- Email: [email protected]
Effect of ultrasonic treatment on heavy metal decontamination in milk
Ultrasonics Sonochemistry xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry journal homepage: www.elsevier.com/locate/ultson
Effect of ultrasonic treatment on heavy metal decontamination in milk Nataliya Porova a, Valentina Botvinnikova a, Olga Krasulya b, Pavel Cherepanov c, Irina Potoroko a,⇑ a Federal State Funded Educational Institution of Higher Professional Education, ‘‘South Ural State University’’ Sub-division: Quality Expertise of Consumer Products, Chelyabinsk, Russia b Moscow State University of Technology and Management, Moscow, Russia c Physical Chemistry II, University of Bayreuth, Universitaetsstrasse 30, Bayreuth, Germany
a r t i c l e
i n f o
Article history: Received 30 November 2013 Received in revised form 26 March 2014 Accepted 27 March 2014 Available online xxxx Keywords: Food sonochemistry Cavitation Heavy metal contamination/ decontamination
a b s t r a c t Ultrasound has been found useful in increasing the efficiency and consumer safety in food processing. Removal of heavy metal (lead, mercury, and arsenic) contamination in milk is extremely important in regions of poor ecological environment – urban areas with heavy motor traffic or well established metallurgical/cement industry. In this communication, we report on the preliminary studies on the application of low frequency (20 kHz) ultrasound for heavy metal decontamination of milk without affecting its physical, chemical, and microbiological properties. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Satisfying the needs of human population in biologically and environmentally safe dairy products is a complex strategic task for modern food industry [1]. Among negative factors that determine population health risks, the most significant are ecological problems [2]. Regions with well developed metallurgical industry such as mining or steel production, or simply highly populated urban areas with heavy motor traffic are notorious for being chemically contaminated [3]. Within those areas high concentrations of toxic heavy metals such as lead, mercury, or arsenic is detected in the air, water, and plants, which consequently results in contamination of dairy and meat products available on the market [4,5]. Considering, for example, hepatotoxic (arsenic) or neurotoxic (lead, mercury) properties of heavy metals which cause human brain and liver damage, it is important to minimize their content in foods. Development of heavy metal decontamination approaches will ensure more efficient use of natural resources and safer quality of derived products. One of the possible approaches for resolving heavy metal contamination problem could be use of low frequency (20 kHz) ultrasound (US) in the production of dairy products. To date, there have been many reports published dedicated to ultrasonic food processing [6–9], revealing positive effects of caused by acoustic cavitation ⇑ Corresponding author. Tel.: +7 9507259750. E-mail address: [email protected] (I. Potoroko).
on the properties of food products, namely quality, extended shelf life, as well as on the efficiency of energy consumption during production process [10–12]. In this communication, we report on the preliminary results on the potential use of low frequency ultrasound for the removal of heavy metals such as lead, mercury and arsenic from contaminated milk. The key aspect in present report is to show how homogenizing effect [13] of ultrasound can enhance sorption properties of lignin based biopolymer sorbent polyphepan for heavy metal removal. First, we evaluated particle size distribution change in milk samples with variable fat content with respect to duration of sonication to ensure the permeation of fat and protein particles through polyphepan sorbent. Further, to evaluate the efficiency of milk decontamination from heavy metals, we compared their concentration levels in control and ultrasonicated samples after filtering through sorbent. In addition, we carried out quality assessment of US/sorbent treated milk to determine whether its physical, chemical, and microbiological properties [14,15] can meet state regulation standards.
2. Experimental section Whole milk samples with variable fat content (4.5%, 3.7%, and 2.6%) were obtained from a local farm. Ultrasound treatment of milk was carried out in an ultrasonic reactor USTA-0.4/22 OM (Volna,Russia) operating at a frequency of 22 ± 1.65 kHz and 30% of maximum (400 W) output power. All chemicals were highest
http://dx.doi.org/10.1016/j.ultsonch.2014.03.029 1350-4177/Ó 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: N. Porova et al., Effect of ultrasonic treatment on heavy metal decontamination in milk, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.029
2
N. Porova et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
grades available and were used without further purification. Biopolymer sorbent polyphepan was purchased from SAJNTEK (Russia). The amount of sorbent for milk treatment and duration of exposure (stirring) were preliminary optimized and set to 5 g/ L for 3 min. Heavy metal concentration was determined with use of Atomic Absorption Spectrometer SpectrAA 250 plus (Varian, Australia). Microscopic studies were performed on Jeol JEM-2100 (Jeol Ltd., Japan). Particle size distribution was evaluated with use of Nanotrac 253 Ultra (Microtrac, USA). Optical microscope Altami-136T (Altami, Russia) was used for studying microbacterial
growth in milk samples. Methylene blue dye was used as a microbial viability indicator.
3. Results and discussion In the first stage, to assess the possibility of using low frequency ultrasound in combination with sorbent for heavy metal decontamination, we evaluated the size distribution of dispersed milk emulsion particles. Fig. 1a–b shows particle size distribution of
Fig. 1. Particle size distribution in 4.5% fat milk samples.
Please cite this article in press as: N. Porova et al., Effect of ultrasonic treatment on heavy metal decontamination in milk, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.029
3
N. Porova et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
Table 1 Quality parameters of control and sonicated milk samples with variable fat content.
Milk fracon Fat (%) (%) Fat mass 3.7 %
Ultrasound exposure time (min)
3 min
1 min
control
2.6 %
*
Quality parameters Milk fat (%)
MSNF (%)
2.8–6.0* 0 (control) 1 3 5
Density (L)
Milk protein (%)
Freezing temperature (°C)
P8.20* P27.0*
2.8*
6 0.502*
4.52 4.82 4.52 3.97
8.23 8.30 7.93 8.13
27.93 27.97 26.77 29.28
2.94 3.07 2.55 2.39
0.519 0.523 0.501 0.529
0 (control) 1 3 5
3.67 3.67 3.65 3.60
9.34 9.29 8.98 8.70
32.85 32.69 31.51 30.46
2.63 2.60 2.45 2.33
0.529 0.529 0.529 0.529
0 (control) 1 3 5
2.66 2.80 2.58 2.51
8.29 8.26 7.96 7.66
29.67 29.45 28.46 27.35
3.08 3.03 2.76 2.50
0.523 0.521 0.503 0.485
Russian state standard parameters for milk products
1 μm
5 min
Duraon of Ultrasound treatment
4.5 %
Milk Fat (%)
As
7.41% decrease 0.027
1 min 3 min
heavy metals such as lead, arsenic, or mercury complexed with them. As mentioned earlier, the most pronounced particle size reduction effect was observed after 5 min of US treatment. 4.5% fat milk sample treated with US for 5 min and having an average particle size in the range of 75–370 nm was expected to be the
Hg
14.71% decrease
0.025
0.00034
control
50.0% decrease
Fig. 4. Optical images confirming the presence of Lactococcus lactis bacteria in control and ultrasonically treated milk samples.
US 5min
Pb
0.072
2.6 %
5 min
milk emulsions as a function of sonication time. Initially, 4.5% fat milk sample contained three distinct fractions with average particle sizes of 6 lM, 1.28 lM, and 140 nm, respectively (Fig 1a). Upon US treatment, the size distribution of particles in milk has changed with the most pronounced effect after 5 min of sonication possessing the average values in the range from 75 to 370 nm (Fig 1d). Similar trends of particle size reduction were observed for other milk samples containing 3.7% and 2.6% fat. Additionally, we evaluated all milk samples using electron microscopy. The particle size ranges observed in the images shown in Fig. 2 are in good agreement with the results obtained with particle size analyzer. Overall, it can be clearly seen that US treatment leads to a particle size reduction confirming the homogenizing effect of ultrasound. Ultrasonic homogeinsation of emulsion particles in milk has been reported in the literature [6]. The particle size reduction is primarily caused by the shear forces generated during acoustic cavitation. In the next stage, we applied sorbent to show that homogenizing effect of ultrasound can be very beneficial for heavy metal decontamination of milk. In the present study, we used one of the most common natural organic polymer sorbents which is lignin based sorbent called polyphepan. Polyphepan while being nontoxic and applied in medicine is known for its ability to bind heavy metals, thus, stimulating detoxification. The average pore size of this biopolymer is in the range of 100–150 nm, which allows permeation of protein molecules accompanied by the removal of
Duraon of Ultrasound treatment
Fig. 2. SEM images of particle aggregates present in milk.
3.7 %
control
4.5 %
0.00029
US 5min
control
US 5min
control
0.036
Fig. 3. Heavy metal content (mg/L) in 4.5% fat milk samples before (control) and after 5 min US + sorbent treatment (US 5 min).
Please cite this article in press as: N. Porova et al., Effect of ultrasonic treatment on heavy metal decontamination in milk, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.029
4
N. Porova et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
Fig. 5. Development of Lactococcus lactis bacteria in buttermilk prepared from non-treated milk (a), buttermilk prepared from US treated for 5 min and exposed to polyphepan sorbent milk (b), and soured milk product prepared from US treated for 5 min and exposed to polyphepan sorbent milk (c).
most favorable candidate for the treatment with polyphepan sorbent to ensure successful heavy metal decontamination. Indeed, we observed a significant decrease in heavy metal content of milk samples treated with combination of US and sorbent (5 g/L, stirring for 3 min) in comparison to control. The results for heavy metal content in control and 5 min sonicated 4.5% fat milk samples are shown in Fig. 3. We observed that the concentration of lead has decreased by 50%, arsenic by 7%, and mercury by 14%. Thus, we suggest that homogenizing effect caused by ultrasonic cavitation and resulting in overall particle size reduction enhances the accessibility of sorbent pores to protein molecules for their subsequent heavy metal decontamination. Further, in order to assure quality of milk that underwent ultrasound treatment and sorbent treatment, we carried quality assessment experiments. Obtained data on change in milk fat, milk solid-non-fat (MSNF) and protein contents, as well as density and freezing temperature values for control and sonicated samples are summarized in Table 1. Importantly, almost all values remain within or close to permitted by Russian state standards levels. Slight deviation from standard is observed after 1 min of sonication. Increase in fat, protein, and MSNF contents after 1 min of US treatment might be explained in terms of more efficient incorporation of ‘‘free’’ water molecules formed due to cavitation. At the same time slight decrease in these values after US exposure for 5 min most likely is due to reduced particle size which allows proteins to be carried away upon removal of sorbent. Nevertheless, through the adjustment of sorbent quantity, exposure time and sonication time, it is possible to control the quality of consumable milk product. Another important aspect which has to be taken into account when discussing quality of milk is effect of US treatment on the growth of an important bacteria, Lactococcus lactis, which is responsible for milk souring in the process of buttermilk or cheese production. Fig. 4 data clearly shows that lactobacteria present in control milk samples are not affected by ultrasound treatment. In addition, our studies have also shown that presence of lactobacteria in dairy products (soured milk and buttermilk) prepared from US treated milk is not affected (Fig. 5). Thus, US treatment does not create unfriendly environment for lactobacteria growth.
4. Conclusions In the present study we reported on the effect of low frequency ultrasound for milk treatment. We showed that ultrasound treatment leads to significant changes in size distribution of fat and protein particles present in milk, resulting in more uniform milk emulsion with particle size ranging from 75 to 370 nm. We also showed that the reduction in particle size has positive effects in terms of enhancing permeability of reduced-size proteins on lignin based biopolymer polyphepan, allowing successful decontamination of milk from heavy metals such as lead, arsenic, and mercury. Importantly, the quality of milk treated with ultrasound is not sacrificed. In addition, it is shown that ultrasound does not prevent growth of lactobacteria present in milk and dairy products such as soured milk and buttermilk. Overall, low frequency ultrasound can be potentially used for heavy metal decontamination without significant effect on the quality of consumable milk products.
References [1] A. McLeod, Human nutrition and dairy development: trends and issues, in: E. Muehlhoff, A. Bennett, D. McMahon (Eds.), Milk and Dairy Products in Human Nutrition, FAO, Rome, 2013, pp. 355–375. [2] B.K. Mandal, K.T. Suzuki, Arsenic round the world: a review, Talanta 58 (2002) 201–235. [3] A. Shapiro, C. Mercier, Safe food manufacturing, Sci. Total Environ. 143 (1994) 75–92. [4] B. Dhanalakshmi, G. Gawdaman, Determination of heavy metals in goat milk through ICP-OES, Asian J. Dairy Food 32 (2013) 186–190. [5] P.H. Kiyataka, S.T. Dantas, L. Pallone, J. Azevedo, Method for assessing lead, chromium, mercury and arsenic in high-density polyethylene packaging and study of the migration into yoghurt and stimulant, Food Addit. Contam. Part A Chem. Anal. Control 31 (2014) 156–163. [6] J. Chandrapala, C. Oliyer, S. Kentish, M. Ashokkumar, Ultrasonics in food processing, Ultrason. Sonochem. 19 (2012) 975–983. [7] B. Zisu, J. Chandrapala, High power ultrasound processing in milk and dairy products, in: N. Datta, P. Tomasula (Eds.), Emerging Dairy Processing Technologies: Opportunities for the Dairy Industry, Wiley – Blackwell publisher, 2013. [8] M.J.W. Povey, Ultrasonics of food, Contemp. Phys. 39 (1998) 467–478. [9] S. Shestakov, O. Krasulya, V. Bogush, I. Potoroko, Technology and Equipment for Food Processing Environments Using Cavitation, GIORD, St. Petersburg, 2013.
Please cite this article in press as: N. Porova et al., Effect of ultrasonic treatment on heavy metal decontamination in milk, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.029
N. Porova et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx [10] A.E. Torkamani, P. Juliano, S. Ajlouni, T.K. Singh, Impact of ultrasound treatment on lipid oxidation of Cheddar cheese whey, Ultrason. Sonochem. 21 (2014) 951–957. [11] M. Ashokkumar, J. Lee, B. Zisu, R. Bhaskarcharya, M. Palmer, S. Kentish, Hot topic: sonication increases the heat stability of whey proteins, J. Dairy Sci. 92 (2009) 5353–5356. [12] J. Chandrapala, C. Oliver, S. Kentish, M. Ashokkumar, Ultrasonics in food processing – food quality assurance and food safety, Trends Food Sci. Technol. 26 (2012) 88–98.
5
[13] A.W.M. Sweetsur, D.D. Muir, Effect of homogenization on the heat – stability of milk, J. Dairy Res. 50 (1983) 291–300. [14] P.H.P. Prassanna, A.S. Grandison, D. Charalampopoulos, Bifidobacteria in milk products: an overview of physiological and biochemical properties, exopolysaccharide production, selection criteria of milk products and health benefits, Food Res. Int. 55 (2014) 247–262. [15] A. Shanmugam, J. Chandrapala, M. Ashokkumar, The effect of ultrasound on the physical and functional properties of skim milk, Innovative Food Sci. Emerg. Technol. 16 (2012) 251–258.
Please cite this article in press as: N. Porova et al., Effect of ultrasonic treatment on heavy metal decontamination in milk, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.029
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry journal homepage: www.elsevier.com/locate/ultson
Effect of ultrasonic treatment on heavy metal decontamination in milk Nataliya Porova a, Valentina Botvinnikova a, Olga Krasulya b, Pavel Cherepanov c, Irina Potoroko a,⇑ a Federal State Funded Educational Institution of Higher Professional Education, ‘‘South Ural State University’’ Sub-division: Quality Expertise of Consumer Products, Chelyabinsk, Russia b Moscow State University of Technology and Management, Moscow, Russia c Physical Chemistry II, University of Bayreuth, Universitaetsstrasse 30, Bayreuth, Germany
a r t i c l e
i n f o
Article history: Received 30 November 2013 Received in revised form 26 March 2014 Accepted 27 March 2014 Available online xxxx Keywords: Food sonochemistry Cavitation Heavy metal contamination/ decontamination
a b s t r a c t Ultrasound has been found useful in increasing the efficiency and consumer safety in food processing. Removal of heavy metal (lead, mercury, and arsenic) contamination in milk is extremely important in regions of poor ecological environment – urban areas with heavy motor traffic or well established metallurgical/cement industry. In this communication, we report on the preliminary studies on the application of low frequency (20 kHz) ultrasound for heavy metal decontamination of milk without affecting its physical, chemical, and microbiological properties. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Satisfying the needs of human population in biologically and environmentally safe dairy products is a complex strategic task for modern food industry [1]. Among negative factors that determine population health risks, the most significant are ecological problems [2]. Regions with well developed metallurgical industry such as mining or steel production, or simply highly populated urban areas with heavy motor traffic are notorious for being chemically contaminated [3]. Within those areas high concentrations of toxic heavy metals such as lead, mercury, or arsenic is detected in the air, water, and plants, which consequently results in contamination of dairy and meat products available on the market [4,5]. Considering, for example, hepatotoxic (arsenic) or neurotoxic (lead, mercury) properties of heavy metals which cause human brain and liver damage, it is important to minimize their content in foods. Development of heavy metal decontamination approaches will ensure more efficient use of natural resources and safer quality of derived products. One of the possible approaches for resolving heavy metal contamination problem could be use of low frequency (20 kHz) ultrasound (US) in the production of dairy products. To date, there have been many reports published dedicated to ultrasonic food processing [6–9], revealing positive effects of caused by acoustic cavitation ⇑ Corresponding author. Tel.: +7 9507259750. E-mail address: [email protected] (I. Potoroko).
on the properties of food products, namely quality, extended shelf life, as well as on the efficiency of energy consumption during production process [10–12]. In this communication, we report on the preliminary results on the potential use of low frequency ultrasound for the removal of heavy metals such as lead, mercury and arsenic from contaminated milk. The key aspect in present report is to show how homogenizing effect [13] of ultrasound can enhance sorption properties of lignin based biopolymer sorbent polyphepan for heavy metal removal. First, we evaluated particle size distribution change in milk samples with variable fat content with respect to duration of sonication to ensure the permeation of fat and protein particles through polyphepan sorbent. Further, to evaluate the efficiency of milk decontamination from heavy metals, we compared their concentration levels in control and ultrasonicated samples after filtering through sorbent. In addition, we carried out quality assessment of US/sorbent treated milk to determine whether its physical, chemical, and microbiological properties [14,15] can meet state regulation standards.
2. Experimental section Whole milk samples with variable fat content (4.5%, 3.7%, and 2.6%) were obtained from a local farm. Ultrasound treatment of milk was carried out in an ultrasonic reactor USTA-0.4/22 OM (Volna,Russia) operating at a frequency of 22 ± 1.65 kHz and 30% of maximum (400 W) output power. All chemicals were highest
http://dx.doi.org/10.1016/j.ultsonch.2014.03.029 1350-4177/Ó 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: N. Porova et al., Effect of ultrasonic treatment on heavy metal decontamination in milk, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.029
2
N. Porova et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
grades available and were used without further purification. Biopolymer sorbent polyphepan was purchased from SAJNTEK (Russia). The amount of sorbent for milk treatment and duration of exposure (stirring) were preliminary optimized and set to 5 g/ L for 3 min. Heavy metal concentration was determined with use of Atomic Absorption Spectrometer SpectrAA 250 plus (Varian, Australia). Microscopic studies were performed on Jeol JEM-2100 (Jeol Ltd., Japan). Particle size distribution was evaluated with use of Nanotrac 253 Ultra (Microtrac, USA). Optical microscope Altami-136T (Altami, Russia) was used for studying microbacterial
growth in milk samples. Methylene blue dye was used as a microbial viability indicator.
3. Results and discussion In the first stage, to assess the possibility of using low frequency ultrasound in combination with sorbent for heavy metal decontamination, we evaluated the size distribution of dispersed milk emulsion particles. Fig. 1a–b shows particle size distribution of
Fig. 1. Particle size distribution in 4.5% fat milk samples.
Please cite this article in press as: N. Porova et al., Effect of ultrasonic treatment on heavy metal decontamination in milk, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.029
3
N. Porova et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
Table 1 Quality parameters of control and sonicated milk samples with variable fat content.
Milk fracon Fat (%) (%) Fat mass 3.7 %
Ultrasound exposure time (min)
3 min
1 min
control
2.6 %
*
Quality parameters Milk fat (%)
MSNF (%)
2.8–6.0* 0 (control) 1 3 5
Density (L)
Milk protein (%)
Freezing temperature (°C)
P8.20* P27.0*
2.8*
6 0.502*
4.52 4.82 4.52 3.97
8.23 8.30 7.93 8.13
27.93 27.97 26.77 29.28
2.94 3.07 2.55 2.39
0.519 0.523 0.501 0.529
0 (control) 1 3 5
3.67 3.67 3.65 3.60
9.34 9.29 8.98 8.70
32.85 32.69 31.51 30.46
2.63 2.60 2.45 2.33
0.529 0.529 0.529 0.529
0 (control) 1 3 5
2.66 2.80 2.58 2.51
8.29 8.26 7.96 7.66
29.67 29.45 28.46 27.35
3.08 3.03 2.76 2.50
0.523 0.521 0.503 0.485
Russian state standard parameters for milk products
1 μm
5 min
Duraon of Ultrasound treatment
4.5 %
Milk Fat (%)
As
7.41% decrease 0.027
1 min 3 min
heavy metals such as lead, arsenic, or mercury complexed with them. As mentioned earlier, the most pronounced particle size reduction effect was observed after 5 min of US treatment. 4.5% fat milk sample treated with US for 5 min and having an average particle size in the range of 75–370 nm was expected to be the
Hg
14.71% decrease
0.025
0.00034
control
50.0% decrease
Fig. 4. Optical images confirming the presence of Lactococcus lactis bacteria in control and ultrasonically treated milk samples.
US 5min
Pb
0.072
2.6 %
5 min
milk emulsions as a function of sonication time. Initially, 4.5% fat milk sample contained three distinct fractions with average particle sizes of 6 lM, 1.28 lM, and 140 nm, respectively (Fig 1a). Upon US treatment, the size distribution of particles in milk has changed with the most pronounced effect after 5 min of sonication possessing the average values in the range from 75 to 370 nm (Fig 1d). Similar trends of particle size reduction were observed for other milk samples containing 3.7% and 2.6% fat. Additionally, we evaluated all milk samples using electron microscopy. The particle size ranges observed in the images shown in Fig. 2 are in good agreement with the results obtained with particle size analyzer. Overall, it can be clearly seen that US treatment leads to a particle size reduction confirming the homogenizing effect of ultrasound. Ultrasonic homogeinsation of emulsion particles in milk has been reported in the literature [6]. The particle size reduction is primarily caused by the shear forces generated during acoustic cavitation. In the next stage, we applied sorbent to show that homogenizing effect of ultrasound can be very beneficial for heavy metal decontamination of milk. In the present study, we used one of the most common natural organic polymer sorbents which is lignin based sorbent called polyphepan. Polyphepan while being nontoxic and applied in medicine is known for its ability to bind heavy metals, thus, stimulating detoxification. The average pore size of this biopolymer is in the range of 100–150 nm, which allows permeation of protein molecules accompanied by the removal of
Duraon of Ultrasound treatment
Fig. 2. SEM images of particle aggregates present in milk.
3.7 %
control
4.5 %
0.00029
US 5min
control
US 5min
control
0.036
Fig. 3. Heavy metal content (mg/L) in 4.5% fat milk samples before (control) and after 5 min US + sorbent treatment (US 5 min).
Please cite this article in press as: N. Porova et al., Effect of ultrasonic treatment on heavy metal decontamination in milk, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.029
4
N. Porova et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
Fig. 5. Development of Lactococcus lactis bacteria in buttermilk prepared from non-treated milk (a), buttermilk prepared from US treated for 5 min and exposed to polyphepan sorbent milk (b), and soured milk product prepared from US treated for 5 min and exposed to polyphepan sorbent milk (c).
most favorable candidate for the treatment with polyphepan sorbent to ensure successful heavy metal decontamination. Indeed, we observed a significant decrease in heavy metal content of milk samples treated with combination of US and sorbent (5 g/L, stirring for 3 min) in comparison to control. The results for heavy metal content in control and 5 min sonicated 4.5% fat milk samples are shown in Fig. 3. We observed that the concentration of lead has decreased by 50%, arsenic by 7%, and mercury by 14%. Thus, we suggest that homogenizing effect caused by ultrasonic cavitation and resulting in overall particle size reduction enhances the accessibility of sorbent pores to protein molecules for their subsequent heavy metal decontamination. Further, in order to assure quality of milk that underwent ultrasound treatment and sorbent treatment, we carried quality assessment experiments. Obtained data on change in milk fat, milk solid-non-fat (MSNF) and protein contents, as well as density and freezing temperature values for control and sonicated samples are summarized in Table 1. Importantly, almost all values remain within or close to permitted by Russian state standards levels. Slight deviation from standard is observed after 1 min of sonication. Increase in fat, protein, and MSNF contents after 1 min of US treatment might be explained in terms of more efficient incorporation of ‘‘free’’ water molecules formed due to cavitation. At the same time slight decrease in these values after US exposure for 5 min most likely is due to reduced particle size which allows proteins to be carried away upon removal of sorbent. Nevertheless, through the adjustment of sorbent quantity, exposure time and sonication time, it is possible to control the quality of consumable milk product. Another important aspect which has to be taken into account when discussing quality of milk is effect of US treatment on the growth of an important bacteria, Lactococcus lactis, which is responsible for milk souring in the process of buttermilk or cheese production. Fig. 4 data clearly shows that lactobacteria present in control milk samples are not affected by ultrasound treatment. In addition, our studies have also shown that presence of lactobacteria in dairy products (soured milk and buttermilk) prepared from US treated milk is not affected (Fig. 5). Thus, US treatment does not create unfriendly environment for lactobacteria growth.
4. Conclusions In the present study we reported on the effect of low frequency ultrasound for milk treatment. We showed that ultrasound treatment leads to significant changes in size distribution of fat and protein particles present in milk, resulting in more uniform milk emulsion with particle size ranging from 75 to 370 nm. We also showed that the reduction in particle size has positive effects in terms of enhancing permeability of reduced-size proteins on lignin based biopolymer polyphepan, allowing successful decontamination of milk from heavy metals such as lead, arsenic, and mercury. Importantly, the quality of milk treated with ultrasound is not sacrificed. In addition, it is shown that ultrasound does not prevent growth of lactobacteria present in milk and dairy products such as soured milk and buttermilk. Overall, low frequency ultrasound can be potentially used for heavy metal decontamination without significant effect on the quality of consumable milk products.
References [1] A. McLeod, Human nutrition and dairy development: trends and issues, in: E. Muehlhoff, A. Bennett, D. McMahon (Eds.), Milk and Dairy Products in Human Nutrition, FAO, Rome, 2013, pp. 355–375. [2] B.K. Mandal, K.T. Suzuki, Arsenic round the world: a review, Talanta 58 (2002) 201–235. [3] A. Shapiro, C. Mercier, Safe food manufacturing, Sci. Total Environ. 143 (1994) 75–92. [4] B. Dhanalakshmi, G. Gawdaman, Determination of heavy metals in goat milk through ICP-OES, Asian J. Dairy Food 32 (2013) 186–190. [5] P.H. Kiyataka, S.T. Dantas, L. Pallone, J. Azevedo, Method for assessing lead, chromium, mercury and arsenic in high-density polyethylene packaging and study of the migration into yoghurt and stimulant, Food Addit. Contam. Part A Chem. Anal. Control 31 (2014) 156–163. [6] J. Chandrapala, C. Oliyer, S. Kentish, M. Ashokkumar, Ultrasonics in food processing, Ultrason. Sonochem. 19 (2012) 975–983. [7] B. Zisu, J. Chandrapala, High power ultrasound processing in milk and dairy products, in: N. Datta, P. Tomasula (Eds.), Emerging Dairy Processing Technologies: Opportunities for the Dairy Industry, Wiley – Blackwell publisher, 2013. [8] M.J.W. Povey, Ultrasonics of food, Contemp. Phys. 39 (1998) 467–478. [9] S. Shestakov, O. Krasulya, V. Bogush, I. Potoroko, Technology and Equipment for Food Processing Environments Using Cavitation, GIORD, St. Petersburg, 2013.
Please cite this article in press as: N. Porova et al., Effect of ultrasonic treatment on heavy metal decontamination in milk, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.029
N. Porova et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx [10] A.E. Torkamani, P. Juliano, S. Ajlouni, T.K. Singh, Impact of ultrasound treatment on lipid oxidation of Cheddar cheese whey, Ultrason. Sonochem. 21 (2014) 951–957. [11] M. Ashokkumar, J. Lee, B. Zisu, R. Bhaskarcharya, M. Palmer, S. Kentish, Hot topic: sonication increases the heat stability of whey proteins, J. Dairy Sci. 92 (2009) 5353–5356. [12] J. Chandrapala, C. Oliver, S. Kentish, M. Ashokkumar, Ultrasonics in food processing – food quality assurance and food safety, Trends Food Sci. Technol. 26 (2012) 88–98.
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Please cite this article in press as: N. Porova et al., Effect of ultrasonic treatment on heavy metal decontamination in milk, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.029