Aroma characterisation and retention after heat treatment and drying of fruits using extraction and GC-MS analysis
Author
Summary, in English
This study concerns the identification and characterisation of volatile
components of fruits, and evaluation of the effect of heat treatment and
drying on retention or loss of volatiles of fruits. The investigation included
developing a procedure to extract volatile components from the fruit
matrix, a purification step, separation, identification and quantification.
Initial experiments with Vangueria infausta L. showed that some
components, especially sugars, degrade during heating in the GC analysis,
producing furfural, hydroxyl methyl furfural (HMF) and other volatiles.
These compounds are obtained together with the native aroma components
of the fruit, making analysis difficult.
We developed a procedure using a hydrophobic column that could retain
the hydrophobic aroma components and eliminate sugars that could
disrupt the analyses. The extract was analysed by GC.
The volatile components found in pulp of Vangueria infausta were
primarily hexanoic acid, octanoic acid, ethyl hexanoate, ethyl octanoate,
methyl hexanoate and methyl octanoate. Based on the odour activity
values, it could be concluded that the odour of the fruit is mainly attributed
to ethyl hexanoate and ethyl octanoate (paper I).
Drying is often used to process and preserve food stuff but many food
attributes including aromas which are important for palatability and
consumer interest are affected by the process. Our research showed that
the principal aroma components are well preserved during the initial phase
of drying (down to about a relative water activity of 0.65). However the
aromas are lost after more extensive drying. A possible explanation for
volatilisation is the sugar crystallisation that occurs below a RH of around
0.70. (paper II).
Also we evaluated the effects of drying with or without blanching on
volatiles of mango (Mangifera indica L.). Fresh, blanched and dried
mango samples were analysed (paper III). The fresh sample presented a
very large number of peaks. The blanching was carried out in water and
microwave at 70°C during 10 minutes and at 90°C during 2 minutes.
Blanching increased the levels of aroma components. Both blanching
procedures had no dramatic effect on the impact of the blanching.
Prolonged hot air drying (aw=0.65) reduced most of the aroma. α-pinene
vi
and 1-butanol were strongly affected due their volatility. Drying had no
great effect on components with high boiling points, which displayed
significant retention even after extensive dehydration. Ethyl butanoate was
high retained despite its high volatility.
To evaluate a possible influence of sugar crystallisation on aroma
retention a further study involved three model matrixes based on
carbohydrates aqueous solution plus oils: I) pectin-sucrose-oils, II) pectinmicrocrystalline
cellulose-sucrose-oils and III) microcrystalline cellulosesucrose-
oils. The oil phase comprised the reference materials of the most
powerful aroma components found in Vangueria infausta (hexanoic acid,
ethyl hexanoate and ethyl octanoate). The model mixture was dried at
80°C, 3 m/s for 60-420 min prior to GC analysis (Paper IV). The aroma
components were preserved in all models throughout the drying process
(until aw ≈0.8). So sugar crystallisation did not induce the loss of volatiles.
However noticeable sugar crystallisation was observed in model II. We
assume that the presence of pectin and microcrystalline cellulose increased
the ability of the matrix to compact, as water activity decreased during
drying. So sugar crystallisation is probably the reason for aroma retention
within the matrix.
The results of the studies in this thesis illustrate what happens to volatiles
during thermal processing of fruits. These results could help design a
better strategy for aroma isolation and characterisation, and explain the
aroma entrapment due to sugar crystallisation during drying of fruits. The
results can also be used to design a strategy for sustainable utilisation of
volatile components of fruits like Vangueria infausta, one of the wild
fruits to be included in a formulation of new industrial food products.
However, more studies are needed in order to learn more about sustainable
utilisation of various wild fruits growing in Mozambique and southern
Africa.
components of fruits, and evaluation of the effect of heat treatment and
drying on retention or loss of volatiles of fruits. The investigation included
developing a procedure to extract volatile components from the fruit
matrix, a purification step, separation, identification and quantification.
Initial experiments with Vangueria infausta L. showed that some
components, especially sugars, degrade during heating in the GC analysis,
producing furfural, hydroxyl methyl furfural (HMF) and other volatiles.
These compounds are obtained together with the native aroma components
of the fruit, making analysis difficult.
We developed a procedure using a hydrophobic column that could retain
the hydrophobic aroma components and eliminate sugars that could
disrupt the analyses. The extract was analysed by GC.
The volatile components found in pulp of Vangueria infausta were
primarily hexanoic acid, octanoic acid, ethyl hexanoate, ethyl octanoate,
methyl hexanoate and methyl octanoate. Based on the odour activity
values, it could be concluded that the odour of the fruit is mainly attributed
to ethyl hexanoate and ethyl octanoate (paper I).
Drying is often used to process and preserve food stuff but many food
attributes including aromas which are important for palatability and
consumer interest are affected by the process. Our research showed that
the principal aroma components are well preserved during the initial phase
of drying (down to about a relative water activity of 0.65). However the
aromas are lost after more extensive drying. A possible explanation for
volatilisation is the sugar crystallisation that occurs below a RH of around
0.70. (paper II).
Also we evaluated the effects of drying with or without blanching on
volatiles of mango (Mangifera indica L.). Fresh, blanched and dried
mango samples were analysed (paper III). The fresh sample presented a
very large number of peaks. The blanching was carried out in water and
microwave at 70°C during 10 minutes and at 90°C during 2 minutes.
Blanching increased the levels of aroma components. Both blanching
procedures had no dramatic effect on the impact of the blanching.
Prolonged hot air drying (aw=0.65) reduced most of the aroma. α-pinene
vi
and 1-butanol were strongly affected due their volatility. Drying had no
great effect on components with high boiling points, which displayed
significant retention even after extensive dehydration. Ethyl butanoate was
high retained despite its high volatility.
To evaluate a possible influence of sugar crystallisation on aroma
retention a further study involved three model matrixes based on
carbohydrates aqueous solution plus oils: I) pectin-sucrose-oils, II) pectinmicrocrystalline
cellulose-sucrose-oils and III) microcrystalline cellulosesucrose-
oils. The oil phase comprised the reference materials of the most
powerful aroma components found in Vangueria infausta (hexanoic acid,
ethyl hexanoate and ethyl octanoate). The model mixture was dried at
80°C, 3 m/s for 60-420 min prior to GC analysis (Paper IV). The aroma
components were preserved in all models throughout the drying process
(until aw ≈0.8). So sugar crystallisation did not induce the loss of volatiles.
However noticeable sugar crystallisation was observed in model II. We
assume that the presence of pectin and microcrystalline cellulose increased
the ability of the matrix to compact, as water activity decreased during
drying. So sugar crystallisation is probably the reason for aroma retention
within the matrix.
The results of the studies in this thesis illustrate what happens to volatiles
during thermal processing of fruits. These results could help design a
better strategy for aroma isolation and characterisation, and explain the
aroma entrapment due to sugar crystallisation during drying of fruits. The
results can also be used to design a strategy for sustainable utilisation of
volatile components of fruits like Vangueria infausta, one of the wild
fruits to be included in a formulation of new industrial food products.
However, more studies are needed in order to learn more about sustainable
utilisation of various wild fruits growing in Mozambique and southern
Africa.
Department/s
- Department of Food Technology, Engineering and Nutrition
Publishing year
2015
Language
English
Full text
Document type
Dissertation
Publisher
Lund University (Media-Tryck)
Topic
- Chemical Process Engineering
Keywords
- Fruits
- Vangueria infausta
- Mangifera indica
- volatile
- aroma
- blanching
- drying
- encapsulation
- modelling
- GC-MS.
Status
Published
Supervisor
ISBN/ISSN/Other
- ISBN: 978-91-7422-415-3
Defence date
26 November 2015
Defence time
10:00
Defence place
Lecture hall C, Kemicentrum, Getingevägen 60, Lund University, Faculty of Engineering LTH, Lund
Opponent
- Tara Grauwet (Dr.)