Characterization of lactococci and lactobacilli isolated from semihard goats' cheese

Safety evaluation of Lactococcus lactis IDCC 2301 isolated from homemade cheese

For applications of microorganisms as probiotics in the food industry, safety evaluation has increasingly become important to ensure the health of consumers. Although people have been using various lactic acid bacteria for different purposes, some studies have reported that certain lactic acid bacteria exhibit properties of virulence and produce toxic compounds. Thus, it is necessary to examine the characteristics associated with lactic acid bacteria that are safe for use as probiotics. This research aimed to assess the safety of Lactococcus lactis IDCC 2301 isolated from homemade cheese using in vitro and in vivo assays, including antibiotic resistance, hemolytic activity, toxin production, infectivity, and metabolic activity in immune-compromised animal species. The results demonstrated that the strain was susceptible to nine antibiotics suggested by the European Food Safety Authority (EFSA). Whole-genome analysis revealed that L. lactis IDCC 2301 neither has toxigenic genes nor harbors antibiotic resistance. Moreover, L. lactis IDCC 2301 showed neither hemolytic nor β-glucuronidase activity. Furthermore, none of the D-lactate and biogenic amines were produced by L. lactis IDCC 2301. Finally, it was demonstrated that there was no toxicity and mortality using single-dose oral toxicity tests in rats. These results indicate that L. lactis IDCC 2301 can be safely used as probiotics for human consumption.

Selection of Leuconostoc strains isolated from artisanal Serrano Catarinense cheese for use as adjuncts in cheese manufacture

BACKGROUND

Serrano Catarinense cheese is a raw bovine milk cheese produced in the region of Santa Catarina, Brazil. Twelve representative strains of Leuconostoc isolated from 20 samples of this artisanal cheese were selected and submitted for evaluation of the acidifying, proteolytic, autolytic, aminopeptidase and lipolytic activities, NaCl and acid resistance, production of dextran and biogenic amines and antimicrobial activity. The aim was to genetically and technologically characterize the Leuconostoc strains in order to use them in mixed starter cultures for cheese manufacture.

RESULTS

Leuconostoc mesenteroides subsp. mesenteroides was the species that accounted for the largest proportion of isolates of Leuconostoc genus. Two leuconostoc isolates stood out in the acidifying activity, with reduction in pH of 1.12 and 1.04 units. The isolates showed low proteolytic and autolytic activity. Most of the isolates were dextran producers, presented good resistance to the salt and pH conditions of the cheese and showed antimicrobial activity against cheese pathogen bacteria, and none of them produced biogenic amines.

CONCLUSION

These results allowed the selection of five strains (UEL 04, UEL 12, UEL 18, UEL 21 and UEL 28) as good candidates for use as adjunct cultures for cheese manufacture. © 2018 Society of Chemical Industry.

Antibiotic susceptibility and heterogeneity in technological traits of lactobacilli isolated from Algerian goat's milk

The objective of this study was to identify and study the heterogeneity of technological traits of lactobacilli from goat's milk of Algeria and to evaluate in vitro their safety aspect. Using API50 CHL system and 16S rDNA sequencing, 51 % of strains were assigned as Lactobacillus plantarum, 34 % as L. pentosus, 7 % as L. rhamnosus and 8 % as L. fermentum. A large variability was noted for the acidifying capacity in skim milk after 6, 12 and 24 h of incubation. All strains expressed aminopeptidase activity against alanine-ρ-NA and leucine-ρ-NA at different levels. All strains were resistant to vancomycin and most of strains showed more susceptibility to β-lactam antibiotic. High susceptibility toward the inhibitors of protein synthesis was also observed. Minimum inhibitory concentrations data obtained revealed that isolates were susceptible to penicillin and chloramphenicol, and resistant to gentamicin and vancomycin. Minimum inhibitory concentrations distribution of other antibiotics showed variability. The analysis of graphical representation of principal component analysis of technological properties of L. plantarum and L. pentosus strains showed diversity among the isolates. Finally, eight L. plantarum (LAM1, LAM3, LAM21, LAM25, LAM35, LF15, LAM34, and LAM35), four L. pentosus (LAM38, LAM39, LF9 and LF16) and two L. rhamnosus (LF3 and LF10) strains, could be good candidates as adjunct culture in dairy product in Algeria.

Genotypic and technological characterization of Leuconostoc isolates to be used as adjunct starters in Manchego cheese manufacture

Twenty-seven Leuconostoc (Ln.) isolates from Manchego cheese were characterized by phenotypic and genotypic methods, and their technological abilities studied in order to test their potential use as dairy starter components. While phenotypic diversity was evaluated by studying the biochemical characteristics of technological interest (i.e. acidifying and aminopeptidase activities), genotypic diversity was evidenced by using Randomly Amplified Polymorphic DNA-Polymerase Chain Reaction (RAPD-PCR). Additional technological abilities such as lipolytic, proteolytic and autolytic activities, salt and pH tolerance and production of dextran, flavour compounds and biogenic amines, were investigated. The marked differences among strains reflected the existing biodiversity in naturally fermented products. After statistically evaluating their performance, strains C0W2, belonging to Ln. lactis, and C16W5 and N2W5, belonging to Ln. mesenteroides subsp. dextranicum, revealed the best properties to be used in mixed dairy starter cultures. This study evidences the fact that natural environments can be considered as a proper source of useful strains, for the dairy industry.

Effect of freezing and frozen storage on the physicochemical, organoleptic and microbiological characteristics of a semi-hard ewes' milk cheese

Physicochemical, organoleptic and microbiological characteristics of semi-hard ewes' milk cheeses, frozen immediately after manufacture under two different conditions at −35 and −80°C and stored at −20°C for 4 months, were studied during subsequent ripening. Frozen storage after either freezing condition did not result in marked alterations in overall composition or rheological and sensory properties of the cheeses after 45 d ripening. Water activity decreased over the ripening period and this decrease was more pronounced in the frozen batches. The water-holding capacities of the protein in the frozen cheese batches were higher than for the control batch. The level of proteolysis, estimated from the level of amino groups, was higher in the previously frozen cheese. Freezing also reduced the viability of the microbial flora in the cheese. The differences in these characteristics for the two freezing conditions were not significant.

Performance and intestinal coliform counts in weaned piglets fed a probiotic culture (Lactobacillus casei subsp. casei CECT 4043) or an antibiotic

The production of biomass and antibacterial extracellular products by Lactobacillus casei subsp. casei CECT 4043 was followed in both batch and in realkalized fed-batch cultures. Enhanced concentrations of biomass and antibacterial extracellular products were obtained with the use of the latter fermentation technique in comparison with the batch mode. The culture obtained by fed-batch fermentation was mixed with skim milk and used to prepare a probiotic feed for weaned piglets. To test the effect of the potentially probiotic culture of L. casei on body weight gain, feed intake, feed conversion efficiency, and on fecal coliform counts of piglets, two groups of animals received either feed supplemented with the probiotic preparation or avilamycin for 28 days. The control group was fed nonsupplemented feed. At the end of the administration period (day 28), the groups receiving probiotic and avilamycin exhibited the highest average body weight gain values, although the mean feed intake and feed conversion efficiency values were not different among the groups (P > 0.05). For the entire experimental period (42 days), the control group exhibited the lowest feed intake value, the probiotic group exhibited the highest feed conversion efficiency value, and the antibiotic group exhibited the highest body weight gain (P < 0.05). Interestingly, no significant difference in body weight gain was observed between the probiotic and the control groups by day 42 (P > 0.05). Fecal coliform values decreased (although not significantly) by day 28 in the three groups. However, the mean counts returned to pretreatment levels by day 42 in all groups.

Genotypic and phenotypic diversity of Lactococcus lactis isolates from Batzos, a Greek PDO raw goat milk cheese

The genotypic and phenotypic variability of 40 Lactococcus lactis isolates obtained from three cheese-making trials of Batzos cheese made one in each, winter, spring and summer was investigated. RAPD-PCR, plasmid profiling and PFGE were used to study the genetic variability and distinguish closely related isolates. Results showed a high degree of heterogeneity among strains. According to PFGE data, all strains except one were clustered together (at a similarity level of approximately 50%) with the L. lactis subsp. lactis reference strain and eleven groups of isolates consisting of 2-8 strains each were distinguished. Plasmid profiling results revealed that there were eight isolates lacking plasmids and nine having unique plasmids. Twenty-three isolates were allocated into six groups. There was an interesting similarity between the plasmid profiling groups and those formed according to PFGE. Clustering of strains according to RAPD-PCR was in agreement with results obtained by both plasmid profiling and PFGE for the majority of the strains. In addition, results obtained by molecular methods indicate a grouping of most of the strains according to the season of cheese production. All strains inhibited the growth of Escherichia coli O157:H7. Their ability to affect the growth of Yersinia enterocolitica, Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes and Enterococcus faecalis was strain dependent. In 42.5% of the isolates high acidifying ability in milk after 24 h was recorded and these were isolates, mainly, from fresh cheese. The 75% of the isolates from winter cheese exhibited higher Lys- than Leu-aminopeptidase activity while the approximately 67% of the isolates from summer cheese showed higher Leu- than Lys-aminopeptidase activity. Their caseinolytic activity after growth in milk for 24 h was significant with preference for alpha(s)-casein degradation. The majority (90%) of the strains formed methanethiol from methionine and this ability was strain dependent. These results suggest that among the wild lactococcal population from Batzos cheese there are interesting strains appropriate to be used as starters for the dairy industry.

Phenotypic and genotypic characterization of lactobacilli isolated from Spanish goat cheeses

Lactic acid bacteria from 18 Spanish goat cheeses produced by seven dairies were isolated to evaluate the genetic diversity of this bacterial community. 136 representative isolates were characterized by phenotyping and Randomly Amplified Polymorphic DNA (RAPD-PCR) analysis. Ten species were identified with predominance of Lactobacillus paracasei subsp. paracasei. The presence of L. curvatus, L. pentosus, L. cellobiosus and L. rhamnosus has not hitherto been reported in Spanish goat cheeses. A high degree of genetic diversity was found for L. paracasei subsp. paracasei, L. curvatus and L. plantarum. Some of the identified strains displayed strong acidifying and proteolytic capacities.

Biological and molecular characterization of a two-peptide lantibiotic produced by Lactococcus lactis IFPL105

The lactic acid bacterium Lactococcus lactis IFPL105 secretes a broad spectrum bacteriocin produced from the 46 kb plasmid pBAC105. The bacteriocin was purified to homogeneity by ionic and hydrophobic exchange and reverse-phase chromatography. Bacteriocin activity required the complementary action of two distinct peptides (alpha and beta) with average molecular masses of 3322 and 2848 Da, respectively. The genes encoding the two peptides were cloned and sequenced and were found to be identical to the ltnAB genes from plasmid pMRC01 of L. lactis DPC3147. LtnA and LtnB contain putative leader peptide sequences similar to the known 'double glycine' type. The predicted amino acid sequence of mature LtnA and LtnB differed from the amino acid content determined for the purified alpha and beta peptides in the residues serine, threonine, cysteine and alanine. Post-translational modification, and the formation of lanthionine or methyllanthionine rings, could partly explain the difference. Hybridization experiments showed that the organization of the gene cluster in pBAC105 responsible for the production of the bacteriocin is similar to that in pMRC01, which involves genes encoding modifying enzymes for lantibiotic biosynthesis and dual-function transporters. In both cases, the gene clusters are flanked by IS946 elements, suggesting an en bloc transposition. The findings from the isolation and molecular characterization of the bacteriocin provide evidence for the lantibiotic nature of the two peptides.

Microbiology and biochemistry of cheeses with Appélation d'Origine Protegée and manufactured in the Iberian Peninsula from ovine and caprine milks

To support legal protection with objective technical data and to promote enforcement of high quality standards a few European countries have created Appélation d'Origine Protegées. This paper reviews and updates fundamental and applied aspects encompassing microbiological and biochemical characteristics of traditional cheeses with Appélation d'Origine Protegée manufactured in the Iberian Peninsula from ovine, caprine, or both milks. Ovine and caprine cheeses with Appélation d'Origine Protegée from Portugal and Spain can be divided into four distinct groups based on milk source and rennet type: 1) Azeitão, Castelo Branco, Evora, Nisa, Serpa, Serra da Estrela, and La Serena cheeses are manufactured with raw ovine milk and coagulated via plant rennet; 2) Terrincho, Idiazábal, Manchego, Roncal, and Zamorano cheeses are manufactured with raw ovine milk and coagulated via animal rennet; 3) Cabra Transmontano and Majorero are manufactured with raw caprine milk and coagulated via animal rennet; and 4) Amarelo da Beira Baixa, Picante da Beira Baixa, and Rabaçal are manufactured with mixtures of raw ovine and caprine milks and coagulated via animal rennet.

Identification and characterization of proteolytic activity of Enterococcus spp. isolated from milk and Roncal and Idiazábal cheese

Roncal and Idiazábal cheeses are manufactured from ewe's milk in the Autonomous Region of Navarre in Spain. Levels of enterococci are high in these cheeses and in other types of ewe's-milk cheeses. The present study has identified enterococci present in the milk used and in the Roncal and Idiazábal cheeses after 120 days of ripening. A total of 282 strains were isolated and identified, and the cytoplasmic and extracellular enzymatic activities of some of the strains were assessed. The dominating species were Enterococcus faecalis, which accounted for 85% of the total both in the milk as well as in the two types of cheese, and Enterococcus faecium, Enterococcus durans, and Enterococcus avium which were present in lower proportions. Aminopeptidase and proteinase activity levels in enterococci were low, and considerable variation between strains of the same species was recorded, highlighting the need to study individual strains when selecting the most suitable bacteria as a starter culture. Aminopeptidase activity levels for the enterococci were appreciably higher at pH 7 than at pH 5.5, hence aminopeptidase activity by enterococci would appear to be less significant in the normal manufacturing conditions of the two cheeses.