New technologies for fermented dairy products

The manufacture of fermented dairy products is a series of several biotechnological and technological processes. In milk, casein micelles build-up a gel network that is partly disrupted after fermentation. The consumer acceptance relies on several sensory parameters of the end product. The type and character of the starter bacteria used for the manufacture of fermented milk determine the overall quality of the final product. The criteria for starter culture selection include their acid and flavour production abilities, stability and texture. Until recently the identification of starter and non-starter for fermented milks has been based on morphological, physiological and biochemical characteristics. Molecular methods have become essential taxonomic tools and they are particularly useful for the differentiation of microorganisms at species and strain level. The starter that produces exopolysaccarides (EPS) is increasingly used in the manufacture of fermented milks. EPS production is often affected by the carbon source, culture, pH, time and temperature of incubation. However, the amount of EPS produced does not correlate with differences in viscosity. In fermented milk production, milk is concentrated or whey-based products are added prior to fermentation. As these measures change the composition of the substrate, the activity of starters and the build-up of the gel structure are affected. The concentration of proteins, milk salts and the way of integrating fat globules into the structure must be considered for any successful industrial development. Changing the composition of the pre-concentrated milk provides several possibilities to develop very different structures. After fermentation the most critical points affecting the texture are: stirring the coagulum, cooling, pumping and filling. Finally, various packaging materials and their permeability influence the structural stability during storage. Sensory parameters of fermented milks are the most important tools for product evaluation since consumer acceptance relies on these aspects. The parameters include texture, flavour and their interaction. In addition, measurements of serum-binding capacity and those of rheological properties are very important in product development and quality assessment. New methods have been developed with special emphasis on the measurement of stirred fermented milks.