Foods are mostly derived from plant or animal-based, so it is an excellent environment to support the growth of the microorganisms because they are rich in nutrients.
Food spoilage is caused by microbial growth, by which the normal form of food is altered which is visible. It affects the aroma, appearance, and taste of the food.
There are several factors that are responsible for food spoilage, such as water content, pH, macromolecule content i.e., carbohydrates and proteins, other factors such as oxygen concentration and temperature are also accountable for spoilage of foods.
In 1857, Louis Pasteur introduced the process of Pasteurisation, it was a revolution for the modern era of food microbiology, and he proved heat can be used to control microbial growth in wine and beers.
In food industries, foods are categories into three groups:
Highly Perishable foods: It includes poultry, eggs, meats, most fruits, vegetables, and dairy products which are rapidly spoiled.
Semiperishable foods: the rate of spoilage is slow, in this category food such as potatoes, nutmeats, apples, etc are included.
Non-perishable foods: It usually includes cereals, rice sugars, etc.
The composition of the foods influences microbial growth which results in the decomposition of the food.
Most carbohydrates are spoiled by the fungal genera, which includes Aspergillus, Penicillium, Rhizopus, and Fusarium but there are some bacterial species that cause food spoilage. For e.g.,
Bread: Spoilage is caused by Aspergillus, Penicillium.
Vegetables: Bacillus, Pseudomonas
Fruits and Juices: Acetobacter and Lactobacillus
On other hand, protein and lipids containing foods are mostly spoiled by a variety of bacterial species. For e.g.,
Fresh meats: Micrococcus, Achromobacter,
Milk and Dairy Products:Streptococcus and Lactobacillus
Eggs: Pseudomonas, Cladosporium
Fish, Shrimp, and Poultry: Achromobacter, Pseudomonas, Flavobacterium
The food preservation objective is to prevent food spoilage caused by microbial growth.
Thus, two principal are used to preserve food which is as follows:
Prevention or delaying of the microbial decomposition:
Techniques opt to remove microbe (e.g., Filtration)
By hindering the rate of microbial growth (e.g., chemical inhibitors, low temperature, drying, or anaerobic conditions)
By eradicating the microbes (by heat or radiation)
By increasing the shelf life of the food by delaying self decomposition of the food:
By inactivating the food enzymes (e.g., blanching)
By preventing chemical reactions (by using antioxidants)
Modern preservation methods of the foods involve:
High temperature is significant to control microbial growth in foods which limits the transmission of foodborne pathogens and spoilage.
In 1809, Nicholas Appert, introduced heating can be helpful in food preservation, which is followed in the canning process at the commercial level
In the canning process, canned food is heated in a container called retorts, it is specially designed for canning, and the temperature range is 115°C up to 25- 100 mins.
The time & temperature depends on the nature of the food.
The process of canning is not likely to kill all microorganisms, but those who cause food spoilage (because the acidity of food doesn’t favor the growth of remaining microorganisms).
Following heat treatments of the can, are subjected to a rapid cooling process with cold water.
Despite the above procedure to eradicate food pathogens, canned food is spoiled, it may be caused before the canning process or during the cooling process, contaminated water may have entered the can.
The characteristics of the food because of spoilage affect its natural color, texture, and taste and it is followed by odor. During the process of food spoilage, organic acids, sulfides, and gases like carbon dioxide and hydrogen sulfide are released.
In food can, if microorganism produces gas, the swelling is quite visible, soft swell and hard swell, it is determined by thumb press.
Highly acidic foods react with the metal of the can container which generates hydrogen which causes hydrogen swell.
The microorganisms Desulfotomaculum, which produce hydrogen sulfide can cause “sulfur stinkers” which are generally found in low acidic food spoilage.
The process of pasteurization includes heating of the food, which is lethal for food pathogens, and also reduces the numbers of other food spoiling microorganisms.
For the processing of dairy, beers, and juices, low-temperature holding (LTH) pasteurization is used, in which the temperature is maintained at 62.8°C for 30 mins.
Another method of pasteurization is high-temperature short-time (HTST), in which products are subjected to a temperature of 71°C for 15 secs.
The milk can be processed by using ultra-high temperature (UHT) for the temperature at 141°C for 2 secs. It improves the flavor and shelf life of the product.
Above heat treatment is given on the basis of probability, the no. of viable microorganisms decrease at a specific temperature of heating.
Removal of Microorganism
The physical removal of microorganisms from water, beer, wine soft drinks is carried out by the process of filtrations.
The large particulates are removed by prefiltration and by the process of centrifugation, which helps to increase filter life and its efficiency of work.
Various brands of beers are filtered rather than pasteurization process to preserve the original aroma and flavor of the product.
The refrigeration process is also used in our day-to-day life; storage at 5°C retards the growth of the microorganism.
Below temperature at -10°C, some food like ice cream, fruit juice concentrates, and some fruits are stored, for better preservation.
The refrigeration process hinders the metabolic activity of most microorganisms; it slows their process but doesn’t reduce the overall microbial populations.
Removal of water i.e., dehydration, is carried out by the process of lyophilization to produce food that is freeze-dried.
In this process, the loss of free water is followed by an increase in the concentration of solute.
This process is often used for the preservation of food like grains, fish, fruits, and meat.
Chemical agents such as organic acids, sulfite, ethyl formate, ethylene oxide used as a gas sterilant, sodium nitrite, are used to preserve foods.
The agents target the plasma membrane of microbes, and cause disruption, even various proteins are denatured.
These compounds also hindered nucleic acid functions and prevent cell reproduction.
Its effectiveness depends on the pH of the food. For e.g., sodium propionate effectively works well in lower pH. It is used for the preservation of bread.
Chemical preservation is often used in the preservation of dairy, vegetables, grains, and fruit products.
For the preservation of meat products such as ham, bacon, and sausage, sodium nitrite is used which prevents the growth of the Clostridium botulinum and its spores.
Both ionizing and non-ionizing are used in food preservation.
UV radiation is used in the laboratory to inhibit the growth of microorganisms, but it is not in food preservation because of its inability to penetrate the foods.
Majorly gamma irradiation from cobalt 60 source is used in sterilization process of food, they are capable of penetrating but only used with moist food because it reacts with water and forms hydrogen peroxide in the microbial cell which results in oxidation of cellular constituents.
The above process is called radappertization, and the pioneer is Nicholas Appert.
It is used in the preservation of seafood, fruits, and vegetables, to sterilize meat 4.5-5.6 megarads are used.
The electron beam is also used as radiation, but it’s not effective as gamma radiation.
Microbial Inhibitory Product- Based Preservation
The bacteriocins produced by bacillus are used in the preservation of the foods but limited against closely related bacteria, which inhibit the cell membrane functions, protein, and RNA synthesis. It forms pores in the membrane. It is mostly used in cheddar cheese preservation.
Nisin, obtained from Lactobacillus lactis, is a protein mostly hydrophobic in nature, it affects gram-positive bacterial species especially Enterococcus faecalis.
Nisin is used in low acidic foods to enhance the inactivation of Clostridium botulinum during the process of canning.