Determination of whey-based medium requirements and growth characteristics for the production of yoghurt starter cultures

Abstract

Yoghurt is an important dairy product which is produced by thermophilic starter cultures including; Streptococcus thermophilus and Lactobacillus bulgaricus. They grow synergistically in milk by acidifying milk, produce specific aroma compounds and lactic acid which impact the quality of the yoghurt. Imported cultures are widely used in dairy industry to stabilize the technological properties which cause a change in our natural flora and flavour. Starters from traditional yoghurts have to be preserved. Under this perspective, the aim of this study was to determine the medium requirements of mixed starter cultures for production of starter bacteria which has been isolated and characterized before.Determination of medium requirements were done in a whey-based media. Since bacteriophages were one of the most important problem in dairy industry, to prevent cultures from phage adsorption, media was treated with different salts which can bind free calcium ions. Salts were examined for cell viability and phage infection effects.From these studies Na2HPO4 + KH2 PO4 with 2% of medium addition was chosen as the most effective. Mineral requirements of the mixed cultures were determined. The best combination; 10, 5, 50 ppm for Fe2+, Mn2+, Mg2+ ions with 0,939 desirability were used for initial mineral content of medium. Fermentation constants for mixed cultures were determined. Pure culture fermentations and mixed culture fermentations were performed. According to results mixed culture inoculations gave higher maximum specific growth rates; 0,9188h-1 and 0,7323h-1 for cocci and bacilli while 0,855h-1 and 0,659h-1 were obtained for cocci and bacilli from single strain fermentations.