Production of Bioactive Peptides in Milk Using Two Native Strains of Levilactobacillus brevis

Background and Objective: Milk proteins are precursors of several biologically active peptides. One of the methods of producing these peptides is fermentation using lactic acid bacteria. The aim of this study was to investigate production of antioxidant and angiotensin-I converting enzyme inhibitory bioactive peptides in cow milk fermented by two strains of Levilactobacillus brevis. Material and Methods: Two strains of Levilactobacillus brevis KX572376 (M2) and Levilactobacillus brevis KX572382 (M8) were used in fermentation of low-fat cow milk. Moreover, pH changes, proteolytic activity, water-soluble extract biological activity (antioxidant activity and angiotensin-I converting enzyme inhibition) of the samples and peptide fraction less than 3 kDa were investigated at 24 and 48 h of fermentation (30 °C). Peptide profile of the superior sample was analyzed as well. Statistical analysis was carried out using one-way of variance, Tukey test and SPSS software v.25. Results and Conclusion: The two strains decreased milk pH to a similar level in the first 24 h. Quantities of free amine groups in the samples treated with M2 and M8 strains within 24 and 48 h of fermentation were significantly different (p≤0.05), compared to the control sample. In the first 24 h of fermentation, no difference was observed in the quantity of free amines of M2 and M8 samples. In the second 24 h, further free amine groups were produced due to the activity of M8 strain in milk. Antioxidant activity of the water-soluble extracts of M2 and M8 samples was significantly (p≤0.05) higher than that of the control sample during fermentation. Antioxidant activity in fractions less than 3 kDa did not show significant differences in M2 and M8 samples at 24 and 48 h of fermentation. In the control sample, no antioxidant activity was observed in fractions less than 3 kDa. The highest ACE inhibitory activity in fractions less than 3 kDa of M8 was observed after 48 h. No angiotensin-I converting enzyme inhibition was seen in fractions less than 3 kDa of M2 and control sample. The RP-HPLC peptide patterns of the fraction less than 3 kDa of M8 and control sample were different, which was a justification for the biological activity in this sample. Conflict of interest: The authors declare no conflict of interest

The Effect of Lactiplantibacillus plantarum from Motal Cheese on the Adhesion of Cronobacter sakazakii to Epithelial Cells

IntroductionCronobacter sakazakii is an opportunistic pathogen, which has been linked to the contamination of powdered infant formula, and associated with outbreaks leading to fatalities in neonatal intensive care units. Few studies have explored the direct interaction between probiotics and C. sakazakii. In this study, the effect of a Lactiplantibacillus plantarum strain (M17) along with the standard strain Lactobacillus plantarum (ATCC 8014) and the well-characterized probiotic strain Lactobacillus rhamnosus GG on the adhesion of C. sakazakii to intestinal epithelial cells was analyzed. Materials and MethodsAcid and bile tolerance of M17 was evaluated in the presence of pepsin and pancreatin. L-arginine hydrolysis was investigated using an arginine-including medium. Auto-aggregation and co-aggregation assays were performed by absorbance measurement. Minimum inhibitory concentrations of the antimicrobials recommended by the European Food Safety Authority were established. Total lactic acid and the ratio of D/L lactate isomers were determined with a Megazyme enzymatic kit. The ability of the isolate to produce biogenic amines was tested by qualitative and quantitative monitoring. Hemolysis was assessed phenotypically on MRS agar enriched with sheep blood. The strain was tested for its capability to adhere to mucin and Caco-2 cells. The antagonistic effects of the strain against C. sakazakii were further evaluated in vitro on mucin and cultured Caco-2 cells. The LAB strain was added simultaneously with, before, and after C. sakazakii to Caco-2 cells for competition, exclusion and displacement assays, respectively. Data analysis was performed in R using one-way analysis of variance, and the experimental groups were compared with the controls using Tukey’s test. P values <0.05 were considered statistically significant. Results and DiscussionThere was no significant difference in the survival rate of M17 and L. plantarum ATCC 8014 at pH = 4. After 2 h of incubation at pH = 2.5, the survival rate of L. plantarum ATCC 8014 was estimated to be higher than strain M17, but this difference was not significant. After 4 hours of incubation at pH = 8, M17 showed a higher survival rate than L. plantarum ATCC 8014, and this difference was significant after transfer from pH = 4. These results confirm the appropriate viability of M17 in the gastrointestinal tract. Both M17 and L. plantarum ATCC 8014 developed the color yellow in the L-arginine hydrolysis assay, which confirms the safety of these strains. The percentage of auto-aggregation for M17, L. plantarum ATCC 8014, and Lactobacillus rhamnosus LGG was estimated at 24.38, 25.28, and 32 after 6 hours, respectively, and no statistically significant difference between the two isolates were noticed. Given the auto-aggregation and co-aggregation parameters of M17, this strain may constitute a defense mechanism against C. sakazakii. Strain M17 showed resistance to kanamycin and clindamycin antibiotics. With intrinsic resistance, the risk of transferring resistance genes is not only speculative, but practically impossible. Intrinsic resistance of lactic acid bacteria may be considered desirable because it ensures their survival when the host is treated with antibiotics. Both D and L isomers of lactic acid were produced by the studied strains. In humans, D(-)-lactic acidosis is a rare metabolic complication that has only been reported in individuals with short bowel syndrome). Clinical studies have shown that the consumption of probiotic bacteria producing D(-)-lactic acid is safe for children and does not cause a long-term increase in blood D(-)-lactic acid. The reference L. plantarum strain and M17 did not produce biogenic amine precursors, and had no ß-hemolytic activity. Mucin adhesion assay exhibited that M17 has less adhesion (12.10 ± 1.14 %) than L. plantarum ATCC 8014 (13.33 ± 2.30 %) and LGG (15.93 ± 2.06 %) although these differences were not statistically significant. However, the amount of adhesion for the positive control sample Escherichia coli K12 (25.19 ± 4.40 %) was significantly higher than those of the other strains. Compared to the positive control, M17 had a significantly lower adhesion rate (6.8 ± 1.41) to CaCo-2 cells. This value was estimated at 13.77 ± 3.53 % for the reference strain and 21.6 ± 7.54 % for Lactobacillus fermentum PCC (positive control). In antagonistic assays, M17 was able to reduce the adhesion of C. sakazakii to mucin and CaCo-2 cells in all three methods of exclusion/inhibition, competition and displacement. Statistical analysis of the results does not show a significant difference between M17 and LGG. Therefore, the performance of M17 is similar to that of the standard probiotic LGG. ConclusionLactic acid bacteria with acceptable ability to adhere to epithelial cells can be suitable for colonization in the intestine. They can act as a barrier to fight pathogens through various competitive mechanisms, such as co-aggregation with pathogens and adhesion. The M17 strain has an acceptable immune profile and probiotic properties because it shows an acceptable antagonistic activity against C. sakazakii invasion. AcknowledgementThis study was supported by Ferdowsi University of Mashhad (Research affairs) [project No.:46718] and the research infrastructure at the University of Copenhagen

Proline-specific peptidases from Lactobacillus casei subspecies

The objectives of this study were (l) to screen out active proline-specific peptidases from Lactobacillus casei subspecies, (2) to study growth kinetic and enzyme production from enriched medium (MRS) and cheese whey medium, (3) to purify and characterize two active proline-specific enzymes, and (4) to investigate the action of purified enzyme on bitter tryptic digests of $beta$-casein as well as bitter enzyme-modified cheese. Lactobacillus casei subsp. casei LLG and Lactobacillus casei subsp. rhamnosus S93 were examined for extra- and intra-cellular proline-specific peptidase activities. Both strains showed strong activity for x-prolyl dipeptidyl peptidase and proline iminopeptidase but had weak activities for prolidase, prolinase, and post proline endopeptidase. Histochemical staining of crude enzyme extract from Lactobacillus casei ssp. casei LLG with different substrates revealed a distinct protein band for x-prolyl dipeptidyl peptidase as well as for proline iminopeptidase. The growth kinetics showed that the intracellular proline-specific peptidases increased gradually at the beginning of the exponential phase and reached a maximum at the beginning of stationary phase.Storage stability of x-prolyl dipeptidyl peptidase and proline iminopeptidase in crude extract, with and without stabilizers showed no significant loss in activity of these two enzymes at 4$sp circ$C for 9 days without adding any stabilizers. The levels of x-prolyl dipeptidyl peptidase, proline iminopeptidase, and post proline endopeptidase activities of cells grown in whey did not vary markedly from cells grown in MRS broth. X-prolyl dipeptidyl peptidase and proline iminopeptidase were purified from crude cell-free extract of Lactobacillus casei ssp. casei LLG by Fast Protein Liquid Chromatography (FPLC) equipped with ion-exchange and gel-filtration columns. X-prolyl dipeptidyl peptidase was found to be a serine-dependent enzyme with molecular mass of 79 kDa. The pH and the temperature optima by the purified enzyme were 7.0 and 50$sp circ$C, respectively. Proline iminopeptidase was sulfhydryl enzyme with molecular mass of 46 kDa. The maximum enzyme activity was observed at pH 7.5 and 40$sp circ$C. This is the first report describing the purification and characterization of x-prolyl dipeptidyl peptidase and proline iminopeptidase from Lactobacillus casei to homogeneity.The debittering of tryptic digests from $beta$-casein by x-prolyl dipeptidyl peptidase was studied by reversed phase high performance liquid chromatography (RP-HPLC) and liquid chromatography/mass spectrometry. The results showed that two bitter peptides (f53-97 and f03-209) containing X-Pro-Y-Pro in their amino acid residues were completely hydrolyzed and many other peptides with high hydrophobicity were decreased in peak area. The addition of purified x-prolyl dipeptidyl peptidase on bitter enzyme-modified cheese (EMC) also showed that at least one bitter peptide with X-Pro-Y derived from $alpha$-casein hydrolysis was removed

Production of bacteriocins by Enterococcus spp. isolated from traditional, Iranian, raw milk cheeses, and detection of their encoding genes

Strong bacteriocins, or bacteriocins with a wide range of activity against pathogens and spoilage microorganisms, are actively sought for use as natural food preservatives. This work reports the inhibitory activity of 96 enterococcal isolates from two Iranian, raw milk cheeses against five indicator organisms (including Listeria innocua). Forty-eight isolates inhibited at least one indicator in spot agar assays. Of these, 20 isolates corresponding to 15 different strains were shown to produce bacteriocin-like substances in liquid cultures. PCR analysis revealed the genes coding for enterocins (enterococcal bacteriocins) A, B, P or X, or their combinations, in all but one of these 15 strains. In addition, the gene coding for enterocin 31 was detected in two strains. No amplification was obtained in one strain when using specific primers for all 13 bacteriocin genes sought. Three different enterocin genes were identified in most strains and four in one strain. Although the concomitant production of bacteriocins is still to be verified, producers of multiple enterocins could be of great technological potential as protective cultures in the cheese industry. © 2012 Springer-Verlag.This research was partially supported by a project from the Spanish Ministry of Science and Innovation (MICINN) (AGL2007-61869-ALI). A.A. was awarded a scholarship of the Severo Ochoa program from FICYT (BP08-053). S. Delgado was sup- ported by a research contract from MICINN under Juan de la Cierva program (JCI-2008-02391). The authors wish to thank the Iranian Ministry of Industries and Mines, as well as Razavi Dairy Industry (Mash- had, Iran) and the O Y ce of Industrial Relationships (OIR) of Ferdowsi University of Mashhad (FUM).Peer Reviewe

Iranian kishk as a source of lactic acid bacteria producing exopolysaccharide

Trabajo presentado en el XIII International Scientific Agriculture Symposium AGROSYM 2022, celebrado en Sarajevo (Bosnia y Herzegovina), del 6 al 9 de octubre de 2022Exopolysaccharides are high molecular weight polymers composed of sugar subunits. Produced exopolysaccharides by lactic acid bacteria (LAB) play a significant role in improvement of organoleptic properties of fermented dairy products such as yogurt. Diversely, the probiotic function of these bacteria and the prebiotic properties of their produced biopolymers promote consumer¿s health. For this purpose, a traditional dairy product known as ¿Kishk¿ was selected. 143 strains of lactic acid bacteria were isolated from Iranian Kishk in Khorasan Province and cultured in formulated MRS mediums with different sugars such as glucose, fructose, sucrose and, lactose (40 g/L) and incubated in anaerobic conditions at 30 and 37°C for 48 hours. The microscopic features of the isolates were assessed and the production of exopolysaccharide in the culture medium was evaluated by disk and ruthenium red methods. The phenol-sulfuric and weight method were used to quantify exopolysaccharide production. Results showed pH of Kishk samples ranged from 3.60 to 4.08 and the average of total mesophilic count and LAB count of samples were 6.50 and 5.89 log CFU/g, respectively. Analysis of data exhibited 79 out of 143 lactic acid bacteria isolates were exopolysaccharide producer and 70% of them were cocci. The average of maximum and minimum production by weight method were 2.61 g/L and 0.08 g/L, respectively. The average of highest and the lowest amount of exopolysaccharide by phenol sulfuric method were measured 1.87 g/L and 0.06 g/L, respectively. This study indicates the potential of exopolysaccharide production by Iranian native species from dairy products

Evaluation of antioxidant, antibacterial and cytotoxicity activities of exopolysaccharide from Enterococcus strains isolated from traditional Iranian Kishk

In this study, the antimicrobial effect of exopolysaccharide (EPS) extracted from Enterococcus strains [E. durans K48 (MT437,248), E. faecium R114 (MT437,249) and E. faecium T52 (MT437,250)] isolated from Kishk was applied against some foodborne pathogenic bacteria using well diffusion and microdilution methods. The antioxidant activity of EPS was also evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging assay and ferric reducing antioxidant power (FRAP) method. The cytotoxicity effect of EPS on human Gingival Fibroblast (HGF) cell line was also assessed. The results obtained by antimicrobial test showed that the most resistant bacteria to the examined EPS was Listeria monocytogenes, and the most susceptible were Staphylococcus aureus and E. faecalis. The results showed that the DPPH inhibitory percentage of EPS (25 mg/mL) from E. durans K48, E. faecium R114, and E. faecium T52 was 53%, 58% and 64%, respectively. EPS from E. faecium T52 displayed the highest reducing power, but statistically, there was no significant difference between the reducing power of EPS T52 and EPS R114 (P ≥ 0.05). The lowest toxicity percentage of EPS k48, EPS T52, and EPS R114 on normal human cell line at a concentration of 0.2 mg/mL was 10%, 15%, and 13%, respectively, which was statistically significant (P < 0.05). The obtained results in the present study indicate that EPS from the examined LAB strains with no in vitro cytotoxicity can be a potential source of natural antioxidant and antibacterial agent to be used in food and pharmaceutical industries.This work was financially supported by a Grant (No. 47333) from Ferdowsi University of Mashhad (Research affairs), Iran

Biodiversity of exopolysaccharide-producing lactic acid bacteria from Iranian traditional Kishk and optimization of EPS yield by Enterococcus spp

The production of polysaccharides derived from lactic acid bacteria (LAB) can be a valuable alternative to current polysaccharides. In this study, eight samples of Kishk (traditional dairy product) were collected in sterile conditions and directly cultured on MRS agar medium. Following purification and examination of microscopic, macroscopic characteristics and doing biochemical tests, 143 isolates were selected, and the production of exopolysaccharide (EPS) was investigated by the ruthenium red and disc methods. The EPS production of 79 isolates was confirmed. Total carbohydrate of EPS was determined by the phenol sulfuric acid method. Finally, Enterococcus durans K48, Enterococcus faecium R114, and Enterococcus faecium T52 strains were selected as the best EPS producers. The optimization of EPS production was then performed using Central Composite Design (CCD) and Response Surface Methodology (RSM) approaches. Optimization plots showed the highest EPS yield for E. durans K48, E. faecium R114, and E. faecium T52 occurred at 38.4, 37.4 and 36.7 °C and pH of 5.9, 5.6 and 5.8, respectively, cultured in a Sucrose-MRS medium. Under optimal conditions, the maximum predicted and actual production of EPSs for the examined isolates were 3.18, 3.21, 2.99 and 3.02, 3.15, 3.15, g L, respectively. As determined by Gel Permeation Chromatography, the EPSs molecular weights were in the range of 2.93 × 10 to 3.52 × 10 Da. Analysis of the component monosaccharides by HPLC showed that all three tested EPSs were heteropolysaccharides. After appropriate evaluation, the EPSs produced by native species of LAB isolated from Iranian Kishk could be of interest for industrial applications or as functional food ingredients.This work was financially supported by a grant (No. 3/47333) from the Ferdowsi University of Mashhad (Research Affairs), Iran