Application of pulsed electric fields and vacuum impregnation to improve the freezing tolerance of fresh Origanum vulgare leaves
(2018) KLTM01 20171Food Technology and Nutrition (M.Sc.)
- Abstract
- One of most ancient food preservation methods is freezing because there are not caused significant changes the sensory characteristics and nutritional value of foods. Last decade, have been made great steps for the optimization of freezing tolerance of fresh vegetables, fruits and species. Cold injury occurs when the cells are exposed to temperatures lower than 0oC. Cold injury is a consequence of the ice formation in the plant tissue and cell membrane injury . Freezing tolerance of organic fresh oregano leaves is optimized by applying two pre-treatments: vacuum impregnation and pulsed electric fields using a trehalose as cryoprotectant.
Firstly, it was applied vacuum impregnation. An essential part of the vacuum impregnation system was... (More) - One of most ancient food preservation methods is freezing because there are not caused significant changes the sensory characteristics and nutritional value of foods. Last decade, have been made great steps for the optimization of freezing tolerance of fresh vegetables, fruits and species. Cold injury occurs when the cells are exposed to temperatures lower than 0oC. Cold injury is a consequence of the ice formation in the plant tissue and cell membrane injury . Freezing tolerance of organic fresh oregano leaves is optimized by applying two pre-treatments: vacuum impregnation and pulsed electric fields using a trehalose as cryoprotectant.
Firstly, it was applied vacuum impregnation. An essential part of the vacuum impregnation system was the chamber in which the pressure was automatically regulated to increase or decrease. The fresh oregano leaves were vacuum impregnated while they were immersed in isotonic trehalose solution 10 % (w/v). The ideal conditions for the vacuum impregnation on fresh oregano leaves were determined by applying different combinations of vacuum-atmospheric pressures and durations. To decide the most suitable the leaves were weighted. The fresh oregano gained 24% weight in isotonic solution. Secondly, it was applied the process of pulsed electric fields. The conditions of PEF were chosen according to the descriptions of Phoon et. al., 2008. These conditions (field strength, pulse width, number of trains, space between trains, number of pulses in a train, space between trains) allowed the homogenous and reversible electroporation of fresh oregano leaves. Next, it was followed resting time of 1, 2 and 3 days at 4oC. The leaves were frozen and immediately thawn. The combination of vacuum impregnation and pulsed electric fields treatment optimized the freezing tolerance but not for a very long time. When the leaves were frozen and thawn, they started to die gradually. The rate of dying of the pretreated leaves that were rested for 1,2 and 3 days was different. The longer the resting time the slower the dying rate of the leaves. Dying of pretreated leaves presented a pattern. Small dark brown spots started to form on the leaves. These spots were agglomerated latter until the whole surface of the leaves was covered. The problem was not solved, thus it is needed further research. (Less) - Popular Abstract
- Fresh spinach and ruccola can survive freezing. What about fresh oregano?
Freezing is one of the oldest food preservation methods since it preserves better the original color and flavor of foods. However, freezing and thawing of fruits, leafy vegetables and herbs causes quality degradation. This can be overcome by a new method that was developed by scientist from Lund University. This method includes two pretreatments before freezing and thawing: vacuum impregnation and pulsed electric fields. This innovative method managed to improve drastically the freezing tolerance of spinach and ruccola. However, in the case of oregano this method is successful only for short period, since are formed dark brown spots on the leaf surface. The brown... (More) - Fresh spinach and ruccola can survive freezing. What about fresh oregano?
Freezing is one of the oldest food preservation methods since it preserves better the original color and flavor of foods. However, freezing and thawing of fruits, leafy vegetables and herbs causes quality degradation. This can be overcome by a new method that was developed by scientist from Lund University. This method includes two pretreatments before freezing and thawing: vacuum impregnation and pulsed electric fields. This innovative method managed to improve drastically the freezing tolerance of spinach and ruccola. However, in the case of oregano this method is successful only for short period, since are formed dark brown spots on the leaf surface. The brown spots are dead areas of the leaf surface. Iliana Karasa, a master student from Lund University describes how the resting time after the pretreatments and before freezing and thawing affects the time that leaves remain viable.
It is an undeniable fact that the trends in food market have changed. Humans have an innate sense to attach to natural things. Thus, it is not surprising that nowadays consumers prefer to buy less processed food products. According to consumers, natural foods are healthier option. Food scientists need to adapt to the customers preferences and develop new methods of preservation. Freezing is one of the oldest food preservation methods, used widely for many food products. Nevertheless, freezing and thawing damages the integrity of frozen foods such as spinach and berries. This problem can be avoided thanks to the development of two pretreatment methods before freezing.
A decade ago, a group of food engineers at Lund University in Sweden developed a new revolutionary preservation method for leafy vegetables, to conserve their freshness, integrity and naturalness after freezing and thawing. Thanks to this method, leafy vegetables such as spinach can retain their freshness. This method can reduce the costs of off-season food and volume of food waste. The damage on fruits and leafy vegetables is caused by the formation of ice crystals during freezing. Ice crystals harm cells and cause leakage, thus their natural characteristics are lost. The solution for naturalness loss is the avoidance of cell damage. The method consists of two pretreatments (vacuum impregnation and pulsed electric fields), resting time, freezing and thawing. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/8936421
- author
- Karasa, Iliana LU
- supervisor
- organization
- course
- KLTM01 20171
- year
- 2018
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Oregano leaves, Freezing, Freezing tolerance, Pretreatments, Vacuum Impregnation, Pulsed electric fields, food engineering, livsmedelsteknik
- language
- English
- id
- 8936421
- date added to LUP
- 2018-03-12 11:51:35
- date last changed
- 2018-03-12 11:51:35
@misc{8936421,
abstract = {{One of most ancient food preservation methods is freezing because there are not caused significant changes the sensory characteristics and nutritional value of foods. Last decade, have been made great steps for the optimization of freezing tolerance of fresh vegetables, fruits and species. Cold injury occurs when the cells are exposed to temperatures lower than 0oC. Cold injury is a consequence of the ice formation in the plant tissue and cell membrane injury . Freezing tolerance of organic fresh oregano leaves is optimized by applying two pre-treatments: vacuum impregnation and pulsed electric fields using a trehalose as cryoprotectant.
Firstly, it was applied vacuum impregnation. An essential part of the vacuum impregnation system was the chamber in which the pressure was automatically regulated to increase or decrease. The fresh oregano leaves were vacuum impregnated while they were immersed in isotonic trehalose solution 10 % (w/v). The ideal conditions for the vacuum impregnation on fresh oregano leaves were determined by applying different combinations of vacuum-atmospheric pressures and durations. To decide the most suitable the leaves were weighted. The fresh oregano gained 24% weight in isotonic solution. Secondly, it was applied the process of pulsed electric fields. The conditions of PEF were chosen according to the descriptions of Phoon et. al., 2008. These conditions (field strength, pulse width, number of trains, space between trains, number of pulses in a train, space between trains) allowed the homogenous and reversible electroporation of fresh oregano leaves. Next, it was followed resting time of 1, 2 and 3 days at 4oC. The leaves were frozen and immediately thawn. The combination of vacuum impregnation and pulsed electric fields treatment optimized the freezing tolerance but not for a very long time. When the leaves were frozen and thawn, they started to die gradually. The rate of dying of the pretreated leaves that were rested for 1,2 and 3 days was different. The longer the resting time the slower the dying rate of the leaves. Dying of pretreated leaves presented a pattern. Small dark brown spots started to form on the leaves. These spots were agglomerated latter until the whole surface of the leaves was covered. The problem was not solved, thus it is needed further research.}},
author = {{Karasa, Iliana}},
language = {{eng}},
note = {{Student Paper}},
title = {{Application of pulsed electric fields and vacuum impregnation to improve the freezing tolerance of fresh Origanum vulgare leaves}},
year = {{2018}},
}