effect of storage on anthocyanin degradation in black mulberry juice and concentrates

ORIGINAL PAPER

Effect of Storage on Anthocyanin Degradation in BlackMulberryJuice and Concentrates

Togzhan Boranbayeva & Feryal Karadeniz & Emel Yılmaz

Received: 21 February 2013 /Accepted: 5 March 2014# Springer Science+Business Media New York 2014

Abstract Anthocyanins present in fruits and vegetables arereceiving increased attention because of their potential anti-oxidant activity but are very susceptible to degradation duringprocessing and storage. Effect of storage on kinetics of antho-cyanin degradation and hydroxymethylfurfural (HMF) forma-tion in black mulberry juice and concentrate was determinedduring 8 months of storage at temperatures of 5°, 20°, 30°, and40 °C. The monomeric anthocyanin degradation was in ac-cordance with the first-order reaction kinetics and the activa-tion energies of anthocyanin degradation in black mulberryjuice and concentrate were found as 56.48 and 49.75 kJmol−1,respectively. HMF formation in black mulberry juice andconcentrate increased linearly with storage time and tempera-ture and followed zero-order reactions. The activation ener-gies of HMF formation in black mulberry juice and concen-trate were found as 75.70 and 104.11 kJ mol−1, respectively.The losses of antioxidant activity for black mulberry juice andconcentrate during storage at different temperatures were inthe ranges of 4.87–16.01 and 4.47–33.57 %, respectively.Antioxidant activity in black mulberry juice and concentratewas correlated with total monomeric anthocyanins.

Keywords Mulberry juice and concentrate . Kinetics .

Antioxidant activity . Anthocyanin . HMF . Storage

Introduction

Mulberry belongs to the genusMorus of the familyMoraceae.There are 24 species of Morus and one subspecies, with atleast 100 known varieties (Pawlowska et al. 2008). Mulberry(Morus species) is grown wild or cultivated in many countriesfor its foliage, which is a primary source of food for silkworms(Bombyx mori L.). In general, there are three types of mulber-ry, including white (Morus alba), black (Morus nigra), andred (Morus rubra) (Aramwit et al. 2010). The Anatolia regionof Turkey has growing conditions suitable for cultivating highquality mulberry fruits. The production of mulberry in Turkeyin 2011 was 78.702 tonnes (FAO 2011) and its cultivation inTurkey has been known for more than 400 years. The red-colored fruits are eaten fresh and are also used in marmalades,juices, liquors, natural dyes, and in the cosmetics industry(Ercisli and Orhan 2007).

Epidemiological and clinical investigations have associ-ated diets rich in fruits and vegetables with reduced risk ofheart disease, neurological and chronic diseases, and vari-ous forms of cancer (Hertog et al. 1993). These physiolog-ical functions of fruits and vegetables may be partly attrib-uted to their high phenolic content (Cieslik et al. 2006) suchas anthocyanins. Nowadays, interest in anthocyanins hasincreased because they are potential natural alternatives toartificial colorants in the food and pharmaceutical indus-tries and their antioxidant activity plays an important role inthe prevention of diseases (Alasalvar et al. 2005; Patraset al. 2010). Anthocyanins are highly unstable and easilysusceptible to degradation. Anthocyanin stability is strong-ly affected by pH, temperature, anthocyanin concentration,oxygen, light, enzymes, and other accompanying sub-stances such as ascorbic acid, sugars, sulfites, copigments,and metallic ions. The amount of anthocyanins found infoods decreases during processing and storage as tempera-ture rises (Maccarone et al. 1985).

T. BoranbayevaDepartment of Food Engineering, M. Auezov South KazakhstanState University, Shymkent, Kazakhstan

F. Karadeniz (*)Faculty of Engineering, Department of Food Engineering, AnkaraUniversity, Ankara 06110, Turkeye-mail: [email protected]

E. YılmazFaculty of Engineering and Architecture, Department of FoodEngineering, Trakya University, Edirne 22180, Turkey

Food Bioprocess TechnolDOI 10.1007/s11947-014-1296-8

Another important chemical change occurred in foods dur-ing processing and storage is nonenzymatic browning reac-tions, which involve caramelization, ascorbic acid degradation,and the Maillard reaction (Cornwell and Wrolstad 1981).Brown pigment formation is desired during food processingas in the manufacture of coffee, tea, and beer and in the toastingand baking of bread. This reaction improves the desirablesensory characteristics of these foods, e.g., color, aroma, andflavor. Conversely, it is undesirable in concentrated foods, asmaximum reaction rate occurs at water activities of 0.6–0.7(Eskin 1990). Maillard reactions can also cause losses in nutri-tional value of foods, formation of undesirable compounds, e.g.furfural, hydroxy methyl furfural and brown pigment (Martinset al. 2001). The Maillard reaction, takes place between α-amino groups and reducing sugars, is the most important reasonfor browning in fruit juice during storage (Toribio and Lozano1984). Maillard reaction is influenced by many factors, includ-ing reactant concentration, temperature, time, initial pH, andwater activity (Benjakul et al. 2005).

The stability of anthocyanin content during processing andstorage of foods is one of the most important quality attributesof food products. Several studies have reported the effect ofprocessing and storage on the stability of fruit juice with highanthocyanin content (Garzon and Wrolstad 2002; Wang andXu 2007; Jiménez et al. 2010). However, the literaturecontains no references on the degradation of anthocyaninin mulberry juice and concentrate during storage. Inaddition to this, for the quality of stored fruit juices,hydroxymethylfurfural (HMF) is an important criterion.Therefore, this study was conducted to determine the kineticsof anthocyanin degradation and HMF formation in blackmulberry juice and concentrate during storage at 5°, 20°,30°, and 40 °C, as knowledge of the kinetic parameters, suchas reaction order, rate constant, and activation energy isessential for predicting and controlling food quality. Further-more, antioxidant activity was also analyzed to determine thecorrelations among antioxidant activity, anthocyanins andHMF.

Materials and Methods

Materials

Black mulberry juice (100 %, 15.2°Bx) and concentrate(65.7°Bx) were supplied by one of the fruit juice and concen-trate producers in Turkey (Göknur Foodstuffs Import ExportTrading and Production Company) just after production date.Fruit juice samples have been stored in 200-mL glass bottles,wheres concentrate samples have been stored in 100 g jars at5°, 20°, 30°, and 40 °C for 8 months, and analyses werecarried out eachmonth as two replicates. Black mulberry juiceconcentrate production flow chart is given Fig. 1.

pH, Titratable Acidity, and Water-Soluble Solids Content

pH was measured at 20 °C with a pH meter (Consort P407,Schott Gerate, Belgium) (International Federation of FruitJuice Producers (IFU) 1989). After determination of pH, thesamples were titrated with 0.1 N NaOH up to pH 8.1 andresults were expressed as gram citric acid per 100 mL juiceand gram citric acid per 100 g concentrate (IFU 1996). Water-soluble solid contents of black mulberry juice and concen-trates were determined with an Abbe refractometer (NOW;Nippon Optical Work Co., Ltd, Tokyo, Japan) at 20 °C, and

Fig. 1 Black mulberry juice concentrate production flow chart

Food Bioprocess Technol

results were expressed as °Bx (IFU 2000). Before analyzingthe pH value, total soluble solids (°Bx) and titratable acidity(g citric acid per 100 g sample) were determined. These valueswere found as 3.91, 15.2, and 0.26 in fruit juices and 3.29,65.7, and 2.69 in concentrate, respectively. pH, titratableacidity, and soluble solids were determined during 8 monthsof storage, and no significant changes were observed(p<0.01).

Total Monomeric Anthocyanins Analysis

The total monomeric anthocyanins were determined using thepH differential method described by Giusti and Wrolstad(2005). The dilution factor for the samples was determinedby diluting with potassium chloride buffer, pH 1.0, until theabsorbance of the sample at the λvis-max (520 nm) is withinthe linear range of the spectrophotometer. The absorbance ofsamples at 520 nm for anthocyanin content and 700 nm forhaze was measured on a UV–VIS spectrophotometer (ModelUV2 Unicam, England) against a blank cell filled with dis-tilled water. The monomeric anthocyanin concentrations werecalculated as mg cyanidin-3-glucoside (cy-3-glu) equivalents.

A ¼ Avismax−A700ð ÞpH 1:0− Avismax−A700ð ÞpH 4:5

The monomeric anthocyanin pigment concentration in theoriginal sample was calculated using the following formula:

Monomeric anthocyanin pigment mg=Lð Þ¼ A�MW� DF� 1; 000ð Þ=ε x 1Þ

where MW is the molecular weight (449.2 for cyanidin-3-glucoside), DF is the dilution factor, and ε is the molarabsorptivity (26,900 for cyanidin-3-glucoside).

Determination of HMF

HMF was determined quantitatively, following the procedureby IFU (1984) based on the colorimetric reaction betweenbarbituric acid and HMF, forming a red-colored complex. Theintensity of red color is dependent upon the concentration ofHMF, which was measured at 550 nm using a spectrophotom-eter. A calibration curve of HMF was used to quantify HMFcontents of samples.

Determination of Antioxidant Activity

The antioxidant activity of black mulberry juice and concen-trates was determined by Trolox Equivalent Antioxidant Ca-pacity method described by Re et al. (1999). A 7-mM solutionof 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid)

(ABTS) in double-distilled water was prepared and ABTSradical cation (ABTS+) was formed after addition of potassiumpersulphate (Merck) to the mixture in a final concentrationof 2.45 mM. The mixture was allowed to stand in the dark atroom temperature for 12–16 h before use. The solution wasdiluted with ethanol to an absorbance reading of 0.7 (±0.02) at734 nm. The ethanolic ABTS+ (1 mL) solution is added tothree different concentrations of antioxidant compound (5, 10,and 15 μL), and absorbance readings at 734 nm were taken at30 °C, exactly 1 min after initial mixing and up to 6 min. Thepercentage inhibition of absorbance is calculated and plottedas a function of concentration of Trolox for the standardreference data. The results were expressed in equivalents ofmicromole Trolox (TE) per 100 mL of juices and per 100 g ofconcentrates.

Calculation of Kinetic Parameters

The loss of monomeric anthocyanin content in black mulberryjuice and concentrate followed a first-order kinetic model. Thedegradation of total monomeric anthocyanins was calculatedby using the standard equation for a first-order reaction givenbelow:

lnC ¼ lnCo–kt

where C is the concentration at time t; Co the concentration attime zero; k the first-order rate constant (month−1); and t thestorage time (month).

The accumulation of HMF in black mulberry juice andconcentrate was calculated by using the standard equationfor a zero-order reaction given below:

C ¼ Co–kt

where C is the concentration at time t; Co the concentration attime zero; k the zero-order rate constant (mg HMF month−1);and t the storage time (month).

Temperature dependence of both reactions was determinedby Arrhenius equation given below:

k ¼ koxe–Ea=RT

where Ea is the activation energy (kJ mol−1); k the rate con-stant; ko the frequency factor; R the universal gas constant(8.314×10−3 kJ mol−1 K−1); and T the absolute temperature(°K).

Q10 ¼ k2=k1ð Þ10=T2−T1

where k2 is the rate constant of the HMF formation andmonomeric anthocyanin degradation at T2 temperature; k1 is


the rate constant of the HMF formation and/or monomericanthocyanin degradation at T1 temperature.

The half-life value of monomeric anthocyanin degradationwas also calculated using the equation given below:

t1=2 ¼ ln 2=k

where k is the rate constant (per month).

Statistical Analysis

A statistical program (SPSS 9.05 for Windows andMINITAB14.0) was used for data processing. All experimental datawere evaluated using one way analysis of variance (ANOVAtechnique). Results were expressed as mean values±standarderror of mean (SD).

Results and Discussion

Total Monomeric Anthocyanin Content

Total monomeric anthocyanin content of black mulberry juiceand concentrate decreased with temperature and storage time.Anthocyanin degradation in black mulberry juice and concen-trate during storage is shown in Figs. 2 and 3, respectively.The initial total monomeric anthocyanin contents of blackmulberry juices were 23.38, 23.13, 23.29, and 23.13 mgcy-3-glu L−1 at 5°, 20°, 30°, and 40 °C, respectively, whereasthese values for concentrates were found as 234.84, 235.86,233.96, and 235 mg cy-3-glu kg−1, respectively. Özgen et al.(2009) found total monomeric anthocyanins of black mulber-ry fruits as 253–830 mg cy-3-glu kg−1 f.w. Gerasopoulos and

Stravroulakis (1997) reported values of 100 mg kg−1 f.w. inM. nigra and 10 mg kg−1 f.w. inM. alba cultivated in Greece.In this research, the anthocyanin content of black mulberryjuices was lower than the values reported on the previousstudies. The reason for that might be due to the preparationof juices from the concentrates by reconstitution. As anthocy-anins are decomposed easily because of heat treatment in theconcentrate production (Patras et al. 2010), it is not surprisingto get lower results for juices. As known, single strength fruitjuices always have better quality attributes than that ofreconstituted fruit juices.

The losses of total monomeric anthocyanin at 5°, 20°,30,° and 40 °C for black mulberry juice and concentrateduring storage were in the ranges of 1.96–74.55 and1.26–98.12 %, respectively (Table 1). Linear regressionconfirmed that the degradation of anthocyanin in blackmulberry juice and concentrate followed a first-orderreaction. As the determination coefficient of the equa-tions obtained from the results for 5 °C is too low, theresults were not used for calculation of kinetic parame-ters. The heat dependence of the rate constants of antho-cyanin degradation was represented by Arrhenius equa-tion on the basis of linear regression analysis of naturallogarithms of rate constant against reciprocal absolutetemperature 1/T in Kelvin (Fig. 4). Activation energiesfor anthocyanin degradation in juice samples and con-centrate in the range of 20–40 °C were calculated as56.48 and 49.75 kJ mol−1, respectively (Table 2). Previ-ous studies showed that thermal degradation of anthocy-anins in different fruits and fruit juices followed first-order reaction kinetics (Ochoa et al. 1999; Garzon andWrolstad 2002; Wang and Xu 2007).

The Q10 values of black mulberry juice determined at thetemperature ranges of 20–30 and 30–40 °C were 2.02 and2.17, respectively, whereas these values for concentrates were

Fig. 2 Monomeric anthocyanin degradation of black mulberry juiceduring storage at different temperatures

Fig. 3 Monomeric anthocyanin degradation of black mulberry concen-trate during storage at different temperatures


found as 2.01 and 1.84, respectively. This means that a 10 °Cincrease in the temperature results in an increase approximate-ly two times in the rate of anthocyanin degradation in juiceand concentrate samples.

The t1/2 values for anthocyanin degradation at 20°, 30°,and 40 °C were calculated as 17.4, 8.6, and 4 monthsrespectively for juice samples and 5.5, 2.7 and 1.5 monthsrespectively for concentrate samples. According to t1/2

values, anthocyanins in concentrates are decomposed morequickly. Wang and Xu (2007) reported that anthocyanins inthe 65.0°Bx blackberry juice concentrate degraded morerapidly than that of 8.90°Bx blackberry juice, with theactivation energies of 65.06 and 75.5 kJ mol−1, respectively.The degradation of anthocyanins in raspberry pulpfollowed by a first-order reaction and the value of activa-tion energy was reported as 12.45 kcal mol−1 (Ochoa et al.1999). Garzon and Wrolstad (2002) showed that the t1/2values for anthocyanin degradation in strawberry juice andconcentrate at 25 °C were 8 and 4 days, respectively.

Hydroxymethylfurfural Formation

HMF content of both black mulberry juice and concentrateincreased significantly (p<0.01) with temperature and storagetime (Table 3). HMF contents of black mulberry juiceincreased from initial values of 45.7, 45.85, 45.7, and 45.99to 46.96, 57.2, 76.34, and 124.41 mg L−1 at the end of storagetime at 5, 20, 30, and 40 °C, respectively. There was asignificant increase (p<0.01) of HMF in black mulberry juiceat the end of 8 months storage at all temperatures except at5 °C. At the beginning of storage, HMF contents of blackmulberry concentrate were 93.22, 93.28, 94.69, and93.21 mg kg−1 at 5, 20, 30, and 40 °C, respectively. After

Table 1 The variation of total monomeric anthocyanin content of black mulberry juice and concentrate during storage at different temperatures

Black mulberry Storage (month) Temperature (°C)

5 20 30 40

Juice (mg cy-3-glu/L) 0 23.38±0.17 A a 23.13±0.09 A A 23.29±0.26 A a 23.13±0.25 A a

1 22.88±0.17 A a 22.92±0.04 A A 22.17±0.29 B b 20.25±0.29 C b

2 23.26±0.13 A a 23.21±0.17 A A 18.08±0.13 B c 16.87±0.09 C c

3 23.09±0.13 A a 22.71±0.25 A A 16.53±0.25 B d 15.32±0.29 C d

4 23.59±0.04 A a 21.38±0.26 B B 16.33±0.13 C de 12.65±0.13 D e

5 23.01±0.13 A a 20.37±0.25 B B 15.74±0.04 C e 8.64±0.04 D f

6 23.00±0.21 A a 19.96±0.00 B B 13.74±0.30 C f 8.19±0.09 D f

7 23.55±0.00 A a 18.25±0.13 B B 13.28±0.17 C f 7.39±0.04 D g

8 22.92±0.04 A a 16.70±0.00 B B 11.86±0.00 C g 5.89±0.05 D h

Concentrate (mg cy-3-glu/kg) 0 234.84±1.82 A ab 235.86±4.10 A a 233.96±1.66 A a 235.00±0.81 A a

1 235.89±0.41 A ab 195.59±1.65 B b 165.51±1.24 C b 122.38±0.41 D b

2 233.43±0.41 A b 175.45±4.52 B c 118.64±0.83 C c 82.53±1.22 D c

3 237.54±0.41 A ab 152.03±3.29 B d 99.56±2.49 C d 41.06±2.85 D d

4 249.70±13.9 A a 153.66±0.36 B d 48.56±0.91 C fg 18.30±1.22 D f

5 235.29±0.51 A ab 123.54±2.13 B e 59.26±0.11 C e 26.88±0.89 D e

6 232.39±1.75 A b 109.61±3.58 B f 50.20±0.91 C f 17.11±0.87 D f

7 232.16±2.03 A b 102.22±1.37 B f 42.80±0.08 C g 7.33±0.02 D g

8 231.88±0.97 A b 76.70±1.38 B g 25.20±1.32 C h 4.42±0.55 D h

Significant differences between sample means were assessed by Duncan multiple test. Means within a line followed by different upper case letters aresignificantly different (p<0.01). Means within a column followed by different lower case letters are significantly different (p<0.01)

Fig. 4 Arrhenius plots for anthocyanin degradation and HMF formationof black mulberry juice and concentrate


8 months storage, HMF contents of these samples were foundas 93.28, 177.44, 369.65, and 1,215.70 mg kg−1, respectively.

HMF formation in the black mulberry juice and con-centrate fitted well to the zero-order reaction kinetics.Zero- (Burdurlu et al. 2006), first- (Sancho et al. 1992),and second-order (Shallenberger and Mattick 1983)kinetic models were also reported for HMF accumulationin foods.

The heat dependence of the rate constants of HMF forma-tion was represented by the Arrhenius equation (Fig. 4).

Activation energies for HMF formation in black mulberryjuice and concentrates in the range of 20–40 °C were calcu-lated as 75.70 and 104.11 kJ mol−1, respectively (Table 2).Various researchers had been studied on kinetics of HMFformation in foods and big variations were observed in acti-vation energies. For example, activation energy for HMF incarob pekmez was reported as 114.87 kJ mol−1 in thetemperarture range of 5–45 °C (Özhan et al. 2010), whereasit was determined as 28–39.6 kcal mol−1 in apple juice modelsolution (Resnik and Chirife 1979).

Table 2 Kinetic parameters ofanthocyanin degradation andHMF formation in blackmulberryjuice and concentrate duringstorage

The values within the parenthesesare determination coefficients

Parameters Black mulberry Temperature(°C)

Rate constant(k)

Activation energy(kJ mol−1)

Anthocyanin (first-order reaction) Juice 20 0.0173 (0.8815) 56.4830 0.0350 (0.9594)

40 0.0761 (0.9814)

Concentrate 20 0.0549 (0.9726) 49.7530 0.1101 (0.9356)

40 0.2021(0.9581)

HMF (zero-order reaction) Juice 20 1.3852 (0.8601) 75.7030 3.7042 (0.9351)

40 10.080 (0.9851)

Concentrate 20 9.6904 (0.8184) 104.1130 38.212 (0.9485)

40 148.42 (0.9898)

Table 3 The variation of HMF content of black mulberry juice and concentrate during storage at different temperatures


5 20 30 40

Juice (mg HMF/L) 0 45.70±0.00 A a 45.85±0.15 A g 45.70±0.60 A h 46.00±0.30 A ı1 46.59±0.30 C a 47.40±0.37 C ef 48.82±0.60 B g 51.26±0.52 A h

2 45.85±0.15 C a 46.59±0.30 C fg 49.56±0.15 B g 61.20±0.52 A g

3 45.77±0.22 C a 46.29±0.15 C fg 53.34±0.08 B f 71.36±0.00 A f

4 46.37±0.23 D a 48.15±0.23 C e 54.97±0.37 B e 80.94±0.67 A e

5 46.29±0.15 D a 50.15±0.30 C d 59.94±0.15 B d 87.83±0.00 A d

6 46.22±0.08 D a 52.16±0.08 C c 61.72±0.30 B c 98.29±0.52 A c

7 46.29±0.15 D a 54.97±0.07 C b 71.74±0.23 B b 118.10±0.30 A b

8 46.96±0.08 D a 57.20±0.38 C a 76.34±0.23 B a 124.41±0.08 A a

Concentrate (mg HMF/kg) 0 93.22±1.48 A a 93.29±1.48 A d 94.69±2.96 A i 93.21±4.44 A i

1 92.48±0.74 C a 94.03±0.74 C d 116.88±1.48 B h 247.08±4.44 A h

2 93.00±0.76 C a 95.47±0.46 C d 176.11±2.64 B g 360.29±7.31 A g

3 93.68±1.50 C a 95.82±0.17 C d 206.72±0.12 B f 508.13±4.96 A f

4 94.03±0.84 C a 99.57±0.26 C d 287.64±3.96 B e 751.30±2.06 A e

5 93.52±1.66 D a 111.98±1.65 C c 326.72±0.39 B d 873.50±1.09 A d

6 93.52±1.66 D a 131.87±0.95 C b 348.75±1.20 B c 989.94±4.37 A c

7 94.03±0.84 D a 159.31±0.71 C a 359.40±2.19 B b 1,177.2±1.55 A b

8 93.29±1.57 D a 167.44±3.01 C a 369.65±2.23 B a 1,215.7±4.41 A a

Means within a line followed by different upper case letters are significantly different (p<0.01). Means within a column followed by different lower caseletters are significantly different (p<0.01)


The Q10 values of black mulberry juice for HMF deter-mined at the temperature ranges of 20°–30 and 30°–40 °Cwere 2.74 and 2.65, whereas these values for concentratewere 4.03 and 3.93, respectively. It is pointed out that therate of HMF formation in concentrate samples increased4.03 times when the temperature increased from 20 to30 °C.

Antioxidant Activity

The significant decrease (p<0.01) in the antioxidant activ-ity of black mulberry juice and concentrate during storageat different temperatures and times is shown in Table 4.The initial value of the antioxidant activity in black mul-berry juice was 336.24, 337.12, 337.27, and 336.64 μmolTE 100 mL−1 at temperatures of 5°, 20°, 30° and 40 °Crespectively, and in concentrates it was found as 3,099.4,3,094.1, 3,086.9, and 3,101.6 μmol TE 100 g−1, respec-tively. The loss of antioxidant activity of black mulberryjuice and concentrate during storage at 5, 20, 30, and40 °C were in the ranges of 4.87–16.01 and 4.47–33.57 %, respectively. The loss of antioxidant activitywas also reported by some investigations (Klimczaket al. 2007; Koca and Karadeniz 2008). Koca andKaradeniz (2008) showed that the antioxidant activity ofcarrot was reduced by 31 % during 6 months of cold

storage. Klimczak et al. (2007) found that antioxidantactivity measured by ferric reducing ability of plasma(FRAP) assay of orange juice stored at 18, 28, and38 °C decreased 23, 34, and 57 %, respectively at theend of storage.

Correlations Among Antioxidant Activity, MonomericAnthocyanin Content, and HMF

Antioxidant activity in black mulberry juice and concentratewas correlated with total monomeric anthocyanins (r=0.956,r=0.886, respectively, p<0.01) during storage. The correla-tion coefficient, among total monomeric anthocyanin, TEACand FRAP were reported to be significant (p<0.05) forM. nigra accessions (Özgen et al. 2009). Significant negativecorrelations were found between HMF and total monomericanthocyanin in black mulberry juice and concentrate, respec-tively (r=−0.928, −0.759, p<0.01) which indicates decompo-sition of anthocyanins coincide with the chemical browningreactions. In addition, significant negative correlations werealso found between antioxidant activity and HMF (r=−0.835for juice, r=−0.860 for concentrate, p<0.01). This negativecorrelation may be attributed to the loss of anthocyaninswhich are the main compounds responsible for antioxidantactivity in fruits.

Table 4 The variation of antioxidant activity of black mulberry juice and concentrate during storage at different temperatures


5 20 30 40

Juice (μmol TE/100 mL) 0 336.24±0.00 A a 337.12±0.00 A a 337.27±0.00 A a 336.64±0.00 A a

1 336.25±0.09 A a 334.70±0.94 A ab 335.04±1.72 A a 326.81±0.75 B b

2 336.56±0.11 A a 335.93±0.32 A ab 328.94±0.70 B b 321.78±0.66 C c

3 337.24±0.67 A a 332.39±1.62 B abc 325.68±1.03 C bc 313.77±0.42 D d

4 336.00±0.68 A a 331.37±0.56 B bc 323.89±1.19 C c 307.15±2.10 D e

5 334.75±0.96 A a 329.07±1.69 B c 318.99±0.39 C d 300.66±1.39 D f

6 332.69±1.20 A a 327.61±1.14 B c 314.05±0.75 C e 293.92±1.36 D g

7 333.32±1.91 A a 320.26±3.69 B d 301.89±0.69 C f 288.63±0.86 D h

8 319.88±0.76 A b 312.37±0.84 B e 298.37±0.93 C f 282.73±1.36 D ıConcentrate (μmol TE/100 g) 0 3,099.4±0.00 A a 3,094.1±0.00 A a 3,086.9±0.00 A a 3,101.6±0.00 A a

1 3,083.4±1.59 A a 3,062.8±3.87 A a 3,033.4±2.26 A a 2,960.9±9.49 B a

2 3,076.4±16.1 A a 3,048.1±9.27 A a 2,966.3±16.5 B b 2,843.4±10.1 C b

3 3,053.9±15.2 A ab 2,983.9±32.7 B b 2,883.1±0.02 C c 2,690.3±8.94 D c

4 3,050.5±21.9 A ab 2,901.7±2.14 B c 2,753.2±1.96 C d 2,567.2±5.11 D d

5 3,036.2±10.4 A ab 2,842.3±2.40 B c 2,666.0±26.3 C e 2,428.5±31.0 D e

6 2,993.7±1.23 A bc 2,751.6±42.0 B d 2,578.3±8.89 C f 2,304.3±10.4 D f

7 2,949.5±5.71 A c 2,639.8±12.9 B e 2,434.8±1.24 C g 2,172.7±6.90 D g

8 2,960.8±9.72 A c 2,580.7±29.9 B e 2,313.5±13.3 C h 2,060.4±1.47 D h

Means within a line followed by different upper case letters are significantly different (p<0.01). Means within a column followed by different lower caseletters are significantly different (p<0.01)


Conclusions

Kinetics of anthocyanin degradation and HMF formation inblack mulberry juice and concentrates were investigated dur-ing storage. The present data shows that the degradation ofblack mulberry anthocyanins follows first-order reactionkinetics. The activation energies of anthocyanin degradationin black mulberry juice and concentrate were found as 56.48and 49.75 kJ mol−1, respectively. As increased temperatureand storage time has an important affect on the degradation ofblack mulberry anthocyanin content, mulberry concentratesand fruit juices should be kept lower than 5 °C. HMF accu-mulation fitted to a zero-order kinetic model and activationenergies in black mulberry juice and concentrate were foundas 75.70 and 104.11 kJ mol−1, respectively. It was observedthat the increase of HMF in black mulberry concentrate at30 °C was approximately 4.03 times higher than that of at20 °C. Antioxidant activities of black mulberry juice andconcentrate were found positively correlated with total mono-meric anthocyanins.

Acknowledgments The authors wish to thank Göknur FoodstuffsImport Export Trading and Production Company (Niğde, Turkey) forpreparation of research samples.

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effect of storage on anthocyanin degradation in black mulberry juice and concentrates

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