extraction kinetics and properties of proanthocyanidins from pomegranate peel

Wenjuan Qu*, Shuangqian Shi, Pingping Li, Zhongli Pan and Chandrasekar Venkitasamy

Extraction Kinetics and Properties ofProanthocyanidins from Pomegranate Peel

Abstract: With an objective of developing a safe andefficient method to extract proanthocyanidins productsfrom pomegranate peel for use in nutraceuticals or asfood additives, the effects of extraction parameters onthe production efficiency, product properties, and extrac-tion kinetics were systematically studied. The resultsshowed that both extraction temperature and water–material ratio had significant effects on the proanthocya-nidins content, but the yield was significantly affectedonly by temperature. The moderate temperature andwater–material ratio were beneficial to maintain highproanthocyanidins scavenging activity and good productquality. The second-order extraction and Arrheniuskinetic models were developed and successfully usedto predict the proanthocyanidins yield for givenconditions tested. Extraction temperature of 60°C,water–material ratio of 30:1 g g−1, and time of 10 minare recommended for proanthocyanidins extraction frompomegranate peel, which corresponded to the highestyield of 40.6 mg g−1 and content of 89.1 mg g−1 havinga scavenging activity of 31.5 g g−1, and an attractivereddish yellow color.

Keywords: pomegranate peel, proanthocyanidins, kinetics,scavenging activity

*Corresponding author: Wenjuan Qu, College of Food and BiologicalEngineering, Jiangsu University, 301 Xuefu Road Zhenjiang, Jiangsu212013, China, E-mail: [email protected] Shi, College of Food and Biological Engineering,Jiangsu University, 301 Xuefu Road Zhenjiang, Jiangsu 212013,China, E-mail: [email protected] Li, Key Laboratory of Modern Agricultural Equipment andTechnology, Ministry of Education, Jiangsu University, 301 XuefuRoad Zhenjiang, Jiangsu 212013, China; College of Biology and theEnvironment, Nanjing Forest University, 159 Longpan Road, Nanjing210037, China, E-mail: [email protected] Pan, Healthy Processed Foods Research Unit, USDA-ARSWestern Regional Research Center, 800 Buchanan Street, Albany,CA 94710, USA; Department of Biological and AgriculturalEngineering, University of California, Davis, One Shields Avenue,Davis, CA 95616, USA, E-mail: [email protected]

Chandrasekar Venkitasamy, Department of Biological andAgricultural Engineering, University of California, Davis, One ShieldsAvenue, Davis, CA 95616, USA, E-mail: [email protected]

1 Introduction

Proanthocyanidins are naturally occurring compoundsand are widely found in fruits, vegetables, flowers, bark,and seeds. They are a class of phenolic compoundsthat take the form of oligomers or polymers of polyhy-droxy flavan-3-ol units, such as (þ )-catechin and(−)-epicatechin [1]. Proanthocyanidins are antioxidantsand free radical scavengers which have preventiveeffects on cancers or anti-carcinogenic activities [2–5].Health promoting effects of proanthocyanidins are dueto their remarkably high scavenging activities [6, 7].Human consumption of proanthocyanidins is increasingbecause of the increased awareness on their potentialvalue as a health promoting agent. Pomegranates arecultivated and consumed in large quantities in Chinaand contain substantial amounts of proanthocyanidins[8, 9]. They are popularly consumed as fresh fruit, bev-erages (juice and wine), and other food products (jamsand jellies). Processing of one ton of fresh pomegranatefruit generates about 669 kg of by-products, containing78% of peel and 22% of seeds [10, 11]. The chromato-graphic profiles of pomegranate peel extract showedthat pomegranate peel had a high level of proanthocya-nidins [12]. Therefore, pomegranate peel has a greatpotential to be used for producing natural proanthocya-nidins which could be used as safe food additives ornutraceuticals.

Proanthocyanidins extraction efficiency and qualityare influenced by various factors such as temperature,solvent–solid ratio, and the type of solvent in the process[13, 14]. Therefore, it is important to investigate the effectsof these factors on extraction efficiency, antioxidantscavenging activity, and color of proanthocyanidinsextracted from pomegranate peel in order to develop an

doi 10.1515/ijfe-2014-0034 International Journal of Food Engineering 2014; 10(4): 683–695

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efficient and viable extraction process. The proanthocya-nidins extraction from pomegranate peel is a solid–liquidextraction process. Typical solid–liquid extraction mod-els that apply to the process include unsteady diffusion[15], film theory [16], empirical Ponomaryov equation [17],Peleg model [18], and Fick’s law of diffusion [19]. Thermalmodel of Arrhenius equation is commonly used to deter-mine the rate constant (k0) as a function of temperature(Ta) and activation energy (E) in thermally activatedprocess [20, 21]. However, no information is availableabout systematical studies conducted for extractionkinetics of proanthocyanidins from pomegranate peel.The development of kinetic model is very important fordesigning an efficient extraction process for productionof proanthocyanidins.

The goal of this study was to develop an environ-mentally friendly extraction method for producingproanthocyanidins products from pomegranate peel foruse in nutraceuticals or as food additives. Usuallyproanthocyanidins are extracted using organic solventsand other extraction techniques such as supercriticalcarbon dioxide extraction, subcritical water extraction,and microwave-assisted extraction [22–25]. Organic sol-vent extraction methods show higher proanthocyanidinsyields but they have their own disadvantages of insecur-ity in the health food and higher solvent usage costs. Thesupercritical carbon dioxide extraction is safer thanorganic solvent extraction due to green carbon dioxideas extractant, but, it needs high operation costs and has alow sample throughput. The safe subcritical water extrac-tion technology also gives a higher yield, but the extrac-tion system needs high production costs due to waterpreheating and certain pressure requirement. The micro-wave-assisted extraction is more effective than conven-tional techniques for the extraction of proanthocyanidinsdue to the reduction of extraction time, less solvent use,and increased amount of extracted proanthocyanidins.However, it is not suitable for industrial production dueto smaller raw material processing capacity. By consider-ing the economy and safety, water extraction with opti-mum influencing parameters has been recommended forproanthocyanidins production from pomegranate peel.Therefore, water, an environmentally friendly and naturalsolvent, was used for the extraction of proanthocyanidinsin this research. The objectives of this research were (a) todetermine the influence of extraction parameters such aswater–material ratio (W) and temperature (T) on theextraction efficiency and product properties of proantho-cyanidins, and (b) to develop and validate kinetic modelsfor predicting the proanthocyanidins yield under variousconditions.

2 Materials and methods

2.1 Materials and reagents

The dried pomegranate peel obtained from NanjingYoungmark Biobase Technologies Ltd (Nanjing, China)was ground into fine powder having particle size of< 40-mesh using a FC-160 mill (Shanghai TraditionalChinese Medicine Co., Ltd, Shanghai, China). The powderwas used as the raw material for the extraction ofproanthocyanidins in this research. The pomegranatepeel powder was packed in a sealed plastic bag andstored at 4°C until it was used.

The 2,2-diphenyl-1-picrylhydrazyl (DPPH) waspurchased from Sigma-Aldrich Company (Shanghai,China), and the (þ )-Catechin (of purity > 98%) wasobtained from the National Institute for Food and DrugControl (Beijing, China) and vanillin from GuangdongGuanghua Sci-Tech Co., Ltd (Guangdong, China).Methanol and hydrochloric acid (HCl) were purchasedfrom Sinopharm Chemical Reagent Co., Ltd (Shanghai,China).

2.2 Proanthocyanidins extraction

The proanthocyanidins extraction was performed usingdistilled (DI) water in a conical flask, which was stirredwith a stirrer bar at 1,200 rpm. During the extractionprocess, the conical flask was held in a thermostat-con-trolled water bath, and the flask was entirely coveredwith an aluminum-foil paper to prevent degradationand oxidative changes from light and oxygen. To deter-mine the effect of temperature, each sample with water–material ratio of 50:1 g g−1 was extracted at 25, 40, 60, 80,and 90°C for various times of 0.17, 0.33, 0.5, 1, 1.5, 2, 3, 4,6, 8, 10, and 20 min. To determine the effect of water–material ratio, five samples with 2, 2.5, 3.3, 5, and 10 g ofpomegranate peel were separately mixed with 100 g of DIwater to obtain the water–material ratios of 50:1, 40:1,30:1, 20:1, and 10:1 g g−1, respectively, and each samplewas extracted at 60°C for 0.17, 0.33, 0.5, 1, 1.5, 2, 3, 4, 6,8, 10, and 20 min.

The liquid extracts of all samples were separatedfrom the residue using TGL-16 centrifuge (Xiangyi Inc.,Changsha, Hunan, China) at 4°C for 5 min at 10,000 rpm.The proanthocyanidins in each of extracted sample wereanalyzed for yield, content, scavenging activity (expressedas DPPH scavenging activity), and color characteristics(L*, a*, b*, C*, H*, and ΔE* values).

684 W. Qu et al.: Extraction Kinetics of Proanthocyanidins from Pomegranate Peel



2.3 Development of kinetic models

The experimental data obtained from the proanthocyani-dins extraction process under all tested conditions in thisstudy did not meet the first-order dynamics model due tolow R2 (0.572–0.849). However, they satisfied the second-order kinetics with high R2 (>0.990). Therefore, the sec-ond-order kinetic model was applied to evaluate theextraction rate of proanthocyanidins, which is writtenas [25, 26]:

dCt

dt¼ kðCe � CtÞ2 ð1Þ

where k is the extraction rate constant (L g−1 min−1), Ceis the equilibrium concentration of proanthocyanidinsin the extract (g L−1), and Ct is the proanthocyanidinsconcentration in the extract at a given extraction timet (g L−1).

The integrated rate law for a second-order extractionunder the boundary conditions t¼0 to t and Ct¼0 to Ctcan be written as eq. (2) and as a linearized equation(eq. (3)) as follows:

Ct ¼ Ce2kt

1þ Cektð2Þ

tCt

¼ 1

kCe2 þ

tCe

ð3Þ

When t approaches 0, initial extraction rate (h, g L−1 min−1)can be written as:

h ¼ kCe2 ð4Þ

By rearranging eqs (3) and (4), Ct can be expressed as:

Ct ¼ tð1=hÞ þ ðt=CeÞ ð5Þ

Kinetic parameters h, Ce, and k were determined experi-mentally from the slope and intercept by plotting t/Ctagainst t (eq. (3)). It was assumed that the second-orderkinetic model could be applied to measure the influencesof variables (W and T) on extraction efficiency. Therefore,h, Ce, and k were related to these variables (W and T) andwere fitted by functional models, using Origin Pro 7.5SR1.

Arrhenius equation is used to describe the relationshipbetween extraction rate constant (k) and temperature (Ta),which is written as:

k ¼ k0 exp � 1;000ERTa

� �ð6Þ

where k is the extraction rate constant (L g−1 min−1), k0 isthe temperature-independent factor (L g−1 min−1), E isthe activation energy (kJ mol−1), R is the gas constant(8.314 J mol−1 K−1), and Ta is extraction absolute tempera-ture (K). The values of kinetic parameters k0 and E weredetermined by plotting ln(k) against 1,000/Ta.

2.4 Determination of yield and content ofproanthocyanidins and yield of extract

The actual mass of proanthocyanidins was determined bymultiplying the proanthocyanidins concentration in theextract with volume of extract. The proanthocyanidinsconcentration (Ct) in the extract was determined basedon a modified colorimetric method using (þ )-catechinas the standard [10]. About 1 mL of proanthocyanidinsextract was taken in a test tube of 20 mL and was mixedthoroughly with 3 mL vanillin solution in methanol (4%)and 1.5 mL HCl using a K-550-G vortex mixer (ScientificIndustries Inc., Bohemia, NY, USA). The mixed solutionwas held in a water bath at 25°C for 15 min, and then itsabsorbance was measured at 500 nm using a Unic 7200Spectrophotometer (Unocal Corporation, Shanghai,China). Blanks were prepared using DI water instead ofthe extract. The proanthocyanidins yield (mg g−1) andcontent (mg g−1) were calculated using a standard curveof (þ )-catechin (0.1–0.8 g L−1), using eqs (7) and (8):

proanthocyanidins yield ¼ 1;000CtVt

W1ð7Þ

proanthocyanidins content ¼ 1;000CtVt

W2ð8Þ

where Ct is the proanthocyanidins concentration in theextract at a given extraction time t (g L−1), Vt is thevolume of extract obtained at a given extraction timet (L), W1 is the dry mass of raw material (g), and W2 isthe dry mass of extract (g).

The dry mass of extract was determined with an ovendrying method by drying the extract to a constant weightat 105°C [27]. The yield of the extract was obtained by thecalculation of W2 divided by W1.

2.5 Determination of properties ofproanthocyanidins

Scavenging activity of proanthocyanidins was determinedusing the previously published method [10, 11, 28]. Higher

W. Qu et al.: Extraction Kinetics of Proanthocyanidins from Pomegranate Peel 685



values of DPPH scavenging activity indicate higher valuesof antioxidant capacity. In brief, the proanthocyanidinsextract was diluted to 40-fold using DI water prior toanalysis. About 60 μL of diluent was made to react with3 mL of DPPH solution in methanol (0.05 g L−1). Thesolution was mixed thoroughly using a vortex mixer andheld in a water bath at 25°C for 20 min. The absorbance ofsolution was measured at 517 nm using a Unic 7200Spectrophotometer. DI water was used as the control,and blanks were prepared by combining 60 μL of dilutedextract with 3 mL methanol. The DPPH scavenging activity(g g−1), referred to the gram of DPPH chemical per gramof proanthocyanidins [10, 11], was calculated using thefollowing equation:

DPPH scavenging activity ¼ nVt ½Cc � ðCs � CbÞ�CtVt

ð9Þ

where Ct is the proanthocyanidins concentration in theextract at a given extraction time t (g L−1), Vt is the volumeof extract obtained at a given extraction time t (L), Cc isthe DPPH concentration in control (g L−1), Cs is the DPPHconcentration in extract diluent (g L−1), Cb is the DPPHconcentration in blank (g L−1), and n is the dilution factorof extract which is 40 in this study.

Color characteristics were determined by using aChroma meter (DC-P3, Beijing, China) following the pre-viously reported method [29]. The equipment was set upin diffused illumination and calibrated first against ablank reference plate, and then against a white referenceplate before the actual measurements. The proanthocya-nidins extract of 3 mL was placed in a transparent glasscuvette on a white reference plate, and lightness (L*),redness (a*), and yellowness (b*) values were measured.From the Hunter values of a*, b*, and L*, the chroma(C*), {(a*2þ b*2)1/2}, hue angle (H*, °), (tan−1 b*/a*), andtotal color difference (ΔE*), {[(a*–a0)

2þ (b*–b0)2þ (L*–

L0)2]1/2} values were calculated. The color values of the

DI water were noted as a0, b0, and L0.

2.6 Statistical analysis

All weight and percentage values were reported on drybasis unless otherwise specified. All measurements weremade in triplicate for each sample. The mean (n¼ 3) ofvalues are presented in figures and tables. Data wereanalyzed by analysis of variance (ANOVA) using a SPSS14.0 software (SPSS Inc., Chicago, IL, USA). The differ-ences in the yields, contents, scavenging activities, andcolor characteristics of proanthocyanidins under different

temperatures, water–material ratios, and extraction timeswere compared using Duncan’s multiple range test withsignificance defined as p<0.05.

3 Results and discussion

3.1 Effect of extraction parameters onextraction efficiency

3.1.1 Effect of extraction temperature

Both the extraction temperature and time had signifi-cant effects on the proanthocyanidins yield and content(p<0.05) as shown in Figure 1A and 1B, respectively.The proanthocyanidins yield and content significantlyincreased during the first 3 min of extraction and thendisplayed a slow rate of increase between 3 and 10 min

0 5 10 15 205

10

15

20

25

30

35

40

45

50A

Proa

ntho

cyan

idin

s yi

eld

(mg

g–1)

Extraction time (min)

Extraction temperature (°C) = 25 40 60 80 90

0 5 10 15 2030

40

50

60

70

80

90

100

Proa

ntho

cyan

idin

s co

nten

t (m

g g–1

)



B

Figure 1 Yields and contents of proanthocyanidins extracted frompomegranate peel under different extraction temperatures andtimes with a water–material ratio of 50:1 g g−1




before reaching the equilibrium. The proanthocyanidinsyield significantly increased with the increase in extrac-tion temperature. A similar trend of higher extractionyield of proanthocyanidins at higher temperature wasreported in the proanthocyanidins extraction fromwinery by-products using subcritical water [24]. Thereason for this increased yield could be that the solubi-lity and diffusion coefficient of proanthocyanidins frommaterial increased at a high temperature [30]. Theproanthocyanidins content significantly increased at alower temperature, reached the highest value at 60°C,and then decreased as temperature continues to rise.The result indicated that the proanthocyanidins contentin the extract at the higher temperature was relativelylower. Similarly, Fischer et al. [31] reported that antho-cyanidins content in pomegranate (Punica granatum L.)juices and model solutions decreased with the increasedtreatment temperature and, therefore, the temperaturewas an important influencing factor for heat unstablesubstances. The low proanthocyanidins contents inthe extracts obtained from 80 and 90°C might be eitherdue to other ingredients of pomegranate peel that havealso been extracted along with proanthocyanidins ordue to the thermal instability of proanthocyanidins.The proanthocyanidins yields and contents in theextract obtained from all extraction temperatures of 25,40, 60, 80, and 90°C were reached the equilibrium valueat the same extraction time of 10 min. The correspond-ing equilibrium yields were 30.2, 36.3, 40.6, 42.2, and43.8 mg g−1, respectively, and equilibrium contents were72.5, 81.5, 89.1, 83.0, and 82.0 mg g−1, respectively.Therefore, the recommended temperature for extractionof proanthocyanidins is 60°C.

3.1.2 Effect of water–material ratio

Figure 2A and 2B shows the proanthocyanidins yield andcontent, respectively, under different extraction timesand water–material ratios at the extraction temperatureof 60°C. The water–material ratio had no significanteffect on proanthocyanidins yield (p>0.05) whereas ithad a significantly positive influence on proanthocyani-dins content and extract yield (p<0.05) in the extract.For example, the yields of extract were 443.8, 468.4,451.0, 447.3, and 454.5 mg g−1 under water–materialratios of 10:1, 20:1, 30:1, 40:1, and 50:1 g g−1 respectively,for extraction time of 20 min. Correspondingly, the yieldsand contents of proanthocyanidins were 35.5, 39.3, 41.0,41.3, and 40.5 mg g−1 and 80.0, 83.9, 90.9, 90.1, and89.1 mg g−1 for water–material ratios of 10:1, 20:1, 30:1,

40:1, and 50:1 g g−1, respectively. The statistical analysisof the data showed that only yield of extract andproanthocyanidins content were significantly affected bywater–material ratios. A similar report showed that theextraction of proanthocyanidins in Cortex cinnamomiincreased dramatically with the increased ratio ofliquid–solid [14]. Li et al. [32] also found that the extrac-tion efficiency of chlorogenic acid from Eucommia ulmo-dies Oliv. increased with the increase in solvent–sampleratio. This was because a higher water–material ratioresulted in a larger concentration gradient of proantho-cyanidins during the diffusion from the material into thesolution resulting in increased quantity of proanthocya-nidins being extracted from raw material. Although thedry mass of extract was increased at different water–material ratios, the proportion of proanthocyanidins inthe extract was rising. Therefore, the proanthocyanidinscontent was greatly increased with the increase in water–material ratio. Figure 2A and 2B reiterates that theproanthocyanidins yield and content were significantlyinfluenced by extraction time (p<0.05). Both the yield

0 5 10 15 205

10

15

20

25

30

35

40

45

50A


Water–material ratio (g g–1) = 10 20 30 40 50

0 5 10 15 2030

40

50

60

70

80

90

100B



Proa

ntho

cyan

idin

s yi

eld

(mg

g–1)

Proa

ntho

cyan

idin

s co

nten

t (m

g g–1

)

Figure 2 Yields and contents of proanthocyanidins extracted frompomegranate peel under different water–material ratios and extrac-tion times at a temperature of 60°C




and content of proanthocyanidins significantly increasedwith extraction time until 4 min and then showed slowrates of increase between 4 and 10 min before reachingthe equilibrium. The proanthocyanidins yields and con-tents obtained from different water–material ratios of10:1, 20:1, 30:1, 40:1, and 50:1 g g−1 reached their equili-brium at the same extraction time of 10 min. The corre-sponding equilibrium yields were 38.4, 39.0, 41.1, 41.6,and 40.6 mg g−1, respectively, and equilibrium contentswere 79.9, 83.9, 90.0, 89.1, and 89.1 mg g−1, respectivelyfor the above water–material ratios. Water–material ratioof 30:1 g g−1 was recommended for proanthocyanidinsextraction from pomegranate peel, as there was no sig-nificant change in the proanthocyanidins content for thewater–material ratios of 30:1, 40:1, and 50:1 g g−1 andalso that a higher water–material ratio involves morewater usage in extraction and higher energy consumptionfor concentration in the later processing stage.

3.2 Kinetic model of proanthocyanidinsextraction


The values of kinetic parameters, h, Ce, and k, underdifferent T were determined from the slopes and inter-cepts by plotting t/Ct against t using eq. (3) and arelisted in Table 1. At the extraction temperature of 90°C,the h, k, and Ce values reached their highest, followedby the temperatures of 80, 60, 40, and 25°C. The resultsindicated that the temperature had an accelerative influ-ence on the extraction kinetics of proanthocyanidins.

Similarly, Qu et al. [33] reported that extraction kineticparameters increased with the increase in temperatureand also that the temperature was a major factor influ-encing extraction rate. According to the assumptionof model, kinetic parameters (h, k, and Ce) can beexpressed in terms of the variable T (temperature).Therefore, the relationships between the kinetic para-meters and T were fitted by the same linear functions.The functions are plotted in Figure 3, and the fittingequations obtained are

CeðTÞ ¼ 0:00365T þ 0:59933 R2 ¼ 0:974 ð10Þ

kT ¼ 0:01198T þ 1:46621 R2 ¼ 0:976 ð11Þ

hT ¼ 0:02049T þ 0:29177 R2 ¼ 0:997 ð12Þ

Table 1 Second-order kinetic parameters of proanthocyanidins extraction from pomegranate peel under different extraction temperaturesand water–material ratios (water–material ratio of 50:1 g g−1 and extraction temperature of 60°C)

Variable Level Initialextraction rate,h (g L−1 min−1)

Extractionrate constant,k (L g−1 min−1)

Equilibriumconcentration of

proanthocyanidins,Ce (g L−1)

R2 Temperature-independent

factor, k0(L g−1 min−1)

Activationenergy,

E (kJ mol−1)

R2

Extractiontemperature (°C)

25 0.789 1.749 0.672 0.992 13.518 5.047 0.97440 1.151 2.006 0.758 0.99860 1.485 2.110 0.839 0.99980 1.936 2.455 0.888 0.10090 2.141 2.545 0.917 0.100

Water–materialratio (g g−1)

10 6.592 0.467 3.755 0.99520 3.723 0.902 2.031 0.99830 2.977 1.533 1.394 0.99940 2.276 2.091 1.043 0.99950 1.485 2.110 0.839 0.999

20 40 60 80 1000.0

0.5

1.0

1.5

2.0

2.5

3.0

Extraction temperature (°C)

Initi

al e

xtra

ctio

n ra

te, h

(g

L–1

min

–1)

Equ

ilibr

ium

con

cent

ratio

n of

pro

anth

ocya

nidi

ns, C

e (

g L

–1)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Ext

ract

ion

rate

con

stan

t, k

(L

g–1

min

–1)

h

Ce

k

Figure 3 Equilibrium concentrations of proanthocyanidins (Ce),extraction rate constants (k), and initial extraction rates (h) underdifferent extraction temperatures obtained for the extraction ofproanthocyanidins from pomegranate peel




After substituting hT and Ce(T) into the eq. (5), the extrac-tion kinetic model is

Ct;T ¼ tð1=ð0:02049T þ 0:29177ÞÞ þ ðt=ð0:00365T þ 0:59933ÞÞ

ð13Þ

This extraction kinetic equation can be used to predictthe proanthocyanidins yield and content at a givenextraction temperature and time.

Thermal kinetic parameters k0 and E at different Twere determined from the plot of ln(k) against 1,000/Ta(eq. (6)) as 13.518 L g−1 min−1 and 5.047 kJ mol−1, respec-tively (Table 1). The high coefficient of determination(R2) value of 0.974 indicated that the Arrhenius equationcan be used to describe the relationship between thesecond-order extraction rate constant and temperature.Correspondingly, the thermal kinetic model obtained is

k ¼ 13:518 exp � 5:0478:314� 10�3ðT þ 273:15Þ

� �ð14Þ


Table 1 also shows the extraction kinetic parameters h,Ce, and k at different W values. The proanthocyanidinsextraction with a water–material ratio of 10:1 g g−1 dis-played the highest h and Ce values compared to thoseobtained for water–material ratios of 20:1, 30:1, 40:1,and 50:1 g g−1. This was due to the highest proportionof raw material in the water at the water–material ratioof 10:1 g g−1. The highest k value was achieved for thewater–material ratio of 50:1 g g−1, followed by thoseunder 40:1, 30:1, 20:1, and 10:1 g g−1. Water–materialratio had a positive effect on the extraction rate ofproanthocyanidins. Qu et al. [33] reported that water–sample ratio was a key factor influencing extractionrate. The relationships between the kinetic parametersand variable W were nonlinearly fitted by second-orderpolynomial functions. The functions are plotted inFigure 4, and the equations are

CeðWÞ ¼ 0:00238W2 � 0:21074W þ 5:5214 R2 ¼ 0:983

ð15Þ

kW ¼ � 0:00065W2 þ 0:08354W � 0:3744 R2 ¼ 0:974

ð16Þ

hW ¼ 0:003W2 � 0:29665W þ 9:0094 R2 ¼ 0:965

ð17Þ

By substituting the hW and Ce(W) into the eq. (5), theextraction kinetic model is expressed as:

Ct;W ¼t

ð1=ð0:003W2 � 0:29665W þ 9:0094ÞÞ þ ðt=ð0:00238W2 � 0:21074W þ 5:5214ÞÞð18Þ

This extraction kinetic equation can be used to predictthe proanthocyanidins yield and content at a givenwater–material ratio and time of extraction.

Equations (13), (14), and (18) were the theoreticalkinetic models developed under different extraction para-meters for predicting proanthocyanidins yield. Eventhough these models might not completely explainextraction process, they can be used to assess the influ-ence of extraction parameters in the proanthocyanidinsextraction. It is very important to design an efficientprocess for the extraction of proanthocyanidins to mini-mize production cost. The data obtained from thesemodels can provide the theoretical guidance to obtainincreased extraction yield in a short time to reduceextraction cost in commercial production.

3.2.3 Kinetic model validation

Table 2 shows the predicted and experimental values ofproanthocyanidins concentration under the extractionconditions that were different from the ones used forthe kinetic model establishment. Low errors rangingfrom –0.070 to 0.045% were observed. This indicatedthat the kinetic models developed from this study can besuccessfully used for predicting the performance of

10 20 30 40 500

1

2

3

4

5

6

7

Water–material ratio (g g–1)

0.0

0.5

1.0

1.5

2.0

2.5h

Ce

k

Initi

al e

xtra

ctio

n ra

te, h

(g

L–1

min

–1)

Equ

ilibr

ium

con

cent

ratio

n of

pro

anth

ocya

nidi

ns, C

e (

g L

–1)

Ext

ract

ion

rate

con

stan

t, k

(L

g–1

min

–1)

Figure 4 Equilibrium concentrations of proanthocyanidins (Ce),extraction rate constants (k), and initial extraction rates (h) underdifferent water–material ratios obtained for the extraction ofproanthocyanidins from pomegranate peel




proanthocyanidins extraction from pomegranate peelpowder.

3.3 Effect of extraction parameterson product properties


The DPPH scavenging activities of proanthocyanidins pro-duced with different extraction times and temperatures areshown in Figure 5. The DPPH scavenging activity signifi-cantly decreased with the increase in temperature, whichwas in contrary to the trends observed for proanthocyani-dins yield and content. This revealed that the extractiontemperature had a significantly negative effect on thescavenging activity of proanthocyanidins (p<0.05)because of the heat-sensitive nature of proanthocyanidins.Qu et al. [33] found that the DPPH scavenging activities

of antioxidants from pomegranate peel extract significantlydecreased with the increase in extraction temperature from25 to 95°C. Miranda et al. [34] also reported that the scaven-ging activity of Aloe Vera gel decreased with the increasein extraction temperature. Moreover, the extraction timealso had a significant influence on the DPPH scavengingactivity (p<0.05). DPPH scavenging activity drasticallydecreased during the first 2 min for the extracts obtainedfrom all temperatures. After 2 min, the scavenging activityreduction took place in a slow rate and finally reached theequilibrium at 10min. During the entire extraction period of20 min, the DPPH scavenging activities of proanthocyani-dins reduced from 62.9 to 36.5, 56.2 to 31.0, 51.5 to 29.4, 42.7to 28.0, and 41.9 to 26.7 g g−1 for the extraction temperaturesof 25, 40, 60, 80, and 90°C, respectively. The DPPH scaven-ging activity for all extraction temperatures wasmaintainedat > 50% of the initial value after 20 min of extraction time.Comparing the scavenging activities under extraction tem-perature of 40 and 60°C, there was no significant differencein the scavenging activity after 5 min of extraction.Therefore, extraction temperature of � 60°C is recom-mended to maintain scavenging activity of greater than50% of its initial value.

The effects of extraction temperature and time on thecolor characteristics of proanthocyanidins are shown inTable 3. The statistical analysis of the data showed thatall color characteristics (L*, a*, and b*) were significantlyaffected by extraction temperature and time (p<0.05).This is on par with the findings of Qu et al. [35], whoreported that temperature and time were the two keyfactors influencing color characteristics of pomegranatepeel extract. L* values decreased and a* values increasedwith the increase in extraction temperature, while b*values (except for b* at 25°C) did not change with tem-perature. In addition, L* values decreased and a* valuesincreased with the increase in extraction time. Whereas,b* values were fluctuated with extraction time and

0 5 10 15 2010

20

30

40

50

60

70

DPP

H s

cave

ngin

g ac

tivity

(g

g–1)



Figure 5 Scavenging activities of proanthocyanidins extracted frompomegranate peel under different extraction temperatures andtimes with a water–material ratio of 50:1 g g−1

Table 2 Proanthocyanidins concentrations (Ct) predicted by the kinetic model under different extraction times (t), temperatures (T), andwater–material ratios (W) (water–material ratio of 50:1 g g−1 and extraction temperature of 60°C)

Ct, T (g L−1) Ct, W (g L−1)

C1.7min,

90°C

C2.3min,

90°C

C3.7min,

90°C

C4.3min,

90°C

C4.7min,

90°C

C1.3min,

50 g g−1

C2.7min,

50 g g−1

C3.3min,

50 g g−1

C4.7min,

50 g g−1

C5.3min,

50 g g−1

Pred.a 0.736 0.782 0.830 0.843 0.849 0.659 0.773 0.801 0.835 0.846Exp.b 0.750 0.785 0.822 0.852 0.864 0.688 0.719 0.802 0.810 0.843Errorc 0.018 0.003 −0.010 0.010 0.018 0.045 −0.070 0.001 −0.030 −0.004

Notes: aPred. is the predicted proanthocyanidins concentration using respective mathematical model of each variable; bExp. is the experimentallyobtained proanthocyanidins concentration; cError is the difference between experimentally obtained and predicted values and is expressed aspercentage (%) of experimental value.




achieved the highest value at 4 min. By converting L*, a*,and b* values into C*, H*, and ΔE* values, it can be seenthat C* values for the temperatures 25, 40, and 60°Cincreased with the increase in time and finally reachedthe equilibrium value at 4 min. The C* values for theextraction temperatures of 80 and 90°C increased at theinitial stage (0–4 min) and then decreased after 4 minwith increasing time because of decreased b* values. TheH* values significantly reduced with the increase in

extraction time and temperature (p<0.05). The ΔE*values for the extraction temperatures between 25 and80°C rapidly increased with the increase in time andreached the equilibrium at 4 min, but that of 90°Cdecreased after 4 min. The lower C*, H*, and ΔE* valuesat higher extraction temperatures were due to the factthat proanthocyanidins were heat-sensitive substances,and therefore, a high temperature changed its color char-acteristics [36]. After comprehensive statistical analysis,

Table 3 Color characteristics of proanthocyanidins extracted from pomegranate peel under different extraction temperatures and times(water–material ratio of 50:1 g g−1)

Color C0.17min, 25°C C0.17min, 40°C C0.17min, 60°C C0.17min, 80°C C0.17min, 90°C C3min, 25°C C3min, 40°C C3min, 60°C C3min, 80°C C3min, 90°C

a* 8.8b 8.0a 9.8c 8.8b 12.8d 14.5a 15.9b 18.6c 18.7c 20.0d

b* 51.7b 50.7a 52.6c 52.5c 57.1d 59.0b 60.3c 61.0e 60.7d 57.8a

L* 60.0d 61.1e 58.9c 57.6b 54.8a 53.6e 52.7d 50.0c 49.1b 45.9a

C* 52.4b 51.3a 53.5d 53.2c 58.5e 60.7a 62.4c 63.7d 63.5d 61.1b

H*(o) 1.4a 1.4a 1.4a 1.4a 1.4a 1.3b 1.3b 1.3b 1.3b 1.2a

ΔE* 54.1b 52.7a 55.4d 55.1c 60.3e 63.7a 65.6b 67.7c 67.7c 65.8b


a* 10.4b 8.6a 10.9b 12.0c 14.3d 15.0a 17.4b 17.9c 18.6d 19.9e

b* 54.4b 51.4a 55.1b 58.3c 59.3d 59.1a 60.9c 60.8c 60.8c 59.4b

L* 58.3d 60.4e 58.0c 56.0b 53.9a 52.0e 51.4d 50.4c 48.8b 47.0a

C* 55.4b 52.1a 56.1b 59.5c 61.0d 60.0a 63.3c 63.3c 63.6c 62.7b

H*(o) 1.4b 1.4b 1.4b 1.4b 1.3a 1.3b 1.3b 1.3b 1.3b 1.2a

ΔE* 57.4b 53.6a 58.1c 61.7d 63.0e 63.6a 66.8b 67.2c 67.9d 66.8b


a* 11.5b 10.6a 13.8c 13.6c 15.3d 14.8a 17.3b 18.4c 18.9d 20.5e

b* 55.8b 55.6a 58.8c 59.4d 60.1e 59.2b 60.5c 60.5c 60.4c 55.8a

L* 56.7d 57.7e 54.5c 54.2b 53.2a 53.5e 51.1d 50.3c 48.4b 43.7a

C* 57.0b 56.6a 60.4c 60.9d 62.0e 60.9b 62.9c 63.2cd 63.3d 59.4a

H*(o) 1.4b 1.4b 1.3a 1.3a 1.3a 1.3b 1.3b 1.3b 1.3b 1.2a

ΔE* 59.3b 58.6a 63.2c 63.5d 64.1e 63.9a 66.6c 67.1d 67.8e 65.2b

Color C1min, 25°C C1min, 40°C C1min, 60°C C1min, 80°C C1min, 90°C C8min, 25°C C8min, 40°C C8min, 60°C C8min, 80°C C8min, 90°C

a* 12.7a 14.6b 15.2c 16.2d 17.9e 15.9a 17.6b 18.7c 19.3d 20.2e

b* 57.2a 59.0b 59.8c 60.9d 61.1d 59.1b 60.5c 60.5c 58.9b 55.2a

L* 55.6d 53.8c 53.8c 51.5b 49.8a 52.4e 50.7d 49.9c 46.9b 43.2a

C* 58.6a 60.8b 61.7c 63.0d 63.7e 61.3b 63.0d 63.4e 62.0c 58.8a

H*(o) 1.4b 1.3a 1.3a 1.3a 1.3a 1.3b 1.3b 1.3b 1.3b 1.2a

ΔE* 61.1a 63.7b 64.5c 66.4d 66.7e 64.7a 66.8b 67.4c 67.2c 64.8a


a* 13.9a 15.4b 15.7c 16.9d 18.3e 15.8a 18.0b 19.8d 19.6c 20.2e

b* 58.5b 59.9c 58.0a 60.7d 59.9c 59.1c 60.3d 59.1c 58.5b 54.9a

L* 54.6e 53.7d 49.2b 50.8c 48.7a 52.3e 50.2d 49.0c 46.9b 42.7a

C* 60.2a 61.9b 60.0a 63.0c 62.6c 61.2b 62.9e 62.3d 61.7c 58.5a

H*(o) 1.3a 1.3a 1.3a 1.3a 1.3a 1.3b 1.3b 1.2a 1.2a 1.2a

ΔE* 62.9a 64.8b 64.6b 66.6d 66.1c 64.6a 66.9bc 66.7b 66.9c 64.8a

Color C2min, 25°C C2min, 40°C C2min, 60°C C2min, 80°C C2min, 90°C C20min, 25°C C20min, 40°C C20min, 60°C C20min, 80°C C20min, 90°C

a* 13.7a 15.7b 18.3c 18.3c 19.1d 16.4a 17.7b 19.8c 20.0c 20.9d

b* 58.4a 60.0b 60.7c 60.5c 59.8b 58.8c 60.0d 60.0c 57.5b 53.2a

L* 54.7e 52.3d 50.6c 49.3b 48.1a 50.9e 50.2d 48.1c 45.9b 41.0a

C* 60.0a 62.0b 63.4d 63.2d 62.8c 61.0b 62.6c 62.3c 60.9b 57.1a

H*(o) 1.3a 1.3a 1.3a 1.3a 1.3a 1.3b 1.3b 1.2a 1.2a 1.2a

ΔE* 62.7a 65.3b 67.2d 67.3d 66.5c 64.9b 66.5c 67.0d 66.5c 64.4a

Notes: Different letters denote significant differences under different extraction temperatures for each of the same time (p<0.05).




extraction temperature of � 40°C and extraction time of� 4 min are recommended to maintain the attractivereddish yellow color of proanthocyanidins extract.


Figure 6 shows the DPPH scavenging activities ofproanthocyanidins under different extraction times andwater–material ratios. The scavenging activity signifi-cantly increased with the increase in water–materialratio, similar to the increase in proanthocyanidins con-tent (Figure 2B). This result indicated that the water–material ratio had a significantly positive effect on thescavenging activity of proanthocyanidins (p<0.05). Thehigher scavenging activities at higher water–materialratios were due to the fact that more highly activeproanthocyanidin ingredients were extracted as theincrease in water–material ratio enhanced the concen-tration gradient between the internal material and thesolution. Qu et al. [33] found that the DPPH scavengingactivity of antioxidants from pomegranate peel extractpresented a fluctuating change with different water–sample ratios. It can also be concluded that the DPPHscavenging activity was significantly influenced by theextraction time (p<0.05). The DPPH scavenging activityof extracts rapidly decreased with extraction time of lessthan 4 min and then reached their equilibrium. Duringthe extraction periods from 0.17 to 20 min, DPPHscavenging activities of proanthocyanidins were rangedfrom 51.5 to 29.4, 48.0 to 28.0, 47.1 to 31.0, 39.2 to 26.0,and 37.1 to 19.1 g g−1 for the water-material ratios of 50:1,40:1, 30:1, 20:1, and 10:1 g g−1, respectively. This shows

that the DPPH scavenging activity under all the water–material ratios was above 50% of the initial value forextraction time of 20 min. This result showed thatthe water–material ratios of 50:1, 40:1, and 30:1 g g−1

were suitable in maintaining high scavenging activity.However, a higher water–material ratio results in moreenergy consumption for concentration in the proantho-cyanidins production. Therefore a water–material ratioof 30:1 g g−1 is recommended to maintain > 50% ofscavenging activity of proanthocyanidins for all testedtimes.

Table 4 shows the effect of water–material ratio on thecolor characteristics of proanthocyanidins extract. The sta-tistical analysis of the data showed that water–materialratio had a significant effect on all color characteristics(p<0.05). With the exception of C*, all other color char-acteristics were influenced in the same manner as influ-enced by the extraction time. It can be seen that both L*and b* values significantly increased with increasingwater–material ratio while a* values decreased. In addi-tion, L* and b* values significantly decreased with theincrease in extraction time, while a* values decreased. Byconverting L*, a*, and b* values into C*, H*, and ΔE*values, it can be seen that C* values for the water–materialratios of 50:1, 40:1, and 30:1 g g−1 were at the peak valueduring the entire extraction period. The H* values signifi-cantly decreased with the increase in extraction time, whilethey increased with the increase in water–material ratio.The ΔE* values for the low water–material ratios of 10:1and 20:1 g g−1 decreased with the increase in extractiontime, whereas the ΔE* values for the water–material ratiosof 30:1, 40:1, and 50:1 g g−1 increased with time, and finallyreached the equilibrium after 3 min. The dark red appear-ance of proanthocyanidins extract obtained from higherwater–material ratios was due to the fact that higherwater–material ratios contributed to extract more reddishproanthocyanidins, thereby increasing the intensity of redcolor of the product, which was confirmed by higherproanthocyanidins content in the extracts. The color char-acteristic values reiterated the recommendation of water–material ratio of 30:1 g g−1, which not only maintainedgreater than 50% of DPPH scavenging activity of proantho-cyanidins but also gave an attractive reddish yellow colorat all extraction times used in this study.

4 Conclusions

To develop a method for extraction of value-addedproanthocyanidins from pomegranate peel, the influence

0 5 10 15 2010

20

30

40

50

60

70

DPP

H s

cave

ngin

g ac

tivity

(g

g–1)



Figure 6 Scavenging activities of proanthocyanidins extracted frompomegranate peel under different water–material ratios and extrac-tion times at a temperature of 60°C




of processing parameters on extraction efficiency, kinetics,and product properties was systematically studied byusing water as an environmentally friendly solvent. Theresults showed that both the extraction temperature and

the water–material ratio had significant effects on theproanthocyanidins content, and temperature alone had asignificant effect on the yield. The kinetic models includingsecond-order and Arrhenius mathematical equations were

Table 4 Color characteristics of proanthocyanidins extracted from pomegranate peel under different water–material ratios and extractiontimes (temperature of 60°C)

Color C0.17min,

10 g g−1

C0.17min,

20 g g−1

C0.17min,

30 g g−1

C0.17min,

40 g g−1

C0.17min,

50 g g−1

C3min,

10 g g−1

C3min,

20 g g−1

C3min,

30 g g−1

C3min,

40 g g−1

C3min,

50 g g−1

a* 26.2e 18.6d 13.6c 11.8b 9.8a 27.6d 27.6d 24.8c 20.6b 18.6a

b* 57.8c 60.0e 54.0b 59.0d 52.6a 30.2a 48.1b 55.3c 57.6d 61.0e

L* 40.0a 47.9b 55.0c 57.0d 58.9e 23.3a 33.8b 41.8c 46.7d 50.0e

C* 63.4e 62.8d 55.7b 60.1c 53.5a 40.9a 55.4b 60.6c 61.2d 63.7e

H*(°) 1.1a 1.3b 1.3b 1.4c 1.4c 0.8a 1.0b 1.1c 1.2d 1.3e

ΔE* 71.4e 67.6d 58.5b 62.1c 55.4a 64.4a 67.8cd 68.1d 66.5b 67.7c

Color C0.33min,

10 g g−1

C0.33min,

20 g g−1

C0.33min,

30 g g−1

C0.33min,

40 g g−1

C0.33min,

50 g g−1

C4min,

10 g g−1

C4min,

20 g g−1

C4min,

30 g g−1

C4min,

40 g g−1

C4min,

50 g g−1

a* 28.6e 21.2d 17.4c 11.4b 10.9a 27.7e 26.5d 25.4c 20.8b 17.9a

b* 50.8a 61.0d 54.5b 61.1d 55.1c 27.9a 44.4b 54.8c 56.3d 60.8e

L* 34.4a 46.6b 51.4c 57.1d 58.1e 21.2a 31.8b 41.0c 46.4d 50.4e

C* 58.3c 64.6e 57.2b 62.2d 56.1a 39.3a 51.7b 60.4d 60.0c 63.3e

H*(°) 1.1a 1.2b 1.3c 1.4d 1.4d 0.8a 1.0b 1.1c 1.2d 1.3e

ΔE* 69.8d 69.7d 61.0b 64.1c 58.1a 65.1a 66.1c 68.2e 65.6b 67.2d

Color C0.5min,

10 g g−1

C0.5min,

20 g g−1

C0.5min,

30 g g−1

C0.5min,

40 g g−1

C0.5min,

50 g g−1

C6min,

10 g g−1

C6min,

20 g g−1

C6min,

30 g g−1

C6min,

40 g g−1

C6min,

50 g g−1

a* 29.2e 25.1d 20.5c 15.3b 13.8a 27.7e 27.5d 25.3c 21.2b 18.4a

b* 44.5a 58.1c 56.3b 61.0e 58.8d 26.6a 44.6b 55.4c 57.1d 60.5e

L* 30.1a 40.8b 47.7c 53.2d 54.5e 21.0a 34.0b 41.6c 46.7d 50.3e

C* 53.2a 63.3d 59.9b 62.9d 60.4c 38.4a 52.4b 60.9c 60.9c 63.3d

H*(°) 1.0a 1.2b 1.2b 1.3c 1.3c 0.8a 1.0b 1.1c 1.2d 1.3e

ΔE* 68.3d 70.9e 65.0b 65.9c 63.2a 64.7a 65.2b 68.4e 66.3c 67.1d

Color C1min,

10 g g−1

C1min,

20 g g−1

C1min,

30 g g−1

C1min,

40 g g−1

C1min,

50 g g−1

C8min,

10 g g−1

C8min,

20 g g−1

C8min,

30 g g−1

C8min,

40 g g−1

C8min,

50 g g−1

a* 28.6e 25.6d 21.3c 17.1b 15.2a 27.7e 27.0d 25.5c 21.0b 18.7a

b* 38.1a 57.0b 57.1b 60.2d 59.8c 28.2a 44.0b 55.0c 55.0c 60.5d

L* 26.0a 40.0b 45.8c 51.2d 53.8e 21.9a 31.9b 40.3c 46.6d 49.9e

C* 47.7a 62.5d 61.0b 62.6d 61.7c 39.5a 51.7b 60.6d 58.8c 63.4e

H*(°) 0.9a 1.1b 1.2c 1.3d 1.3d 0.8a 1.0b 1.1c 1.2d 1.3e

ΔE* 66.9c 70.6d 66.7c 66.2b 64.5a 64.7b 65.9c 68.8e 64.5a 67.4d

Color C1.5min,

10 g g−1

C1.5min,

20 g g−1

C1.5min,

30 g g−1

C1.5min,

40 g g−1

C1.5min,

50 g g−1

C10min,

10 g g−1

C10min,

20 g g−1

C10min,

30 g g−1

C10min,

40 g g−1

C10min,

50 g g−1

a* 27.7d 27.6d 23.9c 17.8b 15.7a 27.7e 25.7d 25.3c 22.1b 19.0a

b* 32.7a 52.4b 55.8c 58.9e 58.0d 27.9a 41.5b 53.2c 55.1d 59.4e

L* 23.4a 36.0b 43.4c 49.5e 49.2d 22.1a 30.8b 40.5c 44.7d 49.0e

C* 42.8a 59.2b 60.7d 61.5e 60.0c 39.3a 48.8b 58.9c 59.4c 62.4d

H*(°) 0.9a 1.1b 1.2c 1.3d 1.3d 0.8a 1.0b 1.1c 1.2d 1.3e

ΔE* 65.6b 69.7e 67.4d 65.8c 64.6a 64.4a 64.5a 67.2c 65.8b 66.8c

Color C2min,

10 g g−1

C2min,

20 g g−1

C2min,

30 g g−1

C2min,

40 g g−1

C2min,

50 g g−1

C20min,

10 g g−1

C20min,

20 g g−1

C20min,

30 g g−1

C20min,

40 g g−1

C20min,

50 g g−1

a* 27.7e 27.6d 24.0c 19.4b 18.3a 27.7e 25.8d 25.2c 21.4b 19.8a

b* 29.7a 49.4b 56.1c 59.5d 60.7e 26.3a 42.3b 54.3c 54.3c 59.1d

L* 21.1a 34.6b 43.6c 48.2d 50.6e 21.2a 31.2b 39.9c 45.7d 48.1e

C* 40.6a 56.6b 61.0c 62.6d 63.4e 38.1a 49.5b 59.8d 58.4c 62.3e

H*(°) 0.8a 1.1b 1.2c 1.3d 1.3d 0.8a 1.0b 1.1c 1.2d 1.2d

ΔE* 65.9a 68.3c 67.6b 67.3b 67.2b 64.4a 64.8b 68.3d 64.5a 67.0c

Notes: Different letters denote significant differences under different water–material ratios for each of the same time (p<0.05).




successfully developed for predicting the extraction effi-ciency under different extraction conditions. The activationenergy of proanthocyanidins extraction was determined as5.047 kJ mol−1 from the Arrhenius model. To maintain highscavenging activity and good color characteristics ofproanthocyanidins products, moderate temperature andwater–material ratio were preferred. By comprehensivelyconsidering the proanthocyanidins yield and properties,the recommended extraction conditions are temperatureof 60°C, water–material ratio of 30:1 g g−1, and time of10 min, which gave the highest proanthocyanidins yield of41.1 mg g−1, proanthocyanidins content of 90.0mg g−1, witha DPPH scavenging activity of 31.5 g g−1, and attractivereddish yellow color with L* of 40.5, a* of 25.3, b* of 53.2,

C* of 58.9, and H* of 1.1°. The pomegranate peel could beutilized as a good source for producing proanthocyanidinsproducts which can be used as nutraceuticals or foodadditives.

Acknowledgments: The authors wish to extend theirappreciation for the supports provided by the NationalNatural Science Foundation of China (No. 31301423), theYouth Natural Science Fund of Jiangsu Province (No.BK2012287), the Postdoctoral Funds of Jiangsu Province(No. 1101039C), the Senior Professional Research Start-up Fund of Jiangsu University (No. 10JDG121), and thePriority Academic Program Development Fund ofJiangsu Higher Education Institutions (PAPD), PR China.

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extraction kinetics and properties of proanthocyanidins from pomegranate peel

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