Food is any substance that is consumed to provide nutritional support for an organism. Food is usually of plant, animal, or fungal origin and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals, that are derived from different sources, such as plants and animals, to fulfill energy requirements, nutrient requirements, and help with other metabolite activities for sustaining life. However, if it is not good in quality or in sense of spoilage due to being poorly preserved, it will have detrimental effects on the consumer’s life and ultimately cause death.
There are several key factors that trigger the spoilage activity of food, such as moisture content, microbial, temperature, oxidation, proteolysis, hydrolytic rancidity, putrefaction, Maillard reaction, and pectin hydrolysis. Therefore, food preservation is one way to increase the shelf life of food products; it also maintains or enhances the nutritional value.
If we are focused on the traditional methods of preservation techniques, they were excellent at practicing different preservation techniques such as sun or smoke drying, curing, salting, sugaring, fermentation, pickling, freezing, etc., while canning food preservation techniques caused a revolution in food packaging industries during World War-I and World War-II.
There are several important objectives for developing food preservation techniques to minimize pathogenic bacterial count, maintain food quality, shelf-life, texture, and flavor, enhance the nutritional value and availability of food in remote areas, or ensure food quality is persistent during transportation of food.
The basic principle of all food preservation techniques is to minimize or cease the free water activity in the food because the concentration of free water in food is a determinant factor of microbial colonization and enzymatic activity.
Since the food preservation technique has been practiced for centuries, one of the most effective uses of Hurdle technology in the food packaging industry is to address the consumer demand for natural and fresh foods. Hurdle technology is the combined approach of different preservative factors to regulate microbial safety by enforcing hostile conditions for microorganisms and maintaining nutritional quality and organoleptic properties of food, which brings about the economic viability of food products (Leistner I., 2000).
The principle of Hurdle technology is governed by integrated preservative factors such as temperature (higher or lower), water activity (aw), acidity (pH), redox potential (Eh), chemical preservatives (nitrite, sorbate, sulfite), vacuum packaging, modified atmosphere, HHP, UV, and competitive microorganisms (Leistner, 2000).
Natural methods for food preservation
The basic food preservative technique can be used singly or in combination with the Hurdle technology of optimization. Food preservation comprises two major groups of physical & chemical methods. Drying, Chilling, Freezing, Canning, Smoking, and pasteurization are common physical methods, whereas chemical methods are Salting, Pickling, and Sugaring. Further, chemical preservatives can be divided into classes I and II.
Drying: One of the oldest and simplest techniques to reduce water activity in food is the sundry, or hot air oven technique. The drying method reduces water content and prevents microbial growth of food products. It is mostly used by households or small-scale industries like drying fish, Urad Badi or raw green mango, chili, vegetables, etc.
Chilling: It is a simple method using a refrigerator where food items are kept at a cold temperature of 1-4 °C, or just above freezing temperature. Microbial growth has ceased at this temperature. It is applicable for short-term storage, which is reliant on the type of food items. This method requires cold storage or a refrigerator machine.
Freezing: In this process, liquids such as water solidify into crystal-like ice, halting the metabolite activities of microorganisms. It differs from the chilling method of food preservation in that ice crystallization does not occur in the chilling process, while freezing allows ice crystallization and the removal of latent heat from the products. The freezing method is better for long-term storage in comparison to the chilling method. It is a good preservation technique for maintaining the nutritional quality of food. The quality of frozen food depends on the rate of freezing applied to it. During the freezing process, ice crystals disrupt the osmosis equilibrium of the cell membrane, and the resultant varies in quality. This problem is overcome by quick freezing. In this process, cryogenic freezing may also be used for an exceptionally very fast rate of freezing where liquid nitrogen boils around food at a temperature of -196 °C, which releases a large amount of heat from food products.
Canning: Sir Nicholas Appert was the scientist who first developed the Canning food technique, known as the “father of canning.” Sterilize food items by heating and sealing them inside sterilized containers like cans or jars. In the canning process of food, oxygen is removed, which makes it restricted to aerobic microorganisms. The canning process uses acid or salt to create a hostile environment for microorganisms. Canning food storage is basically two types: water bath canners for high-acid foods and pressure canners for low-acid foods. These days, canned food is getting more popular, and food industries are widely used in household culture.
Smoking: Smoking food preservation is the process of burning wood materials or desired plant materials to produce smoke that is exposed to food. The unique flavor of smoked foods depends on the type of smouldering plant material like hardwood, oak, beech, chestnut, and hickory, whereas other aromatic plant materials like juniper or cherry are also used for the distinctive flavors of smoked foods. During the smoking of wood, several types of compounds are released, such as formaldehyde, phenolic, Nitrogen oxides, Furans, and Carbonylic compounds. Some of these have antibacterial properties. This technique is mostly used in fish and meat preservation. Smoking food can be classified into three types based on temperature:
- Cold smoking, which is done between 20 and 30 °C for mostly raw food preservation.
- Warm smoking, which is done at a temperature of 25 to 40 °C for mostly cooked and flavored foods.
- Hot smoking, which is done at a temperature of 52 to 80 °C for properly cooked and flavored foods.
Pasteurization: Louis Pasteur was the first scientist to introduce a mild heat treatment (below 100 °C) of liquid food like milk or fruit juice to deactivate or kill pathogenic microorganisms to increase the shelf-life of liquid food products. The efficiency of pasteurization, in terms of food quality and the thermal death of heat-resistant microorganisms, is dependent on the combination of temperature and time. Hence, there are three different pasteurization treatments categorized as VAT (Batch) treatment. This process exposes low temperatures with long time duration (63-65 °C for 30 minutes) to kill the vegetative pathogens and it is used for batch treatment of liquid food which can be preserved for several days under the refrigerator; whereas High-Temperature Short Time (HTST) is a continuous process with high temperature at low time exposure to kill vegetative pathogens (72 °C for 15-30 seconds) and it can be preserved for 2-3 weeks under the refrigerator; and Ultra-High Temperature (UHT). It is a continuous process, and food items are exposed to a temperature of 135-150 °C for a few seconds to destroy all bacteria as well as spores. This method very well maintains food quality. It can be preserved for 6 to 9 months in the refrigerator.
Irradiation: It is a physical process to destroy microorganisms under the treatment of a definite dose of ionizing radiation (IR). IR generally uses X-rays, gamma-rays, and high-energy ultraviolet radiation to disinfestation of food items, and these methods are mostly used for raw vegetables, fruits, or food grains. This method improves the shelf life of food by inactivating microorganisms and also inhibiting sprouting or modifying the rate of maturity or aging process.
Chemical methods for food preservation
Sugaring: It is a method widely used in fruit products for preservation. In this method, sugar is used for desiccating food dehydrated. Therefore, microorganisms also lose water from the cell wall and get dehydrated making it inactive. It also increases the shelf life of products
Salting: Salting is also the same principle as sugaring in that it withdraws moisture from food to inhibit bacterial growth. Salt has been used as a preservative for food for centuries. It is the cheapest and easiest way to preserve food products like fish, meat, and vegetables.
Pickling: After cleaning food products, deep into an edible organic acid solution such as vinegar or in a salt solution like brine. This pickling method uses natural preservatives, also known as Class-I preservatives, such as Salt, edible vegetable oil, Sugar, Dextrose, Vinegar or Acetic acid, Honey, and Spice while chemical preservatives class-II as EDTA, Benzoic acid, Sulphureous acid, Nitrates, or Nitrites of Sodium or Potassium, Nisin, Sodium, and Calcium propionate, Methyl or propyl Para Hydroxy-Benzoate, Sodium diacetate etc.
Benzoates (inactivation of bacterial & fungal growth), Nitrates & Nitrites (Used for preservation of Meat & Meat Products), and Sulphites (it makes food appear fresh by stopping the oxidation process).
At present, chemical preservation has limited uses for its side effects. Therefore, the value of chemical preservatives is fixed according to food product requirements, which are controlled by national or international regulatory bodies. Therefore, food products need to be quantified by lab testing for chemical preservatives as per regulatory bodies. Therefore, we are here to provide you with the best testing services for your products according to national and international regulators.
Author: Nitesh Kumar and Dr. Sanjoy Gupta
- Amit, S.K., Uddin, M.M., Rahman, R. et al.A review on mechanisms and commercial aspects of food preservation and processing. Agric & Food Secur 6, 51 (2017). https://doi.org/10.1186/s40066-017-0130-8
- Leistner I (2000) “Basic aspects of food preservation by hurdle technology” International Journal of Food Microbiology, 55:181–186