Starter Cultures for Production of Yoghurt from Sheep’s Milk with Extended Shelf Life

T. ZVANCHAROVA, K. BALTOVA and  Z. URSHEV
LB Bulgaricum PLC, 12A Malashevska str, BG – 1202 Sofia, Bulgaria

Abstract

Zvancharova, T., K. Baltova and Z. Urshev, 2013. Starter cultures for production of yoghurt from sheep’s milk with extended shelf life. Bulg. J. Agric. Sci., Supplement 2, 19: 94–96

 

Originally, Bulgarian yoghurt was prepared from sheep’s milk, but the homemade product had only a few days of shelf life. Today under industrial conditions, yoghurt with shelf life of 20 days is routinely produced. Nevertheless, producers and exporters are still interested in sheep’s milk yoghurt with even longer storage period. In this study, we produced yoghurt with three selected starters and followed up its quality during three months of storage at 5°C. All three starters had low post acidification in the products. The freshly produced yoghurt samples had a pH of 4.17–4.39 which decreased gradually, but after 90 days it was still in the range 4.12–4.30 which was within the acceptable range. Viable cells of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus remained above the critical threshold of 108 and 106 cfu.ml–1 respectively for the whole period of 90 days. With the selected starters, the accumulation of products of proteolysis remained low with a slight increase only during the first month of storage. The limited proteolysis and low post acidification by the starters was achieved by the selection of weakly proteolytic strains of L. bulgaricus and/or a fermentation process with final viable cells of L. bulgaricus not exceeding 107 cfu.ml–1.  Organoleptic tests did not reveal any adverse change of product taste and aroma of yoghurt samples at day 90. In conclusion, production of sheep’s milk yoghurt with selected starters can give a product that will preserve its nutritional and biological value for as long as three months.

Key words: Lactobacillus bulgaricus, proteolysis, sheep’s milk, shelf life, yoghurt

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