316
International Journal of Food Science and Technology 2013, 48, 316–323
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 one of oldest cultivated plants that are widespread in the Middle 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 good source of vitamins A, C and B complex, and calcium, magnesium, phosphorus, zinc, iron, potassium, iodine and low amounts of fat and protein (Vayalil, 2002; Al-Farsi et al., 2007). Low-quality date cultivation comprises 60% of the total plantation. These dates are unsuitable for consumption and usually are sold at low prices as animal feed. But they contain high amount of sugar that can be utilised as date syrup, a main by-product of date. A most common density for date syrup is 75 °Brix at which level it is self-preserving and crystallisation only occurs after prolonged storage. To use date syrup as a source of sugar, it is necessary to clarify it. Clarification not only covers the process of freeing the extracted raw juice from nonsoluble but is also concerned with removal of some *Correspondent: Fax: +98-261-2249453; e-mail address:
[email protected]
soluble (e.g. colouring matter) and semi-soluble (e.g. pectin) (Barreveld, 1993). Extensive technical research and feasibility studies have been conducted especially in the seventies and early to mid-eighties to produce different date by-product such as date liquid sugar and high fructose syrup (HFCS) in the industrial scales (Mohamed & Ahmed, 1981; Samarawira, 1983; Barreveld, 1993; Al-Abid, 2006; Ashraf & HamidiEsfahani, 2011). The most effective methods used to clarify 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 highenergy costs and results in the environmental pollution that cannot be neglected (Gyura et al., 2005). On the other hand, resins involve the use of high levels of water consumption and effluent disposal. Resorting to resins or other adsorbents appears unavoidable (Lewandowski et al., 1999). It is to be noted that, according to the clarification method applied, also some desirable substances like flavour components may be removed, and the final product may, apart from having a different appearance and colour, also have a modified taste and quality.
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
Investigation of TiO2 nanoparticle efficiency M. Nasabi et al.
Pigments of various natures in some fresh dates have been identified as caratonoids, anthocyanins, flavones, flavonoles, lycopene, carotenes, flavoxanthin and lutein (Barreveld, 1993). Mohamed & Ahmed (1981) reported that the colour groups, including degradation products of reducing sugars, melanoidines and iron-polyphenolic complexes, contributed to the colour of date syrup. Colourants in the sugar industry can be divided into two groups, natural and those which formed during processing (Mersad et al., 2003). Titanium dioxide (TiO2), encompassing all its three crystal forms, has wide applications in various fields. One of the most recent applications is as a photocatalyst for the degradation of organic dyes (Goncalves et al., 1999; Tatsuma et al., 1999; Augugliaro et al., 2002; Huang et al., 2008; Han et al., 2009; Oliveira et al., 2011; Szabo-Bardos et al., 2011). Titanium dioxide nanoparticle provides high chemical stability, high resistance in acidic and alkaline media and nonpoisonous characteristics while it is safe and can be easily prepared at low cost. The TiO2 semiconductor absorbs a small portion of solar spectrum in the UV region (band gap energy of anatase TiO2 is 3.2 eV and 3.0 eV for rutile TiO2) (Chatterjee et al., 2008). Therefore, it facilitates the decomposition of organic compounds by UV-light, resulting in production of nontoxic CO2, H2O and some inorganic products (Deshpande et al., 2006). According to Dominguez et al. (1998), photocatalytic oxidation processes can oxidise a wide variety of organic compounds to harmless inorganic compounds such as mineral acids, CO2 and H2O. Also, this process forms some by-products such as halides, metals, inorganic acids and organic aldehydes, depending on the initial materials and the extent of decolourisation (Robinson et al., 2001). Upon illumination of TiO2 with light energy greater than its band gap energy, paired electron (e) and hole (h+) are created (McMurry et al., 2004). In aqueous solution, the photo-induced h+ may react with surface hydroxyl groups or surface-bound water molecules to produce hydroxyl radicals (˙OH), the primary oxidant in the photocatalytic system. Simultaneously, the photo-induced e could be trapped by oxygen to form superoxide radical anions O2. The degradation of organic substrates seems to be mediated by a series of reactions initiated by these primary oxidising species, particularly ˙OH radicals. Owing to the reactivity and nonselectivity of ˙OH radicals, UV/TiO2 process is more destructive of numerous organic substrates than traditional oxidation methods. It was suggested that the ˙OH radicals attack organic substrates present at or near the surface of TiO2 (Chen et al., 2005). Therefore, the adsorption of organic substrates onto the surface of TiO2 plays an important role in the photocatalytic degradation.
To the best of our knowledge, there is no previous research in the literatures which has been employed this technique to decolourise date syrup. Therefore, the objective of this study was to determine the effect of TiO2 nanoparticles photocatalyst in decolourisation of the industrial date syrup. The qualitative and quantitative characteristics of date syrup treatments including sugar content, total phenolic compounds, ash content, and mineral were measured and compared with the initial date syrup. This research could be an initial step for the utility of nanotechnology in decolourising industrial date syrup. Materials and methods
Concentrated date syrup (Sibasan factory, Kerman, Iran) with °Brix 75 was used. The method for date syrup production included date washing, mixing with equal amounts of water, extracting at 60 °C, centrifuging, filtering, evaporating at 70 °C to °Brix 75 and packing. Before each experiment, date syrup was diluted to known Brix in order to perform the process. Titanium dioxide (TiO2) was synthesised in Department of Chemistry (International University of Imamkhomeini, Ghazvin, Iran) with a crystallographic mode of 80% anatase and 20% rutile, an average particle size of 25 nm, and a BET surface area of 50 m2 g1 (Brunauer et al., 1938). All solutions were prepared with analytical grade reagents, and double-distilled water was used to prepare experimental solutions except those used for preparing HPLC analysis solutions, which was deionised water. Photochemical reactor
The photocatalytic experiments were performed inside an 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 heating by a cooling fan at the bottom. The surfaces of the reaction mixtures were positioned 100 mm below the lamps. While radiation, a rotator (RO04 rotator; Parsazma, Tehran, Iran) provided agitation to keep the suspension homogeneous. For each treatment, 50 mL of date syrup (°Brix 10 determined by a refractometer (Belingham + Stanely, England) at 25 °C) with proper amount of TiO2 (according to Table 1) was mixed and prior to irradiation, the dispersions were magnetically stirred in the dark for 10 min. The reaction mixtures were poured into 70-mL glass tubes and sat on the top of the rotator. Samples were irradiated at different times and different lamp power (according to Table 1). At any given irradiation time interval, the dispersion was sampled and centrifuged at 3600 g for 15 min (Universal 320; Hettich centrifuge, 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
317
318
Investigation of TiO2 nanoparticle efficiency M. Nasabi et al.
Table 1 Factorial designed treatments TiO2 Concentration (% w/v)
Time (h)
UV lamp power (w)
1 1 1 1 4 4 4 4
12 48 12 48 12 48 12 48
15 15 30 30 15 15 30 30
Turbidity, ash and mineral measurement
Colour measurement
To study the effect of TiO2-UV process on decolourisation of date syrup, after each treatment, sample was diluted (10 times) by TRIS buffer and neutralised at pH 7 (digital pH meter, GLP22 CRISON, EEC). Then, the absorbance was determined at 420 nm using a spectrophotometer (UNICO2100 series, China). The colour was expressed in ICUMSA units (IU) defined according to equation 1 (ICUMSA, 1994); 100000 A ð1Þ IU ¼ bcq where A = absorbance of the test sample at 420 nm b = length (cm) of the adsorbing path c = °Brix (g per 100 mL) of the test sample ρ = Density (g mL1) of the test sample HPLC analysis
HPLC apparatus (Knauer, Germany) with Vertex column 300 9 8 mm, packing material (Eurokat H-10 lm) was used to determine glucose and fructose content of samples. The mobile phase consisted of H2SO4 0.01 N at a flow rate of 0.5 mL min1. All sample solutions were filtered through hydrophilic cellulose acetate disposable syringe filters (MN, USA) with the pore size 0.45 lm and diameter 25 mm. Twenty microlitres of each sample was injected into the column. The temperature was maintained at 30 °C, and the detection was performed by RI detector (knauer-k-2301; Berlin, Germany). Sugars (glucose and fructose) were identified by comparison of their retention times with a standard. 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 samples was determined according to the Folin– Ciocalteu procedure (Singleton & Rossi, 1965). Samples (1 mL, three repeats) were introduced into test tubes; 0.5 mL
International Journal of Food Science and Technology 2012
of Folin–Ciocalteu’s reagent and 1 mL of a saturated sodium carbonate solution were added (final volume set at 5 mL using methanol). The tubes were mixed and allowed to stand for 30 min. Absorption at 765 nm was measured by spectrophotometer (UNICO2100, China). The total phenolic content was expressed as gallic acid equivalent (GAE) in mg per 100 mL date syrup (°Brix 10, Dayton, NJ, USA).
Turbidity of date solutions was measured by the means of a portable turbidometer (Turbidimeter 350; Weilheim, Germany). Ash measurement was taken according to the method ISIRI -5186 (ISIRI, 1986) using a conductivity meter (Hanna – HI 8633, Italy). Mineral elements including calcium, potassium, sodium and magnesium were measured by flame photometer (ELE, England) after proper sample dilutions. Iron element was measured by atomic absorption spectrophotometer (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), photocatalytic decolourisation process was optimised using response surface methodology (RSM), a Box–Behnken design. The effect of TiO2 (1, 2 and 4%), date syrup concentration (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 the optimum points (maximum colour, turbidity and ash reduction and minimum sugar reduction) were chosen to design treatments in the next step as shown in Table 1 (°Brix was 10 for all treatments). All analytical determinations were performed at triplicate. Values of different parameters were expressed as the mean ± standard deviation (x ± SD). All measured parameters were compared with the corresponding parameter of initial date syrup (°Brix 10, Table 2) and the differences were expressed as a percentage of decrease or increase. To investigate the effect of TiO2 and irradiation separately, one sample include TiO2 addition (4% and 48 h) but without irradiation and another sample without TiO2 addition but include irradiation (15 w and 48 h) were also designed (known as blank experiments in the text and blank (UV-TiO2) in the Figures and Tables). All treatments including the initial date syrup and two blanks (blank UV and blank TiO2) were analysed and compared together using SAS software (version 9.1.3 Service Pack 4. 2008; SAS Institute Inc, Cary, NC, USA). However, to illustrate the effect of selected
© 2012 The Authors International Journal of Food Science and Technology © 2012 Institute of Food Science and Technology
Investigation of TiO2 nanoparticle efficiency M. Nasabi et al.
Table 2 Characteristics of initial date syrup Characteristic
Quantity
°Brix pH Colour (IU) Turbidity (NTU) Glucose (% w/v) Fructose (% w/v) Phenolic compound (GAE mg per 100 mL date syrup) Ash (%) K (ppm) Na (ppm) Ca (ppm) Mg (ppm) Fe (ppm)
10 4.6 491 000 21.90 4.96 4.91 16.30 0.40 884 31 110 61 0.59
parameter (the concentration of TiO2, the processing time and UV lamp power), in the result section comparisons were presented between the initial date syrup and those three parameters and then to probe if any of TiO2 or irradiation parameters alone has been affected the process, they have been compared with initial date syrup, separately. Duncan’s multiple range tests were used to compare any significant difference between the means (P < 0.05). Results and discussion
The effect of photocatalytic procedure on colour
Colour in all the samples was reduced between 30 and 53% in comparison with the initial date syrup (491 000 IU, Table 2). As shown in Fig. 1, TiO2 content of 4% (w/v) was significantly more effective on date syrup decolourisation than TiO2 content of 1% (w/v). The UV lamp powers were not significantly different in colour reduction. A significant reduction in date syrup colour was observed by increasing the time of process from 12 to 48 h. 4 50 000
a c
3 50 000 3 00 000 Colour (IU)
Catalyst TiO2 (1% w/v)
Catalyst TiO2 (4% w/v)
b
4 00 000
cde
cd de
de
e f
2 50 000
f
2 00 000
Treatments TiO2 content 4%, UV power 15 w, 48 h and TiO2 content 4%, UV power 30 w, 48 h had statistically the highest colour reduction among the other treatments. As these two treatments were not significantly different in colour reduction, so it is preferable to use lamp with lower power. Blank experiments including samples without addition of TiO2 did not show significant decolourisation of the irradiated solution compared with the initial date syrup, but samples with 4% (w/v) TiO2 without irradiation significantly decreased date syrup colour after 48 h (381000 ± 572 IU). This is because of the adsorption of colourant molecules on the surface of TiO2. These finding demonstrate TiO2 absorbance ability of the colouring matters could achieve 22% date syrup colour reduction, however oxidation capability of TiO2 photocatalyst reduced colouring matter up to 53%. Mohamed & Ahmed (1981) reported that melanoidine-type compounds (the major part of syrup colourants) showed a low selective adsorption tendency on both charcoal and anion resins. They suggested that use of calcium phosphate precipitation could be an effective clarification for the maximum removal of these colourants. Al-Farsi (2003) reported date juice (total soluble solids 20.5%) colour reduction by filtration (44.6%), activated carbon (29%) in powder form and (57%) in granular form. Fathi (2009) also reported about 56% date syrup (°Brix 75) decolourisation by ultrafiltration method. It has been reported that the main colour groups in date syrup include melanoidines and iron-polyphenolic complexes (Mohamed & Ahmed, 1981). Melanoidins are high molecular weight amino–carbonyl compounds produced by nonenzymatic browning reactions called as Maillard reactions during the food processing. The chemical structure of melanoidins is not understood clearly, however, the unsaturated bonds of C = C and C = N have been suggested to be important for the structure of melanoidins chromophore (Chandra et al., 2008). Melanoidins were suggested to be decolourised by the H2O2, hydroxyl, perhydroxyl and active oxygen radicals (Agarwal et al., 2010). Regarding these radicals are the primary oxidising species in the photocatalytical degradation of TiO2 nanoparticles, it could be explained that date syrup colourants have been oxidised and degraded by TiO2 photocatalyst in presence of UV irradiation.
1 50 000 1 00 000
The effect of photocatalytic procedure on turbidity
50 000 0
12 h- 30 w 48 h- 15 w Blank (UV -TiO2) 12 h- 15 w Time (h) -Lamp power (w)
48 h-30 w
Figure 1 The effect of titanium dioxide content, time of process and UV lamp power on date syrup colour.
To remove TiO2 particles from samples after treatments, each sample was centrifuged at 3600 g for 15 min. To investigate the effect of centrifuge on turbidity, a sample of date syrup without any treatment was centrifuged with the same condition and turbidity
© 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
319
Investigation of TiO2 nanoparticle efficiency M. Nasabi et al.
20
6
a Catalyst TiO2 (1% w/v)
Glucose
Catalyst TiO2 (4% w/v) 5
15 b
bc
10
bc
bc
b
bc
bc c
Sugar content (% w/v)
Turbidity (NTU)
320
c
5
0 Blank (UV-TiO2)
12 h- 15 w 12 h -30 w 48 h- 15 w Time (h) -Lamp power (w)
48 h- 30 w
Figure 2 The effect of titanium dioxide content, time of process and UV lamp power on date syrup turbidity.
was measured and compared with initial date syrup. Result confirmed that centrifuge step had no significant effect on turbidity measurement of date syrup. Initial date syrup sample turbidity was 21.90 NTU (Table 2), and in all the treatments, turbidity was reduced between 47% and 75%. As shown in Fig. 2, TiO2 content of 1% (w/v) was significantly more effective on decreasing date syrup turbidity compared with TiO2 content of 4% (w/v). It seems that higher amount of TiO2, which caused more colour reduction, resulted in the production of some particles from oxidation of organic compounds (Robinson et al., 2001) which is responsible for increasing turbidity. Both of the UV lamps powers and two different times of the process were not significantly different in turbidity reduction. Blank experiments including samples without addition of TiO2 did not show significant changes in turbidity of date syrup, but samples with 4% (w/v) TiO2 without irradiation showed significantly reduced turbidity after 48 h which is related to TiO2 absorption ability. Fathi (2009) reported about 60% reduction in turbidity 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. There was a slight but significant reduction in these sugar contents (sum of glucose and fructose) for all the treatments that was between 3 and 17%. In all treatments, the glucose content was degraded slightly more than fructose. Titanium dioxide content of 4% (w/v) was significantly caused more glucose and fructose reduction in comparison with TiO2 content of 1% (w/v), Fig. 3. Increasing the time of process did not show significant difference in glucose and fructose reduction. UV power of 30 w caused significantly more decrease in the sugar content in comparison with 15 w. Blank experiments did not show significant changes in sugar content (4.84
International Journal of Food Science and Technology 2012
4
a a
a a
a a
a
Fructose a
b b
b c c
b
d d
3
2
1
0
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.
and 4.95 for glucose and 4.86 and 4.90 for fructose in blank TiO2 and blank UV, respectively). It can be concluded that TiO2 nanoparticle photocatalysis did not showed deteriorative effect on sugar content of date syrup. Al-Farsi (2003) compared different date juice clarification methods to improve the quality of date syrup made from date juice. They reported 11.3% and 17.7% reduction in sugar content of date juice (the initial sugar content of date juice was 18.6 g per 100 mL) using filtration plus powder activated carbon and granular activated carbon, respectively. Fathi (2009) also reported 7 –21% and 3–21% reduction for glucose and fructose content of date syrup by ultrafiltration, respectively. The effect of photocatalytic procedure on total phenolic compounds
Total phenolic compounds showed an overall increase for all treatments compared with initial date syrup (16.30 mg gallic acid per 100 mL date syrup), with two exceptions, treatments with 1 and 4% TiO2 at 12 h and 15 w. The two different TiO2 contents showed statistically similar effect on total phenolic compounds increase (Fig. 4). UV power of 30 w caused significantly more increase in comparison with 15 w and a significant increase in date syrup total phenolic compounds was observed by increasing the time of process from 12 to 48 h. Blank experiments did not show significant changes in total phenolic compounds. Total phenolic compounds showed reduction during date syrup decolourisation using methods such as activated carbon, liming or ultrafilteration (Al-Farsi, 2003; Fathi, 2009), probably because of the absorbing methods that were used. However, photocatalytic
© 2012 The Authors International Journal of Food Science and Technology © 2012 Institute of Food Science and Technology
Investigation of TiO2 nanoparticle efficiency M. Nasabi et al.
30 Total phenolics compounds (mg Galic acid/100 mL)
a
a
Catalyst TiO2 (4% w/v)
Catalyst TiO2 (1% w/v)
ab
25
bc
20
bc
bc
c
c
15
c
c
10 5 0
Blank (UV -TiO2) 12 h- 15 w 12 h- 30 w 48 h- 15 w Time (h) -Lamp power (w)
48 h- 30 w
Figure 4 The effect of Titanium dioxide content, time of process and UV lamp power on total phenolic compounds of date syrup.
procedure of TiO2 leads to the degradation of the compounds (aromatic ring cleavage) and could resulted in producing more phenolic compounds.
by TiO2 in the presence of UV could release some minerals from polymeric compound decomposed (dye molecules). Robinson et al. (2001) also reported some mineral production during photocatalytic oxidation processes of dye removal depending on the initial materials and the extent of decolourisation. Al-Farsi (2003) reported reduction of total ash in date juice by filtration (19.5%) and powder activated carbon (7.3%) as adsorption techniques of date juice clarification. 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. K
The effect of photocatalytic procedure on ash content
Ash content was reduced in all treatments between 11 and 15% in comparison with the initial date syrup (0.40%). The maximum ash reduction was observed in the first 12 h (Fig. 5). The two different TiO2 contents showed statistically similar effect on ash content reduction. UV power of 15 w caused significantly more reduction in comparison with 30 w. Blank experiment without TiO2 did not show significant changes in the ash content, while blank experiment with TiO2 show significant reduction in date syrup ash content. This could be explained by high absorption ability of TiO2 nanoparticles. Kanna et al. (2005) also reported high absorption capacity of TiO2 especially in the hydrated form for metal ions. In overall by increasing the photocatalytic procedure, the ash content increased (treatment 4% TiO2, 30 w, 48 h in Fig. 5). It seems in the early stage of the process absorption ability of TiO2 nanoparticles is dominant. However, intensifying the photocatalyst condition which caused more oxidation and degradation Catalyst TiO2 (1 %w/v)
0.5
a
Catalyst TiO2 (4 %w/v)
b
Ash (%)
0.4
There was a slight significant increase in potassium content for all the treatments in comparison with the initial date syrup (884 ppm). By increasing the time of the process and UV power, K content increased which was significantly higher in treatments with TiO2 content of 1% than 4% (Table 3). Blank experiments including samples without addition of TiO2 did not show significant changes in K content, but sample with 4% (w/v) TiO2 without irradiation significantly reduced K content (628 ppm). As potassium had the highest portion in date syrup among other elements and its changes was similar to the ash content changes (increasing as photocatalytic procedure intensified), it could be suggested that ash fluctuations was related to potassium changes. Na
There was a slight significant increase in sodium content for some treatments in comparison with the initial date syrup (31 ppm). Increasing in the both UV power and time of the process led to an increase in the Na content at higher TiO2 content treatments (Table 3). Blank experiments did not show significant changes in sodium content of the date syrup. Ca
c
c
c
c
c
c c
c
0.3 0.2 0.1 0 Blank (UV -TiO2)
12 h- 15 w 12 h- 30 w 48 h- 15 w Time (h) -Lamp power (w)
By increasing the time of the process and UV power, Ca content increased which was significantly higher in treatments with TiO2 content of 4% than 1% (Table 3). Blank experiments including samples without addition of TiO2 did not show significant changes in Ca content, but samples with 4% (w/v) TiO2 without irradiation showed significant reduction of this element (68 ppm).
48 h- 30 w
Figure 5 The effect of Titanium dioxide content, time of process and UV lamp power on date syrup ash content.
Mg
Titanium dioxide content of 4% (w/v) showed significantly different trend in Mg amount during the process
© 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
321
322
Investigation of TiO2 nanoparticle efficiency M. Nasabi et al.
Treatment
K (ppm)
Blank UV Blank TiO2 12 h- 15 w12 h- 15 w12 h- 30 w12 h- 15 w48 h- 15 w48 h- 15 w48 h- 30 w48 h- 30 w-
773 628 911 901 910 903 912 958 1080 947
1% TiO2 4% TiO2 1% TiO2 4% TiO2 1% TiO2 4% TiO2 1%TiO2 4% TiO2
± ± ± ± ± ± ± ± ± ±
5.8f* 5.8g 5.8d 5.8e 5.8d 5.8e 5.8d .58b 7.7a 5.8c
Na (ppm) 29.7 30.1 32.0 31.2 32.8 31.2 33.9 31.2 32.0 43.9
± ± ± ± ± ± ± ± ± ±
0.27c 0.27c 0.27c 0.27c 0.27b 0.27c 0.27b 0.27c 0.27c 0.27a
Ca (ppm) 114 68 109 77 112 140 105 120 130 160
± ± ± ± ± ± ± ± ± ±
2.8bc 2.8c 2.8bc 3.3c 2.8bc 2.8ab 2.8bc 2.8b 2.8ab 2.8a
Mg (ppm) 58 59 80 60 85 49 79 60 91 40
± ± ± ± ± ± ± ± ± ±
0.58d 0.58d 0.58c 0.58d 0.58b 0.58e 0.58c 0.58d 0.58a 0.58f
Fe (ppm) 0.55 0.21 0.39 0.24 0.35 0.14 0.40 0.28 0.35 0.14
± ± ± ± ± ± ± ± ± ±
0.01a 0.01f 0.01b 0.01e 0.01c 0.01g 0.01b 0.01d 0.01c 0.01g
Table 3 The effect of titanium dioxide (TiO2) content, time of process and UV lamp power on date syrup mineral
*Letters in a column with the same letter are not significantly different (P < 0.05).
in comparison with TiO2 content of 1% (w/v). Treatments with less TiO2 led to the increase in Mg content; in contrast, treatments with higher TiO2 had a slight decrease in Mg content in comparison with the initial date syrup (61 ppm), Table 3. Blank experiment did not show significant changes in magnesium content of date syrup. Increasing the lamp power or the time of process was not resulted in similar trend for Mg content of the date syrup. The most reduction in Mg content was observed in treatment of 4% TiO2, 30 W and 48 h. Fe
Fe content was reduced in all treatments in comparison with the initial date syrup (0.59 ppm). As shown in Table 3, TiO2 content of 4% (w/v) was significantly more effective on Fe content reduction in comparison with TiO2 content of 1% (w/v). Increasing the UV lamp power was significantly effective in Fe content reduction. By increasing the time of the process in higher TiO2 contents, a significant reduction in Fe content was observed but in treatments with 1% TiO2 less reduction was measured. Blank experiments including samples without addition of TiO2 did not show significant changes in Fe content, but samples with 4% (w/v) TiO2 without irradiation showed significant reduction of Fe content (0.21 ppm). Kanna et al. (2005) also investigated adsorption isotherms of metal ions onto the hydrated amorphous TiO2 surface in batch equilibrium experiments, using Mn(II), Fe(III), Cu(II) and Pb(II) solutions. They suggested that high specific surface area of hydrated amorphous TiO2 could be useful to be used as a sorbent for metal ions. Our results also demonstrated high adsorption ability of TiO2 nanoparticles when used without UV irradiation which caused a significant decrease in some minerals. In overall among five measured elements in the initial 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
International Journal of Food Science and Technology 2012
caused deteriorative effect in the mineral content of the date syrup; however, some elements such as K, Na and Ca showed slight increases which could be resulted from decomposition of macromolecules and releasing some minerals. Conclusions
The results of this work demonstrated that using TiO2-nanoparticle as a photocatalyst for decolourisation of date syrup is an effective and promising method. According to the results, the process condition would significantly affect the photocatalytic procedure. In this research, the best decolourisation was obtained by the treatment TiO2 4%, 15 w and 48 h which caused 52% colour reduction and 61% turbidity reduction. Determination of the qualitative and quantitative characteristics of date syrup after the process showed that the suggested method did not cause deteriorative effects in comparison to the traditional and industrial methods of date syrup decolourisation (activated carbon and filtration). While more studies are needed to make this novel method more powerful, next step for such a starting research can be the application of hybrid nano structure by which more decolourisation is obtainable even by visible irradiation and also by benefit of physicosorption in collaboration with chemical removal of colouring agents. It could be suggested that other nutritive properties of date syrup such as vitamins content and antioxidant activity is measured and compared with those of date syrup before treatment. Moreover, to underpin the photocatalyst process of TiO2 for date syrup decolourisation, there is need for further research using more powerful technologies and analyse the changes occurred during the process. Although nano-TiO2 is used as a food additive for safety issue, it is possible to quantify the amount of TiO2 (Weir et al., 2012) using scanning electron microscope (SEM) to trace whether there is any residue after TiO2 treatment followed by centrifugation.
© 2012 The Authors International Journal of Food Science and Technology © 2012 Institute of Food Science and Technology
Investigation of TiO2 nanoparticle efficiency M. Nasabi et al.
Acknowledgments
This work was financially supported in part by the Department of Food Science and Technology, Agricultural Engineering and Technology Faculty, University of Tehran and Iran Nano institute. References Abbes, F., Bouaziz, M.A., Blecker, C., Masmoudi, M., Attia, H. & Besbes, S. (2011). Date syrup: effect of hydrolytic enzymes (pectinase/cellulase) on physico-chemical characteristics, sensory and functional properties. LWT – Food Science and Technology, 44, 1827–1834. Agarwal, R., Lata, S., Gupta, M. & Singh, P. (2010). Removal of melanoidin present in distillery effluent as a major colorant: a Review. Journal of Environmental Biology, 31, 521–528. Al-Abid, M.R. (2006). Dates derived industries. Journal of Agricultural Investment, 4, 67–73. Al-Farsi, A. (2003). Clarification of date juice. International Journal of Food Science and Technology, 38, 241–245. Al-Farsi, M., Alasalvar, C., Morris, A., Baron, M. & Shahidi, F. (2005). Comparison of antioxidant activity, anthocyanins, carotenoids, and phenolics of three native fresh and sun-dried date (Phoenix dactylifera L.) varieties grown in Oman. Journal of Agricultural and Food Chemistry, 53, 7592–7599. Al-Farsi, M., Alasalvar, C., Al-Abid, M., Al-Shoaily, K., Al-Amry, M. & Al-Rawahy, F. (2007). Compositional and functional characteristics of dates, syrups, and their by-products. Food Chemistry, 104, 943–947. Ashraf, Z. & Hamidi-Esfahani, Z. (2011). Date and date processing: a review. Food Reviews International, 27, 101–133. Augugliaro, V., Baiocchi, C., Prevot, A.B. et al. (2002). Azo-dyes photocatalytic degradation in aqueous suspension of TiO2 under solar irradiation. Chemosphere, 49, 1223–1230. Barreveld, W.H. (1993). Date palm products. Rome, Italy: FAO Agricultural Services Bultin No. 101. Brunauer, S., Emmett, P.H. & Teller, E. (1938). Adsorption of gases in multimolecular layers. Journal of the American Chemical Society, 60, 309–315. Chandra, R., Bharagava, R.N. & Rai, V. (2008). Melanoidins as major colourant in sugarcane molasses based distillery effluent and its degradation. Bioresource Technology, 99, 4648–4660. Chatterjee, D., Patnam, V.R., Sikdar, A., Joshi, P., Misra, R. & Rao, N.N. (2008). Kinetics of the decolouration of reactive dyes over visible light-irradiated TiO2 semiconductor photocatalyst. Journal of Hazardous Materials, 156, 435–441. Chen, Y., Yang, S., Wan, K. & Lou, L. (2005). Role of primary active species and TiO2 surface characteristic in UV-illuminated photodegradation of acid orange 7. Journal of Photochemistry and Photobiology A: Chemistry, 172, 47–54. Deshpande, S.B., Potdar, H.S., Khollam, Y.B., Renu, P., Pasricha, K.R. & Jacob, N.E. (2006). Room temperature synthesis of mesoporous aggregates of anatase TiO2 nanoparticles. Materials Chemistry and Physics, 97, 207–212. Dominguez, C., Garcia, J., Pedraz, M.A., Torres, A. & Galan, M.A. (1998). Photocatalytic oxidation of organic pollutants in water. Catalysis Today, 40, 85–101. Fathi, G. (2009). Decolourisation of date syrup by ultrafiltaration. MS Thesis. Karaj, Iran: Department of Food Science and Technology, University of Tehran. Goncalves, M.S.T., Oliveira-Campos, A.M.F., Pinto, E.M.M.S., Plasencia, P.M.S. & Queiroz, M.J.R.P. (1999). Photochemical
treatment of solution of azo dyes containing TiO2. Chemosphere, 39, 781–786. Gyura, J., Seres, Z. & Eszterle, M. (2005). Influence of operating parameters on separation of green syrup colored matter from sugar beet by ultra- and nanofiltration. Journal of Food Engineering, 66, 89–69. Han, F., Kambala, V.S.R., Srinivasan, M., Rajarathnam, D. & Naidu, R. (2009). Tailored titanium dioxide photocatalysts for the degradation of organic dyes in wastewater treatment: a review. Applied Catalysis A: General, 359, 25–40. Huang, H.H., Tseng, D.H. & Juang, L.C. (2008). Titanium dioxide mediated photocatalytic degradation of monochlorobenzene in aqueous phase. Chemosphere, 71, 398–405. ICUMSA (1994). International Commission for Uniform Methods of Sugar Analysis. Germany: ICUMSA Methods Book, Method GS1-8. ISIRI (1986). Standard methods, Method 5186. Iran: Institute of Standards & Industrial Research of Iran. Kanna, M., Wongnawa, S., Sherdshoopongse, P. & Boonsin, P. (2005). Adsorption behaviour of some metal ions on hydrated amorphous titanium dioxide surface. Songklanakarin Journal of Science and Technology, 27, 1017–1026. Kovacs, K. & Nagy-Gasztonyi, M. (1985). Clarification and purification of date extract with the enzyme pectin lyase. Acta Alimentara, 4th Conference on Enzymology, Budapest (Hungary), 14 , 77–78. Lewandowski, R., Zghal, S., Lameloise, L. & Reynes, M. (1999). Purification of date juice for liquid sugar production. International Sugar Journal, 101, 125–130. McMurry, T.A., Byrne, J.A., Dunlop, P.S.M., Winkelman, J.G.M., Eggins, B.R. & McAdams, E.T. (2004). Intrinsic kinetics of photocatalytic oxidation of formic and oxalic acid on immobilised TiO2 films. Applied Catalysis A: General, 262, 105–110. Mersad, A., Lewandowski, R., Heyd, B. & Decloux, M. (2003). Colorants in the sugar industry: laboratory preparation and spectrometric analysis. International Sugar Journal, 105, 269–281. Mohamed, M.A. & Ahmed, A.A. (1981). Libyan date syrup. Journal of Food Science, 46, 1162–1166, 1174 Oliveira, D.F.M., Batista, P.S., Muller, P.S. Jr et al. (2011). Evaluating the effectiveness of photocatalysts based on titanium dioxide in the degradation of the dye Ponceau 4R. Dyes and Pigments, 92, 563–572. Robinson, T., Mcmullan, G., Marchant, R. & Nigam, P. (2001). Remediation of dyes in textile effluent - a critical review on current treatment technologies with a proposed alternative. Bioresource Technology, 77, 247–255. Samarawira, I. (1983). Date palm, potential source for refined sugar. Economic Botany, 37, 181–186. Singleton, V.L. & Rossi, J.A. (1965). Colorimetry of total phenolics with phosphomolybdic-phosphotungstic acid reagents. American Journal of Enology and Viticulture, 16, 144–158. Szabo-Bardos, E., Markovics, O., Horvath, O., Toro, N. & Kiss, G. (2011). Photocatalytic degradation of benzenesulfonate on colloidal titanium dioxide. Water Research, 45, 1617–1628. Tatsuma, T., Tachibana, S., Miwa, T., Tryk, D.A. & Fujishima, A. (1999). Remote bleaching of methylene blue by UV-irradiated TiO2 in the gas phase. The Journal of Physical Chemistry B, 103, 8033–8035. Vayalil, P.K. (2002). Antioxidant and antimutagenic properties of aqueous extract of date fruit (Phoenix dactylifera L. Arecaceae). Journal of Agricultural and Food Chemistry, 50, 610–617. Weir, A., Westerhoff, P., Fabricius, L., Hristovski, K. & von Goetz, N. (2012). Titanium dioxide nanoparticles in food and personal care products. Environmental Science and Technology, 46, 2242–2250.
© 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
323
