The changing of milk microbiota composition in collection tank due to two-day collection was investigated. Each out of 10 independent cycles of every two-day collection was sampled 4 times and ...microbiologically examined. PCA medium supplemented with skim milk powder was used to determine the total counts of mesophilic aerobic bacteria, proteolytic bacteria, psychrotrophic and proteolytic psychrotrophic bacteria, respectively. MRS and M17 media were used to determine the counts of lactobacilli and cocci (lactococci and enterococci), respectively. As expected the counts of microbial groups increased but particularly the ratio between the groups of microorganisms was changed. The most evident shift in composition of milk microbiota was detected for psychrotrophic, particularly proteolytic psychrotrophic bacteria that are of particular concern to the dairy industry. Proteolytic psychrotrophs are notorious for their proteolytic activities which adversely influence milk proteins. Moreover, secreted proteolytic enzymes cannot be destroyed by heat treatment processes that are normally used in milk processing. The counts of microbial groups sharply increased on the second day of two-day collection. From selected bacterial consortia, the presence of the individual group of microbes was also PCR examined. Results indicate that the microbiological quality of milk in a two-day collection system is remarkably lower in comparison with daily collection system.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Microbiological analysis of ripened artisanal Tolminc cheese revealed the presence of an enterococcal population in numbers of up to 10
6 per g. All colonies, isolated from the citrate azide tween ...carbonate (CATC) enterococcal selective medium were Gram positive and coccal-shaped and were analysed with PhenePlate™ FS system. This system discriminated 10 PhP clusters among the 90 enterococcal isolates. From each cluster the most representative isolate for that particular type was selected for further study. The 10 representative enterococci were catalase negative and grew in the presence of NaCl (2%, 4% and 6.5%) and bile salts (0.06%). Genus specific primers confirmed all 10 enterococcal representatives as
Enterococcus members, while species specific primers determined them further as strains of
Enterococcus faecalis species. PCR for
vanA and
vanB genes detection, respectively, amplified no PCR products. The absence of
van genes was confirmed with both disc and E-test, as isolates were susceptible to vancomycin according to the National Committee for Clinical Laboratory Standards (NCCLS). The results of disc tests with other antimicrobial agents (ampicillin, vancomycin, kanamycin, penicillin, erythromycin, neomycin, chloramphenicol, clindamycin, rifampin) did not differ much among the tested enterococci: they were all very resistant to clindamycin only. The incidence of enterococcus virulence determinants was as expected: all of the 10
E. faecalis strains tested possessed multiple determinants (between 7 and 11).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
Lactobacillus gasseri LF221 in K7 sta humana izolata, ki proizvajata bakteriocine s širokim spektrom protimikrobne aktivnosti, sta odporna proti nizkim pH vrednostim in žolču, preživita v prebavnem ...traktu miši in pujskov in s tem izpolnjujeta osnovne kriterije za probiotični sev. Proučevali smo možnost izdelave sira z dodatkom sevov LF221 ali K7 in njuno obstojnost med procesom zorenja sira. V raziskavi smo uporabili derivate Lactobacillus gasseri LF221(Rifr) in K7(Rifr) rezistentne proti rifampicinu (250 μg ml–1). V eksperimentalni sirarni smo izdelovali poltrdi sir iz 80 L mleka. Mleko za sir smo cepili samo z živimi celicami LF221(Rifr) ali K7(Rifr) (približno 107 ml–1 mleka za sir) ali pa v kombinaciji s startersko kulturo Streptococcus thermophilus TH-4. Startersko kulturo TH-4 smo uporabili za pospešitev acidifikacije med sirjenjem in stiskanjem sirov. Med šest tedenskim zorenjem smo tedensko aseptično jemali vzorce sira in v g sira ugotavljali število kolonijskih enot (KE) laktobacilov (Rogosa), streptokokov (Chalmer), koliformnih bakterij (VRB) in celic LF221(Rifr) in K7(Rifr) (MRS+rifampicin). Za potrditev sevov LF221 in K7 smo uporabili RAPD analizo in oligonukleotidni začetnik 5’ AGTCAGCCAC 3’. Oba humana izolata počasi rasteta v mleku in ju ne moremo uporabiti kot samostojni starterski kulturi. Z dodatkom starterske kulture TH-4 smo izdelali probiotični sir dobrih senzoričnih lastnosti. Humana izolata nista vplivala na število streptokokov v siru. Medtem, ko se je v kontrolnem siru brez dodanih probiotičnih bakterij število nestarterskih laktobacilov med zorenjem povečevalo, sta v siru z dodanimi probiotičnimi bakterijami prevladovala seva LF221(Rifr) in K7(Rifr). Kolonije, zrasle na MRS agarju z rifampicinom smo z RAPD analizo uspešno potrdili kot seva LF221 in K7. Na koncu 6-tedenskega zorenja so siri vsebovali približno 108 KE g–1 probiotičnih bakterij.
In our experiments the fermentation of lactose at Camembert type cheese by classic and stabilised technology was monitored. In each of the two technologies two experiments were made. The difference ...between these two technologies is in pH level, which drops below 5 by classic technology and remains above 5 by stabilised technology at all times. To achieve the criteria of stabilised technology the fermentation was stopped at a desired level of pH, by dropping the cheese in brine at 14 °C. After salting and moulding cheesewas transferred from the first three experiments into a ripening chamber at 11 °C. With the last experiment (stabilised technology) the cheese ripened for 3 days at 5 °C. During ripening process pH dropped below 5 in all experiments. The process of fermentation was performed by the following lactic acid bacteria: Streptococcus thermophilus, Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris. As these lactic acid bacteria ferment differently D-galactose during manufacture and ripening process, the contentof lactose and D-galactose was measured. Based on the results of our research the following conclusion can be made: the action of lactic acid bacteria can not be stropped even at 5 °C. The native microflora, which remains in the milk after thermisation, might be responsible for the fermentation of Dgalactose. It could be possible that the Streptococcus thermophilus enzymes were not inactivated, causing continuation of lactose fermentation even at low temperature. Mesophilic lactococci were inhibited and for that reason Dgalactose accumulated in cheese. Only after cheese were transferred into a ripening chamber at 11 °C and with low lactose concentration in medium left, mesophilic lactococci started to ferment D-galactose.
The fate of ivermectin (IVM) residues was studied throughout the processing of daily bulk milk from 30 ewes (taken up to 33 d following subcutaneous administration of 0·2 mg IVM/kg b.w.) in the ...following milk products: yoghurt made from raw and pasteurized milk; cheese after pressing; 30- and 60-day ripened cheese; and whey, secondary whey and whey proteins obtained after cheese–making (albumin cheese). The concentration of the H2B1a component of IVM was analysed in these dairy products using an HPLC method with fluorescence detection. The mean recovery of the method was, depending on the matrix, between 87 and 100%. Limits of detection in the order of only 0·1 μg H2B1a/kg of product were achieved. Maximum concentrations of IVM were detected mostly at 2 d after drug administration to the ewes. The highest concentration of IVM was found on day 2 in 60-day ripened cheese (96 μg H2B1a/kg cheese). Secondary whey was the matrix with the lowest concentration of IVM (<0·6 μg H2B1a/kg). Residue levels fell below the limits of detection between day 5 (for secondary whey) and day 25 (for all cheese samples). In the matrices investigated, linear correlations between daily concentrations of IVM, milk fat and solid content were evident. During yoghurt production, fermentation and thermal stability of IVM was observed. During cheese production, approximately 35% of the IVM, present in the raw (bulk) milk samples, was lost. From the results it was concluded that the processing of ewes' milk did not eliminate the drug residues under investigation. The consequences of IVM in the human diet were discussed. Milk from treated animals should be excluded from production of fat products like cheese for longer after treatment with IVM than for lower fat products.
Cilj ovog rada bio je utvrditi promjene u mikrobnoj populaciji skupnog sirovog mlijeka nakon dva dana pohrane u hladnim uvjetima čuvanja. Za svaki od 10 neovisnih ciklusa dvodnevnog sakupljanja ...mlijeka analizirana su 4 uzorka. PCA medij s dodatkom obranog mlijeka u prahu korišten je za određivanje ukupnog broja mezofilnih aerobnih bakterija, proteolitičkih, psihrotrofnih i proteolitičkih psihrotrofnih bakterija. MRS i M17 mediji korišteni su za određivanje laktobacila i koka (laktokoki i enterokoki). Nakon dvodnevne pohrane mlijeka, ukupan broj svih istraživanih mikrobnih skupina se povećao u odnosu na prvi dan pohrane. Međutim, utvrđena je značajna razlika između pojedinih skupina u njihovom udjelu u ukupnoj mikrobnoj populaciji. Najznačajnije promjene utvrđene su za psihrotrofne proteolitičke bakterije koje su od posebne važnosti za mljekarsku industriju. Proteolitički enzimi te skupine bakterija hidroliziraju bjelančevine mlijeka, a konvencionalna toplinska obrada mlijeka ih ne inaktivira. Zastupljenost pojedinih mikrobnih skupina utvrđena je PCR metodom. Rezultati potvrđuju da je mikrobiološka kvaliteta mlijeka kod dvodnevnog prikupljanja značajno lošija u usporedbi s mikrobiološkom kvalitetom mlijeka koje se prikuplja svaki dan.
U našim eksperimentima provedena je fermentacija laktoze u Camembert siru klasičnom i stabilizacijskom tehnologijom. U obje primjenjene tehnologije načinjena su po dva eksperimenta. Razlika u ove ...dvije tehnologije je u pH vrijednosti koja kod klasične tehnologije pada ispod 5, a kod stabilizacijske se zadrži cijelo vrijeme iznad 5. Da bi se dostigli kriteriji stabilizacijske tehnologije fermentacija je zaustavljena kod željene pH vrijednosti, potapanjem sira u salamuru pri 14 °C. Nakon salamurenja i inokulacije s plijesni sir je, iz prva tri eksperimenta, prebačen u komoru za zrenje pri 11 °C. U posljednjem eksperimentu (stabilizacijska tehnologija) sir je podvrgnut zrenju kroz 3 dana pri 5 °C. Tijekom zrenja pH vrijednost sira je u svim eksperimentima pala ispod 5. Proces fermentacije proveden je pomoću slijedećih bakterija mliječne kiseline: Streptococcus thermophilus, Lactococcus lactis subsp. lactis i Lactococcus lactis subsp. cremoris. Kako ove bakterije različito fermentiraju D-galaktozu, tijekom proizvodnje i zrenja, provedeno je određivanje i laktoze i D-galaktoze. Na osnovi dobivenih rezultata mogu se izvući slijedeći zaključci: djelovanje bakterija mliječne kiseline ne može se zaustaviti čak niti na 5 °C. Prirodna mikroflora, koja zaostaje u mlijeku, mogla bi biti odgovorna za fermentaciju D-galaktoze. Moguće je da se Streptococcus thermophilus enzimi nisu aktivirali uzrokujući tako daljnju fermentaciju laktoze čak i na niskoj temperaturi. Mezofilni laktokoki su bili inhibirani zbog čega je došlo do nakupljanja D-galaktoze u siru. Nakon što je sir prebačen u komoru za zrenje, na 11 °C, i pri niskoj koncentraciji laktoze u mediju, mezofilni laktokoki započeli su fermentaciju D-galaktoze.
U radu je proučavana mogućnost proizvodnje mocarela sira za ribanje i pripravu pizze, a uz produljen vijek trajanja sira do 30 dana. U mlijeko za proizvodnju sira dodavana je različita količina ...obranog mlijeka u prahu (0,5; 1,0; 1,5; 2,0; 2,5 i 3,0%) koja je prilagođena sposobnosti rastezanja sirne mase, ovisno o temperaturi rastezanja i pH vrijednosti sirne mase. Pri svakoj količini dodanog obranog mlijeka u prahu testirana je uporaba monokulture: Streptococcus thermophilus i uporaba miješane kulture: Streptococcus thermophilus i Lactobacillus delbrueckii subsp. bulgaricus u omjeru 1:1. Tijekom proizvodnje mocarele podešavano je zakiseljavanje sirne mase, a količina suhe tvari, masti i prinos sira također su određeni. Rezanje i tvrdoća sira određena je uporabom Instron aparature, dok je struktura mocarele analizirana Scanning elektronskim mikroskopom. Nakon 30 dana od proizvodnje mocarela je senzorski ocijenjena. Najbolji rezultati postignuti su pri proizvodnji mocarele od mlijeka uz dodatak 2% obranog mlijeka u prahu i uporabom miješane starter kulture Streptococcus thermophilus i Lactobacillus delbrueckii subsp. bulgaricus u omjeru 1:1.
Cilj istraživanja je bio razviti novi dijetni proizvod na osnovu topljenog sira. Uspjelo je izraditi topljeni sir s dijetnim osobinama. Dobiveni proizvod sadrži 10,9 % manje zasićenih masnih kiselina ...i 10 % više nezasićenih masnih kiselina. Novi proizvod je imao esencijalne linolne masne kiseline 12,43 % ili 7 puta više od prosječnog topljenog sira na tržištu. Dijetni topljeni sir imao je pored odgovarajućeg kemijskog sastava i prijatan okus i teksturu. Dijetni topljeni sir je podesan za dijetnu, dječju i gerontološku ishranu kao i za svakodnevnu zaštitnu prehranu potrošača.
Proučili smo mogućnosti zamjene fosfata solima za topljenje koje ne sadrže fosfate odnosno mogućnosti smanjenja njihove količine, a da pritom senzorska i reološka svojstva topljenog sira ostanu ...nepromijenjenima. Utvrdili smo količinu P2O5, reološke parametre te senzorske osobine uz određenje glavnog kemijskog sastava sirnih mješavina i konačnog proizvoda. Izradili smo devet uzoraka topljenog sira. Za referencijski uzorak odabrali smo topljeni sir koji izrađuju po standardnoj tehnologiji u tvornici Mlekopromet Ljutomer. Upotrijebili smo četiri soli za topljenje na fosfatnoj osnovi i četiri emulgatora. Utvrdili smo da su uzorci izrađeni bez fosfata neprihvatljivi, a da su uzorci, kojih je količina P2O5 na jedinicu proizvoda smanjena do 30% na osnovi senzorskog ocjenjivanja postigli prvi razred. Reološke analize su pokazale da su sirevi s dodatkom P2O5 imali više vrijednosti za povratnost tlačne deformacije (I, II) i tlačni otpor (I, II) od sireva bez ili onih sa smanjenom količinom P2O5.
