Control of Pathogens at Retail - Retail Food Safety - page 10

Typically, bacteria under the right conditions and temperature have a doubling
time of about 20-30 min. Some bacteria need very few cells, e.g., as little as four to
fi ve in the case of Salmonella spp. to cause illness. This is why even if food is left
unattended in the 'Danger Zone' for as little as 2 h, it can lead to foodborne illness.
This effect is cumulative, i.e., even if a food is kept at an improper storage tempera-
ture for only a few minutes at various stages of production such as shipping, receiv-
ing, storage and preparation, it can result in a overall time temperature relationship
which can lead to foodborne illness (Canadian Restaurant and Foodservice
Association 2013 ).

2.3.2.2 Water Activity

Pathogenic bacteria need moisture to reproduce and thrive. This is why moist foods
such as meats, fi sh and dairy products are viewed as potentially-hazardous products.
Dry foods such as powders have a longer shelf-life because they do not support
microbial growth. However, if water is added to these powders (such as water
to milk powder), the subsequent product will be susceptible to bacterial growth.
It should be noted, however, that there has been an increased concern of late with
the entire category of “low moisture” foods as they have been involved in a number
of outbreaks in recent years (Association of Food Beverage and Consumer Products
companies 2009 ). It is important to remember that if water is present on food prepa-
ration surfaces or utensils, it will help to support bacterial growth (Canadian
Restaurant and Foodservice Association 2013 ).

2.3.2.3 Acidity

Most microorganisms do not grow on foods that are acidic (pH 4.6 or lower) or
foods that are alkaline (7.5 or higher). Therefore, if a food falls between these
two pH ranges, it is susceptible to bacterial growth. However, E. coli O157:H7
can survive in low pH products; therefore acidity cannot be solely relied upon
when preserving products. In the hurdle effect, each hurdle aims to inhibit or
inactivate unwanted microorganisms (Leistner 2000 ). When several hurdles are
used together, it is very likely that at least one will inhibit a select microorgan-
ism. The “higher the hurdle, the greater the number of pathogens needed to
overcome it”. A food can be made microbiologically safe and stable when one
uses multiple hurdles that can be used either in combination singly or synergis-
tically. Hurdle technology will become even more important in the future as the
trend toward minimally prepared and healthier, e.g., reduced sodium, food
alternatives continue to grow. This would include the use of some newer non-
thermal technologies such as high-pressure processing in combination with,
e.g., thermal treatments.