Slide 1

Hii, Law - Quality Evolution During Drying of FVFs

The kinetics of colour changes in food materials during drying can be modeled by us-
ing zero order or first order degradation model (Kong et al., 2007; Kahyaoglu and Kaya;
2006 ). The following equations (6. 4-6. 5) were used:

Zero order: Y=Y 0 ±kt (6. 4)

First order: Y=Y 0 exp(±kt) (6. 5)

The constant k refers to the kinetic constant, Y is the measured colour scale (Lab*)
and (±) indicate the formation and degradation of the any quality parameter. The pur-
pose of modeling is to relate the kinetic of colour changes to the moisture content reduc-
tion and product temperature evolution during drying.

6.2.1.2. Texture

Structural collapse in food due to moisture removal from the food product results in
significant changes in texture. This causes shrinkage and change in porosity of the dried
product. Texture attributes such as hardness, fracturability, springiness, chewiness,
gumminess, cohesiveness and resilience can be determined by texture profile analyses
(TPA). This can be carried out by subjecting the sample to two compression test cycles,
which typical TPA profile is shown in Figure 6. 1. The hardness and fracturability can be
determined readily from the force-time curve as the first maximum peak and the first
significant break, respectively. Other texture attributes that can be determined from the
curve are such as springiness, resilience, cohesiveness, adhesiveness, gumminess and
chewiness, which the formulas are given in Figure 6.1

Figure 6.1. A typical force-time curve generated from TPA

These attributes are useful for comparison of textural quality of food product includ-
ing dehydrated food subjects to various drying methods. Results from TPA are influ-
enced by sample size, shape, compression speed and extent of compression (Rahman,
2005 ). These attributes can be correlated with several sensory properties as perceived
by human being (Szczesniak, 2002).

The kinetics of textural changes can be determined using the following equation:

Force

Time

Length 1 (L 1 ) Length 2 (L 2 )

Area 2

Area 1

Area 4 Area 5

Area 3

Hardness

Fractuability

1

2

L

Springiness = L

4

5

A

Resilience = A

1

2

A

Cohesiveness= A

(^) Adhesiveness= A 3
(^) Gumminess= Hardness×Cohesiveness
Chewiness= Hardness×Cohesiveness×Springiness