Influence of high pressure on some biochemical properties of kefir microflora (effect of hpp on kefir microflora)

The effect of high pressure on some biochemical properties of lactic acid bacteria present in kefir was investigated. Three strains of lactococci and three strains of lactobacilli, isolated from lyophilised kefir culture, were activated in milk and subjected, at room temperature, to pressurisation at 500 MPa, for 15 minutes. Both in the unpressurised and pressurised culture the following factors were determined: survivability of microorganisms, aroma-producing activity, acidity, ability to ferment lactose and antibacterial activity. As a result of pressurisation, the initial number of bacteria decreased by ca. 2-4 order of magnitude in the case of lactococci and by ca. 5-6 order of magnitude in case of lactobacilli. After pressurisation, decrease in ability of bacteria to produce aroma was observed. Following pressurisation, an increase of acidity (pH) and slight decrease of titratable acidity (degreesSH) in the cultures was observed. As compared to lactococci, acidity of lactobacilli culture was reduced to a bigger extent. Pressurisation did not effect the capability of lactococci to utilise lactose. In case of lactobacilli it was partly inhibited for the first 24 hours after processing. As a consequence of pressurisation, the studied microorganisms lost their antibacterial activity.