Abstract
During production of concentrated fruit juices, both physical and chemical losses of aroma compounds occur due to heat treatment such as pasteurisation and evaporation. This leads to an inferior quality of the final product. By recovering the aroma complex from fresh juice and then adding it back to the processed juice, heat treatment can be avoided.
Hydrophobic pervaporation is an emerging membrane technique, which provides an interesting alternative when volatile organic compounds are to be separated from dilute aqueous mixtures. The intention of this thesis was to model and to optimise the pervaporation process for the application of aroma recovery from fruit juices, with focus on apple juice.
Pervaporation was shown to be a promising alternative for the application of aroma recovery from natural apple juice, as it offers very high separation efficiency at mild process conditions. The operating conditions were shown to have a major impact on the performance of the process. Improved hydrodynamic conditions in the feed channel, increased feed temperature and decreased permeate pressure favour the aroma recovery. However, this has to be balanced with the energy input. Furthermore, due to the heat sensitivity of the aroma compounds, the temperature has to be kept at a reasonable level. There is also a possibility of controlling the composition of aroma compounds in the permeate via the process conditions. Optimum separation properties could be obtained when applying membranes designed with relatively thin selective layers using a modified silicone rubber polymer with a low degree of crosslinking in combination with a porous support of low resistance.
A model for a poly[octylmethyl siloxane] membrane, which can predict the influence of permeate pressure for any permeant within the chemical groups of alcohols, aldehydes and esters was developed. The model provides a better understanding of the plastication phenomena inside the membrane and its effect on permeabilities. By use of the hydrophobicity, the molecular size and the ability to form hydrogen bonds, it was possible to predict the general trends regarding the permeabilities and their influence on temperature for the organics studied.
Hydrophobic pervaporation is an emerging membrane technique, which provides an interesting alternative when volatile organic compounds are to be separated from dilute aqueous mixtures. The intention of this thesis was to model and to optimise the pervaporation process for the application of aroma recovery from fruit juices, with focus on apple juice.
Pervaporation was shown to be a promising alternative for the application of aroma recovery from natural apple juice, as it offers very high separation efficiency at mild process conditions. The operating conditions were shown to have a major impact on the performance of the process. Improved hydrodynamic conditions in the feed channel, increased feed temperature and decreased permeate pressure favour the aroma recovery. However, this has to be balanced with the energy input. Furthermore, due to the heat sensitivity of the aroma compounds, the temperature has to be kept at a reasonable level. There is also a possibility of controlling the composition of aroma compounds in the permeate via the process conditions. Optimum separation properties could be obtained when applying membranes designed with relatively thin selective layers using a modified silicone rubber polymer with a low degree of crosslinking in combination with a porous support of low resistance.
A model for a poly[octylmethyl siloxane] membrane, which can predict the influence of permeate pressure for any permeant within the chemical groups of alcohols, aldehydes and esters was developed. The model provides a better understanding of the plastication phenomena inside the membrane and its effect on permeabilities. By use of the hydrophobicity, the molecular size and the ability to form hydrogen bonds, it was possible to predict the general trends regarding the permeabilities and their influence on temperature for the organics studied.
| Original language | English |
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| Qualification | Doctor |
| Awarding Institution | |
| Supervisors/Advisors |
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| Award date | 2001 Feb 2 |
| Publisher | |
| ISBN (Print) | 91-7874-109-2 |
| Publication status | Published - 2001 |
Bibliographical note
Defence detailsDate: 2001-02-02
Time: 10:15
Place: Room K:B at the Center of Chemistry and Chemical Engineering
External reviewer(s)
Name: Crespo, Joao
Title: Professor
Affiliation: Portugal
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Article: I. Pervaporation of a model apple juice aroma solution - comparison of membrane performance (1996). Jenny Börjesson, Hans O.E. Karlsson and Gun Trägårdh, Journal of Membrane Science, 119(2), 229-239.
Article: II. Influence of temperature on membrane permeability during pervaporative aroma recovery (1999). Jenny Olsson and Gun Trägårdh, Separation Science and Technology, 34(8), 1643-1659.
Article: III. Influence of feed flow velocity on pervaporative aroma recovery from a model solution of apple juice aroma compounds (1999). Jenny Olsson and Gun Trägårdh, Journal of Food Engineering, 39(1), 107-115.
Article: IV. A new integrated membrane process for producing clarified apple juice and apple juice aroma concentrate (2000). S. Álvarez, F.A. Riera, R. Álvarez, J. Coca, F.P. Cuperus, S. Th. Bouwer, G. Boswinkel, R.W. van Gemert, J.W. Veldsink, L. Giorno, L. Donato, S. Todisco, E. Drioli, J. Olsson, G. Trägårdh, S.N. Gaeta, and L. Panyor, Journal of Food Engineering, 46(2), 109-125.
Article: V. Pervaporation of volatile organics from water. I. Influence of permeate pressure on selectivity (2001). Jenny Olsson and Gun Trägårdh, accepted for publication in Journal of Membrane Science.
Article: VI. Pervaporation of volatile organics from water. II. Influence of permeate pressure on partial fluxes (2001). Jenny Olsson, Gun Trägårdh and Christian Trägårdh, accepted for publication in Journal of Membrane Science.
Article: VII. The influence of permeant and membrane properties on mass transfer in pervaporation of volatile organic compounds from dilute aqueous solutions (2000). Jenny Olsson, Gun Trägårdh and Frank Lipnizki, submitted for publication.
Subject classification (UKÄ)
- Other Engineering and Technologies
Free keywords
- Food and drink technology
- optimisation
- mass transfer
- modelling
- pervaporation
- aroma recovery
- Livsmedelsteknik