Production of probiotic cheese with addition of Lactobacillus gasseri LF221(Rifr) and K7(Rifr)

Abstract

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(Rif^r) and K7(Rif^r) 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(Rif^r) or K7(Rif^r) 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(Rif^r) and K7(Rif^r). 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(Rif^r) and K7(Rif^r) 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.