275
casein to the total protein (casein index, %) is considered to be crucial for efficient
cheesemaking.
Milk quality for fermented milk (yoghurt) can be monitored by determining its
acid coagulation properties (gelation time, the speed of gelation and gel firmness),
using glucono-δ-lactone. Good acid coagulation properties would be short gelation
time and high final gel firmness. Goat milk, compared to sheep and cow milk,
showed rapid changes in pH, probably because of a lower casein content in goat
milk (Salaün et al. 2005). Rysstad and Abrahamsen (1987) found, however, only a
slightly faster decrease in pH of goat milk than in cow milk when fermenting the
milk with a yoghurt starter. After 8 hours of incubation at 43 °C, the pH reached
4.2 in both types of milk. One of the quality attributes of goat milk for yoghurt making is the higher protein content (Tamime et al. 2006). Desired protein content and
total solids (TS) could be achieved by ultrafiltration (UF) technique to achieve the
desired properties for both set and stirred style yoghurts made from goat milk such
as higher curd tension and viscosity, respectively (Abrahamsen and Holmen 1981).
Fluid Milk Beverages
Fluid milk for consumption is a popular product in some western countries. It can
either be low fat (skimmed) or full fat, flavoured or plain. There is limited research
on liquid milk beverages made from goat milk. The standard procedure for the fluid
milk processing of cow milk applies for goat milk, i.e. receiving, filtering, standardisation, homogenisation, pasteurisation, cooling, packaging and distribution
(Park and Guo 2006). Before processing, milk is filtered to remove the foreign
materials, for example, body cells from the udder. Filtration can be achieved by
mechanical filtration (using a clarifier or bactofuge) at a commercial scale (Park
and Guo 2006). In such cases, also a high number of spore-forming bacteria and
somatic cells will be removed from the milk. The aim of homogenisation is to
reduce the size of fat globules. After homogenisation, a new fat globule membrane
is formed from the original material in the MFGM and micellar casein and some
whey proteins. This reduction in fat globule size will change the colour (whitening)
of the milk compared to the unhomogenised milk (Park and Guo 2006). After
homogenisation, milk is pasteurised to reduce the bacteria load and improve the
shelf life of the milk. As mentioned earlier, goat milk has lower heat stability than
cow milk, and higher temperature treatment (UHT) might, therefore, lead to the
coagulation or sedimentation of the milk. The low-temperature long time (LTLT)
pasteurisation such as 63 °C for 30 min could be ideal batch pasteurisation conditions for goat milk, while high-temperature short-time (HTST) pasteurisation
(72 °C for 15 s) is applied in automated processing lines (Park and Guo 2006).
Cream separation is an option, depending on market demand, for example, low-fat
milk beverage (2%). The cream after separation could be used in the production of
high-fat products such as butter, ghee and ice cream. Before such use, the cream
should be pasteurised. Figure 1 shows a process chart for the liquid milk beverage
as adopted from Park and Guo (2006). Development of off-flavour is one of the
Goat Milk Quality and Possible Dairy Products from Rural Households of Tanzania…
casein to the total protein (casein index, %) is considered to be crucial for efficient
cheesemaking.
Milk quality for fermented milk (yoghurt) can be monitored by determining its
acid coagulation properties (gelation time, the speed of gelation and gel firmness),
using glucono-δ-lactone. Good acid coagulation properties would be short gelation
time and high final gel firmness. Goat milk, compared to sheep and cow milk,
showed rapid changes in pH, probably because of a lower casein content in goat
milk (Salaün et al. 2005). Rysstad and Abrahamsen (1987) found, however, only a
slightly faster decrease in pH of goat milk than in cow milk when fermenting the
milk with a yoghurt starter. After 8 hours of incubation at 43 °C, the pH reached
4.2 in both types of milk. One of the quality attributes of goat milk for yoghurt making is the higher protein content (Tamime et al. 2006). Desired protein content and
total solids (TS) could be achieved by ultrafiltration (UF) technique to achieve the
desired properties for both set and stirred style yoghurts made from goat milk such
as higher curd tension and viscosity, respectively (Abrahamsen and Holmen 1981).
Fluid Milk Beverages
Fluid milk for consumption is a popular product in some western countries. It can
either be low fat (skimmed) or full fat, flavoured or plain. There is limited research
on liquid milk beverages made from goat milk. The standard procedure for the fluid
milk processing of cow milk applies for goat milk, i.e. receiving, filtering, standardisation, homogenisation, pasteurisation, cooling, packaging and distribution
(Park and Guo 2006). Before processing, milk is filtered to remove the foreign
materials, for example, body cells from the udder. Filtration can be achieved by
mechanical filtration (using a clarifier or bactofuge) at a commercial scale (Park
and Guo 2006). In such cases, also a high number of spore-forming bacteria and
somatic cells will be removed from the milk. The aim of homogenisation is to
reduce the size of fat globules. After homogenisation, a new fat globule membrane
is formed from the original material in the MFGM and micellar casein and some
whey proteins. This reduction in fat globule size will change the colour (whitening)
of the milk compared to the unhomogenised milk (Park and Guo 2006). After
homogenisation, milk is pasteurised to reduce the bacteria load and improve the
shelf life of the milk. As mentioned earlier, goat milk has lower heat stability than
cow milk, and higher temperature treatment (UHT) might, therefore, lead to the
coagulation or sedimentation of the milk. The low-temperature long time (LTLT)
pasteurisation such as 63 °C for 30 min could be ideal batch pasteurisation conditions for goat milk, while high-temperature short-time (HTST) pasteurisation
(72 °C for 15 s) is applied in automated processing lines (Park and Guo 2006).
Cream separation is an option, depending on market demand, for example, low-fat
milk beverage (2%). The cream after separation could be used in the production of
high-fat products such as butter, ghee and ice cream. Before such use, the cream
should be pasteurised. Figure 1 shows a process chart for the liquid milk beverage
as adopted from Park and Guo (2006). Development of off-flavour is one of the
Goat Milk Quality and Possible Dairy Products from Rural Households of Tanzania…