Microbiological characteristics and technological screening of goat milk lactic acid bacteria from temperate Valley of Salta (Argentina)

TORRES, NANCY; AUDISIO, M. CARINA; CHÁVEZ, MÓNICA

S.M. de Tucumán (Argentina)

Simposio; III Simposio Internacional de Bacterias Lácticas; 2009

The interest of goat milk lactic acid bacteria (LAB) has increased markedly during last years, not only due to its role of starters for cheese manufacture but also because of its potential use in others applications. Published information about LAB from the Temperate Valley of Salta was scarce. The objective of the present work was to characterize microbiologically and technologically goat milk LAB from Valley of Lerma, Salta. Raw goat milk samples were taken during three dates and, every time from three different dairy farms of the Lerma Valley (average temperature 18ºC, annual rain 700-1.000mm and 1.000 m. above sea level) during April and May of 2008. Samples at 4ºC were sent to laboratory immediately. BAL growth was analyzed on M17, MRS and MSS agar media at 37ºC during 24, 48 and 72h. Else, M17 and MRS agar plate conditions were: 7% v/v O2  and 14% CO2 of pressure. Following assays were performed on isolated LAB: colony morphology, motility, Gram stain, catalase and nitrate reactions. Isolated LAB were preserved in MRS broth plus 20%v/v of glycerol in liquid nitrogen. Technological properties were measured according to: acidifying activity (fast meant <24h, slow <48h); galactose fermentation; coagulation time; citrate metabolism; diacetyl and acetoine production; growth in BHI at 45ºC and in BHI with NaCl 6.5% w/v. LAB acidification capacity was measured in milk by pH and acidity (ºD) after 24 h of incubation at 37ºC. Fifty-one cultures were preselected because they were Gram (+) and nitrate, catalase and motility (-). 98% of these strains were cocci. Technological screening was performed on 16 of the 51 isolated strains. Galactose, growth in BHI at 45ºC and in BHI with NaCl 6.5% tests were positive for every of these 16 cultures. Strain H55 was the only citrate and diacetyl positive culture, and it also presented fast acidification with coagulum formation. H55, I54, I35, I53 and I7 generated diacetyl by citrate pathway. H68, H55 and I19 presented fast acidification with coagulum. H48, I35, I18, I44 and I7 showed slow rate of acidification but no coagulum was formed. I54 and I41 presented slow rate of acidification and coagulum was observed. The strains H55, I54, I53, I7, I30 and I64 produced diacetyl. Average range of pH and acidity variation of 16 cultures tested was 6.35 to 5.19 and 16.08 to 55.7, respectively. Strains I51 and I49 did not show any positive result to every technological analysis done in laboratory except acidification tested. Proteolysis and lipolysis assays are still carried on in laboratory. Isolation and characterization of goat milk LAB cultures from mild climate were successfully performed. Cultures with potential technological application were found out. Measured properties allowed detecting different cultures. Further studies should be carried out to identify isolated strains.