Food Biochemistry and Food Processing

550 Part V: Fruits, Vegetables, and Cereals

layers play a secondary role to supplement the
action of the double ionic layer.
Stability from particular aggregation in juice is
also influenced by the viscosity of the dispersion
medium. The viscosity of the dispersion phase or
serum of juices is mainly due to high molecular
mass compounds such as pectin, protein, and starch.
Practically, this is achieved by the addition of such
compounds to the juice. The mechanism of action is
as follows. Upon addition of high molecular mass
compounds (pectin), these compounds 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 dis-
persion medium. Pectin is the stabilizer of choice in
the juice processing industry, over protein and
starch. With an increase in the concentration of high
molecular mass compounds, the sedimentation sta-
bility of the juice increases. It has been established
that with the increase in the concentration of pectin
in the juice, the stability increases to reach a plateau,
after which a further increase does not provide any
added beneficial effect (Idrissou 1992). The mecha-
nism of the sedimentation stability of the juice is as
follows:

• Low adsorption velocity: Lower adsorption
  velocity is observed 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
  23.2, following a typical saturation curve.


• Different configurations of adsorption by
  particles are shown in Figure 23.2. Molecules of
  linear polymers can be adsorbed in three
  different ways, depending on their affinity to the
  liquid phase and the surface of the suspended
  particles, adopting horizontal, vertical, and
  stitch-like configurations.

MINIMALLYPROCESSEDVEGETABLES

Definitions

Rolle and Chism (1987) defined minimally pro-

cessed refrigerated fruits and vegetables (MPR

F&V) as produce which has undergone minimal pro-

cessing such as washing, sorting, peeling, slicing, or

shredding prior to packaging and sale to consumers.

Figure 23.2.Isotherm of adsorption of polymers; polymer adsorption states.