Alpha-amylase activity as an indicator of pasteurisation efficiency
Eggs very are nutritious, but are also used in many food products because of their emulsifying, foaming, gelling and whipping properties. As shell eggs are often contaminated with Salmonellae and other pathogens, liquid egg products have to be pasteurised before use.
Legislation regarding the pasteurisation process differs in several parts of the World; in the USA pasteurisation of liquid whole egg needs 3,5 minutes at 61,1°C, in the European Union this is 2,5 minutes at 64,4°C. The pasteurisation process improves product shelf life as well, as spoilage microorganisms are destroyed. To evaluate the efficiency of pasteurisation, microbiological tests on raw and pasteurised liquid egg products are carried out. These tests are time consuming and the industry needs quickers answers to guarantee product safety at the release of the products from the plant.
Several rapid methods have been studied to evaluate the efficiency of the heat treatment. Some methods concentrated on the activity of the enzyme alpha-amylase which is present in liquid raw egg products, although results obtained varied and therefore these methods were not always validated. One method is UV-visible spectrophotometry and this method was tested and validated to assess the impact of the pasteurisation conditions (61,1°C for 3,5 minutes and 64,4°C for 2,5 minutes) on alpha-amylase enzyme activity and the microbiological quality of liquid whole egg. Samples were collected from 30 lots of liquid raw whole egg products (n = 30), which were divided into three groups: one was raw, so not heat-treated. Alpha-amylase activity, and the microbiological quality of the samples was evaluated by estimating total and thermos tolerant coliforms, mesophilic aerobic microorganisms, Staphylococcus spp and Salmonella spp.
High alpha-amylase activity was estimated in raw egg samples, in the liquid whole egg pasteurised at 61,1°C, partial inactivation of the enzyme was observed. In liquid whole egg pasteurised at 64,4°C, there was no enzyme activity. After pasteurisation a significant decrease in the counts for all the studied microorganisms, including the frequency of Salmonella spp was estimated. After pasteurisation, one sample was positive for Salmonella spp., indicating failure of the pasteurisation process, which was confirmed by the alpha-amylase test. The validated spectrophotometric method for testing alpha-amylase activity proved adequate for assessing the efficiency of the pasteurisation process.
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