Measuring pH levels of food to maintain safety

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Measuring pH levels of food to maintain safety

http://www.ferret.com.au/articles/cd/0c03c4cd.asp

PH levels of food or liquids can often yield information about

whether the item, for example fruit, is fresh or not, or whether

wine will taste sweet or bitter.

Measuring pH levels with Testo's pH meter.

The pH value is a direct function of the free hydrogen ions present

in that food. Acids present in foods release these hydrogen ions,

which give acid foods their distinct sour flavours. Thus, pH is

defined as a measure of free acidity.

The range of pH is commonly considered to extend from zero to 14. A

pH value of 7 is neutral, because pure water has a pH value of

exactly 7. Values less than 7 are considered acidic, while those

greater than 7 are considered basic or alkaline. A few foods, such

as egg whites, sweet corn and some baked goods may be basic.

Most foods are naturally acidic, with pH less than 7, but the pH

value of a particular food may have a dramatic effect on the type of

processing needed to safely preserve it.

Micro-organisms, including yeasts, moulds and bacteria are sensitive

to a food's pH. Very low or high pH values will prevent microbial

growth.

No unprocessed food has a pH value high enough to offer much

preservative value but many foods do have values low enough to offer

some protection from microbial growth.

Very few foods have pH values low enough to completely inhibit the

growth of micro-organisms, so food manufacturers have to combine

other microbial controls - such as heat processing, refrigeration,

freezing or drying - to help preserve the food. The most common of

these is heat processing or canning.

Canned foods may be defined as any food sold in a hermetically

sealed (water or air-tight) container at non refrigerated

temperatures.

Some of the most important pieces of information used in a canning

operation are processing times and temperatures.

Processing times do not refer to the time needed to cook the food -

it means the heating times needed for canned food products to reach

what is known as " commercial sterility " .

Commercial sterility may be defined as the point when any harmful

micro-organisms capable of growing in the food have been killed.

Examples of low-acid foods (pH value less than 4.6) are meat,

poultry and most vegetables. Heating must kill these spores during

the canning process, however these spores are very heat resistant -

meaning canned low-acid foods must be pressure cooked at high

temperature for long periods of time. Because of the necessity of

insuring the proper processing of low-acid foods, there are numbers

of detailed regulations governing their production.

Anyone wishing to can low-acid foods must be registered and required

to keep extensive records by using calibrated equipments. Examples

of high-acid foods include jams and jellies, pickles and most

fruits. These foods require much less heating than low-acid foods as

they only need to reach pasteurisation temperatures.

The correct pasteurisation temperature is sufficient to kill all

micro-organisms except for bacterial spores. Since these spores will

not grow because of low pH, the food is considered commercially

sterile.

An effective pH meter needs to be easy to use, offer reliable

results and a have a long life span.

Testo has introduced a new compact, low cost pH and temperature

measurement unit that features interchangeable heads. This means it

can be used to test liquids, semi-solids, for penetration into meat

or poultry, or by using pH electrode it becomes sensitive to

hydronium ions.

Plus, it features a large volume of gel reference electrodes,

guaranteeing a long service life.

Another bonus is that Testo pH meters allow users to read pH and

temperature values at the same time.

Temperature plays a key role in pH measurement because the pH value

may change with the temperature.

The unit's measuring tip can be washed under water tap after it is

used, therefore preventing contamination.

23 January 2006