Effect of Ultrasonic Treatment on Buffalo Milk Homogenization and Numbers of Bacteria

The effect of ultrasonic treatment on milk homogenization and numbers of bacterial were studied. The results showed that ultrasound treatments with high power had an important effect on milk homogenization. The lowest homogenization indices (high efficiency) were 2 and 3% at 430 and 338W respectivily. The homogenization index was reduced with increasing time of homogenization with ultrasonic treatments. The mean D-values were 12.17 and 5.49 min. for ultrasonic treatments of 338 and 430 W respectively.


INTRODUCTION
Historically, the effectiveness of low intensity Utilization of high intensity ultrasound in food by the protection afforded to the organisms by the food technology and biotechnology is in the sense of this environment. Recently, however, systems with high progressive technology usage on most usable processes output of ultrasonic energy at low frequency have greatly in food industry. Those include mixing, drying, increased the lethal effect on bacteria [5]. In general, homogenization, crystallization, grinding and many inactivation of the cells is more pronounced at an elevated other operations. High intensity ultrasound is capable power level and as the processing time increases. to change physical and chemical characteristics of treated One of non traditional types of milk processing is materials [1]. ultrasonic processing. At present time, ultrasonic devices Ultrasound is of great investment in food processing for homogenization are used at milk processing [7]. for many reasons [2]. This technique can be generally Ultrasound treatment with high amplitude (power) hands used in systems which are liquids and can be defined as an impotent effect on milk homogenization compared to waves with high frequency [3]. High amplitude of ultra conventional homogenization. As exposure time and sound and longer exposure time ensure greatest effect on power levels increase homogenization efficiency also rise. degree of homogenization. The mechanisms which are The highest homogenization efficiency and the smallest contributing to fat globules disruption is known as the fat globule diameter are 3.22 and 0.725 µm at power level capillary wave's mechanisms. Decreasing of fat 100 (450 W) for 10 min. respectively. The fat globule globules is possible only if the diameter of fat globules diameters at power level of 40 (180 W) for 10 min are is significantly larger than the oscillation wave length similar to those of conventional homogenization [8]. and for oil -water systems is approximately 10 µm.
Increase of the power (100Watt) lead to increase of Cavitation is the most accepted mechanism for degree of stated homogenization and decrease in size of ultrasound emulsification. This mechanism is based on fat globules in soybean milk [9]. Homogenization must the implosion bubbles which produce powered shock always be sufficiently efficient to prevent creaming. waves in the milk surrounding the ultrasonic probe and The result can be checked by determining the jets of high velocity. This micro jet effectively causes homogenization index. The index for homogenized fat globules disruption [4]. Ultrasound has various milk should be in the range of 1 to 10. The effect of applications in the food industry, including killing or homogenization on the physical structure of milk has inhibiting bacteria. many advantages: Smaller fat globules leading to no ultrasound in inactivating bacterial cells has been limited cream-line formation, whiter and more appetizing color, =((a-b)/a)*100 (1) reduced sensitivity to fat oxidation, more full-bodied flavor, better mouth feel and better stability of cultured where a, b, are the fat content of sample for the upper part milk products [10]. Ultrasound treatment with high and from the bottom. amplitude (power) has an important effect on milk homogenization compared with conventional D-Calue: D-value was calculated from the following homogenization and the best homogenization and the equation [11]: smallest fat globule diameter (0.725µm) are obtained at a power level of 10 minutes [8]. The objective of our study D = (t -t )/(log(c)-log(d)) (2) was to investigate the effect of different of ultrasound treatments on buffalo milk homogenization and numbers where c and d represent the survivor counts following of bacterial cells during different times to compare these heating for t and t min, respectively. D is the time needed with conventional homogenization.
to destroy 90% of the micro-organisms (to reduce their numbers by a factor of 10) is referred to as the decimal MATERIALS AND METHODS reduction time or D-value.  (Fig. 1). tip and working at a constant frequency (28 kHz) was

Materials
The maximum homogenization index was in the control. used to homogenize 150 ml of buffalo milk for each Homogenization index was reduced with increasing time treatment. The ultrasound probe was immersed in to the in the ultrsonic treatments. Reducing homogenization milk at depth of approximately 4 cm. The experiment was index that means high homogenization efficiency. A carried out using different power levels. Exposure minimum homogenization index was 2 and 3% at 430 W times were 5, 10 and 15 min for each trail. The samples and 338W respectivily at 15 min.These results agree were kept at 20°C. The power trail of 99 and 77% with Teknatext [10] who stated that homogenization corresponding to approximately 430 and 338 W, must always be sufficiently efficient to prevent creaming. respectively was used.
The result can be checked by determining the Homogenization Index: The homogenized milk was placed should be in the range of 1 to 10%. The impircal equations in to a graduated cylinder of 150 ml and kept in a for calculating homogenization index (%) at 338W and refrigerator for 48 hr. then the fat content of sample for the 430W were: upper part, i.e. 1/10 (a) and from the bottom, i.e. 9/10 (b) of the graduated cylinder was determined by using the = -0.0427t +1.3053t -12.904t+45.333 (3) Gerber method [9]. The following equation was use to = -0.0299t +1.0014t -11.134t+45.333 (4) calculate the homogenization index (refer to reverse homogenization efficiency) of the sample [8, 10].
where t is the time (min.), R =0.999 for eq. 1 and 2.

D-Value:
The microbial destruction rate is generally decreased compared with samples of control and the defined in terms of a decimal reduction time (D-value) logarithms of numbers of bacteria were (3.6 and 3.8 which is the heating time in minutes at a given logCFU/ml) at 388 and 430w respectively for a period of temperature required to result in one decimal reduction in 15 minutes while the control samples had (4.19 and 4.17) the surviving microbial population. In other words, D at 388 and 430w respectively (Fig. 2-3). value represents a heating time that results in 90% Ultrasound causes cavitation's in aqueous solutions, destruction of the existing microbial population [11].
which is an effective factor in damaging the cell wall of the The mean D-values were 6.47 and 5.49 min. for micro-organisms, when a bubble collapses, a strong shear ultrasonic treatments at 338 and 430 W, respectively rate is generated in the environment that breaks the (Table 1) Table (2) bacteria in samples of buffalo milk and shows that the illustrates the percentage of fat directly after the treatment logarithms of numbers of bacteria were decreased with and after 48 hour. Ultrasonic treatment of milk produced increasing power and increasing time of exposure buffalo milk with homogenized fat globules distributed compared with the control sample. The logarithms of the uniformly in all parts of the sample. The percentages of fat total numbers of aerobic bacteria after treatment directly in the upper layer of non -treatment sample was 7.4 and in were (5.87and 4.71 CFU/ml) when the powers were 388 and the bottom of sample was 6.5, but after 48 h, the 430w respectively for a period of 15 minutes and got percentages of fat in the upper layer of non -treatment increased by for storage where the logarithms of the total sample was 7.5 and in the bottom of sample was 6.5. The numbers of bacteria on the sixth day became (7.04 and results showed the percentage of fat in the upper and 7.08 logCFU/ml) at 388 and 430w respectively for a period bottom layers of homogenized milk samples by using of 15 minutes and the logarithms of the numbers of ultrasonic treatments were better than non-treatment bacteria were (8.34 and 8.32 logCFU/ml) at 388 and 430w samples, this due to ultrasonic treatments which causing respectively ( Fig. 2-1).
of reducing of fat globule size. The homogenization of The effect of ultrasonic treatment was evident in milk was increased with increasing power and time. This reduction of the logarithms of numbers of the coliform results agree with Luque and Priego [8] whose stated that bacteria (Fig. 2-2) as the logarithms of numbers after ultrasound treatment with high amplitude (power) has an treatment directly were (2.11 and 2.14 logCFU/ml) at important effect on milk homogenization compared with 388 and 430w respectively for a period of 15 minutes conventional homogenization and the best compared with samples of control (3.64 and 3.08), homogenization and the smallest fat globule diameter respectively. Also, the staphylococci numbers were (0.725µm) are obtained at a power level of 10 minutes. The obtained data from using ultrasonic treatments À01J11/16 The way of the production of high-fat milk in the buffalo milk homogenization showed that the products and the devices of its realization, Appl., homogenization index was reduced with increasing time 26.04.96, publ. 21.01. and increased with increasing power. D-value was 8. Ertugay, M.F., M. eng l and M.E. eng l, 2004. increased with increasing time and power. The logarithms Effect of ultrasound treatment on milk of numbers of bacteria were decreased with increasing homogenization and particle size distribution of fat. power and increasing exposure to ultrasonic compared Turkish Journal of Veterinary and Animal Sciences, with sample of control.