Isolation and characterization of lactic acid bacteria as autochthonous starter cultures

master's thesis

• Title: Izolacija i karakterizacija bakterija mliječne kiseline kao autohtonih starter kultura
• Author: Ana Ružić
• Mentor: Blaženka Kos (mentor)
• Granter: University of Zagreb; Faculty of Food Technology and Biotechnology; (Department of Biochemical Engineering); (Laboratory for Antibiotic, Enzyme, Probiotic and Starter Cultures Technology); Zagreb
• Defense date and country: 2010-10, Croatia
• Scientific / art field, discipline and subdiscipline: BIOTECHNICAL SCIENCES; Biotechnology

Abstract

Iz tradicionalnog svježeg ovčjeg sira izolirano je 12 gram-pozitivnih, katalaza-negativnih bakterijskih sojeva. Mikroskopiranjem je utvđeno da je između 12 izoliranih sojeva, 5 štapićastih, a 7 bakterijskih sojeva u obliku koka. Svi izolirani sojevi su u tekućim MRS podlogama proizvodili mliječnu kiselinu, pri čemu se pH vrijednost podloge snižavala. Na temelju SDS-PAGE elektroforeze ukupnih staničnih proteina odabrana su 3 različita bakterijska soja, a RAPD metoda s oligonukleotidnom početnicom za bakterije mliječne kiseline je potvrdila da se radi o sojevima iz roda Lactobacillus. Fenotipskom identifikacijom API 50 CHL testom utvrđeno je da se radi o dvije bakterijske vrste: Lactobacillus brevis i Lactobacillus paracasei ssp paracasei. Hidrolizom kazeina na MRS agaru s obranim mlijekom, ustanovljena je proteolitička aktivnost sva 3 izoliranih soja što je važno funkcionalno svojstvo starter kultura za fermentirane mliječne proizvode. Liofilizacijom su pripremljeni suhi aktivni preparati odabranih bakterijskih sojeva te su uz dodatak probiotičkih kultura korišteni kao starter kulture za proizvodnju svježih sireva od pasteriziranog ovčjeg mlijeka. Kemijskim analizama proizvedenih sireva je utvrđeno da su oba uzorka zadovoljavajuće kvalitete. Senzorske analize, koje su provedene 1. i 10. dan nakon proizvodnje, su pokazale da dodatak komercijalnih starter kultura umanjuje senzorske ocjene. Nakon 10 dana čuvanja broj živih stanica primjenjenih kultura se održao visok (ca 1010 CFU/g), što je važno svojstvo s tehnološkog aspekta priprave i čuvanja svježeg sira.

Abstract (english)

12 gram-positive, catalyse-negative bacterial strains have been isolated from traditional fresh sheep cheese. After studying theese 12 isolated strains under the microscope, it is determined that 5 of the 12 strains are lactobacilli and the remaining 7 cocci. All isolated strains. grown in MRS broth media, have produced lactic acid, during which the pH value of the growth media was decreased. Based on SDS-PAGE electrophoresis of all cell proteins, 3 different bacterial strains were chosen, and RAPD method with primers for lactic acid bacteria has confirmed that strains belong to the genus Lactobacillus. Phenotype analysis of the strains by API 50 CHL test has determined two different species, Lactobacillus brevis and Lactobacillus paracasei ssp paracasei. Casein hydrolysis on MRS agar with skim milk have shown proteolytic activity in all 3 isolated strains, which is very important functional property of starter cultures for the production of fermented milk products. Chosen bacterial strains were prepared as dry active preparations by freeze-drying process. After adding probiotical cultures to the preparations of bacterial strains, they were used as starter cultures for the production of fresh cheese from pasteurized sheep milk. Chemical analysis of produced cheeses, have revealed that both samples are of satisfying quality. Sensoric analyses, which were performed on the 1st and 10th day after production, have indicated that adition of commercial starter cultures has decreased sensoric grade. After 10 days of storage, the number of live cells of the cultures maintained high (ca 1010 CFU/g), which is a very important technological aspect property of producing and preserving fresh cheeses.

• Keywords: svježi ovčji sir; probiotik; starter kulture; senzorska svojstva
• Keywords (english): fresh sheep cheese; probiotic; starter cultures; sensoric properties
• Language: croatian
• URN:NBN: urn:nbn:hr:159:164030
• Study programme: Title: Biotehnologija; smjerovi: Biokemijsko inženjerstvo; Study programme type: sveučilišni; Study level: dodiplomski; Academic / professional title: diplomirani inženjer biotehnologije; smjer biokemijsko inženjerstvo (diplomirani inženjer biotehnologije; smjer biokemijsko inženjerstvo)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Restricted access
• Created on: 2017-08-28 10:31:59