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Optimization of Pulse Electric Field Treatment and Vacuum Impregnation for Reducing Freezing Injury of Thawed Rucola Leaves

Christiana Nyoto, Imelda LU (2018) KLTM01 20181
Food Technology and Nutrition (M.Sc.)
Abstract
Freezing injuries usually take place in thawed plant-based food products. To reduce freezing injuries, Pulse Electric Field (PEF) treatment and Vacuum Impregnation (VI) of cryoprotectant were used before the freezing process. The aim of PEF is to provoke electroporation to the membranes of the plant cells, thereby allowing the cryoprotective solution impregnated by VI to penetrate the cells.

PEF treatment was optimized to use the minimum possible pulse width in order to obtain a homogeneous electroporation of rucola leaves. In order to achieve this minimum pulse width, several combinations of electric field strengths, pulse numbers, and number of trains were tested. The verification for the electroporation was done first by observing... (More)
Freezing injuries usually take place in thawed plant-based food products. To reduce freezing injuries, Pulse Electric Field (PEF) treatment and Vacuum Impregnation (VI) of cryoprotectant were used before the freezing process. The aim of PEF is to provoke electroporation to the membranes of the plant cells, thereby allowing the cryoprotective solution impregnated by VI to penetrate the cells.

PEF treatment was optimized to use the minimum possible pulse width in order to obtain a homogeneous electroporation of rucola leaves. In order to achieve this minimum pulse width, several combinations of electric field strengths, pulse numbers, and number of trains were tested. The verification for the electroporation was done first by observing the treated sample with a microscope after it had been stained with Propidium Iodide and then by monitoring the tissue leakage by measuring its conductivity over time. VI treatment was done straight after the PEF treatment and then the sample was stored in a refrigerator to rest before freezing and thawing.

The initial experiment attempted to optimize the PEF parameters, while the second experiment was carried out to determine the optimal concentration of cryoprotectant for VI when combined with an optimized PEF treatment. The leaves were then rested, frozen and thawed before being observed. The initial experiment was done using commercial rucola leaves from Italy. Due to the seasonal availability of commercial rucola leaves, the second experiment was done using rucola leaves planted in the greenhouse at the Biology Department of Lund University.

The results show that the samples treated with PEF and VI with the highest concentration of the cryoprotectant (SC4) had the highest survival after freezing and thawing. This treatment resulted in 88.41 ± 5.23 % of survival 5 min after leaves were taken out from a freezer and decreased to 57.97 ± 5.80 % after 1 hour. The microscopic observations showed that viable cells of frozen and thawed leaves were mostly located near the main veins. (Less)
Popular Abstract
In the United Nations Sustainable Development Goals, food is a key aspect as it is aimed to “Ensure sustainable consumption and production patterns” (United Nations Sustainable Development, 2018). As 45% of fruit and vegetables are wasted in the world every year, preserving them is still trend in food processing activities (Food and Agriculture Organization of the United Nations, 2018). Freezing is one example of food preservation methods; however, the quality of frozen and thawed plant-based food products is usually decreased in terms of texture, taste and appearance (Phoon et al., 2018). Rucola was used in this project due to its popularity, the rucola was subjected to be frozen and thawed, meanwhile, its demand to be used as a fresh... (More)
In the United Nations Sustainable Development Goals, food is a key aspect as it is aimed to “Ensure sustainable consumption and production patterns” (United Nations Sustainable Development, 2018). As 45% of fruit and vegetables are wasted in the world every year, preserving them is still trend in food processing activities (Food and Agriculture Organization of the United Nations, 2018). Freezing is one example of food preservation methods; however, the quality of frozen and thawed plant-based food products is usually decreased in terms of texture, taste and appearance (Phoon et al., 2018). Rucola was used in this project due to its popularity, the rucola was subjected to be frozen and thawed, meanwhile, its demand to be used as a fresh product made the project challenging.

This thesis project aimed at reducing the degradation of quality, especially the texture and general appearance, of rucola due to freezing and thawing. The leaves were treated using a combination of two methods: Pulse Electric Field (PEF) treatment and Vacuum Impregnation (VI) which then is followed by freezing and thawing process. Pulse Electric Field treatment is an application of short electrical pulses to a biological tissue. The electrical pulses produce pores on the cell membrane and allows material flow from inner cell to outer cell and vice versa (Gómez Galindo, 2016). Vacuum Impregnation is a method of infusing liquids to a porous structure of plant by decreasing the pressure into a vacuum condition and then return the pressure back to the atmospheric condition. In this thesis, cryoprotectant is impregnated into the rucola leaves. Cryoprotectant is a chemical solution which is used to prevent damage of the biological cell due to freezing. Both PEF and VI parameters were optimized during the experiment.

Leaves were analysed after freezing and thawing to understand how much tissue was damaged due to freezing and to find the optimal parameters for the treatment resulting in the highest survival rate (88.41%). It showed that the damaged cells were usually located in the edges of the leaves, far from the main vein. (Less)
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author
Christiana Nyoto, Imelda LU
supervisor
organization
course
KLTM01 20181
year
type
H2 - Master's Degree (Two Years)
subject
keywords
food engineering, livsmedelsteknik
language
English
id
8960452
date added to LUP
2019-04-11 14:17:26
date last changed
2019-04-11 14:17:26
@misc{8960452,
  abstract     = {Freezing injuries usually take place in thawed plant-based food products. To reduce freezing injuries, Pulse Electric Field (PEF) treatment and Vacuum Impregnation (VI) of cryoprotectant were used before the freezing process. The aim of PEF is to provoke electroporation to the membranes of the plant cells, thereby allowing the cryoprotective solution impregnated by VI to penetrate the cells.

PEF treatment was optimized to use the minimum possible pulse width in order to obtain a homogeneous electroporation of rucola leaves. In order to achieve this minimum pulse width, several combinations of electric field strengths, pulse numbers, and number of trains were tested. The verification for the electroporation was done first by observing the treated sample with a microscope after it had been stained with Propidium Iodide and then by monitoring the tissue leakage by measuring its conductivity over time. VI treatment was done straight after the PEF treatment and then the sample was stored in a refrigerator to rest before freezing and thawing. 

The initial experiment attempted to optimize the PEF parameters, while the second experiment was carried out to determine the optimal concentration of cryoprotectant for VI when combined with an optimized PEF treatment. The leaves were then rested, frozen and thawed before being observed. The initial experiment was done using commercial rucola leaves from Italy. Due to the seasonal availability of commercial rucola leaves, the second experiment was done using rucola leaves planted in the greenhouse at the Biology Department of Lund University. 

The results show that the samples treated with PEF and VI with the highest concentration of the cryoprotectant (SC4) had the highest survival after freezing and thawing. This treatment resulted in 88.41 ± 5.23 % of survival 5 min after leaves were taken out from a freezer and decreased to 57.97 ± 5.80 % after 1 hour. The microscopic observations showed that viable cells of frozen and thawed leaves were mostly located near the main veins.},
  author       = {Christiana Nyoto, Imelda},
  keyword      = {food engineering,livsmedelsteknik},
  language     = {eng},
  note         = {Student Paper},
  title        = {Optimization of Pulse Electric Field Treatment and Vacuum Impregnation for Reducing Freezing Injury of Thawed Rucola Leaves},
  year         = {2018},
}