Impact of autolytic, proteolytic, and nisin-producing adjunct cultures on biochemical and textural properties of cheddar cheese

The effect of incorporating a highly autolytic strain (Lactobacillus delbrueckii subsp. bulgaricus UL12) a proteolytic strain (Lactobacillus casei subsp. casei L2A), or a nisin Z-producing strain (Lactococcus lactis, subsp. lactis biovar diacetylactis UL719) into Cheddar cheese starter culture (Lactococcus lactis KB and Lactococcus cremoris KB) on physicochemical and rheological properties of the resultant cheeses was examined. Cheeses were ripened at 7 degrees C and analyzed over a 6-mo period for viable lactococcal and lactobacilli counts, pH, titratable acidity (TA), lipolysis, proteolysis, and textural characteristics. The combination of the nisin-producing strain and autolytic adjuncts significantly increased the production of water-soluble nitrogen, free amino acids, and free fatty acids. The effect of Lc. diacetylactis UL719 alone or of Lb. casei L2A on water-soluble nitrogen and free amino acid contents were also significant, whereas their effect on free fatty acids was not. Viable counts of Lb. bulgaricus UL12 were significantly reduced in the presence of Lc. diacetylactis UL719. Lactobacilli-containing cheeses showed significantly lower values for hardness, fracturability, and springiness. It could be concluded that the addition of Lb. bulgaricus UL12 together with a nisin-producing strain produces a greater increase in cheese proteolysis and an improvement in Cheddar cheese texture.     

Esterolytic and lipolytic activities of lactic acid bacteria isolated from ewe's milk and cheese

In the present work, we report on the esterase and lipase activities of lactic acid bacteria representing the genera Lactococcus, Leuconostoc, Lactobacillus, and Enterococcus isolated from ewe's milk and cheeses. Esterase activity was studied using alpha- and beta-naphthyl derivatives of 2 to 12 carbon atoms and postelectrophoretic detection. The lactic acid bacteria evaluated had intracellular esterase activities, which preferentially degraded the alpha- and beta-naphthyl derivatives of 2 to 6 carbon atoms. By studying postelectrophoretic patterns, it was found that some strains presented more than one esterase. Lactobacillus plantarum O236 showed four enzymes that hydrolyze carboxyl ester linkages with different specificity. Lipase activity was studied in intracellular and extracellular fractions using tributyrin, tricaprylin, triolein, and milk fat as substrates. The intracellular and extracellular fractions of Leuconostoc mesenteroides O257, Lactobacillus plantarum O236, and Lactobacillus acidophilus O177 were able to hydrolyze tributyrin. L. plantarum O186, L. acidophilus O252, Enterococcus faecium O174 and O426, and Enterococcus faecalis Ov409 showed lipase activity associated with the intracellular fraction on tributyrin. Lactococcus lactis O233, L. plantarum O155, and Lactobacillus casei O190 did not hydrolyze triglycerides. Not all strains that showed esterase activity exhibited high activity on triglycerides. Esterase and lipase activities were species- and strain-specific. Wide variations in activity between strains highlight the need for selecting appropriate starters to produce enzyme-modified cheese as well as accelerated ripened cheese.     

Characterization of certain bacterial strains for potential use as starter or probiotic cultures in dairy products

The present work was aimed at characterizing 12 strains of lactic acid bacteria (LAB) to obtain improved potential starter or probiotic cultures that could be used for making dairy products from ewe's milk and cow's milk. Eight strains with antimicrobial properties, isolated from ewe's milk and from cheese made from ewe's and/or cow's milk, were studied. They were identified as Enterococcus faecalis (five strains), Lactococcus lactis subsp. cremoris, Leuconostoc mesenteroides, and Lactobacillus paracasei subsp. paracasei (one strain of each species). Additionally, four strains were obtained from the American Type Culture Collection: Lactobacillus casei 393 (isolated from cheese), L. lactis subsp. lactis 11454 (origin nonspecified and a producer of nisin), and two strains isolated from human feces (L. paracasei subsp. paracasei 27092 and Lactobacillus rhamnosus 53103, antibacterial agent producer). All E. faecalis strains showed at least one virulence factor (either hemolysin or gelatinase), which emphasizes the importance of these studies in this species. Both L. lactis strains and most Lactobacillus spp. were good acidifiers in ewe's milk and cow's milk at 30°C. High β-galactosidase activity, as well as aminopeptidase activities that favor the development of desirable flavors in cheese, were detected in all Lactobacillus spp. strains. Furthermore, L. rhamnosus ATCC 53103 showed α-fucosidase activity (thought to help colonization of the intestine) and lack of α-glucosidase activity (a trait considered positive for diabetic and obese humans). This last enzymatic activity was also lacking in L. lactis ATCC 11454. L. mesenteroides was the only strain D(2)-lactic acid producer. The selection of any particular strain for probiotic or dairy cultures should be performed according to the technological and/or functional abilities needed.     

Technological characterization of the natural lactic acid bacteria of artisanal Turkish White Pickled cheese

The aim of this study was to characterize the lactic acid bacteria (LAB) isolated from White Pickled cheeses produced with traditional methods; and to improve the quality of cheesemaking with a selection of bacterial cultures from artisanal White cheeses. LAB were isolated and identified from 30 White Pickled cheese samples collected from various cities in Turkey. Also, the numbers of several microbial groups (total aerobic mesophilic bacteria, LAB, enterococci, coliforms, moulds and yeasts) of cheese samples were enumerated. Lactobacilli, lactococci and enterococci were the most abundant microbial groups. The numbers of Enterococcus and Lactobacillus isolates were higher than those of the other LAB. Enterococcus faecalis (24.43%), Enterococcus faecium (17.61%) and Lactobacillus fermentum (19.88%) isolates were the most frequently isolated species. Lactococcus strains showed the highest acidifying activity, followed by Enterococcus and Lactobacillus strains. Proteolytic activity of Enterococcus faecalis strains was higher than that of the other enterococci species, except Enterococcus avium strains. Within lactobacilli strains, the highest mean proteolytic activity was that of Lactobacillus bifermentans, Lactobacillus brevis and Lactobacillus casei strains.     

Combined effects of concentrated thermophilic and mesophilic cultures and conditions of curd acidifications on the manufacture and quality of kasseri cheese

The effect offour process variables on the biological acidification of curd to be usedfor the manufacture of kasseri cheese was examined. The variables were (i) concentrated starter cultures: a thermophilic mixture of Streptococcus thermophilus and Lactobacillus delbrueckii subsp bulgar-icus compared with a blend of Lactococcus lactis subsp lactis, Lactococcus lactis subsp cremoris and Lactobacillus casei subsp casei, and (ii) acidification temperatures: 30 and 40° C for the thermophilic cultures and 20 and 30°C for the mesophiles. The use of concentrated starter cultures enabled the cheese to be made in one day as compared with three in the traditional system usually using raw milk and no culture. The mesophilic blend combined with a lower scalding temperature (35°C) gave a higher yield than the alternative culture, and the cheeses were higher in total solids, acidity andsalt; the same cheeses were also harder and less elastic. The use of mesophilic cultures and a low acidification temperature (20° C) is recommended.     

Starter strain related effects on the biochemical and sensory properties of Cheddar cheese

A detailed investigation was undertaken to determine the effects of four single starter strains, Lactococcus lactis subsp. lactis 303, Lc. lactis subsp. cremoris HP, Lc. lactis subsp. cremoris AM2, and Lactobacillus helveticus DPC4571 on the proteolytic, lipolytic and sensory characteristics of Cheddar cheese. Cheeses produced using the highly autolytic starters 4571 and AM2 positively impacted on flavour development, whereas cheeses produced from the poorly autolytic starters 303 and HP developed off-flavours. Starter selection impacted significantly on the proteolytic and sensory characteristics of the resulting Cheddar cheeses. It appeared that the autolytic and/or lipolytic properties of starter strains also influenced lipolysis, however lipolysis appeared to be limited due to a possible lack of availability or access to suitable milk fat substrates over ripening. The impact of lipolysis on the sensory characteristics of Cheddar cheese was unclear, possibly due to minimal differences in the extent of lipolysis between the cheeses at the end of ripening. As anticipated seasonal milk supply influenced both proteolysis and lipolysis in Cheddar cheese. The contribution of non-starter lactic acid bacteria towards proteolysis and lipolysis over the first 8 months of Cheddar cheese ripening was negligible.     

Characterization of microflora in homemade semi-hard white Zlatar cheese

The Zlatar cheese belongs to the group of traditionally homemade cheeses, which are produced from nonpasteurized cow's milk, without adding of any bacterial starter culture. Changes were followed in lactic acid bacteria population and chemical composition during the ripening period of cheese up to 60 days. Results showed that the percentage of lactic acid cocci was higher in raw milk and one day old cheese and their percentage was gradually decreasing, whereas the number of lactobacilli was increasing. After 30 days of cheese ripening the number of cocci increased again, reaching the number of lactobacilli. The results of API 50 CH system and rep-PCR analysis showed that Lactobacillus paracasei subsp. paracasei, Lactobacillus brevis, Lactococcus lactis subsp. lactis, Enterococcuus faecium and Enterococcus faecalis were the main groups present during the ripening of Zlatar cheese. Results revealed that in older cheeses (45 and 60 days old) enterococci were the main group present. It was also demonstrated that 57 isolates showed antimicrobial activity. The number of bacteria showing antimicrobial activity slowly decreased during the ripening period and in samples of 60 days old cheese producers of antimicrobial activities were not detected.     

The microbiology of South African traditional fermented milks

A total of 15 samples of traditional fermented milk were collected from individual households in South Africa and Namibia. Lactic acid bacteria dominated the microflora of these samples, especially the genera Leuconostoc, Lactococcus and Lactobacillus. Other groups identified included pyogenic streptococci and enterococci. The dominant lactococci species was Lactococcus lactis subsp. lactis. Eighty-three percent of the leuconostoc isolates were identified as Leuconostoc mesenteroides subsp. dextranicum. Other species identified included Leuconostoc citreum, Leuconostoc lactis, Lactobacillus delbrueckii subsp. lactis and Lactobacillus plantarum.     

Impact of Autolytic and Proteolytic Lactobacilli and Nisin-Producing Culture on Proteolysis and Sensory Characteristics in Cheddar Cheese

ABSTRACT: Cheddar cheeses were made using a nisin-tolerant starter culture with either Lactobacillus delbrueckii subsp. bulgaricus UL12 (autolytic strain), Lactobacillus casei subsp. casei L2A (proteolytic strain), Lactococcus lactis subsp. lactis biovar. diacetylactis UL719 (nisin producer), or of Lb. bulgaricus UL12 and Lc. diacetylactis UL719. Lb. bulgaricus UL12 produced more trichloroacetic acid-soluble nitrogen than did Lb. casei L2A, which produced more phosphotungstic acid-soluble nitrogen than did Lc. diacetylactis UL719. High-performance liquid chromatography analyses showed that either lactobacilli or Lc. diacetylactis UL719 increased the hydrophilic and hydrophobic peptide contents. Cheeses containing both Lb. bulgaricus UL12 and Lc. diacetylactis UL719 had the most intense old Cheddar cheese flavor after 6 mo of ripening.     

Contribution of Lactococcus lactis subsp lactis IFPL 359 and Lactobacillus casei subsp casei IFPL 731 to the Proteolysis of Caprine Curd Slurries

ABSTRACT: Proteolysis was studied in low-fat caprine curd slurries pre-incubated (24 h at 30 °C) with an extra dose of rennet, 10.0 or 22.0 μg g^-1 (LR and HR slurries, respectively), and treated at 70 °C for 15 min prior to incubation with sonicated cells of Lactococcus lactis subsp lactis IFPL 359 alone or combined with Lactobacillus casei subsp casei IFPL 731. The addition of lactobacilli to slurries containing lactococci increased the conversion of water-soluble nitrogen to nonprotein nitrogen and amine nitrogen. Major differences were found for some free amino acids, such as glutamic acid and proline, and hydrolysis of most hydrophobic peptides produced by lactococci, which are associated with bitterness in cheese.     

Peptidase and proteinase activity ofLactococcus lactis,Lactobacillus casei andLactobacillus plantarum

The proteolytic system of several non-commercial strains of lactococci and lactobacilli that were isolated directly from traditional-Spanish, semi-hard, goats' milk cheese was studied. The aminopeptidase, X-prolyldipeptidyl aminopeptidase, dipeptidase and proteinase activity of these new strains was measured for the cytoplasmic, cell-wall/membrane and spontaneously released fractions. The aminopeptidase activity was exclusively intracellular and higher forLactobacillus casei subsp.casei than forLactococcus lactis subsp.lactis. Lactobacillus plantarum showed higher dipeptidase activity thanL. casei. The highest level of proteinase activity was recorded for the cell-wallmembrane fraction ofLactococcus lactis subsp.lactis IFPL 359, and was higher on β-casein than on α_s-casein for all the strains studied. These results suggest some different contribution of these strains to the proteolysis of cheese during ripening and they seem to complement each other when used together in the starter culture.     

Influence of selected lab cultures on the evolution of free amino acids, free fatty acids and Fiore Sardo cheese microflora during the ripening

Fiore Sardo Protected Denomination of Origin is a traditional Sardinian (Italy) hard cheese produced exclusively from whole raw ovine milk and coagulated with lamb rennet paste. Currently, Fiore Sardo is still produced by shepherds at the farmhouse level without the addition of any starter culture and the cheese-making process is characterized by significant waste. The first objective of the present work was to investigate the autochthonous microflora present in milk and Fiore Sardo cheese in order to select lactic acid bacterial (LAB) cultures with suitable cheese-making attributes and, possibly reduce the production waste. Secondly, the ability of selected cultures to guarantee cheese healthiness and quality was tested in experimental cheese-making trials. In this study, we show that the typical lactic microflora of raw ewe's milk and Fiore Sardo cheese is mostly composed of mesophilic LAB such as Lactococcus lactis subsp. lactis, Lactobacillus plantarum and Lactobacillus casei subsp. casei. Moreover, strains belonging to the species were selected for cheese-making attributes and used in experimental cheese-making trials carried out in different farms producing Fiore Sardo. The evolution of the cheese microflora, free amino acids and free fatty acids during the ripening showed that the experimental cheeses were characterized by a balanced ratio of the chemical constituents, by a reduced number of spoilage microorganisms and, remarkably, by the absence of production waste that were significant for the control cheeses.     

Proteolysis and formation of volatile compounds in cheese manufactured with a bacteriocin-producing adjunct culture

Hispánico cheese, a semi-hard Spanish variety, was manufactured from a mixture of pasteurized cows' and ewes' milks (4:1) using a commercial mesophilic LD-type starter comprising Lactococcus lactis subsp. cremoris, Lc. lactis subsp. lactis, Lc. lactis subsp. lactis var diacetylactis and Leuconostoc mesenteroides subsp. cremoris. Varying amounts (0-1.0 g/kg) of an Enterococcus faecalis INIA 4 culture in milk were added as a bacteriocin-producing adjunct. Differences in pH between cheeses manufactured with and without the bacteriocin producer did not exceed 0.11 pH units. Starter lactococci lost viability more rapidly in cheeses made with the bacteriocin producer, which reached counts of up to 6 x 10(7) cfu/g during ripening. Aminopeptidase activity in 1-d-old cheese made from milk inoculated with 1.0 g bacteriocin-producing culture/kg was twice that in control cheese. Degrees of overall proteolysis and levels of total free amino acids in 45-d-old cheese made with 1.0 g bacteriocin-producing culture/kg were 1.80-fold and 2.17-fold those in control cheese of the same age. Inoculating milk with 1.0 g/kg bacteriocin-producing culture reduced the level of hydrophobic peptides in the resultant cheese, increased the concentrations of 3-methyl-1-butanal, diacetyl and acetoin, and resulted in the highest scores for flavour quality and flavour intensity throughout ripening.     

Indigenous raw milk microbiota influences the bacterial development in traditional cheese from an alpine natural park

Nostrano di Primiero is a 6-month ripened cheese produced from raw milk collected in the Paneveggio-Pale di San Martino Natural Park area in the Italian Dolomites. In summer, this cheese is made using milk collected from two different areas, Passo Rolle and Vanoi, in the Paneveggio Natural Park. During the experiment, the milk from the two areas was separately processed, and cheeses were made in the same cheese factory using the same technological process. The microbiota of raw milk and cheeses of the two areas was isolated and the dominant population was monitored by RAPD analysis and identified by 16S rRNA sequence. The milk of the Passo Rolle area was mainly composed of mesophilic strains, thermophilic Streptococcus thermophilus, and low amounts of enterococci were also found; the milk of the Vanoi area was dominated by mesophilic microbiota mostly Lactococcus lactis ssp. cremoris and ssp. lactis and Lactobacillus paracasei ssp. paracasei. The plating of the natural starter culture revealed the presence of a relevant community of thermophilic cocci and lower amounts of enterococci. The dynamic population analysis showed the importance of the natural starter culture in the first 2 days of cheese ripening in both cheeses. Moreover, the large biodiversity observed in the raw milks was also detected in the cheeses during ripening. The Vanoi cheese was dominated by Enterococcus faecium and Streptococcus macedonicus in the first two days and mesophilic 21 Lb. paracasei ssp. paracasei became the most represented population after 15 days of ripening. In the first few days, the Rolle cheese was characterized by being mainly composed of thermophilic S. macedonicus and S. thermophilus and secondarily by mesophilic cocci. During ripening, the microbiota composition changed, and at 15 days, mesophilic lactobacilli were the dominant population, but later, this was mainly composed of mesophilic cocci and lactobacilli. The taxonomical identification by 16S rRNA sequence confirmed a large biodiversity related to raw milk microbiota and only five strains of S. macedonicus, Lactobacillus plantarum, 21 Lb. paracasei ssp. paracasei, Lactobacillus fermentum and E. faecium were detected in both cheeses.     

Microbiological study of semi-hard goat's milk cheese (Majorero)

The development of microbial flora in industrially produced semi-hard cheese made from pasteurized goat's milk was studied during manufacture and over a 90-day ripening period.
Estimates of total count, streptococci, lactobacilli, leuconostocs, coliforms, micrococci and staphylococci, Staphylococcus aureus and yeasts and moulds were carried out at various stages of the ripening process; streptococci and lactobacilli were identified by species.
Initially, the total count increased rapidly, primarily as a result of the growth of mesophilic lactic streptococci mainly Streptococcus lactis and Strep, cremoris. Subsequently, both these counts stabilized or decreased. Lactobacilli increased, and by the end of the ripening period were the predominant microorganisms. Most common were Lactobacillus casei var. casei. , especially at the end of storage; L. casei var. rhamnosus , L. casei var. plantarum and L. cellobiosus were also isolated. Leuconostocs were not found in any of the cheeses, and hence no eye formation took place. Coliforms, enterococci, yeasts and moulds remained below 10²–10³ c.f.u. g⁻¹. Maximum levels of micrococci and staphylococci were found after 15–30 days of ripening and decreased gradually towards the end of the ripening period. Neither the milk curd, nor cheese contained Staph. aureus.     

甘肃牧区优良乳酸菌株风味研究

以甘肃牧区筛选的优良乳酸菌分离株E2,G12,J6为研究对象,采用溶剂萃取法提取E2,G12,J6发酵酸乳中的风味物质,结合GC-MS对风味成分进行分析和研究,并与市售酸奶风味物质进行比较。结果表明:E2,G12,J6三株菌发酵酸乳含有的风味物质分别为42种、41种和42种,市售酸奶中含有35种风味物质,其中,酮类物质大大增加,并出现了δ-十二内酯、十一烷酮、己酸乙酯,乳酸、2,3-丁二酮及3-羟基-2-丁酮含量大大提升。乳酸、2,3-丁二酮、3-羟基-2-丁酮及δ-十二内酯、丁酸乙酯、己酸乙酯也许就是以甘肃牧区牦牛乳筛选的优良乳酸菌分离株E2、G12、J6所产生的主体特征风味。     

Homofermentative lactic acid bacteria of a traditional cheese, Comlek peyniri from Cappadocia region

Comlek peyniri is a typical artisanal cheese in Central Anatolia. This type of cheese was made by using the indigenous lactic acid bacteria (LAB) flora of cow or ewes' milk. Majority of the samples were taken from fresh cheese because the aim was to isolate homofermentative LAB. Initially 661 microbial isolates were obtained from 17 cheese samples. Only 107 were found to be homofermentative LAB. These isolates were selected and identified by using both phenotypic and molecular methods. Phenotypic identification included curd formation from skim milk, catalase test, Gram staining and light microscopy, growth at different temperatures and salt concentrations, arginine hydrolysis, gas production from glucose, and carbohydrate fermentation. Molecular identification was based on the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) of the 16S rRNA gene-ITS (internally transcribed spacer) region. By combining the phenotypic and molecular identification results, isolates belonging to each of the following genera were determined at species or subspecies level: 54 Lactococcus lactis subsp. lactis, 21 Enterococcus faecium, 3 Ec. faecalis, 2 Ec. durans, 10 Ec. sp., 15 Lactobacillus paracasei subsp. paracasei, and 2 Lb. casei strains. Technological characterisation was also performed by culturing each of the strains in UHT skim milk, and by monitoring pH change and lactic acid production at certain time intervals through the 24 h incubation. Results of the technological characterisation indicated that 33% of the isolates (35 strains) were capable of lowering the pH of UHT milk below 5.3 after 6 h incubation at 30 degrees C. Thirty four of these strains were Lc. lactis subsp. lactis, and only one was an Ec. faecium strain.     

Genetic diversity, dynamics, and activity of Lactobacillus community involved in traditional processing of artisanal Manchego cheese

A total of 248 strains of predominant lactobacilli isolated during the manufacture and ripening of artisanal Manchego cheeses obtained from two dairies were obtained and the genetic diversity of 197 investigated using random amplified polymorphic DNA (RAPD-PCR). 51 isolates could not be lysed and were therefore not genotyped. Forty-two distinct RAPD patterns, grouped in six major clusters at a similarity level of 54%, were obtained. Phenotypic characterization of isolates enabled their assignment to the species L. plantarum, L. brevis, L. paracasei subsp. paracasei, L. fermentum, L. pentosus, L. acidophilus and L. curvatus. In samples from both dairies, the species L. plantarum, L. brevis and L. paracasei subsp. paracasei dominated during ripening. Three genotypes showed excellent physiological characteristics and were therefore proposed as adjunct cultures for Manchego cheese manufacture.     

Influence of starter and nonstarter on the formation of biogenic amine in goat cheese during ripening

Two commercial starters were investigated for their potential ability to decarboxylate amino acids during goat cheese ripening. Two batches of goat cheese were produced with identical pasteurized milk but different starter cultures. One of them contained Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris and the other Lactococcus lactis subsp. lactis. The amine contents, microbial counts, proteolysis-related parameters, pH, total solids and salt content were studied in raw materials and cheeses. In raw materials, polyamines were the prevailing amines, whereas the main amines in cheeses were putrescine, tryptamine and, in particular, tyramine (94.59 mg/kg). Aerobic mesophilic microorganisms and Lactococcus counts increased throughout ripening, while Enterobacteriaceae were no longer detectable in cheese after 30 days of ripening. Amine concentration rose during cheese ripening in both batches. Moreover, the decarboxylase activity of microorganisms isolated from samples during cheese ripening was assayed and discussed.     

Potential of lactic acid bacteria isolated from specific natural niches in food production and preservation

Autochthonous strains of lactic acid bacteria (LAB) have been isolated from traditionally homemade cheeses collected from specific ecological localities across Serbia and Montenegro. Genetic and biochemical analysis of this LAB revealed that they produce bacteriocins, proteinases and exopolysaccharides. LAB produces a variety of antimicrobial substances with potential importance for food fermentation and preservation. Apart from the metabolic end products, some strains also secrete antimicrobial substances known as bacteriocins. Among the natural isolates of LAB from homemade cheeses, bacteriocin producers were found in both lactococci and lactobacilli. Lactococcus lactis subsp. lactis BGMN1-5 was found to produce three narrow spectrum class II heat-stable bacteriocins. In addition to bacteriocin production, BGMN1-5 synthesized a cell envelope-associated proteinase (CEP) and shows an aggregation phenotype. Another isolate, L. lactis subsp. lactis BGSM1-19 produces low molecular mass (7 kDa) bacteriocin SM19 that showed antimicrobial activity against Staphylococcus aureus, Micrococcus flavus and partially against Salmonella paratyphi. Production of bacteriocin reaches a plateau after 8 h of BGSM1-19 growth. Bacteriocin SM19 retained activity within the wide pH range from 1 to 12 and after the treatment at 100 degrees C for 15 min. Among collection of lactobacilli, the isolate Lactobacillus paracasei subsp. paracasei BGSJ2-8 produces heat-stable bacteriocin SJ (approx. 5 kDa) polypeptide. It retained activity after treatment for 1 h at 100 degrees C, and in the pH range from 2 to 11. In addition to isolates from cheeses, bacteriocin-producing human oral lactobacilli were detected. Most of them showed antimicrobial activity against streptococci, staphylococci and micrococci, but not against Candida. Isolate BGHO1 that showed the highest antimicrobial activity was determined as L. paracasei. Interestingly, Lactobacillus helveticus BGRA43, which was isolated from the human intestine showed strong activity against Clostridium sporogenes, but it was not possible to detect any bacteriocin production in this isolate by using standard procedures. Further analysis of antimicrobial activity revealed that BGRA43 has a relatively broad spectrum. Lactobacilli resistant to nisin were also detected among natural isolates. They produce bacteriocins, which have no activity against nisin producing lactococci.