The Commercial Canning Process

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The commercial canning process uses pressurized steam in an industrial-sized autoclave called a retort. Conditions of the process are designed to ensure that endospores of Clostridium botulinum are destroyed. This is critical because surviving spores can germinate and the resulting vegetative cells can grow in the anaerobic conditions of low-acid canned foods, such as vegetables and meats, and produce botulinum toxin, one of the most potent toxins known. Because ingestion of even minute amounts of botulinum toxin can be lethal, the canning process of low-acid foods is designed to kill all endospores of C. botulinum. In doing so, the process also kills all other organisms capable of growing under normal storage conditions. Endospores of some thermophilic bacteria may survive the canning process, but these are usually of no concern because they only can grow at temperatures well above those of normal storage. Because of this, canned foods are called commercially sterile to reflect the fact that the endospores of some thermophiles may survive. Figure 5.5 shows the steps involved in the commercial canning of foods. ■ botulism, p. 672

Several factors dictate the time and temperature of the canning process. First, as discussed earlier, the higher the temperature, the shorter the time needed to kill all organisms. Second, the higher the concentration of bacteria, the longer the

(a)
Chemical Indicator For Autoclave

Figure 5.4 Indicators Used in Autoclaving (a) Chemical indicators.The pack on the left has been autoclaved. Diagonal marks on the tape have turned black with heat, indicating that the object was exposed to heat. (b) Biological indicators. Following incubation, a change of color to yellow indicates growth of endospore-forming organisms.Why would a biological indicator be better than other indicators to detect if sterilization had been completely effective?

Figure 5.4 Indicators Used in Autoclaving (a) Chemical indicators.The pack on the left has been autoclaved. Diagonal marks on the tape have turned black with heat, indicating that the object was exposed to heat. (b) Biological indicators. Following incubation, a change of color to yellow indicates growth of endospore-forming organisms.Why would a biological indicator be better than other indicators to detect if sterilization had been completely effective?

heat treatment required to kill all organisms. To provide a wide margin of safety, the commercial canning process is designed to reduce a population of 1012 C. botulinum endospores to only one. In other words, it is a 12 D process. It is virtually impossible for a food to have this high a level of initial concentration of endospores, and so the process has a wide safety margin.

Dry Heat

Heating in the absence of moisture is frequently used to destroy microorganisms. For example, in microbiology laboratories, wire loops that are continually reused to transfer bacterial cultures can be sterilized by heating them in a flame until they are red hot. Glass Petri dishes and glass pipets are sterilized in ovens with noncirculating air at temperatures of 160°C to 170°C for 2 to 3 hours. The process essentially burns the cell constituents, oxidizing them to ashes or irreversibly denaturing proteins. Dry heat has an advantage over moist heat in that it can be used for

Nester-Anderson-Roberts: I I. Life and Death of I 5. Control of Microbial I I © The McGraw-Hill

Microbiology, A Human Microorganisms Growth Companies, 2003

Perspective, Fourth Edition

Chapter 5 Control of Microbial Growth n

. Foods are sorted to remove any that are damaged, and then are washed. Washing reduces the number of microorganisms on the food.

. Blanching with hot water or steam destroys enzymes that alter the flavor of the food as well as lowers the number of microorganisms.

6. The cans are heated by steam under pressure. They are cooled by spraying with water or submerging in cold water.

Sterilization

6. The cans are heated by steam under pressure. They are cooled by spraying with water or submerging in cold water.

Sterilization

Cooling

Cooling ooooooooooo

7. Cans are labeled, packaged, and shipped. Figure 5.5 Steps in the Commercial Canning of Foods powders and other anhydrous materials that moist heat does not effectively penetrate. It also does not dull sharp instruments or corrode metals.

Dry heat takes much longer than wet heat to kill microorganisms. For example, 200°C for 11/2 hours of dry heat is the killing equivalent of 121°C for 15 minutes of moist heat. Ovens with a fan that circulates the hot air can sterilize in half the time because of the more efficient transfer of heat.

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Responses

  • Eija
    What are dry heat treatment and autoclave conditions require to kill endospore?
    2 years ago
  • bryce shaw
    How does commercial canning kill bacteria?
    1 year ago
  • Reima
    Which bacterium is a villain of canning process?
    10 months ago

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