Nitrite ( \(\mathrm{{NO}_2}^{-}\) ) is often added to food as a food additive, but the overuse of nitrite will pose a threat to human health, so it is important to establish a rapid detection method for nitrite in related food. In this work, gold nanoparticles (AuNPs) were synthesized by in situ reduction of methanobactin (Mb); it is a small bioactive peptide. HS-β-cyclodextrin (HS-β-CD) with supramolecular recognition function was coordinated with Mb/AuNPs by Au-S bond to form HS-β-CD@Mb/AuNPs. HS-β-CD@Mb/AuNPs were modified onto the surface of gold electrode by electrodeposition to successfully prepare the biosensor (HS-β-CD@Mb/AuNPs/Au). The HS-β-CD@Mb/AuNPs/Au was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), ultraviolet spectroscopy (UV), Fourier infrared spectroscopy (FTIR), fluorescence spectrometer (FL), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The established biosensor was successfully applied to the detection of nitrite in real samples, and the mechanism of NO 2 − oxidation was analyzed. The detection limit of the established detection system was as low as 0.013 μM in the linear range of 0.1–10,000 μM, the recoveries were 96.53–102.54%, and the selectivity of the sensor is demonstrated by anti-interference experiment. Also compared to the previously described electrochemical sensors, the newly developed ones have better sensitivity (50.7137 μA μM −1 cm −2 ) and selectivity. These results suggest that the work provides a new way for the accurate monitoring of nitrite in environmental and food safety.
Menaquinone-7, a form of vitamin K 2 , plays a critical role in the treatment of hemorrhagic diseases caused by vitamin K deficiency and in the prevention of bone fractures. Microbial fermentation has emerged as a promising method for MK-7 production due to its high product optical purity and significant physiological activity. However, the current production efficiency of MK-7 remains insufficient to meet industrial demands. In this study, we employed a combination of single-factor experiments, Plackett-Burman design, steepest ascent experiments, and Box-Behnken design to optimize the fermentation medium for MK-7 production by Bacillus subtilis BS - Δ ackA . Through regression analysis and consideration of practical production constraints, the optimal fermentation medium parameters were determined as follows: 20 g/L sucrose, 20.7 g/L glycerol, 47.3 g/L soy peptone, 4 g/L yeast extract, and 1.9 g/L KH 2 PO 4 , 0.1 g/L MgSO 4 ·7 H 2 O. Under these optimized conditions, the MK-7 yield reached 154.6 ± 1.32 mg/L. The experimental results demonstrated excellent stability and reliability, aligning closely with the model predictions. This study significantly enhances MK-7 production at the shake-flask fermentation level, providing valuable insights for large-scale industrial applications.
Menaquinone-7 (MK-7), a multipotent vitamin K2, possesses a wide range of biological activities, a precise curative effect and excellent safety. A simple and rapid LC-APCI-MS/MS method for the determination of MK-7 in human plasma with single liquid–liquid extraction (LLE) extraction and 4·5-min analysis time has been developed and validated. Four per cent bovine serum albumin (BSA) was used as surrogate matrix for standard curves and endogenous baseline subtraction. This method was reproducible and reliable and was used to analyse of MK-7 in human plasma. The endogenous circadian rhythm and bioavailability of MK-7 were investigated in two randomised single-dose, open, one-way clinical trials (Study I and Study II). A total of five healthy male subjects were enrolled in Study I and 12 healthy male subjects in Study II. Single-dose (1 mg) of MK-7 was given to each subject under fasting condition, and all eligible subjects were given a restricting VK2 diet for 4 d prior to drug administration and during the trial. The experiment results of Study I demonstrated that endogenous MK-7 has no circadian rhythm in individuals. Both studies showed MK-7 are absorbed with peak plasma concentrations at about 6 h after intake and has a very long half-life time.
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