Buffalo’s Milk Yoghurt

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In Egypt, small producers manufacture zabadi by boiling buffalo’s milk for 30 min, cooling it to 40–42°C, inoculating with a starter (i.e. previous day zabadi) and incubating in the retail container. By contrast, the industrial process is similar to yoghurt making since the fat content is standardised to about 3g 100 g-1 , the milk is then heated (e.g. 85–90°C for 5–10 min) and finally the milk is fermented in the retail container; the addition of flavour(s) is optional (Shalaby et al., 1992; Mahran, 1996; Iniguez et al., 1997; see also Garg, 1988). It is of interest to point out that homogenisation is not used during the preparation of buffalo’s milk yoghurt, perhaps because the milk contains (g 100 g-1 ) protein 4.3 and fat 8.6 (Spanghero and Susmel, 1996), which is suitable for the production of a set-type yoghurt with a creamy layer. Furthermore, a similar processing approach (i.e. non-homogenisation of the milk) is found in countries where buffalo’s milk is used for the production of other fermented milk products; Singh (1979) homogenised buffalo’s milk, but the pressure(s) was not reported. As with cow’s milk, different fortification and/or fat standardisation methods have been used for buffalo’s milk yoghurt. Table 5.2 illustrates some examples and the processing parameters. The use of buffalo’s milk powder for fortification of the milk is not widespread because it is not readily available, but recent studies of such a powder made from skimmed UF retentate have been reported by Patel and Mistry (1997). The gross composition (g 100 g-1 ) of skimmed buffalo’s milk powder is protein 67.5, fat 1.6, ash 8.6 and lactose 18.7.
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Miscellaneous additives such as whey proteins (Ahmed and Ismail, 1978a, b), groundnut protein (Venkateshaiah et al., 1982), defatted soyabean flour (El-Deeb and Hassan, 1987; Magdoub et al., 1992), cooked wheat grain (Hamzawi and Kamaly, 1992) and cow’s SMP (El-Shibiny et al., 1977) have been used to fortify milk to produce an acceptable buffalo yoghurt. The use of membrane filtration is somewhat limited for the industrial production of buffalo yoghurt, but studies in this area have suggested: (a) a two-fold concentration by UF and standardisation of the fat content to 5.5 g 100 g-1 was recommended by Haggag and Fayed (1988), (b) UF could be used to manipulate buffalo’s milk, for example 10 g SNF100 g-1 or 11 g SNF100 g-1 plus 3 g fat100 g-1 for the production of zabadi (Khorshid et al., 1992), and (c) RO of buffalo’s milk >1.5-fold produced dahi that was very thick, lumpy, lacking flavour and had low acidity (Kumar and Pal, 1994).
Milk obtained from buffalos given a yeast culture in their feed affected the growth and biochemical behaviour of two mesophilic and three thermophilic single strains of lactic acid bacteria (Ibrahim, 1991). As the starter cultures employed for the production of dahi are not well defined, the general consensus is that yoghurt microfloras have been used, even though the preference in India may be to use mixed mesophilic strains including Lac. lactis biovar diacetylactis (Gosh and Rajorhia, 1990a). However, the antibacterial activity of S. thermophilus MD-2, MD- 8 and D-3 strains in buffalo’s milk dahi (i.e. 4.5 g fat 100 g-1 and 10.5 g SNF 100 g-1 ) against pathogenic micro-organisms was greater in the cell free extracts which may suggest that inhibitor substance(s) other than lactic acid may be present (Gupta and Tiwari, 1990; Dave et al., 1992; see also Dzurec et al., 1992). b-galactosidase activity of the same starter culture strains in dahi made up to 21 g 100 g-1 TS was reported by Dave et al. (1993), whilst the incorporation of nisin into dahi and its effect on the yoghurt starter culture was studied by Gupta and Prasad (1988, 1989).
The microstructure of buffalo dahi is influenced by the level of heating applied to the milk. According to Tomar and Prasad (1989) milk heated to 70°C resulted in a product which was soft, had an open structure and the casein was near spherical in shape (i.e. a size of about 300 nm), whilst milk heated at 90°C for 30 min gave a firm curd and the micelle size was about 235nm and elongated in shape; the protein matrix consisted of a long micellar chain (see also Turambekar and Kulkarni, 1991).
Thermisation of misti dahi at 65°C for 30min decreased the starter cultures count (i.e. consisting of Lac. lactis biovar diacetylactis and subsp. cremoris) by about 3 log10 colony forming units (cfu) ml-1 and a further 1 log10 cfuml-1 after storage at 30°C for 30 days (Chander et al., 1989, 1992). A similar observation was reported by Sarkar et al. (1992a, b) when the product was heated at 60°C for 10 min (see also Mann and Joshi, 1997).
It was suggested that the nutritive quality of zabadi could be improved by the addition of electrolytic iron or ferric chloride up to 8mg100 g-1 with no effect on the quality of the product (Mahran et al., 1996). However, buffalo’s milk fortified with groundnut or soya milk enhanced the growth of Bifidobacterium bifidum, whilst the addition of 3mM glycine produced the firmest curd with a starter count >1 ¥ 108 cfuml-1 at pH 3.89 (Murad et al., 1997).

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