By: Gagan Dip and Damini Sahu *
In the current situation, food preservation has become a very important aspect of our lives. As we see, food production and supply do not always go well with the demand or meets of the people. Several foods e.g. fruits and vegetables are available in a specific season and are not available throughout the year. At some places, there is a surplus production of a particular food product, while at the same time at different places there is an inadequate supply. Certain foods are highly perishable, they quickly turn bad or deteriorate because of high microbial growth; and semi-perishable like juicy fruits, vegetables, mangoes, tomato, papaya and many more, which very quickly gets spoilt. It is therefore very important in order to maintain seasonal foods intact for later use. This can be done by improving the shelf-life of food by maintaining proper storage with effective preservation techniques. Food preservation helps in addressing all of the above mentioned problems such as: increasing the shelf-life of foods; increasing the availability of seasonal foods throughout the year; reducing wastage of food by preventing decay or spoilage of food; etc.
In order to effectively combat with such scenarios, modern age scientists are busy in developing techniques to maintain seasonal foods intact for later use. They believe that effective preservation ensures the availability of food at all times and its supply is maintained. Among various other techniques of preservation, canning is one of the widely used options for the preservation of food. Some examples of foods which can be packed using can packaging include: juices; sweets; fresh fruits & vegetables; fish; meat; ready to eat foods; soups; pet foods; etc.
What is Canning?
Canning is a technique for protection and preservation of food in which the food is heated and hermetically sealed in containers such as: glass bottles; metal cans; thermostable plastic; or multilayer flexible. The shelf life of canned foods is between six months to 5 years and it can be even extended longer under controlled conditions. Heating involved in the canning process destroys microorganisms and spore-forming bacteria. The air is driven out of the can and as it cools the can is vacuum sealed. This vacuum seal prevents air from getting back into the product and protects it from contamination.
Purpose of Canning
The presence of high moisture in various foods like fresh fruits & vegetables makes them more susceptible to spoilage. The microorganisms present on fresh food multiply quickly and accelerate the spoilage process. Proper canning procedures help to minimize the effect of microorganisms and make the food safe for consumption for a longer period of time.
The process used for canning food is determined primarily by the acidity of the food or mixture of foods being canned. Based on their pH, foods are categorised into the following classes:
Low acid Foods: The foods with a pH range of 5.0 to 6.8 fall in this category. The examples include: vegetables; meats; poultry; seafood; dairy, etc.
Acid Foods: The foods with a pH range of 4.5 to 3.7 fall in this category. The examples include: pear; oranges; apricots; tomatoes; and other citrus foods.
High acid Foods: The foods with a pH range of 3.7 down to 2.3 fall in this category. The examples include: highly acidic foods like pickled products and fermented foods.
Methods of Canning
Boiling Water Bath Method: The boiling water bath method can be utilised for high-acid foods such as: jams; marmalades; pickles; fruits; tomatoes; fermented foods; foods with vinegar; etc. The safe processing temperature of these types of foods is 100°C. A large deep cylindrical shaped metal container is used in this method. The container should be large enough so that the water can come over the top of packed jars or cans by leaving some headspace for boiling. The canning vessel is tightly fitted with dividers to separate and keep the cans away from the bottom of the container. Inside racks are also present to prevent the cans form knocking together or tipping over during the processing. The container is filled with water and preheated before loading cans. The boiling process of water should be maintained uniformly throughout the canning process.
Pressure Canning Method: Pressure canning method is used to preserve low-acid foods such as: vegetables; meats; poultry; and seafood. The shape of the canning vessel is designed like a pressure cooker where the food cans are placed in 2 to 3 inches of water and the cooker is heated to a temperature of at least 116°C.
Low-acid foods require special care as they might support the production of the deadly Clostridium botulism toxin if they are not processed properly in a pressure canning method. Though these bacterial cells are usually killed at boiling temperatures, they have a tendency to form spores that can withstand these high temperatures. These deadly spores grow well in low acid foods; in the absence of air they produce the deadly botulinum toxins.
Can Packaging is Better than Other Preservation Methods
Can packaging is a more cost efficient method as compared to other preservation methods like freezing, high-pressure processing, etc. The canned foods can be stored and utilised for a longer period of time at normal room temperatures from approx six months to 5 years. In other preservation methods shelf-life of foods is comparatively less and as well as the processed food products require specific storage conditions like refrigeration, etc. The canned products are easy to transport from one place to another and chances of microbial contamination are very less as well.
In contrast to various advantages, canned foods also have their disadvantages. The heat during the canning process destroys heat sensitive vitamins and minerals such as: Vitamin A, Vitamin C, folic acid, etc. The amount of sodium, salt, sugar and other preservatives used in the canned foods can be harmful to health. In order to avoid them, consumers should read the labels and choose the low-sodium, low-sugar, and low-salt canned goods. Also, the presence of BPA in the lining of cans has negative effects on human health and environmental condition. All in all, canned foods provide you convenience, are good for you and for the environment. The only thing that needs to be remembered is to eat them moderately and don’t forget to recycle them!
* M.Tech Scholar Food Science and Technology, Indian Institute of Food Processing Technology, Thanjavur (TN)
* M.Tech Scholar, Indira Gandhi Krishi Vishwavidyalaya, Raipur (CG)