In this study, research was based on influence of high intensity ultrasound on inhomogeneous sheep milk. Ultrasonic processor (maximal nominal power – 100W) with the constant frequency of 30 kHz was used for milk homogenization. Changes on temperature, pH – value, density, viscosity and absorbance (500nm) are followed by given process parameters: amplitude (A = 20, 60 and 100 %); time of treatment (t = 2, 6, 10 and 15 minutes), full cycle (c = 1), probe diameters (d = 7, 10 and 14 mm). Statistical analysis was conducted and infl uence of process parameters and temperature was expressed over p – value (p<0.05; ANOVA; ANCOVA). Applications of different probe diameter have significant influence on all observed physical properties. Longer time of treatment and amplitude showed significant infl uence on temperature, absorbance and changes on viscosity of sheep milk, while on pH – value and density has no infl uence. Analyses of covariance (ANCOVA) showed significant
influence of the temperature on increasing of absorbance and viscosity, while temperature has no influence on pH – value and density of ultrasonically treated milk

Branko Tripalo

Damir Ježek

Filip Dujmić

Mladen Brnčić

Sven Karlović

Tomislav Bosiljkov

English

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CROATIAN JOURNAL OF FOOD TECHNOLOGY, BIOTECHNOLOGY AND NUTRITION44IntroductionUltrasound process parameters had infl uence on the tem-perature increase as result of wave propagation throughout me-dium. Cavitation as the most accepted mechanism is based on the implosion of bubbles in surrounding media (Bosiljkov et al., 2011; Brnčić et al., 2010; Price et al., 2010; Thiemann et al., 2011). Effi ciency of cavitation mechanism depends on applied frequency, intensity and physical properties of observed sam-ple. When applied frequency increase, the number of formed bubbles gets higher, while diameter of bubbles is smaller with minimal quantity of released energy during implosion. At the frequency of 132 kHz the bubble has twice smaller than at 68 kHz (Figure 1) (Price et al., 2010; Feng and Barbosa – Cáno-vas, 2011; Ashokkumar, 2011). Fat content is the most important component in raw milk. Propagation of ultrasonic waves in milk with a lower propor-tion of fatty phase is faster which helping to create a large number of smaller cavitation bubbles whose implosion re-leased a large amount of heat energy which causes an immedi-ate rise in temperature (Cucheval and Chow, 2008). Increasing of temperature as a consequence of high intensity ultrasound may cause alternation on physical properties of milk as chang-es in temperature, pH – value, density and absorbance. Bry-ORIGINAL SCIENTIFIC PAPER Infl uence of High Intensity Ultrasound Treatments on Physical Properties of Sheep MilkTomislav Bosiljkov*, Branko Tripalo, Damir Ježek, Mladen Brnčić, Sven Karlović, Filip Dujmić Faculty of Food Technology and Biotechnology, Pierottijeva 6, 10000 Zagreb, CroatiaSummaryIn this study, research was based on infl uence of high intensity ultrasound on inhomogeneous sheep milk. Ultrasonic processor (maximal nominal power – 100W) with the constant frequency of 30 kHz was used for milk homogenization. Changes on temperature, pH – value, density, viscosity and absorbance (500nm) are followed by given process parameters: amplitude (A = 20, 60 and 100 %); time of treatment (t = 2, 6, 10 and 15 minutes), full cycle (c = 1), probe diameters (d = 7, 10 and 14 mm). Statistical analysis was conducted and infl uence of process pa-rameters and temperature was expressed over p – value (p<0.05; ANOVA; ANCOVA). Applications of different probe diameter have signifi cant infl uence on all observed physical properties. Longer time of treatment and amplitude showed signifi cant infl uence on temperature, absorbance and changes on viscosity of sheep milk, while on pH – value and density has no infl uence. Analyses of covariance (ANCOVA) showed signifi cant infl uence of the temperature on increasing of absorbance and viscosity, while temperature has no infl uence on pH – value and density of ultra-sonically treated milk. Keywords: ultrasound, sheep milk, temperature, physical propertiesCorresponding author: tbosilj@pbf.hrant and McClements (1999) were studied infl uence of various whey protein solutions at different pH – values on attenuation coeffi cient. At the pH over attenuation coeffi cient increased as the temperature increased. Maximum attenuation was realized at 80 °C. Water has the lowest attenuation factor of any liquid measured at low frequencies (Suslick, 1988; Povey, 2006). Ultrasonic wave during the propagation through the liq-uid medium become absorbed (P) and dissipated which is ex-pressed with attenuation coeffi cient (α) represented over equa-tion (1):                        20xP Pe a−=                                      (1)where: P0 – preliminary power of ultrasonic wave (starting amplitude        of ultrasonic wave)  x – wavelength of the expanded wave [m]α – attenuation coeffi cient [Neper/m]Dissipation and absorbing caused by liquid medium, af-fect on conversion of mechanic energy into heat which results by increasing of temperature in observed system. Absorption of ultrasonic wave increase as a consequence of internal fric-tion initiated by variation in viscosity, thermal conductiv-ity and lower surface tension. Ultrasonic wave propagation through medium of unequal composition infl uence on attenu-ation increases, while mechanic energy of the wave remains constant. Changing in direction of the wave causes a problem in their detec-tion (Hæggström and Luukkala, 2001; Ay and Gunasekaran, 2003; Dukhin et al., 2005; Cho, 2010; Bosiljkov et al., 2010).Materials and Methods Inhomogeneous sheep milk with follow-ing chemical structure: protein content: 4.6 % (N×6.25); total sugars: 4.2 %; fat content: 6.25 %; minerals: Ca – 1730 mgkg-1, P – 790 mgkg-1. Physical properties of inhomogeneous sheep milk: Temperature: 20 °C; pH – value: 6.763; Density (ρ): 1.0341 gcm-3, Absorbance (500 nm): 2.292.Figure 1. Infl uence of frequency on intensity and diameter of cavitation bubbles (Bosiljkov, 2011).T. BOSILJKOV et al.: Croatian Journal of Food Technology, Biotechnologyand Nutrition 7 (Special Issue) 44-48 (2012)CROATIAN JOURNAL OF FOOD TECHNOLOGY, BIOTECHNOLOGY AND NUTRITION45Figure 2. Infl uence of process parameters on temperature of sheep milkFigure 3. Infl uence of process parameters on pH – value of sheep milkT. BOSILJKOV et al.: Croatian Journal of Food Technology, Biotechnologyand Nutrition 7 (Special Issue) 44-48 (2012)CROATIAN JOURNAL OF FOOD TECHNOLOGY, BIOTECHNOLOGY AND NUTRITION46Figure 4. Infl uence of process parameters on density of sheep milkFigure 5. Infl uence of process parameters on absorbance (500 nm) of sheep milkT. BOSILJKOV et al.: Croatian Journal of Food Technology, Biotechnologyand Nutrition 7 (Special Issue) 44-48 (2012)CROATIAN JOURNAL OF FOOD TECHNOLOGY, BIOTECHNOLOGY AND NUTRITION47Ultrasonic treatmentInhomogeneous sheep milk was homogenized with 30 kHz ultrasonic processor “UP 100 H” produced by “Dr Hiels-cher” company (Teltow, Germany)  with constant frequency of 30 kHz, using cylindrical probes with different diameter: (d = 7, 10, 14 mm).  Ultrasonic treatments was performed by ampli-tude (A = 20, 60, 100 %); time of treatment (t = 2, 6, 10 and 15 minutes) and full cycle (c = 1). Volume of the sample was 150 ml with immersion depth of the probe 3 cm. Measuring of temperature Starting temperature was 20 °C. During the ultrasonic treatments temperature was measured every 30 seconds using IR – measurer “Rytek” (MiniTemp FS). Measuring of pH – value Measurements of pH – value were performed at 20 °C us-ing a calomel electrode of pH – meter „WTW 330i / SET”.Measuring of densityTemperature of density meter “Mettler Toledo DE 40” was setting on 20 °C. After the correction of the sample tem-perature density of sample was displayed.Measuring of absorbance Absorbance was measured by spectrophotometer CONI-CA-MINOLTA CM – 3500 – d. The values of absorbance are read off using software “Spectra MagicTM NX Ver.1.7.”, “Color Data Software CM – S100w”. The measuring of absorbance was performed at 500 nm.Results and discussionInfl uence of process parameters on temperature, pH – val-ue, density and absorbance are showed with 3D diagrams cat-egorized by probe diameter (Figures 2 – 5).In accordance with represented 3D diagrams analyses of variance (ANOVA) showed infl uence of process parameters on all observed physical properties (Table 1).Amplitude and time of treatment (higher β) have slightly higher impact than probe diameter on temperature increase. Changes in pH – value can be observed in two ways. Increas-ing of probe diameter infl uence on decreasing of pH – value which is indicated with negative value of β-coeffi cient. As the probe diameter increasing, interaction between amplitude and probe diameter leads to increasing of pH – value. Probe diam-eters have infl uence on decreasing of density while amplitude and time of treatment have no infl uence. Interval of β – coef-fi cient between 3.6 – 6.8 indicates a similar infl uence of all process parameters on increasing of absorbance and viscosity of sheep milk. Covariance is a value that tells us how two of the observed size working together. Propagation of ultrason-ic waves with constant frequencies, amplitude and cycle through the selected period of time change the temperature during ultrasonic treatment in the surrounding medium. Mechanical wave motion includes the features of output values, which signifi cantly changes the physical properties of milk samples in the reference system. In accordance with infl uences of process parameters on physical properties, analyses of covariance (ANCOVA) showed signifi cant in-fl uence of the temperature on increasing of absorbance and viscosity, while temperature has no infl uence on pH – value and density of ultrasonically treated milk (Table 2). ConclusionsInfl uence of highest values of process parameters was expressed on increasing of absorbance and viscosity. The highest infl uence on increasing of temperature has the high-est values of amplitude and time of treatment. Consequence Statistically signifi cant when (p<0.05)Physical properties Parameters p – value -coefficientd [mm] 0.001079 3.360528A[%] 0.000000 7.12006Temperature  [°C] t[min] 0.000000 10.5983d [mm] 0.000000 -7.1277A[%] 0.041420 2.064168pH-valuet[min] 0.434271 -0.784859d [mm] 0.000004 -4.83556A[%] 0.942664 0.0720905Density[gcm-3]t[min] 0.127702 1.535138d [mm] 0.000367 3.807091A[%] 0.000025 4.617619Viscosity[mPas]t[min] 0.000680 3.609852d [mm] 0.000001 5.114579A[%] 0.000009 4.657709Absorbance (A500)t[min] 0.000000 6.849882Table 1.  ANOVA Infl uence of process parameters on physicalproperties of sheep milk (p<0.05)Physical properties p-valuepH-value 0.754744Density[gcm-3] 0.093134Viscosity[mPas] 0.000004Absorbance (A500) 0.000000Table 2. ANCOVA Infl uence of temperature on physical properties of sheep milk (p<0.05)Statistically signifi cant when (p<0.05)T. BOSILJKOV et al.: Croatian Journal of Food Technology, Biotechnologyand Nutrition 7 (Special Issue) 44-48 (2012)CROATIAN JOURNAL OF FOOD TECHNOLOGY, BIOTECHNOLOGY AND NUTRITION48of these signifi cant changes is increasing of temperature during ultrasonic treatment. As well as infl uence of all input levels on physical properties, infl uence of output level (temperature) has the same infl uence on wave motion in observed system.ReferencesAshokkumar M. (2011) The caracterization of acoustic cavitation bubbles – An overwiev. Ultrasonic Sonochemistry, 18 (4) 864 – 872.Ay, C., Gunasekaran, S. (2003) Numerical method for de-termining ultrasonic wave diffusivity through coagulating milk gel system. Journal of Food Engineering, 58 (2) 103 – 110.Bosiljkov, T. (2011) Infl uence of high intensity ultrasound on degree of homogenization and physical properties of soy-bean, cow, sheep and goat milk. PhD Thesis. University of Zagreb.Bosiljkov T., Tripalo B., Brnčić M., Ježek D., Karlović S., Jagušt I. (2011) Infl uence of high intensity ultrasound with dif-ferent probe diameter on the degree of homogenization (vari-ance) and physical properties of cow milk. African Journal of Biotechnology, 10 (1) 34 – 41.Bosiljkov, T., Karlović, S., Tripalo, B., Brnčić, M., Ježek, D., Rimac Brnčić, S., Penava, A., Karlović, D. (2010) Primje-na ultrazvuka niskog intenziteta („puls – jeka“) u otkrivanju oštećenja ambalažnog materijala i stranih tijela unutar pako-vanja. Hrvatski časopis za prehrambenu tehnologiju bioteh-nologiju i nutricionizam, 5 (1 – 2) 31 – 37.Brnčić, M., Karlović, S., Rimac Brnčić, S., Penava A., Bosiljkov, T., Ježek, D., Tripalo, B. (2010) Textural properties of infra red dried apple slices as affected by high power ultra-sound pre-treatment. African Journal of Biotechnology, 9 (41) 6907-6915.Bryant, C.M., McClements, D.J. (1999) Ultrasonic spec-trometry study of the infl uence of temperature on whey protein aggregation. Food Hydrocolloids, 13 (6) 439 – 444.Cho B.K. (2010) Nondestructive Evaluation of Food Quality, Springer, London, UK. Cucheval A., Chow R.C.Y. (2008) A study on the emulsi-fi cation of oil by power ultrasound. Ultrasonic Sonochemistry, 15 (5) 916 – 920.Dukhin, A.S., Goetz, P.J., Travers, B. (2005) Use of Ul-trasound for Characterizing Dairy Products. Journal of  Dairy Science, 88 (4), 1320-1344.Feng H., Barbosa – Cánovas G.V. (2011) Ultrasound Technologies for Food and Bioprocessing (ed: Weiss J.) Spring Street, New York, NY 10013, USA.Hæggström E., Luukkala E. (2001) Ultrasound detection and identifi cation of foreign bodies in food products. Food Control, 12 (1) 37 – 45.Povey, M.J.W. 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Influence of High Intensity Ultrasound Treatments on Physical Properties of Sheep Milk

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Influence of High Intensity Ultrasound Treatments on Physical Properties of Sheep Milk

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