278
textural properties of yoghurt is the amount of inoculation and the incubation temperatures. Stronger gel firmness at the same incubation temperature was obtained at
higher inoculation rate compared to the lower inoculation rates (Tamime and
Robinson 2007b). Lower incubation temperature triggers slower acidification,
which gives more time for the colloidal calcium phosphate (CCP) to dissolve from
the casein micelles before pH 5.1. A larger proportion of CCP would be dissolved
from the casein micelles, and a firmer gel is expected at pH 4.6 (iso-electric pH for
casein) (Tamime and Robinson 2007b). The events occurring during acidification of
milk are described in two main categories, i.e. the changes of the pH due to acidification, which alters the ζ-potential on the surface of CN micelles, and the solubilisation of colloidal calcium phosphate from CN micelles (Heertje et al. 1985).
A review of the fermentation of goat milk with yoghurt starter bacteria was given
by Abrahamsen and Rysstad (1991). One of the most characteristic differences
between metabolites produced in cow and in goat milk yoghurt was found to be a
considerable higher production of CO 2 in goat milk yoghurt than in yoghurt from
cow milk (Rysstad and Abrahamsen 1987). The other typical difference was the
production of the most characteristic flavour compound in yoghurt, namely acetaldehyde. Far more acetaldehyde was produced in the cow milk yoghurt than in the
goat milk yoghurt. This observation was further studied and elucidated by Rysstad
et al. (1990), who concluded that the reason for lower production of acetaldehyde in
goat milk yoghurt was the relatively high amount of glycine in this milk compared
to the content in cow milk. Acetaldehyde is mainly produced by the yoghurt culture
by fermenting of the amino acid threonine. By the help of the enzyme threonine,
threonine aldolase is transformed directly to acetaldehyde and glycine. A feedback
inhibition of threonine aldolase produced by the presence of higher amounts of free
glycine in the goat milk took place. This indicates that it may be rather difficult to
obtain the same level of typical yoghurt flavour in yoghurt from goat milk as normally can be obtained from the fermentation of cow milk with yoghurt cultures.
Cheeses
The history of goat cheese manufacturing started back during the Mesopotamia era,
and then further developments were made along the Mediterranean basin and some
EU countries. Today, goat cheese is an important dairy product in many parts of the
world. In most countries in SSA, there is a limited cheese consumption in general,
but urbanisation and the growth of tourism in East and Southern African countries,
including Tanzania and Malawi, will most likely stimulate the consumption of
cheese in the near future.
Principally, cheeses can be classified into three main groups: hard, semi-hard,
and soft and acid fresh cheeses; in each group, cheese can either be flavoured with
spices or be plain (Park and Guo 2006). In some traditions, some of the goat cheese
varieties are made from unpasteurised milk, and they have often unique texture and
flavour compared to the cheeses made from pasteurised milk (Delgado et al. 2011).
However, due to public health concerns (EFSA 2015), pasteurisation of cheese milk
I. A. Ketto et al.
textural properties of yoghurt is the amount of inoculation and the incubation temperatures. Stronger gel firmness at the same incubation temperature was obtained at
higher inoculation rate compared to the lower inoculation rates (Tamime and
Robinson 2007b). Lower incubation temperature triggers slower acidification,
which gives more time for the colloidal calcium phosphate (CCP) to dissolve from
the casein micelles before pH 5.1. A larger proportion of CCP would be dissolved
from the casein micelles, and a firmer gel is expected at pH 4.6 (iso-electric pH for
casein) (Tamime and Robinson 2007b). The events occurring during acidification of
milk are described in two main categories, i.e. the changes of the pH due to acidification, which alters the ζ-potential on the surface of CN micelles, and the solubilisation of colloidal calcium phosphate from CN micelles (Heertje et al. 1985).
A review of the fermentation of goat milk with yoghurt starter bacteria was given
by Abrahamsen and Rysstad (1991). One of the most characteristic differences
between metabolites produced in cow and in goat milk yoghurt was found to be a
considerable higher production of CO 2 in goat milk yoghurt than in yoghurt from
cow milk (Rysstad and Abrahamsen 1987). The other typical difference was the
production of the most characteristic flavour compound in yoghurt, namely acetaldehyde. Far more acetaldehyde was produced in the cow milk yoghurt than in the
goat milk yoghurt. This observation was further studied and elucidated by Rysstad
et al. (1990), who concluded that the reason for lower production of acetaldehyde in
goat milk yoghurt was the relatively high amount of glycine in this milk compared
to the content in cow milk. Acetaldehyde is mainly produced by the yoghurt culture
by fermenting of the amino acid threonine. By the help of the enzyme threonine,
threonine aldolase is transformed directly to acetaldehyde and glycine. A feedback
inhibition of threonine aldolase produced by the presence of higher amounts of free
glycine in the goat milk took place. This indicates that it may be rather difficult to
obtain the same level of typical yoghurt flavour in yoghurt from goat milk as normally can be obtained from the fermentation of cow milk with yoghurt cultures.
Cheeses
The history of goat cheese manufacturing started back during the Mesopotamia era,
and then further developments were made along the Mediterranean basin and some
EU countries. Today, goat cheese is an important dairy product in many parts of the
world. In most countries in SSA, there is a limited cheese consumption in general,
but urbanisation and the growth of tourism in East and Southern African countries,
including Tanzania and Malawi, will most likely stimulate the consumption of
cheese in the near future.
Principally, cheeses can be classified into three main groups: hard, semi-hard,
and soft and acid fresh cheeses; in each group, cheese can either be flavoured with
spices or be plain (Park and Guo 2006). In some traditions, some of the goat cheese
varieties are made from unpasteurised milk, and they have often unique texture and
flavour compared to the cheeses made from pasteurised milk (Delgado et al. 2011).
However, due to public health concerns (EFSA 2015), pasteurisation of cheese milk
I. A. Ketto et al.