Search

Bisphenol A (BPA) exposure primarily occurs through dietary intake. This study aimed to estimate the extent of dietary BPA exposure among Koreans. A thorough literature search was conducted to establish a BPA content database encompassing common foods consumed in Korea, including various food raw materials and processed food products. Dietary exposure levels were estimated by integrating the constructed BPA database with comprehensive nationwide 24 h-dietary recall datasets. The finding revealed that dietary BPA exposure was low for most Koreans, with a mean of 14.5 ng/kg bw/day, but was higher for preschool-age children (over 23 ng). Canned foods accounted for 9–36% of the total dietary exposure of the highest dietary exposure groups; while across all age groups, a considerable amount was derived from canned tuna, contribution of canned fruits and canned coffee (milk-containing) was high for preschool-age children and adults, respectively. Notably, for adults, a substantial proportion also stemmed from beer packaged in cans. While diet contributed over 80% of aggregate exposure for most age groups, preschool-age children experienced 60% exposure through diet due to additional exposure from indoor dust. Even at the high exposure scenario, aggregate BPA exposure levels remained lower than the current tolerable daily intake (TDI) set by the Korean agency (20 μg/kg bw/day). Nevertheless, most Koreans were exposed to BPA levels surpassing the strictest TDI (0.2 ng/kg bw/day) set by the European Food Safety Authority. [ABSTRACT FROM AUTHOR]

Electrofermentation actively regulates the bacterial redox state, which is essential for bioconversion and has been highlighted as an effective method for further improvements of the productivity of either reduced or oxidized platform chemicals. 1,3‐Propanediol (1,3‐PDO) is an industrial value‐added chemical that can be produced from glycerol fermentation. The bioconversion of 1,3‐PDO from glycerol requires additional reducing energy under anoxic conditions. The cathode‐based conversion of glycerol to 1,3‐PDO with various electron shuttles (2‐hydroxy‐1,4‐naphthoquinone, neutral red, and hydroquinone) using Klebsiella pneumoniae L17 was investigated. The externally poised potential of −0.9 V vs. Ag/AgCl to the cathode increased 1,3‐PDO (35.5±3.1 mm) production if 100 μm neutral red was used compared with non‐bioelectrochemical system fermentation (23.7±2.4 mm). Stoichiometric metabolic flux and transcriptional analysis indicated a shift in the carbon flux toward the glycerol reductive pathway. The homologous overexpression of glycerol dehydratase (DhaB) and 1,3‐PDO oxidoreductase (DhaT) enzymes synergistically enhanced 1,3‐PDO conversion (39.3±0.8 mm) under cathode‐driven fermentation. Interestingly, a small current uptake (0.23 mmol of electrons) caused significant metabolic flux changes with a concomitant increase in 1,3‐PDO production. This suggests that both an increase in 1,3‐PDO production and regulation of the cellular metabolic pathway are feasible by electrode‐driven control in cathodic electrofermentation. [ABSTRACT FROM AUTHOR]

Microbial electrosynthesis (MES) systems can convert CO2 to acetate and other value-added chemicals using electricity as the reducing power. Several electrochemically active redox mediators can enhance interfacial electron transport between bacteria and the electrode in MES systems. In this study, different redox mediators, such as neutral red (NR), 2-hydroxy-1,4-naphthoquinone (HNQ), and hydroquinone (HQ), were compared to facilitate an MES-based CO2 reduction reaction on the cathode. The mediators, NR and HNQ, improved acetate production from CO2 (165 mM and 161 mM, respectively) compared to the control (without a mediator = 149 mM), whereas HQ showed lower acetate production (115 mM). On the other hand, when mediators were used, the electron and carbon recovery efficiency decreased because of the presence of bioelectrochemical reduction pathways other than acetate production. Cyclic voltammetry of an MES with such mediators revealed CO2 reduction to acetate on the cathode surface. These results suggest that the addition of mediators to MES can improve CO2 conversion to acetate with further optimization in an operating strategy of electrosynthesis processes. [ABSTRACT FROM AUTHOR]

The conversion of C1 gas feedstock, such as carbon monoxide (CO), to useful platform chemicals has attracted considerable interest in industrial biotechnology. One conversion method is electrode-based electron transfer to microorganisms using bioelectrochemical systems (BESs). In this BES system, acetate is the predominant component of various volatile fatty acids (VFAs). To appropriately separate and concentrate the acetate produced, a BES-type electrodialysis cell with an anion exchange membrane was constructed and evaluated under various operational conditions, such as applied external current, acetate concentration, and pH. A high acetate flux of 23.9 mmol/m2∙h was observed under a −15 mA current in an electrodialysis-based bioelectrochemical system. In addition, the initial acetate concentration affected the separation efficiency and transportation rate. The maximum flux appeared at 48.6 mmol/m2∙h when the acetate concentration was 100 mM, whereas the effects of the initial pH of the anolyte were negligible. The acetate flux was 14.9 mmol/m2∙h when actual fermentation broth from BES-based CO fermentation was used as a catholyte. A comparison of the synthetic broth with the actual fermentation broth suggests that unknown substances and metabolites produced from the previous bioconversion process interfere with electrodialysis. These results provide information on the optimal conditions for the separation of VFAs produced by C1 gas fermentation through electrodialysis and a combination of a BES and electrodialysis. [ABSTRACT FROM AUTHOR]