Determination of the number and persence of aerobic mesophilic bacteria species in raw unperserved and perserved milk

Broj aerobno mezofilnih bakterija u mlijeku jedan je od pokazatelja higijenske kvalitete mlijeka. Njihova identifikacija je za modernu mljekarsku industriju od velike važnosti pa je tako i prioritet što brže i efikasnije dobivanje rezultata. Danas se uz klasične metode njihova određivanja javljaju i novije, brže metode kao što je MALDI-TOF tehnika čija se primjena u identifikaciji aerobno mezofilnih bakterija ispitivala u sklopu ovog rada. U 40 uzoraka sirovog i konzerviranog mlijeka azidiolom određivao se ukupan broj aerobno mezofilnih bakterija metodom protočne citometrije i klasičnom metodom brojanja kolonija na hranjivoj podlozi prema međunarodnoj normi HRN EN ISO 4833-1:2013. Na temelju rezultata uočen je trend smanjenja broja izraslih kolonija u mlijeku konzerviranom azidiolom, ali je broj uzoraka premali da bi se mogao zaključiti negativni utjecaj azidiola na ukupan broj aerobno mezofilnih bakterija u mlijeku. Identifikacija bakterija provodila se usporedbom MALDI-TOF spektra masa s referentnim spektrima pohranjenim u biblioteci mikroorganizama i obradom pomoću MALDI Biotyper računalnog programa. MALDI-TOF tehnikom uspješno je identificirano 298 bakterijskih kolonija u uzorcima sirovog mlijeka i 243 kolonije u uzorcima konzerviranog mlijeka. U uzorcima sirovog mlijeka identificirano je 29 rodova i 45 bakterijskih vrsta, a u konzerviranim uzorcima 25 rodova i 36 bakterijskih vrsta.The number of aerobic mesophilic bacteria in milk is one of the indicators of the hygienic quality of milk. Their identification is of great importance for the modern dairy industry, so it is a priority to get the results as quickly and efficiently as possible. Today, in addition to the classical methods of their determination, newer, faster methods appeared, such as the MALDI-TOF technique whose use in identifying of aerobic mesophilic bacteria was being determined within this thesis. In 40 samples of raw and preserved milk with azidiol, the total number of aerobic mesophilic bacteria was determined by flow cytometry and the classical method of counting colonies on a nutrient medium according to the international standard HRN EN ISO 4833-1: 2013. Based on the results, a decreasing trend of the number of grown colonies in milk preserved with azidiol was observed, but the number of samples was too small to conclude the negative impact of azidiol on the total number of aerobic mesophilic bacteria in milk. Bacterial identification was performed by comparing the MALDI-TOF mass spectra with reference spectra stored in a database and processing using a MALDI Biotyper computer program. The MALDI-TOF technique successfully identified 298 bacterial colonies in raw milk samples and 243 colonies in preserved milk samples. In raw milk samples, 29 strains and 45 bacterial species were identified, and in preserved samples 25 strains and 36 bacterial species