applications and opportunities for ultrasound assisted extraction

7/27/2019 Applications and Opportunities for Ultrasound Assisted Extraction

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Applications and opportunities for ultrasound assisted extraction

in the food industry A review

Kamaljit Vilkhu a,, Raymond Mawson a, Lloyd Simons a, Darren Bates b

a Ultrasonics Processing Group, Food Science Australia, 671 Sneydes Road, Werribee, VIC 3030, Australiab Innovative Ultrasonics Pty Ltd, P.O. Box 321, Noosaville, QLD 4566, Australia

Abstract

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 i nterest from an industrial point of vi ew, since the t echnology is a n 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.

1. Introduction

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 followingApplications 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

attempted under an EU Copernicus grant (ERB-CIPA-CT94-0227-

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 protected] (K. Vilkhu).
mailto:[email protected]://dx.doi.org/10.1016/j.ifset.2007.04.014mailto:[email protected]


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components to be extracted with respect to tissuestructures, (2) pre-

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, &

Mason, 2001). In tissues where the desired components are located

within cells, pre-ultrasoundtreatmentby size reductionto maximise

surface area is critical for achieving rapid and complete extraction

(Riera, Gols, Blanco, Gallego, Blasco, & Mulet, 2004; Balachan-

dran et al., 2006;Vinatoru, 2001). Where pre-hydration is necessary

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

hydrophobic character of the extraction medium. Thus it is possible

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

by Vinatoru (2001), Chemat, Lagha, AitAmar, Bartels, and Chemat

(2004), Haizhou, Pordesimo, and Weiss (2004), Balachandran et al.

(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

future opportunities.

2. Applications

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 cm2

the extractionyield 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.

Table 1

List of ultrasound assisted extraction studies from the literature on various food components

Product Ultrasound Process Solvent Performance Author

Almond oils Batch, 20 kHz Supercritical carbon

dioxide

30% increased yield or extraction

time reduction

Riera et al. (2004)

Herbal extracts (fennel, hops,

marigold, mint)

Stirred batch,

20 to 2400 kHz

Water and ethanol Up to 34% increased yield over stirred Vinatoru (2001)

Ginseng saponins Batch, 38.5 kHz Water, methanol

and n-butanol

3-fold increase of extraction rate Wu et al. (2001)

Ginger Batch, 20 kHz Supercritical carbon

dioxide

30% increased yield or extraction

time reduction

Balachandran et al. (2006)

Soy protein Continuous, 20 kHz,

3 W per gram

Water and alkali

(sodium hydroxide)

53% and 23% yield increase over

equivalent ultrasonic batch conditions

Moulton and Wang (1982)

S oy is ofla vones Bat ch, 24 kHz Wat er and sol vent U p to 15 % i ncr eas e in e xtr act ion e ffici enc y Rostagno et al. (2003)

Rutin from Chinese Scholar Trees Batch, 20 kHz Water and methanol Up to 20% increase in 30 min Paniwynk et al. (2001)

Carnosic acid from rosemary Batch, 20 and

40 kHz

Butanone and ethyl

acetate

Reduction in extraction time Albu et al. (2004)

Polyphenols, amino acid and

caffeine from green tea

Batch, 40 kHz Water Increased yield at 65 C, compared with 85 C Xia et al. (2006)

Pyrethrines from flowers Batch, 20 and

40 kHz

Hexane Increased yield at 40 C, compared with 66 C Romdhane and Gourdan

(2002)


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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.,

2004).

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

disruption of cell walls in soybean flakes (Haizhou et al., 2004) andcaraway 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

or extraction. These effects were identified under scanning electron

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 soyprotein 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

2.3.1. Polyphenols

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

characteristics colour and flavour in wine, and in pharmaceutical

industry for its benefits on human health (Brenna, Buratti, Cosio,

& Mannino, 1998). Polyphenols are associated with reduced risk

of cardiovascular disease by inhibiting in-vitro oxidation of low-

density lipoproteins possess anti-ulcer, anti-mutagenic, anti-

inflammatory activity and anti-carcinogenic properties (Flamini,

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 Sangiovesegrape 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

to the insufficient power of the solvent used (aqueous methanol) or

due to the degradation of samples during extraction process. Their

study was focused on the efficiency of supercritical fluid extraction

(SFE) rather than other methods used in the experiment. The


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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).

2.3.2. AnthocyaninsAnthocyanins 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

sap of mature cells in grape skin (Springett, 2001). The pigments

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 30750 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

extraction procedures (Cacace & Mazza, 2003). UAE of crushed

Shiraz and Merlot grapes by Food Science Australia showed 15

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, togetherwith 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

the UAE conditions for the recovery of tartaric and malic acid from

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 compoundsOver 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 4060% water

Table 2

Examples of bioactive ultrasound assisted extraction work completed at Food Science Australia

Extract target Product Solvent Process Processing conditions Improvement range (%)

Beta-carotene Carrot Aqueous Laboratory; 24 kHz, 207 W s ml1 Ambient 1525

Ethyl-acetate Laboratory; 24kHz, 2075 W s m1 Ambient 820

Polyphenols Red grape marc Aqueous Laboratory; 24 kHz, 2075 W s ml1 Ambient 1135

Polyphenols Black tea Aqueous Laboratory; 24 kHz, 8

10 W s ml1

Hot processing 90 C 6

18Polyphenols Apple Aqueous Laboratory; 40 kHz, 2075 W s ml1 Hot processing 80 C 6

Gingerol Ginger Supercritical carbon dioxide Laboratory; 20 kHz Pressure 160 bar 30


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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 wasattributed 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 activecomponent 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 glycanchitin 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 thesonochemical modification of two polysaccharides. Further

improvement in immunological as well as anti-tumour activi-

ties of these complexes were reported on animal trials.

UAE can enable extraction at lower temperatures, Xu, Zhang,

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, Rosngela 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 in which the solute can be trapped. However the efficiency

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

reactions.

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 causesimpingement 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 micrography on peppermint plant leaves and trichomes.

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


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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

C24C34 linear saturated fatty alcohols), a rich source of

nutrients and pharmacologically active compounds. Both the

first bran fraction from rice polishing and the discarded waxfrom 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

their effects.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

activity. A short exposure of ultrasound (4 min) to sliced peanuts

and further incubation for 36 h at ambient temperature resulted in

an 8-fold increase oftrans-resveratrol as compared to untreated

control samples. It was also reported that the anti-oxidative

activity in stressed peanuts was 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 g 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


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plant metabolites from the plants while maintaining the plant's

viability.

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 increasein 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-

nules in the slurry wereattributed to the phenomenonof cavitation.

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 duringprocessing 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 forindustrial 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-

tribution (Moholkar, Rekveld, & Warmoeskerken, 2000; Swamy

& 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 theextraction 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).

To improve effectiveness the material to be extracted should bereduced 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 radicalinitiated covalent bonding and microsphere formation. To suc-

cessfully accomplish this, the encapsulating material should have a

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.


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7. Conclusion

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 ultrasonicaided extraction. Potential exists for applying UAE for en-

hancement of aqueous extraction and also where 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.

Acknowledgement

This work was supported by CSIRO - Food ScienceAustralia, Food Futures Flagship. This work was partially pre-

sented at Food innovation: Emerging Science, Technologies &

Application (FIESTA), 3rd Innovative Foods Centre Confer-

ence held at Melbourne, Australia on 1617 October, 2006.

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