DEVELOPMENT OF ISOTHERMS OF WHEAT FLOUR AND EGG WHITE POWDER
Loading...
Files
Date
2018
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Acharya N.G. Ranga Agricultural University
Abstract
Moisture sorption isotherms describe the relationship between moisture content
of the food product and its equilibrium relative humidity. Isotherms are useful in drying
and storage of the products. These help us to optimize the drying processes thus
minimizing the energy utilization. Egg white powder (EWP) is the ingredient in many
of the bakery foods, bakery mixes, mayonnaise and salad dressings, confections, ice
cream, pastas, and many convenience foods. Similar to the EWP, wheat flour (WF) is
used to prepare various types of breads and pastries, pasta, breakfast cereals and other
products used for human consumption. The EWP and WF are subjected to the thermal
treatments for improving the safety and functionality. The poultry products are
associated with pathogenic Salmonella. The spray drying of egg white and milling of
wheat do not produce sterile EWP and WF, respectively. However, the traditional
thermal treatments take long time to reach the treatment temperature because of lower
thermal conductivity. Hence, novel thermal processing methods such as radio-frequency
and microwave methods were found to reduce processing times. These methods raise
the temperature of the produce in package many times faster than that of the traditional
methods. Taking the advantage of these novel methods, pasteurization methods for the
powder/flour are found suitable to carry at higher temperatures upto 90 °C in order to
reduce processing times and to improve productivity. As the product is being processed
in package and heating rates are faster, there is a possibility of moisture losses from the
product and deposition of moisture on inside package surfaces. The phenomenon of loss
of moisture and deposition depends on the product moisture content and temperature
which is not clearly understood. To understand such phenomenon the EMC-ERH data is
needed. The EMC-ERH data of EWP and WF is available at lower temperatures.
However, EMC-ERH data at higher temperatures throughout the relative humidity
range is not available.
Equilibrium moisture content (EMC) of EWP and WF were obtained by
equilibrating their samples at 10-78% equilibrium relative humidity (ERH) at 50, 60,
70, 80 and 90 °C above saturated inorganic salt solutions by using static gravimetric
method. At a constant relative humidity, equilibrium moisture content decreased with
increasing temperature. Similarly, at a constant temperature EMC increased with an
increase in ERH and exhibited typical sigmoidal shape (Type-2 curve). The EMC
values in the present study for both EWP and WF were lower than the literature values
reported at lower environmental temperatures. Seven EMC-ERH models namely
Henderson, modified Henderson, modified Chung-Pfost, modified Oswin, modified
Halsey, modified GAB and Chen-Clayton were fitted to the observed data and were
evaluated using mean relative percent error, standard error of estimate and residual
plots.
The models namely Henderson, modified Henderson and Chen-Clayton were
found suitable to describe the EMC-ERH relationships of EWP and the best among the
three is found to be the modified Henderson. The isotherm models namely modified
Henderson, modified Chung-Pfost and Chen-Clayton were found suitable to describe
the EMC-ERH relationships of WF in the experimental range. Among these suitable
models, Chen Clayton model was found to be the best for WF. The heat of vaporization
for both the EWP and WF was calculated separately in the moisture content range from
3 to 15% d.b. and at the temperatures 50, 60, 70, 80 and 90 °C using the Clausius-
Clapeyron equation. The heat of vaporization of EWP and WF increased as moisture
content and temperature decreased and remained higher than that of pure water.
Keywords: Egg white powder, Equilibrium moisture content, Heat of vaporization,
Wheat flour.
Description
D5558
Keywords
null