Cu(II) adulteration in preserved vegetables by unreliable producers to increase their visual appeal or compensate for natural colour changes is most common. Methanobactin (Mb) is a Cu(II)-coordinated peptide, which plays crucial role in Cu(II) capture and absorption and the catalysis
of Cu(II)-containing methane monooxygenase in methanotrophs. In this study, Mb-functionalized gold nanoparticles (Mb-AuNPs) was applied to develop a dual readout colorimetric detection for Cu(II) adulteration in preserved vegetables. In the presence of Cu(II), Mb-AuNPs was assembled into nanocluster
driven by Cu(II)/Mb coordination, and the assembly process was monitored by the visible spectrum on the variation of surface plasmon resonance peak. The results showed that, Mb-AuNPs possessed excellent peroxidase-like activity after Cu(II) coordination. In the presence of Mb-AuNPs, the amount
of Cu(II) obviously affected the rate of hydroquinone oxidation by H2O2 and the change of A246. The visible and ultraviolet dual-readout detection system containing Mb-AuNPs, hydroquinone and H2O2 exhibited high sensitivity and selectivity
for Cu(II). The linear range of visible and UV detection towards Cu(II) was 0.05–0.4 μmol/L, the limit of detection were 37.50 nmol/L and 4.48 nmol/L, respectively. In conclusion, the Cu(II) coordination driven Mb-AuNPs assembly makes it able to detect Cu(II) adulteration in
preserved vegetables by dual channel methods to eliminate the occurrence of false positives and improve the accuracy of measurement results. Such non-spatially separated Mb-AuNPs assembly and it catalyzed hydroquinone oxidation dual channel readout was simple, fast, reliable and significantly
facilitated the detection efficiency of Cu(II).
Yang Chunlei,Xu Guiju,Hou Chenghao,Peng Lizeng,Wang Weiting,Zhang Hongwei,Zhang Xiaoling
A fluorometric and colorimetric dual-modal nanoprobe (denoted as Fe 2+ -Phen/SiNPs) has been developed for selective and sensitive determination of nitrite (NO 2 − ). The mechanism is based on fluorescence quenching between silicon nanoparticles (SiNPs) and Fe(II)-phenanthroline complex (Fe 2+ -Phen) via inner filter effect and redox. With the addition of increasing NO 2 − , Fe 2+ is oxidized to Fe 3+ , recovering the fluorescence of SiNPs. Meanwhile, the color of the system gradually changes from orange-red to colorless, which enables colorimetric measurement. The NO 2 − concentration shows a wide linear relationship with fluorescence intensity from 0.1 to 1.0 mM ( R 2 = 0.9955) with a detection limit of 2.4 μM in the fluorometric method (excitation wavelength: 380 nm). By contrast, the linear range of the colorimetric method ranges from 0.01 to 0.35 mM ( R 2 = 0.9953) with a limit of detection of 6.8 μM (proposed selective absorbance: 510 nm). The probe has been successfully applied to nitrite determination in water, salted vegetables, and hams demonstrating broad application prospects for the determination of nitrite in complicated matrices. Graphical Abstract
Han Tan,Dandan Huang,Yu Zhang,Yuanli Luo,Dejun Liu,Xiaoyong Chen,Huayi Suo
Low-salt pickled vegetables are in line with a healthier diet, yet ensuring consistent quality of such products is challenging. In this study, low-salt tuber mustard pickles fermented with Lactiplantibacillus plantarum LPP95 in the presence of chitosan and inulin were analyzed over a 30-day period, and quality changes were evaluated. Total acid productions along with high bacterial counts (10 6 CFU/mL) were observed in the initial 20 days during indoor storage temperature, in which the reduced fiber aperture was found significantly lead to an increase in crispness (16.94 ± 1.87 N) and the maintenance of a low nitrate content (1.23 ± 0.01 mg/kg). Moreover, the combined pickling treatment resulted in higher malic acid content, lower tartaric acid content, and a decrease in the content of bitter amino acids (e.g., isoleucine and leucine), thus leading to an increase in the proportion of sweet amino acids. Additionally, combined pickling led to the production of unique volatile flavor compounds, especially the distinct spicy flavor compounds isothiocyanates. Moreover, the combined pickling treatment resulted in an increase in the abundance of Lactiplantibacillus and promoted microbial diversity within the fermentation system. Thus, the synergistic effect among chitosan, inulin, and L. plantarum LPP95 significantly enhanced the quality of pickles. The study offers a promising strategy to standardize the quality of low-salt fermented vegetables.
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