Abstract
In this study, the effects of proteolytic activity of yogurt starter bacteria on physicochemical and technological properties of yogurt were investigated. Moreover, impact of proteolytic activity and production of exopolysaccharide (EPS) on the performance of each strain were screened. In order to compare the textural properties of yogurt samples, four parameters were evaluated: syneresis, water‐holding capacity, cohesiveness, and hardness. Results showed that strains with high proteolytic activity had lower acidifying activity during fermentation and storage. Samples containing EPS‐producing starter cultures had low proteolytic activity except samples K, L, and M. These differences related to nature and characteristics of each strain. Counts of starter cultures in samples produced using strains with high proteolytic activity were higher than other samples. Textural analysis data showed significant differences (p < .05) among strains in the four tested parameters. Strains with high proteolytic activity showed lower texture properties than other samples. Evaluation of sensory characteristics also showed samples prepared using strains with low or medium proteolytic activity and produced with EPS‐producing strains have higher overall acceptability than other samples. Accordingly, microbial, physicochemical, and sensory properties of produced yogurts confirm that proteolytic activity is one of the most effective factors in quality of product and performance of each strain.
Highlights
Organoleptic characteristics of yogurt are affected by several factors, including the type of milk, microbiological quality, the technology used in making the yogurt, and others
L. delbrueckii ssp. bulgaricus strains 109 and 110p in combination with the three strains of S. thermophilus showed the highest proteolytic activity with low acidification activity. These results confirm that isolates showing the highest acidifying activity need not necessarily have the most proteolytic activity, as reported by other authors (Durlu-Ozkaya, Xanthopoulos, Tinail, & Litopoulou- Tzanetaki, 2001; Nieto-Arribas, Poveda, Seseña, Palop, & Cabezas, 2009)
Nature and characteristics of each strain led to different ability; some strains with high proteolytic activity do not have ability for degradation of lactose and consumption of its products for lactic acid production
Summary
Organoleptic characteristics of yogurt are affected by several factors, including the type of milk, microbiological quality, the technology used in making the yogurt, and others. The starter culture has outstanding role in technological and organoleptic characteristics in fermented product. Lactic acid bacteria have different technological properties; one of the important technological properties is proteolytic activity that is needed for growth of bacteria in milk and has impact on properties of fermented product. Lactic acid bacteria (LAB) are characterized by their high demand for essential growth factors such as peptides and amino acids. Milk does not contain sufficient free amino acids and peptides to allow growth of LAB (Abu-Tarboush, 1996). These microorganisms use their own proteolytic activity, a complex system of proteinases and peptidases, which enable them to use milk casein as a source of amino acids and nitrogen.
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