Different thermal and non-thermal methods were used for food preservation. All methods of maintaining and protecting the food pieces of stuff are reviewed in this essay.
Different methods are used to increase shelf life. These methods can be thermal, non-thermal, physical, chemical, etc. In general, these methods are as follows, which are briefly reviewed:
Physical methods include thermal methods (heating and cooling), dehydration (drying and freezing methods), and irradiation (X-ray, gamma, X-ray, ionizing beams) and chemical methods include salting, processing, acidifying, smoking, and using natural and synthetic preservatives.
Types of thermal cooling methods
Using the refrigerator to maintain the temperature at +4 to +6 °C by keeping the temperature steady during storage and control fluctuations to prevent the growth of microorganisms.
Using minus zero temperature for freezing is one of the best technics to preserve foods. Freezing tunnels, cold surfaces, cryogenic surfaces, and so on are used in freezing. Protein products are mainly frozen at -30 to -40 °C in the freezing tunnel at a speed of 3-6 m/s. In addition, temperatures of -18 to -40 °C are used to inhibit the enzymatic activity of bacterial growth.
Types of thermal cooling methods
As explained, pasteurization is a heat process with temperatures below 100 °C (65-100) at various times of 1-30 min. It is almost classified as a medium heating process. This method is used to preserve liquid and semi-solid foods.
According to our previous article, a temperature of 130-150 °C is used for a few seconds and the pre-sterilized containers are filled through the pump in this process. This method is divided into two types, thermal and non-thermal. This process is mostly used in canning. This process damages yeasts, molds, vegetative forms, and bacterial spores.
Dehydration is performed by various Industrial devices and dryers, Industrial Dryers for Foodstuffs. This method prevents the biological activity and enzymes that cause food spoilage by reducing the moisture in foods such as fruits and vegetables, meat, etc. Reducing the active water reduces the speed of microorganisms. As a result, it delays the spoilage of foods. Thus, it increases the food shelf life.
The freeze-drying method, described in another article, converts water directly into steam by creating freezing and reducing the pressure of the frozen water inside the food and leaving the contents waterless. This method is one of the best drying methods because it does not damage the tissue of food and minimizes protein denaturation. The basis of this method is the evaporation of water in frozen food in a vacuum.
Irradiation is a physical method to kill microorganisms and increase the shelf life of the product, which is done by gamma-ray, X-ray, and ionizing radiation methods. Radiation is described in detail on Food Lord site, which you can visit. Food Lord uses the irradiation method to extend the life of its products such as dried fruits, dried vegetables, and nuts.
One way to preserve food is to add salt (salting) or put it in saltwater (brining). The presence of salt and impurities on one side of the tissue makes a different osmotic pressure and interstitial water is expelled from the food. In addition, salt kills some microorganisms, so increases the shelf life of food.
Processing means performing any physical and chemical process on food to increase the performance and longevity of food. It is generally used for meats. In this way, various preservatives such as sugar, salt, sodium nitrite, and sodium nitrate, etc. are added to reduce the moisture content of the material and increase the shelf life of the food.
Acidifying reduces the microorganisms’ growth. Acetic acid is commonly used to produce acidic media.
Smoking through incomplete fuel stops the growth of microorganisms and has an antimicrobial effect. Moreover, smoking reduces moisture in food. Therefore, this method is used as one of the old methods of food preservation.
Natural and artificial preservatives
A specific preservative is used within the permitted food range that has a specific definition for each food preservative. These materials do not change the taste and flavor of food but have antimicrobial properties and prevent spoilage. The preservatives include benzoic acid, parabens, sorbic acid, its salts, phenolic compounds, nitrites and nitrates, and antioxidants such as phenols, butylated hydroxyanisole, and dibutyl hydroxytoluene.