**2. Composition, physico-chemical and antimicrobial properties of bovine raw milk**

Milk is synthetised in the secretory cells of the alveolar epithelium (also called alveolar cells) and further secreted into the lumen, the core of the alveolus. Alveoli, the functional units of milk synthesis and secretion, are spherical bodies found only in the mammary gland, the unique organ of the mammals. The four mammary glands of the cow (female bovine) form the single anatomic unit called udder.

Milk is the first and essential food for the newborn of the mammal, and accordingly, milk needs to fulfil all its *nutritional* needs. These needs are varying among mammalian species and consequently, the composition of milk varies considerably in carbohydrate (mainly milk sugar called lactose, as energy source), protein (source of amino acids for protein synthesis), lipid (energy source and membrane components) and mineral contents (**Table 1**). For example, bovine (cow) milk has lower lactose and higher protein contents than human (mother's) milk. In addition, the milk composition varies during the lactation period and especially, during the first days that follow calving.

 The nutritional properties are not only the important characteristics of milk, but additional *protective* and *regulatory* functions are of importance, too. The protective functions are related to the survival of the newborn in the presence of various environmental microbes. Bovine milk contains antimicrobial elements like leucocytes (somatic cells), immunoglobulins, lactoperoxidase, antiadhesive glycoconjugates (oligosaccharides linked to lipids and proteins) of milk fat globule membrane (MFGM) and sialic acid residues of oligosaccharides (**Table 1**). The protective functions also may include particular prebiotics like amino sugars of the oligosaccharides that contribute to establish the optimal microbiome in the gastro-intestinal track of the newborn. The milk components having regulatory functions include hormones (e.g. insulin, somatotropin, and growth hormone), regulatory proteins (e.g. cytokines), particular bioactive lipids, and membrane-enclosed extracellular vesicles (EV) like exosomes containing bioactive miRNAs and proteins [3, 4].

 All these intrinsic components of milk are of crucial importance for the growth and development of the newborn. The balance and the spectrum of the milk components are unique for each mammalian species. Because the cow (*Bos taurus*) is globally and economically the most important dairy husbandry animal, the knowledge on the bovine raw milk has the most significant impact on the dairy industry.

### **2.1 Sources of microbial contaminations in fresh raw milk**

Raw milk is widely considered as sterile in the lumen of the alveolus in the case of a healthy cow; bacteria may be however transmitted to milk via the cow's blood in case of systemic infection. The intrinsic features of raw milk and its handling favour the presence and growth of many microbes; consequently, various viruses, moulds, yeasts, and especially bacteria take advantage of raw milk production conditions to either persist or proliferate. Bacteria by exhibiting contrasted roles in raw milk can be truly categorised as "good, bad or ugly": for ages, some are key

*Quality and Safety of Bovine Raw Milk: Present Challenges and Technological Solutions DOI: http://dx.doi.org/10.5772/intechopen.83507* 


### **Table 1.**

*Some characteristics of bovine raw milka .* 

### *Milk Production, Processing and Marketing*

 agents in the manufacture of numerous milk-based products reflecting traditions and cultures around the world; others are involved in the spoilage of raw milk and dairy products; finally, some are authentic pathogens causing severe illnesses, which have largely contributed to build the reputation that raw milk is a vehicle for spreading diseases.

Depending on the ambient conditions, the farming practices or the health of the animals, various contamination sources raise the bacterial load in raw milk. The sources of bacterial contaminations can be categorised as such:


Due to numerous contamination sources, a rather diverse microbiota is present in raw milk; many Gram (+) or Gram (−) bacterial representatives can be present in significant numbers; their relative importance is variable and greatly depends on the elapsed time since milking. Gram (+) dominates in fresh raw milk, whereas Gram (−) takes over after cold storage [11]. If it is possible to relate high levels of coliforms to faecal contaminations, it may be more difficult to trace the source of the ubiquitous pseudomonads.

Many reports often highlight multiple, sometimes similar, contamination sources.

For example, in Brazil, the difficulties for farmers to fulfil the goals set by the Ministry of Agriculture were attributed to several causes: at first, most dairy farms

### *Quality and Safety of Bovine Raw Milk: Present Challenges and Technological Solutions DOI: http://dx.doi.org/10.5772/intechopen.83507*

had their water contaminated with coliforms [12]. A water of poor quality combined to poor hygienic conditions (for example, in the case of insufficient cleaning of tanks) raise the contamination of raw milk; the authors also mentioned insufficient training of the farmers, which resulted in a not regular cleaning of the udders before and after milking; moreover, a majority of farmers did not systematically control mastitis in their animals [12].

In Tanzania, which belongs to the East African Community Countries (EACC) organisation, two bacteriological criteria were defined for total bacterial counts (TBCs) and for total coliform counts (TCCs) [13]: grade I, II and III raw milk is characterised by total bacterial counts below 2.105 , between 2.105 and 106 , and between 106 and 2.106 cfu/ml, respectively; raw milk of very good and good quality is characterised by coliform counts below 103 , and between 103 and 5.104 cfu/ml, respectively. Three major factors, that impacted milk quality and caused milk-borne diseases, were identified: the doubtful health status of animals, the lack of good milking and handling practices, and the distribution, which occurs out of relevant regulations [2].

In Western African countries (Burkina Fasso, Mali, and Senegal), a campaign entitled "My milk is local" aims to replace the large consumption of imported milk powders and urges local farmers to respond to increasing demands. Producers, mainly organised as small holders, suffer to meet the challenge of producing raw milk of sufficient microbiological quality. A study reported that over 75% of raw milk samples exhibited excessive bacterial counts, with an average of 4.5 × 107 cfu/g of raw milk; the poor microbiological quality of raw milk at the farm level was due to contaminations resulting from a lack of adequate equipment and facilities, of good hygiene practices along the collection and processing steps [14].

Raw milk is frequently identified as a source of food-borne disease outbreaks. However, the consumption of raw milk continues in low-income countries because of traditions and lack of processing facilities; in high-income countries, the consumption of raw milk is encouraged by certain lobbies and life style groups for health benefit claims that vary from superior nutritional properties, lower allergenicity, reduced lactose intolerance or more efficient antimicrobial systems. In practice, the use of raw milk remains marginal, and fortunately, the consumption of milk mostly relies on processed dairy products.
