In this article we will discuss about the spoilage of non-canned and canned foods.
Spoilage of Non-Canned Foods:
Spoilage of Canned Foods:
Canned foods may spoil either due to biological or chemical reasons. We would discuss only the biological spoilage as it is the point at issue.
Biological spoilage of canned foods:
Biological spoilage of canned foods occurs due to the action of various microorganisms. Spore forming bacteria, e.g., Clostridium, Bacillus represent the most important group of canned food spoiling microorganisms because of their heat resistant nature (thermophilic nature).
In addition, there are other microorganisms which are not heat resistant (mesophilic) but enter through the leakage of the container during cooling and spoil the food.
In this way, we can divide biological spoilage of canned foods into following two categories:
(a) Biological spoilage by thermophilic bacteria:
Under-processing of canned foods results in spoilage by thermophilic bacteria, the bacteria that grow best at temperature of 50°C or higher. Five types of this spoilage can be recognised.
(i) Flat sour spoilage:
In canned foods, production of acid and no gas is referred to as flat-sour spoilage because the food becomes sour, but the can shows no evidence of food spoilage because no gas is produced, i.e., the can remains flat.
Thus, the spoilage cannot be detected unless the can is opened. The spoilage is caused by Bacillus spp. such as B. coagulans and B. stearothermophilus resulting in sour, abnormal odour, sometimes cloudy liquor in food content of the can.
(ii) Thermophilic anaerobic (TA) spoilage:
Clostridium thermosaccharolyticum, an obligate thermophile, causes spoilage. The can swells and may burst due to production of CO2 and H2. The food becomes fermented sour, cheesy, and develops butyric odour.
(iii) Sulfide spoilage:
Clostridium nigricans is involved in this spoilage. It produces H2S gas which is absorbed by the food product. The latter becomes usually blackened and gives “rotten egg” odour.
(iv) Putrefactive anaerobic spoilage:
Clostridium sporogenes causes spoilage through putrefaction. The can swells and may burst. Putrefaction may result from partial diction of the food. The latter develops typical “putrid” odour.
(v) Aerobic sporeformer’s spoilage:
Bacillus spp., the aerobic bacteria, cause spoilage. If the canned food is cured meat, swelling of the can is observed.
(b) Biological spoilage by mesophilic microorganisms:
Bacillus spp., Clostridium spp., yeasts, and other fungi which are mesophilic (an organism growing best at moderate temperature range of 25 to 40°C) are mainly responsible for this type of canned food spoilage. As stated earlier, these organisms enter through the leakage of the container during cooling.
Clostridium butyricum and C. pasteurianum result in butyric acid type of fermentation in acidic (tomato juice, fruits, fruit juices, etc.) or medium acidic (corn, peas, spinach, etc.) food with swelling of the container due to the production of CO2 and H2. Bacillus subtilis and B. mesentroides have been reported as spoiling canned sea-foods, meats, etc.
Other mesophilic bacteria which have been reported in cans are Bacillus polymixa, B. macerans, Streptococcus sp., Pseudomonas, Proteus, etc. Yeasts and moulds have also been found present in canned foods. Yeasts result in CO2 production and swelling of the cans.