270
lactic acid bacteria in order to get a product with the preferred nutritional, health and
organoleptic properties (colour, odour and texture) to the consumer. Variables like
milk composition, SCC and the presence of inhibiting substances such as antibiotics
and pesticides determine the processability, nutritional, health and organoleptic
properties of the milk products. The presence of antibiotics in milk slows down or
prevents the lactic acid fermentation of milk (Raynal-Ljutovac et al. 2005) and consequently affects the production of fermented milk. It is important to understand
how these variables can be influenced to improve the quality of milk as a raw material for processing. At the farm, milk should be stored at 4 °C after milking; cold
storage of milk reduces the growth of bacteria and improves the keeping quality of
milk. However, cold storage of milk changes the structure and physicochemical
properties of casein (CN) micelles by the dissolution of β-CN and micellar calcium
(Raynal-Ljutovac et al. 2005). Furthermore, it creates growth possibilities for psychrotrophic bacteria such as Pseudomonas in milk (Raynal-Ljutovac et al. 2005).
These bacteria produce heat-resistant lipolytic and proteolytic enzymes, which
hydrolyse lipids and proteins, respectively, and may, therefore, induce the development of rancid and bitter taste in milk and milk products (Paludetti et al. 2018).
In developing countries, especially in the rural areas where dairy goat farming is
practised, cold storage of milk to control the bacterial growth is a challenge because
of the power outage and lack of facilities and equipment for rapid cooling of milk at
the farm. The use of hydrogen peroxide and thiocyanate, which activates the lactoperoxidase system (LPS) in milk, could be an option in tropical countries. The LPS
is the most important natural antibacterial system in milk, which prevents the growth
of both pathogenic bacteria and psychrotrophs, hence prolonging the keeping quality of raw milk. If LPS is the option adopted in enhancing the keeping quality of the
raw milk, understanding of its possible effect on the processing and quality properties of fermented milk is important. Nakada et al. (1996) reported that LPS treated
milk gave yoghurts made from mixed cultures (Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus (ratio 1:1)) the desired acidity at the same
time as the control yoghurts. The LPS treated yoghurts showed limited postacidification, and this contributed to yoghurts with a favourable balance between
sweetness and sourness. The effects of LPS on the rheological properties of yoghurts
were evaluated by Özer et al. (2003). This study showed that viscosity and storage
modulus of the products were decreased by the increase in the concentration of LPS
in yoghurt milk.
The high level of somatic cell count (SCC) in milk is another factor which limits
the quality and processability of goat milk. The SCC in dairy goats varies between
parity, breed and stage of lactation, with the highest levels being towards the end of
lactation (Skeie 2014). Higher SCC in goat milk compared to cow milk is due to the
higher basal levels of SCC in bacteria-free udder in goat milk compared to cow milk
(300,000 vs. 70,000 ml
−1
) (Paape et al. 2007). A different set of standards for udder
health using SCC is practised between countries. For example, legal limit for SCC
varies between countries; for example, most of the European countries have adopted
lower levels (400,000 ml
−1
) for both cow and goat milk, while in the United States
of America, higher levels (750,000 and 1,000,000 ml
−1
) are used for goat and cow
I. A. Ketto et al.
lactic acid bacteria in order to get a product with the preferred nutritional, health and
organoleptic properties (colour, odour and texture) to the consumer. Variables like
milk composition, SCC and the presence of inhibiting substances such as antibiotics
and pesticides determine the processability, nutritional, health and organoleptic
properties of the milk products. The presence of antibiotics in milk slows down or
prevents the lactic acid fermentation of milk (Raynal-Ljutovac et al. 2005) and consequently affects the production of fermented milk. It is important to understand
how these variables can be influenced to improve the quality of milk as a raw material for processing. At the farm, milk should be stored at 4 °C after milking; cold
storage of milk reduces the growth of bacteria and improves the keeping quality of
milk. However, cold storage of milk changes the structure and physicochemical
properties of casein (CN) micelles by the dissolution of β-CN and micellar calcium
(Raynal-Ljutovac et al. 2005). Furthermore, it creates growth possibilities for psychrotrophic bacteria such as Pseudomonas in milk (Raynal-Ljutovac et al. 2005).
These bacteria produce heat-resistant lipolytic and proteolytic enzymes, which
hydrolyse lipids and proteins, respectively, and may, therefore, induce the development of rancid and bitter taste in milk and milk products (Paludetti et al. 2018).
In developing countries, especially in the rural areas where dairy goat farming is
practised, cold storage of milk to control the bacterial growth is a challenge because
of the power outage and lack of facilities and equipment for rapid cooling of milk at
the farm. The use of hydrogen peroxide and thiocyanate, which activates the lactoperoxidase system (LPS) in milk, could be an option in tropical countries. The LPS
is the most important natural antibacterial system in milk, which prevents the growth
of both pathogenic bacteria and psychrotrophs, hence prolonging the keeping quality of raw milk. If LPS is the option adopted in enhancing the keeping quality of the
raw milk, understanding of its possible effect on the processing and quality properties of fermented milk is important. Nakada et al. (1996) reported that LPS treated
milk gave yoghurts made from mixed cultures (Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus (ratio 1:1)) the desired acidity at the same
time as the control yoghurts. The LPS treated yoghurts showed limited postacidification, and this contributed to yoghurts with a favourable balance between
sweetness and sourness. The effects of LPS on the rheological properties of yoghurts
were evaluated by Özer et al. (2003). This study showed that viscosity and storage
modulus of the products were decreased by the increase in the concentration of LPS
in yoghurt milk.
The high level of somatic cell count (SCC) in milk is another factor which limits
the quality and processability of goat milk. The SCC in dairy goats varies between
parity, breed and stage of lactation, with the highest levels being towards the end of
lactation (Skeie 2014). Higher SCC in goat milk compared to cow milk is due to the
higher basal levels of SCC in bacteria-free udder in goat milk compared to cow milk
(300,000 vs. 70,000 ml
−1
) (Paape et al. 2007). A different set of standards for udder
health using SCC is practised between countries. For example, legal limit for SCC
varies between countries; for example, most of the European countries have adopted
lower levels (400,000 ml
−1
) for both cow and goat milk, while in the United States
of America, higher levels (750,000 and 1,000,000 ml
−1
) are used for goat and cow
I. A. Ketto et al.