Aroma characterisation and retention after heat treatment and drying of fruits using extraction and GC-MS analysis
Författare
Summary, in Swedish
Popular Abstract in English
Fruits are a key complement to the diet of many people in the southern
region of Africa, especially in rural areas. maphilwa (Vangueria infausta
L.), maçanica (Ziziphus mauritiana), maçala (Strychnos spinosa),
mapsincha (Salacia kraussi), cajú (Anacardium accidentale L.),
mavungwa (Landolpia kirki) are some of the most commonly found fruits
in sub-Saharan Africa, particularly in Mozambique, Botswana,
Madagascar, South Africa, Zambia and Zimbabwe. They play an
important role in the diet and gastronomy of the rural communities.
Several investigations of nutritional aspects have been carried out, and
showed that the fruit is rich in dietary fibre and sugars and have a high
micronutrient content in the form of minerals and vitamins. Vengueria
infausta L. belongs to the family Rubiaceae. The common names are
African medlar in english or maphilwa in ronga (one of local language
in southern Mozambique). The fruit is usually harvested between
February and April. It is brownish orange when ripe and is spherical in
shape. The fruit is about 2-5 cm in diameter and contains 3-5 seeds. The
fresh fruit is sweet and tastes like medlar (Mespilus sp.), although with
some similarities to green apple and pineapple. The fruit can be
eaten fresh, cooked or dried. It’s used also to prepare juice, jam
puddings and marmalade. We assume that the fruit may be useful and
the taste and aroma profile attractive and appreciated. Information
about identification of aroma on African medlar is limited.
The investigation included developing a procedure to extract volatile
components from the fruit matrix, a purification step, separation,
identification and quantification. The extraction procedure used solvents
(ethanol, diethyl ether and pentane). Initial experiments showed that some
components, especially sugars, are degraded during the heating in the Gas
Chromatography (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 with a
capability to retain the hydrophobic aroma components and wash out
the hydrophilic components (sugars) using water. The aromas were
released using a mixture of pentane and diethyl ether prior injection
viii
into the GC. The aroma components were separated on the basis of their
retention times, followed by identification through MS. The identification
was verified using standards. Each peak was quantified, taking into
account the peak areas of components relating to the internal standard.
The main aroma components identified in Vangueria infausta were
hexanoic acid, octanoic acid, ethyl hexanoate, ethyl octanoate, methyl
hexanoate a n d methyl octanoate. The esters (methyl hexanoate and ethyl
octanoate) are the main contributors to the aroma of the fruit (Paper I).
The second aspect of this work was to evaluate the effect of drying upon
aroma components of the fruits. Samples of Vanueria infausta pulp were
convectively dried at 80°C, 3 m/s for up to 480 min. The results showed
that the principal aroma components of pulp are well preserved during the
initial phase of drying down to a relative water activity of about 0.65, but
are lost after more extensive drying. This is due to the volatilisation
induced by sugar crystallisation that is likely to occur below a
relative humidity of around 0.70 during the drying process (Paper II).
The third study of this thesis aimed to evaluate the effect of blanching
and drying on the aroma of mango (Mangifera indica L.). Three samples
of mango (fresh, blanched and dried) were analysed (Paper III). The
blanching was carried out in water at 70°C during 10 min and in a
microwave at 90°C during 2 min. The most relevant aromas Mangifera
indica are 1-butanol, α-pinene, 3-carene, myrcene, limonene, terpinolene,
and ethyl butanoate. The experiments show that the levels of aroma
components are increased when the material is blanched while hot air
drying reduced most of the aroma when the drying is prolonged below
0.65 in aw. Also the study shows that water blanching, microwave
blanching, long period/low temperature or short period/high temperature
had no marked effect on the impact of the blanching.
Another goal of this thesis was to investigate the influence crystallisation
of carbohydrates on retention or loss of aroma. (Paper IV). Three models
were evaluated: I -pectin-sucrose-aromas; II -pectin-microcrystalline
celulose-sucrose-aromas and III -microcrystalline cellulose-sucrosearomas.
The aroma fraction was composed of the main aroma components
identified in Vangueia infausta: hexanoic acid, ethyl hexanoate and ethyl
octanoate. Each model was dried on over at 80°C, 3 m/s during 60-420
min. GC results showed considerable aroma retention in all models at least
ix
starting when the aw value reached 0.8. Model with pectin and
microcrystalline cellulose rapidly exhibited low aw values and more
consistency. Our assumption is that the crystallisation of sugars could play
a role on aroma retention during the drying of fruits.
The results from these studies show what happens to aroma during heat
treatment of fruits. It is useful to understand the encapsulation of aroma
due to sugar crystallisation during drying. The results can help design a
better strategy for sustainable utilisation of aroma components of fruits,
like the African medlar, one of the wild fruits now included in local
industrial processing of new products. We believe that greater knowledge
on volatiles can be useful in sustainable utilisation of wild fruits grown in
Mozambique and southern Africa.
Fruits are a key complement to the diet of many people in the southern
region of Africa, especially in rural areas. maphilwa (Vangueria infausta
L.), maçanica (Ziziphus mauritiana), maçala (Strychnos spinosa),
mapsincha (Salacia kraussi), cajú (Anacardium accidentale L.),
mavungwa (Landolpia kirki) are some of the most commonly found fruits
in sub-Saharan Africa, particularly in Mozambique, Botswana,
Madagascar, South Africa, Zambia and Zimbabwe. They play an
important role in the diet and gastronomy of the rural communities.
Several investigations of nutritional aspects have been carried out, and
showed that the fruit is rich in dietary fibre and sugars and have a high
micronutrient content in the form of minerals and vitamins. Vengueria
infausta L. belongs to the family Rubiaceae. The common names are
African medlar in english or maphilwa in ronga (one of local language
in southern Mozambique). The fruit is usually harvested between
February and April. It is brownish orange when ripe and is spherical in
shape. The fruit is about 2-5 cm in diameter and contains 3-5 seeds. The
fresh fruit is sweet and tastes like medlar (Mespilus sp.), although with
some similarities to green apple and pineapple. The fruit can be
eaten fresh, cooked or dried. It’s used also to prepare juice, jam
puddings and marmalade. We assume that the fruit may be useful and
the taste and aroma profile attractive and appreciated. Information
about identification of aroma on African medlar is limited.
The investigation included developing a procedure to extract volatile
components from the fruit matrix, a purification step, separation,
identification and quantification. The extraction procedure used solvents
(ethanol, diethyl ether and pentane). Initial experiments showed that some
components, especially sugars, are degraded during the heating in the Gas
Chromatography (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 with a
capability to retain the hydrophobic aroma components and wash out
the hydrophilic components (sugars) using water. The aromas were
released using a mixture of pentane and diethyl ether prior injection
viii
into the GC. The aroma components were separated on the basis of their
retention times, followed by identification through MS. The identification
was verified using standards. Each peak was quantified, taking into
account the peak areas of components relating to the internal standard.
The main aroma components identified in Vangueria infausta were
hexanoic acid, octanoic acid, ethyl hexanoate, ethyl octanoate, methyl
hexanoate a n d methyl octanoate. The esters (methyl hexanoate and ethyl
octanoate) are the main contributors to the aroma of the fruit (Paper I).
The second aspect of this work was to evaluate the effect of drying upon
aroma components of the fruits. Samples of Vanueria infausta pulp were
convectively dried at 80°C, 3 m/s for up to 480 min. The results showed
that the principal aroma components of pulp are well preserved during the
initial phase of drying down to a relative water activity of about 0.65, but
are lost after more extensive drying. This is due to the volatilisation
induced by sugar crystallisation that is likely to occur below a
relative humidity of around 0.70 during the drying process (Paper II).
The third study of this thesis aimed to evaluate the effect of blanching
and drying on the aroma of mango (Mangifera indica L.). Three samples
of mango (fresh, blanched and dried) were analysed (Paper III). The
blanching was carried out in water at 70°C during 10 min and in a
microwave at 90°C during 2 min. The most relevant aromas Mangifera
indica are 1-butanol, α-pinene, 3-carene, myrcene, limonene, terpinolene,
and ethyl butanoate. The experiments show that the levels of aroma
components are increased when the material is blanched while hot air
drying reduced most of the aroma when the drying is prolonged below
0.65 in aw. Also the study shows that water blanching, microwave
blanching, long period/low temperature or short period/high temperature
had no marked effect on the impact of the blanching.
Another goal of this thesis was to investigate the influence crystallisation
of carbohydrates on retention or loss of aroma. (Paper IV). Three models
were evaluated: I -pectin-sucrose-aromas; II -pectin-microcrystalline
celulose-sucrose-aromas and III -microcrystalline cellulose-sucrosearomas.
The aroma fraction was composed of the main aroma components
identified in Vangueia infausta: hexanoic acid, ethyl hexanoate and ethyl
octanoate. Each model was dried on over at 80°C, 3 m/s during 60-420
min. GC results showed considerable aroma retention in all models at least
ix
starting when the aw value reached 0.8. Model with pectin and
microcrystalline cellulose rapidly exhibited low aw values and more
consistency. Our assumption is that the crystallisation of sugars could play
a role on aroma retention during the drying of fruits.
The results from these studies show what happens to aroma during heat
treatment of fruits. It is useful to understand the encapsulation of aroma
due to sugar crystallisation during drying. The results can help design a
better strategy for sustainable utilisation of aroma components of fruits,
like the African medlar, one of the wild fruits now included in local
industrial processing of new products. We believe that greater knowledge
on volatiles can be useful in sustainable utilisation of wild fruits grown in
Mozambique and southern Africa.
Avdelning/ar
- Department of Food Technology, Engineering and Nutrition
Publiceringsår
2015
Språk
Engelska
Fulltext
Dokumenttyp
Doktorsavhandling
Förlag
Lund University (Media-Tryck)
Ämne
- Chemical Process Engineering
Nyckelord
- Fruits
- Vangueria infausta
- Mangifera indica
- volatile
- aroma
- blanching
- drying
- encapsulation
- modelling
- GC-MS.
Status
Published
Handledare
ISBN/ISSN/Övrigt
- ISBN: 978-91-7422-415-3
Försvarsdatum
26 november 2015
Försvarstid
10:00
Försvarsplats
Lecture hall C, Kemicentrum, Getingevägen 60, Lund University, Faculty of Engineering LTH, Lund
Opponent
- Tara Grauwet (Dr.)