Commercial sterility

Definition of commercial sterility

The term “commercially sterile foods” refers to food defined by Deibel & Jantschke (2001) as products that have been subjected to heat treatments and subsequently filled in hermetically sealed containers capable of preventing the entry of microorganisms. Filling can be done into cans, glass packages, flexible packages (pouches) or carton packages. In general, the cans and glass packages are vacuum-sealed, whereas the pouches and cartons may contain little or no vacuum. These products are microbiologically stable, and may be kept indefinitely at room temperature.

According to Deibel & Jantschke (2001) commercial sterility is achieved in the following conditions:

a)  Application of a sufficient amount of heat to make the food free from (1) microorganisms capable of growing in the product under conditions of non-refrigerated storage and distribution and (2) viable pathogenic microorganisms, including spores.

b)  Combined application of heat and reduction in pH or the combined application of heat and water activity reduction, to an extent or degree sufficient to make the food free from microorganisms capable of growing in the product, when stored under non-refrigerated conditions.

Classification of commercially sterile foods

The definition of commercial sterility makes clear that a commercially sterile food may contain viable microorganisms, provided they are not capable of multiplying in the product at ambient temperature. The dimensioning of thermal processes, that is, the amount of heat that must be applied, depends on the heat resistance of the microorganisms capable of multiplying under this condition. The microbial types that may grow depend, in their turn, on the pH and the water activity of the product, because these two factors interfere with the growth of the microorganisms. As a function of the pH and water activity values, commercially sterile foods are divided into low-acid or acidified food product.

 Low-acid food products: Includes products with pH values above 4.6 and water activity greater than 0.85 (Deibel & Jantschke, 2001). Examples of low acid products are processed meats, seafood, milk, meat and vegetable mixtures and “specialties” (spaghetti, soups), and vegetables (asparagus, beets, pumpkin, green beans, corn, lima beans). These foods allow the growth of most microorganisms, since their pH and water activity values are not restrictive. Both pathogenic and non-pathogenic bacteria can grow, including spore-forming and non-spore-forming species. The target of the sterilization process, in this case, are bacterial spores and, among these, more specifically those of  Clostridium botulinum, since this is the species that poses the greatest risk to public health.

 Acid food products: This group includes the products with a pH value smaller than or equal to 4.6 (Deibel & Jantschke, 2001). Examples of cid products are acidified vegetables, (hearts of palm, pickles, olives), canned fruits (figs, peaches, pineapples, berries) and fruit juices in cans or cartons. These products may allow the growth of molds, yeast and aciduric bacteria. Among the aciduric bacteria are the  Lactobacillus and other  lactic acid bacteria (non-spore forming), in addition to some spore forming species of the  Bacillus, Clostridium,  Alicyclobacillus and  Sporolactobacillus genera. The target microorganisms of the process, in this case, are not pre-established, because they will depend on each specific product. In the case of foods with a slightly acid pH (4.2–4.4), the saccharolytic clostridia ( C. butyricum,  C. pasteurianum,  C. tyrobutyricum, C. beijerinckii and  C. acetobutylicum) should be considered, as well as  Bacillus coagulans. In more acid foods, only  Alicyclobacillus, molds, yeasts and lactic bacteria can grow. In products with low water activity, only molds and yeasts are relevant.

References

Deibel, K.E. & Jantschke, M. (2001) Canned foods – tests for commercial sterility In: Downes, F.P. & Ito, K. (eds). Compendium of Methods for the Microbiological Examination of Foods. 4^th edition. Washington, American Public Health Association. Chapter 61, pp. 577–582.

Silva, N.D .; Taniwaki, M.H. ; Junqueira, V.C.A.;  Silveira, N.F.A. , Nasdcimento , M.D.D. and Gomes ,R.A.R .(2013) . Microbiological examination methods of food and water a laboratory Manual. Institute of Food Technology – ITAL, Campinas, SP, Brazil .