Total bacterial count and somatic cell count in refrigerated raw milk stored in communal tanks

The current industry demand for dairy products with extended shelf life has resulted in new challenges for milk quality maintenance. The processing of milk with high bacterial counts compromises the quality and performance of industrial products. The study aimed to evaluate the total bacteria counts (TBC) and somatic cell count (SCC) in 768 samples of refrigerated raw milk, from 32 communal tanks. Samples were collected in the fi rst quarter of 2010, 2011, 2012 and 2013 and analyzed by the Laboratory of Milk Quality – LQL. Results showed that 62.5%, 37.5%, 15.6% and 27.1% of the means for TBC in 2010, 2011, 2012 and 2013, respectively, were above the values established by legislation. However, we observed a signifi cant reduction in the levels of total bacterial count (TBC) in the studied periods. For somatic cell count, 100% of the means indicated values below 600.000 cells/mL, complying with the actual Brazilian legislation. The values found for the somatic cell count suggests the adoption of effective measures for the sanitary control of the herd. However, the results must be considered with caution as it highlights the need for quality improvements of the raw material until it achieves reliable results effectively.


Introduction
Through the technical regulation of identity and quality of refrigerated raw milk, the Brazilian legislation provides quality microbiological standards that indicate the hygienic conditions of processed milk.In establishments under federal inspection, the entire volume of milk began to be analyzed by the Brazilian Network for Milk Quality (BNMQ) laboratories, credentialed by the Ministry of Agriculture (BRASIL, 2011).
An impor tant resource for monitoring the microbiological quality of refrigerated raw milk is the somatic cell count (SCC), whose function is to combat bacteria which cause mastitis and possible economic losses arising there from (DONG et al., 2012).All cells in milk and those originating from both apoptotic desquamation of alveoli, as those removed during the fl ow of the bloodstream, are considered somatic cells (GAIATO et al., 2012).
Another measure that allows knowing the concentration of microorganisms in milk is the total bacterial count (TBC) that assists the evaluation of milking and storage procedures in the rural property and, at the same time, allows us to infer the likely adverse effects on industrial productivity and safety of the milk (GARGOURI et al., 2013;SILVA, 2011).
The objective of this study was to verify the characteristics related to the microbiological quality through somatic cell count and total bacterial count of refrigerated raw milk stored in communal tanks for industrial processing.

Material and methods
Refrigerated raw milk was collected in 32 communal tanks, from rural properties at Colorado do Oeste, Rondônia, Brazil.The collection procedure consisted of milk homogenization, through activation of the tank agitator for 5 minutes, followed by the collection and transference of the samples to appropriate containers, which were sent to the Milk Quality Laboratory, at the Federal University of Goiás (CPA, 2010).
Data collection refers to samples analyzed during the months of January, February and March, in 2010, 2011, 2012and 2013, period classifi ed as rainy (October to April) (RONDÔNIA, 2007).Two samples of milk were collected every month, once for CBT and one for CCS.Therefore, in the quarter, six samples per tank were analyzed, allowing the calculation of the geometric mean, according to the methodology suggested by the Normative Instruction nº 51 (NI-51) and the Normative Instruction nº 62 (NI-62) (BRASIL, 2002;2011).
Table 1 shows the amount of communal tanks of the milk suppliers and the geometric mean size used to infer the results.12.5% (4) ---10.000cells/mL.Buying milk with high bacterial counts, the company may be putting at risk the safety of dairy products produced with this type of raw material.TBC values above the reference parameters of the legislation are among the major deficiencies in microbiological quality of milk as stated by Ponsano et al. (2011), based on studies on training farmers to improve the quality of raw milk produced in Araçatuba, SP.Then, it becomes evident the need to adopt control measures to improve the microbiological quality of milk before submitting it to industrial processing.
It is observed that over the study period (Figure 1) there were reductions of TBC in compliance with the legislation in 2011 and 2012, with a slight increase in 2013.This result is alarming, since in the second half of 2014 the limit for the TBC must present 300.000cells/mL.Increased TBC in the fi rst quarter of 2013 can be explained by the gradual reduction of the maximum allowable values for the microbiological requirements of milk (BRASIL, 2011).
Although the percentage of TBC samples in disagreement with the legislation is high, it is noted (Figure 1) that, over the analyzed period, there were reductions of TBC, in compliance with the Brazilian legislation (BRASIL, 2002;2011) with a slight increase in 2013.Studies by Paiva et al. (2012) showed an annual quality evolution of refrigerated raw milk with a reduction rate of TBC due to technical guidance to farmers.However, Ponsano et al. (2011) warns that it is necessary a greater time working together with farmers so that they may assimilate information and put them into practice, until improvements in milk quality are met.
Therefore, in this research, one of the factors that may have contributed to improvements in the levels of TBC are the intensifi cation of technical orientation performed by the milk collection companies in line with the requirements of Brazilian legislation, which gradually is being implemented throughout the national territory (BRASIL, 2002;2011).
For somatic cell count, no statistical differences between the studied periods (Figure 2) occurred.In Figure 2, the SCC had amplitude ranging from 53.000 to 483.000 cells/mL, results compliant to the legislation (BRASIL, 2002;2011).
Regarding the description of SCC variable, on average, samples showed 346.000 cells/mL, with a standard deviation of 93.33.The SCC variable had a coefficient of variation of 27%, showing an average variability (FONSECA and MARTINS, 1996).
Similarly to the results of this survey, Silva (2011) found mean values below 600.000 cells/mL in the fi rst six months of 2007, 2008 and 2009 in refrigerated raw milk stored in communal tanks of northeastern Brazil, concluding that the elevation of SCC in milk (up to 200.000 cells/mL), which indicates the occurrence of (Table 2), that is 1.0x10 6 cells/mL for 2010; 7.5x10 5 cells/mL for 2011 and 2012 and 6.0x10 6 cells/mL for 2013 (BRASIL, 2002;2011).
In several studies on the incidence of TBC in milk, it was observed that high microbial counts are sourced from disability in washing and sanitizing of the equipments, milking utensils and inadequate cooling system (TRONCO, 2008).In Lacerda et al. (2010), high bacterial counts were due to failure in handling, especially with regard to hygiene and health care in milking.Another explanation for high values of TBC is the season, which infl uences the feeding of the herd and milk production, interfering with the bacterial content (HOOGERHEIDE and MATTIODA, 2012;PAIVA et al., 2012).This aspect can be seen in a study about the quality of refrigerated raw milk in Ouro Preto do Oeste, Rondônia, Brazil, showing that the mean TBC in March, a period considered rainy (October-March), of 1.891.000cells/mL, was higher than the average of July, a period considered dry, of 760.000 cells/mL (ALMEIDA, 2010).
According to the results, there were signifi cant reductions in the levels of TBC of refrigerated raw milk; however, values in disagreement with the legislation were found (Figure 1).
The values in disagreement to TBC found in 2010 (62.5%, Figure 1) is a serious problem for the industry regarding to quality, especially in the results above Although all parameters of somatic cell counts were within the microbiological standards established by legislation, this result must be considered with caution as it highlights the need for improvements in the quality of the raw material until it achieves reliable results effectively.mastitis, affects the composition of the milk and the shelflife of products.Hortet et al. (1999) found losses of 0.30 kg of milk, which occurred for 100.000cells/mL, and 0.61 kg, for 200.000 cells/mL.In addition, with the increase in SCC, milk composition, enzymatic activity, clotting time, productivity and quality of dairy products, are negatively infl uenced (KITCHEN, 1981).
Considering the results in accordance to the SCC, it was expected a better result for TBC, since the practices that prevent mastitis are largely the same that prevent bacterial contamination of the milk.However, it must be considered that crossbreed and low production animals are less susceptible to mastitis, which most often affects purebreds and high production animals (BELOTI et al., 2011).
Further, according to the results shown in Figure 2, it is observed that the values for somatic cell showed a similar behavior.These results also indicate that milk somatic cells varied slightly depending on the period studied.Corroborating this behavior Mesquita et al. (2008), researching the quality of milk in the central west and northern Brazil in January 2007 to July 2008 found that the geometric mean for SCC (300.000CFU/mL) had no signifi cant change over the period.With the results obtained in this research (Figure 2), milk suppliers would not have diffi culties to meet the parameters set by legislation (BRASIL, 2002;2011).

Conclusions
The high percentages for total bacterial count in milk indicate failures in milking hygiene procedures and/or storage that affect the quality of the raw material.However,

Figure 1 .
Figure 1.Percentage of quarterly geometric means (from 2010 to 2013; n=128) in disagreement with the legislation, for total bacterial count of refrigerated raw milk at Colorado do Oeste.

Figure 2 .
Figure 2. Box plot of the geometric mean for somatic cell count of refrigerated raw milk in the fi rst quarter of 2010 -2013 (Colorado do Oeste).

Table 1 .
Sample data and geometric mean of milk suppliers in Colorado do Oeste in the fi rst quarter of 2010 -2013.

Table 2 .
Percentage results of geometric means (n=128) of refrigerated raw milk for TBC in the fi rst quarter of 2010 -2013 (Colorado do Oeste, RO).