While thermal processes such as pasteurization and sterilization are commonly used for the inactivation of microorganisms during the production of milk and dairy products, alternative methods have been needed due to nutrient and aroma losses caused by heat treatment, non-enzymatic browning and sensory changes in the products. Non-thermal high pressure (HP), pulsed light (PL), ultraviolet irradiation (UV), supercritical carbon dioxide (SC-CO2) and pulsed electric field (PEF) methods are used to extend the shelf life of milk.
High Pressure Method
This method generally involves the application of pressure between 100 MPa and 1000 MPa, in particular between 100 MPa and 600 MPa, the principle of which is based on the principle of compressing the water surrounding the material. The HP method does not adversely affect the taste of the products and acts to stop the activity of microorganisms. It leads to changes in the physical appearance and texture of the food, while prolonging the shelf life of the food and inactivating the disrupting microorganisms after the application of pressure in the food. Pathogen microorganisms have been reported to affect cell / cell membrane leading to cell death. During application, factors such as pressure, time and temperature can damage microorganisms.
PL application is a non-thermal sterilization method with radiation light which provides antimicrobial effect without damaging the content and surface of the product used. In this method, broad spectrum wavelengths (200–1000 nm) in the UV region close to the infrared region are used. A surface to be sterilized is exposed to at least 1 pulse of light with an energy density of approximately 0.01–50 J / cm2, in which case a wavelength distribution of 170–2600 nm should be used. The duration of the pulses ranges from 1 μs to 0.1 s, with a flash of 1–20 per second. It shows antimicrobial effect on disrupting microorganisms in foods.
UV forms a small portion of the electromagnetic spectrum within the range of 100–400 nm. UV-C; It has a lethal effect against microorganisms such as bacteria, viruses, protozoa, yeast, mold and algae. In order to achieve microbial inactivation, food must be exposed to an energy of at least 0.04 J / cm2. UV light causes mutations and cell death by causing cross-linking between thymine and cytosines in the same DNA sequence. Factors such as species, strain, culture determine the degree of UV exposure of microorganisms. The type and structure of food are also effective. UV method has a lethal effect on microorganisms in 3 ways as liquid sterilization, air disinfection and inhibition of microorganism on the surface.
Super Critical Carbon Dioxide
If the gases are heated above their critical temperature and pressure is applied, they pass to a fourth phase called supercritical phase. The SC-CO2 method is a method known as the green method, using a critical temperature of 31.1 ° C and a critical pressure of 7.38 MPa. SC-CO2 method; It is an effective method which ensures the preservation of food quality with minimum loss from traditional thermal application methods.
Pulsed Electric Field
PEF method; It is used to inactivate microorganisms which are effective on the physical, chemical and nutritional properties of foods. In this method, the electric field in the range of 12–35 kV / cm is applied to liquid foods with short accents (1–100 μs) and has a fatal effect on microorganisms. Furthermore, in this method, liquid food is preheated (40 ° C) between two electrodes in special PEF chambers and exposed to a high voltage electric field (20–80 kV / cm).