Improvement of quality attributes of commercially sterile egg product by the use of improved formulation and optimized thermal process
Kandala, Raghunandan Narasimha
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Improved formulations and high temperature short time thermal processing produced good quality shelf stable ready-to-eat retorted eggs in quad-laminate pouches. Processing at 130°C reduced browning discoloration, and minimized off-flavors. Formulations consisting of liquid whole egg, liquid margarine, citric acid, and hydrocolloids prevented green discoloration, rubbery texture development, and syneresis. Use of xanthan effectively stopped syneresis and consumer panelists gave the highest preference for the formulation with 0.2% xanthan. The effective heat transfer coefficients (h) during the various stages of retort processing of the egg mix in quad-laminate pouches and half steam-table trays were determined using a best-fit between the measured centre-point temperature and values calculated by a finite difference heat transfer model using retort temperatures measured during actual thermal processes in three different retorts. The h-values were dependent on the type of retort, container type, container holding racks, exposure of the container to the heat transfer medium, and the product. Quality retention values for the egg mix processed in quad-laminate pouches and half-steam-table trays in the three retorts were calculated using a formula that took into account the D-value for quality degradation. The D-value for quality degradation of the eggs was determined as a change in color expressed as the a*-value and was calculated to be 910 min at 100 C. Data on a*-value of cooked egg processed at 100, 115, and 130°C was used to calculate a z-value of about 25°C. Using these values, the volume average quality retention for the quad-laminate pouches was between 0.67-0.78 when processed to commercial sterility in the three retorts. The quality retention values in eggs processed in the half-steam table trays were between 0.55 and 0.58. When thermal processes were simulated using the heat transfer model and values of effective heat transfer coefficients determined under actual thermal processing conditions, it was shown that processing at the higher temperature of 130°C resulted in higher quality retention values compared to traditional processes at 122°C. A pre-heat step at 100°C before raising retort temperature to the scheduled processing temperature also resulted in higher quality retention values compared to direct processing at the designated processing temperature.