Behavior of the Physiochemical Parameters of Raw Milk Stored in Temporary Horizontal Storage Tanks

Milk is a product with a high nutritional value, and it may appear in daily meals in its natural form or processed and transformed into various milk products. To be processed in industry, milk must have the proper quality conditions for its consumption, and the levels of its constituents must fall within the standards indicated by Normative Instruction no. 62 (2011). Due to its composition, its constituents tend to separate when at rest. In this context, the objective of this work was to evaluate the behavior of the physiochemical parameters of chilled raw milk stored in temporary horizontal storage tanks. With the milk at rest in the tank, collections were made of the milk at the times of 0, 60, 120, 180, 210, 240, 270 and 300 minutes. These collections were performed at two points of the tank: at the top collection point (Ps) and the bottom collection point (Pi) of the tank. After the collection of the samples, the following parameters were determined: fat (G), non-fatty solids (SNF), density (D), cryoscopic index (95), protein (P), lactose (L) and solids (SI). After completion of the tests, it was possible to verify that the solid constituents of the milk showed different behaviors, since the fat separated completely at 210 minutes promoting a stabilization in the separation of the fat. This same behavior was found for Density and the Cryoscopic Index. The other solid constituents of the milk didn't separate, maintaining themselves stable in both the bottom and top of the tank. As such, the conclusion can be drawn that fat is the only physiochemical compound that separates from milk at rest, thus affecting its Density and Cryoscopic Index.


INTRODUCTION
Milk is a white and opaque liquid. It's appearance is the result of the reflection of light by fat globules, insoluble phosphates and casein, with variations ranging from cream to bluish. It has a slightly sweet taste because of the presence of lactose, sodium chloride, fats and proteins. It is a homogeneous mixture with a high nutritional value and it plays a fundamental role in human nutrition, in addition to providing energy and nutrients for subsistence (Koblitz, 2011;Gonzaga et al., 2015). According to the Normative Instruction no. 62/2011 of the Ministry of Agriculture, Livestock and Food Supply (MAPA), milk is the product arising from the complete and uninterrupted milking of healthy. well-nourished and rested cows in hygienic conditions (Brazil, 2011). Controlling the physiochemical and microbiological quality of the milk arriving in industrial and processing units is crucial to ensure the health of the population and should be a routine procedure (Tronco 2008;Azevedo 2014). To be processed in industry, the milk must have the proper quality and consumption conditions and levels within the standards indicated by the Normative Instruction No. 62 of December 29, 2011 from the Ministry of Agriculture, Livestock and Food Supply (MAPA), whose parameters are used as indicators to provide the conditions in which the milk was obtained and processed or to identify any fraud of the product (Brazil, 2011). When the milk arrives at the reception platform of the dairy industry, milk samples should be collected directly in the truck and go through a series of analyses through rapid tests. Standing out as one of the main analyses required by legislation are the acidity, density, color, smell and texture tests, but the most important factor to be analyzed is the temperature of the milk. This temperature should remain in a range of 7ºC to 10ºC (Brazil, 2011). The minimum quality requirements that refrigerated raw milk in rural properties must comply with, and which can be considered as the acceptable contamination limits of milk, are: a fat content of at least 3% titratable acidity between 0.14 and 0.18 g of lactic acid, density at 15°C between 1.028 and 1.034 g/cm³, dry degreased extract (ESD) of at least 8.5g/100g, cryoscopic index of -0.530°H to -0,550°H, equivalent to -0,512°C and 0.531°C, and a minimum of 2.9 g of proteins (Brazil, 2011; Moura et al., 2013;Liu et al., 2016). Dairy industries pay producers not only for the volume of milk, but also for its quality, where a low TBC (Total Bacteria Count), a low SCC (Somatic Cell Count), and high levels of protein and fat contribute to more remuneration (Rezende et al., 2012;Almeida, 2013). The physiochemical characteristics of milk and their inter-relationships are a valuable tool to evaluate the productive performance of dairy cattle, to provide information about the physiological state of the lactation, and to diagnose metabolic disorders and their possible impacts on the industrial processing and the final quality of milk products (Rowbotham and Ruegg, 2016). In the tanks of the trucks arriving at the dairy industry, samples are collected for laboratory tests, which must be taken after agitation for five to ten minutes by means of an agitator of the total volume of the tank (Di Domenico, 2009;Ponce, 2009;Bittante et al., 2012;Tonini, 2014) The fat globules are suspended in water and have a lower density than it. This causes the formation of a fat layer on top of the rest of the milk, which must be constantly stirred to prevent the formation of a too thick layer of fat at the top. In milk that hasn't been sufficiently homogenized, differences show up in the composition of the milk removed from the bottom of the cooler, through the tap, and from the top, with the aid of the collection ladle (Durr et al., 2001;Buza et al., 2014). Due to the differences in the chemical composition of the milk, the exact behavior of the physiochemical parameters of the milk stored in the isothermal tanks of the trucks waiting for analysis in the platform of dairy industries so its quality can be determined, is not known. In this context, the objective of this work was to evaluate the behavior of the physiochemical parameters of chilled raw milk stored in temporary storage tanks.

MILK SAMPLES
This study used chilled raw milk 'in natura' granted by a dairy producer located in the city of Chapecó -Santa Catarina. The milk samples supplied by the dairy producer were of milk collected on the same day as the analysis. These samples were transported in a cold chamber to the test laboratories of the Universidade Comunitária da Região de Chapecó -Unochapeco. The official analyses were performed in the Food Technology Laboratory of the Chapecó Campus. The samples were kept in the temporary horizontal tank, in a controlled temperature environment of 7.00 ºC ± 2.0, as determined by the Normative Instruction no. 62 (Brazil, 2011) of the Ministry of Agriculture, Livestock and Food Supply -MAPA, which establishes that chilled raw milk in Brazil must pass through an analysis to assess its quality. All analyses were performed in triplicate.

STORAGE TANK
In order to carry out this experiment, an isothermal, horizontal temporary storage tank was designed and built with a capacity of 33 liters of milk, with similar characteristics as the truck tanks used for the transport of milk in bulk to the dairy industries. The tank was built in stainless material and jacketed according to  The tank was constructed with two collection points for the milk samples, called: Top Collection Point (Ps) and Bottom Collection Point (Pi). These points allowed for the collection of milk samples during the evaluation times. At each collection point, a faucet was installed to perform the collection without contaminating the rest of the stored milk. The faucets used are in accordance with sanitary legislation.

BEHAVIOR OF THE MILK'S SOLID CONSTITUENTS
With the milk at rest in the tank, collections were made of the milk at the times of 0, 60, 120, 180, 210, 240, 270 and 300 minutes. These collections were performed at two points of the tank: at the top collection point (Ps) and the bottom collection point (Pi). After the collection of the samples, the following parameters were determined: fat (G), non-fatty solids (SNF), density (D), cryoscopic index (95), protein (P), lactose (L) and solids (SI). The centesimal composition of the milk's constituents was determined through the Master Mini milk analyzing equipment from AKSO, which uses ultrasound technology to analyze the samples. The method is based on an ultrasound spectroscopy based on the undulating movement that propagates in the medium where the product is inserted. The deformations of the milk molecules indicate if it was altered in its composition. In addition, the physiochemical analysis of the milk through ultrasound spectroscopy has advantages over traditional methods since samples don't need to be prepared, minimal volumes of the intact samples need to be used, no chemical reagents or specific glassware are necessary and results can be obtained in few minutes. Before the analyses, the equipment was properly calibrated and cleaned according to the manufacturer's instructions. After adding a milk sample to a 25 ml cuvette, the device sucks in the quantity of milk needed for analysis and shows the values of the constituents of the milk under analysis on the screen (Ponsano et al., 2007).

STATISTICAL ANALYSIS
The Microcal Origin software, version 7.0 (Microcal Software Inc., Northamptomn, MA, USA), was used for the statistical data analysis, ANOVA using the Tukey test, with a significance level of 5%, was used for the analysis of variance. The physiochemical parameters were evaluated by the difference of the sample means according to the Normative Instruction no. 62 (2011). All activities were performed in triplicate.

III. RESULTS AND DISCUSSION
The behavior of the physiochemical parameters of the milk stored in a temporary horizontal tank is presented in Table 1, 2 and 3. In Table 1 and Figure 2 the fat behavior can be seen. The analysis of the data in Table 1 reveals that there were variations in the fat levels, both in the samples collected from the top point and those collected from the bottom point. One can see that at the starting time (zero minutes), the observed levels in both points were of 3.85±0.05 and 3.75±0.05 for the top and bottom evaluation points, respectively. As can be seen, the levels don't differ significantly among themselves at the level of 5% in Tukey's Test.
After the 60 minute mark of the milk at rest, one can see that the fat levels increased until the time of 210 minutes, with values of 4.95±0.05, 9.70±0.60, 13.60±0.20 and 15.75±0.15 at the times of 60, 120, 180 and 210 minutes, respectively. As can be seen, the levels found differ significantly among themselves at the level of 5% in Tukey's Test. This behavior can be observed in the curves for the fat separation from the milk, shown in Figure 2. After 210 minutes, a stabilization of the fat levels can be observed, because the values found were 15.85±0.05, 16.25±0.05 and 16.67±0.05 at the times of 240, 270 and 300 minutes, respectively. When these data are analyzed, they show that there is no statistically significant differences between the data at the evaluation times. This behavior suggests that the movement of the fat from the lower to the higher regions of the tank stabilized. One can therefore infer that the time of separation of the fat and milk when stored under the conditions of this study is 210 minutes, or 3.5 hours. bottom points through a faucet, in Thailand the milk samples were collected by means of a pipette at the top (between 250 and 200 ml), middle (between 150 and 100 ml) and lowest point (between 50 and 0 ml) of the container in which the sample was stored.
In the Thai study, there was a significant influence of time on the fat levels, starting at the top point, where the fat content increased from 3.85 to 5.07%, an increase of about 31.69% after a time interval of 2 hours. The fat content continued to increase in the top sample and at the end of the 8 hours of the milk at rest, the fat content increased to 7.07%, consisting in a total increase of 83.63% compared to the initial fat content of 3.85%. This is corroborated in the present study, where in 120 minutes (2 hours), the fat content increased from 3.85±0.05 to 9.70±0.60, an increase of 152% from the initial value of 3.85% and the value continued to increase, but the rate of change decreased with the increase of time intervals. The behavior of the fat content obtained from the samples collected at the bottom collection point (Pi) is the opposite of the one obtained from the samples collected at the top collection point (Ps), because as the analysis time progresses, the fat content of the collected samples can be seen to decrease after 180 minutes of storage, moving from 3.15±0.05 to 2.75±0.05% at 210 minutes. As such, one can see that there is a statistically significant difference between the two means in these times. It is also clear that from 210 minutes to 300 minutes of rest, there was a stabilization in the fat content, going from 2.75±0.05 at 210 minutes to 2.70±0.20 at 300 minutes. As shown in Table 1 and Figure 2, there was a gradual reduction of the fat content at the bottom collection point and one can see that the largest value occurred at 120 minutes (2 hours), which was 81.33%, going from 3.75±0.05 to 3.05±0.05. Just as in the work by Wandi, Vijchulata and Chairatanayuth (2014), who found a gradual reduction in fat content in the middle and lowest points, with an average decrease of around 8.05% and 12.99% for the medium and lower fractions, respectively.   /dx.doi.org/10.22161/ijaers.4.8.3  ISSN: 2349-6495(P) | 2456-1908(O) the density values across the test times. The density can be modified by adding water or prior skimming, because water has a higher density than fat, 1g/cm 3 and 0,9301g/cm 3 , respectively. The behavior of density in this study is corroborated by the literature, which points out that the higher the fat content, the lower the density, with skimmed milk having a higher density than whole milk, because according to Castro (2005), density is the relationship that exists between the mass and volume of a body. As such, one can see the relationship between the solids and the solvent in milk. This study revealed that in the 300 minutes of storage, the samples collected in Ps and Pi had a density of 1.012±0.70 and 1.045±0.20, respectively. It should be emphasized that these samples show levels of 16.67±0.05 and 2.70±0.20% for fat in the samples collected at the time of 300 minutes in the Ps and Pi, respectively.   4 Lactose -Bottom Point. 5 Solids -Top Point. 6 Solids -Bottom.

#Means and deviations followed by the same small case letter in the vertical axis and capital letters on the horizontal axis do not differ statistically between themselves by the Tukey test at the level of probability of 5%.
The density of the milk may be associated to the Cryoscopic Index (IC), a test serving to control the volume of water present in the milk, recommending the addition of water or removal of its components, or even the addition of some compound to mask a problem (Tronco, 2008;Botaro and Santos, 2016). The cryoscopic point is defined as the temperature at which the milk passes from a liquid to a solid state. The freezing temperature of milk is lower than water due to the substances contained in it, such as lactose and mineral salts. The freezing point can vary depending on the season of the year, feed, breed, health status, age, among others (Alberton, 2012). The higher the freezing point, therefore, the greater the water content in the milk (Robim et al., 2012). The behavior of this parameter on the data obtained in this study corroborate the fat content found in the samples taken at the established times in each collection point.

International Journal of Advanced Engineering Research and Science (IJAERS)
[ , comprise all the elements of the milk minus the water and fat. They also include, therefore, the solids (SI), also known as ashes, the lactose (L) and the proteins (P). For the dairy industry, the fat, protein, lactose, total dry extract (EST) and degreased dry extract (ESD) contents are criteria used to pay producers, assign raw material within the processes and to predict industrial yield (Beloti et al., 2008;Costa, 2014). With respect to these evaluated parameters, one can see that they didn't show variations in relation to storage time, not undergoing sedimentation or flotation and remaining stable, therefore. It should be emphasized that the lactose content found was 4.52% at time zero and 4.69% at 300 minutes of storage. No significant differences (p<0.05) were therefore observed in the Ps and Pi at the evaluated times.
The lactose values of this study were similar to the results obtained by Teixeira (2003), who found 4.66% while studying the lactation of Holstein cows. The results obtained here were similar to those in a study performed by Machado (2000), who obtained a mean lactose level of 4.51% in milk samples from expansion tanks (Oliveira and Santos, 2012  The data collected in this study revealed that the quantified protein levels had higher values than the requirements of IN-62 from MAPA, which requires values higher than 2.9%. When analyzing these data, one can see that the protein levels determined in the Ps samples in relation to the levels of the Pi samples did not have significant differences at the level of probability of p<0.05. Brazil et al., (2012) studied the storage of milk and found protein contents of 3.34% in a isothermal tank and of 3.35% in an industrial silo, while Castro and Luz (2015) found that the protein contents remained between 2.90 to 3.19%, values in accordance with the IN 62 (2011) and considered excellent for chilled raw milk, similar to this work. Several environmental factors influence the protein composition of milk, especially breed, feed and disease management, followed by season of the year, lactation stage and age of the cow. An unbalanced and nutritionally poor diet can cause changes in the composition of the milk, especially regarding the fat and protein levels and the saline balance, causing, for example, low yields in the production of cheeses and a decrease in the milk's thermal stability (Silva, 2009).

International Journal of Advanced Engineering Research and Science (IJAERS)
[ The results obtained in this study can serve as support for the technical departments of dairy industries to monitor and qualify the raw material and consequently improve the industrial yield. It is also hoped that this work will strengthen the commercial relations system between economic agents acting in the milk production chain. It is also expected that Milk Production Associations can use this information as indicators and to assist in the interface between primary production, industry and the consumers of the product.

IV. CONCLUSION
Through this study analyzing the solid constituents of milk, one can conclude that only the fat separates completely from the other constituents, concentrating on the top of the cold milk. Milk samples taken improperly or without homogenization from the isothermal tanks awaiting unloading of the milk on reception platforms, may compromise the quality of milk and the physiochemical and microbiological characteristics of the product. Payment by quality is a motivating factor for the producer, but it is not enough that the milk leaves the property in compliance with standard IN 62 (2011). If the sample taken on the platform does not match the sample from the property, the producer will be penalized.