P1: SFK/UKS BLBS102-c29 P2: SFK BLBS102-Simpson March 21, 2012 13:27 Trim: 276mm X 219mm 578 Printer Name: Yet to Come Part 5: Fruits, Vegetables, and Cereals Table 29.8 Physicochemical Parameters of Tomato Fruits and Processed Juice from Transgenic and Control Tomato Properties Fruit weight (g) Firmness (N) Redness (a+) Acidity (%) Brix Dry matter-NSS (%) Ash (%) Vitamin C (mg/100g) PPT (%) Serum viscosity (mpa·s) Brookfield viscosity (mpa·s) Lycopene (mg/100g) Control Table 29.9 Sedimentation of Spherical Mineral Particles in Water and in Juice With a Depth of cm Transgenic 95.14 ± 36.56a 34.87 ± 21.57b 4.97 ± 0.59a 5.99 ± 1.03b a 29.6 ± 0.70 31.70 ± 1.67a a 0.36 ± 0.00 0.38 ± 0.05a 4.55 ± 0.71a 4.75 ± 0.71b 3.54 ± 0.05a 5.15 ± 0.03b a 0.63 ± 0.03 0.089 ± 0.13b a 3.9 ± 0.00 10.4 ± 0.016b a 15.70 ± 0.33 16.17 ± 0.48a 1.0919 ± 0.04a 1.2503 ± 0.010b 1075 ± 35a 1400 ± 35b a 11.73 ± 2.10 17.47 ± 0.58b a,b The values showing different superscripts are significantly different at P < 0.05 aldehydes Table 29.8 provides a comparison of various quality parameters between a genetically modified tomato and a control, which shows improvements in several quality parameters due to the transformation Physicochemical Stability of Juices There are two categories of juices, clear and comminuted Clear juice such as apple juice contains no visible vegetal particles, whereas a comminuted juice such as tomato juice contains mostly vegetal particles suspended in a liquid To be stable, a clear juice needs to remain clear (without sediment) during its shelf life On the other hand, a comminuted juice may not separate into distinct phases during the shelf life of the product An important quality attribute of juices such as tomato juice is the stability of their disperse system In order to be stable, a juice needs to be kinetically and physically stable Kinetic Stability The ability of a poly-disperse system containing suspended particles to maintain its homogenous distribution without agglomeration is called kinetic or sedimentation stability Kinetic stability depends on many factors, the most important of which include size of suspended vegetable particles, viscosity of the disperse medium and the intensity of the Brownian motion In a liquid medium, heavier or larger particles sediment faster than the lighter ones in response to gravity The sedimentation velocity of any particle is described by the following Stokes Equation: V = 9r (ρ1 − ρ2) (1/η)g (2) where V is the sedimentation velocity, m/s (meter/second); r is the radius of the suspended particles (m); ρ1 and ρ2 are the densities of the particles and the serum, respectively (kg/m3 ; serum = liquid medium in which particles are suspended); Particle Size (µ) Velocity (m/s) Sedimentation Time in Water Sedimentation Time in Juice 10 0.1 0.001 3.223 × 10−4 3.223 × 10−8 3.223 × 10−12 31.03 s 86.2 h 100 yrs 2.29 16 d 436 yrs η is the viscosity of the juice (Pa·s; Pascal·second); and g is the gravitational force (g = 9.81 m/s2 ; meter/second2 ) The sedimentation time of a given particle is about times longer in a juice than in water (Table 29.9.) Particles larger than 10 µm 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 The physical force that affects the sedimentation of particles in a juice is called normal force and can be calculated by: f = mg, (3) where m is the mass (kg) of the suspended particle In general, a particle with a spherical shape has a mass represented by: m = 4/3 πr ρ1 (4) where π = 3.14, r is the radius of the particle and ρ1 is the density of the particle For particles with nonspherical shape (most of suspended particles), r is equal to the nearest equivalent 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 between particles results in a reduction in their movement The frictional force f = 6πρ rv (5) where η is the viscosity of the medium; r is the radius of the particle in meters; and v is the velocity of the particle (m/s) Friction between the particles increases depending on the density of the medium, higher the density, higher the friction When f = f , sedimentation of the particles occur Kinetic stability of a heterogeneous dispersion system also depends on Brownian motion The most dispersed particles have a very complex motion due to collisions from molecules in the dispersed medium Because of this, the suspended particles are subjected to constant changes in their velocity and trajectory Molecular kinetics shows that dispersed particles with colloidal size change their path 1020 times/second These particles may also acquire a rotational Brownian motion This is why colloidal particles have higher sedimentation stability than larger particles With an increase in the mass of the suspended particles, their momentum also increases Particles smaller than × 10−4 cm in diameter that oscillate around a point not sediment, whereas larger particles that not experience as much Brownian motion as smaller particles easily sediment Thus, when particles have reduced motion, they tend to aggregate P1: SFK/UKS BLBS102-c29 P2: SFK BLBS102-Simpson March 21, 2012 13:27 Trim: 276mm X 219mm Printer Name: Yet to Come 579 29 Biochemistry of Vegetable Processing and enhance sedimentation Under ideal conditions, obtaining a colloidal particle size will enhance the stability of a juice preparation where P is the increase in osmotic pressure; δ is thickness of the double ionic layer; and the number relates to the energy changes between particles P = Physical Stability Physical stability results from the property of a polydisperse system that inhibits the agglomeration of suspended particles In a system with low physical stability, suspended particles agglomerate to form heavier particles (> × 10−4 cm in diameter) that easily sediment Physical stability depends on two opposing forces, attracting and repulsing forces Attracting forces between molecules are referred to as van der Vaals forces, which reduce the physical stability of heterogeneous colloidal system The intensity of attractive forces increases as the distance between suspended particles decreases Repulsing forces between particles are caused by the charges surrounding the particles designated by their ζ - potential When ζ -potential is zero, the net charge surrounding the particle is also zero, and the suspended particles are said to be at their isoelectric point Agglomeration of particles begins at a given value of ζ -potential called as the critical potential This is the point at which equilibrium is reached between van der Vaals forces (attraction) and repulsing forces Different heterogeneous colloidal disperse systems have different values of critical potential When the ζ -potential (repulsive forces) of a particle is higher than the critical potential, hydrophilic colloids are stable due to the repulsion between particles, whereas at a lower potential than the critical potential ζ , the particles tend to aggregate The effective energy of interaction between particles of a heterogeneous colloidal system is expressed by: E = E A + ER , nKT (9) where n is the increase in the ionic charge between the particles; K is the Boltzman’s constant; and T is the temperature in degrees Kelvin (◦ K) Assuming that the two particles are spherical, the formula (8) can be expressed by: ER ≈ εrψ02 exp {−χh} repulsing energy exponentially decreases as the distance between the particles increases; and repulsing energy quadratically increases as the surface potential increases and as the radius linearly increases For particles with radius r and a constant surface potential, ER depends on χ Figure 29.2 shows the interaction between two particles (1 and 2) under constantly increasing χ As a result of decreasing the thickness of the double ionic layer and a decrease in ζ -potential, the distance between the two particles decreases + ER Emax E M – where, h is the distance between surfaces of the two particles, and A is the Hamaker constant (10−1 –10−21 J) Consequently, attracting forces decrease as the distance between particles increase On the other hand, particles can come closer to one another up to a certain distance after which they start repulsing each other because of their ζ -potential When two particles are very close, their similar ionic charge (positive or negative) layers create a repulsive force, which keeps them apart The repulsing energy between two particles with the same radius r and the same surface potential is expressed by: + ER = −2 P dδ, (8) h EA (7) EA = −Ar/12h (10) where ε is the dielectric constant; r is the radius of particles; h is the distance between the two particles; ψ is the surface potential, and χ is a constant which characterizes the double ionic layer The inferences from the Equation 10 are that: (6) where EA is the attracting energy, and ER is the repulsing energy Attracting energy is actually the integration of the sum of all attracting forces between molecules of two colloidal particles For two particles with radius r, the potential energy is expressed by: 2, (A) ER E E h EA M (B) – Figure 29.2 Interactive energy between two particles P1: SFK/UKS BLBS102-c29 P2: SFK BLBS102-Simpson 580 March 21, 2012 13:27 Trim: 276mm X 219mm Printer Name: Yet to Come Part 5: Fruits, Vegetables, and Cereals leading to an increase in the repulsing energy according to the Equation (10) For a given h, the residual energy reaches the maximum value (Emax ), which must be overcome by particle in order to aggregate with particle Continual increase of χ and a decrease in the distance between particles h reduces the effect of repulsing energy ER over the residual energy E (ER – EA or Emax ), which reaches its minimal value M At this stage, the attracting energy EA dominates and the particles aggregate 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 aggregation When Emax > (Fig 29.2A), the aggregation process is slow, whereas when Emax < (Fig 29.2B) the process is quick, since the particles of the system not have to overcome Emax (When EA > ER , ER – EA is