No abstract

Mercury, as a global toxic pollutant, is easy to be accumulated in aquatic products and poses a great threat to human health. In this work, we proposed a mix-to-read, label-free, and robust assay for detecting mercury pollution in aquatic products by engineering a ratiometric-enhanced G-quadruplex probe. The transformation from the G-quadruplex to a hairpin-like structure allows us to confer a ratiometric and leveraged response to Hg 2+ , amplifying the signal-to-background ratio for Hg 2+ detection. Hg 2+ response was further improved by screening parallel-and antiparallel-, single-, and multiple-stranded G-quadruplex structures. Compared to the common aptamer probes, the ratiometric-enhanced G-quadruplex probe increased the sensitivity for Hg 2+ detection by 4.7 times. This proposed sensing system allowed a simple and one-tube homogenous detection of Hg 2+ at room temperature using a single unlabeled DNA sequence. Its application for Hg 2+ detection in fish and shrimp conferred satisfactory recovery rates ranging from 98.5 to 105.9%. The label-free and mix-to-read assay is promising for the onsite detection of mercury pollution and facilitating food safety of aquatic products.

An antibacterial compound, pyrrole-2-carboxylic acid (PCA), was isolated from an endophyte named Bacillus cereus ZBE in this study. RNA sequencing identified 14 genes encoding 9 key enzymes involved in PCA biosynthesis in B. cereus ZBE. The PCA production was enhanced 21-fold (149.63 mg/L) by optimization with the Plackett−Burman design and the response surface methodology. The optimum fermentation conditions were found to be 0.5% glycerinum, 1% peptone, 25% loaded liquid, initial pH at 7.0, inoculum size of 4%, incubation temperature at 37.72 °C, rotating speed of 120 rpm, and incubation for 48 h. In addition, PCA showed broad-spectrum antibacterial properties against a variety of foodborne pathogens. A further mechanism study demonstrated that PCA might exhibit antibacterial activity by inducing severe membrane damage in bacterial cells with a loss of membrane integrity. These findings suggested that PCA might be a promising source of natural antibacterial compounds used as preservatives in the food industry.

A plant‐derived phenolic compound, namely 3‐p‐trans‐coumaroyl‐2‐hydroxyquinic acid (CHQA), has recently been reported to exhibit antibacterial and antibiofilm activities against Staphylococcus aureus. In this study, the combined transcriptomic and proteomic analyses was used to elucidate the molecular mechanism of CHQA against S. aureus. The results showed that subinhibitory concentration of CHQA induced wide and significant changes in S. aureus at both transcriptional and translational levels with 935 differentially expressed genes and 438 differentially expressed proteins. Bioinformatic analysis indicated that the changed genes and proteins were mainly involved in cell membrane, ribosome and translation, DNA repair, fatty acid biosynthesis and metabolism, amino acid biosynthesis, peptidoglycan synthesis, and bacterial infection. Moreover, downregulation of various surface proteins associated with cell adhesion was observed, which probably further inhibited the biofilm formation of S. aureus. These results revealed that CHQA exerted antibacterial activity through multifarious mechanisms, which especially targeted bacterial cell membrane and then triggered diverse cellular dysfunctions.

Blend of starch and polysaccharide is a secure and feasible modifying method for starch. Effects of konjac glucomannan (KGM) on pasting, retrogradation, rheological and structural properties of low-amylose rice starch were evaluated. KGM addition reduced the pasting temperature, breakdown and setback values, but raised the peak viscosity. When KGM concentration increased, the storage and loss moduli showed an upward trend. Fourier transform infrared spectroscopy (FTIR) showed redshifts at 3450 and 1640 cm−1 and suggested the formation of intermolecular hydrogen bond between KGM and starch molecules. X-ray diffraction (XRD) indicated that KGM decreased the relative crystallinity from 11.88 to 3.10%. Scanning electron microscopy (SEM) of KGM induced samples showed looser network structures, and confocal laser scanning microscopy (CLSM) detected less cloud-like blurry pastes surrounding around the starch ghosts. KGM addition suppressed the starch retrogradation. These results could be used to broaden the application of KGM in the food industry.