Characteristics of lactobacilli growth and activity in UF milk

Abstract

The application of ultrafiltration has an increasing importance in the manufacture of dairy products, primarily of soft cheeses. However, in semi-hard and hard cheeses, manufac­ture ultrafiltration has not been applied at industrial level yet. Considering that UF milk is characterised by increased buffer capacity, lactic acid bacteria, that could be used as starter cultures, must have an expressed acidogenic ability. Also, practice has shown that cheeses manufactured of UF milk ripen slowly, because it is necessary that starter cultures have an expressed and proteolytic activity. The buffer capacity of milk equivalent (CF=1) and retentates (CF=3 and CF=4) were studied. Furthermore, the influence of milk equivalent and these retentates on the growth and activity of two strains of lactic acid bacteria: Lactobacillus lielveticus HD-50 and Lactobacillus acidophilus MC. The growth and production of lactic acid of the tested strains in UF milk were being observed during eight hours of fermentation. Proteolytic activity of these strains was examined by determination of tyrosine value and electrophoretic detection prt+ strains which were capable to hydrolyse p casein. In strain iMctobacillus helveticus HD-50 was detected better acidogenic ability, but in strain Lactobacillus acidophilus MC was detected better proteolytic activity.

Primena ultrafiltracije ima sve veći značaj u proizvodnji mlečnih proizvoda, u prvom redu mekih sireva, dok je u proizvodnji polutvrdih i tvrdih sireva zastupljena u manjem obimu. S obzirom da se UF mleko karakteriše povećanim puferskim kapacitetom, bakterije mlečne kiseline koje bi se mogle koristiti kao starter kulture, moraju se odlikovati izraženom acidogenom sposobnošću. Takodje, praksa je pokazala da sirevi dobijeni iz UF mleka sporije sazrevaju, zbog čega je neophodno da starter kulture poseduju izražena i proteolitička svojstva. U radu je prikazan puferski kapacitet UF mleka različitog stepena koncentrovanja i to mlečnog ekvivalenta (CF=1) i retentata CF=3 i CF=4. Zatim je ispitivan uticaj UF mleka navedenih koncentracija na aktivnost i rast dva soja bakterija mlečne kiseline i to : Lactobacillus helveticus HD-50 i Lactobacillus acidophilus MC. Rast i acidogena sposobnost ispitivanih sojeva je praćena tokom osam sati fermentacije u mlečnom ekvivalentu i retenlatima. Proteolitička aktivnost ispitivanih sojeva je determinisana određivanjem tirozinske vrednosti i elektroforetskom detekcijom prt+ sojeva koji hidrolizuju P kazein. Ispitivanja su pokazala da soj Lactobacillus helveticus HD-50 ima bolju acidogenu sposobnost, a soj Lactobacillus acidophilus MC je pokazao bolju proteolitičku aktivnost.