Agriculture Reference
In-Depth Information
meet the above criteria has resulted in an alternative approach. This alternative
approach - widely known as 'hurdle technology' - is the use of natural
preservatives in combination with an intrinsic properties of the food (low pH, low
water activity), and/or extrinsic factors such as heat processing, low temperature
of storage or modifi ed atmosphere packing, and/or other preservatives (synthetic
or natural), and/or a novel means of processing such as ultra high pressure (UHP)
sterilisation or use of pulsed electric fi eld technology (Leistner 1978; Leistner and
Gorris 1995). Other interesting novel approaches are the use of edible coatings
containing preservatives and the use of preservative active packaging (Joerger
2007).
A natural food preservative needs to be easily extractable and be produced in a
cost-effective manner. Roller and Board (2003) provide, as an example, the
possible case of a useful compound present in a rare tropical plant. They propose
that, if diffi cult to cultivate economically, it would be unlikely to achieve
realisation as a food preservative in the developed world unless the gene
controlling its production can be expressed in a microorganism allowing large-
scale production by industrial fermentation. However, although considerable
advances in the knowledge of genetic and protein engineering probably allows
use of such a technology, the current strong consumer resistance to genetically
modifi ed organisms prevents such an approach. Whether such consumer concern
can be reversed in the future, as the world's food resources diminish, remains
uncertain.
Natural preservation of foods is a huge topic and many thousands of research
papers have been published. There are also a number of reviews and topics on the
topic (see Section 6.9 Sources of further information and advice). Because this
chapter has to be selective and is not intended to be encyclopaedic, it concentrates
on natural preservatives that are already in use, show the most promise or have
been the attention of considerable research. The chapter does not include the use
of salt, curing agents, wood smoke and organic acids such as acetic, lactic,
benzoic, propionic acid and their salts, some of which occur naturally but in the
main are synthesised. However, it should be noted that the use of propionibacteria
fermented whey, dextrose or starch as a natural alternative to synthesised
propionate addition to fl our is being used as a method of bread preservation.
6.2 Natural antimicrobials derived from microorganisms
Use of microorganisms and microbial metabolites as food preservatives falls into
three categories. First there are defi ned antimicrobials such as nisin and natamycin
produced by fermentation, concentrated and purifi ed by fi ltration processes or
solvent extraction, and spray-dried. These have strong antimicrobial activity but
are subject to legislation and require labelling. Secondly there are undefi ned
fermentates such as the Danisco MicroGARD™ range. These are again produced
by fermentation and are spray-dried, but are undefi ned and not purifi ed. They are
less powerful than defi ned antimicrobials but in the US not subject to strict
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