Scientists say the best conditions for using this method are a weak acid environment at pH 4.5 at 4-15 °C. Acidic foods such as freshly cut fruits and ready-to-eat meat can be kept fresh without further chemical treatment in low temperature and blue LED environments.
Although LEDs are often used as energy-saving light sources, they also have bacteriostatic effects. Bacterial cells contain light-sensitive compounds that absorb visible parts of the electromagnetic spectrum (400-430 nm) and this part is mainly blue LED light. Exposure to a blue LED triggers a series of reactions inside the cell that eventually lead to its death.
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In the past, the study of the antibacterial effect of LED light was mainly carried out by adding a photosensitizer to a food sample or verifying the effect when the light source was very close (less than 2 cm). These conditions cannot be truly applied to food preservation. Scientists from the National University of Singapore have for the first time demonstrated food-related factors such as temperature and pH, and how they affect the bacteriostatic effect of LED light.
The team placed three major food-borne pathogens, Listeria monocytogenes, E. coli O157:H7 (Escherichia coli O157:H7), and Salmonella Typhimurium, under blue LEDs and adjusted them separately. To different pH values.
It was found that the bacteriostatic effect was better than neutral under acidic or alkaline conditions. Acidic conditions are more inhibitory against Listeria, while for E. coli O157:H7 and Salmonella typhimurium, the alkaline environment works best, but the acidic environment can also achieve effective inhibition. A 2013 study by the research team found that blue LEDs have the strongest inhibitory effect on bacteria at low temperatures.
Associate Professor Yuk Hyun-Gyun, the research director, said: "Combining these results, we have found a possible way to preserve acidic foods without chemical treatment at low temperatures. This may satisfy the growing demand for natural foods without It is necessary to rely on chemicals such as sour agents and artificial preservatives to preserve food."
These findings have potential value for food storage and food supplies, serving fresh cut fruits, ready-to-eat seafood such as sushi and smoked salmon, and cold meat products. This technology can also be used by retailers such as food courts and supermarkets.
Yuk said: "Next, we hope to apply this LED technology to real food samples, including fruits, seafood and meat, to see if it can effectively kill pathogens without destroying the food." Research to use LED technology to preserve freshness or increase nutrients in stored vegetables.
Oil immersed transformer thermometers include oil level thermometers and winding thermometers, including WZT series, BWY series and BWR type. Dry Type Transformer thermometers check the transformer temperature by inserting the sensor probe into the low-voltage winding side through a digital display; It can work normally under extreme severe weather conditions, and the maximum measuring temperature can reach 500 ℃.
The pressure thermometer is a thermometer for temperature measurement based on the change relationship between the saturated vapor pressure and temperature of the vaporized liquid in the closed temperature measurement system.
The principle of the pressure thermometer is based on the change relationship between the saturated vapor pressure and temperature of the vaporized liquid in the closed temperature measurement system. When the temperature bulb senses the temperature change, the saturated steam in the closed system will generate corresponding pressure, causing the curvature change of the elastic element, causing the displacement at the free end. Then the gear amplification mechanism will change the displacement to the indicated value. This thermometer has the characteristics of small temperature bulb, fast response, high sensitivity, and intuitive reading. It almost combines all the advantages of glass rod thermometer, bimetallic thermometer, and gas pressure thermometer, It can be made into shockproof and anti-corrosion type, and can realize remote contact signal, thermal resistance signal, 0-10mA or 4-20mA signal. It is the most widely used and comprehensive mechanical temperature measuring instrument.
For oil level thermometer, when the temperature package experiences temperature changes, the saturated steam in the closed system will generate corresponding pressure, causing the curvature of the elastic element to change and the free end to shift, and then the gear amplification mechanism will change the displacement to the indicated value. The thermometer has the characteristics of small temperature package, fast reaction speed, high sensitivity and intuitive reading. It almost collects all the advantages of glass rod thermometer, bimetallic thermometer and air pressure thermometer, and can produce anti-seismic and anti-corrosion type, realizing remote contact signal, thermal resistance signal, 0-10mA or 4-20mA signal.
The temperature indicating controller is mainly composed of elastic element (bellows), capillary tube and temperature package. The sealing system composed of these three parts is filled with temperature sensing liquid. When the measured temperature changes, the volume of temperature sensing liquid in the temperature package will also change. This volume increment is transmitted through the capillary to the elastic element (bellows) in the instrument, resulting in a corresponding offset. The offset can be amplified by the mechanism to indicate the measured temperature, drive the micro switch, and output the signal to drive the refrigeration system to control the temperature rise of the transformer.
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