SummaryRetardation of microbial spoilage of bread can be achieved by the use of spontaneous sourdough with an antimicrobial activity. This study was undertaken to identify lactic acid bacteria naturally occurring in spontaneous sourdough and use them for quality improvement and prolonging shelf life of rye, wheat and rye with wheat bread. Identifi cation of isolates from spontaneous sourdough by pyrosequencing assay showed that Lactobacillus reuteri were dominant lactic acid bacteria. The isolates showed a wide range of antimicrobial activity and displayed a synergistic activity against other lactobacilli, some lactococci and foodborne yeasts. The best application of spontaneous sourdough was noticed in the rye bread with the lowest crumb fi rmness of the fi nal product, although the sensory results of wheat and rye with wheat bread did not statistically diff er from control bread. L. reuteri showed a high preserving capacity against fungi during storage. This may be due to bacteriocins and various fatt y acids secreted into the growth medium that were identifi ed by agar well diff usion assay and gas chromatography. L. reuteri showing high antimicrobial activity have the potential to be used as a starter additive that could improve safety and/or shelf life of bread.
The aim of the study was to determine the impact of residues of detergents and disinfectants on the results of most commonly used inhibitor tests for raw milk. Microbiological test (Delvotest SP-NT)and three rapid tests (Charm 3 MRL BL/TET2, Charm ROSA MRL BL/TET and Penzym)were used in the study. Three concentrations (recommended by the manufacturer, 10 times lower and twice higher) of36 detergents and disinfectants in raw milk were investigated. All methods did not detect concentrations of detergents and disinfectants of alkaline and acid origin 10 times lower than recommended by the manufacturer. 39% of the investigated substances of alkaline origin were detected by Delvotest SP-NT and Penzym; Charm testsshowed non-typical results only. Delvotest SP-NT did not detect substances of acid origin; Penzym detected 50% of these substances, Charm testsshow abstract
The aim of the study was a detail evaluation of genetic diversity among the lactic acid bacteria (LAB) strains having an advantage of a starter culture in order to select genotypically diverse strains with enhanced antimicrobial effect on some harmfull and pathogenic microorganisms. Antimicrobial activity of LAB was performed by the agar well diffusion method and was examined against the reference strains and foodborne isolates of Bacillus cereus, Listeria monocytogenes, Escherichia coli, Staphylococcus aureus and Salmonella Typhimurium. Antifungal activity was tested against the foodborne isolates of Candida parapsilosis, Debaromyces hansenii, Kluyveromyces marxianus, Pichia guilliermondii, Yarowia lipolytica, Aspergillus brasiliensis, Aspergillus versicolor, Cladosporium herbarum, Penicillium chrysogenum and Scopulariopsis brevicaulis.A total 40 LAB strains representing Lactobacillus (23 strains), Lactococcus (13 strains) and Streptococcus spp. (4 strains) were characterised by repetitive sequence based polymerase chain reaction fingerprinting which generated highly discriminatory profiles, confirmed the identity and revealed high genotypic heterogeneity among the strains. Many of tested LAB demonstrated strong antimicrobial activity specialised against one or few indicator strains. Twelve LAB strains were superior in suppressing growth of the whole complex of pathogenic bacteria and fungi. These results demonstrated that separate taxonomic units offered different possibilities of selection for novel LAB strains could be used as starter cultures enhancing food preservation.
The study was undertaken to compare intraspecific variation of fatty acid (FA) profiles of Bacillus cereus isolated from different foods in order to find out if these profiles could be used for assessment of diarrheal-type enterotoxin producing and nonproducing strains. A total of 123 strains of presumptive B. cereus were isolated from ready-to-eat foods, dried milk products, and dry products of nonmilk origin and identified by pyrosequencing assay. About 29.3% of B. cereus isolates were found to be enterotoxic. Statistical hierarchical cluster analysis did not show relation among diarrheal-type enterotoxin producing and nonproducing B. cereus based on FA profiles in individual isolates. The profiles of cellular FA in B. cereus depended on the food type; however, all isolates produced 10 common FAs. Production of common FA within diarrheal-type enterotoxin producing and nonproducing B. cereus changed when B. cereus was cultivated on tryptic soy agar supplemented with various additives or in liquid medium.
PRACTICAL APPLICATIONSFoodborne pathogens are one of the major sources of infectious diseases in humans. The Ministry of Health of the Republic of Lithuania, while releasing the report on the morbidity of various diseases including diarrhea, did not emphasize cases related to B. cereus. The data collected in this study demonstrated the pathogenicity level of B. cereus found in food products getting into the Lithuanian market. The classical microbiological method for B. cereus confirmation is time consuming, and genetic identification is rather expensive. Therefore, it is appropriate to seek faster and cheaper methods for the identification of these bacteria. Studies on detailed FA produced in B. cereus strains could be used for the characterization of intrinsic features of B. cereus, while common butyric, myristic, palmitoleic, stearic, oleic and linoleic acids could be used as biological markers for differentiation of diarrheal-type enterotoxin producing and nonproducing B. cereus origin from foods of different type.
This study examined the changes in antagonistic activity of selected lactic acid bacteria (LAB) in response to technological factors used in food production. The antimicrobial activity of 12 selected LAB strains was assessed against the bacterial and fungal strains using the agar well diffusion method. Sodium chloride (NaCl) 6.5–8.0%, glucose 20-30% and pH 4.0, pH 8.0 and higher were the most crucial factors in reducing the spectra of the microorganisms antagonized. Heating at 80 °C or 100 °C had a greater negative impact than 63 °C on the antifungal activity of LAB. Freezing at –72 °C eliminated the antifungal activity, or it changed from fungicidal to fungistatic. Although each LAB demonstrated the ability to retain antimicrobial activity induced by various technological factors, Lactococcus lactis 768/5 was superior in retaining high antimicrobial activity against tested indicator strains.
The effect of antimicrobials produced by lactic acid bacteria (LAB) on the inhibition of Listeria monocytogenes ATCC 19111 in minced salmon was analysed and compared to the sodium lactate and bacteriophage action during storage at 6 °C. All tested additives showed a quite noticeable reduction of L. monocytogenes counts by 30–95% compared with control samples. Antimicrobials produced by the tested Enterococcus faecium strains showed moderate inhibitory activity while the greatest inhibitory activity was observed for antimicrobials produced by Streptococcus thermophilus 43 directly in the same way as the additive sodium lactate. The correlation was determined within inhibitory efficiency and produced total fatty acid amounts. S. thermophilus 43 showed the exceptionally stronger inhibition index for L. monocytogenes and yielded the higher monounsaturated fatty acid amount (42%) than E. faecium strains. Both E. faecium strains showing the lower inhibition efficiency produced the highest polyunsaturated fatty acid amounts (21.7–29.5%). E. faecium L41-2B-2v and S. thermophilus 43 were found to produce bioactive compounds like omega-3 and omega-6 FAs.
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