Food Biochemistry and Food Processing

23 Biochemistry of Vegetable Processing 547

cles, the viscosity of the disperse medium, and the
intensity of the Brownian motion. In a disperse med-
ium, heavier or larger particles sediment faster than
the lighter ones (in response to gravity). The sedi-
mentation velocity of any particle is described by
the Stokes equation:

(2.2)

whereVis the sedimentation velocity (m/s);ris the
radius of the suspended particles (m); 1 and 2 are the
density of the particles and serum, respectively
(kg/m^3 ; serumliquid medium in which particles are
suspended);is the viscosity of the juice (Pascal sec-
ond, Pa.s); and g is gravitational force (g9.81 m/s^2 ).
The sedimentation time of a given particle is
about four times longer in a juice than in water
(Table 23.7).
Particles larger than 10
will sediment in a few
seconds. This is the reason why the sedimentation
stability of juices, especially comminuted juices such
as tomato juice, is a serious processing issue.

V

r

=−

⎛

⎝⎜

⎞

⎠⎟

2

9

1

2 ()ρρ^12 η g

The physical force that affects the sedimentation

of particles in a juice is called normal force and can

be calculated by

f
mg (2.3)

where m is the mass (kg) of the suspended particle.

In general, a particle with a spherical shape has

(2.4)

Where 3.14, ris the radius of the particle, and

 1 is the density of the particle.

For particles with nonspherical shape (most of

suspended particles), ris equal to the nearest equiv-

alent value of a spherical particle with an identical

mass and an identical density.

During particle sedimentation, another important

force, friction, also comes into play. Friction be-

tween particles results in a reduction in their move-

ment.

The frictional force f 6  (2.5)

mr=

4

3

3

πρ 1

Table 23.7.Sedimentation of Spherical Mineral Particles in Water and in Juice with a Depth
of 1 cm

Particle Sedimentation Sedimentation
Size (
) Velocity (m/s) Time in Water Time in Juice

10 3.223  10 -4 31.03 seconds 2.29 minutes
0.1 3.223  10 -8 86.2 hours 16 days
0.001 3.223  10 -12 100 years 436 years

Table 23.6.Physicochemical Parameters of Tomato Fruits and Processed Juice from

Transgenic and Control Tomato

Properties Control Transgenic

Fruit weight (g) 95.14±36.56a 34.87±21.57b

Firmness (N) 4.97±0.59a 5.99±1.03b

Redness (a) 29.6±0.70a 31.70±1.67a

Acidity (%) 0.36±0.00a 0.38±0.05a

°Brix 4.55±0.71a 4.75±0.71b

Dry matter—NSS (%) 3.54±0.05a 5.15±0.03b

Ash (%) 0.63±0.03a 0.089±0.13b

Vitamin C (mg/100g) 3.9±0.00a 10.4±0.016b

PPT, % 15.70±0.33a 16.17±0.48a

Serum viscosity (mPas) 1.0919±0.04a 1.2503±0.010b

Brookfield viscosity (mPas) 1075±35a 1400±35b

Lycopene (mg/100g) 11.73±2.10a 17.47±0.58b

Note:The values showing different superscripts are significantly different at P 
0.05.