Effect of Cysteine and Lysine on Some Technical Properties of Yoghurt Starter Culture Bacteria

Abstract

Objective: The purpose of the present study is to introduce the application of certain materials in fermented media for enhancing the growth and acid production, reduction of fermentation time, optimizing the structure and yoghurt a well as reducing starter culture consumption which result in balancing the corresponding expenditures. Methods: By using local starter culture consisting lactobacillus bulgaricus- ssp delberueky and Streptococcus thermophilusin 50:50 ratio, four samples of set yoghurt were prepared in duplicated tests. Three of four samples were supplemented by L-lysine, L-cysteine and the mixture of the two and the remaining sample as a control. The factors were studied based on fermentation time, bacterial viability, acid forming, sensory evaluation and the amount of syneresis. Results: The results showed a significant effect on reducing fermentation time, increasing titratable acidity, optimized viability; besides, the end product had firmer structure and a lower syneresis. Probably lysine has been responsible for optimization of Streptococcus thermophiles growth. Accordingly, there was an increase in the number of Streptococcus thermophilus which later led to a stronger start for fermentation process. On the other hand, as a result of cysteine reduction property enhanced condition for lactobacillus bulgaricus led to a higher acid production, hence a stronger texture and lower wheying off. Conclusions: According to faster acidification, increasing bacterial activity that speed up production of fermented dairy products and reduce the amounts of starter culture used, leads to a decrease in overall energy consumption in dairy industry, this media fortification is suggested for applying in industerial starter culture production.