Review
Extraction of secondary
This review article intends to give an overview of the developments in the extraction technology of secondary metabolites
from plant material. There are three types of conventional extraction techniques. In order of increasing technological difficulty, these involve the use of solvents, steam or supercritical
fluids. Each of these types of extraction methods is described
in detail with respect to typical processing parameters and
recent developments. Following the discussion of some technical and economic aspects of conventional and novel sepa-
metabolites from plant
material: A review
I Dick A.J. Starmans and Herry H. Nijhuis
ration processes, a few general conclusions about the applicability of the different types of extraction techniques are
drawn.
Although chemistry has provided humankind with a
large number of different materials to make life easier,
we still cannot make some compounds as efficiently as
mother nature does. Plant cells synthesize a vast supply
of natural compounds that are not strictly necessary for
growth or reproduction, but whose presence can be
demonstrated genetically, physiologically or biochemically. The natural function of these so-called secondary
metabolites is often closely related to their function
when used in a pure form. Thus, natural sprout suppressants, insecticides, fungicides, as well as aromas, oils
and fragrances originate from plant material (see Table
1). To exploit plant material resources, extraction techniques have been developed to obtain such secondary
metabolites commercially.
In addition to the well-known extraction processes,
some new techniques for the separation of compounds
from plant material have received a considerable
amount of attention. These techniques are largely
focused on finding technological solutions to diminish
or even prevent the use of organic solvents in extraction
processes, to obtain more highly purified products containing fewer additional toxins, rendering them useful in
a wider range of applications. Furthermore, the use of
plant material as the source of such products allows
consumer demands for the replacement of synthetic
compounds with natural substitutes to be met.
tea. Basically, pretreated plant material is put into contact with hot water, which takes up the flavour compounds and colouring agents. After filtering off the solid
residue, the ‘extract’ is ready for consumption.
In the case of the isolation of certain compounds
from plant material by means of liquid extraction, some
technological problems have to be overcome. First, the
plant material has to be pretreated in order to obtain
reasonable extraction yields. Convenient methods are
maceration and cutting, followed by drying and breaking. A somewhat newer method is cryogenic milling,
which results in a product with a large surface area and
minor losses of volatile organic compounds owing to
the low temperature used. Therefore, pretreatment using
cryogenic milling can lead to a more efficient extraction.
Another problem is the need for special (i.e. toxic organic) solvents to be used in the extraction procedure.
Extraction has been performed using edible oils’, and
some common organic solvents (e.g. hexane*, ether,
chloroform3, benzene, ethano14). With these solvents,
antioxidants from well-known spices such as rosemary3,
sage5, thyme and marjoram6 have been isolated as natural replacements for the synthetic antioxidants butylated
hydroxyanisole and butylated hydroxytoluene.
More recently, attention has broadened from the isolation of specific antioxidants towards the extraction of
other valuable organic compounds that can be used in
the food industry. Of particular interest is the isolation
of aromas and fragrances from plant essential oils’,* and
fruit9.
Solvent extraction
Processing
Solvent extraction on an industrial scale is often performed using an inclined diffusor (Fig. 1). In this type
of apparatus, a pair of intermeshed helical screws transports the material through a heated solvent phase. The
pulp is pressed and the press liquid is heated before it is
returned to the diffusor. The extraction liquid is then
drawn off at the bottom of the trough. The total volume
of solvent in the diffusor is kept constant by feeding
fresh solvent into it at the upper end.
Following extraction, simple evaporation of the solDick A.1. Starmans and Herry H. Nijhuis are at the Agrotechnological vent is often sufficient to obtain the final product in its
ResearchInstitute (ATO-DLO), PO Box 17, NL-6700 AA Wageningen, The pure form, but legislation requires the removal of orNetherlands(fax: +31-317-412260; e-mail: [email protected]).
ganic solvents to a prescribed maximum residual level
In the 18th century, scientific research regarding the
isolation of valuable compounds from plant material
focused on the isolation of odours from flowers. In a
technique called enfleurage, fat was brought into direct
contact with flowers, thus extracting the odours from the
plant matrix.
Nowadays, in practically all households worldwide,
solvent extraction is practised while making coffee or
Trends in Food Science & Technology June 1996 [Vol. 71
01996.
19
Elsevier Science Ltd
PII: SO924-2244(96110020-O
Steamdistillation to obtain essential
oils from plant material has been a
research subject for many years, and
Function
Source/compound
Application
many famousresearchershave given it
their attention. As early as 1910, von
Colorant
Beetrootjuice
Ice cream
Rechenberg’
l explained the phenomSpearmint oil
Aroma
Toothpaste,chewing gum
enon that oxygen-richcompoundswith
Carsonic acid
Antioxidant
French fries
a high boiling point will be isolated
before oxygen-poorcompoundswith a
Antioxidant
Rosemaryoil
Preventionof fat oxidation
low boiling point, becauseoxygen-rich
Carvone
Sprout suppressant
Potato storage
compoundswill dissolve more easily
Palm oil
Food additive, cosmetics
Food industry, skin softener
in the watery phasepenetratingthe plant
material. For instance, when caraway
(i.e. 5-30mg hexaneper kg of product) if the product is seedsare extracted,the releaseof carvone (T,., = 71°C
to be used in food applications. Also, the thermal in- solubility = 1.32g/l) is promoted despiteits high boiling
stability of the compoundsof interest may lim it the use point, becauseit dissolves in water, unlike limonene
of elevated temperatures during the extraction and (T,, = 60-61°C insoluble in water).
evaporationprocesses.In addition, the extra emissionof
Vapour-phaseextraction can also be performed on
toxic chemicals into the environment and the fact that liquid samples. For instance, steam distillation of the
higher-boiling impurities are retained in the final prod- volatile componentsof black tea was used to separate
uct have brought about serious interest in alternative aroma m ixtures into basic and neutral components12,
thus allowing the further characterizationof the whole
liquid-solid and liquid-liquid separationprocesses.
aromaof black tea. Another two examplesof steamdistillation are the recovery of antioxidants from the waterNew developments
Not only is the recovery of the solvent from the ex- dispersed ‘concrete’that is obtained after evaporation
tract phaseimportant, but it is also important to recover of the solvent used in the extraction of herb spices6,
the solventpresentin the residuephase.A new technique and the isolation of essentialoils that have antioxidant
which frees residuesof a solvent activity from caraway,clove, cumin, rosemary,sageand
is flash desolventizinglO,
from a solid phaseby evaporationat low temperaturein thyme13.
a high-velocity streamof superheatedsolvent.
Processing
Steamdistillation is the most commontype of vapourSteamextraction
Besides liquid extraction procedures,there are also phaseextraction. In this extraction technique,a packed
vapour-phaseextraction procedures.A vapour can pen- bed of plant material, which is placed on a porous supetrate coarsely pretreated plant material better than a port, is continuouslyflushedwith steam(Fig. 2). Volatile
liquid can becauseof its low viscosity, and thereforere- organic compounds present in the plant material are
sults in a larger effective contact area. Furthermore,the taken up by the vapour phasebecauseof their low pardiffusion of small compoundsin a vapour phaseis much tial vapour pressure. Thus, compoundscarried by the
higher than in a liquid phase. Thus, although the solu- vapour streamare easily separatedfrom it by decreasing
bilizing capacity of a vapour phaseis far less than that the solubility. This is achievedby lowering the temperaof a liquid phase,the net recovery of secondarymetab- ture of the vapour stream by forced condensationin a
olites using an extraction procedure with a gaseous heat-exchangeunit. The resulting liquid m ixture is led
phasecan surpassthat of one that usesa liquid phases. into a separator,where static separationof the oil phase
from the water phaseoccurs. The isolated compoundswill redistribute bePress liquid
tween both the oil and watery phase,
according to their respective partition
ter
coefficients. Thus, any water-soluble
componentswill reside to someextent
in the water phase(‘hydrolate’).
Legislationregardingindustrialwaste
water is rapidly increasing. This im0 0
plies that ways will have to be found
Qm
to cope with renewed (i.e. decreased)
maximum emission standards.AddiResidue
Extract
tionally, the loss of valuable volatile
compounds should be restricted for
Fig*l economicreasons.The total amountof
Table 1, Examplesof applications of secondary metabolites from plant material
A schematic representationof a diffusor (shown in cross-sectionat left) for continuous solvent
extraction of a solid sample.
192
waste cm h decreased by p&d
con-
densationof the vapour phase. When
Trends in Food Science & Technology June 1996 [Vol. 71
this is sufficient to separate the oil phase from the vapour phase, the vapour phase can be reheated and repressurized before it is re-circulated. Thus, the oil phase
is in equilibrium with only a fraction of the total amount
of the aqueous phase, leading to a decrease in the total
amount of waste. Furthermore, by applying re-circulation, the process is much more energy efficient.
Another possibility for decreasing the total amount of
waste water generated is the application of new membrane-based processes such as pervaporation. This technique is still gaining ground in processes that require the
removal of volatile organic compounds from liquid systems; consequently, it will be described in more detail in
a later section.
Condenser
Sample
Divider
tray
Steam
generator
Separator
+
Watery
)
/
New developments
Although the use of vapours and gases for the isolation of organic compounds is already well established,
innovations in this area are still being reported in the
literature. For instance, much research has been carried
out on instant coffee. By changing process parameters
such as temperature, pressure and residence time of the
coffee beans in the extractor, the total efficiency of
the extraction can be altered. Futhermore, by adjusting
these parameters, the unwanted extraction of typical offflavours can be counteracted to a moderate extent, albeit
at the cost of the total yield of instant coffee. A new
multistage method of steam extraction of ground coffee
to obtain instant coffee with a natural taste has therefore
been patented14.
Not only have the process conditions been optimized,
but also the hardware used in extraction processes has
been subjected to modernization. Recovery of organic
contaminants from dairy products proved possible up
to the parts-per-trillion range by using a simultaneous
steam distillation and solvent extraction technique15.
Although this technique has not yet been used for the
isolation of secondary metabolites from plant material,
further improvements to increase the capacity of this
laboratory-scale system might be worth looking into.
Because of the low solubilizing power of vapours and
gases, research has been carried out on gas-phase extractions performed at elevated pressures and temperatures. When a gas is compressed and heated, it can reach
a state of aggregation at which no distinction between
the gas and liquid can be observed. Such a so-called
supercritical gas has improved solubilizing properties
that are roughly comparable to those of liquids, yet has
an extremely high diffusion coefficient, resembling that
of a natural gas. A supercritical gas also has a viscosity
similar to that of a gaseous phase, which means that the
contacting area between the plant material and a supercritical fluid is also similar. The orders of magnitude of
physical data for extraction agents in various phases are
given in Table 2 (Ref. 16).
When the pressure of a supercritical gas is decreased,
the extracted organic compounds will easily separate
from the gaseous phase. The gas can be re-pressurized
Trends in Food Science & Technology June 1996 [Vol. 71
phase
Fig. 2
A schematic representation of a steam distillation setup.
and subsequently recycled. There are five motives for
choosing supercritical carbon dioxide as the extraction
medium:
l
l
l
l
l
Supercritical extraction
Organic
phase
It has a critical temperature of 31’C; this means that
extractions can be conducted at temperatures that are
low enough not to harm the physicochemical properties of the extract.
It is inert in nature; thus, there is no risk of side reactions such as oxidation.
It is nontoxic; carbon dioxide is a harmless material
that is often used in beverages. It has been accepted by
most European food and drugs acts as an extraction
medium for the isolation of food-related compounds.
It has a low polarity; the polarity of carbon dioxide is
close to that of pentane and hexane, which are solvents commonly used in liquid extraction procedures.
Thus, a similar range of compounds can be extracted
using both techniques.
It allows fractionated separation; by simply choosing
different temperature and pressure conditions for a
number of sequential separator vessels, a fractionated
separation of the organic compounds can be achieved.
Processing
Extraction with supercritical fluids is rather similar to normal liquid-extraction methods. A simplified
Table 2. Orders of magnitude of physical data for extraction agents in
various phases
Phaseof the extraction agent
Property
Gaseous
Supercritical
Liquid
Diffusion coefficient (cm2/s)
0.1
1O-3
5 x 10-6
Density (g/cm3)
10”
0.3
1
Viscosity (g/cm.s)
10-h
1o-4
10-2
Extractor
Separator
Condenser
.t::x
R
r-+-l-
A
. . . . .t..
::::.:::.
l . ..-•..
separatorvessels,each operatedat different temperature
and pressurecombinations” . This results in the fractionation of the organic compoundsaccordingto their solubility in the gaseousphaseat particular conditions.
New developmentsin supercritical extraction
Removal of undesirable constituents
::::,:~.,.
Processdesign and material handling are often easier
when dealing with small material streamsthan with bulk
quantities. Therefore, the selective removal of small
amountsof undesirableconstituentspresentin an otherExtract
wise desirableproduct is preferred to the selective removal of the desirable product itself. Some foodstuffs
contain compounds that have to be removed before
consumption.In certain corn-derivedproducts,naturally
present glucosinolates’*,undesiredflavourslg,and even
toxins such as pesticideszOJ1
can be selectively extracted
with supercriticalcarbondioxide.
Fig. 3
The common awarenessthat saturatedfatty acids and
A simplified representationof a supercritical extraction processsetup. cholesterolplay a crucial role in the developmentof cardiovasculardiseaseshas triggeredresearchon de-fatting
representationof a possible process is given in Fig. 3. procedures.Becauseof the low polarity of supercritical
The materialthat is to be extractedis put into a cylindrical carbon dioxide, fatty products can be extracted with
container that has porous ends, which is placed inside a ease,leading to products such as reduced-fatrice bran22,
thermostaticallycontrolledextractor,vesselA. The super- malt23,peanuts”and other foodstuffs25.
critical fluid is circulatedthroughthe extractor,dissolving
organiccompoundsfrom the materialinsidethe container. Aroma extraction from seeds and other foods
Terpene hydrocarbonsfound in the essential oils of
Subsequently,the pressureis partly releasedin the separator, vesselB, which convertsthe supercriticalfluid into plants are among the most important flavour and frathe gaseousphase. The dissolved organic compounds grancecompounds,and offer a wide variety of pleasant
are separatedfrom the gas, which is then liquefied in the and floral scents.In addition to their usagein perfumes
condenser,C, by decreasingthe temperature.Finally, the and perfumedproducts,thesehydrocarbonscan be used
liquefied gas is re-pressurizedto supercriticalconditions to flavour foods and beverages,underlining their value
in modern-daychemistry.
with a pump, before it is re-circulatedto the extractor.
Flowers, fruit and herbs are typical sources of fraThe temperatureand pressureof the extraction medium in the extractor, separatorand condenserare indi- grance and aroma compounds. When aroma components are incorporated into processedfoods, by using
catedby points A, B and C on Fig. 4, respectively.
The separationof organic compoundscan also be ac- hydrodistilled essential oils or by adding solvent-excomplished in more than one step by choosing several tracted oleoresins,they do not fully resemblethe natural
aromas. This may be the result of heat- and waterinduced changes taking place during the distillation
processor the presenceof solvent residue in the oleoI
I
resin. However, by using extraction with supercritical
Liquid
Supercritical
,olid 1
I
fluids, at moderatetemperatures,fragrancesand aromas
can be isolatedwithout any process-inducedchanges.
I
I
Current developmentsin the extraction of terpene
,---+A
hydrocarbons
concernthe isolations28and enantiospecific
I
.J=
I
characterization2gof limonene derivatives and higher
I
I
terpenessuch as sesquiterpenes30
and triterpenes31.The
I
enantiospecificcharacterizationof terpenescan be apI
I
;/’ Critical Ipoint
i
plied as an analytical tool to distinguish betweennatural
and nature-identical flavours and fragrances.Essential
oils from spices32
have also receivedspecialinterest.
.g$,$
:$--
t
Fractionation of low vapour pressure oils
Temperature
-
Fig. 4
A pressure-temperaturediagram of carbon dioxide.
94
Usually, essential oils isolated from plant material
containa m ixture of interestingcompounds.The essential
oils of plant materialsuchas ginger,cinnamonand pepper
contain non-volatile, pungentcompoundsthat determine
to an importantextentthe overall flavourprofile. However,
Trends in Food Science & Technology June 1996 [Vol. 71
in the essential oils of other plant material such as the
members of the Umbelliferae family (e.g. celery, fennel,
caraway, anise, dill, coriander), high levels of odourless
triacylglycerol oils are present. The valuable organic
compounds in essential oils can be separated from such
contaminants by passing the supercritical carbon dioxide
extract through two or more individually controlled
separator vessels, each operated at a particular pressure
and temperature. The resulting stage-wise decrease in
solubility of the multicomponent extract thus leads to
the separation of pure secondary metabolites at low temperatures33. Other authors have reported the enhanced
isolation of palmitate by fractionation of rice-bran oiP4,
and the elaborated countercurrent purification of the
otherwise inedible lampante olive oiP5.
New supercritical solvents
The drawback of using supercritical carbon dioxide
for the extraction of organic compounds from plant
material is the fact that extraction performance is decreased considerably when the material contains water.
In addition, only compounds that have a moderate
polarity and contain nonpolar components are extracted
well. To circumvent these problems, polar solvents such
as ethanol (?!=516K, Pc=6.2 MPa) are often mixed
with supercnttcal carbon dioxidez8. For example, the
isolation of theobromine from cocoa beans with supercritical carbon dioxide is enhanced 30-fold by the addition of 30% (w/w) ethano136.
Also, supercritical fluid extraction is not limited to the
use of carbon dioxide. Small gases such as methane,
ethylene and chlorotrifluoromethane also display supercritical behaviour, even below the supercritical temperature and pressure of carbon dioxide (304 K, 7.38 MPa),
although the toxicity of chlorotrifluoromethane may
limit its practical use. Higher alkanes such as ethane and
propane have increasingly higher supercritical temperatures (305 K and 370 K, respectively), which restricts
their usage when temperature-sensitive organic compounds are involved.
Other new developments
Pervaporation
Pervaporation is currently being developed as a technique for the recovery of organic compounds from
liquid media. In pervaporation, non-porous membranes
are used, which have a high affinity for such compounds. With hydrophilic membranes, trace amounts of
water can be removed from an organic phase. Analogously, by using hydrophobic membranes, organic compounds can be removed from an aqueous phase37.This
has opened up possibilities for the isolation of aroma
compounds from apple juice38 and grape juice9 before
they undergo industrial processing.
Nowadays, special membranes are developed for the
separation of mixtures of organic compounds39. The ongoing developments in membrane technology will undoubtedly result in the fabrication of highly (enantio)
selective membranes for separations at the molecular
leve140.
Trends in Food Science & Technology June 1996 [Vol. 71
Microwave heating
Treatment of plant material with microwave irradiation before and/or during an extraction procedure can
result in an enhanced recovery of secondary metabolites
and aroma compounds. The forced heating of water in
the core of the material can cause the steam-induced
opening of the outer layers of the plant material. Such
opening (or puffing) of the matrix material effectively
shortens the path of diffusion of the secondary metabolites, and therefore promotes a more successful extraction of the material.
The extracted compounds are taken up by a suitable
surrounding medium to facilitate the separation from the
remaining plant material. This surrounding medium can
be either a liquid4’ or a gas42.In the case of a liquid, a
somewhat more elaborate separation step is necessary to
obtain the pure compounds, whereas in the case of a gas,
only a simple condensation step is sufficient. The final
choice depends largely on the ease of volatilization of
the desired compounds43.
Conclusions
Investigations concerning the extraction of valuable
organic compounds from plant material have received a
great deal of attention in the literature. A synopsis of the
characteristics of the conventional extraction processes
is presented in Table 3. On comparing the different extraction methods listed in this table, it is clear that each
method has some distinct advantages. The total costs are
closely related to the level of technology necessary to
reach safely the temperature and pressure values required for the specific extraction method: In this respect,
liquid extraction is favoured over both steam extraction
and supercritical fluid extraction.
Another important aspect on comparing the different
extraction methods is the quality of the resultant extracts. This is especially important if thermolabile components are to be extracted. Thus, a high-temperature
process such as steam distillation for the isolation of fragrances and/or aromas from plant material can result in
the formation of off-notes due to unwanted decomposition of the desired product. Furthermore, such temperature conditions can even cause the generation of additional (unwanted) compounds from precursors present
in the plant material.
In general, low-temperature extraction and processing
of plant material with inert solvents results in extracts
with aroma and/or flavour compositions close to those
of the plant material they were derived from. Therefore,
the low-temperature extraction of plant material using
supercritical carbon dioxide results in extracts whose
chemical composition more closely resembles that of
the original material than is possible with the hightemperature extracts obtained by steam distillation44.
Future perspectives
A large part of the aforementioned work has been
motivated by consumer demands for high end-usage
of natural resources, which in turn can lead to the improvement of existing preparation techniques and the
195
1 Table 3. Characteristics of conventional extraction processes
Method
Total costs
(capital + operating)
Mode of
operation
Liquid extraction
$4
Steam extraction
Supercritical extraction
Pros
Cons
Contitiuous
Low processing costs,
easy operation
Toxic solvents, expensive
recovery, explosion hazard
$ +$$
Batch
No toxic solvents
High temperatures, high
energy needs
$34 •t $$$
Batch
High quality, no toxic
solvents, rapid extraction
High-pressure precautions,
high capital costs
“Given as approximaterelative orders of magnitude:$ = low; $$$ = high
invention of new proceduresfor the isolation of valuable
compoundsfrom such resources.
Promising techniquesinclude the isolation of volatile
compounds using a gas stream led over m icrowaveheated plant materia145.
As well as resulting in the invention of new techniques,researchhas led to increased
knowledge about existing extraction techniques. The
numerical simulation of binary m ixtures in a vapourpermeation system allows, for instance, the numerical
solution of complex hybrid distillation processeP.
In general, the art of separation is still improving,
with new methods and new proceduresrapidly following each other. But not only the proceduresare changing. The ongoing quest for new materials, new natural
sources,is also ever increasing.
References
1 Bracco,U., Liiliger,J. and Viret,J-L.(1981) ‘Productionand Use of Natural
Antioxidants’ in 1. Am. Oil Chem. Sot. 58, 686-690
2 Inatani, R., Nakatani, N. and Fuwa, H. (1983) ‘Antioxidative Effect of the
Constituents of Rosemary (Rosmarinus officinalis L.) and Their Derivatives’
in Agric. Biol. Chem. 47,521-528
3 Chang, S.S., Ostric-Matijasevic, B., Hsieh, O.A.L. and Huang, C-L. (1977)
‘Natural Antioxidants from Rosemary and Sage’in 1. Food Sci. 42,
1102-1106
4 Hartmann, V.E., Racine, P., Garnero, R.J. and d’Audiffret, Y.T. (1980)
‘Les Extraits de Romarin (Rosmarinus oficinalis Linnaeus) Antioxygenes
Naturels Utilisables dans la Protection des Huiles Essentielles’in Parfums,
CosmBt., ArGmes 36, 33-40
5 Kimura, Y. and Kanamori, T. (1982) ‘Method of Frying Foods in the Presence
of a Spice Antioxidant’, US Patent 4 363 823
6 Yajima, M. (1985) ‘Method for Prevention of Oxidation of Oils and Fats and
Soft Capsules Containing the Treated Oils and Fats’, US Patent 4 525 306
7 Brueske, C.D. (1993) ‘Oil/Meal Separation Processes’in World Conference on
Oilseed Technology and Utilization (Applewhite, T.H., ed.), pp. 126-l 36,
AOCS Press, Champaign, IL, USA
8 Cu, J.Q., Perineau, F., Delmas, M. and Gaset, A. (1989) ‘Comparison of the
Chemical Composition of Carrot Seed Essential Oil Extracted by Different
Solvents’ in Flavour Fragrancel. 4,22S-231
9 Rajagopalan, N. and Cheryan, M. (1995) ‘Pervaporation of Grape Juice Aroma’
in 1. Membr. Sci. 104,243-250
10 Vavlitis, A. and Milligan, E.D. (1993) ‘Flash Desolventizing’ in World
Conference on Oilseed Technology and Utilization (Applewhite, T.H., ed.),
pp. 286-289, AOCS Press, Champaign, IL, USA
11 von Rechenberg, C. (1910) Theorie der Gewinnung und Trennung der
Atherischen Ole, Selbstverlag von Schimmel & Co.
12 Vitzthum, O.G., Werkhoff, P. and Hubert, P. (1975) ‘New Volatile Constituents
of Black Tea Aroma’ in I. Agric. Food Chem. 23, 999-1003
13 Farag, R.S., Badei, A.Z.M.A., Hewedi, F.M. and El-Baroty, C.S.A. (1989)
‘Antioxidant Activity of Spice Essential Oils on Linoleic Acid Oxidation in
Aqueous Media’ in 1. Am. Oil Chem. Sot. 66,792-799
96
14 Vitzthum, 0. and Koch, K.D. (1992) ‘Verfahren zur Herstellung von Laslichem
Kaffee’, German Patent 40 38 526 Al
15 Seidel, V. and Lindner, W. (1993) ‘Universal Sample Enrichment Technique for
Organochlorine Pesticides in Environmental and Biological Samples Using a
Redesigned Simultaneous Steam Distillation-solvent Extraction Apparatus’ in
Anal. Chem. 65,3677-3683
16 Paulaitis, M.E., Krukonis, V.J., Kurnik, R.T. and Reid, R.C. (1983) ‘Supercritical
Fluid Extraction’ in Reviews in Chem. Eng. l(2), 180-249
17 Reverchon, E., Ambruosi, A. and Senatore, F. (1994) ‘Isolation of Peppermint
Oil Using Supercritical CO, Extraction’ in Flavour Fragrance). 9, 19-23
18 Diosady, L.L. and Rubin, L.J. (1993) ‘A New Approach to Canola and
Rapeseed Processing’in World Conference on Oilseed Technology and
Utilization (Applewhite, T.H., ed.), pp. 498-504, AOCS Press, Champaign, IL,
USA
19 Wu, Y.V., King, J.W. and Warner, K. (1994) ‘Evaluation of Corn Gluten Meal
Extracted with Supercritical Carbon Dioxide and Other Solvents: Flavor and
Composition’ in Cereal Chem. 71,217-219
20 Thomson, CA. and Chesney, D.J. (1992) ‘Supercritical Carbon Dioxide
Extraction of 2,4-Dichlorophenol from Food Crop Tissues’in Anal. Chem.
64,848-853
21 King, J.W., Hopper, M.L., Luchtefeld, R.C., Taylor, S.L. and Orton, W.L. (1993)
‘Optimization of Experimental Conditions for the Supercritical Carbon Dioxide
Extraction of Pesticide Residues from Grains’ in 1. AOAC Int. 76, 857-864
22 Ramsay, M.E., Hsu, J.T., Novak, R.A. and Reightler, W.J. (1991) ‘Processing
Rice Bran by Supercritical Fluid Extraction’ in Food Technol. 45,98-104
23 Ono, M., Arakawa, K., Furukubo, S. and Hamatani, K. (1992) ‘Lipid-removed
Malt for Brewing, Beer Using the Said Malt and Method of Preparing the Said
Beer’, European Patent 0 509 432 A2
24 Santerre, C.R., Coodrum, J.W. and Kee, J.M. (1994) ‘Roasted Peanuts and
Peanut Butter Quality are Affected by Supercritical Fluid Extraction’ in
). Foo&Sci. 59,382-386
25 Forster, A. (1991) ‘High-pressure Extraction with CO, in the Food Industry’ in
Weihenstephaner 59,147-l 51
26 Ayano, S. etal. (1992) ‘Extraction of Limonoids and Limonoid Glucosides with
Supercritical Carbon Dioxide’ in 1. Ipn. Sot. Food Sci. Technol. 39,684-689
27 Shin, D.H., Shimoda, M., Kawano, T. and Osajima, Y. (1992) ‘Supercritical
Carbon Dioxide Extraction of Terpene Hydrocarbons from Citrus Peel Oil’ in
1. jpn. Sot. FoodSci. Technol. 39, 377-382
28 Shimoda, M., Shin, D.H., Kawano, T. and Osajima, Y. (1992) ‘Effects of
Ethanol as an Entrainer in Preparation of Terpeneless Oil by Supercritical
Carbon Dioxide Extraction’ in 1. jpn. Sot. Food Sci. Technol. 39,339-343
29 Weinreich, B. and Nitz, S. (1992) ‘Influences of Processing on the
Enantiomeric Distribution of Chiral Flavour Compounds. Part A. Linalyl
Acetate and Terpene Alcohols’ in Chem. Mikrobiol. Technol. lebensm.
14,117-124
30 Castaneda-Acosta, J., Cain, A.W., Fischer, N.H. and Knopf, F.C. (1995)
‘Extraction of Bioactive Sesquiterpene Lactones from Magnolia grandir7ora
Using Supercritical Carbon Dioxide and Near-critical Propane’ in ). Agric.
Food Chem. 43,63-68
31 Sewram, V., Nair, J.J., Mulholland, D.A. and Raynor, M.W. (1995) ‘Open
Tubular Supercritical Fluid Chromatography of Triterpene Acids from
Dysoxylum pettigrewianum (Meliaceae)’ in ). High Resolut. Chromatog. 18,
363-366
32 Nitz, S., Kollmannsberger, H. and Punkert, M. (1992) ‘CO,Hochdruckextraktion von Cewiirzen’ in Chem. Mikmbiol. Technol. lebensm.
14,108-116
Trends in Food Science & Technology June 1996 [Vol. 71
33 Nguyen, U., Evans, D.A., Berger, D.J. and Calderon, LA. (1992) ‘Process for
the Supercritical Extraction and Fractionation of Spices’, US Patent 5 120 558
34 Saito, N., tkushima, Y., Hatakeda, K., Ito, S. and Coto, T. (1991) ‘Fractional
Extraction of Rice Bran Oil and Its Esterswith Supercritical Carbon Dioxide’
in 1. Agric. Gem. Sot. Ipn 65, 153-l 61
35 Bondioli, P. etal. (1992) ‘Lampante Olive Oil Refining with Supercritical
Carbon Dioxide’ in 1. Am. Oil Chem. Sot. 69,477-480
36 Li, S. and Hartland, S. (1992) ‘Influence of Co-solvents on Solubility and
Selectivity in Extraction of Xanthines and Cocoa Butter from Cocoa Beans
with Supercritical CO,’ in 1. Supercrit. Fluids 5, 7-l 2
37 Karlsson, H.O.E. and Tragdrdh, G. (1993) ‘Pervaporation of Dilute
Organic-Water Mixtures. A Literature Review on Modelling Studies and
Applications to Aroma Compound Recovery’ in 1. Membr. Sci. 76,121-146
38 Bengtsson, E., Trlgardh, C. and Hallstrom, B. (1993) ‘Concentration
Polarization During the Enrichment of Aroma Compounds from a Water
Solution by Pervaporation’ in 1. Food Eng. 19, 399407
39 Park, H.C., Ramaker, N.E., Mulder, M.H.V. and Smolders, C.A. (1995)
‘Separation of MTBE-Methanol Mixtures by Pervaporation’ in Sep. Sci.
Technol. 30,41 g-l33
40 Cuperus, F.P. and Nijhuis, H.H. (1993) ‘Applications of Membrane
Technology to Food Processing’in Trends FoodSci. Technol. 4,277-282
41 Pare, J. (1992) ‘Microwave Extraction of Volatile Oils and Apparatus
Therefore’, European Patent 0 485 668 Al
42 Craveiro, A.A., Matos, F.J.A., Alencar, J.W. and Plumef, M.M. (1989)
‘Microwave Oven Extraction of an Essential Oil’ in Flavour Fragrancel.
4,43-44
43 Lindstrom, T.R. and Parliment, T.H. (1994) ‘Microwave Volatilization of
Aroma Compounds’ in Thermal/y Generated F/avows. Maillard, Microwave
and Extrusion Processes(ACS Symposium Series 543) (Parliment, T.H.,
Morello, M.J. and McCorrin, R. J., eds), pp. 403-413, ACS Press, Washington,
DC, USA
44 Moyler, D.A. (1993) ‘Extraction of Essential Oils with Carbon Dioxide’ in
Flavour Fragrance J 8,235-247
45 Craveiro, A.A., Matos, F&A., Alencar, J.W. and Plumel, M.M. (1989)
‘Microwave Oven Extraction of an Essential Oil’ in FlavourFragrance/.
4,43-44
46 Pettersen, T. and Lien, K.M. (1995) ‘Design of Hybrid Distillation and Vapor
in /. Membr.Sci. 99, 21-30
Permeation Processes’
Review
1 Yroteinase inhibitors
Enzymatic protein hydrolysis plays a major role in various
physiological processes, including digestion, and is regulated
by proteinase inhibitors. Inhibitors in foods and food ingredients can reduce the absorption of free amino acids, and can
I
Fernando his Garcia-Carreiio
impair protein hydrolysis in industrial processes. However,
inhibitors can be useful tools in pest control, in the prevention and treatment of diseases such as cancers and AIDS, and
in the elimination
of unwanted proteinase activity in food
processes. Proteinase inhibitors are also useful biochemical
tools for studying proteinase classes and specificities. This
article discusses how proteinase inhibition
is involved in
some processes of current interest to food scientists and
technologists.
Enzymatic protein hydrolysis is a major concern for biological scientists. The hydrolysis of proteins is catalyzed
by peptide-bond-splitting enzymes (Box 1). Proteinases
and peptidases are involved in the hydrolysis of protein
during digestion, and have important roles in physiology
and pathology. Enzymatic protein hydrolysis is controlled in several ways, including by the use of specific
inhibitors (Box 2). Proteinase inhibition is a common
process in nature. Proteinase-inhibitor interactions are
involved in protein digestion, various physiological
processes (e.g. blood coagulation, fibrinolysis, complement activation and phagocytosis), pathological
processes (e.g. cancers and hypertension) and infection
Fernando his Carcia-CarreRo
is at Centro de lnvestigaciones Biologicas del
Noroeste, PO Box 128, La Paz, BCS, 23000, Mexico (fax: t52-112-5-4710;
e-mail: [email protected]).
Trends in Food Science & Technology June 1996 [Vol. 71
(e.g. with AIDS or invasive parasites). Another natural
method of controlling proteinase activity is the synthesis
of an inactive form of the enzyme, the zymogen.
Zymogens are activated, usually by the action of another proteinase, in the digestive system and also during
regulatory physiological processes. When an enzyme is
in its active form, proteinase inhibition is an exquisite
means of enzyme control in physiological processes,
which is achieved by highly specific inhibitors. The importance of the control of proteolytic activity by inhibitors in physiological processes is demonstrated by
the fact that inhibitor molecules exceed 10% of the total
protein in human plasma.
The fact that the control of proteolysis by inhibitors is
so specific makes it a valuable tool in medicine, agriculture and food technology. The human immune deficiency virus proteinase, the digestive systems of crop
pests, and fish muscle proteases are some examples of
targets for study. Most organisms produce proteinase
inhibitors as a means to control proteolytic processes.
Some organisms store huge amounts of inhibitors, for
example legume seeds and some leaves. This seems to
be an evolutionary response to predation.
Inhibitors for digestive proteinases in food and feed
Some food ingredients contain so-called antinutritive
factors: lectins, phenols, and other factors, including
certain proteins that inhibit proteinases. The presence of
proteinase inhibitors in living tissues seems to be a natural regulatory process, well represented by the case of
01996,
197
Elsevier Science Ltd
PII: SO924-2244(96110023-6