Functional properties of microwave pasteurised and oil coated whole shell eggs

Abstract

Food borne infections due to Salmonella enterica serovar Enteritidis (S. Enteritidis) has shown a dramatic increase in many countries. Different egg pasteurisation treaments have been developed in the past but are still not providing practical or optimal solutions. A method is required that ensure that eggs are microbiologically safe, that does not affect the functional quality and possibly also extend the egg shelf life. This research project formed part of a larger study, “Project 32438: The development of a novel microwave system for the pasteurisation of raw whole shell eggs” funded by the National Research Foundation Innovation Fund and conducted by a consortium consisting of the Council for Scientific and Industrial Research (CSIR), Delphius Technologies, Eggbert Eggs and University of Pretoria. One of the phases in the development of the microwave system was an evaluation of the effectiveness of applying different microwave power levels (250W and 300W) on eliminating or reducing S. Enteritidis as well as evaluating the effect on the functional properties of the eggs. The microbiological tests were conducted by the CSIR while the latter evaluation was the focus of the study reported here. Microwave pasteurised eggs had lower foaming capacity but higher Haugh values than control (unpasteurised) eggs. Albumin foam stability did not differ between control and microwave pasteurised eggs and the pH of the albumin was almost similar. The yolk pH of pasteurised eggs was higher than that of unpasteurised eggs. Significant differences were found for the sensory properties of broken out eggs as evaluated by a trained sensory panel. At 300W, pasteurised eggs collected from the left side of the oven had partially coagulated albumin that was not clear. The visual appearance of pasteurised eggs at 300W from left side was more adversely affected than the eggs collected from the right side oven position and all eggs pasteurised at 250W. The albumin foaming capacity, visual appearance and sensory properties of raw eggs pasteurised at 250W were slightly affected by microwave heating. A triangle taste test showed that there was a significant difference between control and pasteurised (300W) eggs. A home use consumer test showed that control and microwave pasteurised (250W) eggs were equally acceptable. Pasteurisation could extend the shelf life of whole shell eggs (WSE) by reducing or destroying spoilage microorganisms. Another phase of the project therefore focused on obtaining background data pertaining to the shelf life of eggs. The effect of coating of egg shells with mineral oil on the functional properties and shelf life of WSE stored at 16ºC (58 % RH); 25ºC during the day and 15ºC at night (55% RH) and 32ºC (32 % RH) for a period of six weeks, were evaluated. These conditions were selected to reflect typical temperatures that are used for storing eggs in South Africa. Haugh units of eggs decreased with storage time at all storage conditions but for coated eggs it decreased at a slower rate. The pH of both the yolk and albumin of coated shell eggs was lower than that of uncoated shell eggs. Coating did not have an influence on the foam stability of egg albumen. Foaming capacity of albumen was negatively affected by oil coating. Coated shell eggs stored at the three conditions had a prolonged shelf life compared to uncoated eggs stored in the same manner. If the prototype microwave oven can be optimised to ensure even distribution of microwaves, microwave pasteurisation of shell eggs has potential to become a significant break through in the poultry industry.