In recent years, food safety issues have attracted increasing attention. Escherichia coli, as a typical foodborne pathogen, is often spread through contaminated food and water sources, posing a great threat to public health. Although traditional chemical preservatives can effectively inhibit the growth of bacteria, they are gradually rejected by consumers because of their potential harm to the human body and adverse effects on the environment. In contrast, naturally derived preservatives have gradually become a research hotspot in the food industry because of their high safety, non-toxicity, and biodegradability. As one of the natural plant-derived preservatives, dihydroquercetin (DHQ) has gradually attracted attention from academia and industry due to its significant antibacterial activity.
Dihydroquercetin (DHQ), also known as taxifolin is a flavonoid that is widely present in plants such as larch. Research shows that DHQ has strong antibacterial activity and has a significant inhibitory effect on a variety of bacteria, especially foodborne pathogens such as E. coli. This article will introduce the antibacterial mechanism of DHQ in detail based on the research results of Associate Professor Cai Jin of Shanxi University and others, and explore its application potential as a natural preservative in the field of food safety.
Antibacterial activity of DHQ
First, through experimental research on six common foodborne pathogenic bacteria, it was found that DHQ has a significant antibacterial effect on these bacteria. Experimental results show that DHQ has the strongest inhibitory effect on E. coli, and its inhibition zone diameter reaches 21.13 mm, far exceeding other bacteria, such as Proteus vulgaris (18.88 mm), Candida tropicalis (18.40 mm), and Bacillus subtilis. (14.67 mm), Enterobacter aerogenes (13.90 mm), and Staphylococcus aureus (12.35 mm). Through ANOVA analysis, the antibacterial effect of DHQ on E. coli was significantly better than that of other bacteria, indicating that E. coli is the most sensitive bacterial species to the antibacterial activity of DHQ.
In addition, the minimum inhibitory concentration (MIC) test further confirmed the potent inhibitory effect of DHQ on E. coli. When E. coli was treated with different concentrations of DHQ, it was found that DHQ at a concentration of 0.625 mg/mL could completely inhibit its growth, indicating that DHQ has a low MIC value for E. coli, thus proving its effectiveness as an antibacterial agent.
Morphological effects of DHQ on E. col
Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results further revealed the damaging effects of DHQ on E. coli cell morphology. In the control group, E. coli cells showed a normal rod-shaped structure and a smooth cell surface. After treatment with DHQ, cell morphology changed significantly. As the concentration of DHQ increases, cells gradually show phenomena such as swelling, aggregation, and plasmolysis, and even extremely serious cell structure damage such as content spillage and bacterial cell rupture occur.
Especially when E. coli was exposed to 2 MIC of DHQ, the cell shape became extremely irregular, indicating that DHQ destroyed the integrity of the cell wall and cell membrane, causing the leakage of cell contents and ultimately the death of the bacteria.
Effect of DHQ on reactive oxygen species (ROS) in E. coli cells
Further studies have shown that the antibacterial effect of DHQ is closely related to the excessive accumulation of intracellular reactive oxygen species (ROS). ROS is a highly reactive molecule produced during cell metabolism and has strong oxidizing properties. Bacteria usually rely on enzyme systems on the cell membrane to generate ROS and participate in the physiological metabolism of cells through their oxidation.
The study found that ROS levels in E. coli treated with DHQ increased significantly. Specifically, when E. coli was exposed to DHQ at concentrations of 1/2 MIC, MIC, and 2 MIC, the intracellular fluorescence intensity increased from 36.65 in the control group to 41.14, 56.99, and 65.94, respectively, indicating that DHQ can significantly promote cell Internal ROS production. These ROS will cause damage to the membrane structure by oxidizing lipids in the cell membrane, thereby increasing membrane permeability and causing serious damage to the cells.
Effects of DHQ on cell membranes
The cell membrane is an important barrier for bacterial life activities and is responsible for maintaining cell stability and selective permeability. The cell membrane of E. coli treated with DHQ showed significant damage. Through Annexin V-FITC/PI double staining experiments, researchers observed that E. coli gradually transformed into dead cells and necrotic cells after treatment.
As the concentration of DHQ increases, the proportion of normal cells significantly decreases and the proportion of damaged cells increases significantly. These phenomena indicate that DHQ can destroy the integrity and permeability of E. coli cell membrane, leading to cell physiological dysfunction.
Effect of DHQ on E. coli cell membrane potential
Changes in membrane potential are another important sign of impaired cell membrane function. Depolarization of cell membrane potential will cause ion imbalance and affect the normal metabolism and physiological activities of cells. Studies have shown that E. coli cell membrane potential significantly decreased after DHQ treatment.
When E. coli was exposed to 1/2 MIC, MIC, and 2 MIC of DHQ, its fluorescence intensity dropped from 68.97 in the negative control group to 43.38, 35.07, and 34.69 respectively, indicating that DHQ treatment caused depolarization of the cell membrane. This phenomenon further supports that DHQ can change the potential difference between inside and outside the cell by damaging the cell membrane, leading to the loss of cell function.
Effect of DHQ on Ca2+ content in E. coli cells
Intracellular calcium ions (Ca2+) are important ions in bacterial physiological activities and participate in cell signal transduction, membrane stability and metabolic processes.
The research results showed that after DHQ treatment, the Ca2+ content in E. coli cells was significantly reduced. Specifically, after treatment with different concentrations of DHQ, the fluorescence intensity of E. coli decreased from 44.31 in the control group to 33.13 (1/2 MIC), 29.82 (MIC), and 28.33 (2 MIC). This phenomenon shows that DHQ can damage the cell membrane and cause the outflow of Ca2+ ions, thereby further affecting the normal physiological activities of cells.
Effect of DHQ on E. coli cell cycle
The cell cycle is the process of normal cell division and proliferation, and its normal operation is crucial to cell growth. The study found that DHQ significantly affected the cell cycle of E. coli. After treatment with DHQ, the proportion of E. coli in phase I (growth phase) significantly decreased, while the proportion of E. coli in phase R (repair phase) increased significantly.
This result shows that DHQ interferes with the normal cell cycle of E. coli by damaging the cell membrane and promoting the accumulation of ROS, resulting in the inhibition of its proliferation.
Conclusion
In summary, DHQ, as a natural compound of plant origin, has significant antibacterial activity, especially showing a strong inhibitory effect on foodborne pathogenic bacteria such as Escherichia coli. DHQ effectively inhibits the growth and reproduction of bacteria by increasing the accumulation of intracellular ROS, destroying the integrity of the cell membrane, changing the cell membrane potential, causing Ca2+ efflux and cell cycle interference. The experimental results provide a strong theoretical basis for the application of DHQ as a natural preservative in the field of food safety. As the demand for natural preservatives continues to increase, dihydroquercetin is expected to become an ideal substitute and is widely used in the field of food preservation and antisepsis to ensure food safety and health.
The above research results not only provide scientific basis for the antibacterial mechanism of DHQ, but also provide theoretical support for its application in food processing, food storage and other related fields. As the understanding of natural preservatives continues to deepen, DHQ will play an increasingly important role in future food safety prevention and control.
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