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Effect of guard cells electroporation on drying kinetics and quality characteristics of Genovese basil leaves

Vicente Damas, Maria Elena LU (2017) KLTM01 20161
Food Technology and Nutrition (M.Sc.)
Abstract
Culinary herbs are fragrant plants that are used to enhance the flavour of dishes. They are highly perishable food products susceptible to microbial spoilage. One technique widely used to extend their shelf life is drying. However, during this process, aromatic compounds are lost and changes in colour and texture occur. This thesis investigates the effect of tissue impregnation with hypertonic solution of trehalose and electroporation of guard cells on the drying kinetics and quality of dried basil. The influence of the electrical treatment on the aperture of the stomatal pore during the drying process is also examined, as well as its effect on the metabolism of the rehydrated basil leaves, studied through isothermal calorimetry.
The... (More)
Culinary herbs are fragrant plants that are used to enhance the flavour of dishes. They are highly perishable food products susceptible to microbial spoilage. One technique widely used to extend their shelf life is drying. However, during this process, aromatic compounds are lost and changes in colour and texture occur. This thesis investigates the effect of tissue impregnation with hypertonic solution of trehalose and electroporation of guard cells on the drying kinetics and quality of dried basil. The influence of the electrical treatment on the aperture of the stomatal pore during the drying process is also examined, as well as its effect on the metabolism of the rehydrated basil leaves, studied through isothermal calorimetry.
The results show that by applying certain electrical parameters, guard cells are electroporated and remain open until the end of the drying process. It was observed that leaves with electroporated guard cells dry faster than leaves with non-electroporated guard cells (35% faster when dried at 50℃, 62,5% when dried at 40℃, and 60% when dried at room temperature). Colour measurements show that the difference in hue between dried and fresh leaves is smaller when the leaves have electroporated guard cells and, likewise, the lower the drying temperature, the smaller the difference in hue. Therefore, samples with higher difference in hue from that of the fresh leaves were untreated leaves dried at 50℃ (ΔH = 44,66). In contrast, PEF treated leaves dried at room temperature presented the smaller difference in hue (ΔH = 34,83). Rehydration results show that PEF treatment prior to drying results in a higher rehydration capacity of the dried product when compared to dehydrated untreated leaves. The focus group discussion carried out by untrained panelists shows that the preference towards PEF treated dried basil is higher than the preference to untreated basil, being noticeably higher when lower drying temperatures are applied. Samples PEF treated and impregnated with hypertonic trehalose solution resulted in longer drying time, lower rehydration capacity and lower sensorial acceptance when compared to only PEF treated leaves. (Less)
Popular Abstract
Genovese Basil (Ocimum Blabliblu sp.) is a fragrant herb used to elaborate sauces and to enhance the flavour of poultry, fish and meat dishes. Basil is usually consumed in its fresh or dry form. However, drying of herbs provokes a loss of quality regarding to flavour, colour, and rehydration characteristics. The extent of the impact of the drying process on the quality characteristics of the product depends on the drying method. Convective air drying is a drying technique in which pre-heated air is delivered to the food product. Water is evaporated from the food product and the vapour is released via stomata, a specialised pore formed by the guard cells. The stomata can be open or closed, and when open, it facilitates the evaporation... (More)
Genovese Basil (Ocimum Blabliblu sp.) is a fragrant herb used to elaborate sauces and to enhance the flavour of poultry, fish and meat dishes. Basil is usually consumed in its fresh or dry form. However, drying of herbs provokes a loss of quality regarding to flavour, colour, and rehydration characteristics. The extent of the impact of the drying process on the quality characteristics of the product depends on the drying method. Convective air drying is a drying technique in which pre-heated air is delivered to the food product. Water is evaporated from the food product and the vapour is released via stomata, a specialised pore formed by the guard cells. The stomata can be open or closed, and when open, it facilitates the evaporation therefore, the drying procedure.
Pulsed electric fields (PEF) is an emerging technology that consists on applying a voltage to the product. This technology affects the guard cells, inducing stomatal pore openings. Vacuum impregnation (VI) is a technique in which pressure changes are utilised to infuse a solute into a product. Molecules, such as trehalose, can be added to the food product. Trehalose has been found to improve the quality characteristics of some dried products, such as dried strawberry puree and dried vegetables.
The aim of this thesis is to study the impact of the application of PEF and to infuse trehalose by using VI on the drying kinetics and quality characteristics of Genovese basil leaves.
The results showed that the application of certain electrical parameters induced a permanent stomatal pore aperture during the drying process. Consequently, the drying times were reduced in a 35-65%. The product achieved by application of PEF prior to drying presented better rehydration characteristics and a colour more similar to the fresh basil leaf. A sensorial analysis was performed. Semi-trained panellists identified the PEF treated dried product as the one with a more fresh-like and intense aroma, especially when the leaves had been dried at lower temperatures. However, when the leaf tissue was infused with trehalose and then PEF treated, the drying kinetics were slower and the final product had worse rehydration capacity, weaker aroma, and a colour more different to the fresh product.
To conclude, the application of certain electrical parameters affecting the guard cells results in reduction of drying time. The final product is a dried product of higher quality, regarding rehydration capacity, colour and aromatic characteristics. (Less)
Please use this url to cite or link to this publication:
author
Vicente Damas, Maria Elena LU
supervisor
organization
course
KLTM01 20161
year
type
H2 - Master's Degree (Two Years)
subject
keywords
pulsed electric fields, basil, trehalose, vacuum impregnation, stomata, air drying, electroporation, food engineering, livsmedelsteknik
language
English
id
8914575
date added to LUP
2017-06-29 09:04:36
date last changed
2017-06-29 09:04:36
@misc{8914575,
  abstract     = {Culinary herbs are fragrant plants that are used to enhance the flavour of dishes. They are highly perishable food products susceptible to microbial spoilage. One technique widely used to extend their shelf life is drying. However, during this process, aromatic compounds are lost and changes in colour and texture occur. This thesis investigates the effect of tissue impregnation with hypertonic solution of trehalose and electroporation of guard cells on the drying kinetics and quality of dried basil. The influence of the electrical treatment on the aperture of the stomatal pore during the drying process is also examined, as well as its effect on the metabolism of the rehydrated basil leaves, studied through isothermal calorimetry. 
The results show that by applying certain electrical parameters, guard cells are electroporated and remain open until the end of the drying process. It was observed that leaves with electroporated guard cells dry faster than leaves with non-electroporated guard cells (35% faster when dried at 50℃, 62,5% when dried at 40℃, and 60% when dried at room temperature). Colour measurements show that the difference in hue between dried and fresh leaves is smaller when the leaves have electroporated guard cells and, likewise, the lower the drying temperature, the smaller the difference in hue. Therefore, samples with higher difference in hue from that of the fresh leaves were untreated leaves dried at 50℃ (ΔH = 44,66). In contrast, PEF treated leaves dried at room temperature presented the smaller difference in hue (ΔH = 34,83). Rehydration results show that PEF treatment prior to drying results in a higher rehydration capacity of the dried product when compared to dehydrated untreated leaves. The focus group discussion carried out by untrained panelists shows that the preference towards PEF treated dried basil is higher than the preference to untreated basil, being noticeably higher when lower drying temperatures are applied. Samples PEF treated and impregnated with hypertonic trehalose solution resulted in longer drying time, lower rehydration capacity and lower sensorial acceptance when compared to only PEF treated leaves.},
  author       = {Vicente Damas, Maria Elena},
  keyword      = {pulsed electric fields,basil,trehalose,vacuum impregnation,stomata,air drying,electroporation,food engineering,livsmedelsteknik},
  language     = {eng},
  note         = {Student Paper},
  title        = {Effect of guard cells electroporation on drying kinetics and quality characteristics of Genovese basil leaves},
  year         = {2017},
}