An investigation into the occurrence, growth properties and characteristics of psychrotrophic coliform organisms in refrigerated pasteurised bovine milk in the Western Cape

Abstract

The Dairy industry, one of the larger food industries in South Africa processes probably the most perishable and possibly the most regulated foodstuff, namely mille The unique combination of vitamins, proteins, carbohydrates, lipids, moisture and near neutral pH, offers a suitable environment for the proliferation of microbes. Milk is therefore highly susceptible to microbiological activity resulting in the irreversible spoilage of this food (Frazier & Westhoff, 1988). The coliform group of organisms comprises all aerobic and anaerobic, gram-negative, non-spore-forming rods that are able to ferment lactose with the production of acid and gas at 32°C within 48 hours (Richardson, 1985). The primary purpose of the coliform detection test is to measure the quality of the practices used to minimise bacterial contamination of processed dairy products (Richardson, 1985). IDF Standard 132A: (1991) defines psychrotrophic organisms as organisms forming countable colonies when incubated aerobically at 6.5°C for 10 days under the conditions specified in IDF standard 101A. Shelf-life tests conducted in the fresh milk laboratory of a processing plant, revealed significant growth of coliforms in samples stored at 5°C. Luch, (1985) reported that other contaminating psychrotrophs together with the coliforms reduce the shelf-life of the milk when the storage temperature thereof is above 10°C.