Food Process Engineering in a Changing World - 11th International ...

Rehydration characteristics of freeze-dried avocado (Persea americana)
D. S. Souza a ; J. D. R. Pimentel a ; M. M. Prado b ; L. G. Marques b ;N. Narain a
a
Post-Graduate Program in Food Science and Technology (NUCTA)/ Federal University of Sergipe, São
Cristóvão-SE, Brazil (narendra.narain@gmail.com)
b
Department of Chemical Engineering/Federal University of Sergipe, São Cristóvão-SE, Brazil
(luanda_gimeno@yahoo.com.br)
INTRODUCTION
Avocado (Persea americana Mill.)is a commercially valuable crop whose trees and fruits are
cultivated in tropical climates throughout the world. Approximately 75% of an avocado’s
calories come from fat, most of which is monounsaturated fat [1]. Several researchers have
attempted to obtain stable avocado pulp, using a series of preservation methods. Dried products
are usually rehydrated prior to their use. Rehydration is a complex process aimed at the
restoration of the properties of the raw product. The aim of this work was to evaluate the
rehydration capacity of freeze-dried avocado pulp powder and pieces. Peleg and Weibull
equations were used to describe the rehydration kinetics. The hardness of fresh, freeze-dried
and rehydrated avocado was measured using a texture analyser.
MATERIALS & METHODS
The avocado fruits (variety Collinson) were purchased in the city of Aracaju - SE. In order to
assess the influence of different geometries on the rehydration process, the samples were cut in
the shape of cubes, slabs and disks. Samples of beaten avocado pulp were also prepared. After
freezing, the samples were dried in a laboratorial scale freeze-dryer. Lyophilized avocado
powder was rehydrated in a equipment similar to that proposed by Martins & Pinto [2], while
freeze-dried avocado slices were rehydrated by immersing them in a water bath at room
temperature [3]. The equations proposed by Peleg and Weibull, which can be given by,
respectively:
where k1 is a kinetic constant with dimension of time and k2 is a dimensionless parameter,
which is related to the maximum moisture content at saturation, Xe; X0 is the initial moisture
content (d. b.), X is the moisture content at time (d. b.); and is the shape parameter
(dimensionless), is the scale parameter, with dimension of time. Tests on texture were carried
out with fresh, freeze-dried and rehydrated samples at room temperature using a Texture
Analyser.
RESULTS & DISCUSSION
Figure 1 shows the rehydration kinetics of freeze-dried avocado pieces of different geometries
and the fit of the Weibull equation. It may be noted that the structure in which the samples
were lyophilized influenced the rehydration process. The curves showed a typical behaviour of
11th International Congress on Engineering and Food - Athens, Greece, 2011 2007