Innovative Food Science and Emerging Technologies xxx (2014) xxx–xxx
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Innovative Food Science and Emerging Technologies
j ourna l homepage: www.e lsev ie r .com/ locate / i fset
An integrated process for utilization of pomegranate wastes — Seeds
Eleni Kalamara a, Athanasia M. Goula a,⁎, Konstantinos G. Adamopoulos b
a Department of Food Science and Technology, School of Agriculture, Forestry and Natural Environment, Aristotle University, 541 24 Thessaloniki, Greeceb Department of Chemical Engineering, School of Engineering, Aristotle University, 541 24 Thessaloniki, Greece
In this work, a newmethod for pomegranate seeds application was developed based on the ultrasound-assistedextraction of seed oil and its subsequent encapsulation by spray drying. Extraction temperature, solvent/solidratio, amplitude level, and pulse duration/pulse interval ratio were the factors investigated with respect to ex-traction yield. Ultrasound was sound to increase extraction yield, but mainly to shorten the treatment time byover 12 times. Different materials were used as encapsulating agents. Ratio of core towall material, inlet air tem-perature, drying air flow rate, and feed solids concentration were the factors investigated with respect to encap-sulation efficiency. The resulting microcapsules were evaluated in terms of moisture content, bulk density, andrehydration ability. The optimum operating conditions were found to be: wall material, maltodextrin/Tween80; ratio of core to wall material, 0.23; inlet air temperature, 150 °C; drying air flow rate, 22.8 m3/h; feed solidsconcentration, 30% (w/w).Industrial relevance: Pomegranate seeds, a by-product of pomegranate juice and concentrate industries, present awide range of pharmaceutical and nutraceutical properties. Therefore, the seeds could have more beneficial ap-plications in food industries instead of being used as animal feed or in commercial cosmetic products. In thiswork, a newmethod for pomegranate seeds applicationwas developed based on the ultrasound-assisted extrac-tion of seed oil and its subsequent encapsulation by spray drying.
Food processing wastes have long been considered as a matter oftreatment, minimization, and prevention due to the environmentaleffects induced by their disposal. Nowadays, food wastes account as asource of valuable nutraceuticals (Schieber, Stintzing, & Carle, 2001;Sonja, Canadanovic-Brunet, & Cetkovic, 2009). The renaissance ofnutraceuticals from agricultural by-products is realized due to theexistence of methodologies, which allow not only the recovery, butalso their reutilization inside foods. Production is principally conductedin 5 steps: macroscopic pretreatment, macro- and micro-moleculesseparation, extraction, purification, and nutraceuticals formation(Galanakis, 2012). Thereby, classic processing technologies and specificmethodologies have been developed tomeet the goals of each recapturestep (Galanakis, 2013).
Pomegranate (Punica granatum L.) is one of the oldest known ediblefruits that contain the highest concentration of total polyphenolsin comparison with other fruits studied (Fazaeli, Yousefi, & Emam-Djomeh, 2013). Pomegranates are rich in aril, the percentage of which
, An integrated process for utrg/10.1016/j.ifset.2014.12.00
ranges from 50 to 70% of total fruit and comprises of 78% juice and22% seeds (Mohagheghi, Rezaei, Labbafi, & Mousavi, 2011). Accordingto Eikani, Golmohammad, and Homami (2012), pomegranate seedsshow average contents of about 37–143 g/kg of fruit. Oil content ofseeds varies from 12 to 20% of the seed on a dry weight basis (Al-Maiman&Ahmad, 2002). Pomegranate seed oilwas reported to presentbiological properties (Eikani et al., 2012), such as antioxidant and eicos-anoid enzyme inhibition properties (Qu, Pan, & Ma, 2010), immunefunction and lipid metabolism (Yamasaki et al., 2006), estrogene con-tent (Tong, Kasuga, & Khoo, 2006), skin photoaging inhibition effect(Park et al., 2010), lipoperoxidation and activity of antioxidant enzymes(Melo, Carvalho, Silva, & ManciniFilho, 2010), toxicological evaluation(Meerts et al., 2009), and protective effect against gentamicin inducednephrotoxicity (Asadpour, Boroushaki, & Sadeghnia, 2010).
Therefore, due to the above-mentioned pharmaceutical and nutra-ceutical properties of pomegranate seed oil and also due to the largeannual production of pomegranate seeds as a by-product of the juiceand concentrate industries, the seeds could have more beneficial appli-cations in food industries instead of beingused as animal feed or in com-mercial cosmetic products. Oneway to utilize the seeds is to extract theoil and use it in various food products.
Pomegranate seed oil can be extractedwith various solvents and ex-traction methods (Abbasi, Rezaei, Emamdjomeh, & Mousavi, 2008;
ilization of pomegranate wastes — Seeds, Innovative Food Science and1
Fig. 1. Particle size distribution of milled pomegranate seeds.
2 E. Kalamara et al. / Innovative Food Science and Emerging Technologies xxx (2014) xxx–xxx
Abbasi, Rezaei, & Rashidi, 2008; Eikani et al., 2012). Shortcomings ofexisting extraction technologies, like increase consumption of energy,high rejection of CO2 and more consumption of harmful chemicals,have forced the food and chemical industries to find new separation“green” techniques which typically use less solvent and energy, suchas ultrasound extraction (Chemat, Huma, & Khan, 2011). Extraction en-hancement by ultrasound has been attributed to the propagation ofultrasound pressure waves and resulting cavitation forces, where bub-bles can explosively collapse and generate localized pressure causingplant tissue rupture and improving the release of intracellular sub-stances into the solvent (Knorr, Ade-Omowaye, & Heinz, 2002). Accord-ing to Vilkhu, Mawson, Simins, and Bates (2008), the implosion ofcavitation bubbles generates macro-turbulence, high-velocity inter-particle collisions, and perturbation in micro-porous particles of thebiomass, which accelerates the eddy diffusion and internal diffusion.Moreover, the cavitation near the liquid–solid interface sends a fastmoving stream of liquid through the cavity at the surface, whereas cav-itation on the product surface causes impingement by micro-jets thatresult in surface peeling, erosion, and particle breakdown.
Ultrasound has been recognized for potential application in theextraction of herbals and oils (carnosic acid, ginseng saponins, carvone,limonene, antraquinones, amaranth oil, gingerols, soybeans oil, almondoil, apricot oil), proteins (soy protein), and bioactive compounds fromplant (polyphenols, anthocyanins, tartaric acid, aroma compounds,polysaccharides and functional compounds) or animal (chitin, lutein)materials (Vilkhu et al., 2008). Abbasi, Rezaei, and Rashidi (2008) andGoula (2013) extracted oil from pomegranate seeds applying ultrasonicirradiation. However, the effects of processing factors on the yield ofultrasound-assisted extraction have been studied only for substratesconsisting of particles having a single dimension (Goula, 2013) or for in-direct ultrasound extraction (Tian, Xu, Zheng, & Lo, 2013).
Pomegranate seed oil, like most edible oils, is chemically unstableand susceptible to oxidative deterioration, especially when exposed tooxygen, light, moisture, and temperature. That oxidative degradationmay result in a loss of nutritional quality and a development of unde-sired flavors, affecting shelf stability and sensory properties of the oil(Calvo, Hernandez, Lozano, & Gonzalez-Gomez, 2010). In the food pro-cessing field, microencapsulation techniques have been widely used toprotect food ingredients (i.e. flavors, essential oils, lipids, oleoresins,and colorants) against deterioration, volatile losses or interaction withother ingredients. Microencapsulation is the process by which the sen-sitive ingredients are packed within a coating or wall material. The wallmaterial protects the sensitive ingredient (core) against adverse reac-tion, prevents the loss of volatile ingredient, and controls release ofthe ingredient (Loksuwan, 2007).
Microencapsulation can be accomplished by different techniques.However, spray drying remains the dominant method for microencap-sulation, due to low cost and readily available equipment (Reineccius,2004; Shu, Yu, Zhao, & Liu, 2006). Different encapsulating materialsare used to enclose different core materials. Every encapsulation mate-rial has different encapsulating properties and release characteristics ofthe core materials. Hence, the selection of encapsulation materials foreach core product is an important step in the successful encapsulationprocess (Kim, Morr, & Schenz, 1996). In a previous work (Goula &Adamopoulos, 2012), pomegranate seed oil, obtained by the conven-tional extraction method of normal stirring, was encapsulated byspray drying with dehumidified air using skimmed milk powder aswall material. However, there is lack of publication regarding encapsu-lation of pomegranate seed oil using other encapsulating agents.
Thus, the objective of this work is to optimize a new method forpomegranate seed application in food industries based on theultrasound-assisted extraction of seed oil and its subsequent encapsula-tion by spray drying using differentwall materials. The effects of variousparameters on extraction yield and kinetics, on encapsulation efficien-cy/yield and on the main physical properties of the microcapsules(moisture content, bulk density, solubility) were studied.
Please cite this article as: Kalamara, E., et al., An integrated process for utEmerging Technologies (2014), http://dx.doi.org/10.1016/j.ifset.2014.12.00
2. Materials and methods
2.1. Materials
Fresh, good quality pomegranates (Wonderful variety) procuredfrom the local market were used. Pomegranate seeds were separatedfrom the juice and washed carefully to remove sugars and other adher-ingmaterials. The seeds were dried at 60 °C for 48 h and kept at−30 °Cuntil use. The seeds were ground in a laboratory mill (Type A10, Jankeand Kunkel, IKA Labortechnik, Germany) immediately prior to extrac-tion. The particle size distribution of the milled seeds shows a bimodaldistribution (Fig. 1), due to the two main anatomical parts (germ, seedcoat) of the seeds. The small size (~0.32 mm) may be associated withseed coats, whereas the size of about 0.58mmcould be attributed to ag-gregated germ particles.
2.2. Process for pomegranate seeds utilization
Fig. 2 presents the proposed integrated process for pomegranateseed application in food industries.
2.3. Ultrasound extraction
A 130 W, 20 kHz VCX-130 Sonics and Materials (Danbury, CT, USA)sonicator equipped with a Ti–Al–V probe (13 mm) was used forultrasound-assisted extraction in pulsed mode. A sample of pomegran-ate seeds was mixed with 100 mL hexane to produce different hexane/seed ratios. During the extraction process, the sample container washeld in a thermostat-controlled water bath.
The extracts were collected at 2, 5, 10, 20, 30, and 40 min. Theresulting extracts were evaporated using a rotary evaporator(Rotovapor R114, Waterbath B480, Büchi, Flawil, Switzerland) andthen were dried until a constant weight was reached. The extracted oilwas weighed and recorded as kinetic extraction data at that time. Theresults were the mean of two replications. Extraction yield, Y, (wt.%)was defined as the percent ratio of the total weight of oil extracted tothe sample weight.
The variation of extraction yield during the extraction process wasstudied with various (i) extraction temperatures (T) (20 °C, 65 °C), (ii)hexane/seed ratios (LS) (8/1, 20/1), (iii) amplitude levels (A) (30%,60%), and (iv) pulse duration/pulse interval ratios (DI) (3/4, 2/1). ThePlackett–Burman design was used to screen for significant factors.Twelve experimental runs were carried out and each independent var-iable was tested at high and low levels.
The solid–liquid extraction process can be considered as the reverseof an adsorption operation, therefore the second-order lawwas applied
ilization of pomegranate wastes — Seeds, Innovative Food Science and1
Fig. 2. Integrated process for pomegranate seed application in food industries.
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to experimentally evaluate the extraction rate (Rakotondramasy-Rabesiaka, Havet, Porte, & Fauduet, 2009). The general second-ordermodel can be written as (Pan, Qu, Ma, Atungulu, & McHugh, 2012):
dCt
dt¼ k � Ce−Ctð Þ2 ð1Þ
where k is the second-order extraction rate constant (L/g min), Ce is theequilibrium concentration of seed oil in the liquid extract (g/L) (extrac-tion capacity), and Ct is the oil concentration (g/L) in the liquid extract ata given extraction time t.
The integrated rate law for a second-order extraction under theboundary conditions t = 0 to t and Ct = 0 to Ct, can be written as anEq. (2) or a linearized Eq. (3) (Qu et al., 2010):
Ct ¼k � t � Ce
2
1þ k � t � Ceð2Þ
Please cite this article as: Kalamara, E., et al., An integrated process for utEmerging Technologies (2014), http://dx.doi.org/10.1016/j.ifset.2014.12.00
tCt
¼ 1k � Ce
2 þtCe
: ð3Þ
The initial extraction rate, h (g/L min), when t approaches 0, can bedefined as:
h ¼ k � Ce2: ð4Þ
2.4. Emulsification and spray drying
The wall materials used were maltodextrin (12 DE)/Tween 80 (99/1), skimmed milk powder, maltodextrin/skimmed milk powder (50/50), maltodextrin/whey protein isolate (95% whey protein) (50/50),maltodextrin/gum Arabic (50/50). The solution of coating matrix wasprepared by reconstituting and dispersing dried powder in 40 °C deion-izedwater and after coolingwasmixed overnight to enhance hydration.Pomegranate seed oil was emulsified into the hydrated coating materi-al. Homogenizationwas accomplished by using the VCX-130 Sonics andMaterials sonicator operating at an amplitude level of 40% for 30 min.
The homogenous emulsion was spray dried in a pilot scale spraydryer (Buchi, B-191, Buchi Laboratoriums-Technik, Flawil, Switzerland)with cocurrent regime and a two-fluid nozzle atomizer. The atomizerhad an inside diameter of 0.5 mm and used compressed air with aflow rate that was controlled by a variable area flow meter. Feed wasmetered into the dryer by means of a peristaltic pump. After passingthrough an electrical heater, inlet drying air flowed concurrently withthe feed spray in the main drying chamber. A cyclone air/powder sepa-rator was used to recover powder particles. Dried powder samples werecollected from the base of the cyclone.
In all experiments, the atomizer pressure and the feed ratewere keptat 5.0 ± 0.1 bar and 1.75± 0.05 g/min, respectively. The ratio of core towall material (c/w), the inlet air temperature (Ti), the drying air flowrate (Qa), and the feed solids concentration (S), were varied between1/9 and 1/2.3, 150 and 190 °C, 50 and 66% (17.5 and 22.8 m3/h), and10 and 30% w/w, respectively. A central composite design was appliedto determine the effects of the above parameters on i) encapsulation ef-ficiency, ii) encapsulation yield, and iii) microcapsules properties. Theeffects were studied at five experimental levels −a, −1, 0, +1, and+a, where a = 2n/4 and n is the number of variables.
2.5. Emulsion stability and droplet size
The method used to characterize the emulsion stability consisted ofplacing 100 mL of the emulsion before spray drying in a closed glass jarand keeping it in an oven for 16 h at 50 °C. After storage, the jar was re-moved from the oven and analyzed for surface oil (Beristain, Garcia, &Vernon-Carter, 2001).
Emulsion sampleswere poured intomicroscope slides, coveredwithglass cover slips and observed using an optical microscope (Axiolab A,Carl Zeiss GmbH, Jena, Germany) with 40× and 100× objective lenses.Ten images of each emulsion sample were analyzed with the public do-main software Image J v1.36b (http://imagej.nih.gov/ij/docs/faqs.html).The volume-surface mean diameter (d32) was calculated from 500droplets according to Eq. (5), considering spherical droplets.
d32 ¼X
nid3iX
nid2i
ð5Þ
where ni is the number of droplets with diameter di.
2.6. Encapsulation efficiency and encapsulation yield
Surface oil was determined by the method described by Varavinit,Chaokasem, and Shobsngob (2001) and Tan, Chan, and Heng (2005).Hexane (50 mL) was added to an accurately weighed amount (5 g) of
ilization of pomegranate wastes — Seeds, Innovative Food Science and1
Cavitation inside the cell and rupture/washing out
Enhance diffusionacross the cells
Pigment
Thin cell wall
Oil bodies
Fig. 3. Extraction yield of oil from pomegranate seeds as a function of time.
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powder followed by stirring for 10 min. The suspension was then fil-tered and the residue rinsed thrice by passing 20mL of hexane througheach time. The residual powder was then air dried for 30 min andweighed. The amount of surface oil (SO) was calculated by the differ-ence in weights of the capsules, before and after washing. The total oil(TO), which includes both the encapsulated oil (EO) and SO, was deter-mined using the Soxhlet method. A five-gram sample was extractedusing 180mL hexane for 8 h to ensure complete oil extraction. After ex-traction, the oil-exhausted powder was air-dried to constant weight.The amount of total oil (TO) was calculated by the difference in weightsof the capsules, before and after extraction. The encapsulation efficiency(EE) was calculated as follows:
EE ¼ TO−SOTO
� 100%: ð6Þ
The encapsulation yield (EY) was calculated by dividing the weightof microcapsules solid mass with the total amount of solid mass to bespray dried.
2.7. Characterization of the microcapsules
Moisture (M): The moisture content was determined by dryingin a vacuum oven at 105 °C until consecutive weighings, made at 2 hintervals, gave less than 0.3% variation. The moisture content wasexpressed in terms of the percent wet basis (w.b.) (100 × kg water/kgwet material).
Bulk density (BD): 2 g of powder were transferred to a 50 mLgraduated cylinder. The bulk density was calculated by dividing themass of the powder by the volume occupied in the cylinder (Goula &Adamopoulos, 2008).
Rehydration (R): The rehydration of the powder was carried out byadding 2 g of the material to 50 mL of distilled water at 26 °C. The mix-ture was agitated in a 100 mL low-form glass beaker with a Heidolphmagnetic stirrer (No 50382, MR 82, Heidolph Instruments GmbH & Co.KG, Schwabach, Germany) at 892 rpm, using a 2 mm × 7 mm stirringbar. The time required for the material to be completely rehydratedwas recorded (Goula, Adamopoulos, & Kazakis, 2004).
All analyses were done in triplicate and the averages of these tripli-cate measurements were recorded. Additional determinations werecarried out if the single values from the triplicates deviated by morethan ±1.5% from the triplicate mean.
2.8. Statistical analysis
The data were analyzed using the statistical software MINITAB(Release 13.32). Regression analysis was used to fit a full second orderpolynomial, reduced second order polynomials, and linear models tothe data of each of the variables evaluated (response variables). F valuesfor all reduced and linear models with an R2 N 0.70 were calculated todetermine if themodels could be used in place of full second order poly-nomials to predict the response of a variable to the independentvariables.
3. Results and discussion
3.1. Ultrasound-assisted extraction
In a previous work, Goula (2013) extracted oil from pomegranateseeds applying ultrasonic irradiation. However, the effects of processingfactors on the yield of ultrasound-assisted extraction have been studiedonly for substrates consisting of particles having a single dimension. Inthis work, milled seeds with a bimodal particle size distribution wereused. The direct ultrasound-assisted extraction had a yield varied be-tween 15.66 and 18.16 wt.%. In all experiments, the extraction yieldwas time-dependant and increased with extended ultrasonic times,
Please cite this article as: Kalamara, E., et al., An integrated process for utEmerging Technologies (2014), http://dx.doi.org/10.1016/j.ifset.2014.12.00
especially from 2 to 10 min, but slowly from 10 to 40 min (Fig. 3).Thus, the efficient extraction period for achieving maximum yield ofpomegranate seed oil was about 10 min. This can be attributed to thefact that extraction presents two stages; the first stage, which is charac-terized by a rapid rate, involves the penetration of the solvent into thecellular structure followed by the dissolution of soluble constituents inthe solvent, whereas the second one involves the external diffusion ofsoluble constituents through the porous structure of the residual solidsand its transfer from the solution in contact with the particles to thebulk of the solution (Goula, 2013). Ultrasonic wave could disrupt thecell walls, so larger contact area between solvent and material was cre-ated and more oil was appeared on the surface. However, this effectwould be increasingly weak on the inner cell walls as the distance is in-creased. Thus, the ultrasonic waves affect the mass transfer rate mainlyin the solvent penetration stage (Zhang et al., 2008). In addition, as thepomegranate seed cell walls ruptured, impurities such as insoluble sub-stances, cytosol, and lipids suspend in the extract, lowering the solvent'spermeability into cell structures (Liu, Xu, Hao, & Gao, 2009; Tian et al.,2013). Furthermore, target components also re-adsorb into the rup-tured tissue particles due to their relatively large specific surface areas,lowering yields of seed oil (Dong, Liu, Liang, & Wang, 2010).
Tian et al. (2013), who extracted pomegranate seed oil using the in-direct ultrasound method, reported that the oil yield increased signifi-cantly in the initial 30 min, then slowed until reaching equilibrium.They attributed this behavior to the fact that all pomegranate seed cellwalls cracked completely within the first 30 min from the acoustic cav-itation effect, leading to good penetration of the solvent into the cells(Hemwimol, Pavasant, & Shotipruk, 2006) and enhancing the transferof dissolved oil out of the solid structure (Paniwnyk, Beaufoy, Lorimer,& Mason, 2001). Zhang et al. (2008), who studied the ultrasound-assisted extraction of oil from flaxseeds, also reported that the effectof ultrasound is more effective in the first 30 min. A similar trend wasreported by Pan et al. (2012), who extracted antioxidants from the drypeels of pomegranate marc applying ultrasonic irradiation in continu-ous and pulsed modes.
Abbasi, Rezaei, Emamdjomeh, and Mousavi (2008a,b), Abbasi,Rezaei, and Rashidi (2008), Eikani et al. (2012), and Goula andAdamopoulos (2012) extracted pomegranate seed oil using differentextraction methods (Soxhlet, normal stirring, supercritical fluid extrac-tion, cold pressing) and reported much longer extraction times (up to50 times) to achieve lower or similar extraction yields. Accordingto Goula and Adamopoulos (2012), using the conventional stirringmethod, the yield was about 9.5% at extraction time of 4 h. The samepercentage was obtained for about 1 min of direct ultrasound assistedextraction. Eikani et al. (2012) reported that superheated hexane
ilization of pomegranate wastes — Seeds, Innovative Food Science and1
5E. Kalamara et al. / Innovative Food Science and Emerging Technologies xxx (2014) xxx–xxx
extraction (SHHE) showed a higher extraction efficiency (22.18%)with-in 2 h than Soxhlet extraction (17.94%) for 24 h and cold pressing(4.29%) for 72h,whereas according to Liu et al. (2009), supercritical car-bon dioxide extraction for 2 h achieved a yield of 15.72%. Tian et al.(2013), who extracted pomegranate seed oil using ultrasounds by theindirect method, obtained a higher efficiency of 25.11%. However, theextraction time (35 min) was about 3.5 times longer than this achievedin the present work (10 min). Ultrasonication can be applied in twoways: directly to the sample, or indirectly through thewalls of the sam-ple container using a water bath. In the direct method, the ultrasonicprobe is immersed into the solution and provides an ultrasonic powerthat is at least up to 100 times greater than that supplied by the bath,with sonication time usually 5 min or less (Pico, 2013).
Thus, ultrasound increased extraction yield, but mainly shortenedthe treatment time by over 12 times. Improved oil yields may be ex-plained in terms of cavitational effects caused by the application ofhigh-intensity ultrasound. As large amplitude ultrasound waves travelthrough a mass medium, they cause compression and shearing ofsolvent molecules resulting in localized changes in density and elasticmodulus. As a consequence, the initially sinusoidal compression andshear waves will at a finite distance from the ultrasonic transducer bedistorted into shock waves. The abrupt decrease in pressure at theedge of the saw tooth shaped ultrasonic wave in the negative pressurecycle generates small bubbles. These bubbles collapse in the positivepressure cycle and produce turbulent flow conditions associated withhigh pressures and temperatures (Li, Pordesimo, & Weiss, 2004;Mason, 1997; Price, White, & Clifton, 1995). In addition, ultrasound fa-cilitates swelling and hydration and cause enlargement of the pores ofthe cellwall (Vinatoru, 2001). Diffusion through the plant cellwalls, dis-ruption and washing out of the cell contents were also attributed toimproved extraction performance, whereas the reduction in the parti-cles size by ultrasound disintegration will increase the number of cellsdirectly exposed to extraction by solvent and ultrasonic cavitation(Vinatoru, 2001).
Fig. 4 presents the main effects of extraction temperature (T),hexane/seed ratio (LS), amplitude level (A), and pulse duration/pulseinterval ratio (DI) on extraction efficiency (Y). As it can be seen, in-creased extraction temperature (T) caused a decrease in extractionyield. This effect was also observed during ultrasound-assisted extrac-tion of oil from pomegranate seeds consisting of particles having asingle dimension. This unusual observation was attributed to the fact
6520
17.00
16.75
16.50
16.25
16.00
6030
17.00
16.75
16.50
16.25
16.00
T
A
Data Me
Fig. 4.Main effects of extraction temperature (T, °C), hexane/seed ratio (LS, −), amplitude le
Please cite this article as: Kalamara, E., et al., An integrated process for utEmerging Technologies (2014), http://dx.doi.org/10.1016/j.ifset.2014.12.00
that at higher temperature, the vapor pressure was higher and morebubbles were created, but they collapsed with less intensity due toa smaller pressure difference between inside and outside of bubbles(Hromádková, Kováčiková, & Ebringerová, 1999; Zhang et al., 2008).Another reason may be the surface tension decrease, as a result of tem-perature increase, affecting the bubble formation and collapse. More-over, the tendency of the dissolution of impurities will also increase,and some thermal labile constituents will decompose (Dong et al.,2010). According to Luque-Rodriguez, Luque De Castro, and Preez-Juan (2005), excessive heating gives rise to undesirable formation offree fatty acids from triacylglycerols during extraction. Chemat, Lagha,AitAmar, Bartels, and Chemat (2004), who compared conventionaland ultrasound-assisted extraction of carvone and limonene from cara-way seeds, reported that the activation energies for the ultrasound pro-cedure are much lower compared with those obtained by the controlprocedure, which explains the enhancement of extraction in ultrasoundexperiments at low temperatures.
Fig. 4 presents also the effect of hexane/seed ratio (LS) on extractionyield. As it can be seen, higher solvent/solid ratio resulted in largerconcentration gradient during the diffusion from solid into the solutionand, thus, in higher seed oil concentration in the extract and higheryield (Goula, 2013). As far as the amplitude level (A) is concerned, theextraction yield improved with increased A (Fig. 4). The type andnumber of bubbles created and collapsed are positively correlated tothe amplitude of ultrasonic waves traveling through the solvent; thecollapsing bubbles are believed to create high-shear gradients by caus-ing microstreaming which disrupts the cell walls (Jaki, Franzblau, Cho,& Pauli, 2006; Tian et al., 2013). This significantly accelerates the pene-tration of solvent into cells and the release of components from cellsinto the solvent, and simultaneously significantly enhances the masstransfer rate (Lou, Wang, Zhang, & Wang, 2010). As it can be seen inFig. 4, the extraction yield increased with decreased pulse duration/pulse interval ratio (DI) ratio, since a short interval indicates a shorttotal processing time, which does not allow sufficient time for complet-ing the mass transfer (Goula, 2013).
Using the Plackett–Burman design, the effect of four variables onextraction yield was analyzed. The adequacy of themodel was calculat-ed and the variables evidencing statistically significant effects werescreened via Student's t-test for ANOVA. Solvent/solid ratio, with aprobability value of 0.004, was determined to be the most significantfactor, followed by amplitude level (p = 0.010). The regression
208
2.000.75
LS
DI
ans
vel (A, %), and pulse duration/pulse interval ratio (DI, −) on extraction yield (Y, % w.b.).
ilization of pomegranate wastes — Seeds, Innovative Food Science and1
Fig. 5. Effect of core to wall material ratio (c/w,−), inlet air temperature (Ti, °C), and wallmaterial type on encapsulation efficiency (EE, %).
6 E. Kalamara et al. / Innovative Food Science and Emerging Technologies xxx (2014) xxx–xxx
coefficients were calculated and the equilibrium extraction yield data(Y) was fitted to a second order polynomial equation. The best modelwas found the following (Eq. (7)):
Y ¼ 14:5þ 0:103 � LS−0:00110 � T � LSþ 0:000505 � T � A−0:0106 � T � DI þ 0:0428 � LS � DI: ð7Þ
The coefficient of determination, R2, was 0.980 indicating that 98.0%of the total variability in the response could be explained by the specificmodel; whereas an adjusted R2 value of 0.964 revealed that there was agood agreement between experimental and predicted values of yield.The model F-value was 59.14 corresponding to a p-value of less than0.001, which along with the p-value for lack of fit indicated that themodel fits accurately the experimental data.
For all the factors studied, the plots of t/Ct versus t resulted in linearfunctions. The slopes and intercepts allowed the determination of ex-traction capacities (Ce) and extraction rate constants (k) from Eq. (3)and of initial extraction rates (h) from Eq. (4). Multiple regression anal-ysis was used to develop equations predicting the effect of all extractionfactors on kinetic parameters.
Ce ¼ 25:8−0:783 � LSþ 0:00932 � T � LS−0:00320 � T � A−0:387 � LS � DI þ 0:128 � A � DI R2 ¼ 0:952
� �
ð8Þ
k ¼ 8:11−1:59 � LS−0:00155 � T � Aþ 0:0723 � T � DIþ0:0219 � LS � Aþ 0:264 � LS � DI−0:104 � A � DI R2 ¼ 0:936
� �
ð9Þ
h ¼ 448−99:0 � LSþ 214 � DI þ 1:18 � LS � Aþ21:6 � LS � DI−8:14 � A � DI R2 ¼ 0:856
� �ð10Þ
Substituting Eqs. (8)–(10) into Eq. (3), a kineticmodel for predictingoil extraction from pomegranate seeds can be obtained. Even thoughthe empirical models (8)–(10) cannot account for the phenomenagoverning extraction processes, they could be used to determine the ef-fects of extraction temperature, hexane/seed ratio, amplitude level, andpulse duration/pulse interval ratio on the oil extraction capacity duringthe extraction process.
3.2. Encapsulation efficiency and encapsulation yield
During the stability study, it was found that some emulsions werekinetically unstable, with a small region of phase separation. As it canbe seen, the emulsions prepared with core to wall material ratio (c/w)and feed solids concentration (S) of 1/2.9 and 15% and 1/2.3 and 20%showed anoil upper phase separation. This observationmay be attribut-ed to the fact that, for the same feeds solids concentration, the higherthe oil load, the lower the wall material content and, thus, the lowerthe amount of wall material available to cover the oil droplets, leadingto faster droplets coalescence (Frascareli, Silva, Tonon, & Hubinger,2012). In addition, during the stability study, the emulsions preparedwith maltodextrin and whey protein isolate showed the formation ofa small separation layer and a foam phase, 24 h after their homogeniza-tion. A similar trend was reported by Carneiro, Tonon, Grosso, andHubinger (2013), who encapsulated flaxseed oil using different combi-nations of wall materials. According to Dickinson and Matsumura(1991), this resultmay have been caused by the unfolding of the proteinmolecules at the droplets surface, which would enhance protein–protein interaction leading to flocculation during emulsification andconsequently reducing the emulsion stability.
The volume-surface mean diameter varied from 3.62 to 7.94 μm anddecreased as the feed solids concentration increased. This observation issimilar to that reported by Frascareli et al. (2012), who attributed thiseffect to the emulsion viscosity. According to McClements (2005), vis-cosity enhancement reduces the rate at which particles sediment or
Please cite this article as: Kalamara, E., et al., An integrated process for utEmerging Technologies (2014), http://dx.doi.org/10.1016/j.ifset.2014.12.00
cream, resulting in better emulsion stabilization and, thus, avoidingdroplet coalescence. In addition, the mean droplet size increased asthe ratio of core to wall material increased. Beristain et al. (2001),who encapsulated cardamom essential oil with mesquite gum, men-tioned an opposite effect. This difference may be due to the fact thatthe amount ofmesquite gumwas in excess of that needed for fully coat-ing the droplets and preventing their coalescence.
The encapsulation efficiency, EE, varied between 49.56 and 99.47%.The wall material type, with a probability value of 0.021, was deter-mined to be the most significant factor, followed by drying air temper-ature (p = 0.031), and core to wall material ratio (p = 0.048). Theoptimum levels of each variable were determined to be as follows:wall material, maltodextrin/Tween 80; ratio of core to wall material,0.23; inlet air temperature, 150 °C; drying air flow rate, 22.8 m3/h(66%); feed solids concentration, 30% (w/w).
The encapsulation efficiency values decreased from a mean value ofabout 91.38% for maltodextrin/Tween 80, to 89.32%, 86.96%, 80.73% and76.75%, for skimmed milk powder, maltodextrin/skimmed milk
ilization of pomegranate wastes — Seeds, Innovative Food Science and1
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powder, maltodextrin/whey protein isolate, and maltodextrin/gum Ar-abic, respectively. Maltodextrins offer the advantage of excellent pro-tection to encapsulated core materials such as orange oil, milk fat, soyoil, and fish oil by altering the time and procedure of crust formation.However, lack any emulsifying properties. Therefore, it is desirable touse them in combinationwith a surface active biopolymer such as ester-ified modified starches, gum Arabic or milk proteins (Jafari, Assadpoor,He, & Bhandari, 2008). In the presence of the emulsifier Tween 80,maltodextrin provided the highest encapsulation efficiency. Accordingto Barbosa, Borsarelli, andMercadante (2005), addition of the emulsifierTween 80 to maltodextrin may increase the encapsulation efficiency by20–33%. Jafari, Assadpoor, He, and Bhandari (2008) reported that milkproteins change their structure during emulsification through unfoldingand adsorption at the oil–water interface and by forming resistant mul-tilayer around oil droplets and also with the help of repulsive forces,make significantly stable emulsions which are critical for encapsulationpurposes. Investigations have proven milk proteins to function wellfor encapsulating anhydrous milk fat, orange oil, soy bean oil,caraway essential oil, and fish oil (Jafari, Assadpoor, Bhandari, & He,2008). Thus, milk proteins, alone or in combinationwith carbohydrates,provided encapsulation efficiencies higher than that obtained bymalto-dextrin/gum Arabic. Considering the relatively high hydrophobicity ofproteins, the addition of the carbohydrates enhances the hydrophilicnature of the wall systemwhichmight limit accessibility of encapsulat-ed oil to the diffusion process (Bylaite, Venskutonis, & Mapdpieriene,2001). However, in the present study the addition of maltodextrin toskimmed milk powder has not increased the encapsulation efficiency.This phenomenon may be attributed to the fact that higheramounts of lactose in milk powder enhance the ratio of the capsulesolidification during the drying process and oil droplets are lockedin the dry matrix. A lower encapsulation efficiency was observedfor whey protein isolate as compared to milk powder. This observa-tion is similar to that reported by Baranauskiene, Venskutonis,Dewettinck, and Verhe (2006), who encapsulated oregano, citro-nella and marjoram flavors into milk protein-based matrices. Ac-cording to them, skimmed milk powder encapsulated oregano oilparticles exhibited well-formed spherically shaped, smoothed sur-faced particles that were free of visible cracks and pores, whereasthe surface of few whey protein concentrate capsules exhibitedsome holes and contained some more deep dents and wrinkles onthe surfaces.
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Fig. 6.Main effects ofwallmaterial type (WM,−), ratioof core towallmaterial (c/w,−), inlet air ton encapsulation yield (EY, %) (forWM, 1: MD/Tween, 2: SMP, 3: MD/SMP, 4: MD/WPI, 5: MD/
Please cite this article as: Kalamara, E., et al., An integrated process for utEmerging Technologies (2014), http://dx.doi.org/10.1016/j.ifset.2014.12.00
As it can be seen in Fig. 5, increasing inlet air temperature (Ti), en-capsulation efficiency increased. Air inlet temperature is directly relatedto themicrocapsule drying rate and the final water content. A high inletair temperature leads to a rapid formation of the semi-permeablemem-brane on the droplet surface, giving optimum corematerial retention. Asimilar trendwas reported by Bhandari, Dumoulin, Richard, Noleau, andLebert (1992) and Shiga et al. (2004), who observed higher retention ofcitral/linalyl acetate and shiitake flavor, respectively, at higher dryingtemperatures. On the contrary, Aburto, Tavares, and Martucci (1998)and Finney, Buffo, and Reineccius (2002) showed that the retention ofencapsulated material was independent on the air temperature.
As far as the ratio of core to wall material is concerned, increasingc/w from 1/9 to 1/3.7, encapsulation efficiency increased, whereas anopposite trendwas observedwhen core towall material ratio increasedfrom 1/3.7 to 1/2.3. The first effect is similar to that obtained by manyauthors, who refer that using the highest possible core concentrationthat provides high core retention in microcapsules is advantageous,because less wall material is needed, leading to increased yield andoutput, with positive economic impact (Jafari, Assadpoor, He, &Bhandari, 2008). On the contrary, oil loads higher than 1/3.7 resultedin higher surface oil content of the powder and lower encapsulation ef-ficiency. The same behaviorwas observed by Bertolini, Siani, andGrosso(2001), Hogan, O'Riordan, and O'Sullivan (2003), Tan et al. (2005), Ahnet al. (2008), and Frascareli et al. (2012). This trend can be attributed togreater proportions of core materials close to the drying surface, there-by shortening the diffusion path length to the air/particle interface(Jafari, Assadpoor, He, & Bhandari, 2008). The influence of core to wallmaterial ratio on efficiency can also be related to the emulsion viscosity,since lower oil load results in higher emulsion viscosity (Frascareli et al.,2012), which makes difficult the oil diffusion to the particle surface. Ingeneral, in most of the published studies, a typical core to wall materialratio of 1/4 is adopted and reported as being optimal for various wallmaterials, like gum Arabic and modified starches (Desai & Park, 2005;Jafari, Assadpoor, He, & Bhandari, 2008).
Fig. 6 presents the main effects of wall material type (WM), ratio ofcore to wall material (c/w), inlet air temperature (Ti), drying air flowrate (Qa), and feed solids concentration (S) on encapsulation yield(EY). The feed solids concentration, with a probability value of 0.018,was determined to be the only significant factor. In a spray drying sys-tem, smaller atomized droplets having less inertia do not reach radiallyoutward as far and as a result narrow spray cones are formed and
Fig. 8. Effect of inlet air temperature (Ti, °C) and feed solids concentration (S, % w/w) onmicrocapsules bulk density (BD, g/mL) (for WM, 3: MD/SMP).
8 E. Kalamara et al. / Innovative Food Science and Emerging Technologies xxx (2014) xxx–xxx
relatively little air is drawn inside (Liang & King, 1991). The trajectorieswill be similar in shape to those for bigger droplets, butwill be narrower(Goula & Adamopoulos, 2004a). As a result, droplets will strike thewall at lower parts of the drying chamber, where theirmoisture contentismuch lower and, as a result, residue formationwill be lower. Thus, theeffect of process variables on encapsulation yield may be based on theireffect on atomized droplets size, which usually increases as the feedconcentration or viscosity increases (Goula & Adamopoulos, 2004b).As it can be drawn from Fig. 6, decreasing feed solids concentration,thus decreasing atomized droplets size, encapsulation yield increased.
3.3. Microcapsules properties
Powder moisture content varied between 0.59 and 4.13% (Fig. 7).According to the ANOVA analysis of the optimization study, the inletair temperature (Ti) is the only factor that influenced significantly thepowder moisture content (p=0.009). An increase in inlet air tempera-ture up to values around 180 °C led to a decrease in moisture content.The greater the temperature difference between the drying mediumand the particles, the greater will be the rate of heat transfer into theparticles, which provides the driving force for moisture removal.When the drying medium is air, temperature plays a second importantrole. As water is driven from the particles in the form of water vapor, itmust be carried away, or the moisture will create a saturated atmo-sphere at the particle surface. This will slow down the rate of subse-quent water removal. The hotter the air, the more moisture it willhold before becoming saturated. Thus, high temperature air in the vicin-ity of the drying particles will take up the moisture being driven fromthe food to a greater extent than with cooler air. However, for tempera-tures above 180 °C, the increase in drying temperature led to a small in-crease in powder moisture content. This may be due to the faster crustformation, whichmakes difficult the water diffusion inside the particle.Hsu, Wu, andWalsh (1996) presented a theory based on the fact that askin is formed on the outer surface of spray droplets at high inlet dryingair temperature. This skin is destroyed when the inner water phase isevaporated and the outer surface collapse. Frascareli et al. (2012), whoencapsulated coffee oil, also observed this exception when the inlet airtemperature increases above 175 °C.
Powder bulk density ranged from 0.164 to 0.370 g/mL. The feedsolids concentration (S), with a probability value of 0.010, was deter-mined to be the most significant factor, followed by drying air temper-ature (Ti) (p = 0.046). Bulk density increased with an increase in feed
54321
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M (
% w
.b.)
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Fig. 7.Main effects ofwallmaterial type (WM,−), ratioof core towallmaterial (c/w,−), inlet air ton microcapsules moisture content (M, % w.b.) (forWM, 1: MD/Tween, 2: SMP, 3: MD/SMP, 4:
Please cite this article as: Kalamara, E., et al., An integrated process for utEmerging Technologies (2014), http://dx.doi.org/10.1016/j.ifset.2014.12.00
solids concentration and a decrease in air inlet temperature (Fig. 8).As small particles fill the voids between large ones, bulk density is af-fected by size and size range (Nath & Satpathy, 1998) and a higherproportion of small sizes increases density. Many authors refer thatdecreasing feed solids concentration, thus decreasing atomized drop-lets size, powder particle size decreases and bulk density increases(Frascareli et al., 2012; Hogan, McNamee, O'Riordan, & O'Sullivan,2001). However, the particle size depends upon the skin formationrate, in addition to the atomized droplet size. Generally, the higher thefeed solids content, the shorter the time required for particlefilm forma-tion (Bangs & Reineccius, 1990). According to Upadhyaya and Kilara(1984), higher viscosity resulting froman increase in feed concentrationprevents the circulatory movement in the drops leading to a rapid skinformation. The rapid particulate skin formationmay also affect the pow-der properties. According to Oakley (1997), the speed of crust forma-tion, highly dependent on drying rates, can affect the particle size anddensity. Particle size and particle density are assumed to increase withan increase in feed concentration (Nath & Satpathy, 1998). The effectof air temperaturemay be attributed to the fact thatwith increased tem-perature, evaporation rates were faster and products dried to a more
9E. Kalamara et al. / Innovative Food Science and Emerging Technologies xxx (2014) xxx–xxx
porous or fragmented structure. According toWalton (2000), increasingthe drying air temperature may produce a decrease in bulk and particledensity, since there is a greater tendency for the particles to be hollow.The former can be caused by particle inflation-ballooning or puffing andis particularly common in skin-forming materials.
Rehydration results are given in Fig. 9. According to the ANOVAanalysis of the optimization study, the feed solids concentration (S)is the only factor that influenced significantly the powder solubility(p = 0.016). Rehydration ability showed a decrease with a decrease infeed solids concentration. Generally, in a spray drying system the sizeof the dried particles depends on the size of the atomized droplets. De-creasing feed solids concentration, thus decreasing atomized dropletssize, powder particle size decreased (Goula & Adamopoulos, 2012)and the time required for the powder to be rehydrated increased.Large particles may sink, whereas small ones are dustier and generallyfloat on water, resulting in uneven wetting and reconstitution.
4. Conclusions
An integrated approach for utilization of pomegranate seeds is sug-gested based on ultrasound-assisted extraction of seed oil followed byits encapsulation using a suitable spray drying technique. The effect ofdifferent parameters on extraction yield and kinetics, on encapsulationefficiency and on the main physical properties of the microcapsuleswas studied. It was found that:
• The higher yields obtained in ultrasound-assisted extraction, com-pared to those in conventional extractionmethods, are ofmajor inter-est from an industrial point of view, since solvent amounts werereduced and extraction times shortened.
• Extraction yield increased with an increase in solvent/solid ratio andamplitude level and a decrease in extraction temperature and pulseduration/pulse interval ratio.
• A second-order kinetic model can describe the extraction processunder different ultrasound-assisted extraction parameters.
• Encapsulation efficiency decreased from a mean value of about91.4% for maltodextrin/Tween 80, to 89.3%, 87.0%, 80.7% and 76.8%,for skimmed milk powder, maltodextrin/skimmed milk powder,maltodextrin/whey protein isolate, and maltodextrin/gum Arabic, re-spectively. Efficiency increased with an increase in inlet air tempera-ture, whereas a core to wall material ratio of 1/4 was found optimalfor various wall materials.
Please cite this article as: Kalamara, E., et al., An integrated process for utEmerging Technologies (2014), http://dx.doi.org/10.1016/j.ifset.2014.12.00
• The inlet air temperature is the only factor that influenced significant-ly the powder moisture content. An increase in air temperature led toa decrease in moisture content.
• Powder bulk density increasedwith an increase in feed solids concen-tration and a decrease in air inlet temperature.
• Powder rehydration ability showed a decrease with a decrease in feedsolids concentration.
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