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Composition and microbiological quality of raw milk refrigerated in community tanks

Milk is rich in nutrients, but several factors in the production system interfere with its quality. The objective of this study was to analyze the composition and microbiological quality of raw milk stored in community tanks from the municipality of Aricanduva – Minas Gerais. Samples were collected from eight community tanks at different properties. The milk composition and temperature were analyzed using the digital milk analyzer. The total count of aerobic mesophilic microorganisms was performed at the Laboratory of Science and Technology of Products of Animal Origin, Department of Animal Science, Federal University of Vales do Jequitinhonha and Mucuri, Diamantina – Minas Gerais. The data obtained were compared to the values established by Normative Instruction (IN) n° 76, by means of Student's t-test and Wilcoxon's non-parametric test at the level of 5% of significance. The average levels of fat (3.55 g/100g), protein (3.00 g/100g), lactose (4.45 g/100g) and total solids (11.76 g/100g) were within the standards minimum required. The content of defatted solids (8.21 g/100g) was the limiting factor to the compliance with IN76, with an average value lower than that established (8.40 g/100g). The temperature of the milk was higher than the standard required by the legislation and the count of mesophilic microorganisms did not differ from the legislation. It is concluded that the composition of raw milk stored in community tanks in the municipality of Aricanduva – Minas Gerais, compared to IN 76, did not fully met the legislation in all evaluated parameters.


Introduction
Cattle raising is one of the main activities in Brazil and it employs approximately 6.7 million people both directly and indirectly (Almeida et al., 2019). Dairy farming is expressive in Brazil. The country is ranked the fourth largest producer in the world (FAO, 2019). Among the Brazilian states, Minas Gerais stands out as the largest milk producer with 9,509,423.00 liters/year. This represents about 27.1% of the total production in Brazil, which is approximately 34.8 billion liters of milk (IBGE, 2019). Thus, milk plays an important social and economic role in the country.
Milk play an important role in human nutrition and is consumed at different stages of life, with nutritional relevance especially in childhood and old age. It is composed of water in addition to vitamins, minerals, proteins, fats, and carbohydrates that make up its the solid content (Elias et al., 2014). The fraction of each component of the solid part of milk (12 to 14%) can represent from 3.5% to 4.5% for lipids, carbohydrates 4.6% to 5.2%, proteins 3.2% to 3 .5%, and vitamins and minerals about 1%. (Soares, 2013).
Milk must undergo strict quality control through the assessment of physicochemical and microbiological characteristics to be considered safe for human consumption and suitable for processing. It must comply with the standards required by law and be free of residues of any kind, adulterants, and preservatives. The Brazilian Normative Instruction (IN) 76 of the Ministry of Agriculture, Livestock and Supply covers the technical regulations for the identity and quality of refrigerated raw milk and pasteurized milk (Brazil, 2018). Considering the influence of temperature on microbial growth and, consequently, on the conservation of raw milk, IN 76 also establishes the mandatory cooling of milk. In addition, it should be transported in cooled bulk to preserve its quality until reception in establishments with official sanitary inspection (Brazil, 2018). Thus, the storage bulk tank, also known as an expansion or cooling tank, is a legal requirement.
Community bulk tanks are used by small milk producers, in which a single tank is acquired and shared by a group of producers. This allowed those who produce on a smaller scale and are unable to acquire and/or maintain a refrigeration tank to comply with the legislation. However, since the milk deposited in the tank comes from different farms, a series of factors related to the production system could interfere with the composition and microbiological quality of the milk in community tanks.
The objective of this study was to evaluate the composition and microbiological quality of raw milk refrigerated in community tanks in the city of Aricanduva -Minas Gerais compared to the values established by IN 76.

Methodology
The present study was carried out using a qualitative research methodology, both in the field and in the laboratory (Pereira et al., 2018).

Characterizations of the Aricanduva-Minas Gerais microregion
This work was carried out in Aricanduva, a municipality in the State of Minas Gerais located in the Alto Jequitinhonha region, micro-region of Capelinha (Figure 1), with a territorial unit area of 243,329 km² and an estimated population of 5,269 inhabitants in 2020 (IBGE, 2020). The municipality's climate is tropical, classified as tropical climate with a winter dry season (Aw) according to Köppen and Geiger (1928), with an average temperature of 21.2 °C and an average annual rainfall of 1109 mm (Climate-data, 2020). Source: IBGE (2020).

Milk sampling in community tanks
Samples of raw milk were collected in October 2017, from eight community tanks located in different properties in the municipality of Aricanduva -Minas Gerais. The number of producers using each tank ranged from two to eleven with an Research, Society andDevelopment, v. 10, n. 11, e208101119574, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i11.19574 4 average of seven producers per tank. After homogenization of the milk (performed by mechanisms of the tank itself), the milk samples were collected with the aid of a stainless steel shell that was washed with water and neutral detergent and dried before collection.
Milk samples were collected in duplicates, on the first day of storage, after all producers had already deposited their milk in the tank. In addition, the refrigeration temperature data presented on the panel of each tank and the milk temperature of each sample was recorded using the digital milk analyzer (Vicente et al., 2020).

Milk composition analysis
Composition analyzes, g/100g, of fat, protein, lactose, total solids and defatted solids were performed immediately after collection, using a digital milk analyzer (Vicente et al., 2020).

Microbiological analysis
For the total count of aerobic mesophilic microorganisms, the milk samples were placed in coolers using sterilized Prior to the microbiological analysis, the milk samples were homogenized by inversion and 10 mL aliquots were collected for the preparation of serial decimal dilutions (up to 10-4) in saline medium (NaCl) at 0.85%, homogenized and then submitted to analyzes (Silva et al., 2017). The total count of aerobic mesophilic microorganisms was made by inoculating aliquots of appropriate decimal dilutions on Petri dishes containing standard agar for counting (HIMEDIA -India) and incubated at 35ºC for 48 hours. After counting the colonies, the results were presented in colony forming units (CFU/mL of raw milk), according to Silva et al. (2017).

Statistical analysis
Statistical analyzes were conducted using the R program (2019, version 3.5.3 "Great Truth"), adopting a 5% significance level. From the duplicate observations, one observation was obtained for each tank (n = 8  Table 1 shows the averages of the composition parameters (fat, protein, lactose, total solids, and defatted solids) of raw milk from community tanks in the municipality of Aricanduva -Minas Gerais, compared with the values established by IN 76 (Brazil, 2018). Research, Society and Development, v. 10, n. 11, e208101119574, 2021 (CC BY 4. We observed that the average levels of fat, protein, lactose, and total solids met the minimum standards required by IN 76 (Table 1). In addition, their average values were above those established by the legislation. This would be beneficial to dairy organizations, enabling greater profitability, since high solids content would increase the yield in the transformation of milk into dairy products (Gonçalves et al., 2020). The average content of total solids found, corroborates the average of producer four (11.84 g/100g) in the work by Guimarães et al. (2020) who evaluated the quality of refrigerated fresh milk from four rural properties in the municipality of Rio Verde -GO.

Composition of milk in community tanks
The results of the present work corroborate with the characteristic of the dairy farms in the studied city. They are characterized by extensive breeding systems, with milking alternating between manual and mechanical, and pasture being the main source of food with crossbred Zebu animals. Thus, producers in the region choose to manage more rustic cattle, which adapt better to the climate and relief conditions of the region but produce a smaller volume of milk (average production around 100 kg of milk/day/property) but, with high solids content. Lactose had a low standard deviation (± 0.08) and it was the one with the least variation among the studied parameters. The average lactose content found in this study was similar to that found by Guimarães et al. (2020) which ranged from 4.19 g/100g to 4.50 g/100g. Lactose is one of the most stable components of milk, being related to the regulation of osmotic pressure in the mammary gland. By attracting water into the alveoli, it consequently reduces the concentration of other components such as fat (Peruzzi, Monreal, Caramalac & Caramalac, 2016). Therefore, in rare situations there will be changes in the lactose content in milk.

Temperature and microbiological quality of milk in community tanks
The results for the parameters temperature of the milk sample, milk temperature marked on the tank panel, and count of evaluated microorganisms are shown in Table 2. Milk storage temperature was significantly higher (P<0 .05) than the value recommended by the legislation. Hot milks from different properties are transported in cans, arrive at the tank at different times, and are mixed with already refrigerated milk (Pereira & Magalhães, 2012). This procedure contributes to slower refrigeration of stored milk, which can lead to loss of quality and even refusal by the processing industry. This may explain the higher temperature found in this study (Table 2), considering that the collection was made in the morning, right after the milk was deposited by all registered producers in the sampled tanks.
Microbiological contamination of milk can occur during and after milking and the multiplication of microorganisms can be accentuated if cooling during storage is not appropriate. The cooling of milk following milking at a temperature below 4ºC (Sidney, Thomas & Dhasan, 2020), in cooling tanks and under adequate hygiene conditions, is undoubtedly one of the main points when it comes to microbiological quality. In addition, higher bacterial counts are observed in tanks with higher storage temperature (Gonzalo, Juárez, García-Jimeno & De La Fuente, 2019) and, due to its nutritional richness, milk becomes an important culture medium, enabling the rapid development of different types of microorganisms, such as mesophilic aerobic bacteria.
Aerobic mesophilic bacteria are those capable of growing at temperatures from 20 to 40°C and indicate the quality of the food. These microorganisms predominate in situations where there is a lack of basic hygiene conditions, as well as lack of milk refrigeration . As they multiply, aerobic mesophilic bacteria promote chemical changes in the product, such as fermenting lactose and producing lactic acid, causing acidification of the milk and compromising its use by the industry (Fonseca, 2000). This microorganism is an indicator of the hygiene conditions in which milk is obtained, both in terms of the quality of the water used to clean milking equipment, and in terms of hygiene practices during milking. Although no statistically significant difference (P > 0.05) was observed in this study between the count of mesophilic microorganisms in the samples compared to the permissible limit according to IN 76, it is interesting to note that the variation was high for this parameter (Table 2).
In this sense, it was observed that, if on the one hand the community tanks facilitate compliance with the legislation by the small producer, on the other hand they can present problems in the management of the microbiological quality of the milk. Given that many populations of microorganisms continue their development until the temperature reaches 4°C, there may be losses due to acidification by mesophilic bacteria  and loss of casein stability (Horne, 2020).
Temperature interferes with proteolysis and lipolysis, since plasmin and lipoprotein lipase, which are the main enzymes participating in these processes, are activated when the milk is subjected to inadequate refrigeration temperature, causing high degradation of milk proteins, especially casein, and triglycerides (Ma, Barbano & Santos, 2003).
Cooling milk can mitigate or inhibit microbial growth. However, it does not ensure the microbiological quality of the milk by itself. Allied to this, awareness-raising activities should be carried out regarding good sanitary practices in handling and milking, in order to obtain product of good microbiological quality (Neta et al., 2018). In general, on farms that receive technical assistance, the count of microorganisms tends to be lower (Luz, Bicalho, Oliveira & Simões, 2011). It is essential to provide technical education and training to family farms, which is the case of most milk producers who use community tanks.
Actions regarding the practices of obtaining milk with hygiene, cleaning of milking equipment and the importance of refrigeration of milk, will contribute to the development of dairy farming, in addition to ensuring the food safety of society.

Conclusion
It is concluded that the composition of milk and quality of raw milk stored in community tanks in the municipality of further studies are needed on the composition and microbiological quality of refrigerated raw milk in these community tanks.