application of alternative food-preservation - Bentham Science

Predictive Microbiology Application of Alternative Food-Preservation Technologies 163
Table 1: Targets for MCT for some products [8].
Food Microorganisms
Salad dressings Salmonella sp., Staphylococcus aureus
MAP products Clostridium botulinum, Listeria monocytogenes, Escherichia coli
Bakery items Salmonella sp., Staph. aureus
Sauces and salsas stored at room temperature Salmonella sp., Staph. aureus
Dairy products
Confectionery products Salmonella sp.
Formula with new preservatives
Salmonella sp., Staph. aureus, Cl. botulinum, E. coli, L.
monocytogenes
Salmonella sp., Staph. aureus, Cl. botulinum, E. coli, L.
monocytogenes
Level of Inoculum
The level of inoculum in a MCT depends on whatever the aim of the study is to determine the shelf life or to
validate a preserving treatment. Generally, an inoculum level of 10 2 -10 3 cfu/g (or ml) is used for the evaluation
of the stability of a formulation. Otherwise, an initial cell number of 10 6 -10 7 cfu/g is required to validate the
lethality of a treatment: for example in the USA juice processors require for a MCT an initial level of 6 log units,
as they used a 5D reduction as the goal to bale a processing as effective.
Inoculum Preparation and Method of Inoculation
Inoculum preparation is an important detail for the success of a MCT. Typically for vegetative cells 18-24 h
cultures, revived from slants or frozen aliquots are used; for some challenge studies a preliminary adaptation step
is required: for example, E. coli O157:H7 should be adapted with acidulants before using in acidic foods. Spores
should be diluted in distilled water and heat-shocked before inoculation.
The method of inoculation is another crucial factor for the success of a MCT. There are a variety of modes of
inoculation, depending on food structure; in aqueous matrices with aw>0.96, the cells can be dispersed directly
into the medium by mixing, using water or an appropriate diluent as a carrier.
For individually packed products, the inoculum should be distributed using a sterile syringe through the package
wall; otherwise, for solid foods with aw>0.96 (cooked pasta, meat) spraying is an alternative way to the syringe.
Finally, foods or components with aw