Applications and opportunities for ultrasound assisted extraction
in the food industry — A review
Kamaljit Vilkhua,⁎, Raymond Mawsona, Lloyd Simonsa, Darren Batesb
aUltrasonics Processing Group, Food Science Australia, 671 Sneydes Road, Werribee, VIC 3030, Australia
bInnovative Ultrasonics Pty Ltd, P.O. Box 321, Noosaville, QLD 4566, Australia
Ultrasound assisted extraction (UAE) process enhancement for food and allied industries are reported in this review. This includes herbal, oil,
protein and bioactives from plant and animal materials (e.g. polyphenolics, anthocyanins, aromatic compounds, polysaccharides and functional
compounds) with increased yield of extracted components, increased rate of extraction, achieving reduction in extraction time and higher
processing throughput. Ultrasound can enhance existing extraction processes and enable new commercial extraction opportunities and processes.
New UAE processing approaches have been proposed, including, (a) the potential for modification of plant cell material to provide improved
bioavailability of micro-nutrients while retaining the natural-like quality, (b) simultaneous extraction and encapsulation, (c) quenching of the
radical sonochemistry especially in aqueous systems to avoid degradation of bioactives and (d) potential use of the radical sonochemistry to
achieve targeted hydroxylation of polyphenolics and carotenoids to increase bioactivity.
Keywords: Ultrasound assisted extraction; Cavitation; Particle size; Mass transfer
Industrial relevance: The application of ultrasonic assisted extraction (UAE) in food processing technology is of interest for enhancing extraction of components
from plant and animal materials. This review shows that UAE technology can potentially enhance extraction of components such as polyphenolics, anthocyanins,
aromatic compounds, polysaccharides, oils and functional compounds when used as a pre-treatment step in a unit process. The higher yield obtained in these UAE
processes are of major interest from an industrial point of view, since the technology is an “add on” step to the existing process with minimum alteration, application
in aqueous extraction where organic solvents can be replaced with generally recognised as safe (GRAS) solvents, reduction in solvent usage, and shortening the
extraction time. The use of ultrasonic for extraction purposes in high-cost raw materials is an economical alternative to traditional extraction processes, which is an
industry demand for a sustainable development.
The application of ultrasound as a laboratory based tech-
nique for assisting extraction from plant material is widely
published. Several reviews have been published in the past to
extract plant origin metabolites (Knorr, 2003), flavonoids from
foods using a range of solvents (Zhang, Xu, & Shi, 2003) and
bioactives from herbs Vinatoru (2001). A limited number of
publications have included continuous ultrasonic process deve-
lopment and pilot-scale applications. The range of published
extraction applications include herbal, oil, protein and bioac-
tives from plant materials (e.g. flavones, polyphenolics), sum-
marised in Table 1 and outlined in more detail in the following
Applications section. Much of the work is empirical in nature
and explanations of the mechanisms have been proposed. Some
workers also discuss both the mechanisms involved in UAE and
the likely issues for potential for scale up. The review by Vinatoru
(2001) outlines a program of work where industrial scale up was
1995). They highlight that while it is relatively easy to achieve
extraction on the laboratory bench it is very challenging to attempt
extraction on an industrial scale. Several key issues and ob-
servations relating to UAE have been identified, as follows, (1) the
nature of the tissue being extracted and the location of the
⁎Corresponding author. Tel.: +61 3 9731 3449; fax: +61 3 9731 3250.
E-mail address: email@example.com (K. Vilkhu).
treatment of the tissue prior to extraction, (3) the nature of the
component being extracted, (4) the effects of ultrasonics primarily
involve superficial tissue disruption, (5) increasing surface mass
transfer (Balachandran, Kentish, Mawson, & Ashokkumar, 2006;
Jian-Bing, Xiang-hong, Mei-qiang, & Zhi-chao, 2006), (6) intra-
particle diffusion, (7) loading of the extraction chamber with
substrate, (8) increased yield of extracted components and
(9) increased rate of extraction, particularly early in the extraction
cycle enabling major reduction in extraction time and higher pro-
cessing throughput (Moulton & Wang, 1982; Caili, Haijun,
Quanhong, Tongyi, & Wenjuan, 2006).
Living tissues where the desired components are localized in
surface glands can be stimulated to release the components by
relatively mild ultrasonic stressing (Toma, Vinatoru, Paniwnyk, &
surface area is critical for achieving rapid and complete extraction
(Riera, Golás, Blanco, Gallego, Blasco, & Mulet, 2004; Balachan-
to achieve extraction, ultrasound effectively accelerates the hydra-
tion process (Vinatoru, 2001). Ultrasound induced cavitation bub-
bles present hydrophobic surfaces within the extraction liquid
(Grieser, personnel communication) thereby increasing the net
to extract polar components into otherwise hydrophilic aqueous
extraction media, reducing the need for generally undesirable
hydrophobic or strongly polar extraction media. The disruption of
tissue surface structures is revealed with microscopic examination
(2006). Several of the authors in the work cited below highlight
concerns due to the potential for ultrasonic cavitation to propagate
free radicals, in particular hydroxyl radicals. Where the potential
oxidative damage is a concern radical production can be quenched
by the addition of small amounts of ethanol to lower the
temperatures within the cavitation bubbles and extinguish the
chemistry involved (Sun et al. unpublished work in progress).
This paper provides a compilation of food-related UAE
applications, highlighting the application approaches and per-
formance. Following this, a more detailed discussion is given on
UAE mechanisms, process development, equipment design and
2.1. Herbal and oil extraction
Ultrasound has been recognised for potential industrial ap-
plication in the phyto-pharmaceutical extraction industry for a
wide range of herbal extracts. Vinatoru (2001) published an
overview of the UAE of bioactive principles from herbs. The
improvement in extractive value by UAE compared with
classic methods in water and ethanol for fennel, hops, marigold
and mint was 34%, 18%, 2%, and 3% respectively in water,
whereas 34%, 12%, 3%, and 7%, respectively in ethanol. In
another study, an aqueous extraction of Geniposide from
Gardenia fruit was investigated by Jian-Bing et al. (2006).
When ultrasound was applied at 0.15 W cm−2the extraction
yield of Geniposide was increased by 16.5%, in comparison
with a static process using 40 ml/g of the solvent volume to
fruit weight. The variability in percentage extract yield was
mainly due to the individual product structure. Large scale
ultrasonic extraction designs were proposed for stirred tank
systems with temperature control.
In recent years, Albu, Joyce, Paniwnyk, Lorimer, and Mason
(2004) investigated the effect of different solvents and ultra-
sound on the extraction of carnosic acid from rosemary. Using
conventional stirred extraction ethanol was significantly less
effective then ethyl acetate and butanone. The application of
ultrasound improved the relative performance of ethanol such
that it was comparable to butanone and ethyl acetate alone.
List of ultrasound assisted extraction studies from the literature on various food components
Product Ultrasound ProcessSolvent PerformanceAuthor
Almond oils Batch, 20 kHz Supercritical carbon
Water and ethanol
30% increased yield or extraction
Up to 34% increased yield over stirred
Riera et al. (2004)
Herbal extracts (fennel, hops,
20 to 2400 kHz
Batch, 38.5 kHz
Water and alkali
Water and solvent
Water and methanol
Butanone and ethyl
3-fold increase of extraction rateWu et al. (2001)
Ginger Batch, 20 kHz30% increased yield or extraction
53% and 23% yield increase over
equivalent ultrasonic batch conditions
Up to 15% increase in extraction efficiency
Up to 20% increase in 30 min
Reduction in extraction time
Balachandran et al. (2006)
Soy protein Continuous, 20 kHz,
3 W per gram
Batch, 24 kHz
Batch, 20 kHz
Batch, 20 and
Batch, 40 kHz
Moulton and Wang (1982)
Rutin from Chinese Scholar Trees
Carnosic acid from rosemary
Rostagno et al. (2003)
Paniwynk et al. (2001)
Albu et al. (2004)
Polyphenols, amino acid and
caffeine from green tea
Pyrethrines from flowers
Increased yield at 65 °C, compared with 85 °CXia et al. (2006)
Batch, 20 and
HexaneIncreased yield at 40 °C, compared with 66 °C Romdhane and Gourdan
Thereby ultra-sonication may reduce the dependence on a sol-
vent and enable use of alternative solvents which may provide
more attractive (a) economics, (b) environmental and (c) health
and safety benefits.
Ginsenosides (tri-terpene saponins) are known as the prin-
cipal ingredients of ginseng roots. Ginseng saponins are asso-
ciated with traditional herbal medicine and health foods (Tang
& Eisenbrand, 1992). UAE of ginseng saponins was approx-
imately 3-times faster than the traditional extraction method
involving reflux of boiling solvents in a soxhlet extractor.
Furthermore, the UAE technique was achieved at lower tempe-
ratures which are more favourable for thermally unstable com-
pounds (Wu, Lin, & Chau, 2001). Similar results were reported
on UAE of carvone and Limonene from caraway seeds, which
resulted in 2 fold increases in their contents (Chemat et al.,
Likewise, anthraquinones from roots of Morinda citrifolia
(Noni) are the active compounds which show several therapeutic
effects and used in anti-cancer medical applications. Recently,
Hemwimol, Pavasant, and Shotipruk (2006) investigated the use
of UAE to improve the solvent extraction efficiency of an-
thraquinones from the roots of M. citrifolia. Ultrasound extraction
in an ethanol water system provided a 75% reduction in extraction
time and yield comparable with non-sonicated sample.
Supercritical fluid extraction (SFE) is an intrinsically capital
intensive process where any enhancement of extraction efficien-
cy either in terms of extraction rate or yield is economically
attractive. Over a period of many years it has been shown that
combined action of ultrasound and supercritical carbon dioxide
on extraction could be used to significantly improve extraction
rate or yield of amaranth oil from seeds (Bruni, Guerrini, Scalia,
Romagnoli, & Sacchetti, 2002), almond oil (Riera et al., 2004),
tea seed oil (Rajaei, Barzegar, & Yamini, 2005), gingerols from
ginger (Balachandran et al., 2006), operating parameters such as
temperature, pressure and CO2 flow for Adlay seed (Coix
lachrymal-jobi L. var. Adlay) oil and coixenolide from adlay
seed (Ai-jun, Shuna, Hanhua, Tai-qiu, & Guohua, 2006).
UAE has been recognised for application in the edible oil
industry to improve efficiency and reduce extraction time (Babaei,
Jabbari, & Yamini, 2006). This potential was based on UAE
increases in oil from soybeans; carvone and limonene from cara-
way seeds. The ultrasonically induced cavitation was shown to
increase the permeability of the plant tissues. Microfractures and
caraway seeds cell wall (Chemat et al., 2004) provided more
evidence for the mechanical effects of ultrasound thus facilitating
the release of their contents, in contrast to conventional maceration
microscopy. Importance was given to the effect of solvent vapour
pressure and surface tension on cavitation intensity.
The benefit of using ultrasonic pre-treatment before extract-
ing oil from the seeds of Jatropha curcas L., and almond and
apricot seeds by aqueous enzymatic oil extraction (AEOE)
process was evaluated by Shah, Sharma, and Gupta (2005),
Sharma and Gupta (2006). Ultrasonic pre-treatment of the
almond and apricot seeds before aqueous oil extraction and
aqueous enzymatic oil extraction provided significantly higher
yield with reduction in extraction time. Thus, implementation of
ultrasonic pre-treatment reduced oil extraction time that may
improve through put in commercial oil production process.
2.2. Protein extraction
A small pilot-scale ultrasound batch and continuous soy
protein extraction trials were reported by Moulton and Wang
(1982). The continuous high-intensity application extracted
54% and 23% more protein for aqueous and alkali extraction
respectively, compared with the batch extraction using com-
parable processing times and volumes. During the trials it was
estimated that the continuous process used 70% less energy than
the batch system to extract the same amount of protein and
sonication efficiency improved with the greater load of thicker
slurry, up to 1:10 (flake to solvent) ratio.
2.3. Bioactive extraction from plant materials
Grape marc is the solid waste of the wine-making process.
Consisting of skins, seeds, and small amount of leaves, grape
marc has long been used for alcohol, tartaric acid and more
recently, the recovery of phenolic compound. Phenolic com-
pounds are of particular interest in wine industry as it gives the
density lipoproteins possess anti-ulcer, anti-mutagenic, anti-
2003; Negro, Tommasi, & Miceli, 2003; Bonilla, Mayen,
Merida, & Medina, 1998; Palma & Taylor, 1999). Phenolic
compounds include tannins and colour pigments, anthocyanins
which present at a higher level in red grape marc compared with
white grape marc and are more likely to be found on the grape
seeds (Springett, 2001; Palma & Taylor, 1999).
The application of ultrasound at Food Science Australia has
focused on the use of high-powered systems for extraction of
bioactives. Principle targets have been polyphenols and caro-
tenoids and in both aqueous and solvent extraction systems. The
ultrasound extraction trials have demonstrated improvements in
extraction yield ranging from 6 to 35%, as summarised in
Table 2. Results of ultrasonically treated Shiraz and Sangiovese
grape marc showed 17 and 35% increase in phenolic com-
pounds respectively, However extraction of these compounds
yielded much higher recovery from their respective seeds
(Vilkhu, Food Science Australia unpublished data).
Supercritical carbon dioxide extraction is proposed as a
better method than ultrasound assisted extraction of polyphe-
nolic compounds from grape seeds Palma and Taylor (1999). It
was believed that the lower catechin (used as a measure of
phenolic content) recovery from ultrasound method could be due
totheinsufficient power of thesolvent used(aqueous methanol) or
due to the degradation of samples during extraction process. Their
(SFE) rather than other methods used in the experiment. The
results of catechin recovery using different extraction methods
compared to a control (solvent extraction only) was not available,
therefore it was not possible to determine whether ultrasound
treatment (although having a lower recovery compared to SFE
method) contributed to the increase in catechin recovery relative to
a control. Most importantly though, the frequency of ultrasound
and other extraction conditions (e.g. temperature) was not stated,
therefore it was not known whether suitable frequencies or
application conditions were used.
In recent years it has been shown that pressurized hot water
extraction methods offered higher phenolic compound recovery
when compared to UAE, hydro-distillation and maceration with
70% ethanol (Ollanketo, Peltoketo, Hartonen, Hiltunen, &
Riekkola, 2002). The use of methanol during UAE produced the
lowest recovery with results not statistically different from
maceration with 70% ethanol. Potential exists for combining
ultrasound as an adjunct with the other extraction procedures to
improve efficiency and yield. More recently, Tedjo, Eshtiaghi,
and Knorr (2002) studied the quality attributes of grape juices
for wine-making using non-thermal processes including
ultrasound. The non-thermal processes examined offered a
suitable gentle-action alternative to other cell breakdown
methods with increased grape juice yields. Quality analyses
(e.g. sugar, anthocyanins and mineral concentration, acidity,
colour) showed that non-thermally processed juices had superior
quality to untreated samples and comparable quality to that of
enzyme treated grape juices. Likewise significantly enhanced
contents of tea polyphenols, amino acid and caffeine in tea infu-
sions were recovered with ultrasound assisted extraction when
compared with conventional extraction. The sensory quality of tea
infusion with ultrasound assisted extraction was better than that of
tea infusion with conventional extraction (Xia, Shi, & Wan, 2006).
Anthocyanins are enjoying greater prominence due to in-
creasing public concern with the use of synthetic colouring
agents. Anthocyanins represent a large group of water-soluble
plant pigments based on the 2-phenylbenzophyrylium (flavy-
lium) structure and there are more than 200 compounds in this
category (IPCS, 2001). Anthocyanins are the main colour pig-
ments in wild fruits and berries, and predominantly found in the
present in grape skin consist of di-glucosides, mono-glucoside,
acylated monoglucosides and acylated di-glucosides of peoni-
din, malvidin, cyanidin, petunidin and delphinidin. Anthocya-
nins content in grapes varies from 30–750 mg/100 g (Birdle &
Timberlake, 1997). The wide variation in amount of these
compounds is greatly dependent upon cultivar, season, growing
conditions, degree of ripeness, storage conditions as well as
18% increase in total colour in grape juice (unpublished data).
A study has been conducted on the potential to use
microwave and ultrasound treatments for the extraction of pig-
ments from strawberries. Optimal extraction was achieved using
microwaves at 624 W, with a treatment time of 60 s, together
with ultrasonic processing for 40 s and a ratio of material and
extraction solvent of 1:6. The stability of the pigment extracts
was considerably affected by pH, and achieving a maximum at
pH 5.0. Addition of sucrose or heating at temperatures up to
80 °C had little effect on pigment stability. However, pigment
stability and colour were greatly improved by addition of citric
acid (Cai, Liu, Li, & An, 2003).
2.3.3. Tartaric acid
Tartaric acid occurs naturally in fruits, and found in high
concentrations in grapes and tamarind (Springett, 2001).
Approximately 90% of the total organic acids in grapes are
tartaric and malic acids. Tartaric acid is a by-product in the wine
industry since a tremendous amount of tartaric acid from lees has
to be removed from the wine after yeast fermentation. Tartaric acid
is widely used in bakery operations, wine production, pharma-
ceutical industry, hardening of gypsum, confectionery processing
and in the chemical industry. Palma and Barroso (2002) optimized
red and white variety grapes for quantitative determination in
wine-making by-products. Our studies on UAE of tartaric esters
from red grape marc yielded an increase 16 to 23% from two
different varieties (Vilkhu, unpublished).
2.3.4. Aroma compounds
Over a period of many years it has been shown that ultra-
sound could be used to extract aromatic chemicals, which impart
bouquet to the wines (Cocito, Gaetano, & Delfini, 1995). Solvent
mixtures ofn-pentane and diethyl-ether (1:2) and dichloromethane
were used to study the optimization of the sonication extraction
process. This study emphasised that UAE improved extraction
efficiency with increased reproducibility of most aroma com-
pounds compared to conventional extraction (Vila, Mira, Lucena,
& Fernandez, 1999).
An evaluation of UAE of isoflavones from ground soybeans
was undertaken by Rostagno, Palma, and Barroso (2003), the
efficiency of the extraction was improved by 15% but this was
dependent on the organic solvent used. Notably 40–60% water
Examples of bioactive ultrasound assisted extraction work completed at Food Science Australia
Extract targetProduct Solvent Process
Laboratory; 24 kHz, 20–7 W s ml−1
Laboratory; 24kHz, 20–75 W s m−1
Laboratory; 24 kHz, 20–75 W s ml−1
Laboratory; 24 kHz, 8–10 W s ml−1
Laboratory; 40 kHz, 20–75 W s ml−1
Laboratory; 20 kHz
Processing conditionsImprovement range (%)
Supercritical carbon dioxide
Hot processing 90 °C
Hot processing 80 °C
Pressure 160 bar
Red grape marc
was required to improve the extraction efficiency, which was
thought to be due to the relative polarity of the isoflavones and
increased ultrasound propagation in aqueous systems. Some
aromatic compounds such as rutin from the flower buds of
Chinese Scholar Tree (Sophora japonica) have improved consi-
derably with higher levels of organic solvent compared to
aqueous conditions. The difference in performance was
attributed to hydroxyl radical and hydrogen peroxide formation
in aqueous conditions resulting in degradation of the rutin. The
application of ultrasound in methanol was considered more
effective due to the higher solubility of rutin in methanol and
hydrogen peroxide is not formed by ultrasound in methanol
(Paniwynk, Beaufoy, Lorimer, & Mason, 2001).
In order to extract phycocyanin from Spirulina platensis
(Arthrospira platensis) cells, selection of ultrasonic frequency
was important (Furuki et al., 2003). The purity of phycocyanin
in its crude extract was dependant on ultrasonic frequency. For
example, phycocyanin was extracted with higher purity at 28 kHz
than at 20 kHz, due to the selective extraction of the active
component at these frequencies. It was suggested that rapid and
selective extraction of phycocyanin from S. platensis may be
possible if an optimized ultrasonic application is developed.
2.3.5. Polysaccharides and functional compounds
The extraction of carbohydrates, polysaccharides and other
functional compounds has been studied in the recent years.
Various extraction procedures with and without a short applica-
tion of ultrasound at the beginning of the extraction were used to
examine the effect of sonication on the extractability of the
hemicellulose components of buckwheat hulls (Hromadkova &
Ebringerova, 2003), cellulose from sugarcane bagasse (Sun,
Sun, Zhao, & Sun, 2004), and xyloglucan from apple pomace
(Caili et al., 2006). UAE of these compounds not only acce-
lerates the extraction process but also preserves structural and
molecular properties. In sugar cane bagasse hemicellulose
extraction processes, UAE improved extractability of hemi-
celluloses apparently by destruction of cell walls and cleavage
of links between lignin and the hemicelluloses (Jing, RunCang,
Xiao, & YinQuan, 2004). Whereas ultrasonic aqueous extrac-
tion of polysaccharides from edible fungus, Pleurotus
tuberregium, resulted in the formation of glycan–chitin com-
plexes with higher average molecular weight than compounds
obtained by hot water extraction (Mei, Lina, Chi-Keung-
Cheung, & Eng-Choon-Ooi, 2004), which could be due to the
sonochemical modification of two polysaccharides. Further
improvement in immunological as well as anti-tumour activi-
ties of these complexes were reported on animal trials.
and Hu (2000) have compared UAE with hot water extraction of
flavonoids from bamboo leaves. The laboratory scale trials
results showed that the optimal conditions for extraction were
achieved using UAE at lower temperature, rather than using hot
water bath extraction at 80 °C. More recently, Rosângela et al.
(2007) investigated the chemical composition of Mate tea
extracts (leaves of Ilex paraguariensis, a native tree from
Brazil). The effect of the ultrasonic treatment resulted in
improved mass yield of caffeine and palmitic acid in methanol
solvent. Ultrasound enhanced both the kinetics and yield which
was attributed to increase in the internal diffusion that controls
the transfer of solute to the solvent and also the destruction of
pores inwhichthesolutecanbetrapped.However theefficiency
of the extraction will be dependent on the concentration of the
methanol solvent employed Rostagno et al. (2003).
2.4. Bioactive extraction from animal materials
There is limited number of publications on UAE from animal
material. Attempts were made to extract chitin from fresh water
prawn shells (Kjartansson, Zivanovic, Kristbergsson, & Weiss,
2006) and lutein from egg yolk (Xiaohua, Zhimin, Witoon, &
Joan, 2006) by using sonication. In chitin studies from prawn
shells, it was found that the chitin yield decreased during soni-
cation, this loss was attributed to depolymerization of extracted
chitin in the wash water. Subsequently, the degree of acetylation
of chitins was unaffected by sonication, but the degree of
acetylation of chitosans produced from sonicated chitin decreased.
Egg yolk is one of the major lutein sources in our foods
(Johnson, 2004). Lutein in egg yolk is highly bio-available,
compared with other sources. It was reported that egg yolk
intake significantly increased plasma lutein (Handelman,
Nightingale, Lichtenstein, Schaefer, & Blumberg, 1999).
Recently, Xiaohua, et al. (2006) have reported higher extraction
yield of luetin when ultrasonic used in combination of sapo-
nificated organic solvent. Further to their report, compared with
the traditional saponification solvent extraction method, the
UAE extraction method was more effective in extracting lutein
from the sample matrix, presumably by avoiding degradation
3. Extraction mechanisms and process development
Extraction enhancement by ultrasound has been attributed to
the propagation of ultrasound pressure waves, and resulting
cavitation phenomena. High shear forces cause increased mass
transfer of extractants (Jian-Bing et al., 2006). The implosion of
cavitation bubbles generates macro-turbulence, high-velocity
inter-particle collisions and perturbation in micro-porous
particles of the biomass which accelerates the eddy diffusion
and internal diffusion. Moreover, the cavitation near the liquid–
solid interface sends a fast moving stream of liquid through the
cavity at the surface. Cavitation on the product surface causes
impingement by micro-jets that result in surface peeling,
erosion and particle breakdown. This effect provides exposure
of new surfaces further increasing mass transfer.
This phenomenon was confirmed by performed scanning
electron micrographyon peppermint plantleaves andtrichomes.
After these were ultrasonically treated for menthol extraction,
microscopy results indicated that there were two mechanisms
involved in extraction: (a) the diffusion of product through the
cuticle of peppermint glandular trichomes and (b) the exudation
of the product from broken and damaged trichomes (Shotipruk,
Kaufman, & Wang, 2001).
Acceleration in the extraction kinetics and improved
extraction yield of pyrethrine from pyrethrum was largely
attributed to ultrasonics increasing the intra-particular diffusion
of the solute, considered the rate limiting step (Romdhane &
Gourdon, 2002). If the substrate is dry then ultrasound may be
used to facilitate swelling and hydration and cause enlargement
of the pores of the cell wall (Vinatoru, 2001). Diffusion through
the plant cell walls, disruption and washing out of the cell
contents were also attributed to improved extraction perfor-
mance. The corresponding reduction in the size of the vegetal
material particles by ultrasound disintegration will increase the
number of cells directly exposed to extraction by solvent and
ultrasonic cavitation (Vinatoru, 2001). Intensive ultra-sonica-
tion can also serve the purpose of reducing the particle size in
tomato juice (Food Science Australia unpublished data).
As large amplitude ultrasound waves pass through a mass
media, cavitational bubble collapse can occur in close vicinity
or at the surface of the plant membranes causing microfractures
(Vinatoru, 2001). The occurrence of microfracture by ultra-
sound was demonstrated in soybean flakes (Haizhou et al.,
2004). Cavitation collapse can occur on the plant surfaces,
resulting in a micro-jet directed into the solid surface. Cavitation
at cell surfaces has the ability to punch holes through cell wall as
recently demonstrated with studies of bacterial cell sonication
(Ugarte-Romero, Feng, Martin, Cadwallader, & Robinson,
2006). Preferentially micro-jetting will occur onto hydrophilic
particle surfaces (Arora, Claus-Dieter, & Knud, 2004).
Variation in the extraction yield from different plant varieties
may result from structure, rheology (hardness of the seed
structure) or the compositional differences resulting in varying
degrees of susceptibility to ultrasound shock waves and like-
lihood that cavitation bubble will contact with the plant surface
causing micro-jetting (Haizhou et al., 2004). Factors such as
plant tissue turgor and the mobility of particles such as starch
granules within the cell cytoplasm can be expected to influence
ultrasound energy dispersion and extraction effectiveness
(Zhang, Niu, Eckhoff, & Feng, 2005).
In the study on supercritical fluid extraction enhancement by
ultrasound Balachandran et al. (2006) they were able to demon-
strate that the effectiveness of ultrasound was gained by the
increase in the superficial mass transfer and that effectiveness
declined sharply after the readily accessible surface solute had
been removed. However, by reducing the substrate particle size
major gains in extraction efficiency and extraction time reduc-
tion could be achieved.
Solvent selection is usually based on achieving high mole-
cular affinity between the solvent and solute. When ultrasound
is also applied the cavitation will be affected by the physical
properties of the solvent. Cavitation intensity decreases as
vapour pressure and surface tension are increased. Haizhou
et al. (2004) demonstrated this phenomenon in soybean oil
extraction where greater UAE was achieved by isopropanol
compared with hexane, the later having approximately 5-fold
higher vapour pressure.
4. Adjunct processes
During extraction, ultrasound may also achieve adjunct
processes, whereby the food extract, ingredient or product
functionality may be modified by physical and sonochemical
mechanisms. One such modification has been reported by
Cravotto, Binello, Merizzi, and Avogadro (2004) in rice bran
wax conversion to policosanol (common name for a mixture of
C24–C34 linear saturated fatty alcohols), a rich source of
nutrients and pharmacologically active compounds. Both the
first bran fraction from rice polishing and the discarded wax
from the manufacture of rice oil were convenient and profitable
starting materials for the production of policosanol.
In the date syrup industry, ultrasound was applied for im-
proving the quantity and quality of the syrup extraction. Entezari,
Nazary, and Khodaparast (2004) successfully optimized ultrasonic
processing conditions in laboratory trials which lead to a higher
extraction in a shorter time with improved physical quality of the
date syrup extract. Most importantly, the sonication significantly
decreased the microbial count in comparison to the conventional
method. This study also confirmed the presence of anti-microbial
substances in date fruit, and that ultrasonic waves can accelerate
The anti-oxidative activity provided by phenolic compounds
has been shown to inhibit the oxidation of low-density proteins
(Frankel, Waterhouse, & Teissedre, 1995). Resveratrol (trans-3,
5, 4′-trihydroxystilbene), a stilbene phyto-alexin, is a phenolic
compound possessing anti-oxidant activity. Resveratrol has
been shown to provide health-promoting activities such as
lowering the incidence of coronary heart disease and provide
cancer chemo-preventive activity (Frankel, Waterhouse, &
Kinsella, 1993; Jang et al., 1997). The combined use of ultra-
violet light and ultrasound treatments on peanut kernels was
reported (Rudolf & Resurreccion, 2005) for the elicitation of
trans-resveratrol, total phenolic compounds, and anti-oxidant
an 8-fold increase of trans-resveratrol as compared to untreated
control samples. It was also reported that the anti-oxidative
activityinstressed peanutswas negatively correlated with trans-
resveratrol concentration, indicating that as anti-oxidant activity
decreased trans-resveratrol concentration increased.
To potentially replace the conventional destructive extraction
process of menthol extraction from peppermint plants Shotipruk
et al. (2001) studied the feasibility of using ultrasound to extract
menthol from biologically viable peppermint plants (Mentha
xpiperita). The results showed that plants ultrasonicated for 1 h
at 22 °C in a standard 40 kHz ultrasonic bath released approx-
imately 17.8 μg of menthol per gram of leaf tissue (2% of total
product). The amount of menthol release increased with the
time of treatment and was greatly affected by the temperature of
the ultrasonic bath water. An increase from 2% to 12% of total
product was observed when the temperature was increased from
22 °C to 39 °C. When the temperature effects were isolated, the
mechanism of the product release was found to be that of
cavitation. The treated plants remained viable and were ready
for the subsequent ultrasound extraction after approximately
4 days of recuperation. However, the amount of product re-
leased was reduced in subsequent extractions. This study has
shown the possibility of using an online ultrasonic, non-des-
tructive extraction method to continuously release intracellular
plant metabolites from the plants while maintaining the plant's
The application of ultrasound treatment to yellow dent corn
at different points in the conventional wet milling process
enhanced starch separation, providing an increase in final starch
levels of 6.35 to 7.02% (Zhang et al., 2005). The starches
produced by ultrasonic treatments showed a significant increase
in whiteness and decrease in yellowness that were comparable
to starches produced by conventional wet milling. The ultra-
sound-treated starches exhibited higher paste viscosities. These
viscosity changes during ultrasound treatments to starch gra-
The intense ultrasound treatment which generated localized spots
of very high temperature and pressure might lead to configura-
tional modifications of the granular structure, which could be in
the forms of diffuse erosion or pitting of the starch granules as
earlier observed by Degrois, Gallant, Baldo, and Guilbot (1974).
The cork taint is one the major problem in wine corks.
Trichloroanisoles (TCA) a natural contaminant chemical during
processing of corks is responsible for wine spoilage. There is a
limited efficacy of conventional washing processes for removal
of TCA. The Ultracork process involving UAE of TCA,
followed by application of a silicone barrier coating has provi-
ded an improved approach to overcome cork taint (Rowe, 2003).
5. Industrial extraction application design
The use of ultrasound in food processing has been reviewed
by Mason, Paniwynyk and Lorimer (1996). Recently, the design
of ultrasound processing equipment has advanced to provide
industrially robust processing capability. Enabling design and
operational features have included; (a) automated frequency
scanning to enable maximum power delivery during fluctuation
of processing conditions, (b) non-vibrational flanges on sono-
trodes for construction of high-intensity inline flow-cells and
(c) construction of radial and hybrid sonotrodes to provide
greater range in application design and product opportunities.
Presently, 16 kW is the largest available single ultrasound flow-
cell, which can be configured in-series or in parallel modules.
Industrial ultrasound manufactures within the last 2 years have
promoted industrial processing capability for food extraction
applications (Hielscher, 2006).
Several ultrasound reactor designs have been described by
Chisti (2003) and Vinatoru (2001), the latter specifically for
industrial extraction of plant tissue. These included (a) stirred
ultrasound horn (sonotrode) directly immersed into stirred bath
or reactor, (b) stirred reactor with ultrasound coupled to the
vessels walls and (c) recycling of product from stirred reactor
through an external ultrasonic flow-cell. These configurations
may provide both intermittent and continuous ultrasound ex-
posure, from low intensity in a large volume reactor (0.01 to
0.1 W/cm3) to high intensity (1 to 10 W/cm3) in an external
flow-cell. Mixed frequency reactors have been shown to offer
advantages with respect to process efficiency and energy dis-
& Narayana, 2001; Tatake & Pandit, 2002; Feng, Zhao, Zhu, &
Mason, 2002; Delgadino, Bonetto, & Lahey Jr., 2002). Reactor
geometries that are asymmetrical and polygons preferably with
odd numbered sides using swept frequencies are also reported to
be more effective (Gogate, Mujumdar, Thampi, Wilhelm, &
Pandit, 2004; Puskas, personal communication).
Modern ultrasonic systems include automated frequency
scanning which adjusts operation of the system to the optimal
frequency to ensure that maximum power is transmitted to the
extraction vessel. The benefit of automated frequency scanning
as opposed to a fixed frequency was demonstrated by Romdhane
and Gourdan (2002) where the former achieved a 32% increase in
pyrethrine extraction and a 30% increase in power delivered to the
product. The presence of a dispersed phase contributes to the
ultrasound wave attenuation. The active sonication region in a
reactor is restricted to a zone located at the surface of the probe.
Where it is not a disadvantage to extract oily materials as
stable emulsions, ultrasound can be used to carry out aqueous
extraction of oily materials with yields of the order of 50%
(Food Science Australia, unpublished results).
reduced to as smaller particle size as practical without denaturing
the material to be extracted and commensurate with separation
from the solvent post extraction. If this is done very high yields
and extraction rates are possible with ultrasonic augmentation of
the extraction process (Balachandran et al., 2006).
The proposed benefits of UAE for the food industry include,
(a) overall, enhancement of extraction yield or rate, (b) en-
hancement of aqueous extraction processes where solvents
cannot be used (juice concentrate processing), (c) providing the
opportunity to use alternative (GRAS) solvents by improvement
of their extraction performance, (d) enable sourcing/substitution
of cheaper raw product sources (variety) while maintaining
bioactive levels and (e) enhancing extraction of heat sensitive
components under conditions which would otherwise have low
or unacceptable yields.
6. New opportunities for UAE in the food industry
There is an opportunity to capture new intellectual property
in the area of ultrasound processing particularly where the
technology can provide commercially attractive advantages and
outcomes unique to ultrasound processing. Ultrasound has the
unique capacity to both enhance extraction from substrates
while simultaneously encapsulating the extracted substance with
an encapsulate material in the extraction fluid by hydroxyl radical
initiated covalent bonding and microsphere formation. To suc-
higher reductive potential than the material being extracted and be
relatively more hydrophobic. Preferably a mixed frequency ultra-
sound field is used, a relatively low frequency to facilitate extrac-
tion and a higher frequency under independent amplitude control
to facilitate hydroxyl radical production for cross linking and
microsphere formation. Proteins are suggested encapsulants as the
sonochemistry and conditions favouring sphere development have
been established. Vessel geometries, frequency combinations and
frequency modulation to achieve the desired outcomes on a large
scale suitable for scale up to industrial application would need to
be explored and optimized.
State of the art in UAE can achieve worthwhile gains in
extraction efficiency and extraction rate, which if realised on
industrial scale would represent worthwhile economic gains.
Ultrasonic equipment engineering is such that it is commer-
cially viable and scaleable to consider industrial-scale ultrasonic
aided extraction. Potential exists for applying UAE for en-
hancement ofaqueousextractionand alsowhere organic solvents
can be replaced with generally recognised as safe (GRAS) sol-
vents. UAE can also provide the opportunity for enhanced ex-
traction of heat sensitive bioactive and food components at lower
processing temperatures. There is also a potential for achieving
simultaneous extraction and encapsulation of extracted compo-
nents to provide protection through the use of ultrasonics.
This work was supported by CSIRO - Food Science
Australia, Food Futures Flagship. This work was partially pre-
sented at Food innovation: Emerging Science, Technologies &
Application (FIESTA), 3rd Innovative Foods Centre Confer-
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