colloids of Holey Gd2 O3 Nanosheets Converted from Exfoliated Gadolinium Hydroxide Layers.

This paper proposes a confined solid-state conversion approach using layered metal-hydroxides for the production of a colloidal suspension of porous 2D crystalline metal oxide layers with superior electrochemical H2 O2 sensing performance. This study investigates the conversion chemistry of delaminated layers of gadolinium hydroxide (LGdH), [Gd2 (OH)5 ]+ , encapsulated in a silica nanoshell that provides an antistacking and antisintering environment during the phase-transition at high temperature. Thermal treatment of the LGdH layers within the protected environment results in a dimensionally confined phase-transition into crystalline Gd2 O3 nanosheets with an isomorphic 2D structure. Furthermore, annealing at higher temperatures leads to the evolution of in-plane mesoporous structure on the Gd2 O3 nanosheet. Based on insight acquired from in-depth investigation, the evolution of in-plane porosity proceeds through the in-plane dominant silicate-formation reaction at the interface with the surrounding silica shell. Their 2D-anisotropic and mesoporous morphological features are preserved, producing a colloidal suspension of holey nanosheets that can be used to fabricate a thin and porous film through wet-coating deposition. This study also demonstrates the superior electrochemical H2 O2 sensing ability of the resultant porous Gd2 O3 film, which represents a ≈1000- and 10-fold enhancement of the detection limit and sensitivity, respectively, in comparison to previously reported Gd2 O3 films.

Fate of mesophilic aerobic bacteria and Salmonella enterica on the surface of eggs as affected by chicken feces, storage temperature, and relative humidity.

We compared the microbiological quality of chicken eggshells obtained from a traditional wholesale market and a modern supermarket. We also determined the survival and growth characteristics of naturally occurring mesophilic aerobic bacteria (MAB) and artificially inoculated Salmonella enterica on eggshells under various environmental conditions (presence of chicken feces, temperature [4, 12, or 25 °C], and relative humidity [RH; 43 or 85%]). The populations of MAB, coliforms, and molds and yeasts on eggshells purchased from a traditional wholesale market were significantly (P ≤ 0.05) higher than those from a modern supermarket. In the second study, when we stored uninoculated eggs under various storage conditions, the population of MAB on eggshells (4.7-4.9 log CFU/egg) remained constant for 21 days, regardless of storage conditions. However, when eggshells were inoculated with S. enterica and stored under the same conditions, populations of the pathogen decreased significantly (P ≤ 0.05) under all tested conditions. Survival of S. enterica increased significantly (P ≤ 0.05) in the presence of feces, at low temperatures, and at low RH. These observations will be of value when predicting the behavior of microorganisms on eggshells and selecting storage conditions that reduce the populations of S. enterica on eggshells during distribution.

Behaviour of Aspergillus flavus and Fusarium graminearum on rice as affected by degree of milling, temperature, and relative humidity during storage.

We investigated the survival and growth patterns of Aspergillus flavus and Fusarium graminearum, as well as mycotoxin production, on Korean rice as affected by the degree of milling (rough, brown, and white rice) and storage conditions (21 °C/85% relative humidity [RH], 21 °C/97% RH, and 30 °C/85% RH). When rice was stored at 21 °C/85% RH, the population of A. flavus remained constant and aflatoxin was not produced, regardless of the degree of milling. At 21 °C/97% RH and 30 °C/85% RH, the populations of A. flavus increased significantly (P ≤ 0.05) and aflatoxins were produced. The highest population of A. flavus and highest amount of aflatoxin B1 were observed on brown rice stored at 21 °C/97% RH. For F. graminearum, when stored at 85% RH, the populations were reduced to less than a detectable level (5 CFU/g of rice) within 120 days and no deoxynivalenol (DON) was produced, regardless of the degree of milling and storage temperature. However, at 21 °C/97% RH, the population of F. graminearum increased significantly (P ≤ 0.05) and DON was produced on all types of rice. Findings from this study provide insights concerning storage conditions necessary to prevent growth and mycotoxin production by A. flavus and F. graminearum on Korean rice with different degrees of milling.

Fate of Bacillus cereus and naturally occurring microbiota on milled rice as affected by temperature and relative humidity.

We studied the survival and growth patterns of Bacillus cereus, mesophilic aerobic bacteria (MAB), and molds and yeasts (MY) on rough and milled brown and white Korean rice stored at 12 and 21 °C and 43, 68, and 85% relative humidity (RH) for up to 24 wk. The initial populations of MAB present on rough rice, brown rice, and white rice were 7.7, 5.7, and 3.3 log CFU/g, respectively, and remained constant or decreased (P ≤ 0.05) by 0.7-1.8 log CFU/g during storage. The initial populations of B. cereus on the three types of laboratory-inoculated rice were 3.1-3.8 log CFU/g and remained constant (P > 0.05) during storage, regardless of degree of milling, storage temperature, and RH. The initial populations of MY on rough rice, brown rice, and white rice were 6.2, 4.2, and 2.1 log CFU/g, respectively. At 12 °C and 85% RH, the MY increased significantly (P ≤ 0.05) only on brown rice; however, at 21 °C and 85% RH, MY increased (P ≤ 0.05) on all types of rice during storage. These observations will be useful when assessing conditions affecting survival of B. cereus and determining environmental conditions necessary to prevent growth of potentially mycotoxigenic molds on various types of milled rice during storage.

Reduction of Salmonella enterica on the surface of eggshells by sequential treatment with aqueous chlorine dioxide and drying.

The synergistic effects of sequential treatments with chlorine dioxide (ClO2) and drying in killing Salmonella enterica on the surface of chicken eggshells were investigated. Initial experiments were focused on comparing lethalities of sodium hypochlorite (NaOCl) and ClO2. Eggs surface-inoculated with S. enterica in chicken feces as a carrier were immersed in water, NaOCl (50 or 200 µg/mL), or ClO2 (50 or 200 µg/mL) for 1 or 5 min. For 1-min treatments, lethal activities of sanitizers were not significantly different (P>0.05). However, after treatment with ClO2 for 5 min, reductions of S. enterica were significantly greater (P≤0.05) than reductions after treatment with water or NaOCl. The effect of treatment of eggs with ClO2 or NaOCl, followed by drying at 43% relative humidity and 25 °C for 24 and 48 h, were determined. Populations of S. enterica decreased during drying, regardless of the type of sanitizer treatment. ClO2 treatment, compared to water or NaOCl treatments, resulted in additional reductions of ca. >1.3 log CFU/egg during drying. This indicates that sequential treatments with ClO2 and drying induced synergistic lethal effects against S. enterica on the surface of eggshells. These observations will be useful when selecting a sanitizer to control S. enterica on the surface of eggshells and designing an effective egg sanitization system exploiting the synergistic lethal effects of sanitizer and drying.