How to safely preserve Food – Food preservation, Definition of Food Spoilage, Microbial Contamination, Chemical Deterioration, Sterilization, Pasteurization, Fungi
Learn about food preservation and the various steps to preserve foodstuffs in this article you will learn more about ways of preserving food as well as fruits, with new ideas and methods of preservation.
A number of methods by which food is preserved from spoilage after harvesting or slaughtering. Such practices date to prehistoric times.
Among the oldest methods of preservation are the following:
Modern methods include:
- Irradiation, and
- The addition of chemicals. Advances in packaging materials have help in advancing modern food preservation.
It is defined as any change that renders food unhealthy for human use. However, this change is caused by a variety of factors, as well as contamination by bacteria, infestation by insects, or degradation by endogenous enzymes In addition, physical and chemical changes, such as the tearing of plant or animal tissues or the oxidation of certain constituents of food, may advance food spoilage.
Foods obtained from plant or animal sources begin to spoil soon after harvest or slaughter. The enzymes contained in the cells of plant and animal tissues may be released as a result of any mechanical damage inflicted during postharvest handling. These enzymes begin to break down the cellular material. The chemical effect catalyzed by the enzymes results in the degradation of food quality, such as the increase of off-flavors, the deterioration of texture, and the loss of nutrients. The typical microorganisms that cause food spoilage are bacteria.
Bacteria and fungi (yeasts and molds) are the principal types of microorganisms that cause food spoilage and food-borne illnesses.
Foods may be infected by microorganisms at any time during one of the following:
- Handling or preparation.
Sources of Microbial Contamination: The primary sources of microbial contamination are soil, air, animal feed, animal hides and intestines, plant surfaces, sewage, and food processing machinery or utensils.
Bacteria are unicellular organisms that have a simple internal structure compared with the cell of the other organisms. The increase in the number of bacteria in a population is commonly referred to as bacterial growth by microbiologists. This growth is the result of the division of one bacterial cell into two identical bacterial cells, a process called binary fission. Under optimal growth conditions, a bacterial cell may divide about every 20 minutes. Therefore, a single cell can generate almost 70 billion cells in 12 hours. The factors that control the growth of bacteria include nutrient availability, moisture, pH, oxygen levels, and the presence or absence of inhibiting substances (e.g., antibiotics).
There are two types of fungi that are important in food spoilage they are as follows:
Molds: are multicellular fungi that replicate by the formation of spores. Spores are formed in large numbers and are easily dispersed through the air. Once these spores land on a food substrate, they can grow and replicate if conditions are favorable.
Yeasts are unicellular fungi that are much larger than bacterial cells. They replicate by cell splitting up (binary fission) or budding.
Enzymes are large protein molecules that perform as biological catalysts, accelerating chemical reactions without being consumed to any appreciable extent themselves. The movement of enzymes is specific for a firm set of chemical substrates, and it is reliant on both pH and temperature.
|ascorbic acid oxidase||vegetables||destruction of vitamin C|
|lipoxygenase||vegetables||damage of vitamin A, off-flavour|
|pectic enzyme||citrus juices||destruction of pectic substances|
|polyphenol oxidase||fruits, vegetables||browning, off-flavor, vitamin loss|
|protease||eggs||reduction of shelf life of fresh and dried whole eggs|
|flour||reduction of gluten formation|
|thiaminase||meats, fish||destruction of thiamine|
The time and temperature required for the sterilization of foods are influenced by numerous factors, including the type of microorganisms found on the food, the size of the container, the acidity or pH of the food, and the method of heating.
Pasteurization is the application of heat to a food product in order to destroy pathogenic (disease-producing) microorganisms, inactivate spoilage-causing enzymes, and to reduce or destroy spoilage microorganisms. The relatively mild heat handling used in the pasteurization procedures causes a minimal change in the sensory and nutritional characteristics of foods compared to the severe heat treatments used in the sterilization process.
Selected crop varieties are grown especially for canning purposes. The harvesting schedules of the crops are carefully selected to conform to the cannery operations. A typical canning operation involves cleaning, filling, exhausting, can sealing, heat processing, cooking, labeling, casing, and storage. Most of these operations are performed using high-speed, automatic machines.