Milk is one of the most complex food that contains mainly water, proteins, fats, carbohydrates, minerals, vitamins, and enzymes (Niamah and Verma, 2017; Verma et al., 2017). For centuries, milk is considered one of the most valuable natural food from the human diet (Al-Hilphy et al., 2016). On the other hand, milk nutrients, neutral pH and high water activity provide excellent conditions for many pathogenic microorganisms to be developed, whose multiplication is dependent on temperature and as well as on competing microorganisms (Claeys et al., 2014). Therefore, heat treatment should be applied to guarantee its microbial safety and stability. Moreover, the functional and nutritional properties of milk are changed during heating as a result of various competitive and interdependent reactions that are dependent on heating conditions, milk composition, and origin. The main heat treatments applied in dairy industry include: thermalization (57–68°C, 15–20 s), HTST pasteurization (71–74°C, 15–40 s), sterilization (110–120°C, 20 min.), indirect UHT (135–140°C, 6–10 s), direct UHT (140–150°C, 2–4 s) and ISI (innovative steam injection, 150–200°C, <0.1 s).
A comprehensive review was reported by Claeys et al. (2014), where the authors presented the risks and benefits associated with the consumption of raw and processed cow milk, considering microbiological and nutritional properties. Most of the dairy products available for consumption are obtained from cow milk. The increased interest of consumers for healthy diets generated increased attention for milk and dairy products of nonbovine origin, and especially for caprine and ovine origin. Caprine milk possesses stronger antimicrobial, immunological, and antibacterial system and higher digestibility compared with ovine or bovine milk (Slacanac et al., 2010). The growing interest in goat milk as an alternative food for infants with food allergies should be supported by appropriate studies showing its suitability for human consumption and in terms of milk safety. In most countries, assessment of the milk of non-bovine origin is not yet introduced in routine testing programs. Regulation (EC) 853/2004 lays down regulatory microbial criteria for total plate count and somatic cells, as well as health and hygienic requirements for animal production and production facilities, respectively. In regard to heat treatments applied in the dairy industry, European regulations are mainly based on microbiological platforms, which are time-consuming and expensive to control. Fast, easy control instruments to assess heating process efficiency and severity are scarce.
In the entitled chapter, research findings about some milk enzymes from the bovine and nonbovine origin are presented. Information regarding the activity of alkaline phosphatase (ALP), γ-glutamyltransferase (GT) and lactoperoxidase (LP) in bovine, caprine, and ovine milk, as well as the effect of milk species on the thermal inactivation of these enzymes, is briefly discussed.
1.2 TIME TEMPERATURE INDICATORS
Milk enzymes are distributed in different milk phases (Table 1.1), many of them possessing technological implications (Fox, 2006) as following:
1. Alteration (lipase, acid phosphatase, xanthine oxidase) or preservation (LP, sulphydryl oxidase, superoxide dismutase) of milk quality;
2. Indicators for the assessment of milk thermal processing (ALP, γ-GT, and LP);
3. Mastitis indicators (catalase, acid phosphatase, β-N-acetylglucosaminidase), whose concentration increase during mastitis infection;
4. Antimicrobial activity (lysozyme, LP);
5. Commercial source of enzymes (ribonuclease and LP).
