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T h e A rt o f P re c is io n M e a su re m e n t The meaning of „water activity“

1) The total water / moisture :The moisture content is the total water in a product, including the molecularly bound water, and is expressed in % of the total weight.

2) The relative humidity: It means the relative product equilibrium humidity, the freely available water for micro organisms to grow; its measuring value is called “water activity”, aw-value.

What is the meaning of the measurement parameter

“water activity”?

Water is a basic ingredient in foods, pharmaceuticals and cosmetics.Its control can be critical to guarantee microbial safety during shelf-life and consumption, or for optimising a production process.

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T h e A rt o f P re c is io n M e a su re m e n t Importance of aw

Why is the measurement of aw – water activity

in foods and pharmaceuticals so important?

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T h e A rt o f P re c is io n M e a su re m e n t Microbial Safety

����microbial safety to predict shelf life

����HACCP requirements as part of QC

����fulfil government regulations

EU, USA, Japan ….

���� control chemical reactions,physical properties

to guarantee product quality, good taste, colour, crispness

The importance of „aw“ measurement :

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T h e A rt o f P re c is io n M e a su re m e n t Why to measure „aw“?

• Water activity, pH, temperature, and other parameters,have a direct impact on the growth of micro organisms, thus aw and pH are two of the most important parameters.

• Free water that is available to molds, yeasts, and bacteriais responsible for their growth and even toxin production.Or it may participate in chemical/biochemical reactions (eg.Maillard reactions), which might deteriorate :

• texture, flavour• colour• taste• nutritional value

of a product, and its stability � shelf-life time.

Why to measure the “water activity”?

These are some of the main reasons why a correct measurement of the “water activity” aw is so important.

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T h e A rt o f P re c is io n M e a su re m e n t Bacteria, Molds

• For many food spoilage organisms a minimum aw-value is known, below which its growth and toxin production is inhibited.

Other reasons

Bacteria, for example:Staphylococcus aureus :requires a minimum aw of for growth/toxin production 0.86aw

Clostridium botulinum A and Escherichia coli 0.95aw

Salmonella may start at 0.92aw.

A mold for example:Aspergillus flavus :produces toxin above 0.83aw, but does not grow below 0.78aw.

Fungi, other molds, mildew, yeasts go lower, 0.60aw.but not beyond

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T h e A rt o f P re c is io n M e a su re m e n t Examples

Examples

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T h e A rt o f P re c is io n M e a su re m e n t Water migration

• Two ingredients may have the samemoisture content, but totally differentaw-values.

• The water migrates from regions of high awto regions of low aw, and not between areas of unequal moisture content!

• Water migration between different layers of a multi-component food causes un-desirable textural changes.

• This can be reduced by knowing and influencing the various levels of aw.

Water migration

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T h e A rt o f P re c is io n M e a su re m e n t Regulations

The recognition of the importance of water activity started in Europe over 30 years ago and was then also incorporated into FDA and USDA regulations. Today it is one of the critical parameters of the HACCP requirements.

Draft for regulation 77/99/CEE, A, V, p.26/27, aw-measurement for meat products in general, accuracy: The instrument shall have a measuring range (for meat products) of 0.74 ... 0.99aw, an accuracy of ±0.01aw, a repeatability better than 0.005aw a temperature control (preferably 25.0°C) of ±±±±0.2°C.

The FDA (21 CFR part 113) proposes maximum levels of 0.85awand 4.6pH for low-acid canned foods, and the USDA maximum levels of 0.70aw for peanuts and tree-nuts.

Some Laws

Europe:Europe: The EU required already in 1977 in the Official Journal of the European Communities, No. L 26/97, for imported meat products:

aw < 0.95 and pH < 5.2, or aw only < 0.91

USA :