Abstract
Background: Milk is a healthy human nutrient, which is fermented to yogurt by lactic acid bacteria, mainly Streptococcus salivarius ssp, thermophilus and Lactobacillus. delbrueckii ssp. bulgaricus. This study aimed to isolate thermophilic starter bacteria from homemade yogurt made in Gaza Strip. The study sought to define both the biochemical and molecular characteristics of the isolated bacteria. Results: Three of the isolates were identified as Streptococcus thermophiles while two isolates were recognized as Lactobacillus delbrueckii ssp. bulgaricus. All five identified isolates showed worthy acidification capacity. Based on these characters, strains were applied for making yogurt either as single pure cultures or as mixed cultures. When using mixed cultures from S. thermophiles and L. bulgaricus, all tested combinations showed positive results. Conclusion: Isolated strains showed remarkable biotechnological characters. The isolates are expected to stimulate and improve quality of the yogurt when they are used as mixed starter cultures.
Highlights
Lactic acid bacteria are recognized as important industrial bacteria due to their fermentative capacity and their health and nutritious benefits
M17 agar medium used to isolate of S. thermophilus and MRS agar medium used to isolate L. delbrueckii
According to the results obtained from online ABIS software, API 50 CH fermentation tests showed that the cocci isolates belong to S. thermophilus and the bacilli isolates belong to L. delkbrueckii ssp. bulgaricus and Streptococcus thermophilus strains with high percentage of reliability
Summary
Lactic acid bacteria are recognized as important industrial bacteria due to their fermentative capacity and their health and nutritious benefits. During the traditional homemade process, spontaneous uncontrolled fermentation conditions dominate Such type of fermentation is considered as the primary method used to preserve milk. Milk is a healthy human nutrient, which is fermented to yogurt by lactic acid bacteria, mainly Streptococcus salivarius ssp, thermophilus and Lactobacillus delbrueckii ssp. This study aimed to isolate thermophilic starter bacteria from homemade yogurt made in Gaza Strip. All five identified isolates showed worthy acidification capacity. Based on these characters, strains were applied for making yogurt either as single pure cultures or as mixed cultures. When using mixed cultures from S. thermophiles and L. bulgaricus, all tested combinations showed positive results. The isolates are expected to stimulate and improve quality of the yogurt when they are used as mixed starter cultures
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