Investigation the effects of proteolytic activity and exopolysaccharide production by native starter bacteria on technological and organoleptic properties of yogurts

One of the most important points for yogurt production is the selection of starter culture, and also because of the necessity to preserve our natural starter cultures and to increase the availability of them for industrial use, the aim of this project was to determine the technological and organoleptic properties of yogurts producted by starter culture isolated from Iranian native yogurts. Eleven different yogurt samples were produced using 5 Lactobasillus delbruekii subsp.bulgaricus and 2 Streptococcus thermophiles isolates. Results showed there were no significant differences between acidifying activity of EPS-producing and non-EPS-producing starter cultures. Also isolates with a high proteolytic activity (isolates used in the examples H and I that proteolytic activity reaches during 28 days to 1 unit) have less the ability to produce acid during storage and viability of these isolates had been more than other strains. Samples that produced by EPS-producing starter culture exhibited better texture properties (consistency, syneresis and water holding capacity) than samples that produced using NEPS-producing starter culture. However, H and I samples due to high proteolytic activity and type of the exopolysaccharide is produced had less desirable textural properties. Syneresis reduced during storage and water holding capacity increased. But the synersis and water holding capacity of the samples produced using starters with high proteolytic activity, such as samples E, H, I similar to other samples until day 21, and in the fourth week the trend of changes has was reversed and the amount of synersis increased and water holding capacity is reduced.