Effect of gum arabic as an edible coating on antioxidant capacity of tomato (Solanum lycopersicum L.) fruit during storage

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t Biology and

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Effect of gum arabic as an edible coating on antioxidant capacity of tomato

(

Solanum lycopersicum

L.) fruit during storage

Asgar Ali

∗∗

_{, Mehdi Maqbool, Peter G. Alderson, Noosheen Zahid}

School of Biosciences, Faculty of Science, The University of Nottingham Malaysia Campus, Semenyih, 43500 Selangor, D.E., Malaysia School of Biosciences, Faculty of Science, The University of Nottingham Malaysia Campus, Semenyih, 43500 Selangor, D.E., Malaysia

a r a r t i t i c l c l e e i n i n f of o Article history: Article history: Received 21 June 2012 Received 21 June 2012 Accepted 23 September 2012 Accepted 23 September 2012 Keywords: Keywords: Antioxidant capacity Antioxidant capacity Gaseous exchange Gaseous exchange Gum arabic Gum arabic Solanum lycopersicum Solanum lycopersicum a b s t r a c t a b s t r a c t

Coating of tomato fruit with gum arabic has been found to delay the ripening process and maintain the Coating of tomato fruit with gum arabic has been found to delay the ripening process and maintain the antioxidant capacity. Gum arabic in aqueous solutions of 5, 10, 15 and 20% was applied as an edible antioxidant capacity. Gum arabic in aqueous solutions of 5, 10, 15 and 20% was applied as an edible coating to green-mature tomatoes which were stored at 20

coating to green-mature tomatoes which were stored at 20◦◦_{C and}_{C and 80–9}_{80–90% RH}_{0% RH for 20 days. Fruit coated}_{for 20 days. Fruit coated}

with 10% gum arabic delayed the ripening process by slowing down the rate of respiration and ethylene with 10% gum arabic delayed the ripening process by slowing down the rate of respiration and ethylene production and also maintained total antioxidant capacity, lycopene content, total phenolics and total production and also maintained total antioxidant capacity, lycopene content, total phenolics and total carotenoids during storage as compared to the uncoated control and fruit treated with 5% gum arabic carotenoids during storage as compared to the uncoated control and fruit treated with 5% gum arabic con

concencentrattrationion.. TheresulTheresultsts sugsuggesgestt thatbythatby usiusingng 10%gum10%gum arabarabicic asas anan ediediblecoatinblecoating,g, theripentheripeningprocesingprocesss oftoma

oftomatotoescanescan bedelabedelayeyedd anandd theanttheantioioxidxidantcanantcan bepresbepreserervevedd foforr uptoupto 20daysduri20daysduringstorngstoragagee atat 2020◦◦_C_C

without any negative effects on postharvest quality. without any negative effects on postharvest quality.

1.

1. IntroIntroductiductionon

Tomato (

Tomato (Solanum lycopersicumSolanum lycopersicum L.) fruit consumption is highlyL.) fruit consumption is highly corr

correlateelated d with reducewith reduced d risk of risk of canccancer er and also and also low incidelow incidence of nce of some

some cardcardiaciac diseadiseases,ses, duedue toto somesome impoimportanrtantt conconstitustituentsents presepresentnt inthefruit(

inthefruit(FrancFrancescheschiietetal.,1994al.,1994).). ThemostimporThemostimportantantt ofof ththeseareeseare carotenoids, particularly lycopene and

carotenoids, particularly lycopene and␤␤-carotene which are accu--carotene which are accu-mul

mulateatedd inin plaplasmasma anandd tistissuesuess inin relrelatiationon toto thethe intintakeake ofof tomtomatoatoeses ((Oshima et al., 1996Oshima et al., 1996).). In addition to the carotenoids, tomato fruitIn addition to the carotenoids, tomato fruit are also a rich source of natural antioxidants, which can delay or are also a rich source of natural antioxidants, which can delay or res

restratrainin ththee oxioxidatdationion ofof liplipidsids oror othotherer molmolecueculesles byby inhinhibiibitintingg ththee initiation of oxidative chain reactions (

initiation of oxidative chain reactions ( Yahia et al., 2007Yahia et al., 2007).).

However, tomato being a climacteric fruit, has a short However, tomato being a climacteric fruit, has a short posthar-vest life due to several factors such as high rate of respiration, vest life due to several factors such as high rate of respiration, weig

weightht lossloss andand enhaenhancedripeninncedripening,g, whiwhichch resultinresultin thethe earlydeteri- earlydeteri-ora

oratiotionn ofof frufruitit quaqualitlityy (( Javanmardi JavanmardiandandKubota,Kubota,2006;2006;ZapataZapataetetal.,al.,

2008

2008).). Moreover, during ripening the chemical composition of theMoreover, during ripening the chemical composition of the fruit also changes dramatically, affecting texture, ﬂavour, fruit also changes dramatically, affecting texture, ﬂavour, antioxi-dantconten

dantcontentsts mainmainlyly phenphenoliccompounoliccompounds,ds, ﬂavoﬂavonoidnoidss andand ascoascorbicrbic acid (

acid (Bailén et al., 2006Bailén et al., 2006).).

Generally, low temperature storage is used to reduce the rate Generally, low temperature storage is used to reduce the rate of respiration and thermal decomposition for extending storage of respiration and thermal decomposition for extending storage life of tomatoes. However, the prolonged storage at low life of tomatoes. However, the prolonged storage at low temper-ature causes chilling injury and also contraction of the skin occurs ature causes chilling injury and also contraction of the skin occurs as

as wawaterfromtheterfromthe skiskinn ofof thefruitmovethefruitmovess inintoto thepulpwhicthepulpwhichh lowlowersers dow

downn ththee tastastete anandd alsalsoo damdamageagess thefruitthefruit phyphysiosiologlogyy ((ZapZapataetataetal.al.,,

∗

∗ _{Corresponding author. Tel.: +60 3 8924 8219; fax: +60 3 8924 8018.}_{Corresponding author. Tel.: +60 3 8924 8219; fax: +60 3 8924 8018.}

E-mail address:

E-mail address:[email protected]@nottingham.edu.my(A. Ali).(A. Ali).

2008

2008).). Controlled atmosphere and hypobaric storage techniquesControlled atmosphere and hypobaric storage techniques are

are alsalsoo useusefulful inin extextendendiningg thethe sheshelf-lf-liflifee ofof tomtomatoatoeses butbut thethesese areare very expensive to run on a commercial scale (

very expensive to run on a commercial scale ( Artés et al., 2006Artés et al., 2006).). Thus, edible coatings based on natural products can provide an Thus, edible coatings based on natural products can provide an add

additiitiononalal proprotectectiotionn forfor frefreshsh frufruitit andand vegvegetaetablebless anandd bebe comcomple ple--ment

mentaryary toto lowlow temptemperatuerature,re, concontrolltrolleded atmoatmosphespherere andand hypohypobaribaricc storage techniques (

storage techniques (Baldwin et al., 1995Baldwin et al., 1995).). Appropriate formula-Appropriate formula-tions of an edible coating may provide an excellent barrier against tions of an edible coating may provide an excellent barrier against gaseo

gaseousus exchexchangeandangeand watewaterr lossloss whicwhichh areare detridetrimentmentalal toto posthposthar- ar-vest quality.

vest quality.

Gum arabic, obtained from stems or

Gum arabic, obtained from stems or branches of branches of AcaciaAcaciaspecies,species, is the most common polysaccharide used in the industrial sector is the most common polysaccharide used in the industrial sector beca

becauseuse ofof itsits uniquniqueue emulsemulsificaificationtion,, andfilmandfilm formiformingng andencapsu- andencapsu-lation properties which has received the highest toxicology safety lation properties which has received the highest toxicology safety status by the joint

status by the joint FAO/WHO Expert Committee on Food AdditivesFAO/WHO Expert Committee on Food Additives ((Anderson and Eastwood, 1989; Motlagh et al., 2006Anderson and Eastwood, 1989; Motlagh et al., 2006).). When usedWhen used as an edible coating, gum arabic also showed some positive results as an edible coating, gum arabic also showed some positive results and signiﬁcantly delayed ripening of cold-stored apples (

and signiﬁcantly delayed ripening of cold-stored apples ( El-AnanyEl-Anany

et al., 2009

et al., 2009).). Moreover, in a recent study by our Moreover, in a recent study by our group it was foundgroup it was found that gum arabic not only enhanced shelf-life but also maintained that gum arabic not only enhanced shelf-life but also maintained postharvest quality of mature-green tomatoes for up to 20 days postharvest quality of mature-green tomatoes for up to 20 days during storage at 20

during storage at 20◦◦_C_{C ((Ali et al., 2010}_{Ali et al., 2010}_)._).

In another study by

In another study by Zapata et al. (2008)Zapata et al. (2008),, it was found thatit was found that polys

polysaccaccharidharide-base-based ed edibledible e coatcoatings such ings such as as algialginate or nate or zeinzein showed some beneﬁcial effects in retarding the ripening process showed some beneﬁcial effects in retarding the ripening process and maintaining quality of stored tomatoes. Similarly,

and maintaining quality of stored tomatoes. Similarly, Oms-OliuOms-Oliu

et al. (2008)

et al. (2008)aalso studied the effect of alginate, pectin and gellan-lso studied the effect of alginate, pectin and gellan-based edible coatings on the shelf-life and antioxidant properties based edible coatings on the shelf-life and antioxidant properties of fresh-cut ‘Piel de Sapo’ melon. They found that of fresh-cut ‘Piel de Sapo’ melon. They found that polysaccharide-based edible coatings not only

based edible coatings not only prevented the dehydration but alsoprevented the dehydration but also

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inhibited the ethylene production and triggered the accumulation of total phenolic compounds and other compounds with antiox-idant properties. However, there has been limited information available on the use of edible coatings in delaying ripening pro-cesses and preserving antioxidants during storage, particularly in fresh fruit and vegetables.

Therefore, the aim of this study was to determine whether gum arabichas the potential to be used as an edible coating for delaying ripening whilst maintaining the antioxidant properties of tomatoes during storage.

2. Materials and methods

2.1. Plant material

Tomato (S. lycopersicum L. var. Money Maker) fruit of colour index 2 (greenwithtrace of yellow) according tothe USDA standard tomato colour classiﬁcation chart (USDA, 1991) were obtained from a local supplier in Semenyih, Selangor, Malaysia. Fruit of uni-form size, shape, free from any mechanical damage and insect or pathogenic infection were selected for the experiment.

2.2. Preparation of gum arabic solutions and application of coating treatments

Gum arabic powder (KB-120, Food Grade) was imported from Jumbo Trading Co., Ltd. Bangkok, Thailand. Gum arabic concen-trations were selected on the basis of previous experiments (Ali et al., 2010). Brieﬂy, gum arabic solutions (5, 10, 15 and 20%, w/v), were prepared bydissolving5, 10, 15and 20g of powder in 100 mL puriﬁed water. The solutions were stirred with low heat (40◦_{C) for}

60min on a magnetic stirrer/hot plate (Model: HTS-1003), then ﬁl-tered to remove any undissolved impurities using a vacuum ﬂask. After cooling to 20◦_{C, glycerol monostearate (1.0%) (Sigma) was}

added as a plasticizer to improve the strength and ﬂexibility of the coating solutions. The pH of the solutions was adjusted to 5.6 with 1 N NaOH. Tomato fruit were washed with sodium hypochlorite (0.05%) for 3 min and air-dried at ambient temperature (25±3◦_C).

Afterdrying, tomato fruitwere randomly divided intoﬁve different treatments andeach treatmentwas conducted withfour replicates. Fruitwere dipped in eachconcentration of gum arabic coating solu-tion (5, 10, 15 and 20%) for 2–3min and it was assured that the coating solution was applied uniformly on the whole surface while control fruit were dipped in puriﬁed water only. The fruit were then air-dried, packed in cardboard boxes and stored at 20 ±1◦_C

and 80–90% RH. The data were collected before treatment (day 0) and at 4 day intervals for 20 days.

2.3. Determination of respiration rate and ethylene production

The rates of respiration andethyleneproduction weremeasured according to the method describedby Maqbool et al. (2011). Respi-rationrateas indicatedby CO2production was measured by placing

two tomatofruitin 1 L plastic container for 1 h,and1 mLof gas sam-ple waswithdrawn fromthe headspace witha gastight hypodermic syringe and analysed with a gas chromatograph (GC) (Claru-500, Perkin Elmer, USA) equipped with a stainless steel column (Pora-pak R 80/100). Helium served as the carrier gas at a ﬂow rate of 20mL −1_{min. Temperatures were 60, 100 and 200}◦_{C for the oven,}

injector and thermal conductivitydetector (TCD), respectively. One mL of CO2gas (1.0%) (Scotty gases, Beltifonte, PA, USA) was used as

theexternalstandard for calibration.The amount of CO2production

was expressed in mg−1_kg−1_h.

The ethylene production was measured by taking 1 mL sam-ple from each jar using hypodermic syringe and injecting it into a GC. The GC was equipped with a stainless steel column (PorapakT,

100/120) and a ﬂame ionization detector (FID). Nitrogen, hydrogen and air ﬂow rates were 20 mL −1_{min. Nitrogen served as a carrier}

gas. Temperatures were 150, 200 and 200◦_{C for the oven, injector}

and FID, respectively. One mL ethylene gas (10␮L −1_{mL) (Scotty}

gases, Beltifonte, PA USA) was used as the external gas standard wasinjectedfor calibration.The amount of ethylene wasexpressed in␮g−1_kg−1_h.

2.4. Total phenolic content

Theamountof total phenolic contents intomato fruit wasdeter-mined according to the Folin-Ciocalteau (FC) procedure (Singleton and Rossi, 1965) with slight modifications. Briefly, 0.1 mL of fruit samplefroma mixture of 15fruitin each treatmentwas mixed with 0.5 mL of FC along with 1.5 mL of 7% sodium carbonate solution. Purified water was added to the solution to make the volume up to 10 mL. The mixture was incubated at 40◦_{C for 2 h. The absorbance}

was recorded at 750 nm using a UV-VIS Spectrophotometer (Var-ioskan Flash Multimode Reader, Thermo Fisher Scientiﬁc, USA) and the results were expressed in mg of gallic acid equivalent to 100 g of fresh weight of fruit sample.

2.5. Lycopene extraction

Lycopene extraction was based on the method of Fish et al. (2002) with minor modifications. Briefly, 0.6 mL of fruit juice from a mixture of 15 fruit in each treatment was mixed with 5 mL of 0.05% butylated hydroxytoluene in acetone along with 5 mL of 95% ethanol and 10mL of hexane. The mixture was agitated at 180 rpm for 15 min on ice. Three mL of ice cold water was added and again shaked for 5 min. The absorbance was recorded at 503nm using a UV-VIS Spectrophotometer (Varioskan Flash Multimode Reader, Thermo Fisher Scientific, USA). The amount of lycopene in tissues was then calculated by the following formula:

Lycopene(␮g−1_g)

= ( x/y)× A503×3.12 (1)

where x is the amount of hexanes (mL), y the weight of fruit tis-sue (g), A503the absorbance at 503 nm and 3.12 is the extinction

coefﬁcient.

2.6. Total carotenoids

Total carotenoids were estimated following the method of Lalel et al. (2003). Brieﬂy, 2 g of fruit pulp from a mixture of 15 fruit in each treatment was ground with 0.05g of magnesium carbon-ate and extracted two times with a 20mL of acetone: n-hexane [75:60, v/v]. The pool extract was washed with a 40mL of 10% NaCl and 2×40 mL of distilled water to remove acetone. The n-hexane extract was measured for its absorbance at 436 nm using UV-VIS Spectrophotometer (Varioskan Flash Multimode Reader, Thermo Fisher Scientiﬁc, USA). Total carotenoids were expressed as mg−1_g

of ␤-carotene equivalent to a standard curve of ␤-carotene. 2.7. Antioxidant capacity

Ferric Reducing Antioxidant Power (FRAP) assay was used to measure the total antioxidant capacity in tomato fruit. Brieﬂy, the FRAPreagentcontained2.5 mL of 10 mM 2,4,6-Tripyridyl-s-triazine (TPTZ) solution in 40 mM hydrochloric acid along with 2.5 mL of 20mM FeCl3 and 25 mL of 0.03 mM acetate buffer having pH 3.6

(Benzie andStrain, 1996). The reaction mixture consists of 40␮L of fruit extract from a mixture of 12 fruit in each treatment mixed with 3mL of FRAP reagent followed by incubation at 37◦_{C for}

4 min. Absorbance was recorded at 593nm using UV-VIS Spec-trophotometer (Varioskan Flash Multimode Reader, Thermo Fisher

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Scientiﬁc, USA) and the results were expressed as the concentra-tion of antioxidant having a ferric reducing activity equivalent to 1 mg−1_{g ferrous sulphate (FeSO}

4) of fresh weight of fruit sample.

Total antioxidant capacity was also measured through deter-mining the free radical scavenging effect on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, according to the method described by Elez-Martínez and Martín-Belloso (2007) with slight modiﬁ-cation. Prior to analysis, 25 mg−1_{L of DPPH solution was freshly}

prepared by dissolving in 100% (v/v) methanol. Cuvette was ﬁlled with 3 mL of DPPH solution. Then 5␮L ofsample froma mixture of 12 fruit in each treatment was added into the cuvette and mixed well by using the same pipette tip. The mixture was left to react for 15min. Theabsorbance was measured at 515 nmwavelength using UV-VIS Spectrophotometer (Varioskan Flash Multimode Reader, Thermo Fisher Scientiﬁc, USA) against a blank of methanol with-out DPPH. Results were expressed as a percentage decrease with respect to the absorption value of reference DPPH solution.

2.8. Statistical analysis

The experiment was arranged in a completely randomized design (CRD) with four replications. The data were subjected to analysis of variance (ANOVA) using MSTAT-C software (Version 1.3, Department of Crop and Soil Sciences, Michigan State Univer-sity, EastLansing, Michigan, USA), while LeastSigniﬁcantDifference (LSD) test was used to compare differences between treatments at 95% conﬁdence level of each variable.

3. Results and discussion

3.1. Rate of respiration and ethylene production

Rate of respiration and ethylene production in fresh fruit and vegetables are considered good indexes for the determination of storage life. A decrease in respiration rate was observed initially in fruit treated with higher concentrations of gum arabic while a sharp increase in untreated control and5% gumarabic treated fruit was observed which reached to a peak value after 8 days and after that therewas a continuous decrease until theend of storage period (Fig. 1a). However, fruit treated with 10% gum arabic signiﬁcantly delayed respiration rate and showed the similar peak height after 12days of storage. In the case of 15 and 20% gumarabic coatedfruit, a slight increase in respiration rate was observed during complete storage period.

Ethylene production in untreated control and 5% gum arabic coated fruit increased rapidly and reached a peak after 8 days then decreased sharply during the complete storage period (Fig. 1b). However, 10% gum arabic treated tomatoes showed a maximum value of ethylene production after 12 days of storage and there-after, a slow decrease until the end of storage period. While the fruit treated with 15 and 20% gum arabic showed a slight but con-tinuous increase in ethylene production during complete storage period.

The delayed increase in respiration rate and ethylene produc-tion of 10% gum arabic coated fruit as compared to the untreated control and 5% gum arabic coated fruit suggests that edible coat-ing exerted a barrier to the gaseous exchange. The reduced rate of respiration and ethylene production in tomato fruit might be cor-related with delayed senescence (Ali et al., 2010) and a reduced susceptibility to decay (Maqbool et al., 2010). Similarly, in a pre-vious study on tomato using gum arabic, it was found that fruit coated with 10 and 15% gum arabic had less weight loss during storage as compared to the control which could be attributed to the coatings providing a semi-permeable barrier against gas move-ment and therefore, reduced the rate of respiration and ethylene

Storage Time (Days)

0 5 10 15 20 25 E t h y l e n e ( u g - 1 k g - 1 h ) 0 5 10 15 20 25 30 C O 2 ( m g - 1 k g - 1 h ) 0 2 4 6 8 10 12 14 16 18 20 Control 5% gum arabic 10% gum arabic 15% gum arabic 20% gum arabic a b

Fig.1. Effect of differentconcentrations of gum arabicon (a)respiration rateand (b) ethylene production of tomato fruit during storage (20◦_{C, 80–90% RH). The vertical}

bars represent the standard error of means for four replicates.

production (Ali et al., 2010). The pattern of respiration rate and ethylene production in this study was in agreement with the find-ings of Banks (1984), who reported that coating bananas with TAL Pro-long suppressed the rates of respiration and ethylene produc-tion by modifying the internal atmosphere of the fruit. Similar results were also observed by Ali et al. (2011), where they found that control fruit showedearlyrise in respiration and ethylene pro-duction as compared to 1.5% chitosan coated papayas during five weeks of storage. A reduction in respiration rate and ethylene pro-duction as a result of coating with films has also been reported by many researchers in various fruit, such as papaya, grapes, mango and strawberries (El-Ghaouth et al., 1992; Kittur et al., 2001; Ali et al., 2011).

3.2. Total phenolic content

The maximum amount of total phenolic content was observed in 10% gum arabic coated fruit and reached to a peak after 12 days thendecreased sharply during thecomplete storageperiod (Fig.2a). However, untreated control and 5% gum arabic coated tomatoes showed a maximum value of total phenolic content after 8 days of storage and thereafter, a slow decrease until the end of storage period. While the fruit treated with 15 and20% gumarabic showed a slight but continuous increase in total phenolic content during complete storage period.

The increase in total phenolic content is related with the enhancement of antioxidant capacity(Reyes and Cisneros-Zevallos,

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Storage Time (Days) 0 4 8 12 16 20 24 L y c o p e n e ( µ g g - 1 ) 30 40 50 60 70 80 90 100 T o t a l p h e n o l i c s ( m g g a l l i c a c i d - 1 1 0 0 g F W ) 2 4 6 8 10 12 14 16 18 20 Control 5% gum arabic 10% gum arabic 15% gum arabic 20% gum arabic b a

Fig. 2. Effectof differentconcentrationsof gumarabicon (a)totalphenoliccontent and (b) lycopene content of tomato fruit during storage (20◦_{C, 80–90% RH). The}

vertical bars represent the standard error of means for four replicates.

2003). Therefore, in our study, the maximum amount of total phe-nolic content in 10% gum arabic coated tomatoes means that those fruit maintained higher amounts of antioxidants than uncoated and fruit coated with higher concentrations of gum arabic. A low amount of total phenolic content or a sharp decline after 8 days in untreated control and 5% gum arabic coated fruit might be due to the higherrate of respiration whichresulted in the loss of total phe-nolic contentdue to thedegradationof certain phephe-noliccompounds (Day, 2001). It might also be due to senescence and breakdown of cell structure during storage, as was observed in a previous study on tomato using gum arabic (Ali et al., 2010). The results of the present study are comparable with the previous ﬁndings of Ghasemnezhad et al. (2010), in which they reported the decrease in phenolic content of apricot at higher concentrations of chitosan due to senescence.

3.3. Lycopene content

The lycopene content increased with the storage time in all the treated and untreatedcontrol fruit(Fig.2b). However, the lycopene content in untreated control and 5% gum arabic coated tomatoes increased sharply and reached to a maximum peak after 12 days of storage while the similar peak in 10% gum arabic coated fruit was observed after 16 days of storage. On the other hand, there wereminimumlevels of lycopene contentin tomatoes treated with higher concentrations of gumarabic(15 and20%) evenafter 20 days of storage.

The early increase in lycopene content in untreated control and fruit treated with 5% gum arabicconcentration might be due to the faster ripening of fruit than in the fruit treated with higher con-centrations of gum arabic. The production of lycopene content is directly correlated with ripening ( Javanmardi and Kubota, 2006 ). Similar results were also reported when tomato fruit were stored at 4◦_{C (Giovanelli et al., 1999). It has also been reported that the}

formation of lycopene depends on the temperature range and rate of respiration during storage ( Javanmardi and Kubota, 2006). In a recent study on tomato using gum arabic as an edible coating, a slight change in colour in fruit coated with 15 and 20% gum arabic concentrations was observed even after 20 days of storage which suggest that at higher concentrations the ripening process was blocked and therefore, fruit were still green but off-ﬂavoured after 20 days of storage (Ali et al., 2010).

3.4. Total antioxidant capacity

The maximum amount of total antioxidant contents in terms of both FRAP and DPPH was observed in 10% gum arabic coated fruit and reached to a peak after 16 days and then decreased sharply until the end of storage period (Fig. 3a and b). However, untreated control and 5% gum arabic coated tomatoes showed a maximum value of total antioxidant after 8 and 12 days, respectively, and thereafter, a slow decrease until the end of storage.

It has been shown that the main antioxidants in tomatoes are carotenoids, ascorbic acid and phenolic compounds (Giovanelli

Storage Time (Days)

0 4 8 12 16 20 24 D P P H ( % ) 80 100 120 140 160 180 200 220 F R A P ( F e S O 4 m g - 1 g F W ) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Control 5% gum arabic 10% gum arabic 15% gum arabic 20% gum arabic b a

Fig. 3. Effect of differentconcentrations of gum arabic on totalantioxidant capacity (a) FRAP and (b) DPPH value of tomato fruit during storage (20◦_{C, 80–90% RH). The}

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et al., 1999). However, the antioxidant capacity of tomatoes also depends on several other factors including genetics, environmen-tal conditions, production techniques used, date of harvest and postharvest storage conditions (Dumas et al., 2003). In general, a positive correlation has been reported between total phenolic content and total antioxidant capacity ( Reyes and Cisneros-Zevallos, 2003). The delayed increase in antioxidant activity in fruit treated with 10% gum arabic concentration could be related to the delayed ripening of those fruit as compared to the con-trol and 5% gum arabic coated fruit, and it was quite obvious in a previous study as well where the tomato fruit coated with higher concentrations of gum arabic slowed down the ripening process by delaying the biochemical and physiological changes occurring during storage (Ali et al., 2010). The total antioxi-dant activity is highly dependent on ripening processes of fruit. During ripening, the total antioxidant activity increases and this increase is mainly due to the changes into the lipophilic antioxidant activity (Cano et al., 2003). In addition, some other possible factors such as the amount of ␤-carotene, vitamin C and vitamin E also affect the antioxidant activity ( Dumas et al., 2003).

3.5. Total carotenoids

The amount of total carotenoids increased initially and reached to a maximum in control fruit after 8 days of storage andthe similar peak in fruit treated with 5% and 10% gum arabic concentrations was achievedafter 12and 16days,respectively (Fig.4). However,in fruittreatedwith higher concentrations of gumarabic (15 and20%), there was a slight increase in total carotenoids during complete storage period.

The early increase in total carotenoids in control and 5% gum arabic treated fruit suggests that those fruit were ripened earlier as compared to the fruit treated with higher concentrations of gum arabic as it was observed in a previous study as well, where gum arabic coated fruit at higher concentrations gave better results in terms of quality andshelf-life(Aliet al., 2010). Thegum arabiccoat-ing concentration of 10% delayed the ripenarabiccoat-ing process by slowarabiccoat-ing down the respiration and therefore, maintained higher amount of total carotenoids until day 16 of storage. Yahia et al. (2007) also reported similar results when they exposed tomatoes to 34◦_{C and}

then stored at 20◦_{C for up to 4 weeks.}

Storage Time (Days)

0 4 8 12 16 20 24 T o t a l c a r o t e n o i d s ( µ g g - 1 ) 20 30 40 50 60 70 80 90 100 Control 5% gum arabic 10% gum arabic 15% gum arabic 20% gum arabic

Fig.4. Effect ofdifferent concentrationsof gumarabic ontotal carotenoidsof tomato fruit during storage (20◦_{C, 80–90% RH). The vertical bars represent the standard}

error of means for four replicates.

4. Conclusions

In conclusion, the present study shows that gum arabic, as a preservative material, could delay the ripening process by inhibi-ting the respiration rate and ethylene production in tomato fruit. This suggests that gum arabic not only extends the storage life but also preservesthe antioxidant capacityduringstorage andalso sug-gests that gum arabic is promising as an edible coating to be used in commercial postharvest applications for prolonging the storage life and preserving antioxidant levels of tomato fruit.

Acknowledgements

The authors would like to thank the Ministry of Agriculture (MOA), Malaysia for providing ﬁnancial support under the project grant (05-02-12-SF0031) and Jumbo Trading Co., Ltd. Bangkok, Thailand for providing gum arabic.

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