Encapsulation of herbal aqueous extract through absorption with ca-alginate hydrogel beads

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food and bioproducts processing 8 8 ( 2 0 1 0 ) 195–201

Contents lists available at ScienceDirect

Food and Bioproducts Processing

journa l homepage: www.e lsev ier .com/ locate / fbp

ncapsulation of herbal aqueous extract through absorptionith ca-alginate hydrogel beads

ng-Seng Chan ∗, Zhi-Hui Yim, Soon-Hock Phan, Rachel Fran Mansa, Pogaku Ravindraentre of Materials and Minerals, School of Engineering and Information Technology, Universiti Malaysia Sabah,8999 Kota Kinabalu, Sabah, Malaysia

a b s t r a c t

Encapsulation of herbal aqueous extract through absorption with ca-alginate hydrogel beads was studied. A model

herbal aqueous extract, Piper sarmentosum, was used in this study. The effect of process variables (i.e. alginate M/G

ratio, alginate concentration, extract concentration, bead size and bead water content) on encapsulation efficiency

and biochemical compounds stability were studied. The stability of biochemical compounds was evaluated by using

mass balance analysis and FT-IR spectroscopy. The results show that the encapsulation efficiency was mainly affected

by alginate M/G ratio and bead water content. In general, ca-alginate beads made of higher alginate M/G ratio or

dried to a lower water content were found to absorb significantly more aqueous extract. However, the beads made

of higher M/G ratio were less rigid after the absorption process. Besides, the mass balance analysis reveals that

the encapsulation process and material did not degrade the bioactive compounds, as the total antioxidant content

remained unchanged. This is well supported by the FT-IR analysis where the characteristic bands of chemical groups

remained unaltered. Interestingly, the beads made of lower alginate M/G ratio were found to have higher antioxidant

affinity. In conclusion, this study demonstrates the potential of using absorption process and hydrogel material for

encapsulation of herbal aqueous extract.

© 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Keywords: Encapsulation; Ca-alginate; Absorption; Herbal extract; Antioxidants; Piper sarmentosum

controlled-delivery, extending shelf-life, separating incompat-

. Introduction

he herbal-related products take into account herbs useds food or food additives, food supplements, traditionaledicines, etc. The World Bank has projected the global mar-

et for herbal products to grow from USD 200 billion in 2008o USD 5 trillion in 2050. In Malaysia alone, the herbal indus-ry was reported to be worth USD 2.5 billion and it is growingaster than the general economy at 10% a year (Kamarul, 2006).

A key factor for the rapid growth of the market is therowing knowledge and confidence of consumers in naturalroducts or medicines. Besides, some high profile reports onhe potential cures from plant such as Pacific yew (Taxus bre-ifolia Nutt.) for breast cancer and the Bintangor (Calophyllumpp.) for AIDS and tuberculosis (clinical trials and in vitro find-ngs) have created significant awareness amongst consumers

∗ Corresponding author. Tel.: +60 88 320 000; fax: +60 88 320 348.E-mail addresses: [email protected], [email protected] (E.Received 6 February 2009; Received in revised form 24 July 2009; Accep

960-3085/$ – see front matter © 2009 The Institution of Chemical Engioi:10.1016/j.fbp.2009.09.005

compounds of herbal plants such as antioxidants have shownto have multiple functional and remedial properties thatinclude anti-radical, anti-carcinogenic, reduction of oxidativestress, anti-inflammatory and cardio-protection (Owen et al.,2000; Kris-Etherton et al., 2004). In recent decades, some of thepopular herbal plants in Malaysia have also gained increasingattention from both industrial and academic sectors. Theseinclude Eurycoma longifolia, Piper sarmentosum, Labisia pumila,Andrographis paniculata, Orthosiphon stamineus and Centella asi-atica.

Encapsulation is defined as a process of confining activecompounds within a matrix or membrane in particulateform to achieve one or more desirable effects (Chan et al.,2009). From the standpoint of herbal products, encapsula-tion could achieve a number of desirable effects that includes

-S. Chan).ted 30 September 2009

ible compounds and improving final product qualities (Chanand Zhang, 2002, 2005; Shu et al., 2006; Kosaraju et al., 2006;

neers. Published by Elsevier B.V. All rights reserved.

cessing 8 8 ( 2 0 1 0 ) 195–201

Fig. 1 – Experimental setup of this study: (1) syringecontaining P. sarmentosum aqueous extract; (2) sieve; (3)cylinder; (4) blank ca-alginate beads; (5) cap; (6) connected

196 food and bioproducts pro

Deladino et al., 2008). For example, controlled-delivery couldenhance bioavailability of an active compound by customis-ing the release mechanism or rate in gastro-intestinal tract. Infact, a delivery system may be mandatory if direct consump-tion of a herbal active compound may cause interferenceswith the human body. In addition, encapsulation may pro-mote better product stability by isolating active compoundsfrom the detrimental effects of oxygen, moisture or incompat-ible compounds. Therefore, encapsulation could be a usefultechnological tool for the commercial sector to develop value-added products or to create product differentiation fromcompetitors.

Hydrogel is a commonly used material for encapsulationdue to its capability to absorb large amount of water or biolog-ical fluids. Among many materials, calcium-alginate hydrogelis the most widely used due to several advantageous fea-tures such as non-toxicity, biocompatible, easily produced;thermally and chemically stable (Chan et al., 2009). Sinceliquid herbal concentrates are normally prepared throughan aqueous extraction process, encapsulation could be per-formed through absorption by using pre-prepared ca-alginatehydrogel beads. The absence of published work on the encap-sulation of herbal aqueous extract by using this approach andthe possible interaction between the matrix materials andherbal active compounds have led to the motivation to carryout this work.

In this study, an aqueous extract of P. sarmentosum wasused as the model herbal fluid. P. sarmentosum is one of themost abundant and widely used traditional herbal medicinesin this region. The effect of process variables (i.e. alginate M/Gratio, alginate concentration, extract concentration, bead sizeand bead water content) on encapsulation efficiency was stud-ied. The effect of encapsulation on antioxidant and chemicalstability was evaluated by using mass balance and Fouriertransform infrared analysis respectively.

2. Materials and methods

2.1. Materials

Sodium alginates of high guluronic acid content (ManugelGHB), denoted as high-G and high mannuronic content(Manugel DH), denoted as high-M were obtained from ISPTechnologies Inc., UK. P. sarmentosum aqueous extract was pre-pared and supplied by Furley, Malaysia.

2.2. Preparation of blank beads and aqueous extract

The experimental design of this study is shown in Table 1.Sodium alginate solution was prepared to the desired con-centration with deionised distilled water. The solution wasextruded through a flat tip and allowed to drip into a gelationbath containing calcium chloride 1.5% (w/v) (Mallinckrodt,USA). The ca-alginate beads were then hardened for 4 h. Differ-ent sizes of beads were produced by varying the tip diameter.The beads were air-dried to obtain lower water content, ifrequired.

The herbal aqueous extract was kept at 4 ◦C upon receiptand it was used directly, unless specified. Different concentra-tions of aqueous extract were prepared by diluting the originalextract (1×) with deionised distilled water on a mass basis.

to an air compressor; (7) encapsulated P. sarmentosum; (8)universal bottle; (9) residual extract.

2.3. Encapsulation of herbal aqueous extract

The experimental setup of this study is shown in Fig. 1. Blankca-alginate beads were first prepared by using an extrusionmethod described by Chan et al. (2009). The beads were thenbriefly dried to remove the free water. One gram of beads wasloaded into a cylinder followed by injection of 2 g of aqueousextract. The cylinder was gently tapped until a uniform pack-ing was achieved. The beads were immersed in the aqueousextract and they were left in a dark cabinet for 1 h. Subse-quently, the residual extract was withdrawn with the help ofan air compressor. The overall encapsulation efficiency wascalculated based on the mass of extract absorbed (g) by 1 g ofblank ca-alginate beads, as shown in Eq. (1):

overall encapsulation efficiency(

g extractg beads

)= mEb

mb(1)

where mEb is the mass of extract absorbed by beads (g) and mb

is the mass of beads (g).

2.4. Analysis of antioxidant content

Antioxidant content of herbal extract in ca-alginate beads andresidual extract was determined by using the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) colorimetric method as described byZhou et al. (2004). Ascorbic acid (Sigma, USA) was used asthe reference. Antioxidant stability was determined by usinga mass balance analysis based on the antioxidant content, asshown in Eq. (2):

sum of antioxidant mass fractions =(

mAOXb

mAOXo

)+

(mAOXr

mAOXo

)

(2)

where mAOXb is the mass of antioxidant in beads (mg), mAOXo

is the original mass of antioxidant (mg) and mAOXr is the mass

If the sum of the two fractions is about one, it indicates nosignificant degradation of antioxidant.

food and bioproducts processing 8 8 ( 2 0 1 0 ) 195–201 197

Table 1 – Experimental design of this study.

No Alginatetype

Alginate concentration(%, w/v)

Bead diameter(mm)

Bead watercontent (%)

Extract to beadratio (w/w)

Extractstrengtha

1 2High-G 3 2.2 100 2 1×High-M 4

5

2

High-G 2 1.9 100 2 1×High-M 2.2

3.3

3 25High-G 2 2.2 50 2 1×High-M 75

100

4 0.25×High-G 2 2.2 100 2 0.50×High-M 0.75×

1×

tract.

2

Fewtfiaa4

2

TvTs

3

3

Fehttaelect

btttaha

a 1× designates original concentration of P. sarmentosum aqueous ex

.5. Analysis of chemical stability

ourier transform infrared (FT-IR) spectra of aqueous extract,ncapsulated extract and extract released from alginate beadsere generated by using the Nicolet 5700 FT-IR spectrome-

er (Thermo Electron Corporation, USA). The samples wererst mixed with potassium bromide powder (Sigma, USA)t 5% (w/w) and the mixture was then laminated by usingpellet mold. The wave number used was in the range of

000–600 cm−1.

.6. Statistical analysis

he experiments were repeated at least twice and the meanalues were calculated by using Microsoft Office Excel 2007.he standard deviations of the mean values were also pre-ented.

. Results and discussion

.1. Overall encapsulation efficiency

ig. 2a–d shows the effect of process variables on the overallncapsulation efficiency of ca-alginate beads. In general, theigh-M beads showed higher encapsulation efficiency thanhat of the high-G beads (0.78 ± 0.18 and 0.26 ± 0.06 g/g, respec-ively). The alginate concentration, the extract concentrationnd the bead size did not show clear effect on the overallncapsulation efficiency. On the other hand, the beads withower water content were found to have higher encapsulationfficiency for both types of alginates. The encapsulation effi-iency of the beads improved 2- to 4-fold when they were driedo a quarter of their original mass.

In this study, the physical and chemical properties of theeads were found to have major influence on the encapsula-ion efficiency. The effect was evident when the beads made ofwo different types of alginates, were compared. It was foundhat the size of the high-G alginate beads remained unchanged

The swelling capability of the high-M beads could be causedby two factors. It is generally known that beads made ofhigh-M alginate are elastic and they are susceptible to chelat-ing agent that could destabilise the gel network. Since aherbal extract contains numerous biochemical compounds, itis speculated that some could act as chelating agents. Thisspeculation is supported by the fact that the high-M beadsbecame more fragile after encapsulation. In addition, theresidual extract was found to be more viscous than the orig-inal extract. This indicates partial dissolution of gel network.In comparison, the high-G beads did not show significantswelling and they remained rigid after encapsulation.

Another important factor that influenced the overallencapsulation efficiency was the bead water content. It isknown that a hydrogel contains a large amount of water. Inthis case, the removal of water from the hydrogel matrix wasfound to promote the absorption of extract by the beads. Onthe other hand, drying was found to have different effects onthe beads made from the two types of alginates (Fig. 3). Thehigh-M beads shrunk to a greater extent than that of the high-G beads when dried to a same water content. In addition, theswelling capability of the high-M beads was clearly reducedat a drier state. However, an opposite effect was observed forthe high-G beads. This explains the improved encapsulationefficiency of the beads.

3.2. Antioxidant and chemical stability

In this study, the antioxidant stability was determined througha mass balance method based on the antioxidant contentin ca-alginate beads and residual extract, compared to thatof original extract. In general, the total antioxidant contentremained unchanged as the sum of the mass fractions wasabout one (Fig. 4). The mass fractions of antioxidant found inthe high-M and high-G beads were about 0.3–0.4 and 0.2–0.3respectively and the fractions were not affected by the alginateconcentration, the extract concentration and the bead size. Itwas also found that the high-G beads with a lower water con-tent contained higher antioxidant mass fractions (up to 0.45)

In addition, the chemical stability of herbal extract wasanalysed by using a Fourier transform infrared spectroscopy.

198 food and bioproducts processing 8 8 ( 2 0 1 0 ) 195–201

Fig. 2 – Effect of (a) alginate concentration, (b) bead water contenencapsulation efficiency.

Fig. 3 – Effect of drying and encapsulation on beaddiameter.

Table 2 – Effect of encapsulation on the physical properties of b

High-G beads

Swelling No obvious swelliRigidity Remained rigidViscosity of residual extract No obvious chang

t, (c) extract concentration and (d) bead diameter on

The characteristic bands of extract encapsulated within theca-alginate beads (Fig. 5a) and that released from the beads(Fig. 5b) were compared to the original extract. In general, thebands remained unaltered and they can be assigned as follows(ALS Infrared Beamlines, 2009; Bhatt and Ray, 1998): conju-gated C C or C O stretching vibrations at 1610 cm−1, aromaticring vibrations at 1500–1600 cm−1, methyl group vibrations at1380 cm−1, C O C vibrations of esters at 1240 cm−1, C OHstretching vibrations of secondary cyclic alcohols at 1070 cm−1

and CH out-of-plane bending vibrations at 760 and 625 cm−1.Nevertheless, the hydrogel material could have minor

effects on the signal strength. For example, the absorbancesof encapsulated extract at 918 and 1237 cm−1 are absent orweaker when compared to the original extract (Fig. 5a). How-ever, the signals reappear in the spectra of the extract releasedfrom the hydrogel matrix (Fig. 5b). This indicates that the sig-nals could have been shielded by the hydrogel matrix. On theother hand, it is noteworthy that several new bands appear at

eads and aqueous extract.

High-M beads

ng Swelled to more than 6% in diameterLess rigid

e Became more viscous

food and bioproducts processing 8 8 ( 2 0 1 0 ) 195–201 199

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cn7

cs1to2siwo

Fig. 4 – Mass fractions of antiox

haracteristic bands of alginate that correspond to the man-uronic and guluronic acid blocks are in the range between80 and 1100 cm−1 (Pereira et al., 2003; Leal et al., 2008).

Plant extracts normally contain numerous biochemicalompounds such as alkaloids, amides, prophenylphenols,teroids, hydrocinnamic acid and oxalic acid (Masuda et al.,991). These phytochemical compounds could be an impor-ant source of natural antioxidants and their efficacy couldnly be conferred when they are consumed together (Liu,004). Therefore, the activity and content of these compoundshould be preserved during processing. In general, this study

ith ca-alginate beads did not change the biochemical profilef P. sarmentosum extract. Although some chemical interac-

t in beads and residual extract.

tions (i.e. chelation) could have occurred between the herbalextract and the hydrogel, the reaction did not affect the bio-chemical compounds of the extract. This is clearly shown bythe unaltered FT-IR spectra of the encapsulated herbal extract.The chemical interactions may be caused by other compounds(i.e. metal ions) that were present in trace amounts sincethe extract was provided in a crude form. The finding is ingood agreement with a previous work where no chemicalinteraction was found between a plant-derived essence (i.e.Azadirachta indica A. Juss.) and an alginate-based hydrogelmatrix (Kulkarni et al., 2000). Therefore, it can be deduced

200 food and bioproducts processing 8 8 ( 2 0 1 0 ) 195–201

Fig. 5 – FT-IR spectra of P. sarmentosum extract (a)

Table 3 – Antioxidant affinity of ca-alginate beads.

High-G beads High-M beads

Mean ± s.d. Mean ± s.d.

Alginate concentration (%, w/v)2 2.54 0.52 0.82 0.093 2.12 0.55 0.94 0.044 1.50 0.34 0.89 0.155 1.78 0.41 0.76 0.04

Extract or strength0.25× 1.99 0.11 1.25 0.060.50× 1.98 0.34 1.05 0.060.75× 1.85 0.35 0.95 0.121.0× 2.54 0.52 0.82 0.09

Bead diameter (mm)1.9 2.79 0.41 0.93 0.022.2 2.54 0.52 0.82 0.093.3 2.36 0.39 1.36 0.06

Bead water content (%)25 0.82 0.02 0.40 0.0350 1.23 0.17 0.50 0.0475 1.56 0.34 0.52 0.02

Encapsulation of a model herbal aqueous extract, P. sarmen-

encapsulated in beads and (b) released from beads.

3.3. Antioxidant affinity

In this study, the ratio of antioxidant content in the beads tothe theoretical amount (i.e. based on the original antioxidantcontent in the extract absorbed by the beads) was calcu-lated (see Table 3). It was found that the antioxidant in thehigh-G beads did not correspond to the theoretical amountsince the beads contained 1.5- to 3-fold more antioxidant thanexpected. However, the antioxidant found in the high-M beadswas close to the theoretical amount. The ratio was also foundto decrease with lower water content regardless of the alginatetype.

In brief, the ratio indicates the capability of ca-alginatehydrogel to attract and to concentrate antioxidant of a herbalaqueous extract. This capability could be termed as ‘antiox-idant affinity’. Similar to the encapsulation efficiency, theantioxidant affinity was also found to be influenced by thechemical and physical properties of ca-alginate beads. Theresults indicate that the guluronic acid content of ca-alginatebeads could play a role in accumulating antioxidant withinthe hydrogel matrix. In addition, it was found that water isa requirement to achieve high antioxidant affinity as it couldchange the physicochemical properties of hydrogel beads. Itwas reported that alginate-based materials (e.g. ca-alginatebeads and algal biomass) had varying biosorption capacitiesfor different metallic cations and the mechanisms involved

100 2.54 0.52 0.82 0.09

work is required to ascertain the mechanism for antioxidantaffinity of ca-alginate hydrogel.

3.4. Comparison with other encapsulation methods

Previous studies have shown that the spray-drying methodcould be used to encapsulate herbal compounds such aslycopene, olive leaf extract, Amaranthus betacyanin extracts, �-carotene, d-Limonene and procyanidins (Desobry et al., 1997;Cai and Corke, 2000; Kosaraju et al., 2006; Shu et al., 2006). Thismethod is popular because it is economical and it can achievehigh productivity. However, the use of high processing tem-perature was found to cause degradation of active compounds(Desobry et al., 1997; Cai and Corke, 2000; Kosaraju et al., 2006;Shu et al., 2006). Therefore, this method may not be suitablefor encapsulation of heat-sensitive compounds.

Encapsulation of herbal compounds within hydrogel beadshas also been performed by using the classical direct-extrusion method. A polymeric solution containing an activecompound is extruded through an orifice and the dropletsformed are allowed to fall into a gelling solution. Although themethod is simple, many studies have reported low encapsu-lation efficiency of water soluble compounds due to diffusionof the compounds to the gelling solution (Moses et al., 2000;Kulkarni et al., 2000). We have subsequently conducted anexperiment to verify this findings. By using the same herbalextract and encapsulation materials, it was found that themaximum encapsulation efficiency of the direct-extrusionmethod was about 0.14 g/g. The result is in good agreementwith the finding of Kulkarni et al. (2000) where the encapsula-tion efficiency of liquid pesticide was found to be in the rangeof 0.074–0.267 g/g. In comparison, the absorption method gave2-6 times higher encapsulation efficiency than the direct-extrusion method.

4. Conclusion

tosum, through absorption with ca-alginate beads has beendemonstrated. Depending on the encapsulation objective, a

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uitable encapsulation process and material should take intoonsideration the encapsulation efficiency, stability of bio-hemical compounds and the final particle qualities. In thistudy, it was found that these criteria were closely relatedo the physicochemical properties of ca-alginate beads. Inddition, the encapsulation method and material were foundo have no interaction with the biochemical compounds ofhe extract. Further analysis shows that the high-G beadsad higher antioxidant affinity than the high-M beads. It isnvisaged that this simple and effective process can be eas-ly adopted for industrial production of encapsulated herbalroducts.

omenclature

Eb mass of extract absorbed by beads (g)

b mass of beads used (g)

AOXb mass of antioxidant in beads (mg)

AOXo original mass of antioxidant (mg)

AOXr mass of antioxidant in the residual extract (mg)

cknowledgements

he authors thank the Ministry of Science, Technology andnnovation, Malaysia for the financial support through the E-cience Project (SCF0038-IND2007). The authors also thankhe colleagues and collaborators who have contributed to theevelopment of this work.

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