Health risks of canned Foods

Dr Ngaseppam Iboyaima *

Canned fish tins at the shop and inset the contents of the tin in January 2013 :: Pix - TSE

Very surprised and shocked to know that canned fish which are contaminated with yeasts and moulds are selling openly in some places of Manipur and neighbouring states. In fact, such contaminated foods are dangerous and unfit to consume. Yeasts and moulds are the most heat sensitive microorganisms as compared with bacteria and supposed to be killed easily at boiling water (100 C).

Low acid food like canned fish are universally thermally processed (heated) at 121 C for 30-50 minutes in a retort (pressure cooker, 15 psi) so there is no chance to grow these microorganisms at this temperature. In such case, the only possible way to contaminate the fish with yeasts and moulds is through sealing/seaming defects (leakage) at factory level or leakage during transport resulting loss of vacuum inside the can (head space). Can sealing/seaming defect is one of the major problems facing in the canning industries. Once the cans are leaking, most of the spoilage and disease causing (pathogenic) microbes are grown on food materials and make the foods unfit for eating.

No bulging of can lid or any off appearance of the can will be seen in this problem/case. In fact, bulging of can lids indicates perfect sealing (air tight) which will prevent the escape of hydrogen or carbon dioxide or other gases produced inside the can due to growth of spoilage or harmful microorganisms or chemical reactions between the can (tin plate) and food materials and or over filling of food materials. But, such observations are taken as the cans are spoiled, unfit for human consumption and should be destroyed.

For consumer point of view, canning technology is one of the best food preservation methods which contains no chemical preservatives. Canned fish or meat is the one such product that every NE people likes because of their eating habits, convenient and moreover, the product has a long shelf stable storage life. Only problem is that we cannot see the nature of contents (good or bad) from outside. So, some guidelines to the buyers are:

Do not purchase the canned food if you see any of these problems:
o swelling, and/or leakage
o rust and scratches
o broken tamper-evident seals or expiry dates
o dented or damaged containers
o damaged seams (joins)
o expiry dates or best before
o This could mean the contents are contaminated and may not be safe to eat or in case of expiry dates, poor quality products in terms of nutritive values and sensory quality.

Storage:
o Store the purchased cans in a cool, dry place if not used immediately.

After opening:
o If the contents have an unusual odour or colour, or if you notice that the inside of a metal container (or lid) is rusted or black patches, throw out the contents. Do not taste.
o Once a container containing fish or meat or vegetables has been opened and If not used immediately or partly used, the contents or leftover of the opened container should be emptied into clean plastic or glass container, covered and stored in a refrigerator immediately and throw it out no more than 3-4 days after opening.
o Always cook the contents (e.g. meat or fish or veg) before eating (never attempt to eat or taste without heating)
o Never eat canned foods that are dented, leaking or have bulging ends during transport or storage. If in doubt, throw it out!

Health risks of low acid canned Foods

Botulism is a serious and sometimes fatal illness you can get from eating improperly prepared, canned or bottled food. Botulism is caused by a toxin (botulin) produced by the bacteria called Clostridium botulinum. Botulism bacteria grow in a moist, oxygen-free environment so improper canning and bottling of low acid foods like meat, fish, legumes, vegetables, etc. can provide ideal conditions for it to multiply and produce this deadly toxin.

Botulism doesn't change the colour, odour or taste of food. When in doubt, throw it out! Symptoms of botulism usually appear within 12 to 36 hours after eating the contaminated food. These symptoms may include:
o nausea
o vomiting
o fatigue
o dizziness
o headache
o double vision
o dryness in the throat and nose

Serious health risks can include:
o respiratory failure
o paralysis
o death

These symptoms will usually last 2 hours to 14 days but some can last longer. The groups at higher risk for serious health effects include pregnant women, children under the age of 5, adults over the age of 60, and people with weakened immune systems.

Therefore, always cook the contents (e.g. meat or fish or veg) before eating because cooking destroyed the “botulin toxin” (poison).