Investigation of TiO 2 nanoparticle efficiency on decolourisation of industrial date syrup

Original article

Investigation of TiO2 nanoparticle efficiency on decolourisation of

industrial date syrup

Mahshad Nasabi,1 Mohsen Labbafi,1 Mehri HadiNezhad,1* Mohammadreza Khanmohammadi2 &

Amir Bagheri Garmarudi3

1 Department of Food Science and Technology, Faculty of Agricultural Engineering and Technology, University of Tehran, Karaj, Iran

2 Department of Chemistry, Faculty of Science, Imam Khomeini International University, Qazvin, Iran

3 Department of Chemistry and Polymer Laboratories, Engineering Research Institute, Tehran, Iran

(Received 6 March 2012; Accepted in revised form 20 July 2012)

Summary The TiO2 nanoparticle photocatalyst was used to decolourise industrial date syrup. The effect of TiO2

concentration (1 and 4% w/v), UV power (15 and 30 w) and processing time (12 and 48 h) on date syrup

characteristics was investigated using a factorial design. The colour, turbidity, sugar content, total phenolic

compounds, ash content and mineral (K, Na, Ca, Mg and Fe) of date syrup were analysed. The results

demonstrated that using TiO2 nanoparticle as a photocatalyst for the decolourisation of date syrup is an

effective and promising method. Colour in all treatments was significantly (P < 0.05) reduced between 30

and 53% in comparison with the initial date syrup (491 000 IU), and the reduction was even higher for

date syrup turbidity (between 47 and 75%). The result showed that the process condition significantly

affected the colour and turbidity reduction. On the basis of the result, the best treatment was TiO2 4%,

15 w and 48 h. Under this condition, date syrup colour, turbidity, ash content, sugar content reduced by

52%, 61%, 13% and 9%, respectively.

Keywords Decolourisation, industrial date syrup, photocatalyst, sugar content, TiO2 nanoparticle, turbidity.

Introduction

Date palms (Phoenix dactylifera L., Arecaceae) are oneof oldest cultivated plants that are widespread in theMiddle East and North Africa (Al-Farsi et al., 2005).Fruit of the date palm contains carbohydrates (70–80%) mostly fructose and glucose and is also a goodsource of vitamins A, C and B complex, and calcium,magnesium, phosphorus, zinc, iron, potassium, iodineand low amounts of fat and protein (Vayalil, 2002;Al-Farsi et al., 2007). Low-quality date cultivationcomprises 60% of the total plantation. These dates areunsuitable for consumption and usually are sold atlow prices as animal feed. But they contain highamount of sugar that can be utilised as date syrup, amain by-product of date. A most common density fordate syrup is 75 °Brix at which level it is self-preserv-ing and crystallisation only occurs after prolongedstorage. To use date syrup as a source of sugar, it isnecessary to clarify it. Clarification not only covers theprocess of freeing the extracted raw juice from nonsol-uble but is also concerned with removal of some

soluble (e.g. colouring matter) and semi-soluble (e.g.pectin) (Barreveld, 1993). Extensive technical researchand feasibility studies have been conducted especiallyin the seventies and early to mid-eighties to producedifferent date by-product such as date liquid sugar andhigh fructose syrup (HFCS) in the industrial scales(Mohamed & Ahmed, 1981; Samarawira, 1983;Barreveld, 1993; Al-Abid, 2006; Ashraf & Hamidi-Esfahani, 2011). The most effective methods used toclarify date syrup include active carbon, resins,enzymes and filter aids (Mohamed & Ahmed, 1981;Kovacs & Nagy-Gasztonyi, 1985; Barreveld, 1993;Abbes et al., 2011; Ashraf & Hamidi-Esfahani, 2011).Process of liming and carbonisation involves high-energy costs and results in the environmental pollutionthat cannot be neglected (Gyura et al., 2005). On theother hand, resins involve the use of high levels ofwater consumption and effluent disposal. Resorting toresins or other adsorbents appears unavoidable (Le-wandowski et al., 1999). It is to be noted that, accord-ing to the clarification method applied, also somedesirable substances like flavour components may beremoved, and the final product may, apart from hav-ing a different appearance and colour, also have amodified taste and quality.

*Correspondent: Fax: +98-261-2249453;

e-mail address: [email protected]

International Journal of Food Science and Technology 2013, 48, 316–323

doi:10.1111/j.1365-2621.2012.03189.x

© 2012 The Authors. International Journal of Food Science and Technology © 2012 Institute of Food Science and Technology

316

Pigments of various natures in some fresh dateshave been identified as caratonoids, anthocyanins,flavones, flavonoles, lycopene, carotenes, flavoxanthinand lutein (Barreveld, 1993). Mohamed & Ahmed(1981) reported that the colour groups, including deg-radation products of reducing sugars, melanoidinesand iron-polyphenolic complexes, contributed to thecolour of date syrup. Colourants in the sugar industrycan be divided into two groups, natural and thosewhich formed during processing (Mersad et al., 2003).

Titanium dioxide (TiO2), encompassing all its threecrystal forms, has wide applications in various fields.One of the most recent applications is as a photocata-lyst for the degradation of organic dyes (Goncalveset al., 1999; Tatsuma et al., 1999; Augugliaro et al.,2002; Huang et al., 2008; Han et al., 2009; Oliveiraet al., 2011; Szabo-Bardos et al., 2011).

Titanium dioxide nanoparticle provides high chemi-cal stability, high resistance in acidic and alkalinemedia and nonpoisonous characteristics while it is safeand can be easily prepared at low cost. The TiO2 semi-conductor absorbs a small portion of solar spectrumin the UV region (band gap energy of anatase TiO2 is3.2 eV and 3.0 eV for rutile TiO2) (Chatterjee et al.,2008). Therefore, it facilitates the decomposition oforganic compounds by UV-light, resulting in produc-tion of nontoxic CO2, H2O and some inorganicproducts (Deshpande et al., 2006). According toDominguez et al. (1998), photocatalytic oxidation pro-cesses can oxidise a wide variety of organic com-pounds to harmless inorganic compounds such asmineral acids, CO2 and H2O. Also, this process formssome by-products such as halides, metals, inorganicacids and organic aldehydes, depending on the initialmaterials and the extent of decolourisation (Robinsonet al., 2001).

Upon illumination of TiO2 with light energy greaterthan its band gap energy, paired electron (e�) and hole(h+) are created (McMurry et al., 2004). In aqueoussolution, the photo-induced h+ may react with surfacehydroxyl groups or surface-bound water molecules toproduce hydroxyl radicals (˙OH), the primary oxidantin the photocatalytic system. Simultaneously, thephoto-induced e� could be trapped by oxygen to formsuperoxide radical anions O2

�. The degradation oforganic substrates seems to be mediated by a series ofreactions initiated by these primary oxidising species,particularly ˙OH radicals. Owing to the reactivity andnonselectivity of ˙OH radicals, UV/TiO2 process ismore destructive of numerous organic substrates thantraditional oxidation methods. It was suggested thatthe ˙OH radicals attack organic substrates present at ornear the surface of TiO2 (Chen et al., 2005). Therefore,the adsorption of organic substrates onto the surface ofTiO2 plays an important role in the photocatalyticdegradation.

To the best of our knowledge, there is no previousresearch in the literatures which has been employedthis technique to decolourise date syrup. Therefore,the objective of this study was to determine the effectof TiO2 nanoparticles photocatalyst in decolourisationof the industrial date syrup. The qualitative and quan-titative characteristics of date syrup treatments includ-ing sugar content, total phenolic compounds, ashcontent, and mineral were measured and comparedwith the initial date syrup. This research could be aninitial step for the utility of nanotechnology in deco-lourising industrial date syrup.

Materials and methods

Concentrated date syrup (Sibasan factory, Kerman,Iran) with °Brix 75 was used. The method for datesyrup production included date washing, mixing withequal amounts of water, extracting at 60 °C, centrifug-ing, filtering, evaporating at 70 °C to °Brix 75 andpacking. Before each experiment, date syrup wasdiluted to known Brix in order to perform the process.Titanium dioxide (TiO2) was synthesised in Depart-ment of Chemistry (International University of Ima-mkhomeini, Ghazvin, Iran) with a crystallographicmode of 80% anatase and 20% rutile, an average par-ticle size of 25 nm, and a BET surface area of50 m2 g�1 (Brunauer et al., 1938).All solutions were prepared with analytical grade

reagents, and double-distilled water was used to prepareexperimental solutions except those used for preparingHPLC analysis solutions, which was deionised water.

Photochemical reactor

The photocatalytic experiments were performed insidean ultraviolet (UV) chamber using UV-365 nm lamps(15 and 30 W –Philips, Amsterdam, The Netherlands).Cold air was passed over the chamber to limit heatingby a cooling fan at the bottom. The surfaces of the reac-tion mixtures were positioned 100 mm below the lamps.While radiation, a rotator (RO04 rotator; Parsazma,Tehran, Iran) provided agitation to keep the suspensionhomogeneous. For each treatment, 50 mL of date syrup(°Brix 10 determined by a refractometer (Belingham+ Stanely, England) at 25 °C) with proper amount ofTiO2 (according to Table 1) was mixed and prior toirradiation, the dispersions were magnetically stirred inthe dark for 10 min. The reaction mixtures were pouredinto 70-mL glass tubes and sat on the top of the rotator.Samples were irradiated at different times and differentlamp power (according to Table 1). At any given irradi-ation time interval, the dispersion was sampled and cen-trifuged at 3600 g for 15 min (Universal 320; Hettichcentrifuge, Tuttlingen, Germany) to separate the TiO2

particles.

© 2012 The Authors

International Journal of Food Science and Technology © 2012 Institute of Food Science and Technology

International Journal of Food Science and Technology 2012

Investigation of TiO2 nanoparticle efficiency M. Nasabi et al. 317

Colour measurement

To study the effect of TiO2-UV process on decolouri-sation of date syrup, after each treatment, sample wasdiluted (10 times) by TRIS buffer and neutralised atpH 7 (digital pH meter, GLP22 CRISON, EEC).Then, the absorbance was determined at 420 nm usinga spectrophotometer (UNICO2100 series, China). Thecolour was expressed in ICUMSA units (IU) definedaccording to equation 1 (ICUMSA, 1994);

IU ¼ 100000� A

b� c� qð1Þ

whereA = absorbance of the test sample at 420 nmb = length (cm) of the adsorbing pathc = °Brix (g per 100 mL) of the test sampleρ = Density (g mL�1) of the test sample

HPLC analysis

HPLC apparatus (Knauer, Germany) with Vertexcolumn 300 9 8 mm, packing material (EurokatH-10 lm) was used to determine glucose and fructosecontent of samples. The mobile phase consisted ofH2SO4 0.01 N at a flow rate of 0.5 mL min�1. All sam-ple solutions were filtered through hydrophilic celluloseacetate disposable syringe filters (MN, USA) with thepore size 0.45 lm and diameter 25 mm. Twenty micro-litres of each sample was injected into the column. Thetemperature was maintained at 30 °C, and the detec-tion was performed by RI detector (knauer-k-2301;Berlin, Germany). Sugars (glucose and fructose) wereidentified by comparison of their retention times with astandard. They were quantified according to their area,obtained by integration of the peaks.

Measurement of total phenolics compounds

The amount of total phenolics compounds in sampleswas determined according to the Folin– Ciocalteu pro-cedure (Singleton & Rossi, 1965). Samples (1 mL,three repeats) were introduced into test tubes; 0.5 mL

of Folin–Ciocalteu’s reagent and 1 mL of a saturatedsodium carbonate solution were added (final volumeset at 5 mL using methanol). The tubes were mixedand allowed to stand for 30 min. Absorption at 765nm was measured by spectrophotometer (UNICO2100,China). The total phenolic content was expressed asgallic acid equivalent (GAE) in mg per 100 mL datesyrup (°Brix 10, Dayton, NJ, USA).

Turbidity, ash and mineral measurement

Turbidity of date solutions was measured by themeans of a portable turbidometer (Turbidimeter 350;Weilheim, Germany).Ash measurement was taken according to the

method ISIRI -5186 (ISIRI, 1986) using a conductivitymeter (Hanna – HI 8633, Italy).Mineral elements including calcium, potassium,

sodium and magnesium were measured by flamephotometer (ELE, England) after proper sample dilu-tions. Iron element was measured by atomic absorptionspectrophotometer (AAS canalyst 300; Perkin Elmer,Waltham, MA, USA) after proper sample dilution.

Design of experiments and statistical analysis

In the preliminary test (data are not shown), photo-catalytic decolourisation process was optimised usingresponse surface methodology (RSM), a Box–Behnkendesign. The effect of TiO2 (1, 2 and 4%), date syrupconcentration (10, 20 and 30 °Brix), UV power (10,22.5 and 30 w) and processing time (12, 30 and 48 h)on the colour of date syrup were determined, and theoptimum points (maximum colour, turbidity and ashreduction and minimum sugar reduction) were chosento design treatments in the next step as shown inTable 1 (°Brix was 10 for all treatments). All analyticaldeterminations were performed at triplicate. Values ofdifferent parameters were expressed as the mean ±standard deviation (x ± SD). All measured parameterswere compared with the corresponding parameter ofinitial date syrup (°Brix 10, Table 2) and the differ-ences were expressed as a percentage of decrease orincrease.To investigate the effect of TiO2 and irradiation

separately, one sample include TiO2 addition (4% and48 h) but without irradiation and another samplewithout TiO2 addition but include irradiation (15 wand 48 h) were also designed (known as blank experi-ments in the text and blank (UV-TiO2) in the Figuresand Tables).All treatments including the initial date syrup and

two blanks (blank UV and blank TiO2) were analysedand compared together using SAS software (version9.1.3 Service Pack 4. 2008; SAS Institute Inc, Cary,NC, USA). However, to illustrate the effect of selected

Table 1 Factorial designed treatments

TiO2 Concentration

(% w/v) Time (h)

UV lamp

power (w)

1 12 15

1 48 15

1 12 30

1 48 30

4 12 15

4 48 15

4 12 30

4 48 30

© 2012 The Authors

International Journal of Food Science and Technology © 2012 Institute of Food Science and Technology

International Journal of Food Science and Technology 2012

Investigation of TiO2 nanoparticle efficiency M. Nasabi et al.318

parameter (the concentration of TiO2, the processingtime and UV lamp power), in the result section com-parisons were presented between the initial date syrupand those three parameters and then to probe if anyof TiO2 or irradiation parameters alone has beenaffected the process, they have been compared withinitial date syrup, separately. Duncan’s multiple rangetests were used to compare any significant differencebetween the means (P < 0.05).

Results and discussion

The effect of photocatalytic procedure on colour

Colour in all the samples was reduced between 30 and53% in comparison with the initial date syrup(491 000 IU, Table 2). As shown in Fig. 1, TiO2 con-tent of 4% (w/v) was significantly more effective ondate syrup decolourisation than TiO2 content of 1%(w/v). The UV lamp powers were not significantly dif-ferent in colour reduction. A significant reduction indate syrup colour was observed by increasing the timeof process from 12 to 48 h.

Treatments TiO2 content 4%, UV power 15 w, 48 hand TiO2 content 4%, UV power 30 w, 48 h had sta-tistically the highest colour reduction among the othertreatments. As these two treatments were not signifi-cantly different in colour reduction, so it is preferableto use lamp with lower power.Blank experiments including samples without addi-

tion of TiO2 did not show significant decolourisationof the irradiated solution compared with the initial datesyrup, but samples with 4% (w/v) TiO2 without irradi-ation significantly decreased date syrup colour after48 h (381000 ± 572 IU). This is because of the adsorp-tion of colourant molecules on the surface of TiO2.These finding demonstrate TiO2 absorbance ability ofthe colouring matters could achieve 22% date syrupcolour reduction, however oxidation capability of TiO2

photocatalyst reduced colouring matter up to 53%.Mohamed & Ahmed (1981) reported that melanoi-

dine-type compounds (the major part of syrup colou-rants) showed a low selective adsorption tendency onboth charcoal and anion resins. They suggested thatuse of calcium phosphate precipitation could be aneffective clarification for the maximum removal ofthese colourants.Al-Farsi (2003) reported date juice (total soluble sol-

ids 20.5%) colour reduction by filtration (44.6%), acti-vated carbon (29%) in powder form and (57%) ingranular form. Fathi (2009) also reported about 56%date syrup (°Brix 75) decolourisation by ultrafiltrationmethod.It has been reported that the main colour groups in

date syrup include melanoidines and iron-polyphenoliccomplexes (Mohamed & Ahmed, 1981). Melanoidinsare high molecular weight amino–carbonyl compoundsproduced by nonenzymatic browning reactions calledas Maillard reactions during the food processing. Thechemical structure of melanoidins is not understoodclearly, however, the unsaturated bonds of C = C andC = N have been suggested to be important for thestructure of melanoidins chromophore (Chandra et al.,2008). Melanoidins were suggested to be decolourisedby the H2O2, hydroxyl, perhydroxyl and active oxygenradicals (Agarwal et al., 2010). Regarding these radi-cals are the primary oxidising species in the photocata-lytical degradation of TiO2 nanoparticles, it could beexplained that date syrup colourants have been oxi-dised and degraded by TiO2 photocatalyst in presenceof UV irradiation.

The effect of photocatalytic procedure on turbidity

To remove TiO2 particles from samples after treat-ments, each sample was centrifuged at 3600 g for15 min. To investigate the effect of centrifuge on tur-bidity, a sample of date syrup without any treatmentwas centrifuged with the same condition and turbidity

Table 2 Characteristics of initial date syrup

Characteristic Quantity

°Brix 10

pH 4.6

Colour (IU) 491 000

Turbidity (NTU) 21.90

Glucose (% w/v) 4.96

Fructose (% w/v) 4.91

Phenolic compound

(GAE mg per 100 mL date syrup)

16.30

Ash (%) 0.40

K (ppm) 884

Na (ppm) 31

Ca (ppm) 110

Mg (ppm) 61

Fe (ppm) 0.59

0

50 000

1 00 000

1 50 000

2 00 000

2 50 000

3 00 000

3 50 000

4 00 000

4 50 000

Blank (UV -TiO2) 12 h- 15 w 12 h- 30 w 48 h- 15 w 48 h-30 w

Colo

ur (I

U)

Time (h) -Lamp power (w)

Catalyst TiO2 (1% w/v) Catalyst TiO2 (4% w/v)a

cb

cdecd

de de

f

e

f

Figure 1 The effect of titanium dioxide content, time of process

and UV lamp power on date syrup colour.

© 2012 The Authors

International Journal of Food Science and Technology © 2012 Institute of Food Science and Technology

International Journal of Food Science and Technology 2012

Investigation of TiO2 nanoparticle efficiency M. Nasabi et al. 319

was measured and compared with initial date syrup.Result confirmed that centrifuge step had no signifi-cant effect on turbidity measurement of date syrup.

Initial date syrup sample turbidity was 21.90 NTU(Table 2), and in all the treatments, turbidity wasreduced between 47% and 75%. As shown in Fig. 2,TiO2 content of 1% (w/v) was significantly more effec-tive on decreasing date syrup turbidity compared withTiO2 content of 4% (w/v). It seems that higher amountof TiO2, which caused more colour reduction, resultedin the production of some particles from oxidation oforganic compounds (Robinson et al., 2001) which isresponsible for increasing turbidity. Both of the UVlamps powers and two different times of the processwere not significantly different in turbidity reduction.

Blank experiments including samples without addi-tion of TiO2 did not show significant changes in tur-bidity of date syrup, but samples with 4% (w/v) TiO2

without irradiation showed significantly reduced tur-bidity after 48 h which is related to TiO2 absorptionability.

Fathi (2009) reported about 60% reduction in tur-bidity of the date syrup by ultrafiltration.

The effect of photocatalytic procedure on sugar content

The glucose and fructose content of initial date syrup(°Brix 10) were 4.95 and 4.91%, respectively. Therewas a slight but significant reduction in these sugarcontents (sum of glucose and fructose) for all the treat-ments that was between 3 and 17%. In all treatments,the glucose content was degraded slightly more thanfructose.

Titanium dioxide content of 4% (w/v) was signifi-cantly caused more glucose and fructose reduction incomparison with TiO2 content of 1% (w/v), Fig. 3.Increasing the time of process did not show significantdifference in glucose and fructose reduction. UV powerof 30 w caused significantly more decrease in the sugarcontent in comparison with 15 w. Blank experimentsdid not show significant changes in sugar content (4.84

and 4.95 for glucose and 4.86 and 4.90 for fructose inblank TiO2 and blank UV, respectively). It can be con-cluded that TiO2 nanoparticle photocatalysis did notshowed deteriorative effect on sugar content of datesyrup.Al-Farsi (2003) compared different date juice clarifi-

cation methods to improve the quality of date syrupmade from date juice. They reported 11.3% and 17.7%reduction in sugar content of date juice (the initial sugarcontent of date juice was 18.6 g per 100 mL) using fil-tration plus powder activated carbon and granular acti-vated carbon, respectively. Fathi (2009) also reported 7–21% and 3–21% reduction for glucose and fructosecontent of date syrup by ultrafiltration, respectively.

The effect of photocatalytic procedure on total phenoliccompounds

Total phenolic compounds showed an overall increasefor all treatments compared with initial date syrup(16.30 mg gallic acid per 100 mL date syrup), withtwo exceptions, treatments with 1 and 4% TiO2 at12 h and 15 w. The two different TiO2 contentsshowed statistically similar effect on total phenoliccompounds increase (Fig. 4). UV power of 30 wcaused significantly more increase in comparison with15 w and a significant increase in date syrup total phe-nolic compounds was observed by increasing the timeof process from 12 to 48 h. Blank experiments did notshow significant changes in total phenolic compounds.Total phenolic compounds showed reduction during

date syrup decolourisation using methods such as acti-vated carbon, liming or ultrafilteration (Al-Farsi, 2003;Fathi, 2009), probably because of the absorbingmethods that were used. However, photocatalytic

0

5

10

15

20

Blank (UV-TiO2) 12 h- 15 w 12 h -30 w 48 h- 15 w 48 h- 30 w

Turb

idity

(NTU

)

Time (h) -Lamp power (w)

Catalyst TiO2 (1% w/v) Catalyst TiO2 (4% w/v)

a

c

bbc

bc

bc

c

bcbc

b

Figure 2 The effect of titanium dioxide content, time of process

and UV lamp power on date syrup turbidity.

0

1

2

3

4

5

6

Suga

r co

nten

t (%

w/v

)

Glucose Fructose

a aa a a

bc

cb

d

a baa

db

Figure 3 The effect of Titanium dioxide content, time of process

and UV lamp power on date syrup glucose and fructose content.

Normal and bold letters describe statistical comparison between

different treatments for glucose and fructose content, respectively.

© 2012 The Authors

International Journal of Food Science and Technology © 2012 Institute of Food Science and Technology

International Journal of Food Science and Technology 2012

Investigation of TiO2 nanoparticle efficiency M. Nasabi et al.320

procedure of TiO2 leads to the degradation of thecompounds (aromatic ring cleavage) and couldresulted in producing more phenolic compounds.

The effect of photocatalytic procedure on ash content

Ash content was reduced in all treatments between 11and 15% in comparison with the initial date syrup(0.40%). The maximum ash reduction was observed inthe first 12 h (Fig. 5). The two different TiO2 contentsshowed statistically similar effect on ash content reduc-tion. UV power of 15 w caused significantly morereduction in comparison with 30 w. Blank experimentwithout TiO2 did not show significant changes in theash content, while blank experiment with TiO2 showsignificant reduction in date syrup ash content. Thiscould be explained by high absorption ability of TiO2

nanoparticles. Kanna et al. (2005) also reported highabsorption capacity of TiO2 especially in the hydratedform for metal ions.

In overall by increasing the photocatalytic proce-dure, the ash content increased (treatment 4% TiO2,30 w, 48 h in Fig. 5). It seems in the early stage of theprocess absorption ability of TiO2 nanoparticles isdominant. However, intensifying the photocatalystcondition which caused more oxidation and degradation

by TiO2 in the presence of UV could release someminerals from polymeric compound decomposed (dyemolecules). Robinson et al. (2001) also reported somemineral production during photocatalytic oxidationprocesses of dye removal depending on the initialmaterials and the extent of decolourisation.Al-Farsi (2003) reported reduction of total ash in

date juice by filtration (19.5%) and powder activatedcarbon (7.3%) as adsorption techniques of date juiceclarification.

The effect of photocatalytic procedure on mineral

To investigate the effect of the processing time, TiO2

content and UV power on the mineral of date syrup,five elements in date syrup were chosen including Na,K, Ca, Mg and Fe.

KThere was a slight significant increase in potassiumcontent for all the treatments in comparison with theinitial date syrup (884 ppm). By increasing the time ofthe process and UV power, K content increased whichwas significantly higher in treatments with TiO2 con-tent of 1% than 4% (Table 3). Blank experimentsincluding samples without addition of TiO2 did notshow significant changes in K content, but sample with4% (w/v) TiO2 without irradiation significantlyreduced K content (628 ppm).As potassium had the highest portion in date syrup

among other elements and its changes was similar tothe ash content changes (increasing as photocatalyticprocedure intensified), it could be suggested that ashfluctuations was related to potassium changes.

NaThere was a slight significant increase in sodium con-tent for some treatments in comparison with the initialdate syrup (31 ppm). Increasing in the both UV powerand time of the process led to an increase in the Nacontent at higher TiO2 content treatments (Table 3).Blank experiments did not show significant changes insodium content of the date syrup.

CaBy increasing the time of the process and UV power,Ca content increased which was significantly higher intreatments with TiO2 content of 4% than 1% (Table 3).Blank experiments including samples without additionof TiO2 did not show significant changes in Ca content,but samples with 4% (w/v) TiO2 without irradiationshowed significant reduction of this element (68 ppm).

MgTitanium dioxide content of 4% (w/v) showed signifi-cantly different trend in Mg amount during the process

0

5

10

15

20

25

30

Blank (UV -TiO2) 12 h- 15 w 12 h- 30 w 48 h- 15 w 48 h- 30 w

Tota

l phe

nolic

s co

mpo

unds

(mg

Gal

ic a

cid/

100

mL)

Time (h) -Lamp power (w)

Catalyst TiO2 (1% w/v) Catalyst TiO2 (4% w/v)

c

ccc

bcbc

bc

ab

a a

Figure 4 The effect of Titanium dioxide content, time of process

and UV lamp power on total phenolic compounds of date syrup.

0

0.1

0.2

0.3

0.4

0.5

Blank (UV -TiO2) 12 h- 15 w 12 h- 30 w 48 h- 15 w 48 h- 30 w

Ash

(%)

Time (h) -Lamp power (w)

Catalyst TiO2 (1 %w/v) Catalyst TiO2 (4 %w/v)

b

cc c c c c c c

a

Figure 5 The effect of Titanium dioxide content, time of process

and UV lamp power on date syrup ash content.

© 2012 The Authors

International Journal of Food Science and Technology © 2012 Institute of Food Science and Technology

International Journal of Food Science and Technology 2012

Investigation of TiO2 nanoparticle efficiency M. Nasabi et al. 321

in comparison with TiO2 content of 1% (w/v). Treat-ments with less TiO2 led to the increase in Mg content;in contrast, treatments with higher TiO2 had a slightdecrease in Mg content in comparison with the initialdate syrup (61 ppm), Table 3. Blank experiment did notshow significant changes in magnesium content of datesyrup. Increasing the lamp power or the time of processwas not resulted in similar trend for Mg content of thedate syrup. The most reduction in Mg content wasobserved in treatment of 4% TiO2, 30 W and 48 h.

FeFe content was reduced in all treatments in compari-son with the initial date syrup (0.59 ppm). As shownin Table 3, TiO2 content of 4% (w/v) was significantlymore effective on Fe content reduction in comparisonwith TiO2 content of 1% (w/v). Increasing the UVlamp power was significantly effective in Fe contentreduction. By increasing the time of the process inhigher TiO2 contents, a significant reduction in Fecontent was observed but in treatments with 1% TiO2

less reduction was measured. Blank experimentsincluding samples without addition of TiO2 did notshow significant changes in Fe content, but sampleswith 4% (w/v) TiO2 without irradiation showed signifi-cant reduction of Fe content (0.21 ppm).

Kanna et al. (2005) also investigated adsorption iso-therms of metal ions onto the hydrated amorphousTiO2 surface in batch equilibrium experiments, usingMn(II), Fe(III), Cu(II) and Pb(II) solutions. They sug-gested that high specific surface area of hydratedamorphous TiO2 could be useful to be used as a sor-bent for metal ions. Our results also demonstratedhigh adsorption ability of TiO2 nanoparticles whenused without UV irradiation which caused a significantdecrease in some minerals.

In overall among five measured elements in theinitial date syrup, potassium had the highest amount(884 ppm). After that were calcium (110 ppm),magnesium (61 ppm), sodium (31 ppm) and iron(0.59 ppm). Photocatalytic procedure of TiO2 did not

caused deteriorative effect in the mineral content ofthe date syrup; however, some elements such as K, Naand Ca showed slight increases which could beresulted from decomposition of macromolecules andreleasing some minerals.

Conclusions

The results of this work demonstrated that usingTiO2-nanoparticle as a photocatalyst for decolourisa-tion of date syrup is an effective and promisingmethod. According to the results, the process condi-tion would significantly affect the photocatalytic proce-dure. In this research, the best decolourisation wasobtained by the treatment TiO2 4%, 15 w and 48 hwhich caused 52% colour reduction and 61% turbidityreduction. Determination of the qualitative and quan-titative characteristics of date syrup after the processshowed that the suggested method did not cause dete-riorative effects in comparison to the traditional andindustrial methods of date syrup decolourisation (acti-vated carbon and filtration).While more studies are needed to make this novel

method more powerful, next step for such a startingresearch can be the application of hybrid nano struc-ture by which more decolourisation is obtainable evenby visible irradiation and also by benefit of physico-sorption in collaboration with chemical removal ofcolouring agents. It could be suggested that othernutritive properties of date syrup such as vitaminscontent and antioxidant activity is measured and com-pared with those of date syrup before treatment.Moreover, to underpin the photocatalyst process ofTiO2 for date syrup decolourisation, there is need forfurther research using more powerful technologies andanalyse the changes occurred during the process.Although nano-TiO2 is used as a food additive forsafety issue, it is possible to quantify the amount ofTiO2 (Weir et al., 2012) using scanning electron micro-scope (SEM) to trace whether there is any residue afterTiO2 treatment followed by centrifugation.

Table 3 The effect of titanium dioxide

(TiO2) content, time of process and UV

lamp power on date syrup mineral

Treatment K (ppm) Na (ppm) Ca (ppm) Mg (ppm) Fe (ppm)

Blank UV 773 ± 5.8f* 29.7 ± 0.27c 114 ± 2.8bc 58 ± 0.58d 0.55 ± 0.01a

Blank TiO2 628 ± 5.8g 30.1 ± 0.27c 68 ± 2.8c 59 ± 0.58d 0.21 ± 0.01f

12 h- 15 w- 1% TiO2 911 ± 5.8d 32.0 ± 0.27c 109 ± 2.8bc 80 ± 0.58c 0.39 ± 0.01b

12 h- 15 w- 4% TiO2 901 ± 5.8e 31.2 ± 0.27c 77 ± 3.3c 60 ± 0.58d 0.24 ± 0.01e

12 h- 30 w- 1% TiO2 910 ± 5.8d 32.8 ± 0.27b 112 ± 2.8bc 85 ± 0.58b 0.35 ± 0.01c

12 h- 15 w- 4% TiO2 903 ± 5.8e 31.2 ± 0.27c 140 ± 2.8ab 49 ± 0.58e 0.14 ± 0.01g

48 h- 15 w- 1% TiO2 912 ± 5.8d 33.9 ± 0.27b 105 ± 2.8bc 79 ± 0.58c 0.40 ± 0.01b

48 h- 15 w- 4% TiO2 958 ± .58b 31.2 ± 0.27c 120 ± 2.8b 60 ± 0.58d 0.28 ± 0.01d

48 h- 30 w- 1%TiO2 1080 ± 7.7a 32.0 ± 0.27c 130 ± 2.8ab 91 ± 0.58a 0.35 ± 0.01c

48 h- 30 w- 4% TiO2 947 ± 5.8c 43.9 ± 0.27a 160 ± 2.8a 40 ± 0.58f 0.14 ± 0.01g

*Letters in a column with the same letter are not significantly different (P < 0.05).

© 2012 The Authors

International Journal of Food Science and Technology © 2012 Institute of Food Science and Technology

International Journal of Food Science and Technology 2012

Investigation of TiO2 nanoparticle efficiency M. Nasabi et al.322

Acknowledgments

This work was financially supported in part by theDepartment of Food Science and Technology, Agricul-tural Engineering and Technology Faculty, Universityof Tehran and Iran Nano institute.

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© 2012 The Authors

International Journal of Food Science and Technology © 2012 Institute of Food Science and Technology

International Journal of Food Science and Technology 2012

Investigation of TiO2 nanoparticle efficiency M. Nasabi et al. 323