Production of probiotic cheese with addition of Lactobacillus gasseri LF221(Rifr) and K7(Rifr) | Izdelava probiotičnega sira z dodatkom Lactobacillus gasseri LF221(Rifr) in K7(Rifr)

Inglés. Lactobacillus gasseri LF221 and K7 are human isolates which produce bacteriocins with wide range of inhibition, are resistant to low pH-values and bile, survive in the gastrointestinal tract of mice and pigs, and as such fulfil the basic criteria for probiotic strain. The possibility of cheese production with addition of LF221 or K7 and their survival during cheese ripening was studied. The derivatives of Lactobacillus gasseri LF221(Rifr) and K7(Rifr) strains resistant to rifampicin (250 μg ml–1) were used in the experiments. A semi-hard cheese was produced in an experimental dairy from 80 L of milk. Cheese milk was inoculated with live LF221(Rifr) or K7(Rifr) cells (approximately 107 ml–1 of cheese milk) alone or in combination with starter culture Streptococcus thermophilus TH-4. TH-4 was used in order to speed up the acedification during the cheesemaking and pressing of cheeses. During the ripening for six weeks, cheese samples were weekly aseptically collected and analysed. The microbiological analyses were performed by standard plate count on Rogosa agar for lactobacilli, on Chalmer for streptococci, on VRB for koliforms and on MRS agar with 250 mg ml–1 of rifampicin for selective enumeration of the strains LF221(Rifr) and K7(Rifr). For the confirmation of LF221 and K7 strains the RAPD analysis was performed with the primer 5’ AGTCAGCCAC 3’. Both human isolates grow slowly in milk therefore they can not be used as the only starter culture for cheese production. With the addition of TH-4 culture the probiotic cheeses of good organoleptic properties were produced. No adverse effect of human isolates on streptococcal population was observed. While in the cheeses without added probiotic strains, the number of non-starter lactobacilli increased during the ripening, the strains LF221(Rifr) and K7(Rifr) prevailed in cheeses where added. The colonies grown on MRS agar with rifampicin were successfully confirmed by RAPD analysis as K7 or LF221 strain. After six weeks of ripening the number of probiotic bacteria was still approximately 108 cfu g–1 of cheese.

Esloveno. 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.