Cultured milks yoghurt

Serra M, Trujillo AJ, Guamis B, Ferragut V. 2009. Flavour profiles and survived of starter cultures of yoghurt produced from high-pressure homogenized milk. Int Dairy J 19 100-106. 

The production of fermented milks no longer depends on acid production by the indigenous microflora. Instead, the milk is inoculated with a carefully selected culture of LAB and for some products with LAB plus lactose-fermenting yeasts (Table 10.12). The principal function of LAB is to produce acid at an appropriate rate via the pathways summarized in Figure 10.12. The yoghurt fermentation is essentially homofermentative but the characteristic flavour of cultured buttermilk is due mainly to diacetyl which is produced from citrate by Lactococccus lactis ssp. lactis biovar diacetylactis, which is included in the culture for this product (Figure 10.31). 

Results showed a total of 2.8% of the samples (n 2972) to be inhibitor positive by the Delvotest SP test further examination identified 1.7% as -lactam antibiotics, and 1.1 % as sulfonamides and dapsone. The percentage of chloramphenicol suspicious samples determined by the Charm II test was amazingly high however, tests for confirmation were not available and contamination of the samples by residues of the chloramphenicol-based preservative azidiol could not be excluded with certainty. Low concentrations of streptomycins were also detected in 5.7% of the samples (n 1221), but the MRL was not exceeded. Macrolide and tetracycline residues were not found in significant levels. Model trials with commercially applied yoghurt cultures confirmed how important the compliance to MRLs can be to dairy industry compared to antibiotic-free milk, a pH of 5.0 was reached with a delay of 15 min in the case of contamination with cloxacillin 30 min in the case of penicillin, spiramycin, and tylosin and 45 min in the case of oxytetracycline contamination. 

In the production of yoghurt, milk is initially heated to 90 °C for 15-30 minutes to kill any bacteria in the milk. After cooling to 40 °C, a starter culture of Lactobacillus bacteria is added and the mixture incubated at 40 °C for eight hours (Figure 7.20). The bacteria ferment the lactose... 

The involvement of milk protein-derived cytomodulatory peptides to determine the viability of cancer cells is a field of great interest. Commercial yoghurt starter cultures hydrolyse casein to produce bioactive peptides that control colon cell kinetics in vitro. Bioactive sequences of casein modulate cell viability in different human cell cultures. Peptides from an extract of Gouda cheese inhibited growth of leukemia cells even at 1 pmol/L [223]. They were able to induce apoptosis in the tumor cells. Cancer cells are more reactive to peptide-induced apoptosis than non-malignant cells [224]. Casein-derived peptides could have a role in the prevention of colon cancer by blocking proliferation of the epithelium and by... 

Sour milk products are always cultured dairy products with lactic acid bacteria (depending on the food legislation of the respective country). After increasing the dry matter, pasteurisation and incubation of culture, they are processed into yoghurts of set, stirred or drinking consistency, with or without a final heat treatment. 

For fermented milks, for example yoghurt, acidophilus milk and bifido products, stabilisers are widely used in many countries to improve viscosity and prevent wheying-off. Several types of stabilisers (e.g. gelatins, starch, pectins, carrageenans and cellulose derivatives) are used. The choice depends on the characteristics wanted and the technology used. The main parameters to be considered in the choice of stabiliser for fermented milks are heat stability and sensitivity towards low pH and salts. The effect of stabilisers on the activity of starter cultures must also be taken into consideration (Kalab et al., 1983). 

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