Food preservatives are widely used in the food industry for their broad antibacterial spectrum and strong antibacterial properties. While the effects of dietary food preservatives on the gut microbiota and host health have been studied, a systematic review is lacking. In this paper, the latest research on food preservatives and the gut microbiota is reviewed. It has been found that food preservatives affect lipid metabolism, immunity and intestinal inflammation by altering the diversity of the gut microbiota and regulating the abundance of conditioned pathogens and beneficial bacteria. The future research trends are also discussed. Through this review, we hope that the ‘food preservatives-gut microbiota-host health’chain can arouse the attention of researchers and readers, and provide a new perspective for the existing safety evaluation system of food preservatives, which may be of guiding significance for the maintenance of human health.

With the improvement of living standards and the change of dietary habits, metabolic syndrome has become a major global public health problem. The gut microbiota is one of the research hotspots in recent years. More and more studies have shown that the gut microbiota can conduct bidirectional signal transduction with different body tissues and organs such as the brain, liver and heart through various pathways, which is closely related to body health. Medium-chain fatty acids (MCFAs) exist in coconut oil, palm kernel oil and dairy products mainly in the form of medium-chain triglycerides (MCTs). MCFAs can be rapidly metabolized for energy in the body, and has good regulatory effects on glucose and lipid metabolism. This article reviews the effects of MCTs on gut microbes and their positive effects on metabolic syndrome in order to provide a reference for future research.

Objective: To investigate the sleep-aiding effect of casein-derived peptide TPTLN and explore its possible mechanism of action. Methods: Thirty mice were divided equally into three groups, an experimental, a positive control and a blank control group, which were gavaged with TPTLN at a dose of 5 mg/kg m_b, intraperitoneally injected with diazepam at a dose of 1 mg/kg m_b, and gavaged with sterilized water at a dose of 5 mg/kg m_b, respectively. The body mass of all the mice was recorded every day. After 7 days of continuous administration, a sodium pentobarbital-induced sleep test was carried out to evaluate sleep quality. Following 4 more days of administration, the mice were euthanized and dissected to collect blood and tissue samples for analysis. Enzyme-linked immunosorbent assay (ELISA) was used to determine the levels of 5-hydroxytryptamine (5-HT), γ-aminobutyric acid (GABA), 5-hydroxyindoleacetic acid (5-HIAA), glutamate (Glu), β-endorphin (β-EP), cortisol, norepinephrine (NE) in the serum and brain tissue, and the GABA/Glu ratio was evaluated. Real-time quantitative polymerase chain reaction (qPCR) was used to detect the effect of TPTLN on the mRNA relative expression levels of γ-aminobutyric acid A receptor α1 (GABA_A-α1) and 5-hydroxytryptamine receptor 1A (5-HT1A) in the hypothalamus. Results: Compared with the control group, TPTLN and sodium pentobarbital synergistically increased the sleep onset rate to 100%, significantly shortened the sleep latency by 31.7% (P < 0.05), and extended the sleep duration 2.1 times (P < 0.05); increased the GABA/Glu ratio in the serum and brain tissue by 68.8% and 19.3%, respectively and significantly improved the excitation/inhibition imbalance (P < 0.001, P < 0.0001) as evidenced by a 49.4% increase in the serum GABA level (P < 0.001), a 7.6% increase in the brain 5-HT level, and a 24.3% and 23.4% decrease in the brain levels of cortisol and NE (P < 0.05); and significantly up-regulated the expression levels of the GABA_A-α1 and 5-HT1A genes 1.5 and 1.3 times, respectively (P < 0.01, P < 0.05). Conclusion: Casein-derived peptide TPTLN exhibited a favorable sleepaiding effect, and the underlying mechanism may be associated with the regulation of GABA_A-α1 and 5-HT1A expression levels, as well as the modulation of neurotransmitter contents including GABA, Glu, 5-HT, cortisol and NE in the brain.