Milk and yogurt are important components of the individual diet, because of their high vitamins and minerals and their appealing sensory properties. review. [15], small MFG facilitate the incorporation of fats into the proteins network [5], while their elevated surface favors the interactions between fats and milk proteins, casein and denatured whey, during acidification and subsequent gel development [5,15]. 2.4. HEAT THERAPY Heat therapy of milk is certainly carried out to guarantee the basic safety of the merchandise, whether it’s milk itself or any various other dairy product, also to exploit many results that increased temperatures is wearing certain milk elements facilitating further procedures for milk products manufacture [16]. Heat therapy of milk decreases the amount of pathogenic microorganisms to secure limitations for the customers health. Various high temperature treatments could be used, which are categorized predicated on the timeframe and the temperatures (Table 1). The most typical are referred to as thermalization (known in Section 2.1), low and high pasteurization, sterilization and UHT (Ultra HEAT THERAPY) [3,4,17]. Low pasteurization identifies heat therapy of milk at 63C65 C for 20 min or at 72C75 C for 15C20 s (HTST, TEMPERATURE SMALL AMOUNT OF TIME). In this process, most pathogens, vegetative bacteria, TG-101348 enzyme inhibitor yeast and molds are killed. Additionally, with low heat pasteurization, several enzymes become inactive, while the flavor of milk is usually hardly altered. Furthermore, little or no serum proteins are denatured, and chilly agglutination and bacteriostatic properties remain virtually intact [2,4]. A more intense heat treatment is high temperature pasteurization that requires a heat of 85 C for 20C30 min or 90C95 C for 5 min. During high temperature pasteurization most vegetative microorganisms are killed, except from spores; most enzymes are deactivated (except milk proteinase, plasmin in particular, some bacterial proteinases and lipases); most whey proteins are TG-101348 enzyme inhibitor denatured, and a distinct cooked flavor is developed due to the formation, mostly, of ketones [4,18]; no further irreversible changes occur. Sterilization results in extermination of all microbial content of milk, including bacterial spores, and it is achieved at 110 C for 30 min or at 130 C for 40 s. In addition, sterilization causes inactivation of most milk enzymes (except several bacterial lipases), darkening of the milk color due to TG-101348 enzyme inhibitor the Maillard reaction, evaporation of most flavor volatiles, thus weakening the flavor of the milk, and considerable damage to all milk proteins, even caseins. Finally, UHT is carried out at 145 C for 1C2 s and achieves equal bacterial eradication as from sterilization, minimal flavor deterioration and causes denaturation of several whey proteins (-lactoglobulin, serum albumin, and some immunoglobulins). UHT treatment and high pasteurization produces many volatiles in milk, such as: 2-pentanone, 2-heptanone, 2-nonanone, 2-undecanone, 2,6-dimethylpyrazine, 2-ethylpyrazine, 2-ethyl-3-methylpyrazine, methional, pentanoic acid, benzothiazole vanillin, hexanal, TG-101348 enzyme inhibitor benzothiazole, decalactone, H2S, methanethiol, dimethylsulphide and carboxylsulphide. These sulfur containing molecules are responsible for the cooked off flavor developed during UHT and high temperature pasteurization [18]. It should be pointed out that the most commonly used heat treatment in the yogurt manufacturing process is the high temperature pasteurization at 85 C for 20 min [3,4]. Table 1 Impact of different thermal treatment techniques on milk and yogurt properties affecting flavor and texture. species, subsp. and subsp. in abundance. However, yogurt starter cultures may include other microorganisms as well, like and subsp. (ST) is the only species in the streptococcus genus that is used in dairy starter cultures. ST is usually Gram positive and usually considered thermophilic, TG-101348 enzyme inhibitor however, as the optimum temperature for its growth is 35C53 C; consequently, ST can be considered as thermotolerant. Its cells are spherical in shape, forming chains, during the early stage of their lives and as they mature develop a more rod-like morphology and favor colonial growth. subsp. (LB) is usually rod-shaped, Gram-positive, anaerobic bacteria and its optimum growth heat is 40C44 C. LB can produce very high amounts of lactic acid by metabolizing lactose [5,20]. Both of these species screen synergy in the milk environment, metabolizing lactose into lactic acid and leading to reduced amount of milk pH. The synergism between ST and LB is founded on their specific characteristics, and for that Rabbit Polyclonal to MRPL20 reason higher lactose metabolic process and lactic acid creation is attained in comparison to each one performing separately. ST is even more aerotolerant than LB, lacks great proteolytic ability compared to LB, but possesses better peptidase activity. When grown jointly in milk, ST grows vigorously initially, whereas LB grows gradually. ST, due to the great proteolytic activity, creates a good amount of peptides to stimulate the development of LB. Through the early stage of fermentation, milk.