Mechanisms of Food Additives, Treatments, and Preservation Technology 303
- The initial count and the composition of contaminating microflora,
- The conditions of processing with regards to the possibilities of cross-
contamination and contamination from the environment, workers, pre-
mises, vessels, tools, etc., - The conditions during manipulation, processing, and storage with regards
to the growth of the microorganisms present in the product, and - The count of surviving microorganisms after the antimicrobial treatment
(efficiency of the antimicrobial treatment).
Storability and safety of fresh-cut or minimally processed produce are based on a
combination of several preservation steps that individually may not be sufficient but
in combination make the product stable for its declared shelf life. It is the principle
of “hurdle technology”^ (Leistner, 1995).^ The most important hurdles are summarized
in Table 10.4.
The safety of fresh and fresh-cut fruit and vegetables has received considerable
attention lately. While the consumption of raw fruits and vegetables often causes
outbreaks of human diseases, the number of confirmed cases of illness associated
with raw plant products is lower than that associated with food of animal origin but
is important, especially in developing countries. Raw fruits and vegetables have been
known as vehicles of human disease since the end of the 19th century, when it
became understood that microorganisms are a cause of disease. In 1903 an outbreak
of typhoid fever was attributed to eating watercress grown in soil fertilized with
sewage; in 1913 other cases of typhoid resulted from uncooked rhubarb grown in
TABLE 10.4
The Most Important Hurdles
Hurdle Requirement
Initial microbe count As low as possible
Storage temperature As low as possible
pH Some bacteria are inhibited by a low pH alone; sporulating bacteria (including
toxinogenic) cannot grow in acid food with pH below 4.0a (4.5)b. The lower
the pH value the more efficient heat treatment, more efficient preservatives, etc.
Water activity As low as possible
Oxygen ingress As low as possible (vacuum or inert gas packaged low-acid vegetable products
are good substrate for strictly anaerobic Clostridium)
Degree of heating As high as possible (the process of reduction of microorganisms occurs
according to first-order kinetics; therefore heat treatment should be at
appropriate combination of temperature and duration of heating for an efficient
inactivation effect)
Preservatives Present in adequate concentration; should be added at lag phase of microbial
growth
aFrom Kyzlink, V., Principles of Food Preservation, Elsevier, Amsterdam, 1990, Part 4.
bFrom Bibek, R., Fundamental Food Microbiology, CRC Press, Boca Raton, FL, 1996, Section 6.