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AACC International Approved Methods - AACC Method 42-45.01. Thermophilic and Psychrotrophic Bacteria

AACC International Approved Methods

Microorganisms

AACCI Method 42-45.01
Thermophilic and Psychrotrophic Bacteria

VIEW METHOD

Objective
To make an estimate of total number of thermophilic and psychrotrophic bacteria present in food products or ingredients. a) Thermophilic bacteria possess the characteristic to grow above 43° and optimally at 50-60°. These bacteria may spoil low-acid foods held in this temperature range. Thermophilic bacteria are nonpathogenic spore-formers present in cultivated soils and thus contaminate agricultural commodities in small numbers. Sugars and starches may contain high levels of thermophilic bacteria. These organisms may also occur on processing equipment held warm for extended periods. They can cause spoilage of hermetically sealed products that are inadequately cooled and subsequently stored at high temperature. b) Psychrotrophic bacteria can grow at refrigeration temperatures and are defined as those that produce visible growth at 7 ± 1° within 7-10 days. These microorganisms are commonly associated with refrigerated foods and can cause spoilage if food is held under refrigeration for extended periods of time. Other pathogenic microorganisms, Listeria monocytogenes, may grow below 7°.