Quality improvement and shelf-life of Kareish cheese using some mutants of Streptococcus thermophilus and Lactobacillus delbruekii subsp. bulgaricus

Abd El-Aty, A.M.* and Heller, K.J.**

Abstract

Utilization of mutant Streptococcus thermophillus and Lactobacillus delbreukii subsp. bulgaricus for improving the quality and shelf-life of Kareish cheese was the aim of this research. Kareish cheese was made with different mutant starter cultures and analysed when fresh and during storage (28 days) every week for chemical, bacteriological and organoleptic properties. The results indicated that using mutant strain culture especially T3 and T6 led to increase the yield and the moisture content compared with the control. Acidity and acid development in Kareish cheese treated with T3 and T6 during storage were lower than those of other treatments. Kareish cheese made with T2 and T5 record the highest values of acetaldehyde content when fresh or during storage. Acetaldehyde content increased to reach maximum values up to 7 days then decreased until the end of storage. It was observed that Kareish cheese made with mutant strain culture had the lower viable bacteria and moulds and yeasts count than the control. The count of viable bacteria increased during storage to reach a maximum after 14 days then decreased until the end of storage. The results revealed that using mutant of strain culture in Kareish cheese manufacture improved the yield, quality and shelf-life of the cheese.

Key words

Kareish cheese, Mutants, Streptococcus thermophillus , Lactobacillus delbreukii subsp. bulgaricus.