Technological characterization of lactococci isolated from traditional Chinese fermented milks

Abstract

To screen lactic acid bacteria for starter cultures in cheese production, 21 Lactococcus strains previously isolated from natural fermented milk and koumiss made by herdsman families in the Xinjiang, Gansu, and Qinghai provinces of China were evaluated for optimal growth temperature, acidification activity, proteolytic activity, aminopeptidase activity, and autolytic activity. All isolates presented low acidification rates, and the pH value did not reach 5.3 after 6 h of inoculation in sterile reconstituted skim milk at 30°C. Strains X9C2 and T7C showed the highest proteolytic activity of 24.67 and 23.58 mg of glycine/L of milk, respectively. For aminopeptidase activity, strains X9C2 and T1C2 displayed the highest activities of 30.56 and 27.70 U/mg of protein using L-leucine-p-nitroanilide as substrate, respectively. Autolytic activity in simulated cheese-like buffer ranged from 7.45 to 34.76%, and strains Q14C2 and Q16C showed the highest values of 34.76 and 34.20%, respectively. Collectively, one main finding is that some technological characteristics of Lactococcus isolates from Chinese traditional fermented products varied greatly. Some isolates with potentially important properties could be valuable for application as starter cultures of cheese or could constitute a mixed culture.

Identification and partial characterization of lactic acid bacteria isolated from traditional dairy products produced by herders in the western Tianshan Mountains of China

“…According to reports, strains with autolytic rates of between 25% and 37% are regarded as highly autolytic activity (Ma et al . ). Autolytic rates of LAB strains in our study were higher than those described previously (Franciosi et al .…”

“…; Ma et al . ), and this may play a crucial role in creating the unique sensory characteristics of the traditional dairy food of the western Tianshan Mountain area of Xingjiang.…”

“…() and Ma et al . (). The cell pellets were resuspended in potassium phosphate buffer (10 mmol, pH 5·5) containing 1 mol NaCl and then diluted to OD 650 nm = 1·0.…”

“…bulgaricus and Streptococcus thermophilus (Kimoto-Nira et al 2012). Several studies have been carried out in recent years to characterize the technological properties of LAB isolated from traditional Chinese dairy products Ma et al 2011;Yi et al 2011;Ao et al 2012;. Some of the strains possess desirable properties which may provide valuable references and be of potential use for the rapidly developing Chinese dairy industry .…”

Technological Characterization of Lactic Acid Bacteria Protease Isolated from Traditional Chinese Fermented Milk

“…Proteolytic activity was an exceptional feature for cultures as it could provide the exact substrate for enzymes involved in amino acid catabolism, which were often rate‐limiting for flavor development (Ma et al . ). However, strains with highly proteolytic activities were not always suitable for use as starter cultures as excessive proteolysis could also cause uncontrolled production of bitter peptides and other undesirable compounds, or even excessive hydrolysis of casein can induce the formation of a too‐soft final product (Buffa et al .…”