The Behaviour of Starter Cultures in Concentrated Yoghurt (Labneh) Produced by Different Techniques

Concentrated yoghurts were produced by fermenting milks concentrated by ultra-filtration and reverse osmosis, and by removing whey from batches of natural yoghurt using the same techniques. The choice of procedure influenced the chemical composition of the end-products and also, as indicated by the titratable acidities and acetaldehyde contents of the labnehs, the metabolic activity of the starter culture. Although the behaviour of the cultures varied with the total solids in the milk, the total colony counts of Streptococcus thermophilus and Lactobacillus delbrueckii subsp.bulgaricus recorded after 24 h at 4°C were similar in all samples. A taste panel assessment revealed a definite preference for labneh (230 g/kg total solids) produced at this concentration by ultra-filtration of natural yoghurt (160 g/kg total solids).