Namangan Institute of Engineering and Technology
nammti.uz
10.25.2023
Pg.201
does not present resistance to the measured electrical current. Based on the frequency dependency
of the conductivity of intact and permeabilized tissues, a cell disintegration index Z was calculated
by the following equation:
where K
i
, K’
i
are the electrical conductivities of untreated and treated material, respectively,
at a low-frequency field K
b
, K’
b
are the electrical conductivities of untreated and treated material,
respectively, at a high frequency field. This index characterizes the proportion of permeabilized cell
in a material. For intact tissues, Z ¼ 0; for a tissue where all cells are permeabilized, Z ¼ 1.
Whole tomatoes were immersed into the treatment chamber (10 cm x 5 cm x 8 cm) filled with
tap water. Treatment chambers with different electrode gap widths were used for chopped
tomatoes (4 cm x 5 cm x 4 cm) and tomato wastes (4 cm x 2.5 cm x 4 cm) without tap water, thus
PEF treatment was directly applied to the samples. Electrical conductivities for untreated samples
were calculated prior and immediately after PEF treatment for each condition applied for whole
tomatoes, chopped tomatoes and tomato wastes. The chamber electrodes in all treatment chamber
configurations were made of stainless steel. The treatment chamber
was connected to the
measuring apparatus as shown in Fig. 1 using crocodile clips. The goal of the apparatus is to measure
the electrical impedance of the treatment chamber by recording two voltage drops with the
oscilloscope[2].
800 g of whole tomatoes were cut in cubes of 1.5
𝑥
1.5
𝑥
1.5 cm
3
dimensions. Juice extraction
was performed on a lab-scale paddle type extractor (SpremiTO, Tre Spade, Torino, Italy). Tomato
juice extraction yield was calculated taking into account the mass of the tomatoes (kg) and the
tomato juice (kg). The extraction yield was expressed in percentage (%) of chopped tomatoes to
mass of tomato juice from the first juicing step and the overall extraction yield was expressed in
percentage (%) of chopped tomatoes to mass of overall tomato juice (from the two juicing steps).
The results obtained in our research show that PEF technology at selected conditions could
be applied as pretreatment to critical steps in the tomato industry leading to a decreased energy
consumption, increased productivity and more effective valorization of tomato waste. Generally,
increasing electric field strength and treatment time increased the cell disintegration index Z and in
turn improved the peeling process, the juice yield and the extraction of intracellular compounds
from tomato waste. In the case of peeling, PEF pretreatment performed in mild conditions reduced
the surface resistance of tomato skin and its adhesiveness to the tomato flesh, leading to reduced
peeling loss and low energy consumption compared to commercial peeling processes.
The low
temperatures associated with PEF treatment led to final peeled tomatoes with well-preserved
shape and texture, improved quality and functionality because of high lycopene concentration of
the end product. PEF can easily replace existing conventional peeling processes, leading to reduced
water and energy requirements. In the case of juicing, PEF pretreatment increases the tomato juice
yield up to 20% compared to control at the first step of juicing (equal with total juice yield from both
juicing steps of untreated samples), resulting in increased Bostwick consistency values (>20 cm) of
the
final tomato juices, not suitable for the tomato industry. However, the application of PEF
treatment on the residual tomato wastes at the second step of juicing, led to juice yield increase
and improved final viscosity, as well as decreased energy consumption and processing time for the
tomato industry. PEF can be easily integrated into the tomato processing line, before juicing. Taking
into consideration that PEF has low energy requirements.[3]
