BLBS102-c29 BLBS102-Simpson March 21, 2012 13:27 Trim: 276mm X 219mm Printer Name: Yet to Come
580 Part 5: Fruits, Vegetables, and Cerealsleading to an increase in the repulsing energy according to the
Equation (10). For a givenh, the residual energy reaches the
maximum value (Emax), which must be overcome by particle
1 in order to aggregate with particle 2. Continual increase of
χand a decrease in the distance between particleshreduces
the effect of repulsing energy ERover the residual energy E
(ER–EAor Emax), which reaches its minimal value M. At this
stage, the attracting energy EAdominates and the particles aggre-
gate. The speed of aggregation is an important physicochemical
parameter for the stability of a microheterogeneous system. Emax
is called coagulation energy and determines the speed of aggre-
gation. When Emax>0 (Fig. 29.2A), the aggregation process is
slow, whereas when Emax<0 (Fig. 29.2B) the process is quick,
since the particles of the system do not have to overcome Emax
(When EA>ER,ER–EAis<0, Fig. 29.2A, B). The critical
concentration of coagulation is reached at Emax=0, when both
the attractive and repulsive energies are equal.
In a real situation of polydisperse colloidal system such as
juice, suspended particles have different sizes and differentψ 0
andζ- potential. When two particles with different sizes and
different surfaceζ- potential approach each other, an opposite
charge is induced upon the particle with lowerζ- potential,
which activates the agglomeration. Another important factor in
the stability of juices is the hydrated layer of suspended colloidal
particles. The formation of hydrated layer is due to the orienta-
tion of water molecules towards the hydrophilic groups such as
-COOH, -OH, and so on situated on the surface of the particles.
A decrease inζ- potential leads to a decrease in the hydrated
layer of suspended particles, and therefore, increases the sus-
ceptibility to aggregation. The ability of the hydrated layer to
increase stability is explained by Deryagin theory, which stipu-
lates that when suspended particles are in close proximity, their
hydrated layers are reduced, leading to an increase in repulsive
forces between them. Only strong hydrated layers can affect the
aggregative stability of a polydisperse system. The probability
of the formation of such hydrated layers around vegetal particles
in juices is very low, because of the weak energetic relationship
between the particles and the disperse phase. In this case, hy-
drated layers play a secondary role to supplement the action of
the double ionic layer.
Stability from particular aggregation in juice is also influ-
enced by the viscosity of the disperse medium. The viscosity of
the disperse phase or serum of juices is mainly composed of high
molecular mass compounds such as pectin, protein, and starch.
Practically, this is achieved by the addition of such compound
to the juice. The mechanism of action is as follows. Upon ad-
dition of high molecular mass compounds (pectin), they adsorb
on the surface of the hydrophobic vegetal particles to make a
layer of hydrophilic molecules, circled by a thick hydrated layer,
which gradually blends into the disperse medium. Pectin is the
stabilizer of choice in the juice processing industry, compared
to protein and starch. With an increase in the concentration
of high molecular mass compounds, the sedimentation stabil-
ity of the juice increases. It has been established that with the
increase in the concentration of pectin in the juice, the stabil-
ity increases to reach a plateau after which, a further increase
does not provide an added beneficial effect (Idrissou 1992).The mechanism of the sedimentation stability of the juice is
as follows: Low adsorption velocity: Lower adsorption velocity is ob-
served under lower concentration of stabilizers.
Irreversible adsorption: Stabilizers in most cases are bonded
to the particular phase surface with strong adsorption
bonds.
Adsorption is described by the curve in Figure 29.3, follow-
ing a typical saturation curve.
Different configuration of adsorption by particles is shown
in Figure 29.3. Molecules of linear polymers can be ad-
sorbed in three different ways, depending on their affinity to
the liquid phase and the surface of the suspended particles,
adopting horizontal, vertical, and stitchlike configurations.Enhancing Nutraceutical Quality
of Juice ProductsHealth beneficial effects of enhanced fruit and vegetable con-
sumption through enhanced intake of nutraceuticals (functional
food ingredients) are well established. There are several types of
juice blends from fruits and vegetables available in the market
including those that are blends of fruits and vegetables. An addi-
tional way of enhancing the nutraceutical value of various juices
is by the addition of specific ingredients. In a recent study, Oke
et al. (2010) have described the benefits of adding soy lecithin
to tomato juice and sauce preparations and its effect on stability
characteristics of the juice and sauce. Soy lecithin is enriched
in proteins as well as lipids such as phosphatidylcholine, a key
component in the biomembrane. Choline is also a key compo-
nent of nervous system function linked to the biosynthesis of
acetyl choline, involved in nerve signal transmission, lipid se-
cretion, enhancement in liver function, and so on. Juice/sauce
preparations from fruits and vegetables are generally low in
phospholipids. Thus, addition of soy lecithin to juice could be
beneficial both in terms of nutrition and stability of juice. Ad-
dition of 0.5–1% (w/v) soy lecithin to tomato juice and sauce
enhanced the stability characteristics of the processed products
such as precipitate weight ratio and Brookfield viscosity. Com-
mercially, soy lecithin is not added to juice or sauce preparations
at present.MINIMALLY PROCESSED VEGETABLES
DefinitionsRolle and Chism (1987) defined minimally processed refriger-
ated fruit and vegetable (MPR F & V) as produce which have
undergone minimalprocessing such as washing, sorting, peeling,
slicing, or shredding prior to packaging and sale to consumers.
Odumeru et al. (1997, 1999) defined ready-to-use vegetables as
fresh-cut, packaged vegetables requiring minimal or no process-
ing prior to consumption. It is generally accepted that MPR F &
V are products that contain live tissues or those that have been
only slightly modified from the fresh condition and are freshlike
in character and quality.